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CHEMISTRY. 


BY  /?  , 

WILLIAM  THOMAS  BRANDE,  D.C.L.,  F.K..S.L.  &  E. 

OF  HER  MAJESTY'S  MINT. 

MEMBER  OF  THE  SENATE  OP  THE  UNIVERSITY  OP  LONDON,  AND 
HONORARY  PROFESSOR  OP   CHEMISTRY  IN  THE  ROYAL  INSTITUTION  OP  GREAT  BRITAIN  i 


AND 


ALFRED  SWAINE  TAYLOR,  M.D.,  F.R.S. 

FELLOW  OP  THE  ROYAL  COLLEGE  OP  PHYSICIANS  OF  LONDON, 
AND  PROFESSOR  OP  CHEMISTRY  AND  MEDICAL  JURISPRUDENCE  IN  GUY'S  HOSPITAL. 


EXPERIMENTIS   ET  PR^CEPTIS. 


SECOND  AMERICAN  EDITION  THOROUGHLY  REVISED. 


PHILADELPHIA: 

HEITETO      LEA 
1867. 


PHILADELPHIA: 
COLLINS,  PEIATER,  705  JaYNE  STREET. 


AMERICAN  PUBLISHER'S  NOTICE, 


Dr.  Taylor,  having  kindly  consented  to  give  to  this 
volume  a  thorough  revision,  no  additions  have  been  found 
necessary  to  adapt  it  to  the  wants  of  the  American  stu- 
dent. The  press,  however,  has  been  carefully  supervised 
by  a  competent  chemist,  in  order  to  secure  the  utmost 
typographical  accuracy ;  and  it  is  hoped  that  the  work,  in 
its  present  improved  condition,  will  be  found  worthy  a 
continuance  of  the  very  marked  favor  with  which  it  has 
thus  far  been  received. 

Philadelphia,  August,  ISGt. 


CAVSUH 


PREFACE 


SECOND   AMERICAX  EDITION 


Ix  preparing  a  second  edition  of  the  work  on  Chemistry  by  tlie 
late  Professor  Brande  and  myself,  I  have  endeavored  to  carry  out  the 
principles  which  influenced  us  in  the  selection  of  subjects  and  in  the 
mode  of  treating  them.  We  felt  that  there  was  a  large  amount  of 
useful  chemical  knowledge  available  for  the  student,  but  that  it  was 
too  often  locked  up  in  elaborate  treatises,  and  incorporated  with  sub- 
jects of  no  practical  interest.  Our  object  in  undertaking  this  work 
was  to  furnish  the  reader,  whether  a  student  of  medicine  or  a  man  of 
the  world,  with  a  plain  introduction  to  the  science  and  practice  of 
chemistry.  With  this  view,  we  avoided  as  much  as  possible  the 
introduction  of  questions  connected  with  abstract  science  or  with 
chemical  philosophy,  and  we  excluded  from  our  pages  the  formulae 
and  descriptions  of  substances  which  were  never  likely  to  be  seen 
except  as  rare  and  curious  specimens  in  the  cabinets  of  professors. 
The  chemistry  of  every-day  life  is  quite  sufi&cient  to  give  full  occu- 
pation to  a  medical  student.  If,  after  the  completion  of  his  medical 
education,  he  has  the  time  and  inclination  to  devote  to  the  study  of 
atoms  and  the  numerous  and  conflicting  hypotheses  on  their  combina- 
tions in  groups  and  series,  there  can  be  no  objection  to  his  taking  up 
the  examination  of  these  recondite  subjects,  but  let  him  make  himself 
master  of  what  is  simple  and  practical  before  he  occupies  valuable 
time  in  studying  that  which  is  complex  and  hypothetical. 

The  ordinary  and  well-known  notation,  based  on  the  equivalent  or 
combining  weights  of  bodies  which  was  adopted  in  the  first,  is 
adhered  to  in  this  edition.  Although  not  perfect,  it  is  based  upon 
simple  and  intelligible  principles.  The  new  methods  of  notation 
must  be  regarded  as  still  upon  their  trial.  Gerhardt's  system,  which 
a  few  years  since  was  generally  adopted  by  "  advanced  "  chemists,  has 


yi  PREFACE. 

now  given  place  to  another  system,  and  the  extinction  of  this  is 
threatened  by  a  third  and  an  entirely  different  system,  recently 
propounded  by  Sir  Benjamin  Brodie,  Professor  of  Chemistry  in  the 
University  of  Oxford.  Apart  from  any  advantages  supposed  to  be 
presented  by  these  new  systems,  a  writer  on  chemistry,  in  making  a 
selection,  is  bound  to  consider  the  present  state  of  chemical  literature 
and  the  course  which  has  been  adopted  by  authors  of  repute.  It  will 
be  found  that  in  the  best  modern  works  on  Chemistry  in  the  English 
and  French  languages  and  in  the  great  majority  of  such  works,  the 
ordinary  notation  is  adopted,  and  the  new  notation  ignored  even  by 
writers  who  have  been  or  are  advocates  for  a  change.  In  proof  of 
this,  I  may  refer  to  the  English  translation  of  the  Hand-book  of 
Gmelin,  in  sixteen  volumes ;  the  Traits  de  Chimie  of  Pelouze  and 
Fremy,  in  six  large  volumes,  which  has  already  gone  through  three 
editions ;  the  earlier  editions  of  Dr.  Miller's  Chemistry ;  the  works  of 
Apjohn  and  Bloxam  among  recent,  and  of  Eegnault,  Mitscherlich, 
Graham,  Brande,  Gregory,  and  Turner  among  older  publications  on 
the  science.  In  the  Precis  d' Analyse  Chimique  of  Gerhardt,  pub- 
lished eight  years  after  the  introduction  of  his  proposed  new  but  now 
obsolete  system,  the  ordinary  notation  was  adopted  by  this  author  as 
more  intelligible  to  the  student ;  and  in  the  recently  published  Chimie 
Medicale  of  Professor  Wurtz  (1867)  the  new  views  advocated  by  the 
writer  in  his  Introduction  to  Chemical  Philosophy,  are  laid  aside  and 
the  old  equivalents  are  used.  The  apology  for  this  is  said  to  be  the 
necessity  of  conforming  to  the  official  teaching  in  the  Schools  of  Paris. 
This  may  be  true,  but  it  proves  that  the  official  teaching  in  one  of  the 
greatest  Chemical  Schools  of  Europe  is  opposed  to  these  new  systems 
of  notation.  With  these  examples  before  me,  and  with  a  conviction 
of  the  artificial  and  unsatisfactory  nature  of  the  grounds  upon  which 
the  new  systems  are  based,  I  did  not  feel  justified  in  making  any 
change  in  the  plan  adopted  after  full  consideration  by  the  late  Pro- 
fessor Brande  and  myself.  Nothing  could  be  gained  by  laying  aside 
one  system  because  it  is  imperfect,  for  another  which  at  present  ofiers 
no  prospect  of  stability;  for,  as  Mr.  Bloxam  justly  remarks,  "the 
different  modes  of  representing  chemical  changes  are  almost  as 
numerous  as  chemical  writers.^ 

It  cannot  be  denied  that  a  student  of  chemistry  at  the  present  time 
has  a  heavy  labor  before  him.  Besides  two  or  more  methods  of  chemi- 
cal notation,  he  will  find  in  English  works  on  the  Science,  that  while 
one  author  employs  the  continental  metrical  weights  and  measures, 

»  Chemistry,  Inorganic  and  Organic,  1867. 


PREFACE.  Vll 

giving  quantities  in  grammes  and  cubic  centimetres,  another  adopts 
the  English  system  of  expressing  them  in  grains  and  cubic  inches.  One 
describes  the  barometrical  pressures  in  French  millimetres,  another  in 
English  inches ;  one  describes  degrees  of  temperature  on  the  foreign 
centigrade  scale,  another  on  the  ordinary  scale  of  Fahrenheit,  and  to 
add  to  this  want  of  uniformity,  there  is  a  further  difficulty  that  the 
same  chemical  compound  may  be  described  under  four  or  five  different 
names,  according  to  the  special  views  of  each  writer  regarding  theo- 
ries of  atomicity  and  nomenclature !  This  want  of  agreement  among 
chemical  writers  is  but  little  creditable  to  the  science,  and  is  discourag- 
ing to  a  student.  Instead  of  making  himself  acquainted  by  actual 
experiment  with  the  properties  of  bodies,  so  that  he  may  be  able  to 
identify  and  describe  them,  he  is  induced  to  load  his  memory  with  the 
formulae  of  complex  organic  products,  as  if  chemistry  consisted  simply 
in  knowing  or  calculating  the  number  of  atoms  in  a  compound,  and 
the  precise  order  in  which  they  are  grouped.  This  may  be  know- 
ledge, but  it  is  not  true  chemical  knowledge,  and  to  a  medical  or  general 
student,  it  is  not  in  any  sense  profitable  knowledge.  A  recent  writer 
on  the  Progress  and  Prospects  of  Chemistry,  justly  remarks  that  "ab- 
stract reasoning  has  thrown  more  complication  round  chemical  science 
than  it  has  ever  afforded  of  satisfactory  demonstration.  Eecent  chemi- 
cal works  affecting  a  logical  reasoning,  are  crowded  with  arguments 
and  classifications  that  have  in  a  great  measure  taken  the  place  of 
facts  and  experiments,  and  are  calculated  rather  to  bewilder  than 
assist  the  student.  Logic  is  very  well  in  its  own  place,  but  it  is  easy 
to  carry  it  to  excess  in  sciences  essentially  practical,  more  especially 
when  it  is  built  upon  assumptions  that  never  have  been  and  perhaps 
never  will  be  established  as  truths.  Many  of  the  elaborate  systems  of 
classification  now  brought  forward  are  more  ingenious  than  useful, 
and  even  their  plausibility  seems  but  too  often  to  arise  from  accidental 
circumstances,  rather  than  from  any  foundation  in  fact."^ 

The  student  who  desires  to  succeed  in  this  branch  of  science,  must 
constantly  bear  in  mind  that  chemistry  is  essentially  based  upon  ex- 
periment, and  that  work  in  the  laboratory  offers  a  better  and  surer 
road  to  success  than  the  study  of  the  most  ingenious  speculations  in 
the  closet. 

The  revision  of  the  second  edition,  in  consequence  of  the  death  of 
my  lamented  colleague,  has  devolved  entirely  upon  myself.  Every 
chapter,  and  indeed  every  page  has  been  revised,  and  numerous  addi- 
tions made  in  all  parts  of  the  volume.     These  additions  have  been 

•  Professor  McGauley,  Progress  and  Prospects  of  Chemistry,  1866. 


Viii  PREFACE. 

restricted  chiefly  to  subjects  having  some  practical  interest,  and  they 
have  been  made  as  concise  as  possible  in  order  to  keep  the  book 
within  those  limits  which  may  retain  for  it  the  character  of  a  Student's 
Manual. 

ALFEED  S.  TAYLOR. 

June  29,  1867. 


TTiLLiAM  Thomas  Brande,  D.  C.  L.,  F.  R.  S.,  died  at  Tunbridge 
Wells  on  the  11th  February,  1866.  Mr.  Brande  had  been  long  known 
as  a  skilful  chemist  and  an  assiduous  cultivator  of  science.  For  more 
than  forty  years  he  was  engaged  in  this  metropolis  as  a  lecturer  on 
chemistry.  We  have  now  before  us  an  advertisement  of  his  lectures 
in  October,  1811.  He  was  then  the  colleague  of  the  late  Sir  Benja- 
min Brodie  in  the  Medical  School  of  Great  Windmill  Street.  His 
lectures  subsequently  at  the  Royal  Institution,  where  he  was  the  col- 
league of  Faraday,  gained  for  him  a  high  reputation.  His  explanations 
of  chemical  phenomena  were  lucid,  and  his  experiments  ingenious  and 
well-contrived.  The  substance  of  these  lectures  is  incorporated  in  the 
great  work  by  which  he  acquired  a  European  reputation,  namely,  the 
"  Manual  of  Chemistry."  This  work  was,  in  its  day,  one  of  the  most 
popular  in  the  English  language,  and  there  are  few  recent  treatises,  in 
chemistry  which  are  not  indebted  to  its  pages  for  much  valuable  in- 
formation. The  fact  that,  owing  to  its  bulk,  the  manual  had  gone 
beyond  the  necessities  of  the  medical  students,  and  that  it  had  acquired 
an  encyclopaedic  character  led  the  distinguished  chemist  to  join  with 
me,  in  1863,  in  preparing  the  present  work  in  one  volume  for  the 
special  use  of  students,  and  I  may  here  state  that  the  whole  of  the 
chapters  on  the  Metals,  excepting  those  parts  which  refer  to  Toxi- 
cology, and  the  larger  portion  of  the  section  on  Organic  Chemistry, 
were  contributed  by  my  friend  and  coadjutor.  For  thirty  years  we 
had  known  each  other,  and  during  that  time  we  had  been  frequently 
associated  in  many  important  chemical  investigations  of  a  public  and 
private  nature.  All  scientific  men  who  were  brought  in  contact  with 
Mr.  Brande,  could  not  fail  to  be  struck  with  the  accuracy  and  extent 
of  his  knowledge,  the  retentiveness  of  his  memory,  and  the  truthful- 
ness and  honesty  of  purpose  by  which  he  was  always  actuated.  The 
friend  of  Gay-Lussac  and  Thenard,  and  the  colleague  of  Davy  and 
Faraday,  he  formed  a  connecting  link  between  the  chemists  of  the 
past  and  the  present  generation.     He  lived  to  see  great  changes  in  the 


PREFACE.  IX 

science  which  he  had  himself  so  successfully  cultivated,  but  like  his 
great  contemporaries  Guy-Lussac,  Th^nard,  and  Davy,  he  preferred 
demonstration  to  speculation,  and  although  ready  to  adopt  what  was 
established  by  experiment,  however  it  might  conflict  with  his  previous 
views  (proofs  of  which  will  be  found  in  the  successive  editions  of  his 
manual)  he  was  strongly  opposed  to  innovations  based  upon  mere 
hypotheses. 

In  private  life  it  was  impossible  to  meet  with  a  man  of  more  genial 
character  than  Mr.  Brande.  His  conversational  powers  were  great ; 
he  was  full  of  anecdotes  of  the  scientific  and  non-scientific  celebrities 
of  his  day,  and  no  man  could  pass  an  hour  in  his  society  without 
retaining  a  pleasing  reminiscence  of  him  as  a  companion. 

A.  S.  T. 


CONTENTS. 


CHAPTER  PAGE 

1.  Matter  and  its  Properties        •  .            .           .            .           .           .  17 

2.  Crystallization.    Dimorphism.     Isomorphism  .            .            .            .  25 

3.  Chemical  Force.     Solution.     Electrolysis        ....  40 

4.  Equivalent  Weights  and  Voftimes.     Nomenclature  and  Notation     .  64 


METALLOIDS. 


5.  Metalloids  and  Metals.    Properties  of  Gases  and  Yapors 

6.  Oxygen.     Oxides.     Oxidation   .... 

7.  Oxygen.    Incandescence.     Combustion.     Deflagration 

8.  Ozone.    AUotropic  Oxygen.     Antozone 

9.  Hydrogen  ...... 

10.  Water.    Aqueous  Yapor.    Ice  .... 

11.  Water.    Physical  and   Chemical  Properties.     Hydration.    Mineral 

Waters.    Peroxide  of  Hydrogen 

12.  Nitrogen.     The  Atmosphere      .... 

13.  Compounds  of  Nitrogen  and  Oxygen.     Nitric  Acid    . 

14.  Compounds  of  Nitrogen  and  Hydrogen.     Ammonia  and  its  Salts 

15.  Chlorine.     Compounds  with  Oxygen  and  Hydrogen.    Hydrochloric 

Acid    .  .  . 

16.  Bromine,  Iodine,  Fluorine ;  and  their  Compounds 

17.  Sulphur  and  its  Compounds.     Selenium  and  its  Compounds 

18.  Phosphorus  ;  its  Compounds  with  Oxygen  and  Hydrogen 

19.  Carbon  and  its  Compounds  with  Oxygen.    Carbonic  Oxide.    Carbonic 

Acid    .  .  .  .  .  . 

20.  Carbon.    Compounds  of  Carbon  with  Hydrogen,  Nitrogen,  and  Sul 

phur    ........ 

21.  Boron  and  Silicon.    Boracic  and  Silicic  Acids 


78 
90 
100 
110 
118 
126 

139 
153 
166 
178 

188 
201 
212 
233 

249 

269 

292 


METALS. 


22.  Physical  Properties  of  the  Metals.    Eelations  to  Heat,  Light,  Elec- 

tricity, and  Magnetism  ......  307 

23.  Potassium  ........  312 

24.  Sodium    .........  328 

25.  Lithium.     Caesium.    Eubidum.    Thallium       ....  341 


Zll 


CONTENTS. 


CHAPTER 

26.  Barium.     Strontium.     Calcium.    Magnesium . 

27.  Aluminum.     Glucinum.    Zirconium.    Thorium.    Yttrium.    Erbium 

Terbium.     Cerium.     Lanthanum.     Didymium 

28.  Qualitative  analysis  of  the  Oxides  and  Salts  of  the  preceding  Metals 

29.  Iron         ......•• 

30.  Manganese  ....... 

31.  Zinc.    Tin.    Cadmium   ...... 

32.  Copper.     Lead    ....... 

33.  Bismuth.     Cobalt.    Nickel.     Chromium 

34.  Vanadium.     Tungsten.      Columbium.     Niobium.     Ilmenium.     No 

rium.    Pelopium.    Molybdenum.    Uranium.    Tellurium.    Titanium 

35.  Antimony  ....... 

36.  Arsenic    ........ 

37.  Mercury  ........ 

38.  Silver       .  .  .  .  .         ^  . 

39.  Photography  and  its  Applications         .... 

40.  Gold.     Platinum  ...... 

41.  Palladium.    Ehodium.    Kuthenium.     Osmium.    Iridium 

42.  Qualitative  Analysis  of  the  most  Important  Compounds  of  the  pre- 

ceding Metals  ....... 


PAGE 

346 

367 
376 
380 
398 
406 
417 
437 

448 
459 
465 
479 
492 
503 
515 
526 

531 


Starch.    Gum.    Pectose.    Gelose- 

Alcoholic  Liquids 

Methylic,  Amylic,  and  other  Al 


ORGANIC  CHEMISTHY. 

43.  Constitution  and  Properties  of   Organic  Substanc^.      Proximate 

Analysis 

44.  Ultimate  or  Elementary  Analysis 

45.  Proximate  Organic  Principles. 

Sugar  .... 

46.  Alcoholic  or  Vinous  Fermentation. 

47.  Alcohol.    Aldehyde.    Chloroform. 

cohols.  ...... 

48.  Ether.     Oil  of  Wine.    Compound  and  Double  Ethers  . 

49.  Cellulose.    Pyroxyline.    Wood.    Coal.    Bitumen.     Products  of  the 

Decomposition  of  Wood  and  Coal 

50.  Essential  Oils.    Camphor.    Eesins.    Amber.     Caoutchouc.     Gutta 

Percha  .  . 

51.  Fats  and  Fixed  Oils.    Products  of  their  Decomposition.    Spermaceti 

Wax.    Soaps  . 

52.  Vegetable  Acids 

53.  Alkaloids  and  Organic  Bases.    Substances  Associated  with  or  De 

rived  from  them 

54.  Organic  Coloring-Matters.    Dyeing 

55.  Neutral  Nitrogenous  Substances.     The  Solid  Constituents  of  the 

Animal  Body,  and  Substances  Derived  from  them 

56.  The  Fluid  Constituents  of  Animal  Bodies,  and  the  Substances  De- 

rived from  them 
Appendix 
Index 


535 
545 

560 
673 

583 
595 

603 

613 

622 
634 

657 
669 

685 

706 
729 
749 


CORKIGENDA. 


Pago    ix,     2d  line  from  top,  for  "  Guy-Liissac"  read  "  Gay  Lussac." 
"       43,20th     "       "       *•    /or  "  say"  reac/"  as." 

«'       68,15th     "       "     bottom, /or  "weights  of  oxygen"  rertrf ''weight  of  oxygen." 
««       69,    9th  and  11th  line  from  top,  for  «'  1-44"  read  "  14-4" 
«        «       "     line  from  top, /or  «  1-1557"  read  "1-1057." 
«       72,     "       "       "       "     rfe/e"that" 

"        "    10th    "       "       "    for  "  aqueou|  oxide"  read  "  hydrous  oxide." 
«'       73,25th   "       "       "    /or  "no"  reac/"  an." 
«»       75,14th    "       "      bottom,/or"bisulphate"  read  "bisulphite." 
«       93,18th    "       "      top,/or  "(NIgO)"  read"  (MgO)." 
"       95,     1st    "       "       "    /or  "reasons"  read  "  reason." 

*'  101,  15th  and  16th  lines  from  bottom,  for  "  iodized"  read  "  oxidized." 

*'  224,    5th  line  from  bottom,  for  "  230/'  read  "  2S202-" 

«  710,   22d     "       "     top,/or  "Mr.  Sorly"  read  "Mr.  Sorby." 

««  744,14th    "       "      "    /or  "on  which"  read'" in  which." 

"  745,  table,  4th  symbol,  1st  column,  for  " Ce"  read  "  CI." 


CHEMISTKY. 


CHAPTERI. 

MATTER   AND   ITS   PROPERTIES. 

Chemistry  as  a  science  embraces  the  whole  range  of  animate  an4  inani- 
mate nature.  By  its  means,  man  acquires  a  knowledge  of  the  special  pro- 
perties of  bodies,  and  the  laws  which  govern  their  combinations.  By  the 
application  of  its  principles  he  can  resolve  substances  into  their  elementary 
constituents,  and  out  of  old  materials  construct  new  compounds.  It  confers 
on  him  a  species  of  creative  power,  by  enabling  him  to  unite  elements  or 
compounds,  and  thus  to  produce  a  large  number  of  bodies  which  have  no 
independent  existence  in  nature.  Either  directly  or  indirectly,  Chemistry 
as  an  art  lends  its  aid  to  the  great  purposes  of  civilization.  In  every  civil- 
ized country,  mining  and  metallurgy,  as  well  as  most  branches  of  manufac- 
turing industry,  owe  their  development  and  progress  to  the  proper  cultiva- 
tion of  Chemistry. 

A  chemist  has  to  deal  with  matter,  as  well  as  with  the  forces  which  are 
inherent  in  and  connected  with  it.  Matter  may  be  either  simple  or  compound, 
and  the  forces  that  control  it  may  be  either  physical  or  chemical.  Had  the 
globe  been  constituted  of  only  one  kind  of  substance  or  matter,  the  laws 
of  physics  alone  would  have  sufficed  to  explain  the  phenomena  of  nature. 
There  are,  however,  sixty-five  different  kinds  of  matter  now  known  to 
chemists,  and  as  these  are  resolvable  into  no  other  bodies,  they  are  called 
simple  substances  or  elements.  But  few  of  these  are  found  in  nature  in  their 
simple  or  elementary  condition  ;  they  are  in  general  intimately  combined 
with  each  other,  constituting  the  large  variety  of  compounds  of  which  the 
crust  of  the  earth  is  composed.  These  simple  substances  not  only  differ  in 
properties,  but  their  compounds  also  differ  as  much  from  each  other  as  from 
the  elements  which  form  them.  It  is  the  province  of  a  chemist  to  define 
these  differences,  to  determine  the  laws  by  which  they  are  brought  about, 
and  to  establish  the  relations  of  this  with  other  branches  of  science. 

Chemistry  teaches  us  that  matter  is  in  its  nature  unalterable  and  inde- 
structible :  it  may  change  its  state,  and  undergo  a  change  in  properties,  as 
a  result  of  the  chemical  force,  but  it  may  by  the  same  force  be  restored  to 
its  original  state  with  all  its  properties  unimpaired.  Iron  and  sulphur 
possess  well-marked  characters  by  which  they  may  be  easily  known  from 
each  other;  but  when  combined,  as  in  iron  pyrites  or  bisulphide  of  iron, 
these  characters  are  entirely  lost,  and  new  properties  are  manifested.  •  On 
again  separating  the  two  elements,  each  reassumes  its  original  properties. 
Chemistry,  therefore,  is  not  only  a  science  of  properties,  but  a  science  of 
metamorphoses  or  transformations. 

Recent  researches  have  shown  that  although  elements  are  not  resolvable 
into  other  substances,  they  are  in  some  instances  so  altered  by  chemical  and 
2 


18  ALLOTROPIC    STATE.      ISOMERISM. 

physical  forces,  that  they  apparently  lose  their  identity.  We  have  an  ex- 
ample of  this  metamorphosis  of  elementary  matter,  in  that  condition  which 
is  called  allotropy  (axxoc  -rponoj,  change  of  state),  and  no  substance  presents 
it  in  so  remarkable  a  degree  as  phosphorus.  Common  phosphorus  is  a  waxy- 
looking  solid,  melting  at  or  below  111°,  and  taking  fire  a  little  above  its 
melting  point.  It  is  dissolved  by  sulphide  of  carbon  ;  it  is  luminous  in  the 
dark,  evolves  an  acid  vapor  in  air,  producing  at  the  same  time  ozone,  and  is 
very  poisonous.  By  exposure  to  a  temperature  of  460°,  under  certain  con- 
ditions, this  substance  is  so  completely  changed  in  its  properties  that  it 
would  no  longer  be  recognized  as  phosphorus.  It  presents  itself  as  a  hard, 
brittle,  red-colored  solid,  which  may  be  heated  to  about  500°  before  it  melts 
or  takes  fire,  is  insoluble  in  sulphide  of  carbon,  does  not  evolve  any  lumi- 
nous or  acid  vapors,  does  not  produce  ozone,  and  has  no  poisonous  action 
on  animals.  By  the  application  of  chemical  reagents  and  heat,  the  same 
products  are  obtained  from  it  as  from  common  phosphorus;  and  as  no  other 
matter  or  substance  can  be  extracted  from  it,  and  each  is  convertible  into 
the  othgr,  we  are  compelled  to  ascribe  the  diflference  in  properties  to  mole- 
cular changes.  Oxygen,  sulphur,  carbon,  boron,  and  silicon,  are  bodies 
which  may  also  exist  in  two  or  more  states  in  which  their  properties  are 
widely  difierent.  This  difi'erence  is  sometimes  brought  out  by  physical,  and 
at  other  times  by  chemical  agency.  These  facts  show  us  that  the  elemen- 
tary state  of  matter  is  not  so  simple  as  has  been  hitherto  supposed,  and  they 
point  to  the  probability  that  many  of  the  substances  now  regarded  as  ele- 
ments, may  hereafter  be  proved  to  be  compounds.  The  allotropic  state, 
however,  is  not  confined  to  simple  substances.  Compound  bodies,  such  as 
silicic  acid,  and  the  peroxides  of  iron  and  tin,  present  instances  of  this  con- 
dition. The  physical  and  chemical  properties  of  these  bodies  are  changed 
by  heat,  or  vary  with  the  mode  of  their  production,  while  their  chemical 
composition  remains  unaltered. 

When  two  compounds  can  be  proved  to  be  formed  of  the  same  elements  in 
the  same  proportions  by  weight,  it  would  appear  to  be  a  reasonable  inference 
that  their  properties  should  be  identical  ;  but  chemistry  teaches  us  that  this 
condition  may  exist,  and  yet  the  substances  be  wholly  difi"ereut  in  chemical 
and  physical  properties.  Bodies  which  thus  resemble  each  other  in  atomic 
constitution  are  called  isomeric  (icro?  equal,  and  fii^o^  part),  and  isomerism  is 
the  name  applied  to  this  condition  of  matter.  The  fact  is,  the  properties  of 
the  substance  depend  not  only  on  the  nature  of  the  elements,  and  the  number 
of  atoms  of  each,  but  on  the  mode  in  which  these  elements  are  grouped  or 
arranged.  Gum,  starch,  and  sugar  are  isomeric,  or  are  constituted  of  a  like 
number  of  atoms  of  the  same  elements,  and  the  difference  in  their  properties 
can  therefore  only  be  ascribed  to  a  difference  of  arrangement  among  these 
atoms.  Cases  of  isomerism  are  much  more  numerous  in  organic  than  in 
mineral  chemistry,  for  the  reason  that  organic  compounds  are  composed  of  a 
greater  number  of  atoms  of  each  element,  and  these  admit  of  a  greater 
variety  of  arrangement.  In  some  instances,  the  atoms  are  in  precisely  the 
same  number,  but  the  bodies  which  they  form  are  widely  diflferent.  Thus, 
the  hydrated  cyanate  of  ammonia  is  represented  by  the  formula  NH3,C2NO, 

HO,  while  the  organic  compound  urea  is  C^X^OgHj.  The  properties  of 
these  compounds  are  widely  different.  That  the  differences  must  depend  on 
the  arrangement  of  the  atoms  is  proved  by  the  discovery  of  Wohler,  that  on 
evaporating  a  solution  of  the  hydrated  cyanate  of  ammonia  this  salt  disap- 
peared, and  the  organic  principle  urea  was  produced.  Oil  of  turpentine  and 
oil  of  lemons  present  another  instance  of  similarity  of  atomic  composition 
with  difierent  properties.    Each  of  these  oils  contains  C,^H,„,  but  no  method 


PHYSICAL    FORCES. 


«9 


is  known  by  which  one  can  be  converted  into  the  other.  There  is  a  whole 
group  of  hydrocarbons  similarly  constituted.  Isomeric  bodies  in  which  the 
atoms  are  the  same  in  number  and  relative  proportion  are  called  metameric, 
in  order  to  distinguish  them  from  another  class  called  polymeric,  in  which 
the  relative  proportions  in  100  parts  by  weight  are  the  same,  while  the  abso- 
lute number  of  atoms  differs.  Aldehyd  and  acetic  ether  are  liquids  remark- 
ably different  in  properties,  but  they  are  polymeric.  Aldehyd  is  represented 
by  C^H^O^,  and  acetic  ether  by  CgHyO^.  Two  atoms  of  aldehyd  would 
therefore  be  equivalent  to  one  of  acetic  ether;  but  100  parts  of  each  liquid 
would  yield  precisely  the  same  relative  weights  ftf  carbon  and  hydrogen. 
At  the  same  time  these  liquids  are  not  mutually  convertible  into  each  other. 
In  mineral  chemistry,  a  similar  condition  presents  itself  in  reference  to  the 
compounds  known  as  ferro  and  ferri-cyanogen.  The  former  is  FejCgNg; 
the  latter  has  exactly  double  the  number  of  atoms,  FgjCjaNg.  In  a  state  of 
combination,  their  crystalline  forms,  color,  and  chemical  properties  are  wholly 
different.  These  facts  teach  us  that  the  grouping  of  the  atoms,  apart  from 
the  chemical  composition  of  substances,  has  a  material  influence  on  their 
chemical  and  physical  properties. 

While  physics  relate  to  those  changes,  in  masses  as  well  as  .particles  of 
matter,  which  result  from  the  physical  forces  of  gravitation,  electricity, 
magnetism,  light,  and  heat,  chemistry  relates  to  changes  produced  among  the 
minute  particles  of  bodies  which  are  the  result  of  one  peculiar  force — namely, 
chemical  force,  affinity,  or  attraction. 

Physical  Forces. — Physical  forces  are  manifested  on  the  same  or  on  different 
kinds  of  matter.  The  chemical  force  can  be  manifested  only  between  different 
kinds  of  matter.  As  a  general  rule  physical  forces  produce  no  permanent 
change  in  the  properties  of  bodies,  while  it  is  the  special  character  of  the 
chemical  force,  and  the  leading  feature  of  its  existence,  that  the  properties  of 
the  bodies  on  which  it  has  been  exerted  are  permanently  altered.  Sulphur 
and  iron  will  serve  to  illustrate  the  differences  here  indicated.  Gravitation 
affects  both,  but  in  different  degrees.  A  cubic  inch  of  iron  gravitates  with 
a  force  equal  to  that  of  three  and  a  half  cubic  inches  of  sulphur.  This  is 
indicated  by  a  comparison  of  their  relative  weights  in  the  same  volume  or 
bulk  (specific  gravity).  If  the  mass  of  iron  is  rubbed  with  a  flannel,  and 
held  near  a  light  substance,  such  as  dry  bran,  there  is  no  attraction  ;  when 
brought  near  to  a  suspended  magnet,  each  end  of  the  magnet  is  powerfully 
attracted  ;  when  heated  it  does  not  melt ;  under  reflected  light  it  has  a  gray 
color  and  a  metallic  lustre.  A  small  bar  of  it  held  in  a  flame,  allows  the  heat 
rapidly  to  traverse  its  substance,  and  it  becomes  painfully  hot,  without  under- 
going any  further  change.  On  the  other  hand,  a  mass  of  sulphur  warmed 
and  rubbed  with  dry  flannel,  powerfully  attracts  bran  and  all  light  substances. 
Until  it  has  been  rubbed  it  manifests  no  attraction  for  the  magnet,  and  after 
rubbing,  it  attracts  it  only  as  a  result  of  the  frictional  electricity  produced  in 
it ;  when  heated,  it  readily  melts,  takes  fire,  and  burns  with  a  blue  flame ; 
under  reflected  light  it  has  a  peculiar  yellow  color  without  any  metallic  lustre. 
Here,  then,  we  have  a  manifestation  of  different  physical  properties  in  these 
two  bodies,  and  we  learn  that  iron  is  of  greater  specific  gravity  than  sulphur  ; 
that  while  iron  is  not  rendered  electric  by  friction,  sulphur  becomes  highly 
electric  ;  that  while  iron  is  powerfully  magnetic,  there  is  no  magnetism  in 
sulphur;  that  as  to  the  effect  of  heat,  while  one  is  infusible  and  incombus- 
tible at  ordinary  temperatures,  the  other  readily  melts  and  burns ;  that  the 
light  reflected  by  the  two  is  different,  and  that  while  iron  allows  heat  to  tra- 
verse its  particles  rapidly  from  end  to  end,  sulphur  does  not.  After  having 
manifested  all  these  phenomena  as  a  result  of  physical  forces  brought  to 


2$  CHANGES    IN    MATTER    BY    THE    CHEMICAL    FORCE. 

bear  upon  them,  the  iron  and  the  sulphur  resume  their  original  state, 
unchanged  in  properties. 

The  chemical  differences  which  exist  between  iron  and  sulphur  are  not  less 
remarkable.  If  sulphur  in  fine  powder  is  sprinkled  in  a  jar  inverted  in  a 
saucer  of  water,  it  may  be  kept  for  any  length  of  time  without  undergoing 
any  change.  If  iron-filings  are  sprinkled  in  another  jar,  also  inverted  in 
water,  the  iron  will  be  oxidized  or  rusted,  and  the  water  will  rise  in  the  jar, 
showing  that  a  part  of  its  gaseous  contents  has  been  removed.  The  gas  thus 
removed  may  be  proved  by  experiment  to  be  oxygen,  which,  at  a  low  tem- 
perature, will  combine  with  iron  but  not  with  sulphur. 

If  we  mix  together  iron  and  sulphur  in  the  finest  powder,  in  the  propor- 
tions in  which  we  know  they  will  chemically  combine  to  form  iron  pyrites 
or  bisulphide  of  iron,  namely,  forty-seven  parts  of  iron  and  fifty-three  of 
sulphur,  they  will  remain  as  a  mere  mixture,  each  with  its  physical  properties 
unaltered.  Owing  to  the  presence  of  iron  the  powder  will  have  magnetic 
properties,  and  when  placed  in  water  the  iron  will  rust,  and  remove  oxygen 
from  a  vessel  of  air.  If  a  magnet  be  drawn  over  the  powder,  the  iron  will 
be  removed,  and  the  sulphur  remain.  If  examined  by  a  microscope,  the 
particles  of  sulphur  will  be  distinctly  seen  mixed  with  the  particles  of  iron. 

Chemical  Force. — When  the  sulphur  and  iron  are,  however,  chemically 
united  in  the  proportions  above-mentioned,  as  in  iron  pyrites,  they  will  be 
found  to  have  lost  their  characteristic  physical  and  chemical  properties. 
This  substance  is  seen  in  hard  cubic  crystals  ofr  a  yellow  color  and  of  a 
metallic  lustre.  It  has  no  magnetic  properties  ;  it  is  not,  like  sulphur, 
rendered  electric  by  slight  friction,  and  in  the  state  of  fine  powder  it  does 
not  remove  oxygen  when  placed  in  a  jar  of  air  over  water.  A  magnet  drawn 
over  this  powder  produces  no  effect  upon  it,  the  iron  is  not  separated  from 
the  sulphur.  Neither  sulphur  nor  iron  can  be  seen  in  the  powder,  by  the 
aid  of  the  most  powerful  microscope.  We  have,  in  fact,  an  entire  change  of 
properties,  and  the  new  properties  acquired  are  retained  so  long  as  the  two 
elements  are  chemically  combined.  By  aid  of  the  chemical  force,  the  two 
elements  may  be  separated  and  procured  in  a  pure  state.  The  iron  and  sul- 
phur will  then  be  found  to  have  re-acquired  all  the  properties,  physical  and 
chemical,  which  they  had  lost  as  the  result  of  their  combination. 

Physical  forces,  therefore,  produce  only  temporary  changes  in  bodies, 
while  the  chemical  force  entirely  alters  them ;  and  this  alteration  continues 
until  the  union  of  the  elements  is  dissolved.  Further,  we  learn  that  the 
properties  of  a  chemical  compound  cannot  be  inferred  from  the  properties  of 
its  constituents.  Its  physical  condition  as  gas,  liquid  or  solid,  and  its  chemi- 
cal and  physiological  characters,  can  be  determined  only  by  experiment. 
Nitrogen  and  hydrogen  are  two  comparatively  inert  gases,  while  carbon  is 
an  innoxious  solid.  The  combination  of  these  three  elements  produces  a 
highly  poisonous  liquid,  Prussic  acid.  Hydrogen  has  no  smell,  and  sulphur 
only  a  slight  smell  on  friction  ;  when  chemically  combined  these  bodies  pro- 
duce a  most  offensively-smelling  gas,  sulphide  of  hydrogen.  Carbon,  oxygen, 
hydrogen,  and  nitrogen,  are  innoxious  agents,  and  have  no  taste,  but  when 
combined  in  certain  proportions  they  form  strychnia,  remarkable  for  its 
intensely  bitter  taste  and  highly  poisonous  properties.  Iron  manifests  mag- 
netism most  powerfully,  and  oxygen  is  the  most  magnetic  of  gases,  yet  these 
two  bodies,  when  combined  in  the  proportions  of  two  of  iron  to  three  of 
oxygen,  produce  a  compound  in  which  no  trace  of  magnetism  can  be 
discovered. 

The  properties  of  substances  which  are  referable  to  the  senses  in  the  form 
of  taste,_  odor,  color,  or  touch,  are  called  by  the  French  organoleptic,  to 
distinguish  them  from  physical  and  chemical  properties.     They  are  of  some 


DIVISIBILITY    OF    MATTER.  ,,  21 

importance  in  chemical  analysis,  as  they  often  aid  the  chemist  in  his  search 
after  minute  traces  of  certain  elements  or  compounds. 

Divisibility  of  Matter. — Matter,  in  the  simple  or  compound,  in  the  solid 
or  liquid  state,  is  divisible.  Thus,  a  solid  or  liquid  may,  by  various  pro- 
cesses, be  reduced  into  particles  so  fine  that  they  are  no  longer  perceptible 
to  the  eye.  When  reduced  to  the  l-500,000th  of  an  inch  in  diameter,  the 
particle  would  be  no  longer  visible  under  the  most  powerful  microscope 
(Mitscherlich)  ;  but  lines  closer  together  than  the  100,000th  of  an  inch 
admit  of  no  separation  by  the  most  powerful  modern  object-glass.  The 
minute  particles  of  fine  precipitates,  such  as  sulphate  of  baryta  or  chloride 
of  silver,  are  individually  imperceptible  :  they  are  only  rendered  visible  to 
the  eye  by  aggregation.  So  of  all  solids  in  solution,  the  particles  are  so 
small  that  light  traverses  them.  A  small  quantity  of  mercury  shaken  in  a 
bottle  with  strong  sulphuric  acid,  is  temporarily  split  into  myriads  of  minute 
globules.  Mere  pressure  with  the  finger  will  divide  this  liquid  into  particles 
so  small  that  they  become  gray  and  their  bright  lustre  is  lost  to  the  eye. 
By  subliming  the  metal  in  a  tube,  its  particles  may  be  so  subdivided  as  to 
present  only  a  gray  tarnish  on  the  glass.  If  a  solution  of  chloride  of  tin  is 
added  to  a  solution  of  corrosive  sublimate,  a  grayish-black  precipitate  is 
formed,  which,  when  separated  by  filtration,  appears  on  the  filter  in  the  form 
of  microscopical  globules,  so  minute  that  it  would  be  difficult  to  assign  a 
weight  and  size  to  each.  Platinum,  in  the  form  of  ammonio-chloride,  is 
converted  by  nascent  hydrogen  produced  by  the  action  of  sulphuric  acid  on 
zinc  into  a  black  powder  (platinum-black)  resembling  charcoal.  All  the 
physical  characters  of  a  metallic  substance  are  lost  by  reason  of  the  extreme 
tenuity  of  its  particles.  Gold  admits  of  still  finer  subdivision.  It  has  been 
reduced  to  such  a  state  of  tenuity  that  it  does  not  sink  in  water,  but  allows 
light  to  traverse  it  as  well  as  the  liquid  :  its  particles  giving  to  the  liquid  a 
blue,  green,  or  ruby  color,  according  to  the  degree  to  which  they  have  been 
divided  by  chemical  agency.  According  to  Faraday's  experiments,  the  ruby 
liquids  present  metallic  gold  in  the  finest  state  of  division  ;  the  blue  liquids 
hold  the  gold  in  a  more  aggregated  form.  That  they  are  finely-difi'used  par- 
ticles of  the  metal  is  proved  by  throwing  a  cone  of  sun-rays,  either  by  a  lens 
or  mirror,  into  the  midst  of  the  liquid,  when  the  illuminated  cone  clearly 
proves  them  to  be  undissolved  bodies.  He  estimated  that  a  particle  in  this 
state  formed  1-500, 000th  part  of  the  volume  of  the  fluid.  {Proc.  Roy.  Soc, 
vol.  8,  No.  24,  p.  361.)  Muncke  has  calculated,  from  the  diffusion  of  a 
known  weight  of  gold  over  silver  wire,  that  one  grain  admits  of  subdivision 
into  ninety-five  thousand  millions  of  visible  parts,  ^.  e.,  visible  under  a  micro- 
scope magnifying  1000  times.  {Handb.  der  Naturlehre,  43.)  Films  of  gold, 
finer  than  the  finest  leaves  of  the  metal,  may  be  obtained  by  the  following 
process  :  Place  a  thin  slice  of  phosphorus  on  a  surface  of  a  very  diluted  solu- 
tion of  chloride  of  gold.  Cover  the  vessel  so  as  to  prevent  the  access  of 
light.  In  the  course  of  twenty-four  hours  the  gold  will  be  reduced  to  the 
metallic  state,  for  a  considerable  extent  around  the  phosphorus.  It  will 
present  the  brilliant  color  of  the  metal  by  reflected,  but  will  appear  bluish- 
green  by  transmitted  light.  The  metallic  film  may  be  raised  from  the  surface 
of  the  solution,  by  bringing  into  contact  with  it  a  clean  surface  of  glass.  It 
will  adhere  iOf  and  may  be  dried  and  preserved  upon  the  glass.  Its  tenuity 
is  such,  that  by  mere  appearance  it  is  scarcely  possible  to  determine  on  which 
side  of  the  glass  it  is  deposited.  It  is  probably  less  than  the  millionth  of  an 
inch  in  thickness. 

The  divisibility  of  matter  is  of  interest  to  the  chemist,  inasmuch  as  it 
enables  him  to  speculate  on  the  limits  of  chemical  tests  for  the  detection  of 
substances.     If  half  a  grain  of  nitrate  of  silver  is  dissolved  and  diffused  in 


22  COHESIVE  FORCE  or  matter. 

100  ounces  of  distilled  water,  the  presence  of  the  metallic  silver  throughout 
will  be  indicated  by  the  liquid  being  rendered  opaque,  from  the  production 
of  chloride  of  silver,  by  the  addition  of  a  few  drops  of  a  solution  of  common 
salt.  One  grain  of  silver  may  here  be  proved  to  be  split  into  138,000  parts. 
But  Malaguti  found  in  sea-water  taken  off  the  French  coast,  that  silver  was 
dissolved  in  it  as  a  chloride,  in  the  proportion  of  one  grain  in  100,000,000 
grains,  so  that  each  grain  of  water  would  contain  only  the  100,000,000th  of 
a  grain  of  metallic  silver.  No  analysis  could  reveal  its  presence,  except  by 
an  operation  on  a  large  quantity.  (Quart.  Journ.  of  Chem.  Soc.  1851,  vol. 
8,  p.  69.)  One  quarter  of  a  grain  of  acetate  of  lead  dissolved  and  diffused 
in  100  ounces  of  water,  will  form  a  solution  which  is  turned  of  a  brown 
color  by  sulphuretted  hydrogen,  in  parts  as  well  as  in  the  mass.  The  lead 
is  here  converted  into  sulphide ;  and  a  grain  of  the  metal  is  actually  split 
into  336,000  parts.  With  indigo  the  divisibility  may  be  carried  still  further. 
One-eighth  of  a  grain  of  indigo  dissolved  in  sulphuric  acid  will  give  a  well- 
marked  blue  coly  to  300  ounces  of  water.  This  is  in  about  the  proportion 
of  a  millionth  part  of  a  grain  in  every  drop  of  water.  Muncke,  vrho  has 
ingeniously  calculated  the  weight  of  the  minutest  visible  particle  of  gold 
obtainable  from  the  division  of  a  grain  of  metal,  has  endeavored,  in  reference 
to  indigo,  to  determine  the  size  of  the  minutest  particles  of  this  substance 
from  the  dilution  of  a  measured  quantity  of  its  solution.  He  estimates  it  at 
the  five  hundred  billionth  of  a  cubic  inch.  {Op.  cit.,  p.  44.)  Half  a  grain 
of  iodine  may  be  easily  diffused  in  vapor,  through  five  gallons  of  air,  con- 
tained in  a  glass  vessel.  Each  millionth  of  a  cubic  inch  of  air  contains  only 
the  1-2, Y10,600, 000th  of  a  grain.  In  other  words,  a  grain  of  iodine  is  split 
by  diffusion  into  two  thousand  seven  hundred  and  seventy  millions  of  parts 
— these  minute  atoms  being  easily  detected  throughout  the  whole  of  the  inte- 
rior of  the  glass  vessel  by  the  action  of  iodine  on  paper  wetted  with  starch. 
Assuming  the  specific  gravity  of  iodine  to  be  5,  it  follows  that  the  size  of  the 
atom  of  iodine  under  this  divisibility,  is  less  than  the  three  billionth  of  a 
cubic  inch. 

The  divisibility  of  matter  has  of  late  acquired  an  additional  interest  in  a 
chemical  point  of  view,  by  reason  of  the  discoveries  of  Kirchoff  and  Bunsen, 
in  reference  to  the  diffusion  of  metals.  Their  researches  tend  to  show  that 
sodium,  probably  in  the  form  of  chloride,  is  a  constituent  of  the  atmosphere, 
and  is  diffused  as  a  vapor  over  the  whole  of  the  globe.  The  divisibility  of 
sodium  to  the  extent  in  which  it  may  be  detected  by  prismatic  analysis, 
utterly  defies  the  balance  and  the  microscope.  These  chemists  have  tested 
the  diffusion  of  the  vapor  of  sodium  from  a  minute  quantity  by  weight  in  a 
room  of  known  capacity,  and  they  have  detected  its  presence  by  the  prism 
when  the  quantity  examined  could  not  have  exceeded  the  195,000,000th  part 
of  a  grain  in  weight.  {Phil.  Mag.,  Aug.  1860,  p.  95.)  In  reference  to  this 
mode  of  analysis  they  have  also  announced  the  presence  of  a  metal  (caesium) 
in  a  mineral  water,  of  which  it  could  not  have  formed  more  than  the 
100,000,000th  part. 

These  results  and  calculations  naturally  suggest  the  question,  whether 
there  can  be  any  limit  to  the  divisibility  of  matter.  Without  going  into  the 
metaphysical  part  of  this  question,  we  may  state  that  as  bodies  in  masses 
can  be  proved  to  combine  in  definite  weights,  or  weights  which  are  fixed  for 
each  substance,  it  is  probable  that  the  same  is  true  of  the  minutest  particles 
of  which  they  are  composed.  The  view  most  consistent  with  chemical  facts 
and  theories  is,  that  there  is  a  limit  to  the  divisibility  of  matter,  and  to  this 
limit  the  term  atom  (arojuoj,  undivided)  is  applied.  It  is  believed  that  at 
this  point  matter  is  no  longer  divisible-.  What  that  limit  is  cannot  be 
defined,  and  it  is  unnecessary  for  practical  purposes  to  inquire.     We  can 


ADHESION    AND    COHESION.      CAPILLARY    ATTRACTION.  23 

neither  calculate  nor  estimate  the  size,  shape,  or  absolute  weight  of  atoms, 
but  we  can  say  that  they  are  infinitely  smaller  than  any  particles  which  we 
can  weigh  in  the  most  delicate  balance,  or  measure  in  the  field  of  the  most 
powerful  microscope. 

Cohesion. — The  minute  atoms  of  matter  in  the  solid  or  liquid  state  may 
be  held  together  by  two  forces ;  first,  by  the  force  of  cohesion  ;  and  second, 
by  the  force  of  affinity,  or  the  chemical  force.  In  simple  substances  cohe- 
sion only  is  exerted.  Thus,  in  sulphur  as  a  solid,  and  in  bromine  as  a  liquid, 
the  particles  of  each  element  are  held  together  by  cohesion.  In  compound 
bodies  the  two  forces  are  in  operation.  In  a  mass  of  lime  the  particles  are 
united  by  cohesio7i;  but  the  oxygen  and  calcium  of  which  the  lime  is  consti- 
tuted, are  held  together  by  the  chemical  force. 

The  force  of  cohesion  in  bodies  may  be  destroyed  by  physical  causes,  and 
the  three  states  in  which  matter  exists,  solid,  liquid,  and  gaseous,  depend  on 
the  relative  amount  of  cohesive  force  exerted  among  the  particles.  In  a 
solid  the  cohesive  force  is  strong,  in  a  liquid  it  is  comparatively  slight,  and 
iu  a  gas  it  ceases  to  manifest  itself.  The  cohesion  of  solids  is  destroyed  by 
pulverization,  but  more  completely  by  heat,  which  operates  as  an  antagonistic 
power.  Thus  many  solids  are  reduced  to  a  liquid,  and  ultimately  to  a 
gaseous  or  vaporous  state,  by  the  mere  effect  of  heat.  Ice,  water,  and  steam, 
present  familiar  examples  of  these  states  of  matter,  in  the  well-known  com- 
pound of  oxygen  and  hydrogen.  We  can  see  a  mass  of  ice  or  liquid  water, 
but  no  eye,  even  aided  by  the  microscope,  can  see  the  particles  of  aqueous 
vapor  into  which  water  is  converted  above  212°.  Some  bodies  are  known 
only  in  the  solid  state,  e.  g.,  lime  and  carbon  ;  others  only  in  the  gaseous 
state,  e.  g.,  oxygen  ;  others,  again,  only  in  the  liquid  and  gaseous  states,  e  g., 
alcohol.  From  recent  experiments,  there  is  reason  to  believe  that  bodies 
hitherto  supposed  to  be  of  a  fixed  nature,  such  as  platinum,  iron,  and  even 
carbon,  are  capable  of  assuming  the  gaseous  or  vaporous  state  under  the  in- 
tense heat  of  the  voltaic  battery  ;  and  that  their  particles  may  be  thus  trans- 
ferred from  one  pole  to  another. 

The  destruction  of  cohesion  in  compounds,  whether  brought  about  by 
mechanical  division  or  by  the  effect  of  heat,  does  not,  as  a  general  rule, 
destroy  the  chemical  force  by  which  the  atoms  are  bound  together.  Calomel 
may  be  reduced  to  the  finest  state  of  powder,  or  even  converted  into  vapor, 
by  heat ;  but  each  atom  of  the  compound  still  consists  of  chlorine  and  mer- 
cury. In  the  same  manner  the  invisible  particles  which  constitute  aqueous 
vapor,  contain,  in  their  most  extreme  division,  oxygen  and  hydrogen.  In 
some  instances,  heat  applied  to  solids  or  liquids,  either  directly  or  as  a  result 
of  friction  or  percussion,  will  dissever  atoms  united  by  chemical  affinity. 
Such  effects  are  seen  in  the  solid  iodide  and  in  the  liquid  chloride  of  nitrogen ; 
but  this  is  the  result,  not  of  mechanical  division,  but  of  the  decomposing 
agency  of  heat  on  such  bodies,  brought  out  by  friction  or  percussion.  The 
atoms  of  substances  which  are  once  chemically  combined,  require,  as  a  rule, 
the  chemical  force  for  their  separatiorf. 

Adhesion. — Cohesion  may  take  place  between  substances  of  different  kinds, 
but  this  is  by  contact  of  surfaces,  and  is  sometimes  called  adhesion.  An 
amalgam  of  tin  and  mercury  (used  in  silvering  mirrors)  adheres  closely  to 
a  surface  of  polished  glass.  The  film  of  reduced  metal  in  the  collodio-iodide 
of  silver,  on  which  a  photographic  image  has  been  produced,  adheres  very 
firmly  to  the  glass.  Lastly,  one  metal,  platinum,  by  reason  of  its  expansion 
and  contraction,  when  exposed  to  heat,  not  differing  materially  from  that  of 
glass,  may  be  actually  welded  to  this  substance,  and  on  cooling  it  firmly 
coheres  to  it.  A  platinum  wire  thus  welded  into  a  short  glass  rod,  forms  a 
useful  piece  of  apparatus  for  the  detection  of  small  quantities  of  alkaline 
bases  by  combustion. 


24  CAPILLARY    ATTRACTION. 

Capillary  Attraction. — Closely  allied  to  cohesion  is  that  mutual  attraction 
between  the  surfaces  of  solids  and  liquids  which  gives  rise  to  the  phenomena 
of  capillary  attraction,  so  called  from  its  causing  the  visible  rise  of  fluids  in 
tubes  of  small  bore.  If  a  tube  with  a  capillary  bore  of  one-fiftieth  of  an  inch 
be  dipped  at  one  end  into  a  glass  of  colored  water,  the  water  rises  to  about 
2^  inches,  and  the  rise  is  great  in  proportion  to  the  smallness  of  the  bore, 
and  is  greater  with  water  than  with  any  other  liquid.  If  two  plates  of  per- 
fectly clean  glass  be  so  held  as  to  form  a  very  acute  angle  with  each  other^ 
and  their  lower  edges  be  then  dipped  into  water  colored  by  sulphate  of  indigo, 
the  liquid  will  rise  in  the  form  of  a  curve  (hyperbola)  between  the  plates, 
rising  highest  where  the  space  between  them  is  least.  It  is  in  consequence 
of  this  species  of  attraction  that  a  drop  of  water  upon  a  solid  surface  wets 
and  adheres  to  it ;  and  that  the  surface  of  water  in  a  clean  glass  is  not  truly 
level,  but  a  little  elevated  upon  the  edges.  These  phenomena  depend  upon 
the  nature  of  the  substances  presented  to  each  other ;  thus  water  will  not 
rise  upon  greasy  glass  or  wax  ;  and  hence  also  different  liquids  rise  to  differ- 
ent heights  in  the  same  tube,  independently  of  their  specific  gravities,  and 
of  their  relative  degrees  of  viscidity.  Mercury  not  only  does  not  rise,  but 
is  depressed  in  the  bore  of  a  common  glass  tube  :  so  that,  unlike  water,  it 
presents  a  convex  instead  of  a  concave  surface  when  contained  in  a  glass  tube 
or  vessel,  provided  the  tube  or  vessel  is  clean  and  the  mercury  is  absolutely 
pure.  The  cohesive  attraction  of  the  particles  of  mercury  to  each  other 
is  greater  than  of  the  mercury  to  the  glass  :  hence  they  are  incapable  of 
wetting  it.  This  renders  mercury  well  fitted  for  thermometers  of  a  minute 
capillary  bore. 

The  rising  of  liquids  in  porous  or  spongy  bodies,  the  ascent  of  oil  or  spirit 
in  the  wicks  of  lamps,  in  which  the  fibres  of  cotton  or  asbestos,  by  reason  of 
their  contiguity,  build  up  small  tubes  or  channels — and  the  circulation  of  the 
juices  of  plants,  are  dependent  upon  capillary  attraction.  If  a  lump  of  white 
sugar  is  placed  on  a  few  drops  of  diluted  sulphate  of  indigo,  the  liquid  rises 
and  colors  the  whole  substance  of  the  sugar.  A  heap  of  dry  sand  placed  in 
contact  with  water  soon  becomes  damp  throughout.  If  a  short  piece  of  cane 
is  plunged  into  oil  of  turpentine,  the  liquid  after  a  time  rises  through  tbe 
fibrous  or  tubular  structure  of  the  cane,  and  may  be  burnt  as  with  a  wick  at 
the  top.  A  curious  instance  of  capillary  attraction  operating  with  crystal- 
lization, is  furnished  by  the  following  experiment :  Let  a  Florence  flask  be 
half  filled  with  a  saturated  solution  of  bisulphate  of  potash.  Plunge  into  the 
liquid  a  clean  deal  stick,  so  that  the  end  may  project  one  or  two  inches  above 
the  neck  of  the  flask.  If  kept  in  a  warm  and  dry  place,  the  liquid  will  rise 
by  capillary  attraction,  and  a  dense  crop  of  prismatic  crystals  will  after  some 
days  or  weeks  be  formed  on  the  top  of  the  wood.  As  the  small  prisms  build 
up  tubes,  the  liquid  is  gradually  drawn  through  them,  and  more  crystals  are 
deposited,  until  they  fall  off  as  a  result  of  their  weight. 

The  effect  of  capillary  attraction  is  often  seen  in  crystallizing  solutions. 
The  slender  prisms  deposited  at  the  edge  of  a  vessel  where  the  solution  is  in 
contact  with  it,  draw  up  more  of  the  crystallizing  liquid  and  another  crop  is 
formed,  in  a  ring  or  circle  above  the  liquid.  These  carry  the  liquid  by  capil- 
lary attraction  still  further,  so  that  they  sometimes  creep  up  the  inside  of  a 
vessel  and  descend  on  the  outside.  A  prismatic  crystallization  of  carbonate 
of  soda,  nitrate  of  potash,  and  sulphate  of  soda,  is  often  seen  on  walls,  cover- 
ing a  large  surface,  as  a  result  of  capillary  attraction. 

This  force  is  remarkable  in  the  fact  that,  like  cohesion,  it  is  more  powerful 
than  gravity.  Water  and  other  liquids  are  lifted  perpendicularly  in  spite  of 
gravitation.  It  affects  the  freezing  point  of  water,  which  is  stated  to  be 
much  lower  than  32°  when  the  liquid  is  contained  in  a  capillary  tube. 


CRYSTALLIZATION.      AMORPHOUS    BODIES.  25 

CHATTEE    II. 

CRYSTALLIZATION— DIMORPHISM— ISOMORPHISM. 

The  process  by  which  the  cohesive  force  operates  to  produce  a  symmetrical 
or  regular  form  in  bodies  is  called  crystallization.  A  crystal  (xpvoraxxoj,  ice 
or  crystal)  is  a  polyhedral  or  many-sided  solid,  having  smooth  and  bright 
surfaces  called  planes,  terminated  by  sharp  edges  or  angles.  This  force  is 
chiefly  witnessed  in  bodies  as  they  are  passing  from  the  gaseous  or  liquid  to 
the  solid  state.  The  study  of  this  subject  is  of  some  interest  in  reference  to 
analysis.  As  a  peculiar  crystalline  form  is  observed  in  a  large  number  of 
mineral  and  organic  compounds,  an  analyst,  when  assisted  by  the  microscope, 
is  enabled  to  detect  many  substances  in  quantities  too  small,  or  in  mixtures 
too  complex,  for  the  application  of  ordinary  tests.  Thus  a  crystal  of  white 
arsenic  not  larger  than  a  20,000th  part  of.  an  inch  may  be  easily  identified 
by  its  form. 

This  force  appears  to  be  impressed  on  the  minute  atoms  of  all  kinds  of 
matter.  Simple  and  compound,  solid,  liquid,  and  gaseous  bodies,  all  more 
or  less  assume  a  crystalline  form  when  placed  in  the  conditions  necessary  to 
the  process.  It  appears  to  be  as  closely  associated  with  certain  kinds  of 
matter  as  the  force  of  gravitation  itself.  Salts  not  found  in  nature,  but 
purely  productions  of  art,  acquire  crystallizing  power  in  fixed  and  definite 
forms,  whenever  the  union  of  their  atoms  takes  place  in  certain  chemical  pro- 
portions. Thus  potassium,  iron,  carbon,  and  nitrogen,  when  artificially  com- 
bined., produce  salts  which,  in  one  state,  form  splendid  yellow  octahedral 
crystals  with  a  square  base  (ferrocyanide  of  potassium)  ;  and  in  another  state, 
right  rhombic  prisms  of  a  rich  ruby  color  (ferricyanide  of  potassium),  the 
two  compounds  differing  but  slightly  in  the  proportions  of  one  of  their  com- 
ponent parts.  Crystallization  may  be  regarded  as  an  indication  of  definite 
constitution  in  certain  solids.  Thus,  among  alkaloids  strychnia  and  mor- 
phia are  obtained  perfectly  crystalline,  but  veratria,  digitaline,  and  aconitina 
have  not  been  obtained  in  a  crystalline  state.  It  is  not  improbable  that  these 
oncrystalline  substances  may  consist  of  the  alkaloid  associated  with  other 
alkaloids,  or  principles  derived  from  the  vegetable. 

The/orm*  of  crystals  are  generally  characteristic  of  the  substance  :  thus, 
among  native  or  natural  crystals,  quartz  is  known  by  its  transparent  six- 
sided  prisms,  fluor-spar  by  its  cubes,  and  Iceland  spar  by  its  rhombs. 
Among  artificial  crystals,  nitre  is  known  by  its  long  fluted  prisms,  common 
salt  by  its  cubes,  and  alum  by  its  well-marked  octahedra.  Some  substances, 
such  as  gum,  starch,  and  glass,  cannot  be  made  to  assume  the  crystalline 
state  :  they  are  for  this  reason  called  amorphous  (from  a,  priv.  and  A*opt^, 
form).  Others,  like  sulphur,  assume  it  most  readily,  provided  cohesion  be 
destroyed  h^  fusion,  sublimation,  or  solution. 

Some  bodies,  e.  g.,  the  metals,  can  be  readily  crystallized  by  fusion  ;  othets, 
as  nitre,  alum,  and  the  greater  number  of  salts,  only  by  solution  ;  and  others, 
again,  e.  g.,  calomel,  only  by  sublimation.  Corrosive  sublimate  and  white 
arsenic  may  be  obtained  perfectly  crystallized  either  by  sublimation  or  solu- 
tion, and  in  reference  to  arsenic  the  octahedral  form  is  preserved  in  both 


26  STRUCTURE  OF  CRYSTALLINE  SOLIDS. 

cases.  Hence  it  follows  that  if  a  substance  cannot  be  melted,  dissolved,  or 
sublimed,  it  will  not  admit  of  crystallization. 

Crystallization  hy  Fusion. — If  a  quantity  of  pure  bismuth  is  melted  in  an 
iron  ladle,  and  is  allowed  to  cool  until  a  slight  crust  is  formed  on  the  surface, 
and  two  holes  are  then  made  in  this  crust  to  permit  the  still  liquid  metal  to 
be  poured  out,  a  group  of  cubic  crystals  of  bismuth  will  be  obtained.  Sul- 
phur melted  in  a  crucible  at  a  low  temperature,  and  treated  by  a  similar 
process,  will  yield  a  hollow  cavity  containing  numerous  prismatic  crystals, 
intersecting  each  other  in  all  directions.  The  crystals  thus  obtained  will  be 
large  in  proportion  to  the  quantity  of  bismuth  and  sulphur  melted,  and  the 
slowness  with  which  the  cooling  has  taken  place.  The  melted  substances 
should  be  kept  at  perfect  rest.  Groups  of  crystals  thus  procured  somewhat 
resemble  the  hollow  minerals  found  in  different  strata  called  geodes  {ys^hri^, 
earthy).  They  are  rough-looking  globular  masses  on  the  exterior,  but  when 
broken  are  found  to  be  lined  with  crystals  of  quartz,  fluor,  and  other  mineral 
compounds. 

Advantage  is  taken  in  the  arts  of  this  tendency  of  certain  metals  to  crys- 
tallize by  fusion,  to  separate  silver  from  .commercial  lead.  About  six  tons 
of  lead  are  melted  at  once.  In  the  act  of  cooling  the  lead  crystallizes  in 
octahedra,  and  is  removed  from  the  molten  mass  by  means  of  a  perforated 
iron  ladle.  The  melted  portion  is  thereby  reduced  to  about  seven  hundred 
weight;  and  this  consists  of  a  very  fusible  alloy  of  lead  and  silver,  in  which 
the  silver  is  in  large  proportion,  and  can  be  easily  separated  from  the  lead 
by  other  processes.  The  efficiency  of  this  method  of  separation  may  be 
judged  of  by  the  fact  that  the  average  quantity  of  silver  contained  in  lead  is 
ten  ounces  to  the  ton ;  and  by  the  crystallization  of  the  lead,  the  proportion 
of  silver  is  brought  up  to  two  hundred  ounces  to  the  ton. 

Structure  of  Crystalline  Solids. — The  crystallization  of  sulphur,  bismuth, 
and  other  metals  by  fusion,  shows  that  crystallizable  bodies  are  made  up  of 
groups  of  minute  crystals,  since  but  for  the  pouring  off  of  the  liquid  portion 
of  bismuth  or  sulphur,  the  whole  would  have  set  into  a  confused  mass.  An 
experiment  on  tin  will  further  illustrate  this  condition.  If  a  piece  of  tin- 
plate  (tinned-iron)  is  heated,  and  the  surface  is  then  rapidly  brushed  over 
with  a  liquid  consisting  of  one  part  of  nitric  and  one  part  of  hydrochloric 
acid,  with  eight  parts  of  water,  a  very  beautiful  crystalline  structure  will  be  at 
once  made  apparent.  This  has  been  called  the  moiree  of  tin.  The  tin  in 
cooling  on  the  surface  of  the  sheet-iron,  assumed  a  crystalline  structure,  but 
this  was  concealed  by  a  deposit  of  amorphous  metal  which  the  diluted  acid 
removes.  Spurious  tin-foil,  i.  e.,  sheet-lead  faced  with  tin,  does  not  present 
this  crystalline  character.  When  treated  with  the  mixed  acids,  after  a  short 
interval  a  dark  blue  or  leaden  color  appears,  and  the  spurious  metal  is  par- 
tially dissolved.  Most  metals  by  exposure  to  weak  solvents  which  act  slowly 
on  the  surface,  are  found  to  present  a  crystalline  structure.  Platinum  thus 
assumes  a  crystalline  snrface  from  the  action  of  nitro-hydrochloric  acid,  and 
aluminum  may  be  moireed  by  the  action  of  a  solution  of  potash  or  soda. 
Wrought  iron  irnmersed  in  a  weak  acid  solution  of  chloride  of  platinum, 
presents  a  fibrous  structure ;  and  the  damasking  of  steel  is  produced  by  wash- 
ing the  metallic  surface  with  diluted  nitric  acid. 

Many  salts  which  are  soluble  in  water,  may  be  made  to  present  a  well- 
marked  crystalline  structure  as  a  result  of  partial  solution.  A  rough  block 
of  alum  placed  for  a  few  days  in  a  cold  and  nearly  saturated  solution  of  this 
salt,  will  present  upon  its  surface  the  planes  and  angles  of  numerous  octa- 
hedra. A  crystalline  structure  is  also  thus  brought  out  on  a  mass  of  bichro- 
mate of  potash,  sulphate  of  iron,  or  carbonate  of  soda.  The  cohesive  force 
which  holds  together  the  atoms  of  salt,  appears  to  be  stronger  in  the  planes 


PLANES    or    CLEAVAGE.  27 

and  angles  of  the  crystal  than  in  other  directions ;  hence  these  parts  resist 
solution,  and  the  block  is  unequally  dissolved.  Ice  may  be  made  to  present 
a  crystalline  structure  by  soaking  a  block  in  water  at  about  32^.  This  struc- 
ture, however,  is  rendered  more  apparent  by  the  freezing  of  thin  films  of 
vapor  deposited  on  glass  during  winter.  The  same  phenomenon  is  observed 
with  respect  to  most  solids  which  can  be  dissolved  or  sublimed.  Thus  a 
rough  block  of  camphor  kept  in  a  capacious  bottle  for  some  weeks,  dimi- 
nishes in  bulk  by  reason  of  a  portion  being  volatilized  and  deposited  in 
crystals  in  the  upper  part  of  the  bottle,  which  has  been  exposed  to  light. 
If  the  surface  of  the  camphor  be  now  examined  with  a  lens,  it  will  be  found 
to  be  composed  of  the  planes  and  angles  of  well-defined  rhombohedra,  as  if 
it  had  been  artificially  carved. 

Cleavage. — To  the  crystalline  structure  may  be  i:^ferred  the  property  of 
cleavage,  whereby  crystals  can  be  easily  broken  only  in  certain  directions, 
corresponding  to  the  planes  of  crystallization.  Masses  of  selenite  (sulphate 
of  lime),  Iceland  spar,  and  galena,  when  struck,  will  break  readily  in  sharp 
angular  fragments  of  different  shapes,  but  presenting  bright  surfaces.  When 
these  broken  surfaces  are  examined,  they  are  found  to  correspond  to  the 
planes  or  layers  of  the  primary  form  of  the  crystal,  to  which  each  substance 
may  ultimately  be  reduced  by  cleavage.  Thus  selenite  readily  splits  in  two 
directions,  and  in  one  of  these  so  easily  that  it  may  be  reduced  to  the  thinnest 
plates.  By  fracture  in  another  direction,  the  pieces  break  in  the  angles  of 
a  rhomb,  so  as  to  form  rhombic  plates.  Iceland  spar  (carbonate  of  lime) 
on  the  other  hand,  may  be  readily  cleaved  in  three  directions,  so  as  to  produce 
a  rhomboidal  crystal.  To  this  form,  the  numerous  varieties  of  carbonate 
of  lime  may  be  finally  reduced  by  cleavage.  Galena,  or  sulphide  of  lead, 
is  met  with  crystallized  as  a  cube,  octahedron,  or  rhombic  dodecahedron. 
The  cubic  galena  admits  of  cleavage  in  three  directions,  corresponding  to 
the  rectangular  form  of  the  cube.  If  an  attempt  be  made  to  split  the 
octahedral  or  dodecahedral  crystal  parallel  to  the  planes  of  those  figures,  the 
crystal  will  resist  the  force  in  these  directions,  but  it  may  be  readily  broken 
in  planes  parallel  to  the  cube.  These  three  figures  have  therefore  a  direct 
relation  to  each  other:  they  may  pass  and  repass  into  each  other,  and  they 
constitute  one  of  the  systems  in  which  crystalline  forms  are  arranged. 
Although  the  diamond  is  considered  to  be  the  hardest  substance  in  nature, 
yet  as  a  crystalline  body  it  may  be  cleaved  in  four  directions  parallel  to  the 
surfaces  of  an  octahedron,  and  when  moderate  force  is  applied  in  either  of 
these  directions,  this  hard  solid  readily  gives  way  and  may  be  split  into 
pieces.  The  sapphire,  although  less  hard  than  the  diamond,  cleaves  only  in 
one  direction,  and  therefore  may  bear  a  harder  blow  without  fracture  than 
the  diamond  itself.  When  a  rough  diamond  contains  a  flaw,  it  is  split  into 
two  at  this  point,  and  it  then  makes  two  perfect  stones.  By  practical 
skill  a  workman  knows  how  to  direct  the  cleavage  and  strike  the  blow. 
Tracing  the  plane,  he  makes  on  the  exterior  a  slight  nick  with  another 
diamond.  He  then  places  a  small  knife  in  that  nick,  gives  to  it  a  light  tap 
with  the  hammer,  and  the  stone  is  at  once  cleaved  in  two,  directly  through 
the  flaw.  This  operation  is  daily  practised  in  the  diamond  works  of 
Amsterdam.  {Pole  on  Diamonds.)  Mr.  Pole  states  that  Dr.  Wollaston 
once  made  £1250  by  purchasing  a  large  flawed  diamond  at  a  low  price,  and 
subsequently  splitting  it  into  smaller  and  valuable  stones,  the  principle  of 
the  operation  not  being  then  generally  known. 

•  The  property  of  cleavage  shows  that  the  force  of  cohesion  in  crystals  is 
stronger  in  certain  directions  than  it  is  in  others.  An  amorphous  or 
uncrystalline  solid,  like  chalk  or  starch,  when  struck,  will  break  in  any 
direction  with  a  dull  and  uneven  fracture.     Another  curious  fact  which  was 


28     CRYSTALLIZING  FORCE.   PRODUCTION  OF  CRYSTALS. 

discovered  by  Mitscherlich  is,  that  a  great  number  of  crystals,  when  heated, 
expand  unequally,  i.  e.,  more  in  certain  directions  than  in  others.  As  a 
general  rule,  solids,  when  heated,  expand  equally  in  all  directions.  The 
crystals  belonging  to  the  cubic  or  regular  system  (alum,  common  salt,  white 
arsenic),  also  follow  this  rule  ;  while  in  the  five  other  systems  of  crystallization, 
the  crystals,  when  heated,  expand  unequally  in  one  or  more  directions. 
Thus  a  rhomb  of  carbonate  of  lime,  when  heated  only  from  32°  to  212°, 
undergoes  an  alteration  of  shape.  The  obtuse  angles  become  more  acute, 
and  there  is  by  measurement  a  difference  of  8  J  degrees  in  the  inclination  of 
the  planes  of  the  crystal.  This  can  only  be  ascribed  to  an  inequality  in  the 
cohesive  force  in  two  opposite  directions.  In  cooling,  the  crystal  resumes 
its  original  shape. 

Crystallizing  i^orce.— -The  force  with  which  cohesion  is  exerted  in  crystal- 
lization is  very  great.  In  the  crystallization  of  water  during  freezing,  lead, 
iron,  and  glass  vessels  containing  this  liquid  are  liable  to  burst.  This  is 
owing  to  the  increase  of  bulk  which  takes  place  when  water  passes  into  the 
solid  form  of  ice.  {See  Water.)  The  effects  of  freezing  water  on  rocks, 
earth,  and  porous  stones  are  well  known.  Crystallizing  solutions,  by 
penetrating  into  small  cracks  or  fissures  in  the  vessels  which  contain  them, 
often  cause  their  destruction.  An  alloy  of  eight  parts  of  bismuth,  four  of 
tin,  and  five  of  lead  (fusible  metal),  crystallizes  on  cooling  from  a  state  of 
fusion.  It  expands  so  as  to  fill  a  mould  completely,  and  thus  allows  a 
perfect  impression  to  be  taken.  For  this  reason,  in  the  act  of  crystallizing 
it  sometimes  causes  the  fracture  of  a  glass  vessel  in  which  it  is  melted.  Cast 
iron  crystallizes  on  cooling,  and  expands  to  such  a  degree  that  very  accurate 
impressions  may  be  taken  from  moulds.  The  Berlin  iron  used  for  this  purpose 
contains  phosphorus,  which  increases  the  fusibility  of  the  metal,  and  castings 
are  obtained  from  this  in  imitation  of  the  finest  filigree  work. 

Production  of  Crystals — It  follows  from  what  has  been  stated  regarding 
the  conditions  for  crystallization,  that  substances  which  are  insoluble,  infusible, 
or  fixed  at  a  high  temperature,  cannot  be  crystallized  by  artificial  processes. 
Carbon,  sulphate  of  baryta,  silicic  acid,  and  fluoride  of  calcium,  are  found 
perfectly  crystallized  in  nature,  but  they  do  not  readily  admit  of  crystallization 
by  art.  The  natural  crystallization  of  these  bodies  is  probably  due  to 
the  slow  operations  of  nature  over  very  long  periods  of  time,  and  to  the 
progressive  increase  in  the  size  of  the  crystal  by  gradual  accretion  from 
without. 

In  employing  boracic  acid  as  a  solvent  for  alumina,  magnesia,  and  oxide 
of  iron,  M.  Ebelmen  has  succeeded  in  obtaining  octahedral  crystals  identical 
in  physical  and  chemical  properties  with  the  native  spinelle  ruby.  The 
substances  in  proper  proportions  were  fused  with  boracic  acid,  and  by 
exposing  this  mixture  for  some  days  to  the  heat  of  a  porcelain  furnace,  the 
solid  acid  was  driven  off  and  hard  crystals  of  spinelle  were  formed. 

When  diluted  sulphuric  acid  is  added  to  a  solution  of  nitrate  of  baryta, 
the  sulphate  of  baryta,  owing  to  its  great  insolubility,  falls  at  once  in  an 
amorphous  powder.  It  shows  no  tendency  to  crystallization.  When  the 
same  acid  is  added  to  a  solution  of  tartrate  of  potash,  a  crystalline  precipitate 
(cream  of  tartar)  is  slowly  separated.  This  compound  is  also  produced  in 
crystals  by  suspending  by  a  thread,  in  the  midst  of  a  diluted  solution  of 
potash  to  which  a  small  quantity  of  alcohol  has  been  added,  a  large  crystal 
of  tartaric  acid.  One  or  two  drops  of  a  solution  of  ammonia  added  to  a 
strong  solution  of  oxalic  acid  in  a  watch-glass,  will  slowly  lead  to  the 
production  of  the  well-marked  prismatic  crystallization  of  oxalate  of  ammonia. 
Metallic  lead  may  be  obtained  in  a  beautifully  crystalline  state  by  immersing 
a  piece  of  clean  granulated  zinc  in  a  solution  of  the  acetate  of  lead;  acidulated 


CRYSTALLIZATION    BY    SUBLIMATION    AND    SOLUTION.  29 

with  acetic  acid : — or  still  better,  by  the  introduction  of  a  piece  of  clean  zinc- 
foil  into  a  weak  solution  of  acetate  of  lead,  slightly  acidulated  with  acetic 
acid.  Tin  may  also  be  obtained  crystallized  in  prisms  by  placing  a  piece  of 
granulated  zinc  in  a  diluted  solution  of  chloride  of  tin.  When  iodide  of 
potassium  is  added  to  a  solution  of  nitrate  of  lead,  a  rich  yellow  precipitate 
(iodide  of  lead)  falls  down.  This  precipitate  is  amorphous ;  but  if  the 
supernatant  liquid  is  poured  off,  and  the  yellow  precipitate  is  boiled  for  a 
short  time  in  water,  a  part  of  the  iodide  assumes  a  crystalline  state,  appearing 
under  the  microscope  in  triangular  or  hexahedral  plates  of  a  golden  color, 
with  shades  of  p^reen. 

By  Sublimation. — Among  the  bodies  which  are  easily  obtained  crystallized 
by  sublimation,  i.  e.,  from  a  state  of  vapor,  may  be  mentioned  benzoic  acid, 
naphthaline,  iodine,  white  arsenic,  and  camphor.  The  last-mentioned  sub- 
stance is  slowly  sublimed  at  ordinary  temperatures,  in  hexahedral  plates  or 
rhombohedral  crystals.  These  are  deposited  on  that  side  of  the  glass  vessel 
containing  the  camphor  which  is  subject  to  the  greatest  amount  of  cooling 
by  radiation.  The  following  experiments  will  illustrate  this  method  of 
producing  crystals.  Place  in  a  small  tube  about  a  quarter  of  a  grain  of 
white  arsenic,  heat  the  tube  a  little  above  the  part  where  the  powder  is 
deposited,  then  very  gradually  warm  the  powder.  At  about  3t0°  the  arsenic 
will  be  volatilized,  and  if  not  too  rapidly  heated,  well  defined  and  distinct 
octahedra  will  be  deposited  on  the  cold  part  of  the  tube.  Place  in  another 
tube  a  few  grains  of  the  red  iodide  of  mercury  ;  heat  it  until  it  melts,  then 
moderate  the  heat,  and  the  red  powder  will  be  sublimed  in  splendid  rhombic 
plates.of  a  brilliant  yellow  color. 

By  Solution. — We  must  here  select  a  salt,  such  as  nitre,  alum,  or  sulphate 
of  copper,  the  solubility  of  which  greatly  increases  with  the  temperature. 
A  boiling  saturated  solution  of  the  salt  is  made,  and  the  vessel  is  placed 
aside,  covered  over,  and  kept  undisturbed.  The  cooling  should  be  allowed 
to  take  place  very  slowly  :  100  parts  of  water  at  212°  will  dissolve  246  parts 
of  nitre,  but  at  60^  this  quantity  of  water  will  retain  only  30  parts  of  the 
salt.  Hence  216  parts  are  deposited  on  cooling  in  groups  of  prisms,  which 
are  large  or  small  according  to  the  quantity  of  salt  dissolved,  and  the  slowness 
with  which  the  deposit  has  taken  place.  As  a  general  rule,  small  crystals 
are  more  perfect  in  form  and  and  more  transparent  than  large  crystals.  As 
the  crystals  of  salts  are  of  greater  specific  gravity  than  the  liquid  in  which 
they  are  formed,  they  are  usually  deposited  at  the  bottom  of  the  vessel,  or 
they  will  adhere  to  any  rough  surfaces  of  wood  or  string  which  may  be 
introduced  into  the  crystallizing  solution.  Under  these  circumstances  they 
increase  in  size  by  the  spontaneous  evaporation  of  the  solution,  and  a 
continued  deposit  from  without,  and  as  they  are  in  the  midst  of  the  liquid 
they  retain  a  perfect  form.  We  have  thus  seen  produced  rhombic  prisms  of 
carbonate  of  soda  of  sixteen  inches  in  length,  and  stalactitic  octahedra  of 
alum  of  still  greater  dimensions.  If  the  substance  is  not  very  soluble  in 
water  (arsenious  acid),  the  crystals  are  small  but  perfect,  and  are  slowly 
produced.  If  the  salt  is  equally  soluble  in  hot  and  cold  water,  no  crystals 
are  obtained  on  cooling  the  solution.  Common  salt  (chloride  of  sodium) 
presents  an  example  of  this  kind,  and  by  this  singular  property  it  admits  of 
separation  from  a  large  number  of  salts.  It  can  only  be  obtained  crystallized 
from  its  saturated  solution  by  evaporation,  ^.  e.,  by  the  removal  of  the 
solvent. 

The  liquid  in  which  crystals  are  deposited  on  cooling  is  a  saturated  solu- 
tion of  salt  for  the  temperature  ;  it  is  called  the  mother-liquor.  By  remov- 
ing it  from  the  deposited  crystals  and  carrying  the  evaporation  still  further, 
i.  e.,  until  a  slight  pellicle  appears  on  the  surface,  a  fresh  crop  of  the  same 


30  SEPARATION    OF    SALTS. 

crystals  may  be  procured,  but  not  so  pure  as  those  first  obtained.  If  a  por- 
tion of  the  mother-liquor,  cooled  to  60°,  is  placed  in  a  freezing  mixture,  there 
will  be  a  farther  deposit  of  crystals  of  nitre,  this  salt  being  less  soluble  at 
320  than  at  60°.      " 

Crystallization  as  a  result  of  cooling  is  witnessed  in  many  liquids,  and 
becomes  a  test  of  their  strength  on  chemical  composition.  Acetic  acid 
cooled  to  below  40"^  sets  into  a  mass  of  prisms  resembling  ice.  It  is  hence 
called  glacial  acetic  acid.  It  serves  as  a  test  of  the  strength  of  the  acid,  and 
represents  the  strongest  form  in  which  this  acid  can  be  procured.  Sulphuric 
acid  is  liquid  at  ordinary  temperatures.  When  cooled  to  below  40°  it  forms 
a  solid  crystalline  mass,  like  ice,  which  has  a  definite  constitution  of  one  atom 
of  acid  combined  with  two  atoms  of  water,  a  bihydrate.  As  a  liquid  at  60° 
its  specific  gravity  is  1.78.  If  the  proportion  of  water  is  increased  or  dimin- 
ished, it  no  longer  crystallizes  at  this  temperature. 

In  the  deposition  of  crystals  from  saline  solutions  the  mother-liquor  gene- 
rally retains  the  impurities  associated  with  the  salt,  and  thus  by  repeatedly 
crystallizing  a  substance  in  fresh  quantities  of  water,  we  may  bring  it  to  a 
state  of  great  purity.  In  the  crystallization  of  tartar  emetic,  the  arsenic  con- 
tained in  the  materials  used  remains  in  the  mother-liquid  ;  and  according  to 
Martins,  the  larger  crystals  of  tartar  emetic  which  are  formed  principally  in 
the  mother-liquor  contain  arsenic.  {Gmelin,  vol.  iv.  p.  317.)  The  purifi- 
cation of  alkaloids  by  repeated  solution  in  alcohol,  ether,  or  chloroform,  is 
based  on  a  similar  principle. 

The  more  slowly  the  evaporation  takes  place,  the  larger  and  finer  the 
crystals.  The  small  and  opaque. cubic  crystals  of  common  salt  are  obtained 
by  rapid  evaporation  at  a  boiling  temperature.  The  large  crystals  of  bay 
salt  are  procured  by  the  spontaneous  evaporation  of  brine.  A  viscid  state 
of  the  mother-liquor  from  repeated  evaporations,  is  a  bar  to  the  production 
and  deposit  of  fine  crystals.  Certain  alkaloids  and  other  compounds  which 
do  not  bear  a  high  temperature  are  procured  perfectly  crystallized  by  allow- 
ing the  liquids  to  evaporate  in  vacuo  at  a  low  temperature — a  vessel  of  sul- 
phuric acid  being  placed  under  the  crystallizing  liquid,  to  absorb  the  aqueous 
vapor  as  it  is  evolved.  ♦ 

Crystals  may  be  made  to  grow  or  to  increase  in  size,  by  selecting  those 
which  are  perfect — covering  them  with  the  mother-liquid,  and  allowing  this 
liquid  to  evaporate  spontaneously.  That  the  crystals  may  preserve  their 
regular  form  while  this  increase  is  taking  place,  it  is  necessary  that  they 
should  be  occasionally  turned,  otherwise  the  deposit  will  be  formed  chiefly 
on  the  upper  parts. 

Separation  of  Salts. — When  two  or  more  salts  are  present  in  the  same 
solution,  if  of  different  degrees  of  solubility  and  not  isomorphous,  they  may 
be  separated  by  crystallization.  It  is  observed  that  the  salt  which  is  least 
soluble  for  the  temperature  is  separated  first.  In  the  evaporation  of  sea- 
water,  sulphate  of  lime,  by  reason  of  its  insolubility,  is  first  precipitated  and 
removed.  Chloride  of  sodium  or  common  salt  is  then  separated,  as  this  is 
no  more  soluble  in  hot  than  in  cold  water,  while  the  other  salts  associated 
with  it  are  much  more  soluble  at  a  boiling  than  at  a  low  temperature.  When 
the  water  is  exhausted  of  its  crystallizable  salts,  the  residue  contains  chiefly 
chloride  of  magnesium  with  traces  of  bromide.  It  is  this  chloride  which 
gives  an  intensely  bitter  taste  to  the  liquid,  hence  the  residue  is  called 
I'  bittern.'*  When  two  nearly  equally  soluble  salts  are  present,  that  which 
is  in  larger  quantity  is  usually  separated  first. 

Deposition  of  Crystals. — As  a  general  rule  all  crystals  are  deposited  in  the 
mother-liquor  as  the  solution  cools,  but  there  are  solutions  of  certain  salts 
which  if  kept  at  rest  and  so  covered  as  to  prevent  free  access  of  air  or  dust, 


DEPOSITION    OP    CRYSTALS.  31 

will  either  not  deposit  crystals  on  cooling  or  deposit  them  only  partially.  A 
hot  saturated  solution  of  sulphate  of  magnesia  placed  in  a  vessel  secured 
with  bladder  may  be  cooled  at  60°,  and  yet  will  only  partially  deposit  crys- 
tals. On  agitating  the  cooled  liquid,  more  will  be  deposited.  This  property 
is  more  remarkably  manifested  by  sulphate  of  soda.  This  salt  when  dissolved 
at  a  boiling  heat  in  the  proportion  of  two  parts  by  weight  of  crystals  to  one 
part  by  weight  of  boiling  water,  may  be  placed  in  flasks  or  tubes  and  cooled 
to  60°  or  below,  without  depositing  crystals,  provided  the  vessels  are  kept  at 
rest  and  the  surface  of  the  solution  is  covered  while  hot  with  a  stratum  of  oil, 
or  the  mouth  of  the  vessel  is  firmly  secured  by  caoutchouc  or  bladder.  Upon 
agitating  the  liquid,  or  exposing  it  to  air  by  cutting  through  the  bladder — 
by  plunging  into  it  a  glass-rod  or  a  crystal  of  the  salt,  the  sulphate  immedi- 
ately begins  to  crystallize,  either  from  the  surface  or  around  the  rod  or  crys- 
tal ;  and  the  whole  speedily  forms  a  crystalline  mass.  If  a  quantity  of  this 
hot  liquid  is  allowed  to  cool  in  a  tube  about  twelve  inches  long,  similarly 
secured,  the  process  of  crystallization  may  be  easily  watched  ;  the  mode  in 
which  a  solid  mass  of  salt  is  built  up  of  myriads  of  prisms  intersecting  each 
other  in  all  directions,  will  be  then  at  once  made  evident  to  the  eye.  We 
have  preserved  a  solution  of  this  kind,  with  the  process  of  crystallization 
thus  suspended,  for  three  years,  and  the  ordinary  mechanical  causes  above 
mentioned  brought  about  crystallization  in  the  whole  mass  after  this  long 
period.  From  this  sudden  crystallization  of  sulphate  of  soda,  we  learn  that 
the  production  of  crystals  is  attended  with  the  evolution  of  sensible  heat, 
light,  and  even  electricity.  The  phenomenon  is  considered  to  be  owing  to 
the  fact,  that  in  a  hot  saturated  solution  the  sulphate  of  soda  is  dissolved  in 
an  anhydrous  state,  and  so  remains  on  cooling,  until  slight  mechanical  causes 
operate  on  the  solution.  Agitation,  the  introduction  of  a  crystal,  or  expo- 
sure to  air,  causes  the  formation  of  the  ten-atom  hydrate,  so  that  the  water 
now  enters  into  chemical  combination  with  the  sulphate,  and  the  whole  sets 
into  a  solid  mass.  There  is  also  a  seven-atom  hydrate  of  the  sulphate  of 
soda.  Transparent  crystals  of  this  hydrate  are  frequently  deposited  in  a 
flask  during  the  cooling  of  a  saturated  solution.  They  become  white  on  the 
surface,  probably  from  a  loss  of  water  during  the  formation  of  the  ten-atom 
hydrate.  The  crystallization  of  water  itself  presents  a  similar  phenomenon. 
Water  kept  in  a  narrow  tube  and  at  rest  may  be  cooled  to  26°,  and  yet 
remain  quite  liquid.  If  shaken,  or  disturbed  by  the  introduction  of  a  ther- 
mometer, a  part  of  the  water  immediately  congeals,  and  the  thermometer 
rises  to  32°. 

The  liquid  employed  in  the  Storm-glass  presents  a  remarkable  instance  of 
the  slight  causes  which  lead  to  the  production  and  disappearance  of  crystals 
in  a  solution.  Two  parts  of  camphor,  one  part  of  nitre,  and  one  part  of 
chloride  of  ammonium  are  dissolved  in  a  minimum  of  rectified  spirit,  to  which 
sufiBcient  water  is  added  to  dissolve  the  two  salts,  the  alcohol  being  just  suf- 
ficient to  retain  the  camphor.  If  the  solvents  are  in  too  large  proportion, 
the  liquid  may  be  brought  to  the  point  of  saturation  by  slight  exposure  to 
the  air.  It  should  be  filtered  and  placed  in  a  long  tube.  At  temperatures 
between  40°  and  70°  feathery  crystals,  chiefly  of  chloride  of  ammonium,  are 
produced ;  but  these  disappear  at  the  higher  temperature.  It  is  supposed 
that  their  production  is  also  influenced  by  electrical  changes  in  the  atmos- 
phere ;  but  of  this  there  is  no  proof  whatever.  The  separation  of  paraffine 
from  the  heavy  oil  in  which  it  is  dissolved,  is  the  eS'ect  of  a  change  of  tem- 
perature. When  the  oil  is  cooled  to  below  4|p,  the  solid  paraflQne  crystal- 
lizes, and  may  be  separated  by  pressure  from  tne  liquid. 

Interstitial  and  Combined  Water. — Crystals  which  are  deposited  in  a  liquid 
necessarily  retain  a  portion  of  the  mother-liquor  in  their  interstices.     This 


32  INTERSTITIAL    AND    COMBINED    WATER. 

has  been  called  interstitial  water.  It  is  removed  by  draining  and  drying. 
The  amount  contained  in  any  sample  of  crystals  may  be  determined  in  the 
same  manner  as  hygrometric  water.     (See  Water.) 

Many  saline  substances  in  crystallizing  combine  chemically  with  a  certain 
proportion  of  water,  which  is  specially  defined  for  each  salt.  These  are 
hydrated  salts.  Some  salts,  such  as  the  sulphates  of  soda  and  magnesia,  form 
several  hydrates — the  number  of  atoms  of  water  with  which  they  combine 
depending  on  the  temperature  at  which  crystallization  takes  place.  Sulphate 
of  soda  may  be  obtained  crystallized  in  the  anhydrous  as  well  as  in  the 
hydrated  state.  The  common  sulphate  contains  ten  atoms  of  water.  Sul- 
phate of  magnesia,  crystallized  at  common  temperatures,  combines  with  seven 
atoms  of  water.  If  crystallized  by  evaporation  at  a  high  temperature,  there 
are  six  equivalents  of  water  :  and  if  crystallized  from  its  solutions  below  32^, 
large  crystals  containing  twelve  atoms  of  water  are  obtained.  {Regnault,  2, 
259.)  Some  crystalline  salts  contain  no  combined  water  ;  in  other  words, 
they  are  anhydrous  or  dry.  The  chlorides  of  sodium  and  ammonium,  and 
the  nitrate  and  sulphate  of  potash  are  instances  of  this  kind.  It  is  necessary 
to  observe  that  as  these  words  are  often  used  synonymously,  a  dry  salt  in  a 
chemical  sense  does  not  mean  a  substance  free  from  moisture  or  wetness,  but 
one  which  contains  no  water  in  a  state  of  combination.  In  a  popular  sense, 
the  word  "  dry"  signifies  merely  the  absence  of  moisture.  The  want  of  pre- 
cision in  the  use  of  these  words  has  led  to  costly  litigation  in  reference  to 
patents  for  procuring  colored  products  from  aniline. 

Some  of  these,  when  suddenly  heated,  fly  to  pieces  with  a  cracking  noise, 
to  which  the  name  of  decrepitation  is  given.  Common  salt  and  sulphate  of 
potash  possess  this  property.  On  the  other  hand,  alum  and  phosphate  of 
soda,  the  sulphates  of  iron  and  copper,  and  the  carbonate  and  sulphate  of 
soda,  are  hydrated  crystalline  solids  ;  the  combined  water  in  some  of  them 
forming  more  than  half  the  weight  of  the  solid  salt.  Thus  the  crystals  of 
sulphate  of  soda  contain  56  per  cent,  of  water,  and  those  of  alum  nearly  46 
per  cent.  The  combined  water  is  driven  off  by  heat,  and  the  salt  is  dehy- 
drated or  rendered  anhydrous.  If  the  salt  be  previously  dried,  and  a  given 
weight  of  it  be  then  heated  in  a  platinum  crucible,  the  amount  of  water  may 
be  determined.  The  crystalline  form,  color,  and,  to  a  certain  extent,  the 
properties,  of  the  salt  are  dependent  on  the  presence  of  this  water.  The 
sulphate,  phosphate,  and  carbonate  of  soda  readily  lose  a  portion  of  their 
combined  water  at  a  moderate  heat  in  a  dry  atmosphere.  The  sulphate  of 
soda  becomes  almost  completely  dehydrated  by  exposure ;  the  crystals  lose 
their  transparency  and  fall  to  a  white  powder.  This  spontaneous  change  in 
crystals  is  called  efflorescence :  it  is  in  general  characteristic  of  the  salts  of 
soda.  It  may  be  prevented  by  preserving  the  crystals  in  a  damp  atmosphere. 
On  the  other  ^nd,  some  salts,  such  as  the  chlorides  of  calcium  and  mag- 
nesium, the  nitrates  of  lime  and  magnesia,  and  the  carbonate  and  acetate  of 
potash,  absorb  water  from  the  atmosphere,  not  in  definite  proportion,  but 
until  they  are  reduced  to  a  concentrated  solution  of  the  respective  salts.  To 
this  property  the  term  deliquesce7ice  is  applied.  Many  crystals  undergo  no 
change  in  air ;  they  are  permanent.  This  is  a  character  possessed  by  alum, 
acetate  of  soda,  and  many  other  salts,  as  well  as  by  all  native  crystals. 

The  chemically  combined  water  in  a  crystalline  solid  does  not  manifest  its 
presence  by  da^mpness  or  humidity  when  the  substance  is  powdered.  The 
water,  in  entering  into  combination,  is  in  fact  solidified  in  the  crystal.  Alum 
in  powder  is  perfectly  dry — m  water  can  be  pressed  out  of  it,  yet  it  contains 
nearly  half  its  weight  of  water  in  a  chemically  combined  state.  On  heating 
crystals  of  alum,  they  readily  pass  to  the  liquid  condition  or  melt  in  their 
water  of  crystallization.     This  is  gradually  expelled  as  aqueous  vapor  by 


PEOPERTIES    OF    HYDRATED    CRYSTALS.  33 

continuing  the  heat ;  and  a  light  white  porous  mass  is  left,  in  which  no  ap- 
pearance of  crystallization  can  be  seen.  The  residue  is  anhydrous  or  burnt 
alum.  In  this  state,  and  by  reason  of  the  loss  of  its  water,  the  salt  acts  as  a 
mild  caustic.  When  water  is  poured  over  this  dry  mass  the  salt  recombines 
with  it,  and  heat  is  evolved.  Gypsum  is  the  native  crystalline  state  of  sul- 
phate of  lime:  it  contains  about  21  per  cent,  of  water.  When  roasted  at 
about  260^  this  water  is  expelled,  and  the  crystalline  mass  falls  to  a  white 
powder  known  as  plaster  of  Paris.  When  this  powder  is  mixed  with  suffi- 
cient water  to  form  a  cream,  it  sets  in  a  few  minutes  into  a  firm  mass,  which 
by  crystallization  fills  accurately  every  part  of  a  mould  on  which  it  is  placed. 
The  setting  of  plaster  of  Paris  is  therefore  due  to  the  resumption  of  the  com- 
bined water  which  had  been  expelled  by  heat.  The  strong  tendency  which 
sulphate  of  lime  has  to  unite  to  water  in  the  act  of  crystallizing,  is  well  illus- 
trated by  mixing  together  equal  parts  of  diluted  sulphuric  acid,  and  a  nearly 
concentrated  solution  of  chloride  of  calcium.  When  mixed,  the  liquids  set 
into  a*  solid  mass  owing  to  the  water  of  the  two  solutions  combining  with  the 
sulphate  of  lime  produced.  When  powdered  sulphate  of  copper  is  heated 
to  a  moderate  temperature  it  loses  its  blue  color  and  forms  a  white  powder. 
On  pouring  water  over  it  it  becomes  intensely  hot,  the  water  again  enters 
into  combination  with  the  white  anhydrous  sulphate,  and  the  powder  acquires 
a  blue  color.  The  color  of  the  salt  therefore  appears  to  depend  on  the  water 
of  hydration.  As  a  further  proof  of  this,  the  blue  crystals  become  white  when 
placed  in  strong  sulphuric  acid,  as  a  result  of  a  removal  of  the  water  by  the 
acid.  The  green  crystals  of  sulphate  of  iron  are  also  rendered  white  under 
similar  circumstances. 

The  influence  of  the  proportion  of  combined  water  on  the  color  of  crystals 
is  more  remarkably  seen  in  the  platino-cyanide  of  magnesium  than  in  any 
other  substance.  These  crystals  are  prismatic,  and  are  of  a  ruby  red,  with 
reflections  of  an  emerald  green  color.  A  strong  solution  of  them  imparts  to 
paper  a  carmine  red  color,  and  in  this  state  they  contain  seven  atoms  of  water. 
When  water  is  dropped  on  the  red  compound  on  paper  it  immediately  whitens 
the  paper,  forming  a  colorless  solution  of  the  salt.  By  gently  heating  the 
red  deposit  on  paper,  one  atom  of  water  is  lost,  and  the  substance  becomes 
yellow  ;  at  212^  it  loses  four  atoms  of  water,  and  is  rendered  colorless.  If 
still  more  strongly  heated,  it  loses  all  its  water  and  becomes  yellow.  These 
facts,  as  well  as  the  discovery  of  this  salt — the  type  of  a  remarkable  series — 
we  owe  to  the  late  Mr.  Hadow,  of  King's  College.  We  find  that  the  salt  is 
an  admirable  test  of  humidity.  If  the  paper  stained  with  it  is  rendered  yellow 
or  white  by  a  moderate  heat,  it  rapidly  resumes  its  carmine-red  color,  as  a 
result  of  hydration  either  in  a  damp  atmosphere  or  by  merely  breathing  on  it. 
The  chloride  of  cobalt  is  another  salt  which  presents  changes  of  color  depend- 
ent on  hydration  or  dehydration.  Paper  stained  with  this  Solution  has  a 
light  pinkish-red  color;  when  deprived  of  water  by  heat  it  becomes  blue,  or, 
if  any  iron  is  mixed  with  it,  green,  but  it  resumes  its  pink  color  on  cooling. 

Freezing  Mixtures. — The  rapid  solution  in  water,  of  salts  abounding  in 
water  of  crystallization,  is  always  attended  by  a  diminution  of  temperature; 
and  the  more  water  of  crystallization  they  contain  the  greater  is  their  cooling 
effect  during  solution.  As  the  water  in  these  salts  is  solid,  their  solution 
cannot  take  place  without  at  the  same  time  rendering  latent  a  large  amount 
of  heat.  An  ounce  of  crystals  of  sulphate  of  soda  mixed  with  x)ne  ounce  of 
water  lowers  the  temperature  in  consequence  of  the  solid  hydrated  salt  be- 
coming itself  liquid;  but,  as  it  has  been  above^tated,  if  an  ounce  of  anhy- 
drous sulphate  be  employed,  the  addition  of  water  will  raise  the  temperature, 
because  part  of  the  added  water  enters  into  combination  with  the  anhydrous 
salt,  and  the  latent  heat  of  the  water  is  set  free. 
3 


34  IRREGULAR  FORMS  OF  CRYSTALLIZATION. 

Freezing  mixtures  may  be  made  by  causing  the  rapid  liquefaction  of  the 
combined  water  of  crystalline  salts.  If  to  eight  parts  of  crystallized  sulphate 
of  soda  we  add  five  parts  of  strong  hydrochloric  acid,  each  being  separately 
at  50°,  the  acid  takes  away  water  from  the  sulphate,  liquefying  it  at  the  same 
time,  and  it  thus  renders  latent  so  large  an  amount  of  heat  as  to  reduce  the 
thermometer  from  50°  to  0°.  For  common  purposes,  the  materials  used 
need  not  be  weighed.  The  fresh  crystals  finely  powdered  should  be  drenched 
with  strong  hydrochloric  acid.  The  acid  mixed  with  ice  operates  in  a  pre- 
cisely similar  manner,  namely,  it  causes  the  rapid  liquefaction  of  the  solidified 
water,  and  lowers  the  thermometer  from  32°  to  17°.  Diluted  sulphuric  acid 
in  the  proportion  of  four  parts  to  five  parts  of  the  powdered  crystals  of  sul- 
phate of  soda,  produces  a  mixture  in  which  the  thermometer  sinks  from  50° 
to  3°.  By  taking  advantage  of  these  principles,  the  same  substances  may 
be  employed  to  produce  cold  or  heat.  If  four  parts  of  broken  ice  are  rapidly 
mixed  with  one  part  of  strong  sulphuric  acid  a  freezing  mixture  results  in 
which  the  thermometer  falls  to  15°.  But  if  four  parts  of  the  strong  acid 
are  mixed  with  one  part  of  ice,  the  temperature  of  the  mixture  rises  to  170° 
and  even  higher.  In  the  former  case  the  crystalline  solid  (ice),  is  rapidly 
liquefied  and  absorbs  heat  from  all  surrounding  bodies.  In  the  latter  case 
the  sulphuric  acid  is  in  such  quantity  as  to  enter  into  combination  with  the 
water  formed  producing  a  hydrate  with  the  evolution  of  great  heat. 

Other  curious  phenomena  are  dependent  on  the  setting  free  of  the  com- 
bined water  of  crystals.  Chloride  of  ammonium  contains  no  combined 
water  :  sulphate  of  soda  contains  56  per  cent.  These  are  perfectly  dry  salts, 
but  when  rubbed  together  in  a  mortar  in  equal  parts  by  weight,  for  some 
time,  they  form  a  liquid  mass.  In  fact,  they  produce  by  double  decomposi- 
tion chloride  of  sodium  and  sulphate  of  ammonia.  The  chloride  of  sodium 
takes  no  combined  water,  the  sulphate  of  ammonia  requires  only  18  per  cent. 
Thus  38  per  cent,  of  the  water  of  the  sulphate  of  soda  is  set  free  as  a  liquid, 
and  this  causes  the  liquefaction  of  the  mass.  Sulphate  of  copper  and  sesqui- 
carbonate  of  ammonia,  when  triturated  together,  form,  for  the  same  reason, 
a  semi-liqnid  mass. 

Although  it  is  commonly, laid  down  as  a  principle  that  no  substances  will 
take  on  the  crystalline  state  unless  they  have  undergone  fusion,  sublimation, 
or  solution,  there  are  some  exceptions  to  this  rule  among  the  metals.  In 
the  process  of  cementation,  iron  is  converted  into  steel  by  heating  it  with 
carbon.  The  iron  loses  its  fibrous  character  and  acquires  a  crystalline  struc- 
ture as  steel,  without  fusion.  By  simple  exposure  to  repeated  concussion  or 
vibratioii,  wrought  iron  is  observed  to  acquire  a  crystalline  structure  and  to 
become  brittle.  This  is  a  change  to  which  the  axles  of  railway  carriages  are 
subject,  and  serious  accidents  have  arisen  owing  to  the  brittleness  acquired 
by  the  iron  as  a  result  of  its  assuming  this  crystalline  condition.  Platinum 
and  silver  vessels,  frequently  heated,  undergo,  after  long  use,  a  similar  mole- 
cular change,  and  break  with  a  crystalline  fracture.  The  acquired  brittleness 
of  some  kinds  of  brass  wire,  containing  an  undue  proportion  of  zinc,  may  be 
attributed  to  a  similar  cause. 

Irregular  Forms. — Various  names  are  given  to  the  crystalline  structure  of 
bodies  when  there  is  an  absence  of  regular  form.  1.  Fibrous,  spicular  or 
acicular,  crystallization  is  seen  in  gypsum  and  sulphide  of  antimony.  2.  A 
laminated  or  foliated  structure  is  observed  in  mica,  petalite,  and  other  mine- 
rals. ^  3.  The  substance  may  have  a  granular  structure  still  presenting  bright 
but  irregular  surfaces  on  ^cture.  Loaf-sugar,  marble,  and  alabaster  are 
examples  of  this  kind.  4.  Plumose  or  feathery  crystallization  is  seen  in 
chloride  of^  ammonium,  sulphate  of  strychnia,  and  other  salts.  5.  Stellated 
crystallization  is  seen  in  the  grouping  of  minute  prisms  crossing  each  other 


REGULAR    FORMS    OP    CRYSTALLIZATION.  35 

at  various  angles.  Strychnia  and  many  other  substances  often  present  them- 
selves in  this  form. 

Regular  Forms. — The  external  forms  of  regularly  crystalline  solids  are 
subject  to  great  variation.  The  nature  of  the  solvent,  the  temperature,  and 
the  presence  of  other  substances  in  the  liquids,  modify  the  form,  by  creating 
new  planes  or  angles,  so  that  the  true  shape  of  the  crystal  may  be  no  longer 
recognizable.  The  octahedral  crystals  of  alum  lose  their  solid  angles  when 
an  excess  of  acid  is  present,  and  they  become  converted  into  cubes  when 
alumina  predominates.  Common  salt  deposited  from  an  aqueous  solution 
containing  urea,  crystallizes  in  octahedra  instead  of  cubes,  its  usual  form  ; 
and  sal  ammoniac  under  the  same  circumstances  forms  cubes,  whereas  in 
pure  water  its  crystals  are  octahedral.  Berzelius  states  that  large  crystals  of 
nitre  may  be  obtained  from  its  solution  in  boiling  lime-water,  which  has  no 
other  analogous  effect  upon  other  salts.  Native  crystals  of  the  same  sub- 
stance are  met  with  in  great  variety.  Carbonate  of  lime  is  said  to  present 
itself  in  a  hundred  varieties  of  form  ;  but  these  are  all  reducible  to  one  com- 
mon figure  by  cleavage,  namely  the  rhomb.  Iron  pyrites  may  be  met  with 
either  in  cubic,  octahedral,  or  dodecahedral  crystals  ;  but  these  are  forms 
which  are  reconcilable  with  a  systematic  arrangement  of  the  molecules  around 
similar  axes. 

In  order  to  facilitate  the  study  of  this  subject,  and  to  reduce  the  large 
variety  of  forms  to  a  few  well-marked  classes,  chemists  now  generally  agree 
in  assigning  crystals  allied  in  form,  to  one  of  six  different  systems  of  crystal- 
lization, the  particles  of  the  substance  being  supposed  to  be  symmetrically 
arranged  around  certain  imaginary  axes  of  the  crystal.  A  system,  therefore, 
includes  all  those  forms,  however  varied,  which  can  be  referred  to  the  axes 
which  are  peculiar  to  it.  We  give  on  the  next  page,  a  table  of  the  special 
characters  of  the  six  systems  of  crystallization  as  described  by  Weiss,  includ- 
ing their  allied  forms  and  their  relations  to  heat  and  light. 


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36 


THE    SIX    SYSTEMS    OF    CRYSTALLIZATION. 


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DIMORPHOUS    BODIES.      DIMORPHISM.  87 

[To  the  reader  who  wishes  to  pursue  this  subject,  we  recommeud  the  smnll 
and  concise  "Precis -de  Cristallogruphie"  of  M.  Laurent.  Alodels  in  wliite 
wood,  representing  the  systems  of  crystallization  and  the  principal  allied 
forms,  may  be  obtained  of  dealers  in  chemical  apparatus.] 

The  student  should  make  himself  acquainted  with  the  common  external 
forms  of  well-known  substances,  including  the  cube,  octahedron,  and  its 
derivative,  the  tetrahedron — the  square,  hexahedral,  oblique,  and  rhombic 
prisuks,  and  plates.  A  few  drops  of  a  solution  of  a  substance  in  water  or 
alcohol,  left  to  spontaneous  evaporation  on  a  glass  slide,  will  furnish  a  group 
of  crystals,  of  which  the  forms  can  be  well  determined  by  a  low  power  of  the 
microscope.  If  we  have  to  deal  with  a  soluble  solid  in  fine  powder,  we 
should  dissolve  a  quarter  of  a  grain  in  a  few  drops  of  water  or  alcohol  on  a 
glass  slide,  according  to  the  solubility  of  the  substance  in  either  liquid.  The 
liquid  should  be  warmed,  until  its  circumference  acquires  a  slight  but  visible 
margin  of  saline  matter.  The  glass  may  then  be  placed  aside,  and  the  liquid 
allowed  to  crystallize  slowly.  No  crystals  are  so  perfect  for  microscopical 
observation  as  those  which  are  procured  in  dry  and  warm  weather  by  spon- 
taneous evaporation.  This  micro-chemical  examination  will  not  only  guide 
analysis  by  leading  to  an  immediate  suspicion  of  the  real  nature  of  the  sub- 
stance— but  it  will  sometimes  enable  a  chemist  to  detect  and  pronounce  an 
opinion  on  the  presence  of  impurities  in  the  substance  examined ;  and  in 
medical  practice  it  may  suggest  the  nature  of  the  disease,  and  point  to  a  plan 
for  treatment.  The  sedimentary  deposits  in  urine  are  now  easily  recognized 
by  their  crystalline  forms,  and  the  presence  of  urea,  uric  acid,  or  cholesterine 
in  the  blood  or  other  liquids,  is  known  by  the  peculiar  crystalline  shape 
which  each  assumes. 

Dimorphism  (6tj  and  ^itop^i),  two  forms). — It  is  a  remarkable  fact  that  the 
same  substance  may  present  itself  in  crystalline  forms  belonging  to  two  dif- 
ferent systems  :  such  bodies  are  called  dimorphous.  This  is  the  case  with  sul- 
phur, which  when  crystallized  by  .fusion  yields  oblique  rhombic  prisms  (5th 
system),  but  is  deposited  from  its  solution  in  sulphide  of  carbon  in  octahedra 
with  a  rhombic  base  (4th  system).  Carbon,  in  the  form  of  diamond,  crystal- 
lizes in  octahedra,  but  as  graphite,  in  hexagonal  plates.  Carbonate  of  lime 
in  calcareous  spar  has  the  rhombohedral  structure,  but  in  arragonite  that  of 
the  rectangular  prism  ;  and  there  are  other  analogous  instances.  It  has  been 
found  in  regard  to  these  cases  of  dimorphism,  that  each  form  has  its  peculiar 
density  ;  the  specific  gravity  of  calcareous  spar,  for  instance,  being  2.71  ;  that 
of  arragonite  is  2.94.  The  temperature  too  at  which  the  crystals  are  formed 
is  another  influencing  cause  :  thus  when  carbonate  of  lime  is  precipitated  by 
adding  chloride  of  calcium  to  carbonate  of  ammonia,  the  grains  of  the  pow- 
der are  rhombohedral  if  thrown  down  at  the  temperature  of  50^,  but  octa- 
hedral if  at  150°      (G.  Rose,  Phil.  Mag.,  xiii.  465.) 

The  iodide  of  mercury  presents  a  remarkable  instance  of  dimorphism.  It 
is  of  a  rich  scarlet  color,  and  as  it  is  obtained  crystallized  from  a  saturated 
solution  in  iodide  of  potassium,  it  assumes  the  form  of  octahedra,  with  a 
square  base.  When  heated  it  becomes  yellow,  forms  an  amber-colored  liquid, 
and  may  be  sublimed  in  rhombic  plates  of  a  rich  yellow  color.  In  twenty- 
four  hours  these  crystals,  either  partially  or  wholly,  acquire  a  scarlet  color. 
Mr.  Warington  has  observed  the  rhombic  plates  to  break  into  octahedra  with 
a  square  base,  as  they  changed  from  yellow  to  scarlet.  Hence  it  is  reasonable 
to  infer  that  there  is  a  spontaneous  change  in  the  molecular  condition  of  this 
salt;  indicated  not  merely  by  change  of  form  but  by  change  of  color  in  the 
crystal.  The  scarlet  powder  may  be  crystallized  on  a  card  without  fusion,  by 
heating  it  over  a  spirit-lamp  (thus  furnishing  an  instance  of  the  crystallization 
of  solids):  and  if,  when  cold,  the  yellow  crystalline  compound  is  rubbed 


38  ISOMORPHISM. 

with  a  piece  of  paper,  it  is  reconverted  into  the  red  iodide.  These  differently 
colored  crystalline  forms  may  be  regarded  as  allotropic  states  of  the  sub- 
stance. 

Dimorphous  bodies,  or  substances  crystallizing  in  the  incompatible  forms 
of  two  different  systems,  must  be  regarded  as  exceptional  to  the  general  law 
of  crystallization.  It  is  a  curious  fact,  however,  that  when  this  condition 
exists,  the  substance  frequently  presents  in  its  two  forms  marked  differences 
in  hardness,  specific  gravity,  lustre,  solubility,  fusibility,  optical  characters, 
&c.,  thus  showing  a  molecular  diff'erence  throughout.  In  addition  to  the 
substances  above  mentioned,  dimorphism  has  been  observed  in  specular  iron 
ore,  iron  pyrites,  the  carbonates  of  iron  and  lead,  arsenious  acid,  oxide  of 
antimony,  the  sulphates  of  magnesia,  zinc,  and  nickel,  and  in  the  seleniates 
of  the  two  latter  metals.  It  has  been  noticed  with  respect  to  some  of  these 
cases  of  dimorphism,  that  the  crystal  of  one  system  is  made  up  of  groups  of 
crystals  of  the  other  system.  The  sulphate  of  nickel  crystallizes  in  right 
rhombic  prisms.  Mitscherlich  found  that  when  these  prisms  were  heated  and 
broken  up,  they  were  resolved  into  minute  crystals  of  the  second  system, 
namely,  octahedra  with  a  square  base.  The  crystals  of  sulphur,  recently 
obtained  by  fusion,  are  in  the  form  of  oblique  rhombic  prisms  of  a  yellow 
color,  transparent  and  somewhat  flexible.  In  a  few  days  they  become  opaque 
and  brittle,  and  they  fall  to  a  powder  which,  under  the  microscope,  is  found 
to  consist  of  rhombic  octahedra. 

Isomorphism  (from  ?5oj  similar,  and  jwopti?  form.) — Although  substances  may 
in  general  be  identified  by  their  special  forms,  yet  diff'erent  substances,  like 
white  arsenic  and  alum,  may  present  themselves  in  similar  forms.  Sometimes 
a  similarity  of  form  is  presented  by  substances  which  also  resemble  each  other 
in  atomic  constitution,  or  in  the  number  of  atoms  of  acid,  base,  or  water, 
which  enter  into  their  composition.  In  this  case  it  has  been  found  that 
such  bodies  may  replace  each  other,  or  be  substituted  for  each  other  in  com- 
bination, without  affecting  the  crystalline  form.  Thus  the  arseniate  and  bin- 
arseniate  of  soda  have  the  same  forms  as  the  phosphate  and  biphosphate  of 
soda  ;  and  the  arseniate  and  binarseniate  of  ammonia  resemble  the  phosphate 
and  biphosphate  of  that  alkali.  Such  salts  are  termed  isomorphous.  In  the 
above  instances,  the  equivalents  of  acid,  base,  and  water  of  crystallization 
correspond  ;  and  a  similar  correspondence  has  been  traced  in  the  atomic  con- 
stitution of  the  acids  and  bases  of  the  salts.  Thus  the  arsenic  and  phosphoric 
acids  each  include  one  equivalent  of  base  and  five  of  oxygen,  and  are  therefore 
themselves  isomorphous ;  so  also  phosphorus  and  arsenic  are  presumed  to  be 
isomorphous — isomorphous  compounds,  in  general,  appearing  to  arise  from 
isomorphous  elements.  They  have  the  same  garlic  odor  in  the  state  of  vapor, 
and  combine  with  the  same  number  of  atoms  of  hydrogen  to  form  gases.  So 
also  in  respect  to  the  isomorphism  of  the  sulphates,  seleniates,  chromates, 
and  manganates  of  the  same  base,  each  of  the  acids  in  these  cases  contains 
three  atoms  of  oxygen  to  one  of  the  metalloid  or  metal.  In  respect  to  baseSj 
similar  analogies  are  observable ;  thus  the  salts  formed  by  magnesia,  the 
protoxides  of  zinc,  iron,  nickel,  cobalt,  and  copper,  with  a  common  acid,  are 
isomorphous ;  and  alumina  and  the  sesquioxides  of  chromium,  manganese, 
and  iron,  each  of  which  contains  two  atoms  of  base  and  three  of  oxygen, 
replace  each  other  in  many  combinations  without  change  of  crystalline  Ibrra. 
This  is  seen  in  the  different  varieties  of  alum.  The  following  is  a  tabular 
Tiew  of  some  isomorphous  groups : — 


ISOMORPHOUS    GROUPS. 


39 


Chlorine 

lodiue 

Bromine 

Sulphur 

Selenium 

Chromium 

Manganese 

Phosphorus 

Arsenic 

Arsenic 

Antimony 

Barium 

Strontium 

Lead 

Calcium 

Potassium 

Sodium 

Ammonium 

Calcium 

Magnesium 

Manganese 

Iron 

Zinc 

Cadmium 

Cobalt 

Copper 

Nickel 

Aluminum 

Manganese 

Iron 

Chromium 


Chloric  acid   . 
Iodic  acid 
Bromic  acid    . 
Sulphuric  acid 
Selenic  acid    . 
Chromic  acid 
Manganic  acid 
Phosphoric  acid 
Arsenic  acid  . 


Arsenious  acid  (unusual  form) 
Teroxide  of  antimony     . 


Their  oxides  . 
(in  arragonite) 
Their  oxides 


Their  oxides 


CIO- 

10, 

Brb. 

SO, 

SeOj 

CrOj 

MnOg 

PO, 

AsOg 

ASO3 

Sb03 

BaO 

SrO 

PbO 

CaO 

KO 

NaO 


CaO 
MgO 
MnO 
FeO 
ZnO 
CdO 
CoO 
CuO 
NiO 


Their  sesquioxides 


MU2O3 


Common  alum  consists  of  sulphate  of  alumina  united  to  sulphate  of  potash 
with  water  of  crystallization.  It  crystallizes  in  well-marked  octahedral 
crystals.  Soda  and  ammonia  are  isomorphous  with  potash,  and  each  may 
take  the  place  of  this  alkali  without  affecting  the  form  of  the  crystal.  So 
again  the  oxides  of  manganese,  iron,  and  chromium  are  isomorphous  with  the 
oxide  of  aluminum  (alumina).  Each  of  these  oxides  may  take  the  place  of 
the  alumina,  the  other  constituents  remaining  the  same,  and  the  octahedral 
form  of  the  compound  will  be  unaltered.  A  crystal  of  potassa-alum  may 
therefore  receive  a  deposit  of  ammonia-alum  in  a  solution  of  that  salt,  and  it 
has  even  been  found,  as  a  remarkable  instance  of  the  tendency  of  isomorphous 
salts  to  crystallize  together,  that  a  white  crystal  of  potassa-alum  may  be 
coated  with  a  layer  of  deep  ruby-red  chrome-alum  ;  and  it  is  stated  that  if  a 
solid  angle  be  broken  off,  chrome  alum  may  be  deposited  in  its  place.  From 
this  ready  association  of  isomorphous  salts,  it  is  difficult  to  purify  them  by 
crystallization.  Thus  all  commercial  alum  contains  oxide  of  iron,  which 
replaces  part  of  the  alumina.  Sulphate  of  magnesia  and  sulphate  of  zinc 
are  isomorphous,  and  if  mixed,  they  crystallize,  more  or  less,  together,  so 
that  other  means  must  be  resorted  to  in  order  to  separate  them.  This  obser- 
vation applies  also  to  the  sulphates  of  copper  and  iron,  which  belong  to  the 
same  system.  They  are  isomorphous  in  regard  to  acid  and  base,  and,  when 
mixed,  each  crystallizes  with  seven  atoms  of  water.  It  is  a  curious  fact,  that 
pure  sulphate  of  copper,  in  crystallizing,  combines  with  only  five  atoois  of 
water;  but  if  sulphate  of  iron  is  present,  it  will  crystallize  with  seven  atoms, 
like  this  sulphate.  The  two  are  then  isomorphous,  and  they  cannot  be  sepa- 
rated from  each  other  by  crystallization.  If  a  large  crystal  of  sulphate  of 
copper  is  placed  in  a  nearly  saturated  solution  of  sulphate  of  iron,  it  will  be 
increased  in  size  by  a  deposit  of  this  salt  on  the  outside,  and  a  crystal  may 


I 


40  CHExMICAL    FORCE 

thus  be  constructed  of  successive  layers  of  either  salt.  Although  the  carbon- 
ates of  iron  and  magnesia  are  isomorphous,  the  sulphates  of  these  bases  are 
not.  They  contain  different  quantities  of  water  of  crystallization,  and  when 
a  solution  of  the  mixed  salts  is  concentrated  by  evaporation,  crystals  of  each 
are  separately  deposited. 

Besides  a  reliance  upon  form,  the  measurement  of  the  angles  of  crystals 
when  of  similar  form,  is  sometimes  necessary  for  the  purposes  of  mineralogy. 
An  appropriate  and  beautiful  instrument  for  this  purpose  is  ihe  goniometer  of 
Dr.  Wollaston.  Its  action  depends  on  the  reflection  of  light  from  the 
polished  surface  of  a  crystal,  however  minute.  By  rotating  a  brass  circle, 
the  value  of  the  angle  made  by  any  two  planes  is  at  once  determined ;  and  as 
a  vernier  is  attached  to  the  scale,  a  very  slight  difference  in  the  angles  of  two 
similar  rhombs  may  be  readily  determined,  and  the  identity  of  each,  made 
out.  Thus  the  carbonates  of  lime  and  magnesia  assume  the  rhombohedral 
form,  and  are  alike  in  cleavage.  By  the  goniometer,  however,  it  is  found 
that  in  carbonate  of  lime  the  angles  formed  by  the  two  planes  is  105°  5', 
while  in  the  rhomb  of  carbonate  of  magnesia  the  angle  is  107°  25'.  These 
measurements  supply  means  of  identifying  these  minerals. 


j^.  CHAPTER    III. 

CHEMICALFORC  E— S  0  L  U  T 1 0  N— E  LECTROLYSIS. 

Chemical  Force. — The  special  characters  of  the  chemical  force  have  been 
already  explained.  While  cohesive  attraction  merely  unites  the  atoms  of 
similar  or  dissimilar  kinds  of  matter  without  altering  their  properties,  the 
chemical  force  leads  to  the  union  of  dissimilar  atoms  with  a  more  or  less 
complete  change  of  properties. 

A  chemical  compound  is  known,  1.  By  the  substance  uniting  in  definite 
proportions  by  weight — these  proportions  being  called  atomic,  or  equivalent 
weights.  2.  By  their  union  being  attended  with  the  absorption  or  evolution 
of  heat,  or  the  evolution  of  light,  electricity,  and  magnetism.  3.  By  a 
change  of  properties — thus  the  density,  color,  solubility,  and  crystalline  form 
of  the  compound,  as  well  as  its  reactions  on  other  bodies,  are  in  general 
different  from  those  of  its  constituents. 

This  force  is  only  manifested  between  the  minute  particles  of  matter. 
Place  a  few  grains  of  powdered  iodine  in  a  capacious  jar,  i.  e.,  of  200  c.  t. 
capacity.  After  agitation  for  a  few  minutes  the  particles  of  iodine  will  be 
found  diffused  through  the  whole  of  the  jar.  They  are  quite  invisible,  but  in 
a  mass  they  may  give  a  slight  pink  tinge  to  the  aerial  contents.  If  a  long 
strip  of  bibulous  paper,  soaked  in  a  solution  of  starch,  be  now  gradually 
introduced,  the  presence  of  the  atoms  of  iodine,  and  the  formation  of  a 
chemical  compound  with  the  starch,  will  be  indicated  by  the  gradual  pro- 
duction of  a  purple  or  blue  color  in  the  paper.  Although  five  times  the 
weight  of  water,  and  four  thousand  times  the  weight  of  the  air  in  which 
they  float,  these  imponderable  atoms  clearly  indicate  their  presence  and 
diffusion  by  a  chemical  action  on  starch.  If  the  paper  is  now  removed,  and 
a  leaf  of  silver  (made  to  adhere  to  a  glass-plate  by  breathing  on  it),  is 
brought  over  the  mouth  of  the  jar  so  as  to  close  it,  the  chemical  formation 
of  iodide  of  silver  will  be  indicated  by  the  production  of  circular  films  on 
the  metal,  of  a  straw-yellow,  purple,  blue,  and  brown  color,  each  of  these 
films  indicating  au  infinitesimal  tenuity  of  iodide  of  silver  probably  less 


INFLUENCE    OF    COHESION.  41 

than  the  2,000,000th  of  an  inch  in  thickness.  On  a  thin  purple  film  thus 
obtained,  an  image  may  be  produced  by  light  in  the  Daguerreotype  process. 
Influence  of  Cohesion. — As  a  general  rule,  the  more  perfectly  cohesion  is 
destroyed  in  substance,  the  more  strongly  is  the  chemical  force  manifested. 
A  small  block  of  tin  covered  with  nitric  acid  in  a  glass,  will  show  only  a 
slight  amount  of  chemical  action.  If  an  equal  weight  of  tin  in  the  state  of 
powder  is  similarly  treated,  the  acid  is  decomposed  with  great  violence.  So 
in  acting  upon  equal  weights  of  calcareous  spar  in  lump  and  fine  powder,  by 
adding  to  them  diluted  hydrochloric  acid,  a  striking  difference  will  be 
observed  in  the  relative  amount  of  chemical  action.  The  reduction  of  a 
solid  to  powder  operates  simply  by  increasing  the  surface  for  chemical  action, 
which,  cseteris  paribus,  is  always  proportioned  in  intensity  to  the  surfaces  of 
contact  between  bodies.  A  cubic  inch  of  a  substance  exposes  only  six 
square  inches  of  surface  ;  but  if  divided  into  a  million  parts,  that  small  area 
is  multiplied  into  416  square  feet.  The  finest  pulverization  of  all  solids  is 
therefore  a  necessary  condition  for  a  perfect  and  rapid  chemical  combination. 
A  stream  of  sulphuretted  hydrogen  gas  may  be  allowed  to  fall  on  a  mass 
of  anhydrous  \)xide  of  iron  (hsematite)  without  producing  any  chemical 
changes.  If,  however,  the  gas  is  passed  on  the  anhydrous  oxide  in  fine 
powder,  the  whole  mass  becomes  speedily  red  hot,  and  water  and  sulphide  of 
iron  are  produced.  The  same  gas  may  be  passed  into  pure  water  mixed 
with  coarse  fragments  of  flint-glass  without  indicating  the  presence  of  lead 
in  the  glass  ;  but  if  the  flint-glass  is  very  finely  powdered  and  is  thus  treated, 
it  is  rendered  brown  by  the  conversion  of  the  oxide  of  lead  contained  in  it 
into  sulphide  of  lead. 

Liquids  readily  combine  on  mixture  ;  and  some  gases  combine  on  contact, 
although  in  the  latter  case  heat  or  electricity  is  generally  required  to  bring 
about  their  union.  Solution  facilitates  chemical  action  by  reason  of  the 
infinitesimal  division  to  which  a  solid  is  thereby  reduced  ;  and  so  frequently 
is  this  a  preliminary  to  chemical  processes,  that  the  maxim  corpora  non  aguni 
nisi  soluta  is  a  generally  accepted  truth.  At  the  same  time  in  reference  to 
solids  which  are  not  easily  brought  to  a  state  of  solution,  the  operator  must 
equally  bear  in  mind  the  rule — corpora  non  agunt  nisi  divisa. 

The  effect  of  the  minute  division  of  solids  in  accelerating  chemical  action 
is  well  illustrated  in  pyrophori — substances  which  are  spontaneously  com- 
bustible on  exposure  to  air.  If  finely-powdered  Prussian  blue  is  heated 
intensely  in  a  glass  tube,  and  then  hermetically  sealed,  the  brown-black 
powder  into  which  it  is  converted,  instantly  takes  fire,  with  bright  scintilla- 
tions, on  exposure  to  air.  If  dry  tartrate  of  lead  is  heated  in  a  tube  to  a 
dull  red  heat,  i.  e.,  sufficient  to  carbonize  the  acid  (and  the  tube  is  hermetically 
sealed),  the  residue,  when  exposed  to  air,  will  take  fire  and  burn.  In  the  one 
case,  minute  atoms  of  iron,  and  in  the  other,  of  lead  are  instantly  oxidized 
with  the  phenomena  of  combustion  at  the  ordinary  temperature ;  although 
neither  iron  nor  lead  will  burn  in  air  under  common  circumstances.  Sulphate 
of  potassa  in  powder,  strongly  heated  in  a  covered  crucible,  with  half  of  its 
weight  of  lamp-black,  is  converted  into  sulphide  of  potassium,  which  becomes 
so  rapidly  oxidized  on  exposure  to  air,  that  it  will  take  fire  and  burn.  The 
difference  between  the  combustibility  of  carbon  as  tinder,  and  of  carbon  as 
coke  or  diamond,  is  also  dependent  on  the  different  cohesive  force  and 
amount  of  surface  exposed  by  these  substances.  Again,  thin  shavings  of 
zinc  are  very  combustible  in  the  heat  of  a  spirit-lamp,  while  a  bar  of  the 
metal,  or  stout  foil,  resists  combustion.  There  is  no  case  in  which  this  effect 
of  division  and  surface  is  more  strongly  manifested  than  in  phosphorus.  This 
substance  may  be  exposed  to  air  in  a  mass,  at  a  temperature  below  60°, 
without  taking  fire.     When,  however,  it  has  been  dissolved  in  the  sulphide 


42  CHEMICAL    FORCE.      INFLUENCE    OF    WATER. 

of  carbon,  and  the  solution  is  poured  over  a  slieet  of  thin  paper,  a  layer, 
consisting  of  infinitely  minute  particles  of  phosphorus,  is  left  upon  the  paper 
by  the  evaporation  of  the  solvent ;  and  when  dry,  these  minute  particles  of 
phosphorus  on  the  surface  of  the  paper,  burst  into  a  sheet  of  flame.  We  are 
accustomed  to  speak  of  oxygen  ae  it  exists  in  our  atmosphere  as  passive,  but 
these  facts  show  us  that  its  passivity  is  more  apparent  than  real ;  and  that 
were  it  not  for  the  force  of  cohesion  by  which  the  particles  of  matter  are 
held  together  as  solids,  many  of  the  metals  and  metalloids  could  not  possibly 
exist  in  an  unoxidized  condition. 

In  some  exceptional  cases,  solids  are  found  to  react  upon  each  other. 
Potassium  placed  on  ice  will  decompose  it,  and  burn  at  the  expense  of  the 
oxygen,  which  is  one  of  its  constituents.  If  powdered  iodiue  be  placed  on 
a  freshly-cut  slice  of  dry  phosphorus,  mere  contact  leads  to  the  fusion  of  the 
phosphorus,  and  to  instantaneous  combination  with  combustion.  A  mixture 
of  finely-powdered  chlorate  of  potash  and  allotropic  phosphorus  explodes 
with  the  slightest  friction  and  with  tremendous  violence. 

Influence  of  Water. — The  influence  of  water  on  chemical  aflQnity  is  very 
remarkable.  In  some  cases,  by  its  removal,  chemical  changes  are  entirely 
arrested.  Albumen  or  gelatin,  combined  with  a  small  quantity  of  water, 
speedily  putrefies ;  but  when  desiccated,  or  deprived  of  water,  these  substances 
undergo  no  change.  {See  Water.)  Iron  has  a  great  tendency  to  become 
rusted  or  oxidized  on  exposure  to  air ;  but  if  the  air  is  perfectly  free  from 
water,  there  is  no  rust  or  oxidation.  A  strong  solution  of  nitrate  of  silver 
dried  on  paper  is  decomposed  in  a  few  days,  even  when  kept  from  light. 
The  organic  matter  of  the  paper  reduces. the  silver  to  the  metallic  state  in 
the  dark,  and  the  paper  becomes  discolored.  If,  however,  the  paper  is 
placed  in  a  vessel  containing  anhydrous  chloride  of  calcium,  and  kept  from 
the  light,  it  may  be  preserved  unchanged  for  weeks  and  months.  Sensitized 
papers  used  in  the  art  of  photography,  or  photographic  drawings  when  once 
taken,  are  thus  effectually  preserved  from  change,  so  long  as  they  are  in  a 
dry  atmosphere.  Even  pure  chloride  of  silver,  prepared  as  white  as  snow, 
by  immersing  leaf- silver  in  chlorine  gas,  undergoes  no  change  on  exposure 
to  light,  provided  chloride  of  calcium  is  placed  in  the  vessel  containing  it, 
and  the  vessel  is  accurately  closed.  We  have  thus  kept  the  chloride  of  silver 
for  six  months,  with  its  whiteness  unaltered,  although  during  that  time  it 
was  exposed  to  the  direct  solar  rays.  Chlorine  itself  when  entirely  deprived 
of  moisture,  manifests  no  tendency  to  combine  with  metallic  silver  in  the 
state  of  leaf.  The  film  of  iodide  of  silver,  which  is  used  in  the  collodion 
process  of  photography,  may  be  kept  for  many  months  in  the  dark,  with  its 
sensitive  powers  undiminished,  provided  the  surplus  nitrate  of  silver  is 
removed  by  washing — the  film  itself  is  dried  and  coated  with  a  layer  of 
albumen  or  tannic  acid,  and  lime  of  chloride  of  calcium  is  placed  in  the  box 
to  absorb  any  moisture.  The  color  of  compounds  appears  to  be  in  some 
instances  closely  connected  with  the  presence  of  the  elements  of  water.  If 
Prussian  blue  is  boiled  with  strong  sulphuric  acid,  it  loses  its  color  and 
becomes  of  a  dingy  white.  This  change  appears  to  be  owing  to  the  removal 
of  water;  for  if  the  white  compound  is  poured  into  a  large  quantity  of  water, 
it  immediately  reacquires  its  color,  but  the  color  is  not  restored  when  it  is 
put  into  oxygen  gas.  This  proves  that  the  restoration  of  the  blue  color 
depends  on  hydration. 

In  the  absence  of  water  we  can  get  no  evidence  of  acidity  or  alkalinity  in 
substances.  Thus  sulphuric  acid  in  the  anhydrous  state  is  a  fibrous  selid, 
which  has  no  action  on  litmus,  and  no  corrosive  properties.  Solid  anhydrous 
phosphoric  acid  has  no  acid  reaction  on  test-paper;  this  is  only  manifested 
on  the  absorption  of  some  water  from  the  air.     Boracic  acid  and  silicic  acid 


INFLUENCE    OP    WATER.  43 

are  in  the  same  condition  ;  in  fact,  owing  to  its  entire  insolubility  in  the  free 
state,  silicic  acid  cannot  be  proved  to  have  any  reaction  like  an  acid  on 
vegetable  colors.  Dry  carbonic  acid  gas  has  no  action  on  dry  litmus.  The 
same  remark  may  be  made  of  the  gallic,  pyrogallic,  and  other  vegetable  acids, 
whether  hydrated  or  anhydrous.  They  manifest  no  acid  reaction  on  test- 
paper  until  water  is  added.  It  has  been  supposed  that  this  apparent 
production  of  acidity  by  water  was  a  proof  that  all  acids  must  owe  their 
acidity  to  hydrogen,  and  be  really  hydracids,  hydrides  of  new  radicals,  or,  as 
they  are  termed,  "  salts  of  hydrogen  ;"  but  such  an  hypothesis  is  not  necessary 
for  an  explanation  of  the  facts.  Thus,  in  reference  to  the  elements  of 
phosphoric,  carbonic,  pyrogallic,  and  other  acids,  water  may  simply  act  as  a 
solvent  to  bring  the  constituents  of  the  acid  in  contact  with  the  vegetable 
color.  Anhydrous  potassa,  soda,  ammonia  or  morphia  in  the  absence  of 
moisture  or  water,  cannot  be  proved  to  exert  any  alkaline  reaction  on 
vegetable  colors  ;  and  to  explain  this  reaction,  it  is  not  necessary  to  suppose 
that  the  potash  or  soda  absorbs  another  atom  of  oxygen  and  becomes  a 
hydride  {see  Oxacids,  and  Oxygen),  or  to  assume  therefrom  that  hydrogen 
is  the  cause  of  alkalinity.  An  acid  or  alkaline  reaction,  as  manifested  by 
changes  in  vegetable  colors,  depends  much  on  the  solubility  of  the  substance, 
and  of  the  coloring  principle  employed.  Some  vegetable  acids,  say  the 
tartaric,  when  dissolved  in  alcohol,  have  but  a  slight  effect  on  litmus  paper, 
while  the  solution  of  the  same  acid  in  water  has  a  powerful  acid  reaction. 
Carbonate  of  potash  in  water  has  a  strong  alkaline  reaction  on  test-paper, 
but  this  salt  mixed  with  alcohol  manifests  no  alkalinity.  A  solution  of  pure 
potash,  whether  in  water  or  alcohol,  is  strongly  alkaline.  Magnesia  manifests 
no  alkalinity  to  test-paper  when  mixed  with  alcohol,  but  when  mixed  with 
water  it  is  sufficiently  soluble  to  produce  the  usual  changes  of  colors 
indicative  of  the  presence  of  an  alkali.  Solutions  of  some  of  the  resins  in 
alcohol  give  no  indication  of  acidity  to  test-paper,  but  when  water  is  added, 
to  precipitate  the  resin,  there  is  immediately  an  acid  reaction — litmus  paper 
is  reddened. 

The  intensity  of  reaction  on  vegetable  colors,  whether  acids  or  alkalies,  is 
generally  in  a  direct  ratio  to  the  solubility  of  these  substances  in  water. 
While  tartaric  acid  acts  powerfully  on  infusion  of  blue  litmus — a  solution 
of  boracic  acid  barely  reddens  it — and  silicic  acid  in  its  ordinary  and  insoluble 
state  does  not  alter  the  blue  color.  There  is  an  equally  marked  difference 
of  action  on  vegetable  colors,  which  are  affected  by  alkalies,  in  reference  to 
pure  potash,  lime,  and  magnesia.  Potash  is  soluble  in  half  its  weight  of  cold 
water,  ^ime  requires  700  times  its  weight.  Magnesia  7000  times  its 
weight  for  solution.  Potash  has  an  intense  alkaline  reaction,  while  magnesia 
acts  feebly  and  slowly.  Among  substances  which  readily  decompose  each 
other,  there  is  an  entire  want  of  action,  unless  water  is  present.  Thus  dry 
t&rtaric  acid  has  no  action  on  dry  carbonate  of  soda,  even  when  finely 
powdered.  In  the  cases  above-mentioned,  water  as  such,  may  take  a  share 
in  promoting  chemical  action  without  necessarily  undergoing  decomposition. 
(For  other  instances  see  Water.) 

In  the  chemical  process  of  bleaching  by  chlorine  or  bromine,  it  is  highly 
probable  that  water  is  decomposed.  Dry  chlorine  has  no  bleaching  action 
on  dry  vegetable  colors.  The  slightest  trace  of  humidity  in  the  gas  or  in 
the  colored  material  brings  about  the  destruction  of  color.  As  hydrochloric 
acid  is  found  in  a  liquid  thus  bleached,  some  portion  of  the  water  must  have 
parted  with  its  hydrogen;  and  oxygen  thus  liberated  in  the  nascent  state 
(as  ozone)  enters  into  combination  with  the  coloring  matter  and  probably 
operates  as  the  direct  bleaching  agent.  The  influence  of  water  on  the 
chemical  force  is  well  seen  in  the  production  of  the  so-called  amalgam  uf 


a 


44  INFLUENCE    OF    HEAT. 

ammonium.  If  dry  amalgam  of  sodium  is  placed  in  a  dry  block  of  chloride 
of  ammonium,  there  is  no  chemical  change ;  but  if  water  is  added,  the 
mercury  speedily  increases  in  size  :  it  becomes  soft  and  compressible,  and  is 
everywhere  penetrated  with  the  two  gases,  liberated  by  the  combination  of 
the  sodium  with  the  chlorine.  The  whole  forms  a  light  spongy  mass,  which 
is  rapidly  reconverted  into  mercury,  hydrogen,  and  ammonia.  {See  Am- 
monium.) 

Influence  of  Heat. — Heat  plays  an  important  part  in  reference  to  the 
chemical  force.  By  its  agency  bodies  are  united  and  disunited.  Mercury 
combines  with  oxygen  at  one  temperature,  and  at  a  still  higher  temperature 
the  compound  is  again  resolved  into  mercury  and  oxygen.  Protoxide  of 
barium  will  at  one  temperature  take  another  equivalent  of  oxygen,  to  form 
peroxide;  but  when  this  compound  is  more  strongly  heated,  the  atom  of 
oxygen  will  be  expelled,  and  it  will  revert  to  the  state  of  protoxide.  Gene- 
rally speaking,  the  effect  of  heat  is  to  increase  the  afiBnity  of  bodies  for  each 
other.  The  strongest  nitric  acid  has  no  action  on  aluminum  in  the  cold,  but 
when  heat  is  applied,  there  is  a  violent  action — the  metal  becoming  oxidized. 
This  action  ceases  on  cooling  the  acid,  and  is  renewed  on  again  heating  it. 
Sulphur  and  charcoal  have  no  tendency  to  combine  with  oxygen  unless 
heated  to  about  500^  and  1000°  respectively,  when  they  both  undergo 
combustion,  and  produce  gaseous  compounds.  The  inflammation  of  gun- 
powder furnishes  an  example  of  the  effect  of  heat  on  these  ingredients.  It 
is  only  when  this  substance  is  heated  in  air  to  a  temperature  above  500° 
that  combustion  takes  place,  with  the  conversion  of  the  solid  into  a  large 
volume  of  gases* 

The  solubility  of  substances  in  water  is  generally  increased  by  heat :  in 
some  instances,  the  reverse  condition  is  observed.  Lime  is  twice  as  soluble 
in  cold  as  in  boiling  water  ;  hence  when  a  saturated  solution  of  lime  is 
boiled,  a  portion  of  this  alkaline  earth  is  deposited.  A  very  diluted  solution 
of  persulphate  of  iron  is  decomposed  by  heat,  and  a  basic  salt  with  excess  of 
oxide  is  deposited.  The  effect  of  heat  on  albumen  is  remarkable.  At  a 
temperature  exceeding  110°,  the  soluble  is  converted  into  the  insoluble 
variety,  and  the  properties  of  the  substance  are  entirely  changed.  Heat 
destroys  temporarily  the  combination  of  iodine  with  starch ;  the  liquid  from 
being  intensely  blue  becomes  colorless  ;  but  if  not  too  long  heated  the  color 
of  the  liquid  will  be  restored  on  cooling,  by  the  reabsorption  of  the  vapor  of 
iodine,  which  has  been  temporarily  separated  from  the  starch.  When  this 
experiment  is  performed  in  a  close  vessel  the  colored  compound  is  reproduced ; 
but  when  in  an  open  dish,  the  iodine  is  lost  by  volatilization,  and  the  blue 
color  is  either  not  restored,  or  only  in  a  slight  degree.  A  solution  of 
chloride  of  calcium,  so  diluted  as  to  yield  no  precipitate  with  a  solution  of 
sulphate  of  soda,  undergoes  decomposition  when  heated,  and  sulphate  of  lime 
is  precipitated,  the  salt  being  less  soluble  in  hot  than  in  cold  water.  Again, 
borate  of  soda  produces  no  precipitation  or  apparent  decomposition  of 
sulphate  of  magnesia  in  the  cold,  but  when  a  solution  containing  the  two 
salts  is  boiled,  an  insoluble  borate  of  magnesia  is  thrown  down.  A  solution 
of  bicarbonate  of  soda,  or  of  carbonate  of  lithia,  gives  no  precipitates  with 
sulphate  of  magnesia  until  the  liquids  have  been  boiled.  It  is  unnecessary 
to  specify  additional  instances  of  the  influence  of  heat  on  chemical  affinity. 
Illustrations  will  be  found  in  the  history  of  every  element  and  of  most 
compounds. 

Influence  of  LigJit.^ThQ  influence  of  light  is  seen  in  some  combinations 
of  the  gases,  as  well  as  in  the  changes  produced  in  the  salts  of  certain  metals, 
as  silver,  mercury,  gold,  chromium,  iron,  and  uranium.  When  equal 
volumes  of  chlorine  and  carbonic  oxide  are  exposed  in  a  glass  vessel  to  solar 


INFLUENCE    OP    LIGHT.  45 

light,  they  combine  to  form  a  compound  known  as  phosgene  gas.  In  the 
dark  they  manifest  no  tendency  to  unite.  When  chlorine  and  hydrogen  are 
mixed  and  ex}3osed  to  the  direct  rays  of  the  sun,  they  combine  with  explo- 
sion, and  produce  hydrochloric  acid;  in  the  dark  there  is  no  combination  ; 
and  in  the  diffused  light  of  day  the  union  of  the  gases  takes  place  slowly, 
without  explosion.  So  strictly  does  this  union  depend  on  light,  that  Bunsen 
and  Roscoe  have  made  use  of  such  a  mixture  for  the  purposes  of  photometry, 
in  determining  the  relative  intensity  of  light.  On  the  other  hand,  under  the 
influence  of  light,  aqueous  vapor  mixed  with  chlorine  undergoes  decomposi- 
tion, hydrochloric  acid  and  oxygen  being  the  products  (supra).  Unless  a 
solution  of  chlorine  is  carefully  kept  in  the  dark,  it  is  rapidly  decomposed, 
and  the  liquid  becomes  strongly  acid  from  the  hydrochloric  acid  produced. 
It  is  under  the  influence  of  solar  light  that  carbonic  acid  is  decomposed  by 
the  leaves  of  growing  vegetables,  and  the  carbon  is  fixed,  while  oxy/gen  is 
liberated. 

The  influence  of  light  on  chemical  affinity  is  especially  seen  in  the  changes 
produced  on  the  salts  of  silver.  When  in  contact  with  organic  matter, 
nitrate  of  silver  is  entirely  decomposed  by  exposure  to  light.  The  oxygen 
and  nitric  acid  are  removed  and  the  silver  is  reduced  to  the  metallic  state. 
If  moisture  is  present,  chloride  of  silver  is  also  decomposed  by  exposure  to 
light,  hydrochloric  acid  is  produced,  and  metallic  silver  is  deposited.  In 
reference  to  these  salts,  the  changes  are  physical  as  well  as  chemical — the 
silver  is  visibly  darkened.  Other  salts  of  silver,  such  as  the  iodide  and 
bromide,  undergo  no  visible  change  of  color  when  exposed  to  light ;  but 
they  are  altered  in  their  molecular  state.  (See  p.  52.)  This  subject  will 
be  more  fully  considered  under  Photography.  The  suboxide  of  mercury, 
exposed  to  light,  is  converted  into  red  oxide  and  metallic  mercury.  Turpeth 
mineral,  or  the  basic  sulphate  of  the  peroxide,  is  darkened  by  light.  The 
salts  of  the  peroxide  of  iron,  formed  by  the  citric  and  oxalic  acids  in  contact 
with  organic  matter,  are  reduced  to  proto-salts  by  exposure  to  light,  a  fact 
which  may  be  proved  by  the  application  of  appropriate  reagents,  e.  g.,  the 
chloride  of  gold.  The  persalts  of  uranium  and  the  bichromate  of  potassa 
are  also  reduced  to  lower  degrees  of  oxidation  by  exposure  to  the  solar  rays. 

The  effects  above  described  take  place  under  the  influence  of  ordinary 
light;  but  a  closer  analysis  of  the  phenomena  has  established  the  fact,  that 
this  chemical  influence  is  almost  exclusively  confined  to  the  more  refrangible 
rays  of  the  spectrum,  namely,  the  blue  and  violet.  Thus,  an  intense  light 
passing  through  violet  or  blue  glass  will  cause  the  immediate  explosion  of  a 
mixture  of  chlorine  and  hydrogen  ;  while  the  same  light,  traversing  yellow 
or  red  glass,  has  no  combining  effect  on  the  gases.  Although  a  larger 
amount  of  luminosity  exists  in  the  yellow  than  in  the  blue  light,  the  yellow 
rays  are  powerless  to  bring  about  a  chemical  union  of  the  gases.  This 
peculiar  effect  of  colored  light  is  equally  observed  in  reference  to  the  changes 
produced  on  the  salts  of  silver ;  but  in  different  degrees  in  different  salts. 
The  rays  which  produce  these  chemical  changes  are  called  actinic ;  they  are 
met  with  even  beyond  the^visible  violet  ray.  On  the  undulatory  theory  of 
light,  the  blue  and  the  violet  rays  are  considered  to  produce  a  greater 
number  of  ethereal  undulations,  in  a  given  time,  than  the  yellow  and  the  red 
rays ;  and  the  difference  of  color  is  supposed  to  depend  upon  the  difference 
in  the  number  of  their  undulations.  While  this  theory  derives  great  support 
from  many  physical  phenomena,  it  affords  no  satisfactory  explanation  of  the 
remarkable  influence  of  white  or  colored  light  upon  the  chemical  union  and 
decomposition  of  bodies. 

Influence  of  the  Nascent  State. — Gases  when  once  in  the  free  state  do  not 
readily  combine  with  each  other.     Thus  hydrogen  will  not  combine  with 


46  CHEMICAL    COMPOUNDS. 

nitroj^en  to  form  ammonia,  nor  will  it  combine  with  sulphur  or  arsenic  in 
powder  or  vapor,  to  form  sulphuretted  or  arsenuretted  hydrog^en  ;  but 
there  is  a  condition,  called  the  nascent  state,  which  is  eminently  favorable 
to  the  chemical  combination  of  these  bodies,  either  with  each  other  or  with 
solids.  The  nascent  state  simply  implies  that  condition  in  which  a  body  is 
passing  from  the  solid  or  liquid  to  the  j^aseous  state.  The  ammonia  formed 
by  the  putrefaction  of  substances  containing  nitrogen,  is  the  result  of  the 
combination  of  hydrogen  and  nitrogen,  as  they  are  liberated  from  the 
organic  solid  or  liquid.  When  sulphide  of  iron  is  treated  with  diluted 
sulphuric  acid,  the  nascent  hydrogen  resulting  from  the  decomposition  of 
water,  instantly  seizes  upon  the  sulphur  of  the  sulphide  to  form  sulphuretted 
hydrogen.  When  the  same  acid  is  poured  upon  zinc,  containing  arsenic, 
or  when  the  zinc  and  acid  are  added  to  an  arsenical  liquid,  the  nascent 
hydrogen  instantly  combines  with  the  arsenic  to  form  arsenuretted  hydrogen. 
The  affinity  of  hydrogen  in  the  act  of  liberation  from  water  is  so  exalted, 
that  it  will  combine  with  and  carry  over  minute  traces  of  carbon,  sulphur, 
phosphorus,  selenium,  silicon,  arsenic,  iron,  zinc,  and  other  substances, 
although  in  the  state  of  free  gas  it  has  no  tendency  whatever  to  combine 
with  them.  The  production  of  silicide  of  hydrogen,  as  well  as  of  the  tartaric, 
acetic,  oxalic,  and  other  ethers,  depends  on  the  influence  of  the  nascent  state 
in  effecting  th?  combination  of  bodies. 

Many  chemical  decompositions  in  which  the  results  appear  to  be  conflict- 
ing, receive  an  explanation  from  this  theory  of  a  nascent  state.  A  current 
of  pure  hydrogen  in  a  free  state,  passed  through  solutions  of  permanganate 
of  potash,  bichromate  of  potash,  and  tartar  emetic,  produces  no  chemical 
change  ;  but  if  the  hydrogen  is  generated  in  each  of  these  solutions  by  adding 
sulphuric  acid  to  pure  zinc,  as  it  is  eliminated  from  the  water,  it  deoxidizes 
the  dissolved  substances.  It  discharges  the  color  of  the  permanganate  of 
potash;  it  reduces  the  chromic  acid  to  green  oxide  of  chromium,  and  it 
combines  with  a  portion  of  metallic  antimony  escaping  from  the  vessel  in 
the  form  of  antimonuretted  hydrogen.  In  these  cases  it  matters  not  how 
the  hydrogen  is  produced,  so  that  it  is  slowly  evolved  as  the  result  of  chemical 
decomposition  in  immediate  contact  with  the  substance.  An  amalgam  of 
sodium  and  mercury  evolves  hydrogen,  which  equally  deoxidizes  the  per- 
manganate of  potash.  Hydrogen  in  a  free  current,  when  passed  into 
mixtures  of  ammonio-chloride  of  platinum  in  water  and  of  chloride  of  silver 
in  water,  produces  no  chemical  changes  ;  but  when  the  hydrogen  is  liberated 
in  the  mixture  by  the  reaction  of  an  acid  on  pure  zinc,  metallic  platinum  in 
the  form  of  platinum  black  is  thrown  down  in  the  one  case,  and  pure  silver 
in  the  other.  Free  hydrogen  manifests  no  reducing  power,  while  nascent 
hydrogen  has  a  more  intense  action  and  immediately  combines  with  the 
chlorine,  setting  the  metals  free.  Sodium  amalgam  speedily  reduces  the 
chlorides  of  gold  and  platinum,  the  hydrogen  combining  with  the  chlorine 
and  setting  the  metals  free — the  metallic  gold  entering  into  combination 
with  the  mercury,  forming  a  gold  amalgam.  In  the  rusting  of  iron,  hydrogen 
is  evolved  in  the  nascent  state  by  the  decompqgition  of  water:  it  imme- 
diately combines  with  the  nitrogen  of  the  air,  producing  ammonia,  which  is 
formed  in  most  parts  of  iron  rust.  When  free,  hydrogen  cannot  be  made  to 
combine  with  nitrogen  to  produce  ammonia.  Many  other  instances  might 
be  cited  in  illustration  of  this  mode  of  action.  They  will  be  described 
hereafter. 

What  is  a  CJiemical  Compound? — The  answer  to  this  question  is  involved 
in  the  inquiry — How  may  a  chemical  compound  be  distinguished  from  a  me- 
chanical^ mixture  ?  In  gun-cotton  (pyroxyline)  and  gunpowder  we  have 
illustrations  'of  the  two  states.     Gun-cotton  is  a  chemical  compound  of  the 


CHEMICAL    FORCE.      SOLUTION.  41 

offrnnic  substance  (cotton)  as  a  base  with  the  elements  of  nitrous  or  hypo- 
nitric  acid  (NO4).  The  constituents  cannot  be  separated  without  an  entire 
destruction  of  the  substance.  Gunpowder  is  a  mechanical  mixture  of  char- 
coal, sulphur,  and  nitre,  in  certain  proportions,  the  two  last  beinp^  easily 
separable  from  each  other  and  from  the  charcoal,  by  appropriate  solvents. 
The  chemical  force  is  only  brought  into  operation  among  these  ingredients 
by  heat;  while  in  gun-cotton  this  force  already  binds  together  the  nitrous 
acid  and  the  cotton,  and  heat  merely  produces  a  new  series  of  combinations. 

In  spite  of  these  broad  distinctions,  there  are  some  cases  of  the  union  of 
substances,  of  so  doubtful  a  character,  that  chemists  are  not.  agreed  upon 
the  nature  of  the  force  which  binds  them  together.  Gelatinous  alumina, 
shaken  with  solution  of  cochineal,  removes  the  color  and  is  precipitated  with 
it.  Charcoal  in  the  same  way  removes  the  color  of  indigo,  litmus,  cochineal, 
and  of  other  vegetable  and  animal  substances.  It  will  also  remove  the  blue 
color  of  iodide  of  starch,  and  the  red  color  of  permanganate  of  potavsh, 
which  are  chemical  compounds.  This  is  commonly  described  as  a  surface 
action  or  an  attraction  between  surfaces,  as  the  properties  of  the  bodies 
undergo  no  change. 

When  caoutchouc  is  combined  with  sulphur  at  a  temperature  of  about 
300°,  a  compound  known  as  vulcanized  rubber  is  produced.  The  properties 
of  this  substance  are  different  from  those  of  its  constituents.  Thus  after 
vulcanization  the  rubber  is  altered  in  color;  its  elasticity  is  remarkably  in- 
creased ;  it  does  not  melt  even  at  the  boiling  point  of  mercury,  and  it  does 
not  become  stiff  in  the  cold.  It  is  also  quite  insoluble  in  all  the  liquids  which 
dissolve  rubber.  Here  then  is  a  change  of  properties  sufficient  to  justify  a 
chemist  in  regarding  this  as  a  chemical  compound  of  its  two  constituents. 
On  the  other  hand,  the  two  substances  do  not  combine  in  definite  propor- 
tions :  the  sulphur  may  be  in  the  proportion  of  from  10  to  16  per  cent.,  and 
it  may  be  removed  from  the  rubber,  after  incorporation,  by  the  usual  sol- 
vents, without  materially  affecting  its  properties.  These  conditions  are 
adverse  to  the  hypothesis  of  a  chemical  union,  and  the  result  is,  that  such  a 
compound  can  be  expressed  by  no  chemical  formula.  Again,  in  the  phe- 
nomena of  solution  or  diffusion,  as  of  hydrated  sulphuric  acid,  or  of  anhy- 
drous alcohol  in  water,  we  have  evolution  of  heat  and  a  great  alteration  of 
volume.  Is  this  a  chemical  union  of  the  liquids  with  the  water,  or  is  it  not? 
The  phenomena  accompanying  the  mixture  point  to  something  more  than  a 
mechanical  force  ;  but  there  is  no  change  of  properties,  and  there  is  no  evi- 
dence of  union  in  definite  proportions.  This  subject  is,  however,  of  sufficient 
importance  in  a  chemical  point  of  view  to  receive  a  separate  examination. 

Solution. — The  solution  of  solids  in  liquids,  whether  the  solvent  be  water, 
alcohol,  ether,  benzole,  chloroform,  or  mercury,  has  been  assigned  by  some 
chemists  to  a  species  of  affinity,  and  by  others  to  a  physical  effect  of  adhe- 
sion. By  solution  we  are  simply  to  understand  a  combination  of  a  solid  with  ' 
a  liquid,  in  which  the  solid  itself  assumes  a  liquid  form.  There  is  no  change 
of  properties,  and  here  this  great  feature  of  chemical  force  is  wanting : 
thus  common  salt  dissolved  in  water  possesses  all  its  usual  characters.  This 
observation  applies  equally  to  the  solutions  of  other  salts,  as  well  as  to  solu- 
tions of  acids  and  alkalies.  The  best  solvents  are  generally  those  liquids 
which  are  similar  in  properties  to  the  solid.  Benzole  and  oil  of  turpentine 
readily  dissolve  caoutchouc  and  other  solid  hydrocarbons  ;  oils  dissolve  fats ; 
mercury  dissolves  metals;  alcohol  dissolves  resins;  and  water,  itself  a  neutral 
oxide,  dissolves  neutral  salts  and  neutral  compounds,  such  as  gum,  sugar,  &c. 
Water  is  the  great  solvent  for  chemical  purposes,  and  it  is  by  the  use  of  this 
liquid  that  most  chemical  changes  are  produced  among  solids ;  it  breaks  up 


r'W^      t.l 


8  SOLUTION    OF    SALTS. 


the  cohesion  of  solids  more  effectually  than  pulverization,  and  thus  brings 
their  particles  within  the  sphere  of  each  other's  attraction. 

Solution  is  only  influenced  by  gravitation,  when  the  solid  salt  is  allowed 
to  remain  at  the  bottom  of  the  water.  The  lower  stratum  of  liquid  then  con- 
tains a  much  larger  quantity  of  the  salt  than  the  upper  portion  ;  but  after  a 
time  it  will  spread  by  diffusion,  varying  in  degree  with  the  nature  of  the  salt. 
For  this  reason,  solution  is  always  best  effected  by  suspending  the  solid  sub- 
stance in  the  upper  stratum  of  liquid.  When  the  salt  is  once  dissolved  and 
equally  diffused  throughout  the  liquid  by  agitation,  gravitation  is  not  found 
to  affect  it.  Thus,  although  corrosive  sublimate  has  a  specific  gravity  six 
times  greater  than  water,  yet  a  solution  of  it,  preserved  for  many  years  in  a  long 
tube,  was  not  found  to  contain  any  more  of  this  salt  in  the  lower  than  in  the 
upper  stratum. 

Each  substance  has  its  own  specific  solubility  which  varies  with  tempera- 
ture, and  as  a  general  rule  heat  increases  the  solubility  of  solids  in  water  and 
other  solvents,  but  there  are  some  exceptions  in  reference  to  water.  Thus 
lime,  citrate  of  lime,  sulphate  of  lime,  and  sulphate  of  soda,  are  less  soluble 
at  the  boiling  points  of  their  solutions  than  at  lower  temperature  ;  while 
chloride  of  sodium  is  nearly  equally  soluble  at  a  high  and  a  low  temperature. 
The  fact  that  each  solid  has  a  special  rate  of  solubility,  and  that  this  varies 
with  temperature  is  inconsistent  with  the  theory  that  solution  is  dependent 
on  physical  force. 

A  knowledge  of  the  relative  solubility  of  salts  in  water  is  of  some  import- 
ance in  chemical  analysis.  Many  substances  thus  admit  of  separation  by 
evaporating  the  solutions,  those  which  are  least  soluble  for  the  temperature 
being  first  deposited.  We  subjoin  a  table  of  the  relative  solubility  at  60°  of 
many  salts  in  common  use.  The  figures  represent  in  weight  the  parts  of 
salts  dissolved  by  100  parts  of  distilled  water  by  weight. 


Parts  dissolved  at  60°. 

Parts  dissolved  in  60°. 

Acid  tartrate  of  potash   . 

.     1 

Carbonate  of  ammonia  . 

.     33 

Oxalate  of  ammonia 

.     4 

Nitrate  of  baryta  . 

.     35 

Alum      .... 

.     6 

Chloride  of  barium 

.     36 

Bicarbonate  of  soda 

.    7 

Chloride  of  ammonium 

.     36 

Sulphate  of  potash 

.     8 

Chloride  of  sodium 

.     37 

Sulphate  of  soda     . 

.  10.5 

Sulphate  of  magnesia   . 

.  100 

Bicarbonate  of  potash     . 

.  25 

Carbonate  of  potash 

.  100 

Phosphate  of  soda  . 

.  25 

Tartrate  of  potash 

.  100 

Phosphate  of  ammonia  . 

.  25 

Nitrate  of  ammonia 

.  120 

Chloride  of  potassium     . 

.  29 

Iodide  of  potassium 

.  143 

Ferrocyanide  of  potassium 

.  33 

Chloride  of  magnesium 

.  200 

Nitrate  of  potash    . 

.  33 

Chloride  of  calcium 

.  400 

Nitrate  of  soda 

.  33 

The  term  insolubility  as  applied  to  a  salt  has  only  a'relative  signification. 
Sulphate  of  lime  is  sometimes  described  as  insoluble  in  water.  Compared 
with  the  salts  in  the  preceding  list,  its  solubility  in  water  is  very  slight. 
Thus  it  requires  400  parts  of  water  at  60°  to  dissolve  one  part  of  the  sul- 
phate of  lime,  but  it  is  very  soluble  when  compared  with  the  sulphate  of 
baryta.  Taking  the  sulphates  of  lime,  strontia,  and  baryta,  their  solubility 
in  water  decreases  in  a  decimal  proportion.     One  part  of 

Parts  of  water. 

Sulphate  of  lime      is  dissolved  by 400 

Sulphate  of  strontia       "         « 4^000 

Sulphate  of  baryta         «         « 40,000 

The  sulphate  of  baryta  is  usually  described  as  quite  insoluble,  but  there 
are  compounds  which  are  still  less  soluble  than  it.  Carbonate  of  lime  re- 
quires 16,000  parts  of  water  for  the  solution  of  one  part.     The  presence  of 


SOLUTION    OP    SALTS.  49 

free  carbonic  acid  renders  it  much  more  soluble.  Chloride  of  silver  is  the 
most  insoluble  of  salts,  and  is  said  to  require  113  railliou  parts  of  water  to 
dissolve  it. 

The  comparative  insolubility  in  water  of  the  platina  chlorides  of  the  alkali- 
metals,  enables  chemists  to  separate  some  of  them  from  each  other.  The 
following  table  represents  the  effect  of  water  as  a  solvent  at  60°  and  at  212°. 
One  part  of 


Parts  of  water 

Parts  of  water 

at  60°. 

at  21 2-- 

Platino-chloric 

le  of  potassium  is  soluble  in 

108 

19 

((              « 

ammonium            " 

150 

80 

Rubidium 

u 

740 

157 

Csesium 

(< 

1,308 

261 

Thallium 

« 

15,585 

1,948 

Parts. 

Parts. 

58.49 

Narcotina 

, 

, 

.     31.17 

57.47 

Strjclmia 

. 

, 

.     20.19 

56.70 

Cinchonia 

. 

, 

.      4.31 

51.19 

Morphia   . 

. 

. 

.      0.57 

The  platino-chloride  of  thallium,  it  will  be  seen,  is  as  insoluble  as  chalk. 

The  alkaloids  are  remarkable  for  their  insolubility  in  water.  Strychnine 
is  usually  described  as  insoluble  :  it  requires  7000  parts  of  water  for  the  solu- 
tion of  one  part.  The  alkaloids  are,  however,  dissolved  by  alcohol,  ether, 
benzole,  and  chloroform  in  different  degrees.  The  table  shows  the  different 
quantities  of  eight  important  alkaloids  which  chloroform  will  dissolve  at  60°. 
It  may  be  found  useful  in  the  separation  of  some  of  these  alkaloids  from  each 
other.     100  parts  of  chloroform  by  weight  dissolve  of 

Veratria  . 
Quinia 
Brucia 
Atropia     . 

These  remarkable  differences  in  the  proportion  of  solids  which  the  same 
weight  of  the  solvent  is  capable  of  converting  into  a  liquid,  render  it  impos- 
sible to  admit  that  solution  is  a  mere  physical  adhesion  of  the  atoms  of  one 
body  to  the  atoms  of  another. 

The  solution  of  salts  in  water  is  sometimes  attended  with  great  loss  of  heat 
by  reason  of  the  salt  rapidly  passing  from  the  solid  to  the  liquid  state.  Some 
of  the  cheapest  freezing  mixtures,  in  the  absence  of  ice,  are  based  upon  this 
property.  Thus  one  part  of  crystallized  nitrate  of  ammonia,  dissolved  in  one 
part  of  water  causes  the  thermometer  to  fall  from  50°  to  4° ;  and  five  parts 
of  sal  ammoniac  with  five  parts  of  nitre,  dissolved  in  sixteen  parts  of  water, 
are  nearly  equally  effective.  These  are  anhydrous  salts,  so  that  the  result  is 
the  direct  effect  of  solution,  and  it  appears  to  point  rather  to  chemical  com- 
bination than  mechanical  adhesion.  Another  fact  observed  by  Playfair  and 
Joule  is,  that  salts  containing  water  of  crystallization,  when  dissolved  in  water, 
add  no  more  bulk  to  the  water  than  is  equivalent  to  the  water  of  crystalliza- 
tion (calculated  as  ice)  with  which  their  atoms  are  chemically  combined. 
Thus,  when  alum  is  dissolved  in  water,  the  increase  of  volume  in  the  solution 
is  not  in  proportion  to  the  bulk  of  alum  used,  but  to  the  bulk  of  combined 
water  as  ice  (24  equivalents),  contained  in  it.  The  atoms  of  alum  have 
therefore  disappeared,  or  been  received,  within  the  interstices  of  the  atoms 
of  water  ;  at  any  rate  they  occupy  no  appreciable  space.  If  these  results 
are  confirmed,  it  will  show  that  the  hypothesis  of  mechanical  adhesion  of  a 
liquefied  solid  to  a  liquid  is  not  in  all  cases  sufficient  to  explain  the  phenomena 
of  solution.  The  effect  of  heat  in  increasing  or  diminishing  solubility,  the 
fixed  limit  of  solubility  for  different  salts,  and  the  decrease  or  increase  occa- 
sionally observed  in  the  volume  of  the  solvent,  as  well  as  the  singular  fact 
observed  by  Dr.  Gladstone  (Proc.  R.  S.,  vol.  9,  p.  89),  namely,  the  absorp- 
4 


50  SOLUTION    OF    SALTS. 

live  power  on  light  exhibited  by  strong  solutions  of  salts,  are  adverse  to  the 
hypothesis  of  a  mere  adhesion  of  atoms. 

When  a  liquid  will  dissolve  no  more  of  a  solid,  it  is  said  to  be  saturated-^ 
in  other  words,  its  adhesion  or  affinity  for  the  solid  is  exhausted.  It  is  a 
curious  fact,  however,  that  water  which  is  saturated  with  one  salt  has  still 
the  property  of  dissolving  a  second  and  a  third  salt.  Crystals  of  nitre  may 
be  thus  freed  from  impurities,  such  a^  chloride  of  sodium  by  washing  them 
with  a  saturated  solution  of  nitre.  A  saturated  solution  of  a  salt  exerts  a 
powerful  attraction  on  water.  If  a  saturated  solution  of  sulphate  of  copper 
is  inclosed  in  a  funnel  tube,  secured  at  the  larger  end  by  bladder,  and  the 
tube  is  plunged  in  a  vessel  containing  water,  so  that  the  liquids  inside  and 
outside  are  on  a  level,  in  the  course  of  some  hours  it  will  be  found  that 
although  some  of  the  copper-salt  has  passed  out  through  the  pores  of  the 
bladder,  a  much  larger  proportion  of  water  has  passed  in.  Solutions  of 
common  salt,  sugar,  and  other  substances,  present  this  phenomena,  to  which 
the  term  osmosis  (from  uiOiu  to  push)  has  been  applied.  The  diffusion  of 
liquids  or  their  relative  tendency  to  mix  on  contact  has  been  fully  examined 
by  Mr.  Graham  {Quart.  Jour.  Cliem.  Sac,  vol.  3,  p.  60)  ;  and  the  effect  of 
porous  membranes  in  allowing  liquids  or  dissolved  solids  to  traverse  them, 
has  also  been  made  the  subject  of  experiment  by  the  same  chemist.  Mineral 
substances,  such  as  arsenic,  may  thus  be  separated  from  organic  matter. 
He  has  called  this  process  dialysis.     {Proc.  R.  S.,  1861,  vol.  11,  p.  243.) 

The  dissolved  solid  may  be  separated  from  the  solvent  by  the  addition  of 
another  liquid.  Camphor  is  separated  from  its  solution  in  alcohol  by  adding 
water — gum  from  its  solution  in  water  by  the  addition  of  alcohol — soap  from 
water  by  chloride  of  sodium,  and  corrosive  sublimate  and  chloride  of  gold 
from  water  by  ether.  In  the  latter  case,  the  metallic  salt  changes  its  solvent, 
and  the  compound  of  mercury  or  gold  is  found  dissolved  in  the  ether  as  chloride. 

When  liquids  mix  together,  they  are  said  to  combine  by  diffusion,  accord- 
ing to  various  circumstances.  Alcohol  and  water  readily  combine  with  evo- 
lution of  heat  and  contraction  of  volume.  If  54  parts,  by  measure,  of  alcohol, 
are  mixed  with  50  of  water,  the  reduction  in  volume  on  cooling  is  equal  to 
about  four  per  cent.  {Mitscherlich.)  This  cannot  be  regarded  as  the  mere 
result  of  adhesion  or  any  mechanical  force,  but  rather  of  chemical  union, 
although  the  properties  of  the  mixture  have  undergone  no  change.  If  the 
alcohol  be  poured  carefully  on  the  water  in  a  long  tube,  and  a  piece  of  white 
wax  dropped  through  the  spirit,  to  indicate,  by  floating,  the  exact  level  of 
the  water,  many  months  may  elapse  without  the  position  of  the  wax  under- 
going a  change,  and  therefore  without  combination  of  the  two  liquids.  This 
depends  on  the  smallness  of  the  area  of  contact,  and  the  great  difference  in 
the  specific  gravity  of  the  two  liquids.  Water  will  dissolve  or  combine  with 
alcohol  in  all  proportions,  but  with  ether  there  is  a  fixed  limit :  of  this  liquid 
it  cannot  hold  dissolved  more  than  ten  per  cent,  by  volume.  When  water  is 
added  to  a  mixture  of  ether  and  alcohol,  the  alcohol  is  entirely  dissolved, 
but  the  surplus  ether  is  separated,  and  floats  on  the  top  of  the  liquid.  Chlo- 
roform is  soluble  in  alcohol,  but  only  to  a  limited  extent  in  water  ;  hence, 
for  the  same  reason,  water  separates  it  from  alcohol. 

Some  substances  appear  to  be  held  in  water  by  a  kind  of  suspension  resem- 
bling solution.  Thus  starch  forms  an  opaque  liquid ;  gelatin,  gelose,  and 
certain  silicates  as  well  as  silicic  acid  itself,  are  similarly  suspended  without 
having  formed  a  perfect  combination  with  the  water  as  a  solvent.  They 
appear  to  constitute  hydrates  of  the  respective  substances  with  a  large  sur- 
plus of  water.  For  all  practical  purposes  in  chemistry  they  are  regarded 
and  treated  as  solutions,  although  the  substances  may  be  ultimately  deposited 
in  an  insoluble  form.     When  a  chemical  change  takes^place  on  the  mixture 


AMALGAMS.      PROOFS    OF    CHEMICAL    CHANGE, 


of  a  liquid  and  solid,  as  on  the  addition  of  nitric  acid  to  copper  or  silv 
the  terra  solution  is  no  longer  appropriate ;   the  liquid  is  decomposed,  and 
new  compound  results. 

Solutions  of  metals  in  mercury  are  called  Amalgams.  Some  metals  are 
more  soluble  in  this  liquid  than  others  ;  thus  gold,  silver,  tin,  and  bismuth 
are  rapidly  dissolved,  while  iron,  and  copper  (in  its  ordinary  state),  are  not 
aflfected.  Although  treated  as  solution,  or  the  simple  adhesion  of  metal  to 
mercury,  as  of  salt  to  water,  there  is  every  reason  to  believe  that  there  is  a 
chemical  union  of  the  mercury  with  the  metal  in  definite  proportions,  and 
that  this  compound  is  dissolved  in  the  large  proportion  of  mercury  which 
forms  a  liquid  amalgam.  Tin  and  silver  combine  with  small  proportions  of 
mercury  to  form  crystalline  compounds.  If  a  large  quantity  of  mercury  is 
employed,  both  tin  and  silver  disappear  as  by  solution  ;  but  when  a  smaller 
proportion  is  used  a  soft  amalgam  is  formed,  which  gradually  becomes  hard 
by  crystallization.  The  force  which  holds  the  tin  to  the  mercury  cannot  be 
considered  the  same  as  that  which  holds  the  amalgam  of  tin  and  mercury  to 
a  surface  of  glass.  The  solution  of  metals  in  mercury  is  sometimes  attended 
with  the  production  of  heat  and  cold,  as  well  as  with  a  change  of  state.  If 
equal  parts  of  sodium  and  potassium  are  well  mixed  by  pressure  under  naph- 
tha, and  a  globule  of  mercury  is  poured  on  the  soft  alloy,  there  is  instant 
chemical  union  with  an  evolution  of  heat  and  flame,  and  the  production  of  a 
solid  amalgam.  Melt  together  20Y  parts  of  lead,  118  of  tin,  and  284  of  bis- 
muth. These  form,  when  cold,  a  brittle  alloy.  When  this  is  reduced  to  a 
fine  powder,  and  mixed  with  161 T  parts  of  mercury,  at  a  temperature  of  60°, 
the  thermometer  falls  to  \4P.  This  is  owing  to  the  rapid  conversion  of  the 
solid  metals  to  the  liquid  state,  and  the  absorption  of  heat  from  surrounding 
bodies.  It  resembles,  in  effect,  the  solution  of  crystallized  nitrate  of  ammo- 
nia in  water.  Mercury,  under  certain  conditions,  appears  to  combine  with 
the  gases  hydrogen  and  nitrogen  in  th^  proportions  of  one  equivalent  of 
nitrogen  to  four  of  hydrogen,  producing  the  amalgam  of  ammonium.  It 
then  becomes  semi-solid,  and  assumes  a  crystalline  condition,  like  that  which 
it  acquires  in  combining  with  a  large  quantity  of  tin  or  silver.  The  union  is 
only  of  a  temporary  nature,  and  appears  to  be  physical  rather  than  chemical. 

Most  solids  and  liquids  manifest  a  tendency  to  enter  into  union  or  combi- 
nation. There  is,  however,  one  substance  which  shows  a  remarkable  indif- 
ference to  conbination  of  any  kind,  and  from  this  indifference  it  has  received 
the  name  of  parafiine  {purum  affinis). 

Proofs  of  Chemical  Change. — We  generally  look  for  certain  visible  results 
as  evidence  of  the  chemical  union  or  separation  of  substances ;  but  the 
chemical  force  may  have  acted  without  causing  visible  changes ;  and  on  the 
other  hand  the  condition  of  allotropy  (see  page  31)  in  elements  and  com- 
pounds, shows  us  that  such  changes  may  take  place  without  reference  to  the 
chemical  force.  Photographic  chemistry  furnishes  a  remarkable  instance  of 
the  operation  of  chemical  affinity,  without  any  apparent  physical  alteration 
in  the  condition  of  the  compound.  A  dried  fihn  of  pure  iodide  of  silver  on 
glass,  after  it  has  received  an  impression  from  light,  will  retain  its  surface 
unaltered  for  many  hours,  or  even  days  ;  we  should  not  be  able  to  distinguish 
the  exposed  from  the  unexposed  film  ;  but  if  the  exposed  stirface  is  washed 
with  a  weak  solution  of  pyrogallic  acid  or  sulphate  of  iron,  the  silver  is 
reduced  and  blackened  only  in  the  parts  which  have  received  the  luminous 
impression,  and  in  a  degree  precisely  proportioned  to  the  intensity  with 
which  the  impression  has  been  made.  There  is  perhaps  nothing  so  wonder- 
ful in  the  whole  range  of  chemistry  as  the  fact  of  thus  revealing  a  dormant 
image  which  has  been  produced  without  any  apparent  physical  change  in  the 
iodide  of  silver  by  the  chemical  rays  of  the  spectrum.    As  a  general  rule,  we 


m 


52  SINGLE    AFFINITY. 

cannot  trust  our  senses  as  furnishing  evidence  of  the  chemical  force  being 
brought  into  operation.  We  can  only  arrive  at  a  knowledge  of  this  fact  by 
a  process  well  known  under  the  name  of  analysis  (ava  -kv^,  to  separate),  by 
which  we  separate  the  component  parts  of  a  body.  This  may  be  either 
qualitative,  to  determine  the  nature,  or  quantitative,  to  determine  the  pro- 
portions, of  the  ingredients.  Our  analytical  results  may  be  confirmed  by 
synthesis  {ovv  tcOtjixi,  to  put  together),  ^.  e. ,  by  reconstructing  the  substance 
from  its  constituent  parts.  The  latter  process  is  not  always  available,  and  it 
is  not  indispensable  to  a  correct  view  of  the  constitution  of  a  body.  It  is 
suflBcient  if  we  examine  the  products  of  chemical  combination,  and  compare 
their  weights  and  chemical  properties  with  those  of  their  constituents.  The 
following  experiments  will  serve  as  an  illustration  of  the  processes  of  analysis 
and  synthesis,  as  applied  to  elements  and  compounds.  We  may  analyze  or 
separate  the  constituents  of  hydrochloric  acid — namely,  chlorine  and  hydrogen, 
by  adding  zinc  to  one  portion  of  the  acid,  and  peroxide  of  lead  to  another 
portion.  The  zinc  liberates  the  hydrogen,  and  the  peroxide  of  lead  sets  free 
the  chlorine.  If  we  now  place  a  vessel  containing  chlorine  over  a  jet  of 
hydrogen  burning  from  a  bottle,  hydrochloric  acid  will  be  immediately 
reproduced  by  synthesis  and  by  the  direct  union  of  its  elements.  Among 
compounds  which  readily  admit  of  analysis  and  synthesis,  is  the  chloride 
of  ammonium. 

Place  in  two  Florence  flasks  some  of  the  powdefed  chloride.  Mix  the 
chloride  of  one  flask  with  its  bulk  of  dry  lime,  and  apply  a  spirit-lamp  to  the 
mixture.  Ammonia,  as  a  gas,  will  escape.  Now  add  to  the  chloride  in  the 
other  flask  suflBcient  sulphuric  acid  to  moisten  the  powder.  Fumes  of  hydro- 
chloric acid  immediately  escape.  On  bringing  near  to  each  other  the  mouths 
of  the  flasks,  the  gases  immediately  combine  to  reproduce,  by  synthesis  in 
the  air  the  chloride  of  ammonium  which  had  undergone  analysis,  or  been 
resolved  into  its  constituents  in  the  two  flasks. 

Single  Affinity. — The  chemical  force  is  usually  studied  under  the  heads  of 
single  and  double  aflBnity ;  and  all  analytical  processes  are  dependent  upon  a 
knowledge  of  the  laws  which  govern  these  operations.  In  single  affinity — 
of  three  substances  present,  one  is  found  to  combine  with  another  in  prefer- 
ence to  a  third.  Let  us  assume  that  the  three  substances  are  the  base 
baryta  in  solution  and  two  acids — ^.  e.,  the  sulphuric  and  nitric  acids  diluted 
with  water.  On  adding  the  solution  of  baryta  to  diluted  nitric  acid,  there  is 
no  visible  change  ;  the  base  enters  into  a  soluble  combination  with  the  acid, 
forming  nitrate  of  baryta.  When  the  baryta  is  added  to  sulphuric  acid,  a 
white  insoluble  precipitate  appears  (sulphate  of  baryta).  Both  the  acids 
therefore  combine  with  the  base,  the  one  to  form  a  soluble,  and  the  other  an 
insoluble  salt.  If  we  now  wish  to  discover  which  of  the  acids  has  the 
stronger  affinity  for  the  base,  we  add  sulphuric  acid  to  the  solution  of  nitrate 
of  baryta,  and  an  insoluble  sulphate  of  baryta  immediately  appears — the 
nitric  acid  being  set  free.  If  we  treat  the  precipitated  sulphate  of  baryta 
with  nitric  acid,  it  will  undergo  no  change.  A  minute  quantity  of  the  pre- 
cipitate may  be  dissolved,  but  the  sulphuric  acid  still  remains,  combined  with 
the  baryta.  The  only  conclusion  to  be  drawm  from  these  facts,  is,  that 
sulphuric  acid  hlis  a  stronger  affinity  for  baryta  than  nitric  acid,  and  that  it 
will  take  that  base  to  the  entire  exclusion  and  separation  of  the  nitric  acid. 
As  a  kind  of  choice  is  thus  manifested,  this  has  also  received  the  name  of 
elective  affinity.  The  change  is  represented  by  the  following  equation, 
BaO,^iO,+S03=BaO,S03  +  N05. 

'\^\\ii  i^vva  precipitate  has  here  been  employed  to  indicate  chemical  change, 
and  it  is  desirable  to  define  the  proper  meaning  of  a  term  which  so  frequently 
occurs  in  chemical  language.     It  is  applied  by  chemists  to  signify  that  con- 


ORDER    OF    DECOMPOSITION.  53 

dition  in  which  a  substance  dissolved  in  a  liquid,  is  thrown  down  in  a  solid 
form  as  the  result  of  chemical  change  or  decomposition.  If  the  substance  is 
not  dissolved,  but  diffused  mechanically  through  the  water,  its  falling  to  the 
bottom  is  not  true  precipitation  but  subsidence,  or  the  mere  effect  of  its 
greater  specific  gravity. 

Precipitation  always  implies  that  the  compound  formed  is  less  soluble  in 
the  liquid  than  the  substance  which  produces  it.  Sulphuric  acid  added  to 
lime-water  produces  no  precipitate,  because  sulphate  of  lime  is  more  soluble 
than  lime.  If  carbonic  acid  is  employed,  there  is  an  immediate  precipitate, 
the  carbonate  of  lime  being  much  less  soluble  than  lime.  Precipitation  may 
occur  rapidly  or  slowly,  according  to  the  solubility  of  the  precipitate.  It 
may  take  place  as  the  result  of  natural  causes :  thus  in  petrifying  springs, 
which  owe  their  properties  to  carbonate  of  lime,  dissolved  by  carbonic  acid 
in  the  water,  a  precipitate  of  carbonate  of  lime  takes  place  in  the  form  of 
stalactite,  owing  to  the  escape  of  carbonic  acid.  The  Geyser  water  in  Iceland 
deposits  silicic  acid,  and  all  chalybeate  waters  produce,  on  exposure  to  air, 
ochreous  deposits  of  hydrated  peroxide  of  iron,  under  similar  circumstances. 
The  quantity  of  water  present  influences  the  production  of  a  precipitate.  A 
diluted  solution  of  a  salt  of  lime  is  not  precipitated  by  sulphuric  acid,  while 
an  equally  diluted  solution  of  a  salt  of  baryta  is  precipitated,  the  difference 
depending  on  the  relativeinsolubility  of  the  respective  sulphates.  The  great 
insolubility  of  precipitated  chloride  of  silver  renders  it  easy  to  detect  the 
minutest  traces  either  of  hydrochloric  acid  or  silver.  According  to  Mitscher- 
lich,  one  part  of  hydrochloric  acid  diffused  through  113  million  parts  of 
water  is  rendered  visible,  as  a  white  cloud  or  precipitate,  by  the  addition  of 
a  salt  of  silver. 

The  order  of  affinity  of  sulphuric  acid  for  bases,  may  be   Sulphuric  Acid. 
thus  easily  determined  by  experiment ;  and  upon  this  prin-         ~ 
ciple,  tables  of  affinity  have  been  constructed,  in  which  the    gfj-^t^'a. 
substance  whose  affinities  are  to  be  represented  is  placed  at    potassa.* 
the  head  of  a  column,  and  the  bodies  with  which  it  combines    Soda. 
beneath  it,  in  the  order  of  their  respective  attractions  ;  thus    Lime, 
the  affinity  of  sulphuric  acid  for  several  bases  is  shown  in  the    ^lagnesia. 
table.     From  this  it  would  appear  that  baryta  separates  sul-    Oxidfeof^'ilver 
phuric  acid  from  its  compounds  with  all  the  substances  below 
it,  and  that  ammonia  is  separated  by  all  those  which  are  above  it.     It  will 
be  found,  however,  by  experiment,  that  if  a  solution  of  ammonia  is  added  to 
a  solution  of  sulphate  of  magnesia,  there  is  a  precipitate  of  magnesia.    If,  on 
the  other  hand,  magnesia  is  boiled  in  a  solution  of  sulphate  of  ammonia,  the 
magnesia  combines  with  the  sulphuric  acid,  and  ammonia  is  evolved  as  a  gas. 
Hence  the  table  rather  shows  the  order  of  decomposition  under  one  set  of 
circumstances.     The  relative  affinity  of  the  acid  for  magnesia  or  ammonia 
will  depend  on  the  temperature  of  the  mixture.     If  we  take  the  base  soda, 
and  examine  the  affinity  manifested  by  it  to  the  three  acids — namely,  the 
boracic,  sulphuric,  and  hydrochloric — we  find  that  this  resolves  itself  also 
into  a  question  of  temperature. 

Soda  at  60°.  Soda  at  a  Red  Heat. 

Sulphuric.  Boracic. 

Hydrochloric.  Sulphuric. 

Boracic.  Hydrochloric. 

The  result  depends  on  the  relative  fixedness  and  solubility  of  the  acid  at 
the  temperature  to  which  the  mixture  is  exposed.  If  sulphuric  or  hydro- 
chloric acid  is  boiled  with  borate  of  soda — on  cooling  the  liquid,  the  boracic 


w 


54 


REVERSAL    OF    AFFINITY. 


acid  is  precipitated  by  reason  of  its  insolubility  in  water  at  a  low  tempera- 
ture ;  and  sulphate  of  soda  or  chloride  of  sodium  remains  dissolved.  If, 
however,  the  precipitated  acid  be  mixed  with  the  solid  sulphate,  or  chloride 
obtained  by  evaporation,  and  the  mixture  is  submitted  to  a  full  red  heat, 
borate  of  soda  is  reformed,  and  the  more  volatile  sulphuric  and  hydrochloric 
acids  are  entirely  expelled.  The  fixedness  of  boracic  acid  at  a  hl^h  temper- 
ature here  causes  a  reversal  of  the  order  of  combination. 

These  tables  are  of  great  use  in  analysis,  inasmuch  as  the  exceptional  cases 
are  not  numerous,  and  are  easily  remembered.  They  may  be  made  applicable 
to  elements  as  well  as  compounds.  We  here  give  tables  representing  the 
order  of  affinity  of  lime  in  solution  at  60°  for  four  common  acids  :  also  for 
some  of  the  combinations  of  hydrogen  with  non-metallic  bodies,  and  of 
oxygen  and  chlorine  for  various  metals  : — 


Lime. 

Hydrogex. 

Oxygen. 

,        Chlorine. 

Oxalic. 

Chlorine. 

Hydrogen. 

Magnesium. 

Sulphuric. 

Bromine. 

Magnesium. 

Zinc. 

Acetic. 

Iodine. 

Zinc. 

Lead. 

Carbonic. 

Sulphur. 

Lead. 

Tin. 

Tin. 

Hydrogen. 

Copper. 

Copper. 

Mercury. 

Mercury. 

Silver. 

Silver. 

The  results  thus  arrived  at  are  often  susceptible  of  important  practical 
applications.  The  liquid  in  which  a  salt  is  dissolved  may  cause  a  reversal 
of  the  order  of  affinity.  Thus,  if  to  a  strong  solution  of  carbonate  of  potassa 
in  water,  we  add  acetic  acid,  carbonic  acid  is  expelled,  and  acetate  of  potassa 
is  formed  and  dissolved  (KO,C03+Ac=KO,Ac4-C02  in  water).  If,  how- 
ever, we  pass  a  current  of  carbonic  acid  gas  for  some  time  into  a  saturated 
solution  of  acetate  of  potassa  in  alcohol,  the  gaseous  displaces  the  liquid  acid, 
and  carbonate  of  potassa  is  reproduced  (KO,Ac  +  C03=KO,C0^4-Ac  in 
alcohol).  The  insolubility  of  the  alkaline  carbonate  in  alcohol,  and  its  im- 
mediate removal  by  precipitation,  appear  to  explain  this  change  in  the  order 
of  affinity.  If  water  is  added  to  the  alcoholic  liquid,  the  precipitated  car- 
bonate is  redissolved. 

Oxide  of  lead  combines  readily  with  carbonic  and  acetic  acids,  forming  a 
carbonate  and  an  acetate  of  lead.  If  acetic  acid  is  added  to  carbonate  of 
lead,  the  carbonic  acid  is  displaced,  and  acetate  of  lead  is  formed ;  but  if  a 
solution  of  acetate  of  lead  is  exposed  to  an  atmosphere  containing  carbonic 
acid,  carbonate  of  lead  is  formed  and  the  acetic  acid  is  expelled.  The  manu- 
facture of  white  lead  (carbonate  of  lead)  depends  upon  this  reversal  of  affinity. 
The  metal  is  exposed  to  the  fumes  of  acetic  acid,  and  the  formation  of  an 
acetate  is  the  first  step  in  the  production  of  a  carbonate. 

This  fact  appears  to  support  the  view  of  those  who  believe  that  chemical 
affinity  between  substances  is  to  some  extent  governed  by  the  relative  pro- 
portion or  mass  of  the  displacing  agent.  The  changes  which  chloride  of 
silver  undergoes  b^  exposure  to  light,  also  tend  to  corroborate  this  opinion. 
When  not  absolutely  dry,  chloride  of  silver,  which  is  of  snow-white  appear- 
ance, is  darkened  by  exposure  to  light.  In  fact  it  is  superficially  converted 
into  subchlorlde  (2AgCi=Ag^Cl  +  Cl).  The  quantity  of  chlorine  thus  set 
free  is  small.  Rose  found,  by  using  a  delicate  balance,  that  there  was  no 
difference  in  weight  between  the  white  and  dark  chloride.  Chlorine  water 
added  to  the  dark  chloride  renders  it  again  white. 

Decomposition  by  single  affinity  may  take  place,  although  it  is  not  mani- 
fested by  the  precipitation  of  a  solid  or  the  visible  escape  of  gaseous  matter. 


PREDISPOSING    AFFINITY.       DOUBLE    AFFINITY.  55 

If  we  boil  gold-leaf  with  some  crystals  of  nitre  dissolved  in  water,  there  is 
no  change;  if  we  boil  the  gold  in  pure  hydrochloric  acid,  there  is  no  change  ; 
but  if  the  two  are  mixed,  the  gold  is  immediately  dissolved.  The  solution  of 
the  gold  proves  that  chlorine  has  been  evolved.  This  could  only  proceed 
from  the  decomposition  of  a  part  of  the  hydrochloric  acid  by  the  nitrate  of 
potash.  Under  ordinary  circumstances  a  watery  solution  of  nitre  may  be 
mixed  with  hydrochloric  acid  without  any  perceptible  decomposition  of  either 
body. 

An  interposed  animal  membrane  does  not  prevent  the  manifestation  of  this 
force.  If  a  tube  containing  a  weak  acid  solution  of  acetate  of  lead  is  well 
secured  at  the  mouth  with  a  piece  of  bladder,  and  the  outer  surface  of  the 
bladder  is  then  placed  downwards  on  a  clean  surface  of  metallic  zinc — in 
the  course  of  a  short  time  crystals  of  lead  will  be  deposited  on  the  bladder 
inside  the  tube  ;  and  the  solution  will  contain  acetate  of  zinc,  a  fact  which 
proves  that  the  zinc  has  traversed  the  bladder  either  as  oxide  or  metal,  and 
has  displaced  an  equivalent  proportion  of  lead  in  the  solution.  This  is 
effected  by  capillary  osmosis  of  a  part  of  the  solution  of  acetate  of  lead,  and 
its  simultaneous  conversion  into  acetate  of  zinc. 

Predisposing  or  Concurrent  Affinity. — If  zinc  is  covered  with  hydrochloric 
acid  it  displaces  the  hydrogen,  which  escapes,  and  chloride  of  zinc  is  formed; 
if  covered  with  water,  this  liquid  is  not  decomposed  until  an  acid  (sulphuric) 
is  added,  when  hydrogen  immediately  escapes,  and  an  oxysalt  of  zinc  is  pro- 
duced and  dissolved.  This  has  been  called  predisposing  affinity,  but  it  should 
rather  be  regarded  as  concurrent  affinity.  Two  affinities  are  here  brought 
into  play  :  there  is  the  affinity  of  zinc  for  oxygen,  and  of  the  acid  for  oxide 
of  zinc,  and  these  are  sufficient  to  decompose  the  water.  This  principle  is 
the  basis  of  many  chemical  operations.  In  the  manufacture  of  aluminum, 
carbon  as  charcoal  cannot  alone  remove  the  oxygen  from  alumina  (the  oxide 
of  aluminum) ;  but  if  chlorine  is  passed  over  a  mixture  of  alumina  and  char- 
coal heated  to  a  high  temperature,  the  carbon  readily  takes  the  oxygen,  and 
the  chlorine  now  combines  with  the  aluminum.  Platinum  cannot  be  made 
to  unite  to  oxygen  directly ;  but,  if  caustic  potash  is  fused  on  the  metal,  this 
is  oxidized  and  destroyed  by  reason  of  the  tendency  of  the  alkali  to  combine 
with  oxide  of  platinum.  Iron  does  not  rust  in  air  free  from  moisture,  ^.  e., 
it  will  not  take  the  oxygen  from  dry  air.  Again  it  will  not  combine,  with 
the  oxygen  of  water  at  common  temperatures,  except  when  air  is  present. 
In  order  that  oxidation  may  take  place,  it  is  necessary  that  air  and  water 
should  be  present  at  the  same  time.  It  is  a  well-known  fact  that  gold  is  not 
acted  upon,  or  dissolved  by  sulphuric  acid  or  nitric  aeid,  even  at  a  boiling 
temperature.  But  if  a  drop  of  nitric  acid  is  added  to  the  mixture  of  sul- 
phuric acid  with  gold-leaf  while  boiling,  the  metal  instantly  disappears 
and  enters  into  some  unknown  form  of  combination  with  the  sulphuric  acid. 
When  the  acid  solution  is  cooled  and  added  to  water  the  gold  is  thrown 
down  as  a  purple  precipitate  in  the  metallic  state. 

Double  Affinity. — In  double  affinity  there  is  a  reciprocal  interchange  of 
elements,  or,  in  reference  to  salts,  of  acids  and  bases,  so  that  two  new  com- 
pounds are  produced.  One  of  the  simplest  cases  is  seen  on  the  admixture 
of  hydrochloric  acid  and  a  solution  of  soda.  Chloride  of  sodium  and  water 
result  (XaO  +  HCl  =  XaCl-f-IIO).  Among  numerous  instances  which  may 
be  taken  from  the  class  of  salts,  there  is  the  reaction  of  sulphate  of  potash 
on  nitrate  of  baryta,  by  which  sulphate  of  baryta  and  nitrate  of  potash  are 
produced  (KO,S03  +  BaO,N05==BaO,S03-|-KO,NO.,).  In  this  case  one  in- 
soluble salt  only  is  formed -and  precipitated;  but  two  soluble  salts  may  be 
changed  into  two  perfectly  insoluble  compounds,  as  in  adding  a  solution  of 
sulphate  of  silver  to  chloride  of  barium  (both  soluble)  when  sulphate  of 


56  DOUBLE    AFFINITY.      DECOMPOSITION. 

baryta  and  chloride  of  silver  (both  insoluble)  result.  Thus  AgOjSOg  +  Ba 
Cl=BaO,SO.j4-AgCl.  This  decomposition  forms  one  of  the  steps  in  the 
production  of  pure  peroxide  of  hydrogen.  Double  affinity  generally  furnishes 
to  the  chemist  a  more  perfect  method  of  decomposition  than  single  affinity. 
Thus  oxalate  of  ammonia  more  effectually  precipitates  lime  than  oxalic  acid. 
A  solution  of  arsenious  acid  does  not  readily  decompose  solutions  of  sul- 
phate of  copper  or  nitrate  of  silver;  but  if  the  acid  is  combined  with  a  small 
quantity  of  alkali  (ammonia),  the  precipitation  of  insoluble  arsenites  of  the 
metals  by  double  affinity  is  immediate  and  complete. 

In  general  it  may  be  inferred  that  two  salts  will  decompose  each  other, 
when,  by  interchange,  an  insoluble  compound  or  precipitate  can  result. 
Solubility,  however,  is  a  purely  relative  term,  and  precipitation  must  there- 
fore often  depend  on  the  quantity  of  water  present  in  the  saline  solutions. 
Nitrate  of  baryta  gives  a  dense  white  precipitate  with  a  solution  of  borate 
of  soda,  provided  the  two  solutions  are  concentrated.  If  much  water  is 
present,  there  Vill  be  no  precipitation  on  mixture  ;  a  fact  also  proved  by  the 
re-dissolution  of  the  precipitate  on  adding  a  quantity  of  water.  Sulphate 
of  soda  will  precipitate  a  salt  of  lime,  and  chloride  of  platinum  a  salt  of 
potassa,  provided  the  respective  solutions  are  concentrated ;  but  if  much 
diluted,  there  will  be  no  precipitate.  The  platino-chloride  of  potassium, 
although  precipitated  from  potassa  or  its  salts,  by  a  solution  of  chloride  of 
platinum,  is  sufficiently  soluble  in  boiling  water  to  precipitate  from  their 
solutions  the  salts  of  rubidium  and  caesium,  the  platino-chlorides  of  which 
metals  are  far  less  soluble  than  the  corresponding  salt  of  potassium.  Tliis, 
in  fact,  is  the  only  available  method  of  separating  the  salts  of  the  two  new 
metals  from  the  salts  of  potassium.  While  the  degree  of  dilution  always 
affects  the  production  of  a  precipitate,  it  sometimes  so  completely  changes 
its  character  that  it  might  be  fairly  inferred  that  two  different  compounds 
were  under  examination.  Thus  if  nitrate  of  silver  is  added  to  a  concentrated 
solution  of  borate  of  soda,  a  white  borate  of  silver  is  precipitated  :  if  the 
solution  of  borate  is  much  diluted,  nitrate  of  silver  gives  a  brown  precipitate 
resembling  oxide  of  silver.  Sulphocyanide  of  potassium  produces,  in  a  con- 
centrated solution  of  a  salt  of  copper,  a  black  precipitate  of  sulphocyanide, 
which  slowly  becomes  gray  and  white  ;  in  a  moderately  diluted  solution  a 
gray  precipitate  is  thrown  down,  and  in  a  very  diluted  solution  a  white  pre- 
cipitate of  sub-sulphocyanide  is  slowly  formed. 

Precipitates  are  sometimes  readily  dissolved  by  the  precipitant :  thus  the 
scarlet  iodide  of  mercury  is  easily  dissolved  by  a  solution  of  iodide  of  potas- 
sium. This  renders  it  necessary  to  employ  tests  with  caution,  or  the  pre- 
sence of  a  substance  may  be  overlooked.  When  the  double  decomposition 
of  two  salts  does  not  take  place  in  the  cold,  it  may  be  brought  about  by 
heating  the  mixture. 

Double  affinity  is  liable  to  be  modified  by  all  the  causes  which  affect  single 
affinity.  If  a  mixture  of  dry  chloride  of  sodium  and  sulphate  of  ammonia 
is  heated,  chloride  of  ammonium  is  sublimed,  and  sulphate  of  soda  remains. 
This  is  one  method  of  manufacturing  sal  ammoniac  from  the  ammoniacal 
liquor  of  gas-works.  When  the  two  salts  are  intimately  mixed  with  a  small 
quantity  of  water,  the  temperature  rises  and  the  mass  rapidly  dries.  There 
is  a  double  decomposition,  and  the  sulphate  of  soda  produced  absorbs  water 
of  crystallization.  Each  of  the  salts  alone  lowers  the  temperature  during 
the  act  of  solution.  {Chem.  Neivs,  Sept.  5,  1860.)  But  when  powdered  sul- 
phate of  soda  is  well  mixed  with  chloride  of  ammonium  at  60°,  there  is  a 
reversal  of  the  affinities — anhydrous  sulphate  of  ammonia  and  common  salt 
are  produced,  while  the  water  of  crystallization  of  the  soda-sulphate  is  set 
free,  the  mass  acquiring  a  liquid  consistency.     (See  page  34.)     When  solu- 


PROOFS    OP    INTERCHANGE    OF    ACIDS    AND    BASES.  57 

tions  of  these  two  salts  are  mixed,  there  is,  aocordinp:  to  SchifiF,  an  increase 
of  volume  owing  to  the  setting  free  of  water  of  crystallization. 

Salts  having  the  same  acid  or  base  do  not  precipitate  each  other.  Thus  a 
solution  of  sulphate  of  lime  does  not  decompose  sulphate  of  soda  or  chloride 
of  calcium.  On  this  principle,  the  last-mentioned  salt  is  employed  to  deter- 
mine whether  the  alkalinity  of  river-water  depends  on  the  presence  of  the 
carbonate  of  potassa  or  soda,  or  of  the  bicarbonate  of  lime.  In  the  former 
case,  it  gives  a  precipitate  ;  in  the  latter  none. 

But  double  affinity  may  be  exerted  between  two  salts  in  cases  in  which 
there  is  no  visible  change  or  decomposition.  AYhen  a  solution  of  nitrate  of 
soda  is  mixed  with  chloride  of  potassium,  and  this  mixture  is  boiled,  chloride 
of  sodium,  or  common  salt,  is  separated,  because  it  is  the  least  soluble  of  the 
salts  at  a  boiling  temperature,  and  therefore  requires  the  largest  amount  of 
water  to  hold  it  in  solution.  (See  page  30.)  If  the  saturated  sc^lutions  of 
the  two  salts  are  kept  at  a  low  temperature,  nitrate  of  potassa  crystallizes 
out  of  the  liquid.  In  either  case  there  is  an  interchange  of  acid  and  base 
dependent  on  the  relative  solubility  of  the  salts  at  a  given  temperature 
(NaCNOj-f  KCl=NaCl-f  KO,NO/).  The  process  above  mentioned  has 
been  employed  in  Prussia  for  the  manufacture  of  nitre.  The  manufacture  of 
sulphate  of  magaesia  from  sea-water  is  dependent  on  a  similar  decomposition. 
Sulphate  of  soda  added  to  a  solution  of  chloride  of  magnesium  or  bittern, 
produces  no  visible  change  ;  but  when  boiled,  the  compounds  are  resolved 
into  chloride  of  sodium  and  sulphate  of  magnesia.  The  former  is  separated  by 
evaporation  of  the  liquid  at  the  boiling-point,  the  latter  by  allowing  the  cold 
saturated  solution  to  deposit  crystals  (NaO,S03-fMgCl=NaCl  +  MgO,S03). 

The  production  of  a  color  on  the  admixture  of  colorless  solutions  of  salts 
is  evidence  of  at  least  a  partial  interchange  of  acids  and  bases.  A  very 
diluted  solution  of  ferrocyanide  of  potassium  added  to  extremely  diluted 
solutions  of  sulphate  of  copper  and  persulphate  of  iron,  produces  in  the  one 
case  a  red,  and  in  the  other  a  blue  color  in  the  liquid.  These  results  furnish 
chemical  proofs  that  the  ferrocyanogen  of  the  potassium-salt  has,  at  least  in 
part,  united  to  the  metals  of  the  copper  and  iron  salts.  Sulphocyanide  of 
potassium  may  be  substituted  for  the  ferrocyanide  in  reference  to  iron  ;  and 
in  this  case  a  blood-red  color,  but  no  precipitate,  results.  Berzelius  long 
since  devised  an  ingenious  experiment  by  which  the  interchange  of  acid  and 
base  in  two  salts  was  clearly  proved  by  the  peculiar  color  acquired  on  mixture. 
Of  the  diluted  solutions  of  the  salts  of  copper,  the  nitrate  and  sulphate  remain 
blue  when  boiled ;  but  the  diluted  chloride,  which  is  blue  at  60°,  acquires  a 
bright  green  color  at  212°.  This  change  of  color  is  therefore  a  distinguishing 
test  among  these  salts,  of  the  presence  of  chloride  of  copper  in  a  diluted 
state.  A  solution  of  chloride  of  sodium  is  colorless  and  remains  so  at  all 
temperatures.  When  a  diluted  solution  of  nitrate  of  copper  is  added  to  a 
diluted  solution  of  chloride  of  sodium  and  the  mixture  is  heated,  it  acquires 
a  bright  green  color,  thus  proving  that  some  portion  at  least  of  the  nitrate 
of  copper  must  have  been  converted  into  chloride  of  copper,  and  therefore 
that  an  interchange  of  acids  and  bases  must  have  taken  place.  If  the  two 
solutions  are  highly  concentrated,  the  interchange  takes  place  at  60°,  since 
the  mixture  in  the  cold  has  a  greenish  color — the  color  of  the  chloride  of 
copper  when  in  a  more  concentrated  form. 

We  have  hitherto  treated  the  saline  compounds  as  if  both  were  soluble  in 
water ;  but  cases  of  double  aflBnity  are  witnessed,  in  which  one  salt  is  soluble 
and  the  other  is  insoluble.  If  insoluble  sulphate  of  baryta  or  oxalate  of 
lime  is  boiled  in  distilled  water  with  soluble  carbonate  of  potassa  for  a  short 
time,  and  the  respective  liquids  are  filtered — it  will  be  found  that  a  partial 
interchange  of  acids  and  bases  has  taken  place,  and  while  the  filtrates  (the 


58  CATALYSIS. 

filtered  liquids)  will  contain  two  soluble  salts  (the  carbonate  of  potassa 
associated  either  with  the  sulphate  or  oxalate  of  potassa),  the  white  residues 
on  the  filters  will  contain,  besides  sulphate  of  baryta  and  oxalate  of  lime, 
the  insoluble  carbonates  of  baryta  and  lime.  Four  salts  are  in  each  case 
produced,  as  represented  in  the  following  equation,  in  which  the  decomposi- 
tion is  given  only  for  the  sulphate  of  baryta,  2(BaO,SOJ  +  2(KO,C02)  = 
KO,S03-}-KO,C03andBaO,S034-BaO,CO.,.    This  mode  of  decomposition  is 

^  > '  * '-y  ' 

Soluble.  Insoluble. 

sometimes  resorted  to,  in  order  to  render  an  insoluble  compound  sufficiently 
soluble  for  the  purpose  of  testing.  The  silicification  of  chalk  or  soft  lime- 
stone is  based  on  this  principle.  The  mineral  is  soaked  in  water-glass,  or  a 
solution  of  silicate  of  potash  or  soda,  and  it  is  afterwards  exposed  to  the  air; 
silicate  of  lime  and  bicarbonate  of  potassa  or  soda  result.  The  surface  of  the 
chalk  is  thus  hardened  and  rendered  impermeable  to  water.  It  is  probable 
that  the  presence  of  Epsom  salt,  or  sulphate  of  magnesia,  in  spring  waters 
in  certain  districts,  is  dependent  on  a  natural  reaction  of  this  kind.  Water 
containing  sulphate  of  lime  flowing  over  a  bed  of  magnesian  rock  (carbonate 
of  magnesia)  becomes  impregnated  with  sulphate  of  magnesia,  a  portion  of 
the  lime  being  exchanged  for  this  base.  If  carbonate  of  magnesia  is  agitated 
with  a  solution  of  sulphate  of  lime,  sulphate  of  magnesia  will  soon  be  found 
in  the  filtered  liquid,  by  appropriate  tests. 

Double  affinity  is  not  prevented  by  the  interposition  of  animal  membrane. 
If  the  mouth  of  a  tube  containing  sulphate  of  soda  is  well  secured  with 
bladder,  and  inverted  in  a  vessel  containing  a  solution  of  nitrate  of  baryta — 
or  if  the  nitrate  of  baryta  be  secured  in  a  tube,  and  the  soda-sulphate  is 
placed  in  an  open  vessel,  double  decomposition  is  observed  to  take  place. 
In  performing  this  experiment  many  times,  however,  we  have  noticed  that 
the  white  precipitate  of  sulphate  of  baryta  has  been  formed  in  the  tube 
containing  the  nitrate,  and  not  in  that  containing  the  sulphate  of  soda. 

Catalysis  (from  xara  downwards,  and  -kvc^  to  loosen)  is  a  term  which  was 
first  employed  by  Berzelius,  to  explain  those  cases  in  which  two  or  more 
bodies  are  combined  by  the  presence  of  a  substance  which  itself  takes  no 
share  in  the  chemical  changes.  A  body  is  thus  supposed  to  resolve  others 
into  new  compounds  merely  by  contact,  without  gaining  or  losing  anything 
itself.  When  a  mixture  of  oxygen  and  hydrogen  is  exposed  to  the  action  of 
spongy  platinum,  the  gases  combine  to  form  water;  when  alcohol  is  dropped 
on  platinum-black  under  exposure  to  air,  the  alcohol  is  oxidized  and  con- 
verted into  acetic  acid  ;  when  a  ball  of  spongy  platinum,  made  red  hot,  is 
placed  on  a  mass  of  camphor,  it  continues  to  glow,  and  causes  a  slow 
combustion  of  the  camphor ;  when  a  ball  of  platinum  is  made  white  hot  and 
plunged  into  water,  it  causes  the  separation  of  the  constituent  gases  oxygen 
and  hydrogen  ;  and  lastly,  when  fine  platinum  wire  is  heated  red  hot,  and 
exposed  to  a  mixture  of  coal-gas  and  air,  it  continues  to  glow,  and  leads  to 
a  slow  combustion  of  the  gas.  In  these  cases  the  platinum  has  produced 
combination  as  well  as  decomposition,  but  it  has  undergone  no  change.  We 
have  witnessed  a  similar  effect  with  charcoal  placed  in  a  mixture  of  oxygen 
and  sulphuretted  hydrogen.  The  gases  were  combined  with  explosion,  but 
the  charcoal  underwent  no  change.  The  power  of  charcoal  to  absorb  and 
remove  foul  effluvia,  by  leading  to  their  oxidation,  may  be  regarded  as  a 
similar  phenomenon  ;  but  all  these  are  simple  cases  of  the  absorption  and 
condensation  of  gases  by  the  platinum  and  charcoal,  and  not  referable  to 
any  new  force  or  to  any  occult  effect  of  contact  or  presence. 

Sulphur,  it  has  been  already  stated  (p.  47),  will  unite  at  a  high  tempera- 
ture to  India-rubber,  and  will  then  produce  in  it  the  effects  indicated  by  the 


ELECTROLYSIS.  59 

term  vulcanization — i.  e.,  change  of  color,  infnsibility,  great  increase  of 
elasticity,  and  a  resistance  to  heat  and  cold.  The  vulcanized  rubber  when 
boiled  in  a  solution  of  sulphite  of  potash  is  desulphured  ;  it  reacquires  its 
usual  appearance,  but  it  still  retains  the  properties  which  the  sulphur 
imparted  to  it.  This  has  been  ascribed  to  a  catalytic  action,  for  the  sulphur 
itself  has  undergone  no  change. 

The  production  of  anhydrous  chloride  of  magnesium,  according  to  Mits- 
cherlich,  turns  upon  a  similar  state  of  circumstances.  If  hydrochloric  acid 
is  saturated  with  hydrate  of  magnesia,  and  the  liquid  is  concentrated  and 
cooled,  large  crystals  of  chloride  of  magnesium  combined  with  water  are 
obtained.  If  these  crystals  are  heated,  like  those  of  other  chlorides,  in  order 
to  expel  the  water,  the  hydrochloric  acid  escapes  and  magnesia  remains.  If, 
however,  equal  weights  of  hydrochloric  acid  are  saturated  with  magnesia  and 
ammonia,  and  the  two  solutions  are  mixed  and  evaporated  to  dryness,  the 
residue,  when  heated  to  fusion  in  a  platinum  crucible,  consists  entirely  of 
anhydrous  chloride  of  magnesium  ;  the  whole  of  the  chloride  of  ammonium 
having  been  expelled.  Here  chloride  of  ammonium  causes  a  fixed  combina- 
tion of  the  elements,  apparently  by  a  catalytic  force. 

Catalytic  results  are  obtained  with  compounds  as  well  as  with  simple 
substances.  The  production  of  oxygen  at  a  low  temperature,  from  a  mixture 
of  peroxide  of  manganese,  or  of  iron  with  chlorate  of  potash,  has  been 
referred  to  an  action  by  catalysis  or  presence.  The  facts,  however,  admit  of 
another  explanation.  {See  Ozone.)  The  decomposition  of  peroxide  of 
hydrogen  by  contact  with  a  variety  of  metals  and  oxides,  was  generally 
explained  by  reference  to  catalysis,  until  the  recent  views  of  Schonbeia  had 
been  made  public. 

There  are  many  changes  in  organic  compounds  which  have  been  referred 
to  catalysis — e.  g.,  the  conversion  of  gum  and  starch  to  sugar,  of  alcohol  to 
ether  by  sulphuric  acid,  and  of  sugar  to  alcohol  by  a  ferment ;  but  there  are 
here  numerous  reactions  depending  on  a  variety  of  causes;  and  as  science 
progresses,  and  these  reactions  become  better  understood,  the  use  of  this 
term  may  be  rendered  necessary. 

Electrolysis. — (iJiaxT-pov,  t-vw,  to  loosen  by  electricity.) — This  term  is 
applied  to  the  electro-chemical  decomposition  of  substances  as  a  result  of 
the  electric  current.  The  electric  fluid  serves  to  unite  as  well  as  to  disunite 
bodies ;  and  in  producing  their  disunion  or  separation  there  is  this  remarka- 
ble difference  from  the  chemical  force — namely,  that  as  current  electricity 
it  transports  and  collects  at  particular  points,  called  poles,  the  elements  or 
compounds  which  are  separated. 

When  the  electrodes  or  poles  of  a  voltaic  battery  are  brought  near  to  each 
other  in  certain  liquids,  such,  for  instance,  as  acidulated  water  and  saline 
solutions  ;  or,  in  other  words,  when  these  liquids  are  made  part  of  the  elec- 
tric circuit,  so  that  the  current  of  electricity  can  pass  through  them,  decom- 
position ensues  ;  that  is,  certain  elements  are  evolved  in  obedience  to  certain 
laws.  Thus  water,  under  these  circumstances,  yields  oxygen  and  hydrogen  ; 
and  the  neutral  salts  yield  acids  and  alkalies.  In  these  cases,  the  ultimate  and 
proximate  elements  appear  at  the  electrodes  or  poles — not  indiscriminately, 
or  indifferently  ;  but  oxygen  and  acids  are  evolved  at  the  anode,  or  surface  at 
which  the  electricity  enters  the  electrolyte  ;  and  hydrogen,  and  alkaline  bases, 
at  the  cathode,  or  surface  at  which  the  electric  current  leaves  the  body  under 
decomposition. 

All  compounds  susceptible  of  direct  decomposition  by  the  electric  current 
are  called  electrolytes ;  and  when  electro-chemically  decomposed,  they  are  said 
to  he  electrolyzed.  Those  elements  of  the  electrolyte  which  are  evolved  at 
the  anode  are  termed  anions,  and  those  which  are  evolved  at  the  cathode, 


60 


ELECTROLYSIS. 


cations  {avlov,  that  which  goes  upwards  ;  xa-tlov,  that  which  goes  downwards), 
and  when  these  are  spoken  of  together,  they  are  called  'ions :  thus  when  acidu- 
lated water  is  electrolyzed,  two  'ions  are  evolved,  oxygen  and  hydrogen,  the 
former  being  an  anion,  the  latter  a  cation. 

In  all  /?n/wary  electro-chemical  decompositions,  the  elements  of  compounds 
are  evolved  with  uniform  phenomena  either  at  the  anode  or  cathode  of  the 
electrolyte ;  hence  their  division  into  electro-negative  and  electro-positive 
bodies,  or,  into  anions  and  cations.  The  latter  have  more  recently  received 
the  name  of  hasylous  bodies,  as  by  combining  with  oxygen  they  form  a  large 
class  of  bases.  But  it  frequently  happens  that  the  evolution  of  a  substance 
at  the  electrode  is  a  secondary  effect;  sulphur,  for  instance,  in  the  decom- 
position of  sulphuric  acid,  is  evolved  at  the  cathode  or  negative  pole,  not  by 
direct  electrolysis,  but  in  consequence  of  the  action  of  the  nascent  hydrogen  ; 
and  whenever  sulphur  is  obtained  by  primary  electrolytic  action  from  a  com- 
pound containing  it,  it  is  evolved  at  the  anode,  or  positive  pole  ;  hence,  in 
classifying  the  elements  according  to  their  electrical  relations,  this  distinc- 
tion must  be  observed.  It  is  also  necessary  to  guard  against  the  combina- 
tion of  the  substance  (or  Ion),  with  the  electrode  ;  hence  the  advantage  of 
platinum  electrodes,  that  metal  being  acted  upon  by  very  few  of  them. 

The  following  table  of  simple  and  compou7id  ions  has  been  drawn  up  by 
Faraday ; — 


ELECTRO-NEGATIVE  BODIES  OR  ANIONS. 


Oxygen 

Cyanogen 

Phosphoric  acid 

Citric  acid 

Chlorine 

Sulphuric  acid 

Carbonic  acid 

Oxalic  acid 

Iodine 

Selenic  acid 

Boracic  acid 

Sulphur 

Bromine 

Nitric  acid 

Acetic  acid 

Selenium 

Fluorine 

Chloric  acid 

Tartaric  acid 

Sulphocyanogen. 

ELECTRO-POSITIVE  BODIES  OR  CATIONS. 

Hydrogen 

Tin 

Mercury 

Strontia 

Potassium 

Lead 

Silver 

Lime 

Sodium 

Iron 

Platinum 

Magnesia 

Lithium 

Copper 

Gold 

Alumina 

Barium 

Cadmium 

Protoxides  generally 

Strontium 

Cerium 

Ammonia 

Quinia 

Calcium 

Cobalt 

Potassa 

Cinchonia 

Magnesium 

Nickel 

Soda 

Morphia 

Manganese 

Antimony 

Lithia 

■  Alkaloids  generally. 

Zinc 

Bismuth 

Baryta 

Compounds  only  undergo  electrolysis  :  and  in  order  to  act  as  electrolytes, 
the  compound,  if  a  solid,  must  be  in  a  state  of  solution  or  fusion.  Electro- 
lysis is  always  definite  in  amount.  Thus  the  quantity  of  electricity  produced 
during  the  solution  of  32  grains  of  zinc,  is  equivalent  to  the  decomposition 
of  9  grains  of  water.  Electrolytes  differ  in  the  facility  with  which  they  yield 
up  their  elements  to  the  influence  of  the  electric  current,  or  in  the  resistance 
which  they  offer  to  electro-chemical  decomposition.  The  following  bodies 
are  electrolytic  in  the  order  in  which  they  are  placed,  those  which  are  first, 
being  decomposed  by  the  current  of  lowest  intensity  : — 

Iodide  of  potassium  (solution)  Chloride  of  zinc  (fused) 

Chloride  of  sodium  (solution)  Chloride  of  lead  (fused) 

Sulphate  of  soda  (solution)  Iodide  of  lead  (fused) 

Chloride  of  silver  (fused)  Hydrochloric  acid  (solution) 

Water  acidulated  by  sulphuric  acid. 

The  intensity  of  the  current  is  in  proportion,  1,  to  the  difference  in 
oxidizing  power  (by  the  action  of  the  oxygen  and  the  acid)  on  the  two 


PRISMATIC    OR    SPECTRUM    ANALYSIS.  61 

metals  employed ;  2,  to  the  increase  of  surface  of  the  metals ;  and  3,  the 
increase  of  acid  on  the  intensity  of  chemical  action.  The  first  condition  is 
remarkably  illustrated  by  platinum  and  magnesium.  If  a  coil  of  platinum 
is  placed  round  a  band  of  magnesium  and  this  is  immersed  in  distilled  water, 
an  electric  current  is  slowly  set  up,  and  hydrogen  is  slowly  evolved  with- 
out the  addition  of  an  acid.  If  a  few  drops  of  any  acid  are  added,  there 
is  a  rapid  evolution  of  hydrogen  partly  as  the  result  of  chemical,  and  partly 
of  the  electrical  force. 

As  a  result  of  the  chemical  force,  we  may  deposit  copper  on  iron  or  zinc, 
by  immersing  either  of  these  metals  in  a  solution  of  a  salt  of  copper  ;  but  if 
for  iron  and  zinc  we  substitute  silver  and  platinum,  no  deposit  will  take 
place,  these  metals  having  less  affinity  for  oxygen  and  acids  than  copper. 
If,  however,  we  wrap  a  coil  of  zinc  round  the  bar  of  silver  or  platinum,  and 
then  immerse  it  into  a  solution  of  copper;  the  metal  copper  will  now  be 
deposited  on  the  silver  and  platinum  as  a  result  of  the  electric  current  set 
up  between  the  two  metals.  In  this  case  both  the  chemical  and  electrical 
forces  operate  to  cause  a  separation  and  deposition  of  metallic  copper.  By 
electrolysis  any  metal  may  be  thus  deposited  on  any  other  metal,  or  on  any 
organic  substance,  such  as  a  feather  or  insect,  provided  it  can  receive  a 
metalline  or  conducting  surface. 

Prisinatic  or  Spectrum  Analysis. — Chemists  have  for  many  years  relied 
opon  the  colors  given  by  the  salts  of  various  metals,  to  the  colorless  flames 
of  alcohol,  or  coal  gas,  as  a  useful  aid  to  qualitative  analysis.  MM.  Kirchoff 
and  Busen,  by  their  researches  on  the  colored  flames  of  metals,  have  arrived  at 
an  entirely  new  method,  which  has  enlarged  greatly  the  scope  of  chemical 
reactions,  and  has  led  to  some  important  discoveries.  This  method  consists 
in  not  merely  relying  as,  hitherto,  upon  the  color  imparted  to  a  flame,  but  in 
decomposing  the  colored  light  by  a  prism ;  in  other  words,  in  submitting 
the  colored  flame  to  a  minute  prismatic  analysis.  Their  observations  have 
been  chiefly  directed  to  the  detection  of  the  metals  of  the  alkalies  and 
alkaline  earths.  They  have  employed  pure  salts  of  these  metals,  as  well  as 
various  mixtures  of  them,  and  they  have  found  that  the  more  volatile  the 
metallic  compound  on  which  they  operated,  the  brighter  was  the  spectrum 
which  they  obtained.  A  high  temperature  was  generally  required:  a 
coal-gas  flame  of  a  Bunsen's  burner,  of  which  the  heat  was  estimated  at 
2350^  C,  was  found  to  be  sufiBcientfor  the  alkaline  metals,  and  the  colorless 
nature  of  this  flame  rendered  it  otherwise  well  adapted  for  the  spectralytic 
observations.  The  alkaline  salt  in  minute  quantity  was  placed  on  the  end 
of  a  fine  platinum  wire  (bent  into  a  hook  and  flattened,  if  for  a  solution), 
and  this  was  introduced  into  the  lower  part  of  the  colorless  coal-gas  flame. 
The  light  of  the  colored  flame  was  then  make  to  traverse  a  prism  of  sulphide 
of  carbon,  having  a  refracting  angle  of  60°;  and  as  it  issued  from  the  prism 
it  was  examined  by  a  small  telescope. 

The  reader  will  find  a  description  of  this  apparatus,  and  of  the  method  of 
employing  it,  in  the  Philosophical  Magazine  for  August,  1860,  page  91,  and 
the  PharmaceuiicalJournal,  February,  1862;  but  it  has  since  been  superseded 
by  more  convenient  instruments.  The  colored  flame  of  each  metal,  even  in 
the  minutest  quantities,  was  found  to  give  a  well-marked  and  characteristic 
spectrum.  Compared  with  the  spectrum  of  solar  light,  the  actual  amount 
of  colored  light  was  very  small,  and  this  was  distributed  without  any  kind 
of  order,  in  a  series  of  bands  or  stripes  of  different  widths  and  intensities, 
the  bands  of  color  taking  up  the  situation  of  the  corresponding  spectral 
colors.  Sodium  was  observed  to  give  a  single  or  a  double  line  of  yellow 
light  only,,  in  a  position  corresponding  to  the  orange  rays  of  the  solar 
spectrum.     Potassium,  besides  a  more  diffused  spectrum,  gave  a  red  line  ia 


I 


C2  DETECTION    OF    ALKALINE    METALS. 

the  extreme  red  rays,  and  a  violet  line  in  the  extreme  violet  rajs.  Lithium 
gave  a  dark  spectrum,  with  only  two  bright  lines,  one  a  pale  yellow 
corresponding  to  the  red  rays.  Strontium,  barium,  and  calcium,  the  only 
three  alkaline  earthy  metals  which  give  spectra  (magnesium  not  being 
volatile  in  this  flame),  are  remarkable  for  the  number  and  variety  of  the 
colored  bands  which  they  present.  Strontium  presents  eight  characteristic 
lines — six  red  in  the  part  corresponding  to  the  red  rays,  one  broad  orange 
band  parallel  to  the  orange  rays,  and  at  some  distance  from  these  a  blue 
line,  in  the  situation  of  the  blue  rays.  The  spectra  of  barium  and  calcium 
are  distinguished  from  the  others  by  the  number  of  green  bands  which  they 
present,  ^wo  of  these  in  the  situation  of  the  green  rays  characterize  barium. 
There  are,  besides  these,  three  other  green  bands,  and  several  yellow,  orange, 
and  red  lines.  Calcium  presents  one  broad  green  band  in  the  situation  of 
the  yellow-green  rays;  and  a  bright  orange  band  near  the  red  rays,  besides 
several  smaller  orange  lines.  The  new  alkaline  metal  Ccesium  {ccBsius, 
sky-color),  discovered  by  Bunsen  in  the  waters  of  Durckheim  and  Baden,  as 
well  as  in  most  spring-waters  containing  chloride  of  sodium,  presents  two 
distinct  grayish-blue  lines  in  the  parallel  of  the  blue  rays,  and  no  other 
colored  bands  or  lines.  The  other  new  metal,  Rubidium,  found  by  Bunsen 
in  the  waters  of  Hallein  and  Gastein,  derives  its  name  from  the  two  splendid 
red  lines  in  its  spectrum ;  these  are  of  a  low  degree  of  refrangibility. 
Thallium  gives  the  most  simple  spectrum  known :  it  consists  of  one  bright 
green  band  in  the  situation  of  the  green  rays  of  the  solar  spectra.  The 
optical  characters  of  the  spectra  are  constant  for  each  metal,  and  are  equally 
well  marked  in  size  and  position  under  all  varieties  of  flame,  even  of  that 
given  by  the  electric  discharge. 

Bunsen  estimated  that  the  amount  of  sodium  which  admitted  of  detection 
by  prismatic  analysis  was  the  195,000,000th  part  of  a  grain;  of  lithium,  the 
10,000, 000th;  of  potassium  the  60,000th;  of  barium  the  same;  of  strontium 
the  1,000,000th;  and  of  calcium  the  100,000,000th  of  a  grain  I 

The  delicacy  of  the  sodium  reaction  accounts  for  the  fact  that  all  bodies, 
after  a  lengthened  exposure  to  atmospheric  air,  show  when  heated,  the  sodium 
line.  Even  ignited  air  and  all  kinds  of  dust  show  the  yellow  tinge  of  sodium. 
Fine  platinum  wire  or  foil,  however  clean,  if  exposed  to  air  for  a  short  time, 
has  been  observed  to  give  a  yellow  color  to  flame,  owing,  as  it  is  supposed, 
to  the  deposit  upon  its  surface  of  sodium  derived  from  the  atmosphere. 
Three-fourths  of  the  earth's  surface  are  covered  with  sea-water,  and  the 
niinutely  diffused  chloride  of  sodium  may,  it  is  supposed,  be  thus  spread 
through  the  whole  of  the  atmosphere.  Lithium,  which  was  supposed  to  be 
a  rare  metal,  also  appears  by  this  mode  of  analysis  to  be  very  widely 
distributed.  Bunsen  found  it  in  about  an  ounce  and  a  half  of  the  waters  of 
the  Atlantic  Ocean;  in  the  ashes  of  kelp  from  Scotland ;  the  ashes  of  tobacco, 
of  vine-leaves,  and  of  plants  growing  on  various  soils.  It  was  found  in  the 
milk  of  animals  fed  fronj  these  crops,  and  it  was  detected  by  Dr.  Folsvarczny 
in  the  ash  of  human  blood  and  muscular  tissue.  It  has  also  been  discovered 
in  the  residue  of  Thames-water,  in  Stourbridge  clay,  and  in  meteoric  stones. 
It  is  a  curious  fact  that  the  intermixture  of  these  alkaline  metallic  compounds 
does  not  materially  interfere  with  the  optical  as  it  does  with  the  common 
steps  of  a  chemical  analysis.  Thus  a  drop  of  sea-water  shows  at  first  a 
sodium-spectrum;  after  the  volatilization  of  the  chloride  of  sodium — a 
calcium-spectrum  appears,  which  is  made  more  distinct  by  moistening  the 
platinum  wire  with  hydrochloric  acid.  By  treating  the  evaporated  residue 
of  sea-water  with  sulphuric  acid  and  alcohol,  potassium  and  lithium-spectra 
are  obtained.  The  strontium  reaction  is  best  procured  by  digesting  the 
boiler-crust  of  sea-going  steamers  in   hydrochloric   acid,  and   employing  • 


DETECTION    OF    ALKALINE    METALS.  63 

alcohol  as  a  solvent.  By  this  process  of  analysis,  most  mineral  waters  are 
found  to  contain  all  the  alkalies  and  alkaline  earths  excepting  the  compounds 
of  barium. 

The  different  degrees  of  volatility  in  the  alkaline  metals  are  favorable  to 
their  detection  in  a  state  of  mixture.  Thus  a  solution  containing  less  than 
the  600th  of  a  grain  of  each  of  the  following  chlorides — potassium,  sodium, 
lithium,  calcium,  strontium,  and  barium — was  brought  into  the  flame.  At 
first  the  bright  sodium  line  appeared,  and  when  this  began  to  fade  the 
bright-red  line  of  lithium  was  seen,  while  at  some  distance  from  the  sodium 
line  the  faint  red  line  of  potassium  came  into  view,  and  with  this  two  of  the 
green  barium  lines;  the  spectra  of  the  potassium,  sodium,  lithium,  and  barium 
salts  gradually  faded  away,  and  then  the  orange  and  green  calcium  lines 
showed  themselves  in  their  usual  positions.  {Phil.  Mag.^  Aug.  1860,  p.  106.) 
The  presence  of  organic  matter  in  large  quantity  does  not  interfere  with  the 
production  of  simple  spectra.  Thus  it  has  been  found  that  a  portion  of  the 
dried  liver  of  an  animal,  to  which  a  salt  of  thallium  had  been  given,  yielded, 
when  burnt,  a  spectrum,  in  which  the  peculiar  green  line  of  this  metal  was 
visible.  Among  other  novel  applications  of  this  branch  of  analysis,  may  be 
mentioned  the  proposal  to  employ  it  in  the  manufacture  of  cast-steel.  In 
the  new  process  of  melting  the  metal,  it  is  important  to  know  the  exact^^ 
moment  at  which  to  shut  down  the  cover  of  the  furnace ;  time  must  be  w  # 
allowed  for  the  escape  of  the  gaseous  products  which  are  injurious  to  the 
steel,  but  if  that  time  be  prolonged,  an  injurious  effect  of  another  kind  is  ^ 
produced.  To  meet  this  contingency  it  has  been  proposed  to  test  the  gases 
as  they  fly  off,  by  means  of  the  spectroscope;  and  as  soon  as  the  particular 
color  is  observed,  peculiar  to  the  gas,  which  begins  to  escape  at  the  moment 
the  molten  metal  is  in  proper  condition,  the  manufacturer  will  then  have  an 
infallible  sign  of  the  proper  moment  for  closing  the  furnace. 

It  has  been  successfully  employed  for  the  detection  of  the  coloring  matter 
of  blood.  Every  red  color,  mineral  or  organic,  which  is  soluble  in  water, 
has  its  peculiar  spectrum  with  special  bands  of  absorption. 

An  improvement  has  been  recently  made  in  the  prismatic  apparatus  by 
which  the  spectra  of  two  flames  may  be  examined  at  once.  Thus  any  doubt 
respecting  the  presence  of  the  substance  from  the  colored  bands  in  one 
spectrum,  may  be  removed  by  introducing  a  portion  of  the  suspected  sub- 
stance into  the  second  flame,  so  that  the  two  spectra  may  be  seen  side  by 
side,  and  compared.  In  employing  this  method  of  analysis,  it  is  often 
necessary  to  compare  the  solar  spectrum  with  the  spectrum  of  the  substance 
under  examination.  A  spectroscopic  eye-piece  has  been  invented  by  Mr. 
Sorby,  which  may  be  adapted  to  any  good  microscope.  By  this  invention, 
any  two  spectra  may  be  at  once  examined  and  compared.  This  enables  the 
observer  to  determine  with  accuracy  the  bands  of  absorption  and  their  exact 
position,  compared  with  the  colors  of  the  solar  spectrum. 

It  has  been  observed  that  gases  ignited  by  the  electric  spark  from 
Ruhmkorff's  coil  give  spectra  of  a  remarkable  kind.  Thus  hydrogen  through 
which  the  electric  discharge  is  passed,  gives  a  spectrum  having  an  intensely 
red  line  like  that  of  lithium,  and  a  bright  band  of  green,  which  can  be  split 
up  into  a  j^umber  of  thin  and  beautiful  green  rays  (Roscoe).  Spectra  of 
nitrogen,  chlorine,  and  other  gases  rendered  incandescent,  have  been  obtained 
by  various  observers,  and  it  is  not  improbable  that  gases  generally  and  their 
complex  mixtures  may  be  hereafter  qualitatively  determined  by  this  method, 
like  the  compounds  of  alkaline  metals. 

The  platinum  poles  of  a  battery,  simply  ignited,  give  a  violet  blue  platinum 
spectrum  ;  and  if  a  salt  of  copper,  iron,  chromium,  nickel,  or  other  metal, 
be  placed  upon  them,  a  spectrum  peculiar  to  each  metal  is  brought  out,  but 


i 


i 


64  ATOMIC    OR    COMBINING    WEIGHTS. 

instead  of  a  few  lines  of  color,  as  in  alkaline  metals,  they  occur  in  many 
hundreds.  Dr.  Roscoe  describes  seventy  brilliant  lines  in  the  iron  spectrum, 
of  all  degrees  of  intensity  and  breadth.  The  most  prominent  of  these  lines 
may,  however,  be  selected  for  identity.  Kirchoff  states  that  he  has  thus 
been  able  to  distinguish  the  compounds  of  the  rare  metals — yttrium,  erbium, 
terbium,  lanthanum,  didymium,  and  cerium.  The  spectra  obtained  from  a 
mixture  of  the  common  metals,  are  not  so  distinct  as  those  of  the  alkaline 
series.  Thus  in  German  silver,  the  spectrum  may  show  only  one  of  the 
constituents  (Roscoe).  The  spectra  of  the  common  metals  require  a  much 
higher  temperature  {i.  e.,  the  electric  spark  of  Ruhmkorff's  apparatus)  for 
their  production,  and  they  are  then  liable  to  be  mixed  with  the  spectra  of 
the  platinum  poles,  as  well  as  those  of  the  metalloids,  which  constitute  the 
acids  or  radicals  of  their  salts. 

As  these  discoveries  are  at  present  in  their  infancy,  it  is  difficult  to  specu- 
late upon  the  practical  results  to  which  they  may  ultimately  lead.  In 
reference  to  the  qualitative  analysis  of  the  alkaline  salts,  they  will  enable  a 
chemist  not  only  to  detect  the  respective  metals,  with  great  rapidity,  in 
quantities  inconceivably  minute ;  but  they  may  also  enable  him  to  detect 
these  quantities  in  mixtures  with  each  other,  with  a  certainty  which  no  other 
known  analytical  process  can  furnish.  On  further  research  they  may  serve 
to. identify,  with  nearly  equal  certainty,  the  salts  of  other  metals,  either  alone 
or  in  a  state  of  admixture.  Quantitative  analysis,  by  the  usual  processes, 
must,  however,  be  still  resorted  to,  in  order  to  determine  the  proportion  of 
ingredients  by  weight  in  a  compound;  and  as  it  is  impossible  to  weigh  a 
smaller  quantity  than  the  1000th  part  of  a  grain,  chemists  may  in  future  be 
compelled  to  assign  to  a  compound  many  substances  which  do  not  admit  of 
a  determination  by  weight.  The  extreme  delicacy  of  this  photo-chemical 
method  is  likely  to  create  the  greatest  difficulty  in  its  practical  application. 
When  a  mineral-water  like  that  of  Baden  is  thereby  shown  to  contain  all  the 
metals  of  the  alkalies  and  alkaline  earths,  excepting  barium,  besides  two 
new  metals,  one  of  them  (the  more  abundant)  existing  only  in  the  proportion 
of  one  part  in  a  hundred  million  parts  of  the  water,  the  question  will  really 
be,  whether  there  can  be  any  assigned  limits  to  the  number  of  substances 
which  may  be  discovered  by  such  a  mode  of  analysis. 


CHAPTER    IV. 

EQUIVALENT    WEIGHTS    AND    VOL UME S— NOM ENC L ATURE 
AND   NOTATION. 

Determination  of  Equivalent  Weights. — It  has  been  already  described  as  a 
special  character  of  a  true  chemical  compound,  that  its  constituents  combine 
in  fixed  proportions,  which  are  represented  by  figures,  an'd  are  called  equiva- 
lent or  atomic  weights.  For  the  determination  of  these  weights,  a  series  of 
careful  analyses  of  the  substance  are  made.  To  take  water  as  an  example, 
there  is  no  compound  in  chemistry  of  which  the  constitution  has  been  so 
accurately  determined,  both  analytically  and  synthetically,  as  of  this.  In 
100  parts  by  weight,  it  is  found  to  contain  11.09  of  hydrogen,  and  88.91  of 
oxygen.  These  proportions  reduced  to  their  smallest  denomination  would 
be  represented  by  the  figures  1  and  8  ;  or  if,  instead  of  making  hydrogen 


CALCULATION    OF    EQUIVALENT    WEIGHTS.  65 

unity,  we  assumed  that  oxygen  combined  as  1,  then  hydrogen  would  be 
represented  by  the  decimal  0125.  As,  however,  this  last  assumption  would 
lead  to  a  very  inconvenient  use  of  decimals,  the  standard  of  unity  is  assigned, 
by  most  chemists,  to  hydrogen :  and  the  selection  of  hydrogen  has  this  great 
advantage,  that  being  the  lightest  body  in  nature,  and  combining  relatively 
in  the  smallest  weight,  the  figures  representing  the  equivalents  of  the  other 
bodies  are  comparatively  low  and  are  easily  remembered.  The  numbers  1 
and  8  therefore  respectively  represent  the  atomic  weights  of  hydrogen  and 
oxygen,  on  the  assumption  that  one  atom  of  each  element  is  contained  in 
the  compound,  the  atom  of  hydrogen  being  equal  to  a  whole  volume,  and 
that  of  oxygen  being  considered  to  represent  half  a  volume  of  this  element. 
The  weight  of  the  atom  of  water  is,  therefore,  on  this  assumption,  9,  the  sum 
of  the  weights  of  its  two  constituents. 

All  bodies  combine  either  with  hydrogen  or  with  oxygen,  and  the  atomic 
weight  of  any  body  may  be  therefore  found  by  analyzing  its  compound  with 
either  of  these  elements,  and  determining  by  the  rule  of  proportion  how  much 
by  weight  enters  into  combination  with  1  part  of  hydrogen  or  with  8  parts 
of  oxygen.  The  atomic  weight  of  sulphur  may  be  thus  determined.  100 
parts  of  its  compound  with  hydrogen  {Sulphide  of  Hydrogen)  are  composed 
of  941  of  sulphur  and  5  9  of  hydrogen  :  hence  941  ^5  9=15*9,  or,  allow- 
ing for  differences  of  analysis,  16,  the  atomic  weight  of  sulphur.  Again, 
hydrochloric  acid  consists  in  100  parts  of  9t'26  chlorine  and  274  hydrogen  : 
hence  97*26-7-2-t4  =  35'49,  or,  in  round  numbers,  36,  the  atomic  weight  of 
chlorine. 

It  will  be  understood  that  these  figures  do  not  represent  the  absolute,  but 
merely  the  proportional  weights  in  which  bodies  combine.  We  have  no 
knowledge  of  the  absolute  weight  of  an  atom  of  any  substance,  and  we  are 
unable  to  say  whether  the  combining  weights  thus  determined,  include  one 
or  more  atoms  of  any  element ;  but  it  is  convenient  to  assume  that  the 
figures  represent  the  relative  weights  of  atoms  ;  and  that  however  the  figures 
may  vary,  there  is  only  one  atom  of  each  element  in  the  figures  which  repre- 
sent its  combining  weight.  We  have  thus  arrived  at  two  of  the  laws  of 
chemical  combination. 

1.  The  equivalent  or  atomic  weight  of  a  body  represents  the  smallest 
quantity  by  weight  in  which  it  will  combine  witU  one  part  by  weight  of 
hydrogen  or  eight  parts  by  weight  of  oxygen. 

2.  The  equivalent  weight  of  a  compound  is  the  sura  of  the  equivalents  of 
its  constituents. 

There  is  a  third  law  which  flows  from  the  preceding  : — 

3.  If  a  simple  or  compound  body  combines  with  more  than  one  propor- 
tion of  the  same  substance,  the  other  proportions  are  multiples,  or  sub- 
multiples,  of  the  first. 

Guided  by  these  rules,  it  is  possible  to  determine  the  atomic  weight  of  a 
substance  (fluorine),  which  has  never  yet  been  isolated.  The  compound  of 
this  body  with  calcium  is  a  well-known  mineral.  Assuming  that  we  take  a 
weighed  quantity  of  fluoride  of  calcium,  we  convert  it  into  sulphate  of  lime 
by  heating  it  with  sulphuric  acid.  The  weight  of  the  sulphate  of  lime  being 
known,  the  weight  of  the  calcium  in  the  lime  is  easily  determined ;  and  by 
deducting  the  weight  of  calcium  from  the  original  weight  of  fluoride  employed 
in  the  analysis,  the  exact  amount  of  combined  fluorine  is  known.  The  atomic 
weight  of  this  unknown  element  is  thus  found  to  be  19. 

These  laws  of  combination  are  of  great  aid  to  the  analyst.     If  he  can 

determine  the  weight  of  one  constituent  of  a  compound,  the  weight  of  the 

other  may  be  accurately  determined  by  calculation.     If,  for  instance,  in 

reference  to  sulphate  of  lime — should  the  weight  of  sulphuric  acid  be  deter- 

5 


66  CALCULATION    OF    EQUIVALENT    WEIGHTS. 

mined,  then  as  40  parts  of  sulphuric  acid  unite  to  28  of  lime  to  form  this 
salt ;  the  amount  of  lime  associated  with  the  acid  may  be  readily  known  by 
a  simple  calculation  ;  or,  conversely,  if  the  weight  of  lime  is  determined,  the 
amount  of  sulphuric  acid  which  must  have  been  combined  with  it  may  be 
easily  calculated. 

It  was  at  first  supposed  that  the  equivalents  of  all  simple  substances  would 
be  found  to  be  integers  or  multiples  of  hydrogen,  taken  as  unity  ;  but  experi- 
ence, based  on  accurate  analysis  made  by  Dumas,  shows  that  this  rule  admits 
of  application  only  to  those  elements  enumerated  in  the  subjoined  list,  and 
even  the  accuracy  of  the  results  on  which  this  list  is  based  has  been  recently 
called  in  question  : — 

Hydrogen  1. 

Oxygen  8.  Sulphur  16. 

Carbon  6.  Phosphorus  32. 

Nitrogen  14.  Arsenic  75. 

Calcium  20. 

To  this  number  some  chemists  have  added  fifteen  other  elements.  M. 
Stas,  who  has  recently  investigated  this  subject,  denies  the  existence  of  any 
multiples  of  hydrogen  among  the  equivalent  weights.  He  assigns  as  the 
equivalent  of  nitrogen  14*041,  and  of  sulphur  16'03T1.  These  differences 
are  not,  however,  such  as  to  affect  materially  any  calculations  based  on  the 
elements ;  and  with  respect  to  the  equivalent  weights  of  other  substances,  it 
is  the  common  practice  among  chemists  to  represent  them  by  whole  numbers. 
The  reason  is  obvious.  No  two  chemists  agree  concerning  the  decimals. 
The  equivalent  of  chlorine  is  given  at  35-45,  35*47,  and  35*50,  by  equally 
reliable  authorities.  It  is  usually  taken  at  36.  Strontium  is  given  by 
Stromeyer  at  43*67,  by  Dumas  at  43*74,  by  Rose  and  de  Marignac  at  43  77, 
by  Liebig  at  43*80,  and  by  Graham  and  Pelouze  at  43*84.  It  is  usually 
taken  at  the  whole  number  44.  The  whole  numbers  are  easily  carried  in  the 
memory  ;  and  if  great  accuracy  is  required  in  any  investigation  it  is  easy  to 
substitute  for  them,  the  real  figures  of  any  selected  authority. 

Symbols. — It  will  have  been  perceived  from  frequent  examples  given  in 
the  preceding  pages,  that  a  symbolic  language  has  been  generally  adopted 
by  chemists.  Thus  the  symbols  H,  O,  S,  CI,  stand  respectively  as  abbrevia- 
tions for  hydrogen,  oxygen,  sulphur,  and  chlorine.  When  the  initials  of 
elements  are  similar,  then  the  first  and  second,  or  the  first  and  third  letters 
of  the  name  of  the  substance  are  taken  :  and  in  reference  to  the  metals  the 
corresponding  Latin  names  are  similarly  used  as  distinctive  symbols.  It  is 
important  to  bear  in  mind,  however,  that  these  symbols  not  only  represent 
the  element  but  the  relative  weight  of  it  which  enters  into  combination. 
Thus  the  letters  HO,  not  merely  represent  hydrogen  and  oxygen,  but  1  part 
of  hydrogen  and  8  parts  of  oxygen  ;  and  the  two  associated,  9  parts  of  water. 
The  number  of  atoms  of  each  element  in  a  compound  is  generally  indicated 
by  a  figure  placed  on  the  right-hand  corner.  Thus  the  symbol  HOg  indicates 
2  atoms  of  oxygen  combined  with  1  atom  of  hydrogen  (peroxide  of  hydro- 
gen), while  2H0  represents  two  atoms  of  water — the  figure  thus  placed  on 
a  line,  doubling  all  that  follow  it  up  to  the  addition  sign  +  ,  or  symbols 
included  in  brackets.  Thus  KO.SOg,  represents  sulphate  of  potassa,  but 
KO,2S03  represents  bisulphate  of  potassa.  Sometimes  in  order  to  represent 
2  atoms,  instead  of  a  figure  2  at  the  right  corner,  the  symbol  is  barred,  as 
thus, -9§-,  or  O  S.  These  are  equivalent  to  O3  and  S3.  A  collection  of  sym- 
bols constitutes  a  formula,  as  in  the  formula  for  alum,  KO,S03  4-Ala03,3S03 
-f24HO.  The  plus  sign  is  introduced  to  show  that  in  this  compound  salt, 
the  elements  are  supposed  to  be  arranged  as  sulphate  of  potash,  sulphate 
alumina,  and  water.  It  will  be  perceived  from  this  formula  that  the  atom  of 
crystallized  alum  is  compounded  of  71  atoms,  namely,  40  of  oxygen,  24  of 


SYMBOLS    AND    FORMULA. 


67 


hydrop:en,  4  of  sulphur,  2  of  the  metal  aluminum,  and  1  of  the  metal  potas- 
sium ;  and  the  equivalent  weight  of  the  compound  calculated  from  this  con- 
stitution would  be  474-6.  Formulae  when  so  arranged  as  to  represent 
chemical  decompositions,  constitute  an  equation^  a  term  borrowed  from 
algebra,  to  represent  that  the  quantities  on  the  two  sides  are  perfectly  equal 
— 4.  e.,  that  the  formulae  although  dissimilar  will  represent  an  equal  number 
of  atoms,  and  therefore,  equal  atomic  weights,  as  in  the  reaction  of  common 
salt  on  a  solution  of  nitrate  of  silver,  NaCl-fAgO,N05=AgCl-f  NaO,N05. 
The  meaning  of  the  word  equivalent  will  be  apparent  from  this  equation. 
It  denotes  a  quantity  of  one  substance  which  can  exactly  replace  or  be  sub- 
stituted for  another  in  chemical  combination.  Thus  silver  is  substituted  for 
sodium,  but  in  weights  which  are  to  each  other  respectively  as  108  to  23,  i.  e., 
these  weights  of  the  metals  are  equal  to  each  other  in  the  power  of  satu- 
rating the  same  quantity  of  chlorine,  t.  e.,  36  :  the  8  of  oxygen  combining 
with  the  sodium,  and  exactly  replacing  the  36  of  chlorine  which  have  been 
transferred  to  the  silver. 

The  following  Table  comprises  an  alphabetical  list  of  the  65  elements  now 
known  to  chemists,  with  their  respective  symbols,  and  their  atomic  or  equiva- 
lent weights,  hydrogen  being  assumed  as  unity.  In  this  Table,  the  non- 
metallic  elements  or  metalloids  are  printed  in  italics  to  distinguish  them  from 
the  metals. 

Table  of  Elementary  Substances,  with  their  Symbols  and  Equivalent  or 

Atomic  Weights. 


ELEMENTS. 

05 

1 

■It 

ELEMENTS. 

1 

•s2 

s 

CO 

-2^ 

CO 

Aluminum 

Al 

14 

Molybdenum    .... 

Mo 

48 

Antimony  (Stibium)   .     . 

Sb 

129 

Nickel 

Ni 

30 

Arsenic. 

1    As 

75 

Niobium 

Nb 

Barium 

Ba 

69 

Nitrogen  ,  ' 

N 

14 

Bismuth 

Bi 

213 

Norium 

No 

Boron 

B 

11 

Osmium 

Os 

100 

Bromine 

Br 

78 

Oxygen    

0 

8 

Cadmium 

Cd 

56 

Palladium 

Pd 

54 

Caesium 

C« 

123 

Phosphorus 

P 

32 

Calcium 

Ca 

20 

Platinum 

Pt 

99 

Carbon 

C 

6 

Potassium  (Kalium)  .     . 

K 

39 

Cerium 

Ce 

46 

Rhodium 

Ro 

52 

Chlorine 

CI 

36 

Rubidium 

Rb 

85 

Chromium 

Cr 

26 

Ruthenium 

Ru 

52 

Cobalt 

Co 

30 

Selenium 

Se 

40 

Columbium  (Tantalum)  . 

Ta 

184 

Silicon 

Si 

22 

Copper  (Cuprum)   .     .     . 

Cu 

32 

Silver  (Argentum)     .     . 

Ag 

108 

Didymium 

Di 

48 

Sodium  (Natrium)     .     . 

Na 

23 

Erbium 

Er 

? 

Strontium 

Sr 

44 

Fluorine    .     .     .     .■    ,     . 

F 

19 

Sidphur 

S 

16 

Glucinum 

G 

7 

Tellurium 

Te 

64 

Gold  (Aurum)    .... 

Au 

197 

Terbium 

Tb 

? 

Hydrogen 

H 

1 

Thallium 

Tl 

204 

Indium 

In 

74 

Thorium       ..... 

Th 

60 

Iodine 

I 

126 

Tin  (Stannum)      .     .     . 

Sn 

59 

Iridium 

Ir 

99 

Titanium 

Ti 

24 

Iron  (Ferrum)    .... 

Fe 

28 

Tungsten  (Wolfram) 

W 

92 

Lanthanum 

La 

44 

Uranium 

u 

60 

Lead  (Plumbum     .     .     . 

Pb 

104 

Vanadium 

V 

68 

Lithium 

Li 

7 

Yttrium 

Y 

32 

Magnesium 

Mr 

12 

Zinc 

Zn 

32 

Manganese 

Mn 

28 

Zirconium 

Zr 

34 

Mercury  (Hydrargyrum)  . 

Hg 

100 

68  EQUIVALENT    VOLUMES. 

The  equivalent  weights  have  been  here  placed  in  integers  for  reasons 
already  assigned.  The  figures,  it  will  be  observed,  have  no  relation  to  the 
solid,  gaseous,  or  liquid  form  of  the  elements,  or  to  their  specific  gravity  ; 
some  substances  widely  different  in  chemical  or  physical  properties  have 
similar  equivalent  weights,  while  among  others,  a  common  difference  may  be 
observed.  Thus  lithium  and  glucinum  are  each  represented  by  7  ;  aluminum 
and  nitrogen  by  14  ;  cobalt  and  nickel  by  30 ;  iron  and  manganese  by  28  ; 
and  copper,  zinc,  yttrium,  and  phosphorus  by  32.  Lithium,  sodium,  and 
potassium,  have  a  common  difference  of  16,  these  metals  being  respectively 
7,  23,  39.  The  new  alkaline  metal,  Ccesium,  by  its  high  equivalent  (123) 
disturbs  this  order.  Calcium,  strontium,  and  barium,  being  strictly  20,  43-8, 
and  68"5,  have  nearly  a  common  difference  of  24.  Other  curious  arithmetical 
relations  may  be  found  in  chlorine,  bromine,  and  iodine,  as  well  as  in  other 
groups. 

Equivalent  Volumes. — In  reference  to  elements  and  compounds  which 
exist  in  the  gaseous  state,  it  has  been  determined  by  experiment  that  the 
weights  correspond  in  general  to  very  simj)le  proportions  by  volume.  Thus 
again  taking  water  as  an  example,  it  is  found  that  the  proportion  by  volume 
in  which  hydrogen  combines  is  always  double  that  of  oxygen  ;  and  further, 
that  the  compound  formed,  calculated  as  vapor,  is  exactly  equal  to  the  bulk 
of  hydrogen  which  goes  to  constitute  it.  Assuming  hydrogen  as  unity,  by 
volume  as  well  as  by  weight,  it  follows  that  the  atomic  weight  of  hydrogen 
(1)  corresponds  to  the  atomic  volume  1  ;  and  that  the  above  weight  of  oxygen 
(8)  corresponds  to  0*5,  or  one-half  volume.  So  in  sulphuretted  hydrogen  1 
equivalent  of  hydrogen  represents  1  volume,  but  the  equivalentof  sulphur  (16) 
in  consequence  of  the  great  specific  gravity  of  the  vapor  of  this  element  at 
its  boiling  point  corresponds  to  only  l-6th  of  the  bulk  of  hydrogen,  or  l-6th 
of  a  volume.  This  is  the  greatest  deviation  from  simplicity  among  all  the 
gaseous  bodies  ;  but  its  admission  is  unavoidable,  except  at  greater  inconve- 
nience than  arises  from  retaining  it.  Thus  if,  to  avoid  fractional  parts  of 
volumes,  sulphur  were  made  unity,  ^.  e.,  if  16  parts  of  sulphur  by  weight 
were  assigned  to  1  volume  of  the  vapor,  then  the  atomic  volume  of  hydrogen 
would  be  6,  of  oxygen  3,  and  of  water  6.  Some  chemists  have  compromised 
this  difficulty  by  avoiding  the  fraction  for  oxygen,  but  still  retaining  it  for 
sulphur  ;  although  why,  if  retained  for  one,  it  should  not  be  retained  for  both, 
does  not  clearly  appear.  Thus  they  represent  1  part  by  weight  of  hydrogen 
to  correspond  to  2  volumes  of  the  gas,  and  8  parts  by  weights  of  oxygen  to 
1  volume  of  that  gas.  They  thus  adopt  hydrogen  as  unity  by  weight,  but 
oxygen  as  unity  by  volume.  Continental  writers  reject  both  of  these  arrange- 
ments ;  they  take  hydrogen  at  12-5  by  weight,  and  100  by  volume ;  oxygen 
at  100  by  weight,  and  50  by  volume. 

Water,  therefore,  stands  thus : — 

By  Weight.  By  Volume. 

Hydrogen 
Oxygen     . 

It  will  be  perceived  that  these  numbers  bear  an  exact  ratio  to  each  other. 
To  us  it  appears  desirable  not  to  depart  from  the  simplicity  of  ordinary 
chemical  language,  except  for  some  cogent  reason.  The  atomic  volume 
of  hydrogen  being  1,  the  atomic  volumes  of  oxygen,  phosphorus,  and  arse- 
nic, are  respectively  -J,  and  that  of  sulphur  ^th.  With  these  exceptions  there 
are  no  fractional  volumes  in  the  gaseous  combinations  of  simple  and  compound 
bodies. 

Atomic  Fo^wme,— The  atomic  weight  of  a  gas  or  vapor  divided  by  the 


1          12-5 

1        2        100 

or 

or       or 

8        100- 

I        1          50 

NEW    NOTATION.  '  69 

specific  gravity  (compared  with  hydrogen)  will  give  the  atomic  volume.  Thus 
the  atomic  weight  of  oxygen  is  8  :  bulk  for  bulk,  it  is  16  times  heavier  than 
•  hydrogen  and  8-r  16  =  0'5,  or  h  the  atomic  volume  of  hydrogen.  The  atomic 
weight  of  sulphur  is  16;  compared  with  hydrogen  in  the  same  volume,  its 
weight  is  96  (the  sp.  gr.  of  its  vapor  at  900°  being  6-63).  Thus  16-^-96  = 
0*1666,  or  fractionally  Jth  of  a  volume.  If  we  take  the  ordinary  specific 
gravity  in  which  air  is  made  the  standard,  the  numbers  for  the  atomic  volumes 
of  gases  are  in  the  same  proportions.  Thus  hydrogen  has  a  sp.  gr.  of 
0-0691,  and  1 -i-00691  =  l-44 ;  oxygen,  a  sp.  gr.  of  M55T,  and  8^ 
l-1057  =  7-2;  sulphur  vapor  at  900°  a  sp.  gr.  of  6-63,  and  16^6*63  = 
2*41.  These  quotients  1-44,  7 '2,  and  2'41  are  to  each  other  as  1,  J,  and 
^th  respectively,  and  they  equally  represent  the  atomic  volumes  of  these 
bodies. 

The  atomic  or  equivalent  volumes  of  all  solids  and  liquids,  whether  ele- 
mentary or  compound,  may  be  calculated  on  similar  principles — namely,  by 
dividing  their  atomic  weights  respectively,  by  their  specific  gravities  compared 
with  watei-,  the  atomic  volume  of  which  is  9-t-l  =  9.  The  sp.  gr.  of  the  metal 
lithium,  the  lightest  of  all  solids  and  liquids  is  0  59  :  its  atomic  weight  is  7, 
and  7 -r- 0*59  =  11 '8,  the  atomic  volume.  Platinum,  the  heaviest  of  all  solids, 
has  a  sp.  gr.  of  21-5,  and  its  atomic  weight  is  99,  and  99-^21 -5  =  4  6  ;  the 
atomic  volume  of  this  metal.  The  atomic  volume  of  ice,  which,  according  to 
Playfair  and  Joule,  has  a  sp.  gr.  of  0-9184,  is  found  on  a  similar  principle 
.^y\^  =  9-8.  The  relative  number  of  atoms  in  a  given  volume  of  any  sub- 
stance is  obtained  by  an  inverse  proceeding — namely,  in  dividing  the  specific 
gravity  by  the  atomic  weight. 

It  appears  probable  from  the  researches  of  Petit  and  Dulong  {Ann.  de  Ch. 
et  Phys.,  X.  p.  403),  that  the  atoms  of  all  simple  substances  have  the  same 
specific  heat,  for  by  multiplying  the  specific  heat  of  any  one  of  the  elements 
by  its  atomic  weight,  in  nearly  all  cases  the  quotient  is  the  same,  or  a  mul- 
tiple or  sub-multiple  of  the  figures.  There  are  some  remarkable  exceptions, 
however,  as  in  the  case  of  carbon  :  and  these  can  scarcely  be  explained  by 
any  want  of  accuracy,  either  in  determining  the  specific  heat  or  the  atomic 
weight  of  bodies.  Further  researches  are  required  to  show  that  there  is  that 
exact  relation  which  has  been  supposed. 

New  Notation. — A  new  system  of  notation  was  proposed  by  Gerhardt,' 
with  a  view  to  establish  a  constant  relation  between  the  atomic  weight  of 
bodies,  their  specific  gravities,  and  vapor  volumes.  In  order  to  carry  out 
these  views,  he  has  suggested  that  hydrogen  should  Ije  the  standard  or  unit 
for  the  atomic  weight,  specific  gravity,  and  combining  volume,  and  that,  in 
order  to  meet  this  view,  the  equivalents  of  certain  bodies  should  be  doubled. 
Thus :— 

Symbols.  Atomic  Weights. 

Hydrogen H 

Oxygen    ......  O 

Sulphur  ......  S 

Selenium  ,         .         .         .         .  Se 

Tellurium Te 

Carbon x,     .  C 

The  symbols  are  represented  sometimes  in  Italic  capitals,  but  more  cor- 
rectly in  the  Roman  capitals  barred,  to  show  that  they  are  double  the  usual 
weights.  The  unitary  system  creates  a  difference  in  the  meaning  of  the  terms 
atom  and  equivalent,  as  hitherto  understood.  Thus  while  8  is  the  equivalent 
weight  of  oxygen  in  combining  with  1  of  hydrogen,  16  is  assumed  to  be  the 
atomic  weight  of  that  element,  since  this  is  considered  to  be  the  lowest  pro- 


H 

1 

0 

16 

S 

32 

>               Se 

79 

i               Te 

128.4 

C 

12 

70  NEW    NOTATION. 

portion  in  which  oxygen  enters  into  combination  with  hydrogen  or  any  other 
body.  Upon  this  assumption  water  cannot  be  formed  of  less  than  two  atoms  of 
hydrogen,  and  it  is  therefore  represented  by  the  formula  H^O.  So  with  sul-* 
phur  the  equivalent  weight  is  16,  but  under  the  unitary  system  the  atomic 
weight  is  fixed  at  32 — two  atoms  of  hydrogen  being  here  required  to  form 
the  compound  hydrosulphuric  acid,  H^S.  In  reference  to  chlorine  and 
bromine,  however,  hydrogen  is  supposed  to  combine  with  these  elements  in 
the  one  atom,  and  thus  the  equivalent  and  atomic  weights  are  the  same. 
Upon  this  system  the  various  elements  have  been  divided  into  groups  accord- 
ing to  their  assumed  power  of  combining  with,  or  replacing  different  quan- 
tities of  hydrogen.  We  thus  have  what  is  called  the  atomicity  of  the  elements. 
Those  bodies  which  combine  with  or  displace  one  atom  of  hydrogen  are 
called  monatomic  elements,  or  monads:  they  include  the  group  of  halogens 
CI,  Br,  I  and  F.  In  addition  to  these  there  are  five  metals  of  the  alkaline 
group,  namely,  Li,  Na,  K,  Rb,  and  Cas,  with  Tl,  Ag,  and  hydrogen  itself.  The 
atomicity  is  usually  indicated  by  a  mark  above  the  letter,  thus,  H'.  The 
elements  which  are  assumed  to  combine  with  or  displace  two  atoms  of  hydro- 
gen are  called  Dyads.  Among  non-metals  they  include  0,  S,  Se,  and  Te,  and 
among  the  metals  they  include  those  of  the  alkaline  earths  Ba,  Sr,  Ca,  Mg, 
and  eleven  of  the  common  metals.  Their  atomicity  is  indicated  by  two  marks 
above  the  symbol,  thus,  0"  S'',  &c.  The  triads,  or  those  which  take  three 
atoms  of  hydrogen,  include  among  non-metals  N  P  B,  and  among  metals  As, 
Sb,  Bi,  Al,  Au.  This  atomicity  is  expressed  by  three  marks,  thus,  N'". 
The  tetrads  which  are  supposed  to  take  or  displace  four  atoms  of  H,  include 
C  and  Si  as  well  as  the  following  metals,  Ti,  Zn,  Sn,  Ta,  Pd,  Pt,  Ir,  Os. 
Their  atomicity  is  thus  indicated,  C'\  There  is  a  group  of  Ilexads  repre- 
sented by  the  metals,  Mo^S  V',  and  W^^',  and  also  a  group  of  nine  metals, 
of  which  the  atomicity  has  not  been  determined,  namely,  Th,  Ro,  Ru,  G,  Yt, 
Ce,  La,  U,  and  Di,  being  placed  among  the  tetiads,  and  the  other  metals 
among  the  dyads. 

This  arrangement  of  the  elements  is  based  on  certain  assumptions  which 
may  or  may  not  be  true.  With  respect  to  the  metals,  it  is  notorious  that 
they  form  but  few  compounds  with  hydrogen,  so  that  the  atomicity  must  be 
determined  among  them  indirectly,  ^.  e.,  by  their  combinations  with  chlorine. 
It  places  silver  in  the  same  group  with  the  alkali  metals,  and  transfers  the 
alkaline  earthy  metals  to  the  group  which  includes  copper,  manganese,  iron, 
and  mercury. 

The  doubling  of  the  combining  weight  of  oxygen  destroys  in  some  cases 
that  simplicity  which  has  rendered  chemical  notation  an  easy  subject  to  the 
student.  The  compounds  of  nitrogen  with  oxygen  will  illustrate  the  differ- 
ence in  the  two  systems  : — 


Ordinary  Notation 

Name.                                 TTnitary  Notation. 

Name. 

NO 

Protoxide  of  nitrogen 

NgO 

Nitrous  oxide 

NO. 

Deutoxide  of  nitrogen 

NO 

Nitric  oxide 

NO3 

Hyponitrous  acid 

N2O3 

Nitrous  anhydride 

NO, 

Hyponitric  acid,  Nitrous  acid 

NO2 

Nitric  tetroxide 

NO, 

Nitric  acid 

N2O3 

Nitric  pentoxide. 

Under  the  ordinary  system,  in  which  oxygen  is  represented  by  8,  there  is 
that  progressive  increase  from  1  to  5  atoms,  which  is  in  strict  accordance 
with  the  simple  law  of  multiple  proportions.  On  the  unitary  system  there 
are  three  compounds  vhich  it  is  assumed  cannot  be  formed  except  by  two 
atoms  of  nitrogen  entering  into  combination,  while  there  are  two  other  com- 
pounds of  these  elements  which  can  be  produced  by  one  atom  of  that  ele- 


NEW    NOTATION.  'jl 

merit.  Owin^  to  this  arrangement,  the  oxygen  atoms  have  no  kind  of 
numerical  relation.  No  satisfactory  reason  can  be  assigned  why  one  of  the 
gaseous  compounds  of  these  elements  should  take  one  atom,  and  the  other 
require  two  atoms  of  nitrogen  for  its  production.  The  inconsistency  of  this 
arrangement  is  still  more  strikingly  displayed  in  comparing  the  formulae  of 
the  two  systems,  which  represent  the  anhydrous  nitric  and  the  hydrated 
nitric  acid. 

Ordinary  Notation.  Name.  Unitary  Notation.  Name. 

NOg  Anhydrous  nitric  acid  NjOg        Nitric  pentoxide  or  anhydride 

NO5HO       Hyd'd  nitric  acid  HNO3       Hydric  nitrate. 

The  same  compound  of  the  two  elements  is  represented  on  the  unitary 
system  as  requiring  two  atoms  of  nitrogen  for  its  formation  when  the  elements 
of  water  are  not  present,  and  only  one  atom  when  the  elements  of  water  are 
present.  No  valid  reason  can  be  assigned  for  such  an  assumption  as  this, 
and  it  is  certainly  not  in  accordance  with  the  simplicity  of  the  laws  of  chemi- 
cal combination.  It  would  be  foreign  to  the  purpose  of  this  work  to  occupy 
the  pages  with  controversial  matter.  It  may  be  sufficient  to  state,  the  sup- 
posed advantages  of  the  new  notation  appear  to  be  more  than  counterbalanced 
by  the  disadvantages  which  necessarily  accompany  it.  Some  of  those  chem- 
ists who  use  it,  frequently  violate  their  principles  by  retaining  the  name  of 
the  old  system,  with  which  the  unitary  formula  of  the  compound  is  wholly 
inconsistent.  Others  with  a  desire  to  be  consistent,  have  so  completely 
changed  the  names  of  substances,  that  they  are  now  scarcely  recognizable  by 
scientific  men,  and  are  unknown  to  and  unused  by  those  who  are  engaged  in 
pharmaceutical  or  manufacturing  chemistry. 

The  specific  gravity  of  all  gases  is  referred  by  Gerhardt  to  hydrogen  as  a 
standard,  instead  of  atmospheric  air.  This  certainly  has  the  advantage  of 
representing  generally  by  one  set  of  figures  both  specific  gravities  and  atomic 
weights.  Thus  oxygen  is  16  times  heavier  than  hydrogen.  Its  specific 
gravity  would  be  therefore  16,  and,  as  it  combines  with  hydrogen  in  the  pro- 
portion of  8  to  1,  this  is  in  the  ratio  of  16  to  2  ;  hence  if  the  atomic  weight 
of  oxygen  is  16,  it  will  take  two  atoms  of  hydrogen  to  form  water.  Thus 
hydrogen  is  supposed  to  unite  not  as  one,  but  as  two  atoms  with  one  atom 
of  oxygen,  in  order  to  meet  this  duplication  of  oxygen.  This  is  on  the 
assumption  that  equal  volumes  of  gases,  under  similar  circumstances,  contain 
an  equal  number  of  atoms,  and  that  each  atom  of  an  elementary  gas  repre- 
sents a  volume,  and  vice  versa.  Thus  a  volume  of  oxygen  contains  1  atom 
=  16,  and  a  volume  of  hydrogen  contains  1  atom  =  1*  But  water,  accord- 
ing to  this  view,  cannot  be  produced  by  the  union  of  1  atom  or  volume 
of  hydrogen  ;  hence  it  would  stand  thus  : — 

By  Weight.  By  Volume. 

H2  =2  =  2 

0  =  16  =  1 

= . 1 


H2O  =  18  =  2 

Water  would  therefore  be  a  suboxide  of  hydrogen,  while  the  peroxide  would 
become  the  oxide  (HO).  Protoxide  of  nitrogen  would  in  like  manner  be  a 
suboxide  NgO,  and  the  deutoxide  would  become  the  protoxide  (NO).  In 
respect  to  this  theoretical  constitution,  it  may  be  remarked  that  the  chemical 
properties  of  water  are  really  those  of  a  neutral  oxide,  and  not  of  a  suboxide. 
Faraday  considers  that  the  electrolysis  of  water  proves  it  to  be  a  protoxide, 
^.  e.,  a  compound  of  one  atom  of  each  element,  HO.  On  the  other  hand,  the 
peroxide  of  hydrogen  represented  by  the  unitary  system  as  a  neutral  oxide, 


Y2  .    THE    UNITARY    SYSTEM    OF    NOTATION. 

HO,  has  none  of  the  characters  of  a  neutral  oxide  ;  but  from  the  facilit}^  with 
which  it  parts  with  half  of  its  oxygen,  it  more  strikingly  resembles  a  peroxide, 
HO,. 

The  compounds  of  hydrogen  and  nitrogen  with  oxygen  serve  to  illustrate 
the  inconsistency  of  the  new  system  of  nomenclature.  Thus  N^O  is  described 
as  nitrous  oxide,  but  H^O  is  described  by  the  same  authority  as  hydric  oxide, 
or  oxide  of  hydrogen.  Again,  NO  is  represented  as  nitric  oxide,  while  HO 
stands  as  hydric  peroxide,  or  peroxide  of  hydrogen.  It  is  clear  that  if  this 
view  is  correct,  that  the  compounds  are  respectively  on  the  unitary  system 
suboxides  and  oxides,  and  water  should  be  aqueous  oxide,  and  oxywater 
hydric  oxide.  This  should  be  the  true  nomenclature,  if  the  old  names  of 
nitrous  and  nitric  oxide  have  been  properly  applied  to  the  analogous  com- 
pounds of  nitrogen  with  oxygen. 

It  is  stated  in  favor  of  this  method,  that  it  is  better  adapted  for  expressing 
the  formulae  of  certain  organic  compounds  than  that  now  in  use  ;  and  that, 
in  reference  to  compound  gases  and  vapors,  the  atoms  may  be  so  arranged 
that  they  will  all  yield  two  volumes — the  specific  gravities  of  the  compounds, 
compared  with  hydrogen,  being  then  equal  to  one-half  of  their  atomic  weights. 
Thus  carbonic  oxide  C  0  forms  2  volumes  of  gas  (the  atoms  being  doubled) ; 
the  atomic  weight  is  12 +  16,  or  28,  and  the  specific  gravity,  compared  with 
hydrogen,  equal  to  one-half,  or  13.95.  Alcohol  is  C^IIjiO  ;  it  forms  2  volumes 
of  vapor;  the  atomic  weight  is  24-f  6-|-16— 46,  and  the  specific  gravity, 
compared  with  hydrogen,  is  one-half  of  this,  namely,  23.  Chemical  facts 
are,  however,  somewhat  strained  to  suit  the  requirements  of  this  hypothesis. 
The  specific  gravities  of  arsenic  and  phosphorus  in  vapor,  compared  with 
hydrogen,  are  double  their  atomic  weights,  being  152.79  and  63.71  respect- 
ively. The  atomic  weights  (75  and  32)  therefore  represent  only  half  a 
volume  instead  of  one  volume  of  each  element ;  and  one  volume  of  arsenic 
or  phosphorus  must  represent  two  atoms.  Either,  therefore,  the  system  is 
inconsistent  with  itself,  and  the  assumption  that  the  volume  of  an  element 
represents  one  atom,  or  its  atomic  weight,  is  contrary  to  known  facts — or, 
in  order  to  bring  arsenic  and  phosphorus  within  the  rule,  the  atomic  weights 
of  these  elements  must  be  doubled  on  this  system  of  notation.  So  with  sul- 
phur— the  atomic  weight  being  32,  the  specific  gravity  of  the  vapor,  com- 
pared with  hydrogen,  is  3  times  this  weight,  or  96.  Hence,  instead  of  an 
atom  of  sulphur  corresponding  to  one  volume,  it  would  be  represented  by  J 
of  a  volume.  By  ingeniously  selecting  a  specific  gravity  of  sulphur-vapor 
calculated  for  the  unusual  temperature  of  1900'^,  in  place  of  the  ordinary 
specific  gravity  at  900°,  this  element  is  made  apparently  to  fall  within  the 
rule.  Oxygen  itself  only  falls  within  it  by  doubling  the  equivalents  of  all 
the  bodies  with  which  this  element  combines. 

This  system,  therefore,  introduces  duplicate  or  molecular  atoms  in  place  of 
the  usual  single  atoms.  Elements  are  supposed  to  enter  into  combination 
with  themselves  before  they  can  enter  into  combination  with  other  elements. 
Thus  hydrogen  does  not  exist  in  all  cases  as  H,  but  on  some  occasions  as 
HH  or  H^;  in  other  words,. it  is  supposed  to  form  a  compound  of  itself,  or 
a  hydride  of  hydrogen,  and  nitrogen  is  also  NN,  or  a  nitride  of  nitrogen.  We 
have  here  not  only  a  departure  from  simplicity,  but  from  all  analogy.    Thus 

we  are  told  that  anhydrous  oxide  of  potassium  is  j^  [-  0,  while  the  anhydrous 

chloride,  bromide,  iodide,  and  fluoride,  would  be  represented  by  one  atom  of 
each,  KCl  or  KBr,  &c.  The  analogy  of  composition  between  oxide  and 
chloride  is  thus  set  aside :  and  the  names  of  compounds  are  no  longer  in 
accordance  with  their  chemical  constitution.    The  present  language  has  been 


NOMENCLATURE    OF    SALTS.  T3 

found  adequate  to  explain  all  chemical  changes  that  are  of  any  importance 
and  require  explanation  ;  and  although  in  some  respects  imperfect,  it  has 
this  great  advantage,  that  it  has  taken  a  deep  root  not  only  in  the  arts  and 
manufactures  of  this  country,  but  in  medicine  and  pharmacy. 

Nomenclature.  Constitution  of  Salts. — Elementary  bodies  often  take  their 
names  from  their  peculiar  physical  properties  as  chlorine  and  iodine  in  refer- 
ence to  color,  and  bromine  to  odor :  in  some  instances  the  name  is  derived 
from  the  products  of  combination,  as  oxygen,  hydrogen,  nitrogen,  and  cyano- 
gen. The  general  principle  of  nomenclature  as  applied  to  compounds,  has 
been,  as  far  as  possible,  to  indicate  the  composition  of  the  substance  by  the 
name.  Thus  sulphate  of  potash  implies  at  once  the  constitution  of  this  salt : 
it  was  formerly  called  the  sal  de  duobus.  Its  formula  is  KOjSOg,  and  herein 
its  composition  is  at  once  announced.  The  same  observation  applies  to  other 
salts.  In  regard  to  the  common  metals,  the  salts  receive  the  name  of  the 
metal,  as  sulphate  of  copper  CuO,SOg.  The  acid,  however,  as  in  the  case  of 
sulphate  of  potash,  is  believed  to  be  combined  with  oxide  of  copper,  and  not 
with  the  metal  itself.  Among  the  alkalies  the  oxides  were  known  long  before 
the  metals,  and  received  specific  names,  which  have  been  since  retained.  In 
recent  times  it  has  been  proposed  to  assimilate  the  names  of  metallic  salts, 
by  using  a  common  designation.  Thus  the  sulphate  of  potash  is  described 
as  sulphate  of  potassium,  on  the  hypothesis  that  the  acids  are  not  combined 
directly  with  the  oxides,  but  with  the  metals.  If,  as  we  believe,  this  hypo- 
thesis is  inconsistent  with  chemical  facts,  then  a  retrograde  step  in  nomencla- 
ture has  been  taken,  since  a  name  which  suggests  a  direct  combination  of  an 
acid  or  acid  radical  with  a  metal,  conveys  no  incorrect  idea  of  the  constitu- 
tion of  salts. 

A  salt  is  a  compound  of  an  acid  and  a  base.  An  acid  is  a  compound  which 
has  an  acid  or  sour  taste,  which  reddens  the  blue  color  of  litmus,  and  neu- 
tralizes an  alkali  in  combining  with  it  to  form  a  salt.  But  according  to  some  ■ 
modern  chemists,  an  acid  is  a  salt,  and  all  acids  are  described  as  salts  of 
hydrogen.  There  are  some  acids,  however,  which  neutralize  alkalies  or  bases 
and  form  definite  salts,  but  they  form  no  compound  with  water  and  are  never 
found  associated  with  hydrogen  in  any  form.  Thus  hyponitrousacid  (NO3) 
forms  a  well-known  class  of  salts,  the  hyponitrites — of  the  alkaline  and 
metallic  oxides.  When  water  is  added  to  the  anhydrous  acid,  this  acid  is 
immediately  decomposed.  It  is  the  same  with  hyponitric  (nitrou^  acid  NO^. 
It  forms  however  well-defined  nitro-compounds  with  cellulose,  glycerine,  and 
benzole.  It  performs  all  the  functions  of  an  acid,  but  when  water  is  placed 
in  contact  wi^h  it,  it  undergoes  decomposition.  It  enters  into  no  combina- 
tion with  the  elements  of  water.  It  is,  therefore,  impossible  to  describe  an  acid 
as  a  salt  of  hydrogen,  except  by  ignoring  the  existence  of  a  large  class  of 
substances  which  have  all  the  characters  of  acid,  except  the  power  of  combining 
with  water  or  its  elements.  Even  some  which  combine  with  water  as  a 
solvent,  such  as  the  carbonic  and  sulphurous  acid  gases,  form  no  hydrates 
or  chemical  compounds  with  water.  They  may  be  obtained  perfectly  free 
from  water  or  its  elements — but  they  combine  with  metallic  oxides  and  pro- 
duce well-known  crystalline  salts.  Among  solids  the  fused  boracic  and 
silicic  acids  form  a  large  number  of  saline  compounds  by  uniting  as  acids  to 
bases,  wholly  irrespective  of  the  presence  of  water. 

The  term  base  is  applied  by  chemists  to  signify  a  compound  which  will 
chemically  combine  with  an  acid  :  it  includes  alkalies  (oxides  of  alkaline 
metals,  and  alkalies  of  the  organic  kingdom),  oxides  of  the  ordinary  metals, 
and  a  variety  of  complex  compounds  in  the  organic  kingdom  which  are  not 
alkaline  and  possess  none  of  the  characters  of  metallic  oxides.  The  metals 
which  form  bases  are  are  now  called  basylous  bodies.     An  alkali  is  known 


74  NOMENCLATURE    OF    SALTS. 

by  its  having  an  acrid  or  caustic  taste,  by  its  rendering  a  red  solution  of 
litmus  blue,  and  by  its  being  neutralized  h'j  an  acid,  i.  e.,  having  its  alkaline 
properties  entirely  destroyed.  Further,  it  has  the  property  of  turning  yellow- 
turmeric  to  a  red-brown  color  ;  the  red  color  of  the  petals  of  flowers,  and 
fruits,  to  a  blue  or  green  ;  and  the  red  color  of  woods  and  roots  to  a  crim- 
son tint.  The  basic  metallic  oxides  are  generally  insoluble  in  water,  and 
neutral  to  test-paper  ;  some  have  a  feebly  alkaline  reaction. 

In  reference  to  Oxacids,  or  those  which  contain  oxygen,  the  termination 
ic  indicates  the  higher  degree  of  oxidation,  while  the  termination  ous  im- 
plies a  lower  degree.  Thus  we  have  sulphuric  (SO  J  sulphurous  (SO^)  acids. 
When  there  are  more  than  two  acids,  a  further  distinction  is  made  by  the 
prefix  hypo  (vrto  under)  :  thus  we  have  hyposulphuric  acid  to  signify  an  acid 
containing  a  smaller  quantity  of  oxygen  than  the  sulphuric,  but  a  larger  quan- 
tity than  the  sulphurous ;  and  hyposulphurous,  indicating  a  smaller  quantity  of 
oxygen  than  exists  in  the  sulphurous  acid.  When  an  acid  has  been  discovered 
containing  a  still  larger  amount  of  oxygen  than  the  highest  in  a  known  series, 
it  receives  the  prefix  hyper  (vrtsp  above)  ;  still  retaining  the  terminal  ic. 
Thus  there  is  manganic  acid  (MnO^) ;  and  hypermanganic  or  permanganic 
acid  (Mn^Oy),  which  contains  a  still  larger  proportion  of  oxygen  than  the 
manganic.  The  salts  formed  by  these  acids  terminate  in  ate  when  the  acid 
terminates  in  ic,  and  in  tie  when  it  terminates  in  ous.  The  terminations 
ic  and  ous  have  been  employed  by  Berzelius,  and  other  chemists,  to  dis- 
tinguish the  oxides  and  salts  of  metals.  Thus  the  protoxide  of  iron  would 
be  the  ferrous  oxide,  while  the  peroxide  would  be  the  ferric  oxide  ;  so  there 
ate  also  ferrous  and  ferric  sulphates — stannous  and  stannic  chlorides  and 
sulphides. 

When  there  is  only  one  acid  formed  by  the  same  elements,  its  termina- 
tion is  always  in  ic,  as  the  boracic  acid,  formed  of  boron  and  oxygen,  of 
which  only  one  compound  is  known.  The  class  of  hydracids  includes  those 
binary  compounds  in  which  hydrogen  is  a  constituent ;  and  the  names  imply 
at  once  the  composition  as  hydrochloric  acid  (HCl).  Hydrogen,  unlike 
oxygen,  does  not  form  more  than  one  compound  with  the  same  element  or 
radical.  These  hydrogen  acids  require  no  water  for  the  manifestation  of 
acidity.  The  term  radical,  or  compound  radical,  is  applied  to  a  compound 
which  in  its  order  of  combination  acts  like  an  element.  Thus  the  compound 
gas  cyanog^  (^CJ  is  a  radical ;  it  enters  into  combination  with  the  metals 
and  metalloids,  like  chlorine,  producing  binary  compounds  called  cyanides. 
It  is  a  substitute  for  an  element. 

When  in  the  composition  of  salts  the  atoms  of  acids  preponderate,  the 
prefix  bi  or  ter  is  used  to  indicate  the  number,  as  bisulphate  of  potash 
(K02S0,),  or  tersulphate  of  alumina  (AI3O33SO3).  These  constitute  acid 
salts.  When  the  base  predominates,  the  abbreviated  Greek  prefix  di  or  tri 
is  employed  to  designate  the  surplus  atoms  of  the  base.  Thus,  the  triacetate 
of  lead  signifies  a  compound  in  which  three  atoms  of  oxide  of  lead  are  united 
to  one  atom  of  acid  3PbO,Ac.  The  terra  sesqui  is  used  to  signify  one  and 
a  half  atoms,  or  avoiding  fractions,  3  atoms  of  base  to  2  of  acid,  as  3PbO,2Ac. 
The  following  Table  represents  the  nomenclature  of  salts  in  reference  to  their 
constitution.     M  stands  for  anj  metal : — 

Neutral  (normal)  salt    M0-|-  SO3  Bibasic      ....  2M04-  SO3 

Acid MO4-2SO3  Sesquibasic   .     .     .  3MO4-2SO3 

Sesquisalt     ....  2MO+3SO3  Tribasic    ....  3M0-J-  SO3 

Binary  Oompounds.—The  Binary  System.— ^hm  a  metalloid  is  united  to 
another  metalloid  or  metal,  or  when  a  compound  radical  (salt-radical)  is 


ON    THE    CONSTITUTION    OF    SALTS.  75 

united  to  a  metal  or  metalloid,  the  combination  is  called  Unary,  from  its 
consisting  of  two  elements.  They  are  generally  known  by  the  termination 
ide.  Thus  oxide,  chloride,  sulphide,  carbide,  phosphide,  and  cyanide  indicate 
compounds  of  tlie  elements  or  of  the, radical  (cyanogen)  with  other  elements. 
When  more  than  one  combination  exists,  the  compounds  take  the  Greek  prefix 
proto,  deuto,  trito,  or  di,  to  indicate  the  respective  number  of  atoms  of  the 
constituents.  {See  Oxygen  for  the  series  of  Oxides.)  The  highest  combi- 
nation always  takes  the  prefix/^er.  The  binary  compounds  formed  by  chlorine, 
bromine,  iodine,  and  fluorine,  with  the  alkaline  metals,  are  frequently  called 
haloid  salts,  to  indicate  the  marine  origin  of  the  radicals  (a?.?,  ax6?,  the  sea). 
Chloride  of  sodium  furnishes  an  instance  of  a  binary  compound  ;  and  as 
nitrate  of  silver  or  nitrate  of  potash  equally  forms  a  salt  bearing  a  physical 
resemblance  to  the  chloride,  it  has  been  suggested  that  in  oxacid  salts  the 
elements  may  be  so  arranged  as  to  form  hypothetical  binary  compounds. 
Chloride  of  sodium  is  NaCl  and  nitrate  of  silver  is  AgOjNOg*,  but  the 
accepted  symbolic  language  would  admit  of  the  atomic  arrangement  AgNOg, 
and  by  this  means  all  decompositions  would  become  mere  substitutions  of 
one  metal  for  another,  or  for  hydrogen.  Thus  in  the  production  of  chloride 
of  silver  we  should  have  in  ordinary  symbols  NaCl4-AgO,N05=AgCl-f 
NaO,N05;  ^^^  if  the  oxygen  is  supposed  to  be  associated  with  the  elements 
of  nitric  acid,  forming  a  compound  radical  (nitron),  then  the  changes  would 
be  more  simply  represented  thus:  NaCl  +  AgN0f.=AgCl-f-NaN06.  If,  how- 
ever, this  view  were  correct,  it  should  apply  to  all  salts  and  even  to  hydrates. 
Thus,  to  take  a  few  examples  of  compounds  which  are  intelligibly  represented 
by  the  present  method,  we  should  have,  on  the  binary  hypothesis,  to  make 
the  following  changes :  1.  Carbonate  of  soda,  as  a  type  of  the  carbonates, 
NaO,C03  would  be  rendered  Na,C03 ;  and  for  the  bicarbonate  of  soda, 
KaO,2CO.^  a  new  hypothetical  radical  would  have  to  be  created,  as  NajCgOg 
or  Na,C03-fC02,  neither  of  which  formula  would  convey  the  slightest  know- 
ledge of  the  composition  of  the  salts.  This  objection  equally  applies  to  all 
salts  having  one  atom  of  base  to  two  or  more  atoms  of  acid,  as  the  bisul- 
phates,  bisulphites,  the  binarsenates,  and  others,  as  well  as  to  all  double 
salts  containing  an  oxygen  acid.  2.  In  the  application  of  this  notation  to 
hydrates  (which  could  not  be  fairly  expected),  hydrate  of  potash  KO,HO 
would  be  KjHOa;  but  while  potassium  (K)  has  a  stronger  affinity  for  oxygen 
than  any  other  known  substance,  and  peroxide  of  hydrogen  (HOg)  so  readily 
parts  with  oxygen  that  the  mere  contact  with  metals  or  metallic  oxides  is 
sufficient  for  the  purpose,  it  is  assumed  that  the  peroxide  can  remain  in  com- 
bination with  potassium  without  undergoing  decomposition.  3.  Sulphurous 
acid  by  combining  with  potash  forms  KOjSOg.  It  could  not  be  regarded  or 
written  as  KSOg,  for  this  would  imply  a  combination  of  anhydrous  sulphuric 
acid  with  the  metal  potassium.  The  bisulphate  of  potash  KO,2S03,  would 
present  an  equal  difficulty.  On  the  binary  system  this  would  be  KjSj^O^ — 
the  sulphur  and  oxygen,  in  order  to  form  a  salt  radical,  being  here  associated 
as  in  hyposulphuric  acid,  which  is  a  well-known  and  independent  acid  of  sul- 
phur. 4.  The  anhydrous  salts  formed  of  metallic  bases  and  acids  could  not 
be  consistently  represented  on  the  binary  hypothesis ;  for  there  could  be  no 
definite  principle  on  which  the  oxygen  should  be  wholly  assigned  to  either 
metal.  Thus  chromate  of  lead  is  commonly  represented  as  PbO.CrOg,  but 
as  a  binary  compound  it  would  be  either  Pb.OrO^,  or  CrPbO^.  Of  these 
three  combinations  of  elements,  those  only  which  are  known  and  separable, 
are  oxide  of  lead  and  chromic  acid.  The  necessary  creation  of  an  endless 
number  of  hypothetical  radicals,  some  already  conflicting  with  known  com- 
pounds, is  indeed  fatal  to  the  hypothesis.  It  w^ould  add  complexity  instead 
of  simplicity  to  chemical  formulae.     While  NO^,  SO3  and  COg  have  a  real 


76  NEUTRALIZATION  AND  SATURATION. 

and  independent  existence,  the  binary  radicals  NOg,  SO^  and  COg  are  mere 
assumptions.  It  has  been  supposed  that  the  electrolytic  decomposition  of 
salts  is  in  favor  of  this  view ;  but  although  the  metal  may  be  separated  from 
the  salt  by  an  electric  current,  the  supposed  binary  radical  has  never  been 
obtained,  and  the  facts  are  fully  explained  on  the  supposition  that  it  is 
SO3  +  O,  and  not  SO^.  On  the  other  hand,  ordinary  electrolysis  favors  the 
common  view  of  the  constitution  of  salts  by  acid  and  base,  as  the  following 
simple  experiment  will  show.  Provide  a  piece  of  glass  tube,  bent  at  an  angle, 
and  placed  in  a  wine-glass,  to  serve  for  its  foot  or  support.  Fill  this  siphon 
with  the  blue  infusion  obtained  by  macerating  the  leaves  of  the  red  cabbage 
in  boiling  water  (rendered  blue  by  a  little  potash),  and  put  into  it  a  few 
crystals  of  sulphate  of  soda  ;  then  place  a  strip  of  platinum  foil  in  each  leg 
of  the  siphon,  taking  care  that  they  do  not  come  into  contact  at  the  elbow 
of  the  tube,  and  connect  one  of  these  with  the  negative  and  the  other  with 
the  positive  pole  of  the  pile;  in  a  few  minutes  the  blue  color  will  be  changed 
to  green  on  the  negative  side,  and  to  red  on  the  positive  side  of  the  tube, 
indicating  the  decomposition  of  the  salt,  the  alkali  or  soda  of  which  is  col- 
lected in  the  negative,  and  the  sulphuric  acid  in  the  positive  side.  Reverse 
the  poles,  and  the  colors  will  also  gradually  be  reversed.  In  this  and  ana- 
logous experiments,  it  is  found  that,  whenever  a  neutral  salt  is  decomposed 
by  electricity,  the  oxide  or  base  appears  at  the  cathode,  and  the  acid  at  the 
anode.  The  bases,  therefore,  in  their  electrical  relations,  rank  with  hydro- 
gen, and  are  cathions  ;  and  the  acids  with  oxygen,  and  are  anions  (see  page 
59):  The  least  soluble  salts  may  be  made  to  render  up  their  elements  m 
the  same  way.  If,  for  instance,  we  substitute  for  the  sulphate  of  soda  in 
the  preceding  experiment,  a  little  finely-powdered  sulphate  of  baryta 
moistened  with  water,  baryta  will  be  evolved  at  the  cathode,  and  will  there 
render  the  liquid  green  ;  while  sulphuric  acid  will  appear  at  the  anode,  ren- 
dering it  red. 

If  the  binary  hypothesis  were  adopted,  it  would  be  necessary  to  change 
the  names  of  all  salts.  CO3  is  not  carbonic  acid  ;  it  would  be  necessary  to 
invent  a  new  term  for  this  radical,  to  indicate  its  composition,  e.  g.,a  teroxy- 
carbide,  so  that  dry  carbonate  of  potash  K0,C02,  would  be  a  teroxycarbide 
of  potassium  KCO3.  If  names  are  not  to  express,  as  far  as  may  be,  the 
composition  of  salts,  it  would  be  preferable  to  return  to  the  old  nomencla- 
ture based  on  physical  properties,  and  to  designate  the  sulphate  of  iron 
(FeO,S03)  as  green  vitrol,  rather  than  under  the  binary  hypothesis  as  the 
tessaroxisulphide  of  iron  (FeSOJ.  We  must  bear  in  mind,  in  reference  to 
such  changes,  that  the  supposed  advantages  gained  in  one  part  of  the  science 
may  be  far  more  than  counterbalanced  by  the  disadvantage  of  using  names 
which  either  do  not  express  the  nature  of  the  compound,  or  which  express  it 
in  such  formulas  as  to  deceive  the  student  of  the  science.  As  Dr.  Miller  has 
pointed  out,  there  are  four  ways  in  which  nitrate  of  potash  may  be  repre- 
sented ;  K0,N05;  S:,NOe;  KNOg;  and  KNO3;  but  to  only  the  first  of 
these  is  the  usual  name  of  the  salt  applicable.  The  first,  second,  and  third 
formulae  are  on  the  ordinary  system  of  notation  ;  the  fourth  is  on  the  system 
of  Gerhardt,  which,  except  by  some  conventional  understanding,  cannot 
represent  the  presence  of  potash  or  nitric  acid  in  the  salt  on  any  reasonable 
interpretation. 

There  are  some  cases  in  which  the  binary  theory  of  salts  is  inadmissible 
not  only  with  respect  to  oxacids,  but  to  hydracids.  The  alkalies  of  the 
vegetable  kingdom  form  definite  crystallizable  salts  with  the  hydrochloric, 
sulphuric,  and  nitric  acids.  The  hydrochlorate  and  sulphate  of  morphia 
are  well-defined  salts,  in  which  there  is  every  reason  to  believe  that  acid  and 
base  are  directly  combined.     Even  in  the  mineral  kingdom,  there  is  some- 


DECOMPOSITION    OF    NEUTRAL    SALTS.  It 

times  a  want  of  evidence  of  this  binary  condition.  Magnesia  or  alumina 
may  be  dissolved  in  hydrochloric  acid,  and  it  is  supposed  that  soluble 
chlorides  are  formed.  In  the  case  of  soda  and  potash  there  is  the  strongest 
evidence  of  the  production  of  chlorides  by  the  (act  that  the  binary  salts  are 
obtainable  as  such  by  crystallization.  On  submitting  to  evaporation  the 
hydrochloric  solutions  of  magnesia  and  alumina  and  applying  heat  to  the  dry 
residues,  no  binary  compounds  are  obtained,  but  simply  the  bases  which 
were  originally  employed.  According  to  some  authorities,  cobalt  forms 
both  a  chloride  and  hydrochlorate,  indicated  by  a  different  color  in  the  com- 
pounds ;  the  chloride  or  binary  compound  obtained  by  concentration  at  a 
high  temperature  being  blue,  while  the  hydrochlorate,  like  the  non-binary 
compounds  nitrate  and  sulphate,  although  deprived  of  water,  remain  red. 

Neutralization^  in  reference  to  salts,  must  be  distinguished  from  saturation  : 
the  first  implies  the  destruction  of  the  properties  of  acid  and  alkali  by  com- 
bination, as  manifested  on  organic  colors ;  the  second  the  exhaustion  of 
chemical  affinity.  Potash  is  neutralized  by  combination  with  one  atom  of 
sulphuric  acid.  The  compound,  sulphate  of  potash,  presents  neither  acid 
nor  alkaline  reaction  ;  it  is  a  perfectly  neutral  salt.  Potash  will  however 
combine  with  an  additional  equivalent  of  acid  forming  a  bisulphate;  in  this 
compound  it  is  saturated  with  the  acid,  but  the  alkali  is  more  than  neutralized  ; 
it  possesses  a  well-marked  acid  reaction.  Potash  in  the  state  of  bicarbonate 
is  saturated  with  carbonic  acid  ;  it  will  take  no  more  :  but  it  is  not  neutral- 
ized, for  it  presents  a  well-marked  alkaline  reaction.  These  terms  are  often 
used  as  synonymous,  but  they  have  a  widely  different  signification.  The  term 
neutral  salt  is  however  commonly  employed  to  signify  the  condition  of  a 
compound  without  reference  to  the  action  of  its  solution  on  vegetable  colors. 
Provided  the  same  equivalent  weight  of  acid  is  present,  the  salt  is  neutral 
although  the  solution  may  have  an  acid  reaction.  The  sulphates  of  copper, 
iron,  and  zinc  contain  the  same  proportion  of  acid  to  base  as  the  sulphate  of 
potash,  but  while  the  latter  is  quite  neutral,  the  three  former  are  acid,  and 
redden  litmus.  The  best  test  for  neutrality  is  the  blue  infusion  of  cabbage, 
prepared  in  the  manner  elsewhere  described  (page  76).  It  is  reddened  by 
an  acid,  and  changed  to  a  green  color  by  an  alkali.  To  avoid  confusion  from 
the  use  of  the  term  neutral,  Gmelin  has  proposed  to  call  such  salts  normal. 

In  the  double  decomposition  of  salts  it  is  usual  to  state  that  neutral  salts 
produce  neutral  compounds.  This  may  be  proved  by  adding  to  solutions  of 
sulphate  of  potash  and  chloride  of  barium  respectively  a  small  quantity  of 
blue  infusion  of  cabbage.  When  mixed,  there  is  a  complete  interchange  of 
acids  and  bases,  but  the  mixed  liquids  remain  blue.  Hence  there  must  have 
been  a  complete  substitution  or  replacement  of  acids  and  bases  in  equivalent 
proportions ;  in  other  words,  the  chloride  of  potassium  and  sulphate  of  baryta 
are  just  as  neutral  as  the  compounds  which  form  them.  If  an  equivalent  of 
bisulphate  of  potash  is  employed,  the  blue  liquid  will  be  reddened  by  this 
salt,  and  remain  red  after  mixture,  an  equivalent  of  hydrochloric  acid  being 
set  free.  When  solutions  of  phosphates  of  soda  and  chloride  of  calcium, 
colored  with  blue  litmus,  are  mixed,  the  compounds,  although  neutral,  so 
decompose  each  other  as  to  set  free  an  acid,  and  the  litmus  is  reddened. 
This  is  owing  to  the  formation  of  a  basic  phosphate  of  lime,  ^.  e.,  a  salt  in 
which  the  base  predominates.  An  acid  and  an  alkaline  salt  may  by  double 
decomposition  produce  neutral  compounds.  A  solution  of  alum  reddened 
by  infusion  of  litmus  or  blue  cabbage,  when  mixed  with  a  due  proportion  of 
a  solution  of  carbonate  of  potash  rendered  green  by  infusion  of  cabbage, 
will  give  rise  to  products  of  a  neutral  kind  (sulphate  of  potash  and  hydrate 
of  alumina),  and  both  liquids  will  become  blue. 


78  GASES    AND    VAPORS. 


METALLOIDS  OR  NON-METALLIC  BODIES. 


CHAPTER  V. 

METALLOIDS  AND  META  LS.  — PR  OPERT  IE  S  OF  GASES  AND 

VAPORS. 

Division  of  Elements. — For  the  convenience  of  stndy,  elementary  bodies 
are  divided  into  two  great  classes,  namely,  Metalloids  or  Non-Metals, 
and  Metals.  This  division  is  arbitrary  ;  hence  chemists  have  taken  differ- 
ent views  of  the  substances  which  belong  to  these  two  classes.  Sulphur  may 
be  regarded  as  a  type  of  the  metalloids,  and  gold  of  the  metals.  Here  the 
distinctions  in  physical  characters  are  sufiBciently  marked.  In  some  cases, 
however,  it  is  difficult  to  assign  the  class ;  thus  arsenic,  tellurium,  and  sele- 
nium have  been  regarded  either  as  metallic  or  non-metallic.  It  is  difficult 
to  suggest  any  broad  chemical  distinction  between  the  two  classes.  As  a 
general  rule,  non-metallic  bodies  produce,  in  combining  with  oxygen,  either 
acids  or  neutral  oxides  ;  they  do  not  form  any  salifiable  base.  Water  may 
be  regarded  as  an  exception  to  the  remark  :  since,  although  a  neutral  oxide, 
it  is  believed  by  most  chemists  to  act,  in  some  instances,  the  part  of  a  base 
to  acids,  and  is  known  as  basic  water.  Hydrogen  therefore  ranks  with  the 
metals  as  a  basylous  body,  and  takes  the  first  place  as  an  electro-positive. 
On  the  other  hand,  the  metals,  while  they  produce  acids  in  combining  with 
oxygen,  also  produce  alkalies,  earths,  and  oxides  ;  in  fact,  they  are  the 
chief  source  of  the  bases  from  which  salts  are  formed. 

English  writers  commonly  enumerate  as  non-metallic  13  out  of  the  65 
elementary  bodies  known  to  science.  They  comprise  4  gaseous,  1  liquid, 
and  T  solids,  with  1  the  physical  state  of  which  is  unknown.  They  are  con- 
tained in  the  subjoined  list : — 


Oxygen 
Hydrogen 
Nitrogen    . 
Chlorine    J 


■1 


Bromine  (liquid) 

Phosphorus  ] 

Fluorine  (unknown) 

Carbon          ! 

Iodine       "j  ^ 

Boron            | 

Sulphur   l S 

Silicon          J 

Selenium  J  * 

l« 


The  symbols  and  atomic  weights  of  these  bodies  will  be  found  at  page  67. 

Distinction  of  Gases  and  Vapors. — The  gaseous,  liquid,  or  solid  state,  is 
well  known  to  be  a  physical  condition  of  matter,  depending  on  the  heat 
associated  with  the  atoms  of  the  solid  or  liquid.  By  heating  a  solid,  we 
may  cause  it  to  pass  through  the  liquid  and  vaporous  conditions.  Thus 
camphor  placed  in  a  retort  and  heated  to  347°  melts  or  passes  to  the  liquid 
state.  If  the  temperature  be  raised  to  about  400°,  it  is  rapidly  converted 
into  a  transparent  vapor  or  gas,  which  is  deposited  in  white  flocculent  masses 
on  all  cold  surfaces.    Thus  distilled  from  a  short  retort  into  a  tall  jar  placed 


LIQUEFACTION    OF    GASES.  T9 

npright,  it  forms  a  beautiful  illnstration  of  the  solidification  of  a  vapor  by 
cooling.  Ether,  at  ordinary  temperatures,  is  a  liquid  ;  if  the  liquid  be  heated 
to  96°,  it  is  entirely  converted  into  vapor  or  gas,  having  at  and  above  this 
temperature  all  the  physical  properties  of  gas.  The  best  method  of  proving 
this  is  to  invert  in  a  wide  dish  of  water,  heated  to  above  100°,  a  small  gas- 
jar  filled  with  water  at  this  temperature.  If  a  tube  containing  liquid  ether 
be  opened  under  the  mouth  of  the  jar  in  the  hot  water,  the  ether  will  pass 
into  the  vessel  as  gas  or  vapor,  and  displace  the  water.  The  jar  may  be 
removed,  and  the  contents  inflamed  by  a  lighted  taper,  when  it  will  be  seen 
to  burn  like  coal-gas.  If  another  jar  be  similarly  filled  with  the  vapor,  and 
transferred  to  a  basin  of  cold  water,  or  if  cold  water  be  simply  poured  over 
it,  the  gaseous  contents  will  be  condensed,  the  ether  will  be  liquefied,  and 
the  cold  water  will  rise  and  fill  the  jar. 

Liquefaction  of  Gases. — Experiments  conducted  on  these  principles  led 
Mr.  Faraday  to  the  discovery  that  a  large  number  of  gases  are  merely  the 
condensable  vapors  of  liquids  or  solids.  It  is  a  well-known  fact,  that  when 
any  gas  is  submitted  to  sudden  and  violent  pressure,  great  heat  is  given  out. 
A  small  volume  of  air,  suddenly  compressed,  evolves  so  much  heat  as  to 
ignite  inflammable  substances.  Thus  a  piece  of  amadon,  or  German  tinder, 
may  be  kindled  by  the  sudden  compression  of  a  few  cubic  inches  of  air  in  a 
dry  and  warm  glass  cylinder.  If,  therefore,  a  gas  is  submitted  to  pressure, 
and  at  the  same  time  cooled  as  it  is  compressed,  the  conditions  are  such  as 
to  cause  it  to  pass  into  the  liquid  state.  On  the  other  hand,  when  the 
liquefied  gas  again  assumes  the  gaseous  condition  it  absorbs  from  all 
surrounding  bodies,  a  large  amount  of  heat,  atid  thus  produces  a  great 
degree  of  cold.  The  freezing  of  water  in  a  hot  platinum  crucible  is  a  well 
known  illustrative  experiment.  Liquid  sulphurous  acid  is  poured  in  quantity 
into  a  platinum  crucible,  the  temperature  of  which  is  suflficient  to  bring  out 
a  spheroidal  condition  of  the  liquid.  Water  contained  in  a  thin  tube 
introduced  into  this  liquid  is  speedily  frozen,  owing  to  the  rapid  evaporation 
of  the  sulphurous  acid  and  its  conversion  from  a  liquid  into  gas. 

With  some  gases  no  pressure  is  necessary — mere  cooling  will  be  found 
sufficient.  Sulphurous  acid  is  a  gaseous  body  at  all  temperatures  above 
14°.  When  cooled  to  this  temperature,  it  is  immediately  liquefied.  If 
sulphurous  acid  gas  in  a  dry  state  be  passed  through  a  tube  immersed  in  a 
freezing-mixture  of  pounded  ice  and  salt,  it  will  be  condensed  as  a  liquid  in 
the  bend  of  the  tube,  and  if  the  horizontal  portions  be  drawn  out  in  a 
capillary  form  in  the  first  instance,  the  liquefied  gas,  when  condensed,  may 
be  sealed  up  and  preserved.  If  the  tube  be  broken,  the  liquid  will  rapidly 
pass  to  the  gaseous  state,  producing  a  great  degree  of  cold.  Under 
sufficient  pressure,  the  amount  of  which  varies  with  each  gas,  some  of  these 
bodies  may  be  liquefied  without  cooling,  and  the  pressure  may  be  produced 
by  the  gas  itself. 

The  solid  crystalline  hydrate  of  chlorine  (Cl  +  IOHO)  inclosed  in  a  stout 
bent  tube  sealed,  yields,  when  gently  heated,  chlorine  liquefied  by  its  own 
pressure,  forming  about  one-fourth  of  the  liquid  obtained  in  the  cool  part  of 
the  bent  tube.  The  liquefaction  of  ammonia  may  be  performed  in  like 
manner,  by  saturating  dry  chloride  of  silver  with  the  gas,  and  introducing 
this  into  a  stout  glass  tube  bent  at  an  obtuse  angle  and  securely  sealed.  The 
amwionio-chloride  of  silver  melts  at  about  100°.  The  ammonia  is  evolved, 
and  may  be  condensed  to  a  liquid  by  cooling  the  other  end  of  the  tube.  The 
ammonia  is  reabsorbed  by  the  chloride  on  cooling,  so  that  this  experiment 
may  be  repeated  any  number  of  times  (Mitscherlich).  M.  Carrfe  has 
successfully  used  liquefied  ammonia  for  producing  large  quantities  of  ice  for 
commercial  purposes.     The  machine  consists  of  two  strong  iron  vessels 


80  LIQUEFACTION    OF    GASES    BY    COLD    AND    PRESSURE. 

connected  in  an  air-tight  manner,  with  a  bent  pipe.  When  it  is  desired  to 
procure  ice,  one  of  the  vessels  is  charged  with  a  solution  of  ammonia  in 
water  saturated  at  32°.  This  vessel  is  heated,  and  the  other  acting  as  a 
receiver,  is  placed  in  cold  water.  As  the  results  of  the  heating  the  ammonia 
is  expelled  from  the  water  and  collects  in  the  cool  iron  vessel,  and  when 
the  pressure  amounts  to  about  ten  atmospheres,  the  gas  is  condensed  in  a 
liquid  form.  When  the  greater  part  of  the  gas  has  thus  been  liquefied,  the 
arrangement  is  reversed.  The  vessel  which  contained  the  solution  of 
ammonia,  is  cooled,  while  the  water  intended  to  be  frozen,  is  placed  in  the 
hollow  interior  of  the  receiver,  which  holds  the  liquefied  ammonia.  By  the 
evaporation  of  the  ammonia,  and  its  reabsorption  by  water,  so  great  a  degree 
of  cold  is  produced  that  water  is  rapidly  frozen.  (RoscoE.)  If  a  substance 
like  cyanide  of  mercury,  capable  of  yielding  ten  cubic  inches  of  gas,  is 
inclosed  in  a  stout  tube  of  one  cubic  inch  capacity,  the  gas,  when  evolved, 
will  be  under  a  pressure  of  ten  atmospheres  (15  x  10),  or  150  pounds  on  the 
square  inch,  a  pressure  quite  sufficient  to  make  it  assume  the  liquid  state- 
Faraday  thus  condensed  many  of  the  gases  by  merely  exposing  them  to  the 
pressure  of  their  own  atmosphere.  He  placed  the  materials  for  producing 
them  in  strong  glass  tubes,  bent  at  a  slight  angle  in  the  middle,  and  her- 
metically sealed.  Heat  was  then  applied  to  the  solid  substance;  and  when 
the  pressure  within  became  sufficient,  the  liquefied  gas  made  its  appearance 
in  the  empty  end  of  the  tube,  which  was  artificially  cooled  to  assist  in  the 
condensation.  In  these  experiments  much  danger  may  be  incurred  from 
the  occasional  bursting  of  tubes;  so  that  the  operator  should  protect  his 
face  by  a  mask,  and  his  hands  by  thick  gloves.  The  greatest  caution  should 
be  always  observed  in  performing  the  experiment.  Faraday  succeeded  in 
liquefying  the  following  gases,  which,  as  will  be  seen,  required  various 
degrees  of  pressure  for  the  purpose. 

Pressure  in     j-av-  Pressure  in    -p^y... 

Atmospiieres.  "  .  Atmospheres.  "^'^^^ 

Sulphurous  acid     ...  2  at    45°  Sulphuretted  hydrogen     .  17  at  50° 

Chlorine 4  "60  Carbonic  acid     ....  86  "  32 

Cyanogen 4  "60  Hydrochloric  acid   ...  40  "  50 

Ammonia 6.5  "     40  Nitrous  oxide      .     .     .     .  50  "  45 

Faraday  subsequently  succeeded  in  liquefying  defiant  gas  and  fluosilicic 
acid,  and  solidifying  hydriodic  and  hydrobromic  acid  gases,  oxide  of  chlorine, 
and  protoxide  of  nitrogen  (P/dl.  Trans.,  1823  and  1845;  also  Bunsen., 
Bihliotheque  Universelle,  1839,  vol.  32,  p.  105;  and  Poggeud.  Ann.,  vol. 
12,  p.  132). 

By  employing  a  bath  of  solid  carbonic  acid  and  ether,  Faraday  produced 
a  degree  of  cold  amounting  to  — 106°  in  the  open  air,  and  — 166°  in  vacuo. 
By  simple  exposure  to  a  cold  of  — 106°  without  any  pressure,  the  following 
gases  were  liquefied: — 

Chlorine.  Hydriodic  acid. 

Cyanogen.  Hydrobromic  acid. 

Ammonia.  Carbonic  acid. 

Sulphuretted  hydrogen.  Oxide  of  chlorine. 

With  the  aid  of  powerful  condensing  pumps,  and  a  cold  of  — 166°,  all  the 
gases  excepting  six  were  liquefied,  and  those  above-mentioned  were  solidified, 
as  well  as  the  protoxide  of  nitrogen.  Carbonic  acid  is,  however,  readily 
obtained  in  the  solid  state  as  the  result  of  the  cold  produced  by  the  sudden 
escape  of  its  own  vapor.  The  six  which  resisted  liquefaction  at  this  low 
temperature,  and  under  a  pressure  varying  from  500  to  750  pounds  on  the 
square  inch,  were  the  following : — 


PHYSICAL    PROPERTIES    OP    GASES    AND    VAPORS.  81 

Oxygen.  Nitrogen.  Deutoxide  of  mtrogen. 

Hydrogen.  Carbonic  oxide.  Coal-gas.  (?) 

It  will  be  perceived  that  of  these,  three  are  simple  and  three  are  compound 
gases.  In  employing  a  mixture  in  vacuo  of  liquid  protoxide  of  nitrogen  and 
sulphide  of  carbon,  batterer  succeeded  in  producing  a  degree  of  cold  equal 
to  — 220^,  without  any  effect  upon  these  six  gases.  Dr.  Andrews  reported 
to  the  British  Association  (Sept.  1861),  that  by  pressure  alone  he  had 
succeeded  in  reducing  oxygen  to  l-324th  of  its  volume,  and  by  pressure  with 
a  cold  of  • — 106°,  to  l-554th  of  its  volume  ;  and  atmospheric  air  by  pressure 
and  cold  to  l-675th,  in  which  state  its  density  was  little  inferior  to  that  of  water 
(the  difference  between  air  and  water  at  60°  being  814).  Hydrogen  was 
condensed  by  similar  means  to  l-500th,  carbonic  oxide  to  l-2T8th,  and 
deutoxide  of  nitrogen  to  l-680th.  The  gases  were  compressed  in  the  capillary 
ends  of  thick  glass-tubes,  so  that  any  physical  change  they  might  undergo, 
could  be  easily  observed.  When  thus  highly  condensed,  they  were  not 
liquefied  ;  hence,  although  these  six  gases  are  probably  the  vapors  of  liquids, 
they  must  be  regarded  at  present  as  perrnanent  gases,  since  cold  and  pressure 
conjoined,  and  carried  to  the  utmost  limits,  do  not  cause  them  to  assume  the 
liquid  condition. 

From  these  facts,  we  learn  that  the  greater  number  of  gases,  simple  and 
compound,  are  the  vapors  of  liquids  and  solids.  They  differ  from  ordinary 
vapors  in  the  fact,  that  the  boiling  points  of  their  liquids  are  far  below 
the  ordinary  temperature  of  the  atmosphere;  hence  they  only  admit  of 
condensation  by  artificial  cooling.  A  true  vapor,  like  that  of  ether,  is 
condensed  on  its  production,  because  the  temperature  of  the  air  is  below  its 
boiling-point,  96°  :  it  requires  no  artificial  cooling  for  its  condensation.  In 
any  part  of  the  earth  in  which  the  temperature  was  above  96°,  ether  would 
be  a  permanent  gas,  unless  kept  under  pressure  ;  while  in  any  part  where 
the  temperature  was  below  14°,  sulphurous  acid  gas  would  always  exist  as 
a  liquid.  The  difference  between  vapors  and  gases  is  therefore  merely  a 
physical  difference  dependent  on  temperature.  A  gas  is  permanently,  that 
which  a  vapor  is  temporarily. 

The  sulphide  of  carbon  as  a  liquid  is  stated  to  resist  a  very  low  degree  of 
cold  without  solidifying.  The  intense  cold  produced  by  its  evaporation  is, 
however,  suflQcient  to  bring  the  evaporating  liquid  to  the  solid  state.  Pour 
a  small  quantity  of  sulphide  of  carbon  into  a  watch-glass.  Place  a  few  fibres 
of  asbestos  on  a  slip  of  filtering  paper,  so  that  one  end  may  be  immersed  in 
the  liquid,  and  the  other  passed  freely  over  the  edge  of  the  glass.  In  a  few 
minutes  the  projecting  end  will  be  fringed  with  a  snow-like  crystalline 
deposit  of  a  solidified  vapor.  This  may  serve  as  an  illustration  of  the  cooling 
process  by  which  solid  is  obtained  from  liquid  carbonic  acid. 

The  laws  which  govern  gases  also  govern  vapors,  so  long  as  they  have  a 
temperature  above  the  boiling-points  of  their  respective  liquids. 

Physical  Properties  of  Gases  and  Vapors. — Gases  have  no  cohesion. 
Their  volume  is  determined  by  the  capacity  of  the  containing  vessel ;  and  it 
is  remarkably  affected  by  slight  changes  in  temperature  and  pressure.  (The 
rules  for  calculating  changes  in  volume  from  these  causes  will  be  found  in 
the  Appendix.)  Unless  gases  are  confined  within  a  closed  space,  as  in 
caoutchouc  or  bladder,  or  in  a  gas-jar  inverted  on  water  or  mercury,  we  can 
have  no  knowledge  of  their  materiality,  or  of  the  fact  that  they  exclude  other 
bodies  from  the  space  which  they  occupy.  When  secured  in  meuibranes,  they 
manifest  remarkable  elasticity  ;  they  are  easily  compressed  into  a  smaller  bulk, 
but  immediately  resume  their  original  volume  on  the  removal  of  the  pressure. 
They  gravitate,  and  therefore  have  weight ;  but  as  they  are  light  compared 
6 


82  GASES,      INCREASE    OF    VOLUME    BY    TEMPERATURE. 

with  their  bulk,  their  weights  are  generally  given  for  100  cubic  inches  (nearly 
one-third  of  a  gallon).  Owing  to  their  great  elasticity,  their  volume  is 
affected  by  the  height  of  the  column  of  liquid  in  which  they  are  standing,  as 
well  as  by  the  density  of  the  liquid  itself.  Thus  a  gas  admits  of  accurate 
measurement  in  a  graduated  vessel,  only  when  the  liquid  on  the  outside  of  the 
jar  is  precisely  on  a  level  with  the  liquid  on  the  inside.  If  the  level  on  the 
inside  be  higher,  the  gas  is  under  diminished  pressure  from  the  gravitating 
force  of  the  column  of  liquid  ;  and  the  contents  of  the  graduated  jar,  as  read 
off  in  cubic  inches,  appear  greater  than  they  really  are.  If  by  pressing  the 
vessel  downwards,  the  level  on  the  inside  is  below  that  on  the  outside,  the 
gas  is  under  increased  pressure,  and  the  contents  are  less  than  they  appear 
to  be.  The  substitution  of  water  for  mercury  makes  a  considerable  difference 
in  the  volume  of  a  gas.  Fill  a  long  stout  tube  with  mercury,  and  invert  it 
in  a  basin  containing  just  enough  mercury  for  this  purpose.  Allow  two  or 
three  cubic  inches  of  air  to  pass  up  the  tube,  and  then  mark  the  level  of'the 
mercury.  Now  pour  into  the  basin,  water  covered  with  litmus,  or  indigo, 
and  then  raise  the  tube  into  the  colored  water,  so  that  the  mercury  may  flow 
out.  As  it  flows  out,  the  water  takes  its  place,  and  it  will  be  found  when 
the  substitution  is  complete,  that  the  gas  now  has  only  from  one-third  to 
one-half  of  the  volume  which  it  had  when  over  the  mercury.  The  inside 
column  of  mercury  gravitates  with  more  force  than  that  of  water,  and  the 
expansibility  of  the  gas  allows  it  to  occupy  a  larger  space.  Over  water  the 
gas  contracts  nearly  to  its  proper  bulk. 

The  following  experiments  will  illustrate  the  effects  of  atmospheric  pres- 
sure on  the  volume  of  gases.  Tie  securely  a  piece  of  thin  caoutchouc  over 
the  mouth  of  a  wide  short  jar.  Place  it  under  a  receiver  on  the  air-pump 
plate,  and  exhaust  the  vessel.  As  the  pressure  of  the  air  is  removed  from 
the  interior,  that  which  is  contained  in  the  vessel  expands  and  raises  the 
caoutchouc  considerably.  This  phenomenon  disappears  on  letting  the  air 
pass  into  the  receiver. — Adjust  a  small  bladder  with  a  leaden  weight,  so  that 
it  will  just  sink,  in  a  tall  jar  of  water.  Place  this  under  a  receiver,  as  in  the 
preceding  experiment,  and  withdraw  the  air.  The  air  in  the  bladder  expands 
by  removal  of  pressure  from  the  surface  of  the  water,  and  the  bladder  in- 
stantly rises  to  the  surface,  by  reason  of  the  increased  volume  of  its  contents. 
On  letting  in  the  air,  it  again  falls  to  the  bottom  of  the  vessel. — The  effect 
of  heat  may  be  shown  by  various  experiments.  Invert  a  long  tube,  having 
a  thin  bulb,  of  about  three  inches'  diameter,  at  one  end,  the  other,  or  open 
end,  being  immersed  in  a  solution  of  litmus  contained  in  a  bottle.  Heat  the 
bulb  by  a  spirit-lamp  to  expel  some  of  the  air,  wiien,  on  cooling,  the  colored 
liquid  will  rise  to  one-third  or  one-half  the  height  of  the  tube.  This  will 
now  serve  as  a  delicate  air-thermometer.  On  applying  the  warm  hand  to 
the  bulb,  the  increase  in  the  volume  of  air  will  be  at  once  perceptible  by  the 
descent  of  the  colored  liquid  in  the  tube  ;  and  the  contraction  or  diminution 
of  volume  by  cold  may  be  shown  by  pouring  a  little  ether  over  the  bulb. 
The  cold  produced  by  the  evaporation  of  this  liquid,  condenses  the  contained 
air,  and  the  colored  liquid  rises  in  the  tube. — Heated  air,  by  reason  of  the 
increase  of  volume,  is  lighter  than  cold  air.  Balance  on  a  scale-beam  a  thin 
glass  shade  of  some  capacity,  with  the  open  end  downwards.  Place  a  spirit- 
lamp  under  the  shade;  the  increase  in  volume  and  diminution  of  weight  in 
the  heated  air  are  at  once  manifested  by  the  rising  of  the  shade.  Again,  a 
small  bladder  so  balanced  with  lead  as  just  to  sink  in  cold  water,  will,  by 
the  expansion  of  air  in  the  bladder,  rise  to  the  surface  if  placed  in  a  jar  of 
hot  water. 

Pressure  and  temperature,  with  very  slight  limits,  affect  all  gases  equally, 
whether  compound  or  simple,  however  they  may  differ  from  each  other  in 


INCANDESCENCE.  83 

density.  There  is,  however,  a  peculiarity  in  the  expansion  of  gases  by  heat, 
whereby  they  are  distinguished  from  liquids.  The  same  quantity  of  heat  will 
expand  a  gas,  in  an  equal  degree,  at  a  high  and  a  low  temperature  ;  but  with 
liquids  the  expansion  is,  for  the  same  quantity  of  heat,  proportionably  greater 
at  high  than  at  low  temperature. 

It  has  been  ascertained  by  Dalton  and  Gay-Lussac  that  1000  measures  of 
dry  air,  when  heated  from  the  freezing  to  the  boiling  point  of  water,  undergo 
an  increase  in  bulk  about  equal  to  375  parts  ;  so  that  1000  cubic  feet  of  air 
at  32°  become  dilated  to  1375  cubic  feet  at  212°.  Air,  therefore,  at  the 
freezing-point  expands  ^1  o^h  part  of  its  bulk  for  every  added  degree  of  heat 
on  Fahrenheit's  scale  (for  375-f-180  =  2-08,  and  1000^208  =  480).  Hence, 
assuming  that  the  volume  of  air  is  480  cubic  inches,  thus, 

480  cubic  inches,  at  32°,  become 

481  "  at  33°, 

482  «  at  34°,  &e. 

increasing  one  cubic  inch  for  every  degree.  A  contraction  of  one  cubic  inch 
occurs  for  every  degree  below  32°  :  thus, 

480  cubic  inches,  at  32°,  become 
479  "  at  31°, 

478  "  at  30°,  &c. 

The  volume  of  air,  therefore,  at  32°  would  be  doubled  at  480°,  and  tripled 
at  960° :  the  latter  temperature  being  about  that  of  a  dull-red  heat.  Steam, 
and  all  other  vapors,  when  heated  out  of  contact  of  their  respective  fluids, 
are  subject  to  laws  of  expansion  similar  to  those  of  air.  It  may  be  remarked, 
in  regard  to  the  expansion  sustained  by  gases  as  a  result  of  increase  of  tem- 
perature, that,  although  great  in  amount,  the  actual  force  which  is  thus 
exerted  is  small  (when  compared  with  that  of  solids  and  liquids  under  the 
same  circumstances),  in  consequence  of  their  extreme  elasticity :  thus, 
although  the  volume  of  air  (or  of  vapor)  is  about  tripled  by  red  heat,  vessels 
easily  sustain  the  pressure. 

(For  the  determination  of  the  increase  and  decrease  of  volume  as  a  result 
of  changes  of  temperature,  see  Appendix.) 

Incandescence. — If  is  a  remarkable  fact,  that  gases  which  appear  of  such 
an  attenuated  nature,  can,  even  when  brought  almost  to  a  state  of  vacuum, 
be  rendered  incandescent  by  the  high  temperature  of  the  electric  spark.  No 
oxygen  is  present,  therefore  there  can  be  no  combustion.  Hydrogen,  nitro- 
gen, sulphurous  acid,  and  other  gases,  inclosed  in  tubes  through  which  the 
electric  spark  from  Ruhmkorff's  apparatus  is  discharged,  evolve  an  intense 
light  as  the  result  of  incandescence ;  and  this  light  not  only  presents  a 
different  color  for  each  gas  in  its  vacuous  state,  but  it  is  resolvable  into  a 
spectrum  of  colored  bands  of  different  degrees  of  refrangibility.  Thus  when 
pure  hydrogen  is  placed  in  a  tube,  which  is  afterwards  brought  almost  to  a 
state  of  vacuum  by  an  air-pump,  it  is  found  that  under  a  discharge  from  the 
coil,  a  fine  ruby  red  light  is  evolved ;  while  the  nitrogen  vacuum,'  under 
similar  circumstances,  gives  a  magnificent  violet  light  (Miller).  The 
spectra  produced  by  the  lights  of  these  gases  are  singularly  contrasted ; 
while  the  nitrogen  spectrum  includes  rays  of  high  refrangibility,  that  of 
hydrogen  contains  only  rays  of  low  refrangibility,  and  these  have  scarcely 
any  action  on  the  collodio-iodide  of  silver.  Attenuated  gases  thus  heated 
by  the  electric  discharge,  evolve  the  colors  indicated  in  the  subjoined  table : 


84  SPECIFIC    HEAT    OF    GASES. 

Hydrogen,              ruby  red.  Light  carburetted 

Nitrogen,                violet.  hydrogen,           pale  blue. 

^Oxygen,                  greenish-white.  Olefiant  gas,           pale  red. 

Sulphurous  acid,  blue.  Ammonia,              red  and  violet. 
Carbonic  acid,       violet. 

The  compound  gas  ammonia  evolves  the  colors  of  its  constituent  elements. 

Specific  Gravity. — Density. — Gases  and  vapors  vary  in  specific  gravity. 
As  a  general  rule,  the  air  is  taken  as  a  standard,  and  all  gases  are  compared 
with  it  under  similar  circumstances  of  temperature,  pressure,  humidity, 
dryness,  &c.  The  lightest  of  all  gases  is  hydrogen,  which  is  14-4  times 
lighter  than  air.  Among  the  heaviest  is  the  vapor  of  iodine,  which  is,  bulk 
for  bulk,  nearly  9  times  as  heavy  as  air.  The  greater  number  of  simple  and 
compound  gases  are  of  about  the  same  weight  as  air,  or  a  little  heavier. 
(The  rules  for  calculating  the  specific  gravity  of  gases  and  vapors  will  be 
found  in  the  Appendix.)  It  has  been  proposed  to  substitute  hydrogen  as 
a  standard  of  comparison  instead  of  the  atmosphere,  because  it  is  the  lightest 
of  the  gases,  and  it  will  place  the  equivalent  weights  and  specific  gravities 
of  these  bodies,  with  few  exceptions,  in  a  uniform  relation  ;  but  we  do  not 
take  naphtha  as  the  standard  for  the  specific  gravity  of  liquids,  nor  lithium  as 
the  standard  for  solids  ;  and  the  selection  of  air  for  gases,  and  of  water  for 
liquids  and  solids,  has  been  so  confirmed  by  long  use,  that  any  change  would 
be  attended  with  great  inconvenience.  A  volume  of  air  may  be  obtained  for 
the  purpose  of  weighing,  with  much  greater  certainty  than  a  volume  of  pure 
hydrogen,  not  to  mention  that  for  equal  weights  nearly  fifteen  times  as  much 
hydrogen  as  air  must  be  taken  in  one  experiment — thus  increasing  the 
chances  of  error.  Gerhardt  and  others,  who  have  advocated  this  change  to 
suit  an  hypothesis,  have  entirely  forgotten  that  if  the  standard  is  changed  for 
specific  gravity,  it  will  entail  a  change  for  specific  heat,  the  refractive  power 
of  gases,  the  law  of  diffusion,  &c.,  iu  reference  to  which,  air  is  now  uni- 
versally taken  as  a  standard. 

Specific  Heat. — By  this  it  is  to  be  understood  the  proportional  quantity  of 
heat  contained  in  equal  weights  of  different  gases  at  the  same  thermometric 
temperature.  The  absolute  quantity  of  heat  contained  in  two  gases,  as  well 
as  in  two  liquids,  at  the  same  temperature,  is  very  differgnt.  A  thermometer, 
in  fact,  can  only  show  the  relative  quantity  present.  Gases  are  equally 
expanded  or  increased  in  volume  by  equal  additions  of  heat ;  but  unequal 
quantities  of  heat  will  be  required  to  raise  them  to  the  same  degree ;  and 
for  this  reason  unequal  quantities  will  be  given  out  by  them  in  cooling  from 
a  high  to  a  low  temperature. 

When  equal  weights  of  different  gases,  heated  at  212°,  are  passed  slowly 
through  a  glass  tube  immersed  in  cold  water,  the  temperature  of  the  water  is 
raised  while  the  gas  is  cooled.  The  relative  heating  power  of  gases  has 
been  thus  measured  and  tabulated — atmospheric  air  being  taken  as  the 
standard  of  comparison  : — 


ilydrogen    . 

.  12340 

Air       .         .         . 

.  1000 

Olefiant  gas 

.     1576 

Protoxide  of  nitrogen 

.     887 

Carbonic  oxide   . 

.     lOSO 

Oxygen 

.     884 

Kitrogen     . 

.     1031 

Carbonic  acid 

.     828 

These  figures  represent  the  specific  heat  or  the  capacity  for  heat  of  different 
gases.  As  each  compound  gas  has  its  own  speci,fic  heat,  without  reference 
to  the  specific  heats  of  its  constituents,  it  follows  that  this  physical  property 
of  gas€8  may  be  occasionally  applied  to  distinguish  a  gaseous  chemical 
compound  from  a  gaseous  mixture.  It  has  been  thus  applied  to  the  con- 
stituents of  the  atmosphere. 


INFLUENCE    OF    LIGHT,      MAGNETISM.  85 

Light. — Gases  exert  a  refracting  power  on  lip^ht  peculiar  to  each,  and  the 
refractinf^  power  of  a  compound  gas  is  not  equal  to  the  mean  refracting 
powers  of  its  constituents.  Tlie  refracting  powers  of  the  subjoined  gases 
were  determined  by  Biot  and  Arago,  and  are  as  follows : — air  being  the 
standard. 


Hydrogen   . 

6614 

Nitrogen     . 

.     1034 

Ammonia    . 

3168 

Carbonic  acid 

.     1004 

Carburetter!  hydrogen 

2092 

Air     . 

.     1000 

Hydrochloric  acid 

1196 

Oxygen 

.       861 

Hydrogen  has  the  highest  and  oxygen  the  lowest  refracting  power  among 
these  gases. 

Light  like  the  electric  fluid  or  heat,  has  in  some  instances  a  combining 
power  over  gases.  Thus  a  mixture  of  chlorine  and  hydrogen  is  converted 
into  hydrochloric  acid  with  explosion,  when  exposed  to  the  dfirect  rays  of  the 
sun  or  any  intense  light,  as  the  oxyhydrogen  or  lime  light ;  but  more  slowly 
and  gradually  in  diffused  light,  such  as  daylight.  Bunsen  and  Roscoe  have 
ingeniously  made  the  rate  of  combination  a  measure  of  the  intensity  of  light 
for  photometrical  purposes,  and  have  thus  been  able  to  institute  numerous 
comparisons  on  the  relative  intensities  of  artificial  lights  and  the  light  of  the 
sun.  This  combining  power  resides  in  those  rays  of  the  spectrum  which  are 
near  to  the  raoit  refrangible  colors,  the  violet  and  blue  ;  although  not  visible 
in  the  ordinary  spectrum,  they  may  be  made  visible  by  uranium  glass. 
When  exposed  to  the  yellow,  orange,  or  red  rays,  the  two  gases  show  no 
tendency  to  combine.  This  is  in  accordance  with  the  action  of  light  on  the 
salts  of  silver. 

Magnetism. — Faraday  has  discovered  that  there  is  a  difference  among 
gases,  as  to  their  magnetic  properties,  when  secured  in  glass  tubes  and  deli- 
cately suspended  in  the  field  of  a  powerful  artificial  magnet.  Of  the  follow- 
ing gases,  four  were  found  to  be  magnetic,  taking  up  a  north  and  south 
position  (axial)  like  the  common  magnet;  while  three  were  diamagnetic, 
taking  up  a  position  at  right  angles,  or  east  and  west  (equatorial).  In 
measuring  the  intensity  of  this  power,  it  was  found  that  a  vacuum  in  the 
glass  tube  was  0*0,  and  that  oxygen  manifested  the  greatest  magnetic  force. 
The  following  table  represents  the  relative  intensities : — 

.    0.0 


Oxygen 

.  17.5  "1    d                       Carbonic  acid 

Air      . 

.     3.4  ■    o                       Hydrogen  . 

Oledant  gas 

.     0.6   '    W5                      Ammonia  . 
.     0.3  J    a                      Cyanogen  . 

Nitrogen 

A  vacuum,  0.0. 

0.1)    .: 

0.9) 


[The  reader  will  find  in  the  Appendix  a  Table  of  the  principal  gases  and 
vapors  and  their  compounds,  representing  in  a  concise  form  their  combining 
volumes,  atomic  weights,  specific  gravity,  and  the  weight  of  100  cubic 
inches.] 

Diffusion. — Osmosis. — There  is  a  property  oY  gases  which  is  known  under 
the  name  of  diffusion.  This  implies  a  power  by  which  they  intermingle  with 
each  other  in  spite  of  a  difference  in  specific  gravity,  and  when  they  have  no 
tendency  to  combine  chemically,  and  when  this  intermixture  takes  place 
through  membranes  or  porous  partitions  it  is  called  osmosis.  If  we  half  fill 
a  bottle  with  mercury,  and  pour  upon  this,  ether — it  is  well  known  that  the 
two  liquids  do  not  combine  chemically,  and  that  there  is  a  great  difference  in 
their  specific  gravities.  Hence,  it  is  hardly  necessary  to  observe,  that  how- 
ever long  these  liquids  may  be  in  contact  in  a  closed  bottle,  the  mercury  will 
not  rise  into  the  ether,  nor  will  the  ether  descend  into  the  mercury.  Further, 
if  shaken  together  and  thus  mixed,  they  will  in  a  few  minutes  be  completely 


86  DIFFUSION    OF    GASES    AND    VAPORS. 

separated  according  to  their  specific  gravities.  Carbonic  acid  and  hydrogen 
among  gases  have  no  tendency  to  form  a  chemical  union,  and  they  differ  more 
from  each  other  in  specific  gravity  than  mercury  does  from  ether.  Invert  a  jar, 
well-ground,  containing  hydrogen,  on  a  similar  jar  which  it  will  accurately 
fit,  placed  below — containing  carbonic  acid.  After  from  five  to  ten  minutes' 
contact  at  the  ordinary  temperature,  carbonic  acid  will  be  found  in  the 
upper  jar  (by  the  appropriate  test,  lime-water),  and  hydrogen  will  be  found 
in  the  lower  (by  the  application  of  a  lighted  taper  and  the  combustion  of  the 
gas).  If  this  experiment  is  performed  in  bottles,  it  will  be  found  that  the 
two  gases  when  once  mixed  will  never  again  separate.  If  light  hydrogen 
or  coal-gas  be  thus  placed  over  ajar  of  air,  the  light  gas  will  descend,  and 
render  the  air  explosive.  Air  is  one-third  lighter  than  carbonic  acid  ;  air 
will  support  combustion,  and  it  has  no  effect  on  lime-water.  If  a  jar  of  air 
be  placed  over  one  of  carbonic  acid — in  a  few  minutes  the  heavy  carbonic 
acid  will  have  risen  into  the  air,  a  fact  proved  by  lime-water  being  precipi- 
tated white,  and  a  lighted  taper  being  extinguished  in  the  upper  jar.  This 
property  of  gases  applies  also  to  vapors,  and  it  leads  to  a  uniformity  of  mix- 
ture on  contact,  when  there  is  no  tendency  among  them  to  combine  chemi- 
cally. Such  mixtures  are  of  a  physical  nature,  and  their  properties  are  always 
represented  by  the  sum  of  the  properties  of  their  constituents.  During 
mixture,  there  is  no  evolution  or  absorption  of  heat,  and  no  increase  or  con- 
traction of  volume.  The  atmosphere  itself  forms  a  remarkable  example  of  a 
mixture  of  this  kind.  There  are  numerous  facts  in  chemistry  illustrative  of 
this  property.  That  a  gas  like  ammonia,  with  a  specific  gravity  of  O'SST, 
should  rapidly  diffuse  itself,  and  rise  through  the  air  is  not  surprising  ;  but 
it  may  be  proved  to  fall  as  well  as  to  rise,  or,  in  other  words,  to  diffuse 
itself  in  all  directions.  Place  a  long  (stoppered)  shade  with  its  open  end  in 
a  plate.  Suspend  from  the  stopper  long  strips  of  dry  test-paper  for  alkalies, 
e.  g.,  reddened  litmus,  turmeric,  and  rose.  Now  pour  on  the  plate  a  few 
drops  of  a  strong  solution  of  ammonia,  or  open  a  small  jar  containing  am- 
monia beneath,  the  ascent  and  diffusion  of  the  gas  will  be  indicated  by  the 
progressive  change  of  color  in  the  papers  as  it  ascends.  By  another  method 
of  proceeding,  the  diffusion  downwards  may  be  proved.  Place  a  similar  shade 
in  a  clean  plate  containing  slips  of  the  various  test-papers.  Remove  the 
stopper  of  the  shade  and  place  over  it  a  small  jar  containing  a  few  cubic  inches 
of  ammonia.  In  the  course  of  a  few  minutes  the  descent  (or  diffusion)  of  the 
light  alkaline  gas  will  be  indicated  by  a  change  of  color  in  the  papers.  The 
specific  gravity  of  sulphuretted  hydrogen  gas  is  I  17.  A  few  cubic  inches 
of  this  gas  will,  in  spite  of  its  greater  density,  diffuse  itself  in  the  air,  and  be 
perceptible  in  a  few  minutes  in  every  corner  of  a  large  apartment.  The  same 
is  true  of  other  gases  which  are  not  perceptible  to  smell.  The  vapor  of 
ether  is,  perhaps,  more  remarkable  in  this  respect.  Its  specific  gravity  is 
nearly  2  6.  In  spite  of  this  great  density,  the  diffusibility  of  ether  vapor  is 
so  great,  that  on  opening  a  bottle  containing  the  liquid,  the  odor  of  the 
escaping  vapor  will  be  in  a  few  minutes  perceptible  over  a  large  space. 
Even  metallic  vapors,  such  as  that  of  sodium,  are  observed  to  have  this 
diffusible  property.  Bunsen  found  that  a  small  piece  of  sodium  burnt  in  the 
corner  of  a  room  produced  a  vapor  which  was  easily  detected  at  the  most 
distant  part  of  the  room  by  the  coloring  of  an  invisible  jet  of  gas,  and  by 
the  spectrum  obtained  from  this  light  (p.  22.)  The  great  natural  result  of 
this  property,  is  to  equalize  mixtures  of  gases  and  vapors,  and,  in  open  spaces 
to  prevent  an  accumulation  of  foul  efiQuvia  in  the  air. 

It  must  not  be  supposed,  however,  that  specific  gravity  has  no  influence 
on  diffusion.  On  the  contrary — the  heavy  carbonic  acid  escapes  slowly  by 
diffusion  from  a  narrow  jar  placed  with  its  mouth  upwards,  while  the  light 


DIFFUSION    OF    GASES    AND    VAPORS.  8T 

hydrogen  also  escapes  slowly  from  a  similar  jar  placed  with  its  mouth  down- 
wards. 

A  curious  fact  regarding  this  property,  however,  is,  that  it  is  manifested 
not  only  when  the  sole  communication  between  the  two  gases  is  by  a  narrow 
tube,  but  when  they  are  separated  by  porous  partitions,  such  as  dry  plaster, 
nnglazed  porcelain,  animal  membrane,  caoutchouc,  cork,  or  spongy  platinum. 
To  this  mode  of  diffusion  the  term  osmosis  is  applied,  from  a  Greek  word  sig- 
nifying "to  push  through,"  and  the  terms  endosmosis  and  exosmosis  were 
applied  to  those  cases  respectively  in  which  the  gas  penetrated  into  or  passed 
out  of  the  vessel  through  the  porous  septum.  Dobereiner  first  observed  the 
readiness  with  which  hydrogen  escaped  through  a  small  crack  or  fissure  in  a 
glass  jar  which  had  been  filled  with  the  gas.  The  water  rose  three  inches  in 
a  jar  from  which  the  gas  had  thus  escaped,  clearly  proving  that  the  hydrogen 
had  not  been  replaced  by  an  equal  quantity  of  air  passing  into  the  jar.  Ac- 
cording to  Longet,  hydrogen  will  traverse  a  sheet  of  writing  paper  or  even 
gold  leaf.     It  traverses  nnglazed  porcelain  with  great  rapidity. 

Mr.  Graham,  on  examining  Dobereiner's  results,  observed  that  while  the 
hydrogen  escaped  outwards,  a  portion  of  air,  amounting  to  between  one- 
fourth  and  one-fifth  of  the  lost  hydrogen,  penetrated  inwards;  in  fact,  that  a 
volume  of  air  was  not  replaced  by  a  volume  of  hydrogen,  but  by  3.83  volumes. 
He  also  found  that  every  gas  had  what  he  calls  a  diffusion-volume  peculiar 
to  itself,  representing  the  amount  in  which  it  was  exchanged  for  a  volume  of 
air — air  being  considered  =  l  or  unity.  The  diffusion-volume  was  further 
found  to  depend  on  the  sp.  gr.  of  the  gas.  Of  gases  lighter  than  air,  the 
diffusion-volume  is  greater  than  1 ;  of  those  which  are  heavier,  it  is  less  than 
1.  As  a  general  law  it  may  be  stated  that  the  diffusion-volumes  of  gases,  or 
the  volumes  in  which  they  replace  each  other,  are  inversely  as.  the  square 
roots  of  their  densities.  The  following  table  represents  the  diffusion-volume 
or  the  velocity  of  diffusion  among  different  gases  : — 

Hydrogen  .         .         .  .3.83 

Light  carb.  hyd.  (CH2)  .     1.34 

Carbonic  oxide  .         .  .1.01 

Nitrogen     .         .         .  .1.01 

Olefiant  gas        .         .  .     1.02 

An  experiment  illustrative  of  the  rapid  diffusion  and  osmosis  of  gases,  may 
be  performed  with  hydrogen.  Fill  a  wide-mouthed  jar  with  pure  hydrogen, 
and  secure  the  mouth  (placed  downwards)  with  a  piece  of  thin  sheet  caout- 
chouc. Then  place  the  jar,  mouth  upwards,  under  a  bell-glass  of  air  immerged 
in  water.  The  rapid  diffusion  and  osmosis  of  hydrogen  will  be  indicated  by 
the  caoutchouc  cover  being  gradually  depressed,  and  after  a  time  it  will 
burst.  This  is  owing  to  the  place  of  the  hydrogen  not  being  supplied  with 
sufficient  rapidity  by  the  passage  of  air.  If  a  similar  jar  is  filled  with  air 
and  placed  in  a  bell-glass  of  hydrogen,  the  caoutchouc  will  rise  up  in  a  con- 
vex form,  and  become  so  distended  that  it  will  finally  burst,  thus  showing  that 
the  gaseous  contents  of  the  jar  have  greatly  increased  by  the  rapid  osmosis 
of  hydrogen.  A  layer  of  animal  membrane  (bladder)  may  be  substituted 
for  caoutchouc  with  similar  results. 

The  fact  that  gases  will  thus  traverse  membranes  which  would  be  imper- 
vious to  them  without  rupture  under  direct  piifesure,  has  an  important  bear- 
ing on  numerous  chemical  and  physiological  phenomena.  The  function  of 
respiration  is  partly  dependent  on  the  exchange  of  gases  by  osmosis.  The 
oxygen  of  the  air  is  taken  into  the  lungs  in  all  warm-blooded  animals,  pene- 
trates the  tine  pulmonary  membrane,  as  well  as  the  thin  coats  of  the  capil- 
laries ;  and  it  there  excludes  the  carbonic  acid  of  the  venous  blood.  Besides 


Oxygen 

.     0.94 

Sulpli.  hyd.  (HS)       . 

.     0.95 

Protoxide  of  nit.  (NO) 

.     0.82 

Carbonic  acid     . 

.     0.81 

Sulphurous  acid 

.     0.68 

88       .  DIFFUSION    OF    GASES    AND    VAPORS. 

carbonic  acid,  aqueous  vapor  containing  animal  matter  is  also  largely  elimi- 
nated. Hence  the  cliief  phenomena  of  respiration  are  due  to  an  endosmose 
of  oxygen  and  exosmose  of  carbonic  acid,  which  takes  its  place.  Carbonic 
acid  has  been  found  to  escape  from  blood  which  was  drawn  from  a  vein  into 
a  vessel  containing  hydrogen  ;  thus  proving  that  the  blood  contains  carbonic 
acid  in  a  free  state,  and  that  it  is  not  produced  by  the  combination  of  oxygen 
with  carbon  in  the  blood  circulating  through  the  lungs. 

Gases  and  vapors  which  admit  easily  of  detection  by  chemical  tests  may 
be  proved  to  traverse  membranes  with  great  rapidity.  If  a  wide-mouthed 
bottle  is  filled  with  sulphuretted  hydrogen  gas,  and  the  mouth  is  completely 
closed  by  a  layer  of  bladder  tied  tightly  over  it,  it  will  be  found,  by  the 
application  of  paper  impregnated  with  a  solution  of  a  salt  of  lead,  that  the  gas 
rapidly  escapes  through  the  bladder.     The  paper  is  turned  brown. 

If  into  a  similar  vessel  a  small  quantity  of  prussic  acid  is  put,  and  the 
mouth  is  secured  with  bladder,  the  rapid  escape  of  the  volatile  acid  vapor 
will  be  indicated  by  inverting  on  the  bladder  a  watch-glass  containing  a  drop 
of  a  solution  of  nitrate  of  silver.  The  solution  is  whitened  in  a  few  minutes, 
and  crystals  of  the  cyanide  of  silver  will  be  found  in  the  watch-glass.  A 
practical  application  of  the  property  of  osmosis  of  gases,  has  lately  been  made 
by  Mr.  Ansell,  of  the  Royal  Mint.  Light  carbnretted  hydrogen,  the  explo- 
sive gas  of  coal  mines,  comes  next  to  hydrogen  in  diffusive  power.  Thus,  as 
it  will  be  seen  by  the  table,  every  100  volumes  of  air  will  be  replaced  by  164 
volumes  of  this  gaseous  compound.  A  bladder  containing  air  placed  in  light 
carburetted  hydrogen  gas,  will  rapidly  become  distended.  Mr.  Ansell  has 
contrived  an  instrument  to  give  warning  of  danger  from  explosions,  based 
on  this  osmotic  power  of  the  gas.  He  says  :  "  For  the  purpose  of  indicating 
by  signal,  I  use  a  balloon  of  thin  India-rubber,  with  its  neck  tied  tightly  with 
silk,  and  a  piece  of  linen  is  bound  around  the  equator  of  the  balloon  to  pre- 
vent expansion.  The  balloon  is  placed  under  a  small  lever,  upon  a  stand  of 
wood,  so  as  to  exert  a  gentle  pressure  upon  the  lever.  If  any  gas  accumu- 
lates around  the  balloon,  the  lever  is  pressed,  and,  raising  it,  relieves  a  detent, 
by  which  the  poles  of  a  battery  are  connected,  and  we  thus  get  telegraphic 
communication."  "  It  may  be  so  delicately  set,"  says  the  author,  "  as  to  give 
warning  if  the  mixture  be  still  below  the  explosive  point."  An  ingenious 
piece  of  apparatus  for  showing  the  relative  osmotic  power  of  gases  has  also 
been  invented  by  this  gentleman.  It  consists  of  a  glass  vessel,  with  a  porous 
earthenware  cover  joined  to  it  in  an  air-tight  manner.  This  vessel  forms  the 
air-chamber.  At  the  lower  part  it  is  connected  with  a  thermometer  tube, 
which  bends  upwards,  and  is  fastened  to  a  scale.  Mercury  is  introduced  into 
this  tube  so  as  to  lie  at  the  lower  level  of  the  glass  air  vessel,  and  to  rise  to 
a  certain  height  on  the  thermometer  tube  where  it  marks  a  zero.  If  ajar, 
containing  light  carburetted  hydrogen  is  now  inverted  and  placed  over  the 
porous  glass  vessel,  care  being  taken  that  the  earthenware  septum  is  not 
wetted,  the  osmotic  force  of  the  gas  is  immediately  manifested  by  the  rapid 
rise  of  the  mercurial  column  in  the  thermometer  tube.  This  proves  that  the 
light  carburetted  hydrogen  penetrates  the  air-chamber  much  more  rapidly 
than  the  air  passes  out.  A  rise  of  several  inches  thus  takes  place  in  a  few 
minutes.  A  small  percentage  of  the  explosive  gas  has  been  found  to  be 
sufficient  to  affect  the  column^  mercury  sensibly.  If  in  place  of  this  gas, 
carbonic  acid  is  placed  over  tM  air  chamber,  a  portion  of  the  air  contained 
in  it  passes  out  with  greater  rapidity  than  the  carbonic  acid  passes  in,  and 
the  mercurial  column  is  depressed.  On  the  removal  of  the  gas-jar,  the  mer- 
cury slowly  falls  to  its  level  by  the  whole  of  the  gas  which  had  entered  pass- 
ing oBF  through  the  porous  septum;  after  some  hours,  there  is  nothing  but 
air  in  the  glass  vessel. 


PENETRATION    OF    METALS    BY    GASES.  89 

In  some  further  researches  on  the  property  of  gases,  Mr.  Graham  has  made 
the  discovery  tliat  mixed  gases,  as  atmospheric  air,  for  instance,  do  not  tra- 
verse septa  of  caoutchouc  in  the  exact  proportions  in  which  their  constituents 
are  known  to  exist.  Thus  he  found  that  if  one  side  of  the  rubber  film  was 
freely  exposed  to  the  atmosphere,  while  the  other  side  was  under  the  influ- 
ence of  a  vacuum,  oxygen  and  nitrogen  traversed  the  septum  but  in  very 
different  proportions  from  those  constituting  the  atmosphere.  Instead  of  21 
per  cent.,  the  oxygen  formed  41.6  per  cent.,  so  that  the  rubber  film  kept 
back  one-half  of  the  nitrogen,  and  allowed  the  other  half  to  pass  through  with 
all  the  oxygen.  The  air  was  thus  dialyzed,  and  its  constituents  separated  by 
the  rubber.  Its  properties  were  also  changed.  It  kindled  into  flame,  ignited 
wood,  and,  in  reference  to  combination,  had  all  the  properties  of  a  mixture 
intermediate  between  air  and  pure  oxygen.     {Proc.  R.  S.  1866.) 

Mr.  Graham's  view  is  that  the  gases  are  liquefied  on  the  surface  of  the 
rubber  or  membrane ;  they  thus  penetrate  its  substance  as  ether  or  naphtha 
would  if  placed  in  contact  with  it,  and  they  again  evaporate  into  a  vacuum, 
and  appear  as  gases  on  the  other  side.  The  results  show  that  gases  are 
unequally  absorbed  and  condensed  under  these  circumstances;  oxygen  twenty- 
four  times  more  abundantly  than  nitrogen,  and  that  they  penetrate  the  rubber 
in  the  same  proportion. 

Penetration  of  Metals  hy  Gases — MM.  St.  Clair  Deville  and  Troost 
found  that  hydrogen  would  even  penetrate  red  hot  platinum  and  iron,  and  it 
has  been  suggested  in  this  case  that  hydrogen  as  a  metallic  vapor  is  liquefied 
and  absorbed  by  the  heated  metal,  and  again  escapes  on  the  other  side.  Mr. 
Graham  /ound  that  platinum  in  the  form  of  wire  or  foil  at  a  low  red  heat 
would  take  up  and  hold  3.8  volumes  of  hydrogen  measured  cold;  but  it  is 
by  palladium  that  the  property  in  question  appears  to  be  possessed  in  the 
highest  degree.  Palladium  foil  from  the  hammered  metal  condensed  as  much 
as  643  times  its  volume  of  hydrogen,  at  a  temperature  under  212°.  The 
same  metal  had  not  the  slightest  absorbent  power  for  either  oxygen  or  nitro- 
gen. Hence  a  peculiar  dialytic  action  may  reside  in  certain  metallic  septa 
which  may  enable  them  to  separate  hydrogen  from  other  gases.  According 
to  this  gentleman,  platinum  in  the  form  of  sponge  will  absorb  1-48  times  its 
volume  of  hydrogen,  and  palladium  as  much  as  90  volumes.  In  the  state  of 
platinum  black,  the  metal  absorbs  several  hundred  volumes  of  hydrogen. 
Carbonic  oxide  is  taken  up  more  largely  than  hydrogen  by  soft  iron,  and  this 
absorption  at  a  low  red  heat  is  considered  to  be  the  first  and  necessary  stage 
in  the  conversion  of  iron  into  steel.  The  carbonic  oxide  gives  up  half  of  its 
carbon  to  the  iron  when  the  temperature  is  afterwards  raised  to  a  consider- 
ably higher  degree.  While  heated  platinum  absorbs  hydrogen,  silver  appears 
to  have  a  strong  absorbent  power  over  oxygen.  It  has  been  long  known  that 
it  gives  off  oxygen  in  the  act  of  solidifying  from  the  melted  state,  and  gene- 
rally in  a  sudden  jet,  so  as  to  produce  some  irregularity  on  the  surface  of  the 
button.  Mr.  Graham  found  that  the  sponge  of  silver  fritted  but  not  fused, 
held  in  one  case  as  much  as  7*49  volumes  of  oxygen. 

The  first  of  the  metalloids  which  will  require  consideration  is  Oxygen. 


OXYGEN.      PREPARATION, 


CHAPTER    YI. 

OXYGEN— (0=8)— OXIDES— OXIDATION. 

History. — Oxygen,  one  of  tlie  six  permanent  gases,  was  discovered  by 
Priestley  in  the  year  1174.  He  obtained  it  by  heating  the  red  oxide  of 
mercury.  He  called  it  dephlogisticated  air  ;  it  was  termed  empyreal  air  by 
Scheele,  and  vital  air  by  Condorcet.  The  name  oxygen  was  given  to  it  by 
Lavoisier,  from  its  tendency  to  form  acid  compounds  (6|i;?,  acid,  and  y^wdoi, 
to  generate).  It  is  more  abundantly  diffused  throughout  nature  than  any  of 
the  other  elementary  bodies;  it  forms  eight-ninths  of  the  weight  of  water, 
one-fifth  of  the  bulk  of  the  atmosphere,  and  a  large  proportion  of  the 
mineral  bodies  of  which  tbe  crust  of  the  globe  is  composed.  Oxygen  is  a 
constituent  of  a  large  class  of  acids — the  oxacids,  which  are  solid,  liquid,  and 
gaseous  compounds.  It  is  a  constituent  of  all  the  alkalies,  excepting  am- 
monia, and  of  the  alkaline  earths ;  and  it  enters  largely  into  the  composition 
of  numerous  organic  substances  belonging  to  the  animal  and  vegetable 
kingdoms. 

Preparation. — This  gas  may  be  readily  procured  by  heating  in  an  ordinary 
retort,  by  means  of  a  spirit-lamp,  a  mixture  of  equal  parts  of  finely-powdered 
peroxide  of  manganese,  previously  well  dried,  and  of  chlorate  of  potash.  The 
oxygen  is  entirely  derived  from  the  decomposition  of  the  chlorate,  which  is 
converted  into  chloride  of  potassium  (KO,CI05=KCl-f08).  The  gas  may 
be  collected  in  the  usual  way  over  water  or  mercury.  As  it  is  thus  procured, 
it  generally  contains  traces  of  chlorine,  which  may  be  separated  by  passing 
the  gas,  during  its  collection,  through  a  wash-bottle  containing  a  solution  of 
potash,  or  by  allowing  the  gas  to  remain  for  a  short  time  in  contact  with 
water.  One  hundred  grains  of  the  chlorate  will  yield  thirty-eight  grains,  == 
about  113  cubic  inches  of  oxygen  ;  or  one  ounce  will  yield  nearly  two  gal- 
lons of  the  gas.  This  is  in  the  proportion  of  about  twenty-eight  gallons  of 
gas  to  one  pound  of  the  salt.  A  mixture  in  fine  powder,  of  ten  parts  by 
weight  of  chlorate  of  potash  with  one  part  of  sesquioxide  of  iron,  has  been 
recommended  by  Mr.  Ashby  as  superior  to  the  mixture  with  manganese,  in 
the  facility  with  which  oxygen  is  disengaged,  and  the  great  economy  of  heat. 
Every  grain  of  this  mixture  yields  a  cubic  inch  of  the  gas.  The  result  of 
our  experiments  with  the  mixture  is,  that  the  oxygen  is  liberated  too  suddenly 
and  rapidly. 

Oxygen  may  also  be  procured  by  heating  the  chlorate  of  potash  sepa- 
rately :  but  this  process  requires  a  much  higher  temperature,  and  the  employ- 
ment of  a  retort  or  tube  which  will  not  readily  fuse.  This  is,  however,  the 
only  method  of  procuring  the  gas  absolutely  pure  for  chemical  purposes  ;  it 
should  then  be  collected  over  a  mercurial  bath. 

^^ygsn  is  obtained  on  the  large  scale  by  gradually  heating  to  full  redness 
in  a  wrought-iron  bottle  the  black  oxide  of  manganese  reduced  to  a  coarse 
powder.  The  bottle  should  be  filled  to  not  more  than  two-thirds  of  its  capa- 
city, and  the  heat  gradually  applied.  In  the  first  stage  of  the  operation, 
aqueous  vapor  and  carbonic  acid  escape;  when  an  ignited  match  is  kindled 
into  a  bright  flame  at  the  mouth  of  the  tube  connected  with  the  bottle,  the 
gas  may  be  collected.     The  chemical  changes  which  ensue  are  of  a  simple 


PROCESSES    FOR    PROCURING    OXYGEN.  91 

kind  (3MnO^=Mn30^-f-Oa).  The  oxide  of  manganese,  at  a  full  red  beat, 
parts  with  one-third  of  its  oxygen.  Mitscherlich  states  that  three  pounds  will 
yield  a  cubic  foot  (six  gallons)  of  oxygen  ;  while  Dr.  Miller  assigns  five  gal- 
lons as  the  quantity  obtained  from  one  pound.  This  difiference  probably 
depends  on  the  impurities  contained  in  the  native  oxide.  Among  these  is 
carbonate  of  lime,  which  contaminates  with  carbonic  acid,  the  oxygen  obtained 
from  manganese.  The  carbonate  may  be  removed  by  previously  washing  the 
mineral  with  diluted  hydrochloric  acid  ;  and  if  it  is  subsequently  dried  before 
use,  oxygen  will  be  obtained  from  it  in  a  much  purer  form.  Another  method 
consists  in  mixing  the  peroxide  with  sulphuric  acid  in  such  proportions  as  to 
beoftheconsistencyofcream,  and  heating  the  mixture,  when  oxygen  is  evolved 
(Mn024-S03=MnO,S03+0)  ;  but  there  are  some  inconveniences  attending 
this  process.  The  bichromate  of  potash  heated  with  an  excess  of  sulphuric 
acid  also  yields  this  gas  (KO,2Cr03+5(HO,SO,)=KO,HO,2S03+Cr,03 
3SO3  +  HO  +  O3),  one-half  of  the  oxygen  contained  in  the  chromic  acid 
being  evolved  in  this  decomposition.  A  mixture  named  oxygenriesis  has 
been  lately  much  used  for  the  extemporaneous  production  of  oxygen.  It 
consists  of  equivalent  proportions  of  peroxide  of  -barium  and  bichromate 
of  potash.  Diluted  sulphuric  acid  is  added  and  heat  is  applied  ;  oxygen  is 
liberated,  and  may  be  collected  from  a  retort  in  t^e  usual  way.  The  reac- 
tion of  the  acid  on  the  bichromate  is  as  above  represented,  and  on  peroxide 
of  barium  as  follows  :  BaO,  +  S03=BaO,S03+0.  The  oxygen  from  the 
bichromates  comes  off  as  ozone  and  from  the  peroxide  as  antozone.  If  hydro- 
chloric acid  is  used,  some  chlorine  is  evolved.  Oxygen  may  be  procured 
from  the  red  oxide  of  mercury  by  heating  it  to  redness  in  a  retort 
(HgO  =  0  +  Hg).  This  is  an  expensive  method  of  procuring  the  gas,  and  it 
is  now  seldom  resorted  to ;  but  it  has  an  interest  to  the  chemist  from  its  having 
been  the  compound  in  which  this  important  element  was  first  discovered  by 
Dr.  Priestley. 

Among  recent  processes  for  procuring  oxygen,  two  are  deserving  of  notice. 

1.  The  first  depends  on  the  production  and  decomposition  of  the  peroxide 
of  barium.  The  peroxide  is  procured  by  passing  a  current  of  air,  deprived  of 
carbonic  acid,  over  baryta  heated  to  low  redness  in  a  porcelain  tube.  If  the 
air  is  not  too  dry,  oxygen  is  absorbed  by  the  baryta  at  a  low  red  heat,  and 
the  barium  becomes  peroxidized.  The  presence  of  a  small  quantity  of  aque- 
ous vapor  in  the  air  is  found  to  be  absolutely  necessary  to  this  absorption. 
When  the  peroxidation  is  completed,  the  current  of  air  is  cut  off,  the  tube  is 
heated  to  full  redness,  and  at  this  high  temperature  the  peroxide  is  resolved 
into  oxygen  and  protoxide,  or  baryta.  The  oxygen  may  be  collected,  and 
the  baryta  again  peroxidized  for  a  fresh  supply.  According  to  Boussingault, 
a  pound  of  baryta  will  thus  yield  about  nine  gallons  of  oxygen  gas.  The 
baryta  itself  remains  unchanged  during  the  process.  This  is  the  only  method 
at  present  known  by  which  pure  oxygen,  in  the  gaseous  state,  can  be  readily 
procured  from  the  atmosphere.  2d.  Oxygen  has  been  obtained  by  causing 
the  vapor  of  boiling  sulphuric  acid  to  pass  through  a  porcelain  tube  heated 
to  full  redness.  The  retort  containing  the  sulphuric  acid  is  filled  with  pieces 
of  pumice  previously  heated  with  the  acid  to  drive  off  any  chlorides,  and  the 
porcelain  tube  contains  the  same  material.  At  a  full  red  heat,  the  products 
obtained  are  oxygen,  aqueous  vapor,  and  sulphurous  acid  (S03,H0=0  + 
HO-fSOa).  The  sulphurous  acid  is  removed  by  water  or  by  a  solution  of 
carbonate  of  soda,  through  which  the  gaseous  products  are  passed.  Two 
useful  salts  of  soda  are  thus  procured — 1,  the  sulphite  employed  in  the  manu- 
facture of  hyposulphite ;  and  2,  bisulphite  of  soda,  a  salt  now  much  used  in 
chemistry  and  the  arts  for  the  removal  of  chlorine.  This  process  has  been 
carried  out  on  a  large  scale  by  MM.  St.  Clair- Deville  and  Debray,  and  it  is 


92  *"  PHYSICAL    PROPERTIES    OF    OXYGEN. 

stated,  with  satisfactory  results  (Journal  de  Cliimie,  Mai,  1861).  M.  de 
Luca,  of  Pisa,  agrees  with  these  chemists  in  considering  that  this  is  the  most 
economical  process  for  obtaining  oxygen  on  a  large  scale.  From  a  fluid 
ounce  of  sulphuric  acid  M.  de  Luca  states  that  he  procured  360  cubic  inches 
of  oxygen.  On  the  large  scale,  vessels  of  platinum  must  be  used  {Cosmos, 
July,  1861,  p.  97). 

Properties. — Oxygen  gas  is  insipid,  colorless,  and  inodorous;  it  is  perma- 
nently elastic  under  all  known  pressures  and  temperatures.  Its  specific 
gravity  compared  with  air,  is  as  1-1057  to  1*000.  Compared  with  hydrogen, 
its  specific  gravity  is  =16,  hydrogen  being  =1.  At  mean  temperature  and 
pressure,  100  cubic  inches  weigh  34  24  grains  (Dumas  and  Boussingault). 
Its  refractive  power,  in  regard  to  light,  is  less  than  that  of  any  of  the  gases ; 
compared  in  this  respect  with  atmospheric  air,  it  is  as  0830  to  1000. 
According  to  De  la  Roche  and  Berard,  its  specific  heat,  compared  with  an 
equal  volume  of  air,  is  =  0  9765,  and  with  an  equal  weight  of  air,  =  0*8848, 
that  of  air  being  =1  000.  According  to  Tyndall,  it  has,  in  reference  to 
heat,  a  lower  absorbing  and  radiating  power  than  other  gases.  Faraday's 
researches  have  shown  that  it  is  most  magnetic  of  all  gases,  its  magnetic  force 
comparedwiththatof  the  atmosphere  being  as  17 '5  to  3  4,  a  vacuum  being  taken 
as  0,  or  the  boundary  betvfeen  magnetic  and  diamagnetic  gases  (see. page  85.) 
It  occupies,  among  gases,  the  place  which  iron  holds  among  metals,  and,  as 
with  iron,  its  magnetic  force  is  destroyed  by  a  high  temperature ;  but  it 
returns  on  cooling.  The  magnetic  properties  of  the  atmosphere  are  almost 
exclusively  due  to  the  oxygen  contained  in  it,  and  Faraday  has  suggested  that 
the  diurnal  variations  of  the  needle  may  be  referable  to  the  increase  or 
decrease  of  the  magnetic  force  in  the  oxygen  of  the  atmosphere  as  a  result 
of  solar  heat.  Oxygen  is  evolved  by  electrolytic  action  at  the  positive 
electrode  or  anode,  and  occupies  a  high  position  among  electro-negative 
bodies  or  anions  {see  page  60). 

It  is  dissolved  by  water,  but  only  in  small  proportion.  At  60°  100  cubic 
inches  of  water  will  dissolve  3  cubic  inches  of  the  gas,  and  at  32°,  about  4 
cubic  inches.  All  terrestrial  waters  hold  it  dissolved  in  much  larger  pro- 
portion than  it  exists  in  the  atmosphere-;  and  in  this  condition  as  a  solution 
of  oxygen,  it  is  fitted  for  the  respiration  of  fish,  the  blood  of  these  animals, 
in  circulating  through  the  gills,  being  aerated  by  the  free  oxygen  dissolved 
in  the  w^ater.  Oxygen  in  its  pure  state  is  neither  acid  nor  alkaline.  It  is  a 
perfectly  neutral  gas  ;  it  does  not  alter  the  color  of  blue  or  red  litmus,  and 
shows  no  tendency  to  combine  with  acids  or  alkalies. 

Oxygen  eminently  supports  combustion.  A  lighted  wax  taper  introduced 
into  this  gas  is  rapidly  consumed,  with  enlargement  of  the  flame  and  the 
production  of  an  intense  white  light.  The  wax  itself  in  a  melted  state,  burns 
in  the  gas  as  well  as  the  wick.  If  a  piece  of  wax  taper  three  or  four 
inches  long,  be  lighted  and  introduced  into  ajar  of  oxygen,  with  the  lighted 
end  downward,  it  is  speedily  consumed,  and  the  melted  wax  burns  brightly 
as  it  falls  in  drops  through  the  gas.  A  taper  (of  green  wax)  with  a  glowing 
wick,  (of  which  the  flame  has  been  extinguished) — a  slip  of  wood  with  the 
end  ignited,  but  not  burning  with  flame,  or  a  slip  of  paper  soaked  in  a 
solution  of  nitrate  of  potash,  dried  and  ignited — will  instantly  burst  into 
flame  when  plunged  into  this  gas.  If  the  oxygen  is  pure,  the  wax  taper  or 
wood  may  be  thus  rekindled  into  flame  five  or  six  tinies  successively.  Tow 
saturated  with  ether  or  sulphide  of  carbon,  and  attached  to  the  end  of  a 
copper  wire,  if  inflamed  and  plunged  into  this  gas,  burns  with  surprising 
intensity,  filling  the  jar  with  a  large  volume  of  flame  In  most  of  these 
experiments  water  (HO)  and  carbonic  acid  (CO J  are  the  products  of  com- 


COMBUSTION    OF    CHARCOAL,    SULPHUR,   AND    PHOSPHORUS.      93 

bustion,  by  reasons  of  the  oxygen  uniting  with  the  hydrogen  and  carbon  of 
the  various  combustibles. 

Charcoal  heated  to  redness  and  introduced  into  a  vessel  of  oxygen  will 
glow  more  intensely  but  be  consumed  without  flame.  The  whole  of  the 
oxygen  will  be  removed  and  converted  into  carbonic  acid  gas,  occupying  an 
equal  volume  but  possessed  of  widely  different  properties.  If  charcoal-bark 
is  substituted  for  charcoal,  in  this  experiment,  it  will  be  consumed  with 
bright  scintillations  traversing  the  vessel  of  oxygen  in  all  directions.  Sulphur, 
which  burns  in  the  air  with  a  small  blue  flame,  has  the  flame  enlarged  when 
it  is  immersed  in  ajar  of  oxygen,  and  after  a  time  it  burns  with  a  beautiful 
purple  color,  dissolving  as  it  were  in  the  oxygen,  and  converting  it  into 
sulphurous  acid  gas  (SOJ,  which  is  soluble  in  water.  If,  in  this  experiment, 
the  bell-glass  of  oxygen  be  placed  in  a  white  plate  containing  a  diluted 
solution  of  blue  litmus,  the  neutrality  of  oxygen  will  be  indicated  in  the 
first  instance  by  the  blue  color  being  unchanged  ;  and  the  production  of  an 
acid  by  the  burning  of  sulphur,  will  be  demonstrated  by  the  blue  liquid  being 
reddened  as  the  sulphurous  acid  gas  is  dissolved.  Sulphuric  acid  is  not 
produced  in  this  experiment.  Phosphorus  burns  with  a  bright  yellowish- 
white  light  in  the  atmosphere  ;  but  when  kindled  by  a  heated  wire  and 
introduced  into  oxygen,  or  when  kindled  in  the  gas  after  its  introduction, 
it  will  burn  with  a  still  brighter  light,  gradually  increasing  to  a  dazzling 
whiteness.  If  the  piece  be  sufficiently  large,  the  phosphorus  after  a  time 
will  boil,  its  vapor  will  be  diffused  over  the  whole  bell-glass,  and  burn  with 
equal  intensity  in  every  part.  The  vessel  will  become  an  apparently  isolated 
source  of  the  brightest  light  The  heat  is  so  great,  that  the  vessel  is 
frequently  broken  in  this  experiment.  The  yroduct  of  combustion  in  this 
case  is  solid  phosphoric  acid  (POs),  the  highest  degree  of  oxidation  of 
phosphorus.  The  acid  is  seen  in  dense  white  vapors  which  readily  dissolve 
in  water,  and  produce  a  strongly  acid  liquid  ;  a  fact  which  may  be  proved  by 
placing  a  solution  of  blue  litmus  in  the  plate,  as  in  the  preceding  experiment. 
The  production  of  acids  by  the  union  of  oxygen  with  carbon  in  any  form, 
with  sulphur  and  phosphorus,  led  Lavoisier  not  only  to  give  the  name  of 
oxygen  to  this  body,  but  induced  hira  to  adopt  the  hypothesis  that  the 
acidity  of  compounds  always  depended  on  the  presence  of  oxygen.  But 
oxygen  may  produce  alkalies  as  well  as  acids.  If  potassium  or  sodium  is 
heated  until  it  becomes  ignited,  and  it  is  then  introduced  into  the  gas,  it  is 
consumed  with  a  brilliant  combustion,  and  the  product  is  an  alkaline  solid, 
namely,  peroxide  of  potassium  (KOJ,  in  the  case  of  potassium,  and  ses- 
quioxide  of  sodium  (Naj^Og)  in  the  case  of  sodium.  If  the  experiment  is 
performed  in  a  bell-glass  standing  in  a  white  plate,  in  which  there  is  a 
solution  of  litmus  reddened  by  the  product  of  burning  phosphorus,  the 
formation  of  an  alkaline  compound,  as  a  result  of  the  combination  of 
oxygen  with  these  metals,  will  be  proved  by  the  blue  color  of  the  litmus 
being  restored. 

Although  the  views  of  Lavoisier  respecting  the  acidifying  properties  of 
oxygen  have  been  proved  to  be  incorrect,  there  is  no  non-metallic  body  with 
which  the  production  of  acid  properties  in  compounds  appears  to  be  more 
strongly  associated  than  with  oxygen.  If  a  metal  combines  in  various 
proportions  with  this  element,  the  first  oxide  may  show  no  acid  properties, 
but  act  as  a  base  (^.  e.,  it  will  combine  with  acids)  ;  but  the  other  oxides  are 
often  observed  to  acquire  acid  properties  in  proportion  to  the  amount  of 
oxygen  which  unites  to  the  metal.  This  is  well  illustrated  in  the  oxygen 
compounds  of  the  metal  manganese  {see  page  96).  Among  the  common 
vegetable  acids  it  is  noticed  as  a  general  rule,  that  the  number  of  atoms  of 
oxygen  is  in  excess  of  those  required  to  produce  water  with  the  hydrogen. 


94  OXACIDS.      THEIR    CONSTITUTION. 

Among  inorganic  or  mineral  compounds,  the  oxygen  acids  or  oxacids  are 
numerous  as  a  class.  The  hyponitrous,  phosphorous,  and  arsenious  acids, 
as  well  as  the  sulphuric,  chromic,  boracic,  and  silicic,  contain  three  atoms  of 
oxygen  ;  while  the  nitric,  chloric,  bromic,  iodic,  phosphoric,  arsenic,  and 
antimonic  acids  contain  five  atoms  of  oxygen.  Some  acids  contain  only  two 
atoms,  as  the  carbonic  and  sulphurous  acids,  while  others  contain  only  one, 
as  the  cyanic.  As  oxacids  for  the  most  part  contain  an  atom  of  water,  and 
in  the  absence  of  water,  they  manifest  no  acidity,  it  has  been  supposed  that 
the  oxygen  of  the  water  was  really  a  necessary  component  of  the  acid,  and 
that  hydrogen  was  the  acidifying  principle  {see  page  43).  Thus,  instead  of 
HONO5  representing  nitric  acid,  the  acid  has  been  regarded  as  a  hydracid, 
i.  e.,  an  acid  of  hydrogen,  represented  by  the  formula  HNOe.  According 
to  this  view,  an  acid  is  convertible  into  a  salt  of  hydrogen,  or  a  compound  of 
hydrogen  with  a  radical  which  has  not  been  isolated.  But  if  this  be  admitted 
with  respect  to  inorganic  acids,  it  will  equally  apply  to  those  of  the  organic 
kingdom.  Thus  pyrogallic  acid  (CigHf-Og)  is  a  solid,  anhydrous,  crystalline 
compound,  which  has  no  acid  reaction,  until  it  is  dissolved  by  water  (page 
43).  Under  these  circumstances,  it  must  be  assumed,  either  that  the  acid 
now  becomes  'RC^JIfij,  or  the  hypothesis  is  unfounded.  Although  in  com- 
bining with  chlorine,  bromine,  iodine,  sulphur,  and  cyanogen,  hydrogen 
produces  gaseous  acids  free  from  water,  yet  acid  compounds  exist  which  not 
only  contain  no  water,  but  which  are  decomposed  by  that  liquid.  The 
fluoboric  acid  (BFg)  may  be  taken  as  an  illustration.  This  body  contains 
neither  hydrogen  nor  oxygen,  and  is  at  the  same  time  as  much  an  acid  gas 
as  hydrocyanic,  or  any  of  the  hydracid  gases  above  mentioned.  But,  unlike 
these,  it  is  resolved  by  water  into  two  other  acids.  A  similar  observation 
may  be  made  with  respect  to  the  fluosilicic  acid  (SiFg).  The  manganic 
(MnOg)  and  fulminic  acids  {Cjfi^)  combine  with  bases  to  form  well-defined 
salts,  but  not  with  water,  as  no  hydrates  of  these  acids  are  known.  The 
molybdic,  tungstic,  silicic,  titanic,  and  other  acids,  can  be  obtained  perfectly 
anhydrous,  and  in  this  state  they  will  expel  other  acids  from  bases.  The 
combinations  of  hydrogen  alone  prove  that  there  are  no  sufficient  grounds 
for  adopting  this  hypothesis  of  the  constitution  of  acids.  Hydrogen  com- 
bines with  nitrogen  to  form  a  powerful  alkaline  base,  ammonia ;  but  when 
the  three  atoms  of  hydrogen  in  ammonia  are  replaced  by  three  atoms  of 
oxygen,  a  strong  acid  is  the  result;  and  'the  conversion  of  the  base, 
ammonia,  into  nitric  acid  and  water  by  simple  oxidation,  is  a  matter  of  daily 
experience.  Hydrogen  differs  from  oxygen  in  forming  no  acid  compounds 
with  metals.  The  only  exception  is,  its  compound  with  tellurium.  It  is 
also  a  remarkable  fact,  that  when  the  hydrogen  is  replaced  by  oxygen  in 
some  neutral  organic  compounds,  an  acid  frequently  results.  In  the  acetous 
fermentation,  the  conversion  of  alcohol  to  vinegar  or  acetic  acid  is  the  result 
of  simple  oxidation.  One-half  of  the  hydrogen  is  removed — the  proportion 
of  oxygen  is  increased,  and  as  a  result  of  these  changes,  the  neutral  com- 
pound, alcohol,  is  converted  into  acetic  acid.  Another  remarkable  instance 
of  the  acidifying  effect  of  oxidation  is  furnished  by  the  pure  essential  oil  of 
bitter  almonds.  This  liquid,  dissolved  in  alcohol,  is  perfectly  neutral.  As 
the  alcohol  evaporates,  the  oil  is  oxidized,  and  is  converted  into  solid  crys- 
tallized benzoic  acid.  The  only  chemical  change  here  is  the  substitution  of 
oxygen  for  hydrogen ;  and  as  this  goes  on,  the  neutral  is  observed  to  be 
converted  into  an  acid  compound.  Hydrogen  has  therefore  no  claim  to  be 
regarded  as  an  acidifying  principle  in  preference  to  oxygen.  The  name 
given  to  this  element  by  Lavoisier  is  fully  justified  by  modern  researches, 
with  the  qualification  that  it  is  not  the  only  acidifying  element.  In  fact, 
acidity,  like  alkalinity,  is  a  condition  or  property  resulting  from  the  chemical 


OXYGEN.      OXIDATION.  95 

union  of  bodies;  and  is  not  essentially  dependent  on  the  presence  of  any  one 
substance.  There  appears  to  be  no  good  reason,  therefore,  for  converting 
the  oxygen-acids  to  hydracids  by  the  supposed  decomposition  of  the  water 
associated  with  them. 

Oxygen  not  only  produces,  as  a  result  of  chemical  union,  acids  and 
alkalies,  but  it  forms  with  the  greater  number  of  metals,  binary  compounds 
which  are  quite  neutral;  and  in  order  to  distinguish  these  from  other  pro- 
ducts, they  are  called  oxides.  With  some  of  the  metals,  when  heated  to  a 
high  temperature,  the  phenomena  of  combustion  are  splendidly  manifested. 
Thus  zinc  in  foil  or  shavings,  may  be  formed  into  a  bundle  two  or  three 
inches  long  (the  ends  being  tipped  with  a  little  melted  sulphur,  for  the 
purpose  of  igniting  the  metal)  ;  on  introducing  the  ignited  zinc  into  a  tall 
bell-glass  of  oxygen,  there  is  a  brilliant  combustion  of  the  metal.  The  light 
evolved  is  of  an  intense  greenish  white  color,  and  a  white  flocculent  product 
results,  which  is  oxide  of  zinc  (ZnO).  If  in  this  experiment  magnesium 
wire  is  substituted  for  zinc,  a  bright  white  light,  almost  equal  to  that  of 
intense  sunlight  is  produced,  and  the  metal  becomes  converted  into  the 
alkaline  earth,  magnesia  (NIgO).  The  finest  iron-wire  made  into  a  bundle, 
tipped  with  sulphur,  ignited,  and  introduced  into  a  large  vessel  of  the  gas  in 
a  pure  state,  burns  with  an  intense  white  light,  and  with  scintillations  of 
fused  metal,  which  sometimes  penetrate  the  substance  of  the  glass.  Rounded 
masses  of  the  fused  iron,  oxidized,  fall  at  a  white  heat  (3280°),  with  hissing 
noise,  into  the  water  of  the  vessel  in  which  the  gas  is  placed.  The  com- 
pound produced  in  this  experiment  is  the  magnetic  oxide  of  iron  (FgO^,  or 
FeO  -f-  Fe^Og).  The  heat  being  sufficient  to  drive  off  a  portion  of  the  oxygen, 
which  in  the  first  instance  produces  a  peroxide  of  the  metal. 

Oxidation. — Oxygen  combines  with  some  bodies  directly,  and  at  all  tem- 
peratures. A  jar  containing  deutoxide  of  nitrogen  (NOJ,  when  exposed  to 
oxygen  gas,  or  to  any  mixture  containing  free  oxygen,  forms  deep  ruddy 
vapors  of  an  acid  nature.  The  neutral  deutoxide  is  further  oxidized,  and  is 
converted  to  an  acid  of  nitrogen.  If  iron  filings,  moistened  with  water,  are 
thrown  into  a  jar  of  oxygen  gas,  and  the  particles  of  metal  are  diffused  by 
agitation,  so  as  to  adhere  to  the  inner  surface  of  the  glass,  and  the  jar  is 
inverted  in  a  vessel  of  water,  the  oxygen  is  slowly  but  completely  removed 
without  the  evolution  of  light  and  heat,  while  the  water  rises  in  the  vessel. 
The  iron  takes  the  oxygen  and  is  converted  to  peroxide.  If  this  experiment 
is  performed  in  a  jar  containing  air,  the  water  rises  to  about  one-fifth  of  the 
capacity  of  the  vessel,  thus  indicating  not  only  the  presence  of  oxygen,  but 
the  proportion  of  that  element  in  air.  With  some  substances  oxygen  will 
combine,  but  only  indirectly,  or  by  the  aid  of  complex  chemical  affinity.  As" 
examples  of  this  kind  may  be  mentioned  chlorine,  bromine,  and  iodine. 
Oxygen  as  a  gas  has  no  tendency  to  unite  with  these  elements.  With 
fluorine  it  forms  no  known  combination.  In  order  to  combine  with  oxygen 
in  a  free  state  most  substances  require  to  be  heated  above  the  ordinary  tem- 
perature of  the  atmosphere.  Thus  phosphorus  has  no  tendency  to  form  a 
compound  with  pure  oxygen  below  a  temperature  of  80° ;  but  when  oxygen 
is  mixed  with  nitrogen  (as  in  the  atmosphere),  or  with  other  gases,  phos- 
phorus will  enter  into  combination  with  it  at  32°,  and  even  at  temperatures 
below  this.  The  phosphorus  is  slowly  oxidized,  being  converted  into  a 
deliquescent  liquid — phosphorous  acid  (PO3)  ;  and,  during  the  oxidation,  the 
phosphorus  appears  luminous  in  the  dark.  Phosphorus  does  not  commonly 
enter  into  combustion  in  oxygen  below  its  melting  point  (112°),  while,  in 
the  allotropic  state,  it  may  be  heated  to  nearly  500°  without  taking  fire. 
Free  oxygen,  as  it  exists  in  the  atmosphere,  appears  to  have  no  tendency  to 
combine  with  carbon  below  a  red  heat  (1000°) — with  hydrogen  below  600° — 


96  VARIETIES    OF    OXIDES. 

with  zinc  below  its  vaporizing  point  (1900°)— or  with  sulphur  below  500°. 
This  want  of  action  at  low  temperatures  appears  to  depend  less  on  the 
absence  of  affinity  between  oxygen  and  the  substance,  than  on  the  effect  of 
cohesion  on  the  substance  exposed  to  the  gas.  When  phosphorus,  iron, 
and  even  lead,  are  reduced  to  a  fine  state  of  division,  and  exposed  to  oxygen 
at  any  temperature,  they  will  take  fire,  and  burn  with  the  same  brilliancy  as 
larger  masses  which  have  been  strongly  heated.  (See  Pyrophori,  page  40, 
also  Combustion.) 

In  the  process  of  oxidation  oxygen  may  form  a  gaseous,  liquid,  or  solid 
compound,  either  quiescently  or  with  the  phenomena  of  combustion.  A 
simple  substance  may  enter  into  combination  with  oxygen  in  various  propor- 
tions, and  it  is  then  found  that  while  the  compounds  which  contain  the 
smallest  proportions  of  oxygen  are  neutral  oxides,  those  which  contain  the 
largest  proportions  have  acid  properties,  and  unite  with  bases  like  acids  to 
form  salts.  The  metal  manganese  (Mn)  affords  a  remarkable  instance  of  this 
series  of  combinations.  Thus  we  have  MnO  the  first  oxide  or  protoxide  of 
manganese,  which  combines  with  acids  to  form  the*alts  of  this  metal — MnOg 
the  second  oxide  or  deutoxide  of  the  metal.  Some  have  given  to  this  com- 
pound the  name  of  binoxide,  from  the  Latin  binus,  signifying  double  or  twice 
as  much.  This  term  properly  implies  that  the  oxide  has  twice  as  much 
oxygen  as  the  compound  which  precedes  it.  But  deutoxides  of  metals  are 
not  always  binoxides  in  this  sense.  Peroxide  (hyperoxide  from  vn'sp,  higher) 
is  a  term  applied  to  an  oxide  beyond,  or  a  higher  stage  of  oxidation;  this, 
without  reference  to  the  number  of  atoms,  indicates  the  maximum  degree  of 
oxidation.  Thus  while  the  peroxide  of  copper  has  one  atom  of  oxygen 
(CuO),  and  that  of  iron  one  and  a  half  atoms  (or  three  to  two  of  metal),  the 
peroxide  of  lead  has  two  atoms  (Pb02)  and  that  of  nitrogen  four  atoms 
(NOJ.  The  metal  manganese  furnishes  compounds  in  other  stages  of  oxi- 
dation ;  thus  there  is  a  sesquioxide,  Mn^Og,  signifying  that  the  oxygen  is  1 J 
to  1  of  the  metal,  or,  to  avoid  the  use  of  fractions,  3  to  2.  There  is  next 
in  order  a  compound  of  the  sesquioxide  with  the  protoxide,  called,  from  its 
color,  the  red  oxide  of  manganese,  represented  by  the  formula  (MuO,Mny03), 
or  MuyO^.  Beyond  this  there  are  two  acid  compounds,  manganic  acid  MnOg, 
and  permanganic  acid  Mn^O^.  The  compounds  of  oxygen  and  manganese, 
which  represent  all  the  varieties,  and  at  the  same  time  the  greatest  range 
of  combinations  of  oxygen  in  mineral  chemistry,  stand  as  follows  : — 


Name. 

Formulae. 

Atoms  0. 

Wt.  Ox. 

At.  Mn. 

Vrt.  Mn. 

Protoxide 

.     Mn  0 

1 

= 

8 

1 

= 

28 

Deutoxide 

.     MnO™ 

2 

r= 

16 

1 

= 

28 

Sesquioxide     . 

.     MnJO. 

3 

= 

24 

2 

= 

56 

Red  oxide 

.     MN3O, 

4 

= 

32 

3 

= 

84 

Manganic  acid 

.     Mn  O3 

3 

= 

24 

1 

== 

28 

Permanganic  acid   , 

.     Mn,0, 

7 

= 

56 

2 

= 

56 

There  are  degrees  of  oxidation  in  which  the  metal  is  in  larger  proportion 
than  the  oxygen.  These  are  called  suboxides.  Thus  the  suboxide  of  copper 
is  represented  by  the  formula  Cu^O  ;  it  is  a  compound  of  one  atom  of  oxygen 
with  two  atoms  of  metal. 

The  tendency  of  the  oxides  of  metals  to  combine  with  acids  to  form  salts 
is  materially  influenced  by  the  stage  of  oxidation.  The  protoxide  (MO)  is 
the  compound  which  usually  possesses  strong  basic  properties,  and  which,  by 
combining  with  acids,  produces  the  varieties  of  metallic  salts.  Chemists 
generally  fix  upon  the  jjrotoxide  by  this  combining  character.  If  a  suboxide 
is  acted  upon  by  an  acid,  one  atom  of  the  metal  is  set  free,  and  a  protoxide 
results,  which  then  forms  a  salt.  Thus,  in  boiling  suboxide  of  copper  with 
diluted  sulphuric  acid,  metallic  copper  is  deposited,  and  a  sulphate  of  the 


RANGE    OF    OXIDATION.  9^ 

oxide  of  copper  results  (Cu.^0  =  Cu  -f  CuO).  On  the  other  hand,  when  a  per- 
oxide is  treated  with  an  acid,  an  atom  of  oxygen  is  given  ofif.  Thus  when 
peroxide  of  barium  is  treated  with  sulphuric  acid,  sulphate  of  the  ])rotoxide 
of  barium  is  produced,  while  oxygen  escapes  as  a  gas  (Ba03=BaO  +  0). 
On  this  principle,  as  it  has  been  already  explained,  peroxide  of  manganese 
may  be  made  to  yield  oxygen  by  heating  it  with  sulphuric  acid.  {See  page 
90.)  Sesquioxides  may  combine  with  acids  to  form  salts  ;  this  is  seen  in 
the  sesquio-xides  of  iron,  aluminum,  and  chromium  ;  and  as  the  protoxide, 
containing  one  atom  of  oxygen,  requires  one  atom  of  acid  for  producing  a 
neutral  salt,  so  the  sesquioxide,  containing  three  atoms  of  oxygen,  requires 
three  atoms  of  acid  to  form  the  class  of  sesquisalts.  The  oxides  which  have 
the  peculiar  constitution  of  three  atoms  of  metal  to  four  of  oxygen,  may  be 
regarded  as  compounds  of  two  other  oxides,  and  are  resolvable  into  these  by 
acids.  In  consequence  of  this  union  or  mixture,  they  have  been  sometimes 
called  saline  oxides — the  one  oxide  being  supposed  to  act  as  a  base  to  the 
other.  Examples  of  these  oxygen-compounds  occur  not  only  in  manganese, 
as  above  stated,  but  in  iron  and  lead.  The  magnetic  oxide  of  iron — the 
mineral  which  alone  permanently  retains  magnetic  force — is  a  native  oxide  of 
this  description.  It  is  represented  by  the  formula  FgO^,  which  is  convertible 
into  oxide  (FeO)  and  sesquioxide  (FegOg)  of  iron.  The  substance  called  red 
lead  is  a  compound  oxide,  having  the  formula  PbgO^,  but  resolvable  by  acids 
into  2PbO  and  PbO^.  When  this  oxide  is  digested  in  nitric  acid,  the  acid 
forms  with  the  protoxide  nitrate  of  protoxide  of  lead,  soluble  in  water,  while 
the  peroxide  is  left  unacted  on  as  a  heavy,  dark-brown  insoluble  powder. 

Some  metals  appear  to  have  no  stages  of  oxidation,  in  which  basic  or 
neutral  compounds  are  produced.  In  the  lowest  degrees  of  combination  with 
oxygen  they  at  once  form  acids.  Arsenic  furnishes  an  example  of  this  kind  : 
this  metal  combines  with  three  atoms  of  oxygen  to  form  arsenious  acid 
(AsOo),  and  with  five  atoms  of  oxygen  to  form  arsenic  acid  (AsO^).  Anti- 
mony, which  presents  so  many  analogies  to  arsenic,  forms  a  teroxide  with 
three  atoms  of  oxygen  (SbOg)  acting  as  a  base,  and  an  acid  with  five  atoms 
antiraonic  acid  (SbO^).  These  combine  to  form  a  compound  which  has  the 
remarkable  composition  of  Sb^Og,  and  is  called  antimonious  acid. 

Reduction. — While  the  term  oxidation  implies  simply  the  combination  of 
oxygen  with  bodies,  the  term  reduction  implies  the  separation  of  oxygen  from 
substances  by  chemical  agency,  and  the  conversion  of  them  into  their  original 
state  of  metal  or  combustible.  The  term  regulus  was  formerly  applied  to  the 
metal  thus  derived  from  an  oxide,  and  the  reguline  state,  therefore,  simply 
implies  the  non-oxidized  or  metalline  state.  The  word  reduction,  however, 
is  equally  applied  by  modern  usage  to  the  separation  of  the  metals  from 
chlorides,  sulphides,  and  similar  binary  compounds. 

Respiration  and  Combustion. — Oxygen  is  the  great  supporter  of  respira- 
tion and  combustion,  and  is  largely  consumed  in  these  processes;  hence  air 
deprived  of  oxygen  by  either  process,  or  by  ordinary  chemical  changes,  is 
unfit  to  support  animal  life,  and  will  not  allow  of  the  combustion  of  other 
bodies.  If  a  lighted  wax  taper  is  introduced  into  a  jar  of  air,  in  which  iron 
filings  have  been  sprinkled  with  a  little  water,  it  will  be  found,  after  some 
hours,  that  the  residuary  gas  will  extinguish  it ;  and  any  small  animal  intro- 
duced into  this  residuary  gas,  would  be  instantly  rendered  lifeless.  1.  If  we 
breathe  by  a  wide  tube  into  a  bell-glass  filled  with  water,  and  inverted  on  a 
water-bath,  so  that  the  water  may  be  displaced  by  the  expired  air  as  it  issues 
from  the  lungs — we  shall  find  on  introducing  a  lighted  wax-taper  that  it  will 
be  instantly  extinguished.  2.  A  lighted  taper  introduced  into  a  bell-glass 
of  air,  placed  over  a  water-bath  (the  bell-glass  being  closed  at  the  top  by  a 
brass  plate  or  stopper),  will  be  extinguished  in  a  few  minutes,  owing  to  the 
7 


i 


98  DECAY.      EREMACAUSIS.      PUTREFACTION, 

rapid  consumption  of  oxygen  and  the  absence  of  any  fresh  supply.  On 
removing  the  extinguished  taper  quickly  and  introducing  another,  lighted, 
this  will  also  be  extinguished  ;  and  any  small  animal  placed  in  either  of  these 
mixtures,  thus  deprived  of  a  large  portion  of  their  oxygen,  would  soon  perish. 
It  must  not  be  supposed,  however,  that  all  the  oxygen  is  removed  from  air, 
either  by  respiration  or  by  ordinary  combustion.  That  there  is  still  some 
portion  left  in  the  vessels,  may  be  proved  by  introducing  into  them  a  ladle 
containing  ignited  phosphorus.  This  will  continue  to  burn  at  the  expense 
of  the  residuary  oxygen  not  removed  by  the  lungs  in  breathing,  or  by  the 
wax  taper  in  combustion.  Air,  therefore,  which  is  deoxidized,  or  which  does 
not  contain  a  certain  amount  of  free  oxygen,  is  wholly  unfitted  to  support 
life.  Respiration  and  combustion  vitiate  it  by  withdrawing  oxygen  and  sup- 
plying its  place  with  carbonic  acid.  As  a  general  rule,  an  animal  cannot 
live  in  air  in  which  a  wax-taper  will  not  burn,  and  a  taper  will  not  burn  in 
an  atmosphere,  in  which  there  is  too  small  an  amount  of  oxygen  to  maintain 
respiration. 

If  our  atmosphere  had  consisted  of  oxygen  alone,  combustion  once  set  up 
would  not  have  ceased  until  all  combustible  substances  had  been  consumed, 
and  the  \^ole  face  of  the  farth  changed.  So  in  regard  to  animal  life, 
although  oxygen  is  absolutely  necessary  to  respiration — when  this  gas  is  in 
a  pure  state,  i.  e.,  unmixed  with  nitrogen — it  operates  as  a  powerful  excitant 
to  the  nervous  system  ;  and  a  small  animal  confined  in  an  atmosphere  of 
pure  oxygen  will  die  in  a  few  hours,  apparently  from  the  excessive  stimulus 
produced  by  the  gas.  Mr.  Broughton  determined,  experimentally,  that 
rabbits  died  in  six,  ten,  or  twelve  hours  when  confined  in  oxygen.  On  exa- 
mination after  death,  the  blood  was  found  highly  florid  in  every  part  of  the 
body  ;  and  the  heart  continued  to  act  strongly  even  after  respiration  had 
ceased.  The  dilution  of  the  oxygen  of  the  atmosphere  with  four  times  its 
volume  of  nitrogen  is  therefore  absolutely  necessary  to  animal  life.  It  is 
worthy  of  notice,  however,  in  reference  to  this  noxious  action  of  pure  oxy- 
gen, that  an  animal  will  live  three  times  as  long  in  this  gas  as  when  it  is 
confined  in  an  equal  volume  of  common  air.  The  reason  for  the  difference 
is,  that  the  quantity  of  oxygen  in  air  available  for  respiration  is  not  only 
four-fifths  less,  but  that  which  has  been  consumed  by  the  animal  is  replaced 
by  an  equal  bulk  of  carbonic  acid,  which  is  itself  a  noxious  gas. 

Decay.  Eremacausis.  Putrefaction. — Oxygen  takes  an  important  share 
in  these  processes.  It  is  by  slow  oxidation  that  organic  are  converted  into 
inorganic  compounds  ;  and  these  again,  by  means  of  the  vegetable  kingdom, 
are  reconverted  into  organic  substances  fitted  for  the  food  of  animals.  In 
the  slow  oxidation  of  vegetable  matter,  we  have  an  example  of  that  condition, 
which  has  been  called  by  Liebig  eremacausis  {rjpiixa  slow,  xaicrts  burning). 
If  we  place  in  a  stoppered  bottle  containing  air,  sawdust,  tow,  jute,  or  decayed 
leaves  in  a  damp  state,  and  expose  the  bottle  for  a  few  days  to  a  temperature 
a  little  above  60°,  it  will  be  found  that  the  oxygen  of  the  air  in  the  bottle  has 
been  to  a  greater  or  less  extent  replaced  by  carbonic  acid.  A  lighted  taper, 
introduced  into  the  bottle,  will  be  extinguished,  and  carbonic  acid  may  be 
proved  to  be  present  by  the  usual  tests.  Under  these  circumstances,  there 
is  no  sensible  heat  or  light  evolved ;  hence  the  terra  combustion,  applied  to 
this  kind  of  oxidation,  is  not  strictly  correct.  In  certain  cases,  however,  the 
accumulation  of  heat  as  a  result  of  the  slow  oxidation  of  some  kinds  of  vege- 
table matter  is  such,  that  the  mass,  if  easily  combustible,  may  burst  into 
flame.  Hay  and  cotton  in  a  damp  state,  stacked  or  stowed  in  large  quanti- 
ties, and  under  circumstances  favorable  to  the  accumulation  of  heat,  acquire 
a  high  temperature,  as  the  result  of  oxidation.  Aqueous  vapor  is  at  first 
copiously  evolved,  and  when  the  material  is  sufficiently  dried,  unless  the 


OXYGEN.      EQUIVALENT.      TESTS.  99 

oxidation  ceases  the  orp:anic  matter  becomes  charred  and  may  ultimately 
burst  into  flame.  Flax,  tow,  jute,  and  other  vegetable  substances  of  a  porous 
nature,  in  a  damp  state  also  acquire  a  high  temperature  as  a  result  of  oxida- 
tion of  the  fibre.  We  have  found  a  quantity  of  damp  jute,  six  feet  thick,  to 
have  a  temperature  of  140°.  Aqueous  vapor  with  a  small  quantity  of  car- 
bonic acid  was  evolved.  Spent  tan  and  manure,  and  other  organic  matters 
when  moist,  undergo  oxidation  and  evolve  heat.  Gutta  percha  in  thin  sheets 
appears  to  undergo  both  physical  and  chemical  changes  from  the  absorption 
of  oxygen.  It  becomes  altered  in  color  and  tenacity  by  long  exposure  to 
the  air  ;  and  although  it  does  not  inflame,  it  may,  when  exposed  in  large 
surfaces  to  air,  acquire  a  temperature  sufficient  to  melt  it.  This  is  probably 
the  real  cause  of  the  heating  of  electric  cables  in  the  holds  of  vessels  in  which 
they  have  been  stored.  All  cases  of  oxidation  are  attended  with  the  evolu- 
tion of  heat,  but  when  the  process  is  slow,  the  evolved  heat  is  unobserved 
and  dissipated  without  accumulation  ;  in  'Other  cases,  when  the  process  is 
effected  in  a  shorter  period,  the  heat  becomes  proportionally  sensible ;  and 
when  the  oxidation  is  rapid,  the  whole  of  the  heat  being  evolved  in  a  much 
more  limited  time,  it  is  proportionably  exalted  in  intensity. 

Oxygen  takes  an  important  share  in  the  acetous  fermentation,  as  it  is  by 
the  oxidation  of  the  elements  of  alcohol  that  acetic  acid  is  produced.  In 
some  of  its  combinations  it  exerts  a  deodorizing  or  disinfecting  power.  Thus, 
as  it  is  set  free  from  a  solution  of  permanganate  of  potash  or  soda,  it  oxidizes 
and  destroys  all  the  ofl'ensive  products  evolved  in  the  decomposition  of 
organic  matter,  which  generally  consist  of  compounds  of  hydrogen,  with  sul- 
phur, nitrogen,  phosphorus,  and  carbon.  -r* 

Equivalent. — The  equivalent  or  combining  weight  of  oxygen  is  taken  at  8,4 
when  compared  with  hydrogen  as  unity  ;  and  in  reference  to  its  volume- 
equivalent  in  its  combinations  with  other  gases,  it  is  one-half  of  that  of 
hydrogen,  or  one-half  volume. 

Tests.  Special  Characters. — Oxygen  may  be  known  as  a  gas  in  the  free 
state  :  1.  By  its  insolubility  in  water,  or  in  a  strong  solution  of  potash.  2. 
By  its  entire  solubility  in  potash  to  which  pyrogallic  acid  has  been  added. 
3.  By  its  kindling  into  flame  an  ignited  match  or  the  glowing  wick  of  a 
taper.  There  is  only  one  other  gas  known  which  possesses  this  property, 
namely,  the  protoxide  of  nitrogen  (NO) ;  but  there  are  other  well-marked 
distinctions  between  this  gas  and  oxygen.  4,  Oxygen  produces  red  acid 
fumes  when  deutoxide  of  nitrogen  (NO J  is  added  to  it.  5.  It  changes  the 
white  ferrocyanide  of  iron  to  Prussian  blue. 

When  oxygen  exists  in  the  uncombined  state,  but  dissolved  by  liquids, 
such  as  water,  its  presence  may  be  readily  detected  by  the  white  proto-ferro- 
cyanide  of  iron.  This  test-liquid  should  be  made  for  the  occasion.  It  may 
be  prepared  by  shaking  in  a  small  bottle  a  mixture  of  bright  iron  filings  and 
a  fresh  solution  of  sulphurous  acid  gas.  After  a  few  minutes  the  liquid 
should  be  filtered  and  diluted  with  water ;  a  small  quantity  of  a  solution  of 
ferrocyanide  of  potassium  should  then  be  added  to  it.  A  milky-white  pre- 
cipitate of  the  proto-ferrocyanide  is  thrown  down.  This  rapidly  becomes 
blue  on  the  surface  by  absorbing  oxygen,  and  passing  to  the  state  of  sesqui- 
ferrocyanide  of  iron,  or  one  variety  of  Prussian  blue.  If  this  liquid  is  poured 
into  a  jar  of  oxygen  gas,  and  the  jar  shaken,  it  will  speedily  be  converted 
into  Prussian  blue.  If  poured  in  a  thin  sheet  on  a  white  plate  it  will  reveal 
the  presence  of  oxygen  in  the  atmosphere,  by  its  rapid  change  of  color  on  the 
surface.  If  we  add  a  little  of  the  test-liquid  gradually  to  eighty  or  one 
hundred  ounces  of  water  containing  free  oxygen,  in  a  tall  glass  jar,  it  will  be 
observed  that,  as  it  falls  through  the  water,  it  will  change  from  white  to 
blue,  by  absorbing  and  fixing  the  dissolved  oxygen. 


100  COMBUSTION    WITH    AND    WITHOUT    OXYGEN. 

The  whole  of  the  free  oxygen  may  be  removed  from  a  gaseous  mixture, 
by  dissolving  pyrogallic  acid  in  a  strong  solution  of  potash,  and  introducing 
the  mixture  into  a  vessel  containing  the  gas  over  mercury.  In  a  graduated 
vessel  the  proportion  of  oxygen  present  may  be  thus  determined.  If  car- 
bonic acid,  or  any  other  acid  gas  should  be  present,  these  may  be  removed 
by  first  passing  a  solution  of  potash  only  into  the  tube,  and  when  no  further 
absorption  takes  place,  the  level  may  be  taken,  and  pyrogallic  acid  added  to 
the  potash.  The  further  absorption  will  then  indicate  the  amount  of  oxygen. 
The  quantity  of  free  oxygen  may  be  more  accurately  determined,  by  adding 
to  the  gaseous  mixture  its  volume  of  pure  hydrogen,  and  then  bringing  about 
its  combination  with  oxygen,  either  by  the  electric  spark  or  by  the  aid  of 
spongy  platinum.  This  process  will  be  more  fully  explained  in  treating  of 
the  composition  of  water.  Oxygen  may  also  be  removed  from  a  mixture  of 
gases,  by  causing  it  to  pass  throug-h  a  tube  over  metallic  copper  heated  to 
redness. 


CHAPTER    VIL 

OXYGEN— INCANDESCENCE— COMBUSTION— DEFLAGRATION. 

i^  Combustion  with  and  without  Oxygen. — Combustion,  in  its  most  extensive 
^-meaning,  may  be  described  as  the  result  of  intense  chemical  combination 
between  two  or  more  bodies,  during  which  sensible  light  and  heat  are 
evolved.  All  ordinary  cases  of  combustion  are  dependent  on  the  combina- 
tion of  oxygen  with  bodies  ;  and  the  heat  and  light  are  dependent  on  the 
rapidity  with  which  oxidation  takes  place,  as  well  as  on  the  amount  of  oxygen 
consumed.  Levoisier  believed  that  oxygen  was  the  universal  supporter  of 
combustion,  and  that  there  was  no  combustion  without  it.  In  this,  however, 
he  was  in  error.  The  phenomena  of  combustion  are  seen  in  some  of  the 
combinations  of  chlorine,  bromine,  and  sulphur  with  bodies.  If  phosphorus 
is  introduced  into  a  jar  of  chlorine,  it  speedily  melts,  takes  fire,  and  burns 
with  a  pale  yellowish  flame,  forming  chloride  of  phosphorus.  If  thin  leaves 
of  Dutch  metal  are  introduced  into  chlorine,  they  burn  without  flame,  pro- 
ducing a  full  red  heat,  and  forming  chloride  of  copper.  Freshly-powdered 
metallic  antimony  projected  into  chlorine  gas,  burns  in  scintillations,  evolv- 
ing much  light  and  heat,  and  forming  white  chloride  of  antimony :  if  this 
metal  in  fine  powder  be  projected  into  bromine,  it  burns,  in  contact  with  the 
liquid,  with  bright  scintillations,  forming  bromide  of  antimony.  So  with 
regard  to  sulphur ;  if  this  substance  is  heated  in  a  Florence  flask  to  its 
vaporizing  point,  it  forms  a  dark  amber-colored  vapor,  in  which  thin  pieces 
of  copper  foil,  or  cuttings  of  copper,  glow  and  burn  with  great  splendor, 
producing  sulphide  of  copper.  The  metal  sodium -heated  in  air  until  it 
begins  to  take  fire,  when  plunged  into  a  jar  of  chlorine,  will  burn  with  the 
most  intense  evolution  of  light  and  heat,  and  sometimes  with  explosive 
violence.  The  ladle  holding  the  metal  acquires  a  red  heat  as  a  result  of  this 
combustion.  Fine  iron  wire  previously  heated  to  redness  also  burns  with  a 
deep  lurid  glow  in  chlorine.  These  experiments  clearly  show  that  oxygen 
is  not  in  all  cases  necessary  to  combustion  ;  and  that  the  phenomena  which 
attend  it,  cannot  be  regarded  as  dependent  upon  any  peculiar  principle  or 
form  of  matter ;  they  must  be  considered  as  a  general  result  of  intense  chemi- 
cal union.     Each  substance,  in  fact,  has  its  own  special  properties  in  refer- 


IGNITION.      INCANDESCENCE.  101 

ence  to  combustion.  Sulphur  will  not  burn  in  chlorine  ;  and  to  cause  it  to 
burn  in  oxypren,  it  must  be  heated  to  a  hii^h  temperature.  Copper  will  not 
burn  in  oxygen  gas,  but  it  will  burn  at  the  lowest  temperature  in  chlorine, 
and  readily  in  the  vapor  of  sulphur.  Phosphorus  will  not  undergo  combus- 
tion in  oxygen  below  a  temperature  of  80°  ;  but  it  will  take  fire  in  chlorine 
at  32°.  ^      • 

Some  compound  gases  may  give  rise  to  the  phenomena  of  combustion  with 
alkaline  metals  under  certain  conditions.  Cyanogen  gas  is  a  compound  of 
carbon  and  nitrogen.  If  potassium  is  heated  in  a  current  of  this  gas,  the 
metal  burns,  and  leaves  as  a  product  cyanide  of  potassium.  Again,  if  sodium 
be  heated  in  a  flask  from  which  air  is  entirely  excluded,  and  a  current  of  dry 
carbonic  acid  is  passed  through  the  flask,  a  brilliant  combustion  will  take 
place,  the  oxygen  of  the  carbonic  acid  being  taken  by  the  sodium  to  form 
soda,  while  carbon  is  deposited.  Magnesium  wire  ignited  and  introduced 
into  carbonic  acid,  burns  with  scintillations  and  gives  out  an  intensely  white 
light.  In  most  cases,  bodies  which  burn  in  oxygen  are  immediately  extin- 
guished when  plunged  into  carbonic  acid. 

Oxycomhustion. — Confining  our  views  for  the  present  to  combustion  as  it 
takes  place  in  oxygen,  it  may  be  remarked  that  there  is  no  loss  of  matter  bnt 
merely  a  change  of  state.  If  a  spirit-lamp  is  accurately  balanced  in  a  scale- 
pan,  and  the  wick  then  ignited — as  the  spirit  burns,  there  will  be  an  apparent 
loss  of  matter,  and  the  counterpoised  scale  will  sink.  If  we  hold  over  the 
burning  wick,  the  open  mouth  of  a  gas-jar,  we  may  be  able  to  prove  by  appro- 
priate tests,  that  the  air  of  the  jar  is  replaced  by  carbonic  acid  and  aqueous 
vapor — the  latter  being  condensed  on  the  inner  cold  surface  of  the  glass. 
These  products  are  formed  at  a  high  temperature  by  the  oxidation  of  the 
carbon  and  hydrogen  contained,  in  the  vapor  of  alcohol.  If  collected  in  a 
proper  apparatus,  the  weight  of  these  products  will  be  equal  to  the  weight 
of  alcohol  consumed. 

If  phosphorus  is  heated  in  a  vessel  of  pure 'oxygen,  all  the  oxygen  dis- 
appears, but  it  is  now  solidified  as  phosphoric  acid,  and  the  increase  in 
the  weight  of  the  phosphorus  would  represent  exactly  the  amount  of 
oxygen  consumed.  In  the  burning  of  carbon  there  appears  to  be  no  loss 
of  gaseous  matter ;  but  the  oxygen  in  this  case  is  converted  into  carbonic 
acid  ;  and  it  will  be  found,  although  unaltered  in  volume,  to  have  acquired 
an  increase  in  weight  equal  to  the  weight  of  carbon  consumed.  Sub- 
stances which  undergo  combustion  in  oxygen  are  rendered  heavier;  the 
weight  of  oxygen  taken  during  combustion,  is  always  added  to  the  original 
weight. 

When  a  metal  burns  in  oxygen,  it  is  iodized  with  the  evolution  of  light  and 
beat ;  but  a  metal  may  be  iodized  without  undergoing  combustion  in  the 
ordinary  sense.  Zinc  and  lead  furnish  striking  instances  of  the  difl'erence. 
If  zinc  is  heated  in  air  above  its  melting  point,  it  will  take  fire  and  burn 
with  a  splendid  greenish-white  light  {see  page  106) ;  but  if  lead  is  melted  in 
air,  there  is  formed  on  the  surface  a  dirty  yellowish-looking  film  or  dross 
(oxide  of  lead),  without  the  evolution  of  light  and  heat.  Both  are  instances 
of  oxidation,  but  in  the  latter  case  there  is  no  combustion. 

Ignition.  Incandescence. — Combustion  always  implies  chemical  action; 
either  the  heat  of  the  combining  bodies  or  that  which  results  from  their 
combination  is  set  free,  and  with  this,  a  proportionate  quantity  of  light;  but 
a  body  may  evolve  heat  and  light  without  undergoing  combustion  or  any 
chemical  change.  •  Thus  a  platinum  wire,  some  fibres  of  asbestos,  or  a  piece 
of  lime,  exposed  to  the  strong  heat  of  an  invisible  flame — e.  g.,  of  oxygen 
and  hydrogen — may  be  heated  to  whiteness,  so  as  to  evolve  both  heat  and 
light  of  surpassing  intensity.     To  this  state  the  term  ignition,  or  incandes- 


1 


102  IGNITION.      INCANDESCENCE 

cence,  is  applied.  The  body  evolves  light  as  a  result  of  its  being  intensely 
heated,  without  its  particles  being  materially  altered  in  tlieir  physical  or 
chemical  relations.  It  is  not  fused  at  the  temperature  to  which  it  is  exposed  ; 
and  the  greater  the  amount  of  heat  which  it  is  capable  of  receiving  without 
a  change  or  its  physical  condition,  the  more  intense  the  light  which  is  emitted. 
An.  ignited  body,  therefore,  serves  as  a  temporary  storehouse  of  heat  and 
light.  The  vacuum-light  furnishes  a  remarkable  instance  of  the  results  of 
ignition.  The  charcoal  points,  being  the  terminal  poles  of  a  powerful 
battery,  are  inclosed  in  a  glass  vessel  in  which  a  vacuum  has  been  artificially 
produced.  The  light  issues  in  great  splendor  as  the  result  of  the  ignition  of 
minute  particles  of  charcoal  carried  between  the  poles,  but  the  charcoal  itself 
undergoes  no  combustion.  When  platinum  poles  are  used,  portions  of  that 
metal  are  volatilized  and  so  heated  as  to  give  out  the  intense  violet-blue  light 
which  characterizes  the  spark.  Mr.  Gassiot  has  observed,  that  under  these 
circumstances  the  negative  pole  assumes  the  appearance  of  being  corroded, 
owing,  as  he  found,  to  the  separation  of  particles  of  this  metal  and  their 
deposition  on  the  sides  of  the  vacuum-glass  tube.  Even  gases  attenuated  to 
the  highest  degree — in  fact,  almost  converted  into  a  vacuum  by  the  air- 
pump — are  rendered  incandescent  by  the  discharge  of  the  spark  from 
Ruhmkorff's  coil  {^see  page  83).  In  an  absolute  vacuum  no  discharge  passes, 
as  electrical  conduction  necessarily  requires  the  presence  of  matter  ;  but  Mr. 
Gassiot's  experiments  have  proved  that  what  has  been  hitherto  regarded  as 
a  vacuum,  is  space  filled  with  highly  attenuated  matter,  capable  of  being 
made  incandescent  by  the  electric  discharge.  The  more  attenuated  the  gas 
or  vapor,  the  more  stratified  is  the  light  of  the  discharge.  As  the  gas  is 
increased  in  quantity,  the  stratifications  become  closer,  until,  at  a  certain 
point,  the  discharge  entirely  loses  its  stratified  appearance  and  passes  into  a 
wave  line.  The  vivid  luminosity  and  the  varied  color  of  lightning,  is  pro- 
bably dependent  on  the  incandescence  of  the  gaseous  and  vaporous  consti- 
tuents of  the  atmosphere,  modified  by  the  density  of  the  stratum  in  which  the 
electric  discharge  takes  place. 

It  is  found  that  the  greater  number  of  metals  may  be  converted  into  vapor, 
and  that  these  vapors  when  rendered  incandescent  by  the  current,  emit  a 
light  varying  in  color  for  each  metal.  For  the  purpose  of  obtaining  the 
metals  in  a  volatile  state,  the  platinum  poles  are  moistened  with  the  respec- 
tive solutions.  M.  Faye  found  that  zinc  gave  a  blue  color  in  strata  or  bands  ; 
antimony,  a  lilac  color  :  mercury,  a  pale  blue  ;  cadmium,  an  intense  green  ; 
arsenic,  a  magnificent  lilac ;  and  bismuth,  a  variety  of  colors,  undergoing 
rapid  changes.  {Cosmos,  Sept.  20,  1861,  p.  321.)  It  has  been  further 
proved  that  these  colored  flames  and  incandescent  vapors  present  colored 
spectra  of  differently  refrangible  rays,  in  some  instances  characteristic  of  the 
substance.   {See  page  63.) 

Supporters  and  Combustibles. — Although  oxygen,  chlorine,  and  bromine 
give  rise  to  the  phenomena  of  combustion  with  other  bodies,  they  cannot  be 
made  to  combine  with  each  other,  so  as  to  evolve  light  and  heat ;  and  hence 
they  are  said  to  be  incombustible.  In  ordinary  language  they  are  called 
supporters  of  combustion,  while  the  bodies  to  which  they  unite  have  been 
called  combustibles.  It  is,  however,  generally  admitted  that  the  phenomena 
of  combustion  are  dependent  on  the  union  of  the  two  bodies;  and  that  the 
so-called  supporter  is  consumed  as  well  as  the  combustible,  and  aids  in 
furnishing  light  and  heat.  Thus  copper  and  sulphur,  at  a  high  temperature, 
combine  with  combustion.  Which  is  the  supporter  and  which  is  the  combus- 
tible ?  Both  must  he  regarded  as  combustible  substances — for  copper  burns 
in  chlorine,  and  sulphur  burns  in  oxygen.  Whether  we  put  phosphorus  into 
the  vapor  of  chlorine,  or  chlorine  into  the  vapor  of  phosphorus,  the  same 


HEAT    EVOLVED    IN    COMBUSTION.  103 

kind  of  combustion  equally  ensues,  and  the  products  are  similar.  During 
the  combustion  of  phosphorus  in  oxygen  the  intense  and  sudden  burst  of 
light  which  appears  after  the  phosphorus  has  entered  into  the  boiling  state, 
arises  from  the  difiTusion  of  its  vapor  throughout  the  oxygen  of  the  vessel, 
so  that  there  is  a  combustion  of  both  at  every  point  of  contact.  Up  to  this 
time  the  light  and  heat  may  have  appeared  to  proceed  from  the  solid  phos- 
phorus only  ;  but  it  will  now  be  observed  to  issue  equally  from  all  parts  of 
the  vessel  containing  the  oxygen.  The  oxygen  is  here  as  much  a  combus- 
tible as  the  phosphorus.  In  fact,  the  term  "  combustible"  is  relative  and 
arbitrary  ;  that  body  which  is  for  the  time  in  larger  quantity,  or  in  the  gaseous 
state,  is  called  the  "  supporter."  Coal-gas  burns  in  oxygen  or  air  only 
where  it  can  unite  with  oxygen  ;  and  it  is  therefore  called  a  combustible  gas. 
If  we  kindle  a  jet  of  coal-gas  issuing  from  a  bladder,  and  cause  the  flame  to 
be  projected  into  a  bell-glass  of  oxygen,  it  will  burn  brilliantly.  If  we  fill 
another  bell-glass  with  coal-gas,  ignite  it  at  the  mouth,  and  project  into  it 
through  the  flame  a  jet  of  oxygen,  this  gas  will  appear  to  burn,  and  in  fact 
does  burn,  in  a  jet  precisely  like  the  jet  of  coal-gas;  and  it' will  be  found  to 
give  out  the  same  amount  of  light  and  heat,  and  to  give  rise  to  similar  pro- 
ducts. The  oxygen  and  coal-gas  burn  only  where  they  meet  each  other  at 
a  high  temperature.  The  oxygen  burns  in  an  atmosphere  of  coal-gas  just  as 
certainly  as  the  coal-gas  burns  in  an  atmosphere  of  oxygen.  This  experi- 
ment may  be  performed  with  an  ordinary  argand  gas-burner.  A  long  chim- 
ney-glass should  be  placed  over  the  burner,  and  all  access  of  air  from  below 
cut  off  by  a  cork  and  a  disk  of  card.  If,  after  allowing  the  coal-gas  to  issue 
for  a  few  minutes,  in  order  to  remove  the  air,  it  is  ignited  at  the  top  of  the 
chimney-glass,  a  jet  of  oxygen  may  be  safely  propelled  downwards  through 
the  gas-flame,  and  the  oxygen  will  appear  to  burn  in  the  glass  cylinder  con- 
taining the  coal-gas.  These  facts  show  that  combustion  is  really  a  reciprocal 
phenomenon,  each  body  burning,  or,  in  chemical  language,  combining  with 
the  other  body,  and,  during  this  combination,  evolving  light  and  heat.  The 
terms  combustible  and  supporter  of  combustion  are,  however,  convenient  for 
use,  provided  we  understand  by  them  that  each  substance  shares  in  the  pro- 
cess, and  that  neither  is,  strictly  speaking,  passive. 

Heat  and  Light  of  Combustion. — The  results  of  experiments  on  some  sub- 
stances show  that  the  heat  of  combustion  is  almost  exclusively  derived  from 
the  oxygen.  Thus  it  appears,  from  the  researches  of  Despretz,  that  the  heat 
depends,  not  upon  the  quantity  of  the  combustible,  but  upon  the  weight  of 
oxygen,  consumed.  A  pound  of  oxygen,  in  combining  respectively  with 
hydrogen,  charcoal,  alcohol,  and  ether,  evolved  in  each  case  very  nearly  the 
same  quantity  of  heat,  each  raising  29  pounds  of  water  from  32^  to  212^. 
With  respect  to  the  comparative  heating  powers  of  equal  weights  of  different 
combustibles,  he  obtained  the  following  results  : — 

236  pounds  of  water  from  32°  to  212° 


pound  of  hydrogen  raised  . 

.     236 

"           oil,  wax 

.       90 

"           ether    .... 

.       80 

"           pure  charcoal 

.       78 

"           common  wood  charcoal 

.      75 

"           alcohol 

.       68 

"            bituminous  coal   . 

.       60 

"           baked  wood 

.       36 

"           wood  holding  20  per  cent. 

of  water       27 

« 

it 

u 

"  turf  (peat)  .         .         .         .      25  to  30        "  "  " 

This  table  indicates,  not  the  absolute  amount  of  heat  evolved,  but  the 
relative  heating  powers  of  fuels  burnt  under  similar  conditions;  and  it  further 
appears  to  show  that,  provided  the  same  weight  of  oxygen  be  consumed, 


104  HEAT    EVOLVED    IN    COMBUSTION. 

whatever  may  be  the  nature  of  the  fuel,  the  same  amount  of  heat  will  be 
evolved.  In  order  to  produce  an  intense  heat,  therefore,  the  object  is  not  so 
much  to  consume  the  fuel  as  to  consume  the  maximum  of  oxygen,  or  air  with 
a  minimum  of  fuel.  The  heating  power  of  the  blowpipe  and  of  the  blast- 
furnace, especially  of  the  hot  blast  (to  counteract  the  cooling  effect  of  the 
nitrogen  associated  with  oxygen  in  the  air),  will  now  be  intelligible  on 
chemical  principles.  It  is  not,  kowever,  strictly  true  that  the  same  weight 
of  oxygen  always  produces  by  combination  the  same  amount  of  heat.  Other 
experiments  performed  by  Despretz  have  shown  that  a  pound  of  oxygen,  in 
combining  with  iron,  tin,  and  zinc,  could  heat  nearly  twice  as  much  water  to 
the  same  temperature  as  that  which  in  his  table  he  assigns  to  hydrogen, 
carbon,  alcohol,  and  ether  ;  hence,  in  reference  to  these  metals,  oxygen  alone 
cannot  be  concerned  in  its  production.  So  with  regard  to  phosphorus ;  if 
this  substance  is  burnt  slowly,  to  produce  phosphorous  acid,  a  pound  of  oxygen 
in  combining  with  it  evolves  the  same  amount  of  heat  as  that  assigned  to 
carbon  and  hydrpgen  ;  but  if  the  combustion  is  so  intense  as  to  produce 
phosphoric  acid,  then  the  heat  evolved  is  twice  as  great,  resembling  that 
which  is  given  out  in  the  intense  combustion  of  iron,  tin,  and  zinc.  There 
is  another  fact  which  shows  that  the  rule  regarding  the  evolution  of  heat  is 
not  so  simple  as  Despretz  had  supposed;  namely,  that  when  carbon  is  in  a 
state  of  combination,  as  in  the  form  of  carbonic  oxide,  the  amount  of  heat 
evolved  during  its  combustion  and  conversion  into  carbonic  acid,  is  nearly 
equal  to  that  which  would  be  evolved  by  the  carbon  in  a  separate  state, 
although  the  latter  would  require  twice  the  amount  of  oxygen  to  convert  it 
to  the  same  product  (carbonic  acid).  {Kane''s  Elements  of  CJiemistry,  p. 
244.)  The  later  researches  of  Professor  Andrews  and  other  chemists  have 
shown,  that  the  quantity  of  heat  evolved  as  a  result  of  the  chemical  combina- 
tion of  bodies  is  definite,  and  that  it  has  a  specific  relation  to  the  combining 
number  of  each  substance.  With  a  proper  supply  of  oxygen,  or  air,  a  given 
weight  of  the  substance  always  produces  the  same  amount  of  heat. 

Hydrogen,  carbon,  sulphur,  and  phosphorus  are  the  four  principal  sub- 
stances, with  which  the  phenomena  of  combustion  are  witnessed  in  an 
atmosphere  containing  oxygen.  All  our  ordinary  sources  of  light  and  heat 
for  domestic  and  manufacturing  purposes  are  dependent  on  the  two  first- 
mentioned  elements,  associated  in  variable  proportions  in  coal,  wood,  and 
oil.  The  following  table  will  show  that  according  to  the  experiments  of 
Despretz,  hydrogen  and  carbon,  weight  for  weight,  consume  the  largest 
amount  of  oxygen  in  undergoing  perfect  combustion ;  and  that  hydrogen 
in  uniting  to  oxygen  has  more  tkan  three  times  the  heating  power  of 
carbon : — 


1  pound    of  hydrogen  takes 

6  pounds  of  carbon  take  . 
16  pounds  of  sulphur  take  . 
32  pounds  of  phosphorus  take 

Hence  by  reason  of  this  enormous  consumption  of  oxygen  in  proportion  to 
the  weight  of  material  burned,  hydrogen,  and  bodies  containing  it,  evolve 
the  greatest  amount  of  heat.  Hence  also  in  the  oxy-hydrogen  blowpipe,  we 
have  one  of  the  highest  sources  of  heat  at  present  known ;  and  as  an  indirect 
result  of  the  absorption  of  this  heat  by  the  infusible  substance,  lime,  we 
obtain  a  light  which  rivals  that  of  the  sun  in  intensity  and  chemical  power. 
Lately,  by  the  construction  of  a  close  furnace  of  lime,  and  the  use  of  the  oxy- 
hydrogen  blowpipe,  MM.  Deville  and  Debray  have  not  only  been  able  to 
volatilize  many  of  the  supposed  fixed  impurities  in  commercial  platinum ;  but 


Pounds  of       Ponnds 

Prop,  of  Coml 

Oxygen.          of  Air. 

to  Oxygen. 

8       or      40     . 

, 

.1:8 

16       or       80     . 

, 

.     1  :  2.6 

16       or       80     . 

, 

.     1:1 

40       or    200     . 

, 

.     1  :  1.25 

# 


COMBUSTION.      DEGREES    OF    HEAT.  105 

with  about  43  cubic  feet  of  oxyj^en  they  have  succeeded  in  meltifig  25  pounds 
of  platinum  in  less  than  three-quarters  of  an  hour,  and  casting  it  into  an  ingot 
in  a  coke  mould.  All  metals  are  melted,  and  many  are  entirely  dissipated  in 
vapor  by  the  intense  heat  produced  under  these  circumstances.  The  lime 
itself  is  unaltered  by  the  heat,  and  acts  as  a  powerful  non-conductor,  even 
when  not  more  than  an  inch  in  thickness.  Lime  and  magnesia  appear 
hitherto  to  have  resisted  fusion,  or  volatilization  as  oxides.  The  heat  given 
out  during  the  perfect  combustion  of  hydrogen  in  oxygen  was  calculated  by 
Sir  R.  Kane  {Elements  of  Chemistry,  p.  240)  to  amount  to  5478°  above  the 
freezing  point;  but  this  estimate  falls  far  below  that  assigned  by  the  recent 
experiments  of  Bunsen.  {See  p.  107.)  This  temperature  exceeds  the  heat 
of  other  artificial  sources.  It  can  only  be  surpassed  by  the  heat  of  the 
electric  discharge,  or  by  the  concentration  of  the  rays  of  the  sun  through  a 
powerful  lens  or  mirror.  When  hydrogen  is  burnt  in  atmospheric  air,  the 
cooling  effect  of  the  nitrogen  is  such  that,  according  to  the  same  authority, 
the  heat  does  not  exceed  2739°  above  freezing;  this  is  nearly  equal  to  the 
melting  point  of  cast  iron,  which  is  2786° 

Chemists  assign  different  temperatures  according  to  the  color  emitted  by 
the  incandescent  solid.  A  red,  yellow,  and  white  heat  are  frequently  referred 
to  in  chemical  processes,  bnt  the  temperatures  assigned  to  these,  vary  among 
different  authorities.  Lead  melts  at  620°,  and  zinc  at  773°,  but  neither  of 
these  metals,  at  the  melting  point,  is  visible  in  the  dark.  A  red  heat  seen 
only  in  the  dark,  is  usually  taken  at  about  980°,  but  this  is  invisible  in  day- 
light. The  iron  ladle  containing  melted  lead,  heated  to  this  temperature, 
shows  no  color,  but  if  taken  into  a  dark  closet,  it  will  be  observed  that  the 
iron  of  the  ladle  and  the  molten  lead  are  visibly  and  equally  red,  showing  that 
metals,  however  they  may  differ  from  each  other  in  their  melting  points, 
acquire  the  power  of  emitting  a  similar  light  at  the  same  temperature. 
From  620°  to  980°,  where  a  body  is  strongly,  but  at  the  same  time  is  not 
visibly  heated,  is  comprised  the  range  of  black  heat,  important  in  reference  to 
some  chemical  processes.  The  degree  for  a  visibly  red  heat  in  day-light  has 
not  been  accurately  determined.  From  some  experiments  made  in  conjunc- 
tion with  Dr.  Miller,  we  believe  it  to  be  at  about  the  melting  point  of 
antimony,  or  1160°.  A  cherry  red  is  about  1200°,  and  a  white  heat,  above 
the  melting  point  of  cast  iron  (2786°)  may  be  taken  at  3000°.  We  subjoin 
a  table  of  high  temperatures,  based  on  the  researches  of  Pouillet. 

Incipient  red  heat 

Dull  red 

Incipient  cherry  red  . 
Cherry  red  .... 

Bright  cherry  red       .     ^   . 
Deep  orange       .... 
Bright  orange     .... 
White  heat        .... 
Bright  white  heat 
Dazzling  white  heat  . 
Full  white  heat 

In  reference  to  combustion,  the  improvements  made  in  the  use  of  gas  as  a 
source  of  heat  have  depended  on  the  admixture  of  air  or  on  the  free  supply  of 
air  by  a  variety  of  arrangements  ;  and  in  the  construction  of  all  furnaces,  the 
adoption  of  this  principle  leads  to  an  economy  of  fuel,  the  prevention  of 
smoke,  and  the  production  of  the  largest  amount  of  heat. 

The  light  evolved  in  combustion  depends — 1,  on  the  intensity  of  the  heat; 
and,  2,  on  the  presence  of  solid  non-volatile  matter  which  is  capable  of 


Centigrade. 

Fahrenheit 

525° 

977^ 

700 

1292 

.       800 

1472 

900 

1652 

1000 

1832 

1100 

2012 

1200 

2192 

1300 

2372 

1400 

2552 

.     1500 

2732. 

.     1600 

2912 

106  LIGHT    FROM    COMBUSTION. 

receiving  thg  heat,  and  of  emitting  it  as  light.  When  combustion  takes 
place  at  a  low  red  heat,  as  in  the  aphlogistic  lamp  of  Sir  H.  Davj,  there  is 
bat  little  light.  In  fact,  this  is  only  visible  in  the  dark.  Hydrogen  burns 
with  intense  heat ;  but  as  watery  vapor  is  the  only  product,  there  is  no  solid 
matter  to  absorb  and  emit  the  heat  as  light.  If  platinum  wire,  or  particles 
of  charcoal  lime,  asbestos,  iron-filings,  zinc  or  magnesium,  are  introduced  into 
the  flame,  they  or  these  products  are  heated  and  emit  light.  The  bright 
white  light  emitted  by  coal-gas  is  owing  to  the  particles  of  carbon,  set  free 
during  the  combustion  of  the  gas,  acquiring  a  white  heat,  and  becoming 
incandescent  in  the  flame.  The  naphthalizing  of  ordinary  coal-gas  depends 
on  the  difl'usion  through  it  of  a  hydrocarbon  vapor,  which,  during  com- 
bustion, may  furnish  solid  particles  of  carbon  to  the  flame.  In  burning 
phosphorus  in  chlorine,  a  gaseous  chloride  is  produced,  and  the  phosphorus 
burns  with  a  pale  flame,  emitting  but  little  light;  but  when  it  is  burnt  in 
oxygen  it  forms  dense  solid  particles  of  phosphoric  acid,  which  being  strongly 
heated  emit  an  intensely  white  liglit.  The  difference  of  light  arising  from 
the  products  may  be  shown  by  raising  the  phosphorus,  which  has  been 
burning  in  a  bell-jar  of  chlorine,  into  the  atmosphere.  The  increased 
splendor  of  the  combustion  from  formation  of  a  solid  product  is  at  once 
manifested,  and  the  eff'ect  is  increased  by  plunging  a  ladle  with  burning 
phosphorus  into  a  bell-jar  of  oxygen.  In  burning  zinc  the  same  phenomenon  is 
observed; — the  oxide  of  zinc  produced  isa  solid  body,  which  becomesintensely 
heated  and  emits  a  large  amount  of  light.  If  a  piece  of  magnesium  wire  be 
ignited  in  a  Bunsen's  jet,  a  most  dazzling  white  light  is  evolved,  arising  from 
the  fixed  particles  of  the  oxide  of  magnesium  becoming  strongly  heated,  and, 
as  a  result  of  this,  evolving  a  light  of  the  greatest  intensity.  In  some  photo- 
chemical investigations  made  by  Bunsen  and  Roscoe,  it  was  calculated  that 
the  light  of  the  sun's  disk  was  only  524  times  as  great  as  the  magnesium 
light,  A  wire  of  about  the  1-1 00th  of  an  inch  in  diameter,  produced  by 
combustion  as  much  light  as  74  stearine  candles.  The  light,  therefore, 
arising  from  combustion,  depends  to  a  great  extent  on  the  nature  of  the 
combustible,  as  well  as  on  the  product  of  combustion.  Substances  like  iron 
and  charcoal,  which  are  fixed,  emit  a  great  amount  of  light  in  proportion  to 
the  heat  produced  and  the  constant  renewal  of  surface  leads  to  continuous 
combustion. 

The  intensity  of  the  light  is,  caeteris  paribus,  dependent  on  the  rapidity 
with  which  oxidation  takes  place,  and  the  amount  of  material  consumed. 
The  Bude  light  owes  its  brightness  to  the  introduction  of  a  current  of  oxygen 
into  the  centre  of  the  flame.  There  is  in  a  given  time  a  larger  consumption 
of  the  combustible  matter,  and  a  consequent  increase  of  light. 

The  color  of  the  light  emitted  in  combustion,  is,  to  a  certain  extent, 
dependent  on  temperature.  At  one  degree  of  keat,  the  light  is  red,  at 
another  yellow,  and  in  the  highest  degree  white.  These  three  colors  are 
well  known  in  chemical  processes  as  forming  broad  distinctions  in  the  tem- 
perature of  ignited  solids  {see  page  105.)  According  to  Bunsen,  between 
the  yellow,  red,  and  white  heat,  the  colors  of  intensely  heated  bodies  pass 
through  shades  of  blue  to  violet,  and  the  white  heat  is  the  resultant  of  all 
the  spectral  colors  emitted  by  the  heated  substance.  Apart  from  the  effects 
of  temperature,  there  are  colors  which  are  peculiar  to  the  combustible  sub- 
stance. The  light  evolved  by  burning  sulphur  is  of  a  pale  blue  color,  while 
zinc  gives  a  greenish  white;  potassium,  a  pale  purple  or  violet;  sodium,  an 
intense  yellow;  lithium,  calcium,  and  strontium,  shades  of  red;  barium, 
greenish  yellow  ;  boracic  acid,  green  ;  arsenic,  a  violet  blue  ;  and  antimony, 
a  pale  lemon  color.    It  will  be  perceived,  by  reference  to  page  102,  that  the 


HEAT    AND    OPACITY    OF    FLAMES.  ^^    **lOt 

colors  which  are  thus  produced  during  combustion,  differ  from  those  which 
are  emitted  as  a  result  of  the  incandescence  of  the  same  bodies. 

Among  the  compound  gases,  carbonic  oxide  is  known  by  the  blue  color  of 
its  flame  ;  cyanogen  gas  by  a  violet  flame  with  a  blue  halo  ;  and  phos- 
phuretted  hydrogen  gas  by  the  intense  yellowish-white  light  which  it  emits 
during  combustion. 

Nature  of  Flame. — Flame  arises  from  the  combustion  of  volatile  or 
gaseous  matter  emanating  from  the  heated  solid.  Those  bodies  only  burn 
with  flame  which,  at  the  usual  burning  temperature,  are  capable  of  assuming 
the  vaporous  or  gaseous  state.  Charcoal  and  iron  burn  without  flame  ; 
their  particles  are  not  volatile  at  the  temperature  at  which  they  burn. 
Phospliorus  and  zinc,  on  the  other  hand,  are  volatile  bodies,  and  therefore 
burn  with  flame.  Small  particles  of  each  substance  are  carried  up  in  vapor, 
are  rendered  incandescent  by  the  heat  of  combustion,  and  burn  wherever 
they  meet  with  the  atmospheric  oxygen  ;  the  more  volatile  the  substance, 
the  greater  the  amount  of  flame. 

Flame  is  hollow — a  fact  which  may  be  proved  by  numerous  experiments. 
If  a  piece  of  metallic  wire-gauze  be  depressed  over  a  flame,  this  will  be  seen 
to  form  a  ring  or  circle  of  fire,  dark  in  the  centre  and  luminous  only  at  the 
circumference,  where  the  gaseous  particles  meet  with  oxygen.  The  inflam- 
mable matter  traverses  the  meshes  of  the  gauze,  but  is  so  cooled  by  the  con- 
ducting power  of  the  metal  that  it  ceases  to  burn  above.  A  piece  of  stiff 
paper  suddenly  depressed  on  a  spirit-flame  to  about  its  centre,  presents  a 
carbonized  ring  corresponding  to  the  circularity  of  the  flame.  If  a  thin 
platinum  wire  be  stretched  across  a  wide  flame  of  alcohol,  it  will  be  heated 
only  at  the  two  points,  corresponding  to  the  circumference,  where  combus- 
tion is  going  on,  and  a  thin  deal  splint  will  be  charred  and  burnt  only  at 
these  two  points. 

By  allowing  a  jet  of  gas  to  issue  from  a  glass  cylinder,  in  the  manner 
described  at  page  103,  a  variety  of  experiments  may  be  performed  to  show 
the  hollowness  of  flame,  and  the  comparatively  low  temperature  of  the  gas 
or  vapor  in  the  interior.  A  lighted  wax  taper  fixed  on  wire,  introduced 
suddenly  through  the  sheet  of  flame,  is  extinguished  in  the  interior.  Gun- 
powder introduced  in  a  ladle  may  be  held  in  the  inner  space  within  the  flame 
for  a  long  time,  and  even  withdrawn  without  exploding.  Gun-cotton  will 
not  explode  under  these  circumstances  if  introduced  at  the  end  of  a  copper 
wire,  while  the  coal-gas  is  freely  issuing  from  the  chimney-glass,  and  the  jet 
is  not  kindled  until  after  its  introduction.  That  the  inner  portion  of  every 
cone  of  flame  consists  of  unburnt  gas,  or  combustible  vapor  comparatively 
cool,  may  also  be  proved  by  placing  within  it  the  open  end  of  a  glass  tube, 
supported  by  wire,  and  applying  a  lighted  taper  at  the  other  end  of  the  tube 
which  projects  out  of  the  flame.  The  unburnt  gas  or  vapor  will  be  con- 
ducted off  by  the  tube,  and  may  be  kindled  at  the  end  of  it,  as  from  an 
ordinary  jet.  Thus,  then,  all  inflammable  gases  and  vapors,  when  unmixed 
with  oxygen,  have  only  a  surface  combustion,  which  is  defined  by  the  access 
of  oxygen  and  its  contact  with  the  heated  gas  or  vapor. 

Flame  in  all  cases  consists  of  matter  ignited  to  a  high  temperature.  Sir 
H.  Davy  assigned  a  white  heat  to  ordinary  flame.  Bunsen  has  recently 
examined  the  temperature  of  flames  by  a  series  of  ingenious  experiments 
{Phil.  Mag.,  Aug.,  1860,  page  92),  and  has  arrived  at  the  following  conclu- 
sions :  the  temperatures  here  assigned,  being  those  of  the  centigrade  ther- 
mometer, of  which  5°  are  equal  to  9°  of  Fahrenheit,  plus  32^  for  the  difference 
of  the  zero. 

• 


108  COMBUSTION    BY    OXYGEN    SALTS. 

Sulphur  flame     .         .     1820°  Carbonic  oxide  flame    .     3042° 

Sulphide  carbon  .         .     2195  Hydrogen  flame  (in  air)     3259 

Coal-gas  flame     .         .     2350  Oxyhydrogen  flame      .     8061 

The  heat  of  the  electric  flame  far  surpasses  all  these  temperatures,  and  is 
at  present  undeterminable  in  its  degree  by  any  known  process. 

A  remarkable  announcement  has  been  made  by  KirchofF  and  Bunsen, 
respecting  the  colored  flames  of  metals  brought  to  the  state  of  incandescent 
vapor,  as  the  result  of  the  heat  of  combustion  or  of  the  electric  current — 
namely,  that  they  absorb  light  of  the  same  degree  of  refrangibility  as  that 
which  they  emit;  in  other  words,  their  flames  are  opaque  to  their  own  light. 
If  the  light  of  the  sun,  or  of  the  electric  current,  is  allowed  to  traverse  the 
flame  of  a  spirit-lamp  or  that  of  hydrogen  or  coal-gas,  no  shadow  is  pro- 
duced on  a  white  screen  placed  behind  it :  the  flame  is  quite  transparent,  but 
the  undulating  shadows  projected  for  more  than  a  foot  above  the  flame  by 
the  invisible  gaseous  products  of  combustion  (carbonic  acid  and  water),  are 
plainly  seen.  The  flame  of  a  common  candle  produces  no  shadow  when 
placed  between  a  screen  and  the  flame  of  an  oil-lamp.  The  shadow  of  the 
wick  only  is  seen  on  a  white  surface.  Foucault  observed  that  the  intense 
light  of  the  electric  arc  from  carbon-points,  was  so  transparent  that  the 
solar  rays  converged  upon  it  by  a  lens,  completely  traversed  it,  and  only  a 
slight  shadow  was  cast  upon  the  solar  light.  Bunsen  found  that  the  light  of 
a  sodium-flame  would  not  traverse  another  sodium-flame,  or  even  sodium- 
vapor,  produced  by  heating  sodium-amalgam  in  a  test-tube  much  below  its 
point  of  luminosity ;  and  the  singular  discovery  was  made,  that  direct  sun- 
light, passed  through  the  yellow  flame  of  sodium,  changed  the  yellow  spectral 
band  peculiar  to  that  metal  to  a  dark  double  line.  The  red  band  of  lithium 
was  also  changed  to  a  dark  band  by  sunlight.  {Phil.  Mag.,  August,  1860, 
page  108.)  From  these  results,  and  from  the  fact  that  in  the  pure  solar 
spectrum,  a  dark  line  appears  in  the  position  of  the  sodium-yellow  band, 
Kirchoff  and  Bunsen  have  inferred  that  sodium  must  be  a  large  constituent  of 
the  photosphere  of  the  sun.  For  a  similar  reason,  chromium,  iron,  nickel, 
and  magnesium  have  also  been  assigned  to  this  photosphere — and  sodium  to 
the  light  of  the  fixed  stars.  The  moon  and  Venus  exhibit  lines  correspond- 
ing with  those  of  the  sun.  Sirius  showed  different  lines,  and  Castor  others 
which  were  again  different.  In  Procyon  the  solar  line  D  (sodium),  and  in 
Capella  and  Betelgeux,  the  principal  star  in  Orion  D  (sodium)  and  b  were 
found.  (Miller.)  It  is  to  be  observed,  however,  that  the  light  of  platinum, 
rendered  incandescent  by  the  electric  fluid,  and  the  rays  of  a  Drummond 
light,  equally  changed  the  sodium-yellow  into  a  dark  band.  Opacity  is  the 
great  character  of  metals :  but  it  is  remarkable  that,  in  the  state  either  of 
incandescent  or  non-luminous  vapor,  this  complete  opacity  to  light  emitted 
by  their  own  flames,  should  thus  exist.  If  these  results  are  confirmed,  this 
property  of  metallic  vapors  might  be  made  a  test  of  the  alleged  metalline 
nature  of  certain  gases.  Incandescent  hydrogen  gives  colored  spectral  bands 
of  its  own  (page  63) ;  but  these  have  not  been  found  to  possess  any  absorbent 
power  at  ordinary  temperatures.  This  result  is  adverse  to  the  hypothesis  of 
its  metalline  nature. 

Products  of  Combustion. — The  products  of  ordinary  combustion  in  oxygen 
are  chiefly  water  and  carbonic  acid.  They  are  quite  unfitted  to  sustain  com- 
bustion, and  unless  removed  as  they  are  produced,  they  speedily  arrest  the 
process. 

Combustion  by  Oxygen  Salts.  Defiagration. — It  is  not  necessary  that 
oxygen  should  be  in  the  free  or  gaseous  state,  in  order  that  combustion 
should  take  place.     Salts  w%ich  abound  in  oxygen,  such  as  the  alkaline  per- 


•  DEFLAGRATION.  109 

chlorates,  and  chlorates,  nitrates  and  bichromates,  when  mixed  with  sub- 
stances which  have  a  tendency  to  unite  with  oxgen — e.  g.,  charcoal,  sulphur, 
or  phosphorus — and  heat  is  applied  to  the  mixture,  give  rise  to  combustion 
of  a  most  intense  kind.  The  salts  above  mentioned  contain  a  large  propor- 
tion of  oxgen  by  weight,  and  this  is  readily  evolved  in  contact  with  a  com- 
bustible. Even  the  liquid  acids  of  these  salts,  in  a  free  state,  are  capable  of 
protucing  the  phenomena  of  combustion.  Dr.  Roscoe  found  that  pure'  per- 
chloric acid,  obtained  from  the  perchlorate  of  potash,  was  a  most  powerful 
oxidizing  agent.  A  single  drop  of  the  liquid  brought  into  contact  with 
charcoal,  paper,  wood,  alcohol,  or  other  organic  substances  of  the  like  nature, 
caused  combustion  with  explosion,  falling  not  short  in  violence  of  that  of 
chloride  of  nitrogen. 

The  sudden  conversion  of  gunpowder  into  gaseous  and  vaporous  matter  is 
dependent  on  the  oxygen  of  the  nitre  combining  at  a  high  temperature  with 
the  charcoal  and  sulphur.  Gun-cotton  contains  nitrous  acid  in  large  propor- 
tion. This  readily  parts  with  its  oxygen  at  a  moderate  heat,  and  the  carbon 
and  hydrogen  of  the  cotton  are  entirely  consumed.  If  a  quantity  of  nitre  is 
melted  in  a  flask,  and  a  piece  of  red-hot  charcoal  is  dropped  on  the  melted 
salt,  it  will  continue  to  glow  as  a  result  of  combustion,  at  every  point  at 
which  it  touches  the  nitre,  until  all  the  charcoal  or  the  nitre  has  been  consumed. 
If  chlorate  of  potash  is  melted  in  a  flask,  and  a  splint  of  lighted  wood  is 
introduced  into  the  liquefied  salt,  there  is  violent  and  intense  combustion, 
almost  amounting  to  explosion.  A. mixture  of  finely-powdered  charcoal, 
with  an  equal  portion  of  powdered  nitrate  or  chlorate  of  potash,  burns,  when 
heated,  with  great  violence,  giving  rise  to  the  phenomena  of  deflagration. 
This  process  of  combustion  is  occasionally  resorted  to  by  chemists  for 
oxidizing  carbon,  sulphur,  and  phosphorus  in  organic  substances,  in  order 
to  convert  the  elements  to  salts,  and  determine  the  presence  and  proportion 
in  which  they  exist.  A  mixture  of  twenty-eight  parts  of  ferrocyanide  of 
potassium,  twenty-three  parts  of  white  sugar,  and  forty-nine  parts  of  chlorate 
of  polash,  is  known  under  the  name  of  "  white  gunpowder.''^  In  combustion 
it  produces  a  large  amount  of  gaseous  matter,  consisting  of  nitrogen,  carbonic 
acid,  carbonic  oxide,  and  aqueous  vapor.  This  is  a  dangerous  compound  to 
prepare  or  even  to  preserve.  The  materials  should  be  separately  powdered, 
and  then  mixed.  Mr.  Hudson  has  observed,  that  when  the  materials  are 
ground  together  with  a  little  water  and  dried  at  150°,  the  powder  is  much 
more  explosive.  Even  simple  friction  with  a  spatula,  or  slight  compression, 
was  then  sufficient  to  cause  a  violent  explosion.  A  drop  of  sulphuric  acid 
will  explode  it ;  it  may  also  be  exploded  by  percussion.  This  chemist  found 
that  its  explosive  force  was  twice  as  great  as  that  of  common  gunpowder. 
{Chem.  News,  Aug.  24,  1861.)  It  would  prove  a  dangerous  substitute  for 
gunpowder,  but  it  might  be  serviceable  as  a  composition  for  shells.  An 
explosive  mixture  is  also  formed  by  powdering  separately,  and  mixing  two 
parts  of  "the  black  sulphide  of  antimony  with  one  part  of  chlorate  of  potash. 
This  composition,  when  dry,  is  exploded  by  friction  or  percussion,  by  heat,  or  by 
the  contact  of  concentrated  sulphuric  acid.  It  furnishes  an  instance  of  violent 
combustion,  at  the  expense  of  the  oxygen  of  the  chloric  acid.  The  needle- 
gun  powder  of  the  Prussians  has  a  somewhat  similar  composition.  It  con- 
sists of  five  parts  of  chlorate  of  potash,  three  parts  of  sulphide  of  antimony, 
and  two  parts  of  sulphur.  These  substances  are  separately  reduced  to  fine 
powder,  and  are  then  carefully  mixed  without  trituration. 


110  CONVERSION    OF    OXYGEN    TO    OaONE, 


^1* 


CHAPTER    VIII.  • 

OZONE.  — ALLOTROPIC    OXYGEN.  —  A NTOZONE. 

History. — In  addition  to  the  ordinary  state  in  which  oxygen  is  known  to 
chemists,  it  is  believed  to  exist  in  another  state — that  of  allotropic  oxygen, 
or,  as  it  is  generally  called,  Ozone.  It  had  been  noticed  that  a  peculiar 
pungent  odor,  resembling  that  of  phosphorus,  was  sometimes  evolved  on  the 
discharge  of  the  electric  spark — that  litmus  paper  was  reddened — that 
starch-paper  moistened  with  iodide  of  potassium  was  rendered  blue :  and 
that  paper  moistened  with  potash,  deflagrated  when  dry.  These  efl'ects  were 
generally  referred  to  the  production  of  nitric  acid  by  the  oxidation  of  the 
nitrogen  of  the  air.  In  1840,  Schonbein  of  Bale  announced  that  in  the 
electrolysis  of  water,  this  odorous  body  appeared  at  the  positive  pole  of  the 
battery  (if  of  platinum)  and  that  it  might  be  preserved  in  well-closed  bottles. 
He  considered  it  to  be  an  electro-negative  element,  and  named  it  Ozone 
(from  o^co,  to  smell.)  In  the  Comptes  Rendus  for  1850,  he  described  a 
method  of  procuring  it  from  phosphorus  and  ether,  as  well  as  its  most 
characteristic  properties  ;  and  announced  that  it  was  produced  in  the  atmos- 
phere, especially  during  winter,  as  the  result  of  electrical  changes. 

In  a  lecture  at  the  Royal  Institution,  in  June,  1851,  Mr.  Faraday  gave  an 
account  of  Schonbein's  researches,  with  the  results  of  his  own  observations. 
Fremy  and  Becquerel  in  France,  and  Dr.  Andrews  and  Dr.  Tait  in  this 
country  {Phil.  Trans.,  1855-6)  have  since  investigated  the  subject.  [The 
reader  is  also  referred  to  an  Essay  by  Dr.  Scoutetten,  entitled  D  Ozone,  ou 
VOxygene  electrise,  Paris,  1856  ;  and  for  a  more  recent  account  of  Ozone 
in  its  medical  aspects,  to  a  Paper  by  Dr.  Moffat,  read  at  the  British  Associ- 
ation Sept.  1861.] 

The  results  obtained  by  different  observers  tend  to  show  that  ozone  is 
oxygen  in  an  altered  state ;  and  that  this  conversion  may  be  produced  by 
the  electric  spark  (when  silently  discharged  into  dry  oxygen) — by  current 
electricity  in  the  decomposition  of  water,  and  by  various  chemical  processes; 
further,  that  however  produced,  the  properties  are  the  same.  The  principle 
evolved  is  characterized  by  a  peculiar  odor,  and  by  an  intensely  oxidizing 
and  bleaching  power — so  that  substances  on  which  common  oxygen  produces 
no  effect,  are  rapidly  oxidized  on  contact  with  air  which  contains  only  a 
small  portion  of  this  odorous  principle. 

Preparation. — The  most  convenient  method  of  procuring  ozone,  t)r  rather 
an  ozonized  atmosphere,  is  to  place  in  a  large  bottle  of  air,  which  can  be 
completely  closed,  a  stick  o{ phosphorus  freshty  scraped.  Sufficient  distilled 
water  should  be  poured  into  the  bottle  to  partially  cover  the  phosphorus  ; 
the  vessel  should  then  be  closed  with  the  stopper,  and  kept  in  a  room  at  a 
temperature  between  60°  and  70°.  The  phosphorus  is  oxidized  in  the  bottle 
in  the  usual  way  ;  and  during  this  process  of  oxidation,  a  portion  of  the 
oxygen  passes  to  the  state  of  ozone,  and  is  diffused  through  the  air  of  the 
bottle.  It  is  only  in  the  slow  oxidation  of  phosphorus  at  a  low  tempera- 
ture that  ozone  is  met  with  as  a  product.  When  this  metalloid  is  oxidized 
at  a  high  temperature,  as  in  the  production  of  phosphoric  acid  by  combustion, 
no  ozone  is  found.     The  usual  test  for  the  presence  of  ozone  is  a  slip  of 


CONVERSION    OP    OXYGEN    TO    OZONE.  '  111 

pnper  jnoistened  with  a  solution  of  starch  and  iodide  of  potassium.  {See 
page  114.)  When  ozone  is  present,  this  paper,  on  immersion,  acquires  a 
blue  color,  owing  to  the  oxidation  of  the  potassium  and  the  production  of 
iodide  of  starch.  If  a  similar  slip  of  paper  is  put  into  a  similar  bottle  of  air, 
containing  distilled  water  without  phosphorus,  no  change  is  produced.  In 
a  warm  room,  the  evidence  of  the  presence  of  ozone  in  the  bottle  is  usually 
procured  in  about  ten  or  twelve  minutes ;  but  the  maximum  quantity  of 
ozone  is  found  in  it  in  from  two  to  ten  hours.  Only  a  small  part  of  the  oxy- 
gen (from  l-50th  to  l-200th)  appears  to  undergo  this  change ;  and  if  long 
kept,  the  ozone  may  be  lost  by  combining  with  and  oxidizing  the  phos- 
phorus :  hence  the  phosphorus  should  be  removed  by  inverting  the  bottle  in 
water  so  soon  as  the  test-paper  is  strongly  blued.  The  ozonized  air  will 
then  preserve  its  properties  for  several  days.  So  if  the  iodide-paper  be  left 
in  the  bottle,  the  blue  color  will  after  a  time  disappear,  by  the  ozone  com- 
bining with  the  iodine  to  form  iodic  acid.  It  is  not  produced  in  dry  oxygen, 
nor  in  humid  air  or  oxygen,  when  mixed  with  certain  gases  or  vapors  which 
prevent  the  oxidation  of  phosphorus  ;  but  it  appears  to  be  more  readily  pro- 
duced, ceeteris  paribus,  when  oxygen  is  mixed  with  nitrogen,  hydrogen,  or 
carbonic  acid.  By  washing  and  decantation,  the  ozonized  air,  which  is  quite 
insoluble  in  water,  may  be  deprived  of  the  phosphorus-vapor  associated  with 
it,  and  kept  in  well-closed  bottles.  It  is  speedily  lost  by  diffusion.  Graham 
found  that  ozone  traversed  dry  and  porous  stoneware.  Ozone  may  be  pro- 
duced on  a  small  scale,  by  placing  a  piece  of  phosphorus  with  water  in  a 
watch-glass  and  inverting  over  this  another  glass  containing  the  test-paper 
or  liquid. 

Ozone  is  produced  by  passing  the  electric  spark  silently  into  pure  and  dry 
oxygen.  Fremy  and  Becquerel  found  that  pure  oxygen,  contained  in  a  sealed 
tube,  when  treated  for  a  sufficient  time  with  a  series  of  electric  sparks,  under- 
went a  complete  conversion  into  ozone,  as  the  whole  contents  of  the  tube 
when  broken  were  absorbed  by  a  solution  of  alkaline  iodide,  in  which  it  was 
immersed.  In  the  electrolytic  decomposition  of  water  the  oxygen  at  the 
positive  pole  has  ozonic  properties,  provided  the  poles  employed  are  of  gold 
or  platinum.  The  hydrogen  evolved  gave  no  indication  of  ozone.  Faraday 
found  that  a  mixture  of  iodide  of  potassium  and  starch  was  decomposed  at 
the  positive  pole,  even  after  the  gaseous  oxygen  had  been  made  to  pass 
through  a  tube  containing  a  layer  of  cotton  soaked  in  a  solution  of  potash. 
The  object  of  this  arrangement  was  to  arrest  any  acid  which  might  be  simul- 
taneously produced,  and  thus  lead  to  the  decomposition  of  the  iodide.  Dr. 
Letheby  found  that  the  ozone  thus  evolved  at  the  positive  pole  possessed  the 
same  power  of  coloring  strychnia  or  aniline  as  the  oxygen  (ozone)  liberated 
by  sulphuric  acid  from  the  peroxides  of  manganese  and  lead,  and  from  chro- 
mic acid. 

In  1850,  Schonbein  found  that  ozone  was  a  product  of  the  slow  combustion 
of  ether.  If  a  small  quantity  of  ether  is  poured  into  a  jar  or  bottle,  and  a 
clean  glass  rod,  or  small  iron  bar,  heated  to  about  500°,  is  introduced,  acid 
vapors  are  given  off  which  redden  wetted  litmus  paper  at  the  mouth  of  the 
jar,  and  which  set  free  iodine  from  iodide  of  potassium,  causing  the  blueing 
of  starch-paper  impregnated  with  this  salt.  After  the  removal  of  the  rod  or 
bar  several  strips  of  paper  successively  introduced  into  the  jar  will  undergo 
the  same  change.  Clean  platinum,  and  even  copper,  will  produce  similar 
effects.  The  residuary  ether  in  the  jar  at  the  same  time  acquires  new  pro- 
perties. It  bleaches  sulphate  of  indigo,  and  converts  chromic  into  blue  per- 
chromic  acid  (owing  to  the  presence  of  antozone  or  peroxide  of  hydrogen). 
If  the  rod  or  metal  used  in  this  experiment  is  too  strongly  heated,  the 
ozone  formed  is  reconverted  into  oxygen  ;  and  if  it  is  not  sufficiently  heated, 


112  OZONIDES    AND    THEIR    PROPERTIES. 

no  ozone  is  produced.  In  either  case  the  tests  fail  to  show  the  presence  of 
an  oxidizing  body.  It  has  been  suggested  that  the  results  of  this  experi- 
ment are  explicable  on  the  supposition  that  the  nitrogen  of  the  air  is  burnt, 
or  oxidized  at  a  low  temperature,  and  converted  into  nitric  acid  ;  but  the  fact 
that  they  are  not  observed  at  temperatures  at  which  ozone  cannot,  and  nitric 
acid  can,  exist ;  and  further,  that  the  ether  itself  undergoes  changes  which 
admit  of  no  explanation  on  this  hypothesis,  are  circumstances  adverse  to  this 
view.  Asa  permanent  source  of  ozone,  Boettger  has  recently  suggested  that 
a  mixture  should  be  made  of  two  parts  of  permanganate  of  potash  and  three 
parts^f  sulphuric  acid.  The  pasty  mass  thus  produced  will,  he  states,  con- 
tinue to  give  off  ozone  for  several  months.  (Chetn.  News,  Ang.  1861.)  The 
effects  in  this  case  have  been  referred  to  the  presence  of  chlorine.  {Chem. 
News,  Oct.  26,  1861.) 

Properties. — It  has  been  found  that  in  whatever  manner  ozone  is  produced 
its  properties  are  the  same.  It  is  insoluble  in  water,  alcohol,  and  ether. 
When  much  diluted  with  other  gases,  it  is  destroyed  by  agitation  with  a 
large  quantity  of  water.  It  is  readily  dissolved  by  a  solution  of  an  alkaline 
iodide,  converting  it  into  iodate,  and  it  is  absorbed  by  leaf  silver  in  a  humid 
state.  It  decomposes  the  protosalts  of  manganese  (sulphate  and  chloride), 
producing  peroxide,  and  causing  a  brown  stain  on  paper  immersed  in  these 
solutions.  Silver  leaf,  on  which  common  oxygen  has  no  action  is,  when 
wetted  and  exposed  to  ozonized  air,  slowly  oxidized,  and  the  ozone  disap- 
pears. Andrews  found  that  dry  silver,  whether  in  leaf  or  filings,  entirely 
destroyed  ozone  when  prepared  by  electrolysis  or  by  frictional  electricity, 
and  that  mercury  had  also  the  property  of  absorbing  it.  Thin  films  of  metal- 
lic arsenic  and  antimony  are  oxidized  by  it — the  arsenic  is  rapidly  converted 
into  arsenic  acid  and  disappears.  This  experiment,  which  serves  to  distin- 
guish a  deposit  of  metallic  arsenic  from  one  of  antimony,  may  be  thus  per- 
formed. Place  a  watch-glass,  containing  the  deposit  of  arsenic,  over  another 
containing  a  clean  slice  of  phosphorus  with  a  few  drops  of  water.  In  a  few 
hours  the  arsenical  deposit  will  entirely  disappear,  forming  arsenic  acid. 
Peroxides. of  manganese,  silver,  lead,  and  iron,  as  well  as  oxide  of  copper, 
destroy  it,  or  rather  convert  it  into  oxygen.  Among  other  reactions,  the 
sulphides  of  lead  and  silver  are  changed  into  white  sulphates,  and  cyanide  of 
potassium  into  cyanate  of  potash,  while  the  yellow  ferrocyanide  is  converted 
by  it  into  the  red  ferricyanide  of  potassium. 

Organic  substances  are  variously  affected  by  it.  Vegetable  colors  are 
bleached  or  altered.  Blue  litmus  is  bleached  without  being  first  reddened. 
The  color  of  sulphate  of  indigo  is  discharged  when  the  liquid  is  shaken  with 
ozonized  air.  Filtering-paper,  soaked  in  aniline  or  pyrogailic  acid,  is  rapidly 
turned  brown.  Andrews  found  that  caoutchouc  and  cork  are  rendered  brit- 
tle and  destroyed.  Besanez  noticed  that  uric  acid  in  water,  when  shaken 
with  ozonized  air,  was  dissolved  and  changed  into  urea  and  allantoin.  (Hep. 
de  Pharni.,  1859,  and  Chem.  News,  1,  3t.)  He  also  found  that  ozone  readily 
entered  into  combination  with  tannic  acid,  and  that  oxalic  acid  was  a  pro- 
duct of  this  union.  The  milky  white  precipitate  of  guaiacum  resin  produced 
by  adding  a  few  drops  of  the  tincture  to  a  quantity  of  distilled  water,  is  ren- 
dered blue  or  of  a  pale  bluish-green  color,  when  shaken  with  ozonized  air. 

All  these  chemical  changes  are  due  to  oxidation  ;  and  oxides  alone  result. 
In  many  respects  ozone  resembles  chlorine.  It  readily  displaces  hydrogen, 
oxidizing  it  as  well  as  the  radical  with  which  it  is  associated.  It  will  even 
combine  with  nitrogen  at  common  temperatures,  when  in  contact  with  water 
and  a  base.  Ozonized  air,  placed  over  lime-water,  produced  nitrate  of  lime, 
and  from  this  compound,  nitre  was  procured  by  double  decomposition 
(Schonbein).     It  oxidizes  ammonia,  and  sulphuretted   hydrogen  gas,  land 


OZONIDES    AND    THEIR    PROPERTIES.  113 

converts  nitrous  and  sulphurous,  into  nitric  and  sulphuric  acids.  It  acts  as 
a  powerful  disinfectant,  and  its  influence  in  the  atmosphere  is  considered  to 
be  exerted  in  oxidizing  and  destroying  foul  effluvia.  It  is  at  any  rate  diffi- 
cult to  procure  evidence  of  the  presence  of  ozone  in  the  vicinity  of  these 
effluvia,  or  in  densely  populated  places ;  and  it  is  equally  difficult  to  under- 
stand how  ozone,  in  a  free  state,  can  be  to  any  extent  diffused  through  the 
atmosphere,  when  its  tendency  to  combine  with  all  oxidizable  substances  is 
proved  to  be  so  powerful. 

Although  ozone  is  not  soluble  in  water,  it  appears  to  be  dissolved  by  cer- 
tain liquids.  A  solution  of  pure  iodide  of  potassium  readily  dissolves  it, 
acquiring  a  yellow  or  brown  color  according  to  its  strength.  Iodine  is  set 
free  so  that  this  is  not  a  true  solution  but  a  removal  of  ozone  by  oxidation. 
Oil  of  turpentine,  when  long  kept  in  contact  with  air,  dissolves  and  fixes 
ozone.  If  the  oil  thus  changed  is  mixed  with  a  solution  of  iodide  of  potas- 
sium, and  the  mixture  is  well  stirred,  it  acquires  after  a  time  a  yellow  color, 
owing  to  the  ozone  combining  with  the  potassium  and  setting  the  iodine  free. 
The  vapor  of  oil  of  turpentine  in  contact  with  phosphorus  exposed  to  air  and 
w-ater  either  removes  the  ozone  as  it  is  produced,  or  prevents  its  production, 
for  under  these  circumstances  the  oxygen  of  the  air  is  not  ozonized  by  phos- 
phorus. Oil  of  turpentine  containing  ozone  has  a  bleaching  power.  When 
shaken  with  a  diluted  solution  of  sulphate  of  indigo  the  color  is  speedily  dis- 
charged. Other  essential  oils,  such  as  those  of  cinnamon  and  cloves,  have  also 
been  found  to  absorb  and  fix  ozone.  Ether  long  kept  in  contact  with  air 
contains  ozone  ;  it  decomposes  a  solution  of  iodide  of  potassium — bleaches 
indigo,  and  has  usually  at  the  same  time  an  acid  reaction  on  test  paper. 
Ozone  appears  to  be  a  constituent  of  the  alkaline  permanganates,  and  when 
these  are  dissolved  in  water  it  exists  potentially  in  a  state  of  solution.  The 
destruction  of  the  pink  color  of  the  permanganate  of  potash  by  organic  mat- 
ter, is  probably  owing  to  the  separation  of  the  oxygen  as  ozone.  One  drop 
of  a  solution  of  the  permanganate  added  to  a  mixture  of  iodide  of  potassium 
and  starch,  produces  the  blue  iodide  of  starch  by  oxidizing  the  potassium, 
and  the  precipitated  resin  of  guaiacum  is  rendered  blue  by  it.  Sulphate  of 
indigo  is  bleached  by  this  liquid,  and  foul  effluvia  are  oxidized  and  lose  their 
offensiveness.  An  alkaline  permanganate,  under  the  name  of  ozonized  water, 
Condy's  liquid  has  been  of  late  much  used  in  medical  practice  as  a  deodorizer, 
or  as  an  oxidizer.  The  peroxide  of  manganese — one  of  the  class  of  ozonides, 
presents  similar  properties.  The  peroxide  has  no  action  on  a  solution  of 
iodide  of  potassium  and  starch  ;  but  if  a  little  acetic  acid  is  added,  oxygen, 
as  ozone,  is  set  free,  and  the  liquid  immediately  acquires  a  blue  color.  If 
diluted  sulphate  of  indigo  is  substituted  for  the  alkaline  iodide,  the  color  is 
discharged.  The  compounds  containing  oxygen  as  ozone  are  possessed  of 
similar  properties  :  they  are  called,  by  Schonbein,  ozonides.  The  following 
are  the  principal  : — 

MngO,  Pb02  CrOg  COgOg  MnOg 

MnOa  AgOj  BiOg  NigOg 

Among  these,  peroxide  of  lead  appears  to  have  a  most  energetic  action. 
Without  the  addition  of  any  acid,  it  instantly  sets  free  iodine  from  iodide  of 
potassium,  and  bleaches  a  solution  of  sulphate  of  indigo.  When  one  part  of 
dry  sulphur  is  rubbed  in  a  warm  mortar  with  five  or  six  parts  of  dry  peroxide 
of  lead,  the  oxygen,  as  ozone,  is  suddenly  given  off  with  combustion  of  the 
sulphur,  and  formation  of  sulphide  of  lead. 

Mr.  Spencer  enumerates  the  magnetic  oxide  of  iron  as  one  of  the  com- 
pounds  of  this  metal,  containing  oxygen  in  the  state  of  ozone.     He  has 
constructed  a  filter  in  which  this  mineral  substance  is  the  active  material  for 
8 


114  TESTS    FOR    OZONE    IN    AIR. 

the  puriBcation  of  water,  by  oxidizing  and  destroying  all  organic  matters 
contained  in  it. 

One  of  the  most  remarkable  properties  of  ozone  is,  that  from  whatever 
source  it  may  be  derived — it  is  reconverted  into  oxygen  by  a  moderate  heat. 
If  the  heat  be  between  500^  and  600°,  the  conversion  is  immediate  ;  at  a 
lower  temperature  (450°)  it  takes  place  more  slowly.  Andrews  found  that 
no  water  was  produced  during  this  conversion,  and  that  only  pure  oxygen 
resulted.  Fremy  and  Becquerel  have  confirmed  this  result.  This  disposes 
of  the  question,  whether  ozone  is  a  higher  oxide  of  hydrogen.  It  obviously 
contains  no  hydrogen.  Ozonized  air  passed  through  a  tube  heated  as  above 
mentioned,  produces  the  usual  reaction  on  iodide  paper  on  entering  the  tube, 
but  has  entirely  lost  this  property  when  it  passes  out.  Hence,  while  elec- 
tricity converts  oxygen  into  ozone — heat  reconverts  ozone  into  oxygen. 
Electricity,  in  long-continued  sparks,  will  also  bring  about  this  reconversion 
into  oxygen.  Faraday  has  proved  by  experiment  that  when  electrical  dis- 
charges are  made  through  a  heated  platinum  coil,  no  ozone  is  produced, 
while,  when  the  coil  was  allowed  to  cool,  ozone  reappeared  with  each  spark. 
These  facts  show  not  only  that  ozone  is  oxygen  ;  but  also  that  the  oxidizing 
effects  attributed  to  it  in  the  various  modes  of  its  production  cannot  proceed 
from  the  presence  of  nitric  acid,  hyponitric  acid,  or  chlorine.  A  heat  of 
500°  would  not  destroy  the  oxidizing  action  of  these  compounds. 

When  peroxide  of  manganese  is  heated,  oxygen  is  said  to  be  given  off;  but 
ozone  may,  in  this  case,  be  actually  evolved,  and  converted  into  ordinary 
oxygen  by  heat.  (Schonbein.)  Peroxide  of  manganese,  iron,  and  lead, 
absorb  ozone,  and  convert  it  into  oxygen  at  all  temperatures.  When  either 
of  these  compounds  is  mixed  with  chlorate  of  potash,  and  heated,  it  is  well 
known  that  oxygen  is  obtained  from  the  chlorate  at  a  much  lower  tempera- 
ture than  when  the  oxide  of  manganese  or  chlorate  is  separately  heated  ;  but 
no  oxygen  is  evolved  from  the  peroxide  itself  (see  page  90).  Schonbein 
explains  this  singular  phenomenon  by  assuming  that  the  chlorate  is  a  com- 
pound of  chloride  of  potassium  and  of  oxygen  as  ozone  ;  and  that  this  com- 
bined ozone,  like  free  ozone,  is  changed  by  the  peroxide  into  oxygen,  and  is 
thus  readily  separated  from  the  chloride.  The  oxygen  thus  obtained,  always 
contains  chlorine.  It  has  the  odor  of  this  gas,  bleaches  litmus  paper,  decom- 
poses iodide  of  potassium,  and  precipitates  a  solution  of  nitrate  of  silver.  It 
is  probable  that,  in  this  case,  the  ozone  displaces  a  portion  of  the  chlorine 
from  the  chloride,  and  that  some  manganate  of  potash  is  formed. 

Peroxide  of  iron  has  even  a  more  powerful  effect  by  contact  with  the 
chlorate.  A  thousandth  part  of  the  peroxide  mixed  with  the  fused  chlorate, 
was  found  to  liberate  oxygen  abundantly ;  and  with  one  two-hundredth  part, 
the  oxygen  was  evolved  with  great  rapidity — the  saline  mass  becoming  incan- 
descent. A  mixture  of  one  part  of  peroxide  with  thirty  parts  of  chlorate, 
when  heated  to  the  point  of  fusion,  brought  about  an  ignition  of  the  mass 
with  an  evolution  of  the  gas  almost  amounting  to  explosion.  (Pelouze  et 
Fremy,  Op.  cit.,  1, 194.)  In  this  case,  also,  chlorine  is  set  free,  and  probably 
some  ferrate  of  potassa  is  formed. 

Tests. — Various  methods  are  employed  for  testing  the  presence  of  ozone 
in  a  gaseous  mixture  containing  it.  The  iodide  of  potassium  and  starch 
elsewhere  referred  to  (page  111),  is  generally  employed,  and  is  known  as 
Schonbein's  test.  It  is  thus  prepared:  One  part  oi pure  iodide  (free  from 
iodate)  is  dissolved  in  two  hundred  parts  of  distilled  water  ;  ten  parts  of 
starch,  finely  powdered,  are  mixed  with  the  solution,  and  the  liquid  is  gently 
heated  until  it  is  thickened  from  the  solution  of  the  starch.  White  unsized 
or  sized  paper  is  soaked  in  the  liquid  :  the  paper  is  dried,  cut  into  slips  three 


OZONE    OP    THE    ATMOSPHERE.  115 

inches  long  by  three  quarters  of  an  inch  wide,  and  these  are  preserved  in  a 
stoppered  bottle. 

When  intended  for  use,^  slip  of  the  prepared  paper  is  exposed  to  a  free 
current  of  air  in  a  spot  sheltered  as  mnch  as  possible  from  rain,  light,  and 
foul  effluvia,  for  a  period  varying  from  six  to  twenty-four  hours.  An  inge- 
niously construpted  box  for  testing  the  atmosphere  has  been  contrived  by 
Mr.  Lowe  {Proc.  R.  S.,  vol.  10,  p.  537).  By  exposure,  the  paper  becomes 
brown,  and  when  wetted  acquires  shades  of  color,  varying  from  a  pinkish 
white  and  iron  gray  to  a  blue.  A  chromatic  scale,  covering  10°,  has  been 
contrived  by  Schonbein,  with  which  the  changes  in  the  wetted  paper  may  be 
compared.  Fremy  recommends,  as  a  test,  white  blotting-paper,  soaked  in 
an  alcoholic  solution  of  guaiacum,  and  dried  in  the  dark.  By  exposure  to 
an  ozonized  atmosphere  this  paper  acquires  a  bright  blue  color.  Houzeau's 
test  is  a  s4rip  of  litmus  paper  of  a  wine-red  color,  of  which  one-half  has  been 
soaked  in  a  solution  of  iodide  of  potassium  in  water,  in  the  proportion  of 
one  per  cent.  As  a  result  of  exposure  to  ozonized  air,  the  iodized  portion 
becomes  alkaline,  and  the  paper  acquires  a  deep  blue  tint.  The  other  por- 
tion preserves  its  normal  color  ;  and  by  showing  an  acid  or  alkaline  reaction, 
may  reveal  the  presence  of  vapors  in  the  air,  which  might  otherwise  be  a 
source  of  error. 

As  paper  is  fragile,  slips  of  clean  calico  (containing  starch),  dipped  in 
iodide  of  potassium,  have  been  substituted  by  Mr.  Lowe.  This  gentleman 
found  that  twenty-four  hours'  exposure  was  required  for  a  satisfactory  result. 
The  calico  may  be  used  dry,  and  wetted  after  the  exposure  is  complete.  The 
iodized  calico  acquires  various  shades  of  a  brown  color,  becoming  pink,  gray, 
or  blue,  when  dipped  in  water.  Mr.  Lowe  observed  that  the  strongest  effect 
was  produced  during  the  night,  and  at  some  elevation  above  the  ground ; 
also  that  the  months  of  January,  February,  and  March,  gave  the  largest 
amount,  both  day  and  night.  On  a  great  number  of  days  on  which  obser- 
vations were  made,  there  were  no  visible  traces  of  ozone.  Other  observers 
have  found  it  to  vary  according  to  locality,  the  season  of  the  year,  the  hour 
of  the  day,  the  direction  of  the  wind,  and  the  height  of  the  place  above  the 
level  of  the  sea.  It  is  seldom  found  in  closely  inhabited  spots.  In  some 
observations  made  at  Brighton;  Mr.  Faraday  procured  evidence  of  ozone  on 
test-paper  exposed  to  a  current  of  air  from  the  sea,  close  to  the  sea-shore, 
as  well  as  in  the  air  of  the  open  downs  above  the  town ;  but  none  in  the  air 
of  the  town  itself.  Dr.  Angus  Smith  could  not  detect  ozone  in  the  air  of 
Manchester  ;  but  at  a  distance,  it  was  easily  recognizable  when  the  wind  was 
not  blowing  from  the  town.  Some  strips  of  paper,  prepared  by  the  process 
described  (see  above),  were  exposed  in  Southwark,  and  at  Connemara,  in 
Ireland.  At  the  former  place,  there  was  no  change  in  twenty-four  hours  ; 
while  at  the  latter,  the  paper  acquired  a  brown  color  in  a  few  hours ;  and  on 
dipping  it  into  water  it  became  blue.  It  has  been  objected  to  this  mode  of 
testing,  that  the  change  in  the  alkaline  iodine  under  these  circumstances, 
may  be  due  to  free  chlorine,  bromine,  iodine,  or  to  nitric  and  other  acids,  or 
even  to  some  organic  compounds  diffused  in  the  athaosphere,  and  not  to 
ozone.  But  it  is  to  be  observed,  that  the  test-paper  remains  unchanged 
exactly  in  those  spots  where  such  compounds  would  be  likely  to  exist  («'.  e  , 
in  inhabited  towns) ;  while  the  chemical  effect  is  observed  to  be  at  a  maxi- 
mum on  open  heaths,  or  downs,  on  the  sea-coast,  on  the  open  sea,  and  on 
lofty  elevations,  more  than  20,000  feet  above  the  surface  of  the  earth,  where 
there  is  no  conceivable  source  of  such  impurities  in  the  air.  It  is  possible, 
too,  as  M.  de  Luca  has  suggested,  that  the  nitric  acid,  even  if  really  exist- 
ing in  the  air  of  those  places,  may  itself  be  the  product  of  the  oxidation  of 
nitrogen  by  ozone ;  and  this  may  be  the  source  of  nitric  acid,  often  found  in 


116  ANTOZONE  AND  ITS  PROPERTIES. 

rain-water,  and  even  in  the  atmosphere  (Comptes  Rendus,  and  Chemical 
News,  September  7,  1861,  p.  136).  The  absence  of  any  reaction  for  118 
days  out  of  365,  and  the  greater  effect  by  night  than  by  day,  in  wet  than  in 
dry  weather,  and  in  winter  than  in  summer,  show  that  these  phenomena  are 
not  due  to  the  presence  of  such  impurities  in  the  air  as  those  suggested.  At 
the  same  time,  the  presence  of  a  large  quantity  of  iodate  of  potassa  in  the 
iodide  used,  may  have  been  a  fertile  source  of  error.  A  discoloration  of  the 
paper  may  then  be  produced  by  such  compounds  as  sulphurous  acid  and 
sulphuretted  hydrogen. 

Constitution. — Ozone  has  been  proved  to  be  oxygen  in  a  changed  condition. 
Andrews  found  that  peroxide  of  manganese  in  absorbing  it,  underwent  no 
sensible  increase  of  weight  although  as  much  as  0*9  gr.  were  apparently 
destroyed  ;  no  water  was  produced.  Hence  it  was  transformed  into  oxygen, 
merely  by  contact,  and  it  could  not  have  contained  any  hydrog§n.  In  its 
production  by  electrolysis,  he  also  noticed  that  the  active  oxygen  was  exactly 
equal  to  the  entire  weight  of  the  ozone — and  was  therefore  identical  with  it. 
(Proc.  R.  S.,  vol.  t,  p.  476.)  But  experiment  shows  that  oxygen  under- 
goes a  remarkable  condensation  in  this  conversion.  There  is  a  reduction  to 
one-fourth  of  the  bulk,  the  density  of  ozone  being  4  4224  compared  with 
that  of  oxygen  as  1.  When  oxygen  has  been  contracted  in  bulk  by  the 
electric  spark  in  the  production  of  ozone,  peroxide  of  manganese  restores  it 
to  its  original  volume  (vol.  9,  p.  608).  In  fact,  the  conclusion  drawn  by 
the  writer,  is  in  accordance  with  the  results  of  Schonbein,  Faraday,  Becque- 
rel,  and  others — that  ozone,  from  whatever  source  derived,  is  one  and  the 
same  substance,  and  is  not  a  compound  body,  but  simply  oxygen  in  an  altered 
or  allotropic  condition. 

Antozone. — While  ozone  is  considered  to  be  active  oxygen  in  a  —  state 
or  0,  antozone  is  active  oxygen  in  a  -f  state  or  0.  It  is  less  powerful  as 
an  oxidizer  than  ozone,  and  appears  to  have  a  neutralizing  action  in  it. 

Antozone  at  present  is  believed  to  be  a  constituent  of  certain  peroxides. 
Of  these  compounds,  Schonbein  has  furnished  the  following  list,  under  the 
name  of  antozonides  : — 

HO2  NagO'  SrOg. 

KO3  Ba  O2 

In  its  action  on  alkaline  iodines  and  in  its  bleaching  properties,  antozone 
resembles  ozone.  The  differences  pointed  out  by  Schonbein  are  not  very  well 
marked.  An  ozonide  evolves  chlorine  with  hydrochloric  acid  ;  gives  a  blue 
color  to  the  precipitated  resin  of  guaiacum,  and  turns  aniline  (on  paper) 
red  brown.  It  does  not  produce  peroxide  of  hydrogen.  An  ozonide  (MnOJ, 
with  sulphuric  acid,  produces  a  rich  series  of  purple  colors  with  strychnia. 
An  antozonide  (BaOg)  similarly  treated  does  not.  Although  dealing  with 
peroxides  in  both  cases,  the  oxygen,  as  it  is  evolved,  must  therefore  be 
different  in  its  properties.  The  oxygen  of  an  ozonide  or  antozonide, 
produces  effects  which  common  oxygen  does  not  produce ;  and  it  is  further 
remarkable  that  these  two  oxygens,  which  appear  to  be  in  opposite  polar 
conditions,  have  the  power  of  neutralizing  each  other  on  contact,  and  of 
evolving  ordinary  oxygen  in  a  pure  state.  Thus,  when  a  few  crystals  of 
permanganate  of  potash  or  peroxide  of  manganese  is  mixed  with  a  solution 
of  peroxide  of  hydrogen,  oxygen  gas  with  its  usual  neutral  properties,  is 
given  off  (Mn03+H0jj=Mn03 +  110  +  0).  There  is,  after  the  mixture,  no 
evidence  of  ozone — of  antozone  or  of  allotropic  oxygen  in  any  form. 
Two  tubes  filled  with  peroxide  of  hydrogen  may  be  inserted  over  mer- 
cury. Into  one  may  be  passed  peroxide  of  manganese,  and  into  the 
other  crystals  of  the  permanganate  of  potash  wrapped  in  bibulous  paper. 


ANTOZONE    AND    ITS    PROPERTIES.  117 

Oxyfj^en  is  liberated  in  both  eases,  bnt  with  very  prreat  rnpidity  from  the 
contents  of  the  tube  containino;  the  pertnanj^anate.  When  full,  the  tube  may 
be  removed  and  the  gaseous  contents  examined.  An  ignited  splint  of  wood 
is  liindled  into  a  flame,  and  starch  paper  moistened  with  oxide  of  potasisiura, 
undergoes  no  change.  These  mixtures  therefore  produce  neutral  oxygen. 
If  peroxide  of  barium  is  substituted  in  this  experiment  for  peroxide  of  man- 
ganese, no  oxygen  is  evolved. 

Peroxide  of  hydrogen  added  to  a  solution  of  iodide  of  potassium,  sets  free 
iodine  (by  oxidation).  Peroxide  of  barium  will  produce  a  similar  change, 
provided  a  few  drops  of  acetic  acid  are  added  in  order  to  set  free  antozone, 
acetate  of  oxide  of  barium  being  formed.  Peroxide  of  manganese  produces 
the  same  change  on  the  iodide  only  after  the  addition  of  acetic  acid  and  in  a 
more  intense  degree.  Permanganate  of  potash  requires  no  addition  of  acid 
for  the  oxidation  of  the  iodide.  A  striking  difference  between  the  two  classes 
of  oxides  (ozonides  and  antozonides),  is  further  indicated  by  the  fact  that  a 
mixture  of  peroxide  of  barium  and  acetic  acid  discharges  the  color  of  per- 
manganate of  potash,  while  a  mixture  of  peroxide  of  manganese  and  acetic 
acid  has  no  effect  on  the  permanganate.  A  mixture  of  either  peroxide  with 
acetic  acid  will  discharge  the  color  of  indigo ;  the  peroxide  of  manganese 
acting  much  more  rapidly.  The  permanganate  of  potash  discharges  the 
color  of  indigo  completely,  without  requiring  the  addition  of  an  acid. 

One  of  the  new  methods  of  producing  oxygen,  elsewhere  described  (see 
Oxygen),  is  based  upon  this  decomposition  of  an  ozonide  and  an  antozonide 
in  the  presence  of  each  other,  by  means  of  a  diluted  acid.  The  powder 
called  Oxygennesis,  is  a  mixture  of  peroxide  of  barium  with  bichromate  of 
potash.  The  addition  of  diluted  sulphuric  acid  with  the  aid  of  heat,  liberates 
neutral  oxygen. 

Antozone  in  the  state  of  vapor  or  gas  is  unknown.  Peroxide  of  hydro- 
gen, which  will  be  described  in  a  future  chapter,  may  be  taken  as  the  type  of 
liquid  antozone,  and  peroxide  of  barium  as  the  type  of  solid  antozone.  Per- 
oxide of  barium,  when  mixed  with  solution  of  iodide  of  potassium  and  acetic 
acid  is  added,  sets  free  iodine  by  oxidizing  the  potassium.  It  also  bleaches 
indigo,  but  it  does  not  produce  a  blue  color  with  precipitated  guaiacum 
resin,  and  it  does  not  produce  the  blue  or  purple  colors  with  strychnia  which 
are  produced  under  similar  circumstances  by  peroxide  of  manganese,  lead, 
and  other  compounds  of  the  ozonide  class 

If,  according  to  Schonbein's  theory,  oxygen  is  thus  reduced  from  its  posi- 
tion as  an  elementary  body,  and  it  is  really  a  compound  of  ozone  and  anto- 
zone, it  should  follow  that  whenever  ozone  is  produced  antozone  must  also 
be  a  product.  In  one  of  his  published  papers,  Schonbein  has  stated,  that 
in  the  ordinary  production  of  ozone  by  phosphorus  and  water,  so  soon  as  the 
ozone  appears,  peroxide  of  hydrogen  (HO^,  or  antozone)  may  be  detected 
in  the  water  in  which  the  phosphorus  is  immersed.  By  agitating  the  phos- 
phorus with  the  water,  he  found  that  this  liquid  acquired  the  property, 
which  it  possesses  in  common  with  ozone,  of  oxidizing  potassium,  and 
setting  iodine  free  from  the  iodide.  In  his  view,  by  mere  contact  with 
phosphorus,  neutral  oxygen  is  split  or  decomposed  into  two  oppositely 
active  conditions — the  positive  oxygen  being  absorbed  by  the  water,  to  form 
peroxide  of  hydrogen,  whilst  part  of  the  negative  oxygen  escapes,  on 
account  of  its  gaseous  and  insoluble  nature,  into  the  atmosphere  above  the 
phosphorus.  The  greater  part,  however,  combines  to  form  phosphorous  acid, 
which,  like  phosphorus  itself,  can  remain  in  contact  with  peroxide  of  hydro- 
gen without"  abstracting  its  active  oxygen.  {Chemisch.  Cent.  Blatt,  Jan. 
1860,  and  Chemical  News,  Feb.  11,  1860.)  When  pure  oxygen  is  converted 
into  ozone  by  electricity,  it  is  probable  that  antozone  is  also  produced,  and 


118  HYDROGEN. 

that  by  continuing  the  electric  sparks,  or  increasing  their  intensity,  these 
bodies  are  reconverted  into  ordinary  oxygen.  When  ether-vapor  and  air 
are  combined,  at  a  heat  below  500°,  ozone  is  produced  in  the  surrounding 
air,  while  antozone  (peroxide  of  hydrogen)  is  dissolved  by  the  ether,  giving 
to  it  bleaching  properties,  and  a  power  of  peroxidizing  chromic  acid.  The 
nearest  condition  to  purity  in  which  antozone  has  been  yet  found,  is  in 
peroxide  of  hydrogen,  obtained  by  the  substitution  of  hydrogen  for  barium 
in  the  peroxide  of  that  metal.  (See  Peroxide  of  Hydrogen.)  While  this 
theory  appears  to  account  for  many  curious  facts  which  have  hitherto  been 
vaguely  referred  to  action  by  contact  or  presence,  it  fails  to  explain  satis- 
factorily all  the  phenomena.  In  the  ozonized  air  obtained  by  the  oxidation 
of  phosphorus,  the  antozone  is  held  dissolved  by  the  water  ;  but  the  ozone 
in  ozonized  air  may  itself  be  converted  into  oxygen  by  mere  heat  above 
500°;  hence  the  presence  of  antozone  to  produce  neutral  oxygen  is  not 
always  necessary.  So  the  ozone  evolved  from  mixtures  of  the  peroxides  of 
manganese  and  iron  with  chlorate  of  potash,  is  converted  into  oxygen  by 
heat,  without  reference  to  the  presence  of  antozone. 


CHAPTER    IX. 

HYDROGEN    (H  =  l). 

History. — In  the  form  of  water  and  aqueous  vapor,  hydrogen  is  universally 
diffused  over  the  globe.  One-ninth  part  of  this  liquid  by  weight  consists  of 
hydrogen  ;  and  it  is  from  this  source  that  the  gas  is  readily  and  abundantly 
procured.  The  name  of  the  element  is  derived  from  the  Greek  iJScop,  water, 
and  yfvvaQ,  to  produce.  Hydrogen  is  held  with  such  affinity  by  oxygen  and 
other  bodies,  that  it  is  not  found  in  nature  in  the  free  state.  Bunsen  states 
that  he  found  it  in  a  mixture  of  gases,  collected  by  him  in  1846,  from  the 
volcanic  district  of  Nimarljall,  in  Iceland.  It  existed  in  the  proportion  of 
45  per  cent.  Hydrogen  is  an  important  constituent  of  animal  and  vegetable 
matter,  entering  largely  into  the  composition  of  flesh  and  woody  fibre.  In 
union  with  carbon,  it  forms  a  large  number  of  gaseous,  liquid,  and  solid 
compounds,  known  as  the  class  of  hydrocarbons.  Associated  with  carbon 
and  oxygen,  it  is  a  constituent  of  inflammable  substances,  such  as  alcohol 
and  ether.  Hydrogen  appears  to  have  been  first  examined  in  a  pure  state 
by  Cavendish  in  1766  {Phil.  Trans.,  vol.  56,  p.  44).  Previously  to  this  it 
had  been  confounded  with  several  of  its  compounds,  under  the  name  of 
inflammable  air. 

Preparation. — The  best  method  of  procuring  hydrogen  is  to  place  in  a 
flask,  provided  with  a  bent  tube  ground  to  fit  the  neck — one  part  of  granu- 
lated zinc,  four  to  five  parts  of  water,  and  one  part  of  strong  sulphuric  acid. 
There  is  a  brisk  effervescence  arising  from  the  rapid  escape  of  the  gas.  Tliis 
should  be  reduced,  if  too  violent,  by  the  addition  of  more  water.  It  is  a 
singular  fact  that,  the  purer  the  zinc,  the  less  energetic  is  the  chemical 
action  ;  and,  indeed,  pure  zinc  is  scarcely  affected  by  the  acid.  The  gas 
may  be  collected  in  the  ordinary  water-bath.  The  first  portions  are  always 
contaminated  with  air,  and  at  least  three  times  the  capacity  of  the  flask  used, 
should  be  rejected  before  the  gas  is  collected  for  experiment.  To  ascertain 
whether  the  hydrogen  is  quite  free  from  air,  a  few  bubbles  may  be  passed 


Methods  of  procuring  hydrogen.  119 

into  a  jar  containing  deiitoxide  of  nitrogen  placed  over  the  bath.  If  no 
red  fumes  are  produced,  the  gas  is  sufficiently  pure  for  collection.  The 
chemical  changes  which  take  place  maybe  thus  represented,  S03,H0-fZn  = 
ZnOjSOa+H.  The  hydrogen,  which  is  thus  displaced  by  the  metal  zinc,  is 
entirely  derived  from  the  decomposition  of  water,  and  as  the  gas  is  scarcely 
dissolved  by  this  liquid,  it  is  readily  collected  in  large  quantity.  A  cubic 
inch,  or  rather  more  than  half  an  ounce  of  water  by  measure,  contains 
twenty-eight  grains  of  hydrogen,  representing  1350  cubic  inches,  or  about 
five  gallons  of  the  gas.  In  place  of  a  tubulated  flask,  a  wide-mouthed  bottle, 
provided  with  a  funnel-tube  for  pouring  in  the  acid,  and  a  bent  delivery 
tube  for  the  escape  of  the  gas,  may  be  employed 

Other  methods  have  been  suggested  for  procuring  hydrogen,  but  they  are 
seldom  resorted  to.  Thus,  iron  has  been  substituted  for  zinc,  but  the  gas  is 
much  less  pure,  and  has  generally  an  offensive  smell  from  its  producing  an 
oily  volatile  compound  by  uniting  with  the  carbon  of  the  iron  ;  sulphuretted 
hydrogen  and  other  impurities  may  also  be  present.  2.  Hydrogen  may  be 
obtained  by  passing  the  vapor  of  water  over  iron-turnings  or  wire,  heated  to 
redness  in  a  porcelain  tube.  In  this  case  the  iron  is  converted  into  magnetic 
oxide  [3Fe-f4HO  =  Fe30^  (magnetic  oxide)  +4H].  3.  It  may  be  obtained 
by  introducing  a  ball  of  sodium  or  potassium,  wrapped  in  paper,  into  a  stout 
jar  full  of  water,  placed  over  the  water-bath.  Hydrogen  is  here  evolved 
without  the  intervention  of  an  acid,  and  an  alkali  is  produced  (Na-f  H0=: 
NaO-f-H.).  The  hydrogen  of  water  may  be  set  free  by  alkalies  as  well  as 
by  acids  in  their  reaction  on  metals.  Thus  aluminum  in  a  strong  solution  of 
potash  liberates  the  hydrogen  and  appropriates  the  oxygen  (2Al-f  KO^- 
3HO=Al,03+KO+3H). 

As  both  zinc  and  sulphuric  acid  are  frequently  contaminated  with  arsenic 
and  sulphur,  hydrogen,  as  it  is  usually  obtained,  is  very  impure.  The  purity 
of  the  materials  may  be  determined  by  generating  the  hydrogen  in  a  bulb- 
tube,  and  passing  the  gas  into  diluted  solutions  of  nitrate  of  lead  and  nitrate 
of  silver.  A  brown  discoloration  of  the  lead  indicates  sulphur,  while  a 
brownish-black  precipitate  in  the  silver  solution  indicates  arsenic,  phos- 
phorus, or  antimony.  In  order  to  determine  whether  the  impurity  is  in  the 
zinc,  some  of  the  metal  should  be  treated  with  sulphuric  acid  of  known 
purity,  and  the  gas  thus  produced  separately  tested.  The  presence  of 
arsenic  in  hydrogen  is  a  dangerous  contamination  ;  the  poison  is  not  only 
set  free  during  combustion,  but  if  the  gas  should  be  accidentally  breathed, 
it  may  cause  serious  symptoms,  and  even  death.  A  Dublin  chemist  lost  his 
life  a  few  years  since  by  inhaling  hydrogen  thus  contaminated  with  arsenic ; 
the  purity  of  the  sulphuric  acid  had  not  been  previously  tested.  The  abso- 
lute freedom  of  hydrogen  gas  from  arsenic,  antimony,  phosphorus,  or  sulphur, 
may  be  proved  by  introducing  into  ajar,  with  its  mouth  downward,  a  slip  of 
filtering-paper,  moistened  with  nitrate  of  silver.  The  paper  should  not  be 
discolored  in  the  gas,  if  pure. 

In  order  to  procure  pure  hydrogen,  pure  materials  should  not  only  be  used, 
but  the  gas  should  be  collected  over  mercury.  Hydrogen  may  be  freed  from 
all  the  usual  impurities  by  passing  the  gas,  before  collection,  through  two 
U-tubes,  both  containing  broken  pumice — in  the  one  tube,  impregnated  with 
a  solution  of  potash,  in  the  other,  with  a  solution  of  corrosive  sublimate.  In 
the  first  tube,  the  compounds  of  sulphur  and  carbon  are  separated,  and  in 
the  second,  those  of  arsenic  and  phosphorus.  Hydrogen  may  be  obtained 
perfectly  dry  by  causing  it  to  traverse  a  third  tube  containing  chloride  of 
calcium,  after  it  has  left  the  purifying  apparatus.  It  is  better  however  to 
select  pure  materials.  Very  pure  distilled  zinc  may  now  be  procured,  and 
this  should  be  always  employed  when  the  hydrogen  is  required  to  be  abso- 


120  PROPERTIES    OF    HYDROGEN. 

Intely  pure,  as  for  the  detection  of  arsenic.  Magnesium,  which  mny  now  be 
procured  at  a  comparatively  cheap  rate,  produces  pure  hydrogen  abundantly, 
when  put  into  pure  sulphuric  acid  diluted  with  a  large  quantity  of  water. 
It  forms  at  the  same  time  as  a  product  a  useful  medicinal  salt  in  the  sulphate 
of  magnesia.  Magnesium  is  probably  destined  at  no  distant  date  to  take 
the  place  of  zinc  in  many  chemical  processes,  and  especially  in  the  construc- 
tion of  voltaic  batteries. 

The  hydrogen  liberated  by  the  electrolysis  of  water  from  platinum  surfaces 
(see  Water),  may,  when  dried,  be  considered  as  absolutely  pure.  In  this 
form,  hydrogen  has  been  employed  by  Mr.  Bloxam  for  the  separation  of 
arsenic  and  antimony  from  organic  liquids. 

Properties. — Hydrogen  is  a  gas  which  has  not  yet  been  liquefied  by  cold  or 
pressure  :  it  is  not  dissolved  by  water,  unless  that  liquid  has  been  previously 
deprived,  by  long  boiling,  of  common  air,  in  which  case  100  cubic  inches 
dissolve  about  1.5  cubic  inches  of  the  gas.  When  perfectly  pure  it  has 
neither  acid  nor  alkaline  reaction,  has  no  taste,  and  is  inodorous:  but  as 
it  is  commonly  made,  it  has  a  slightly  disagreeable  smell  from  traces  of 
foreign  matters  associated  with  it.  It  may  be  respired  for  a  short  time, 
although  it  is  fatal  to  small  animals.  It  does  not  act  as  a  poison,  but  causes 
death  by  suffocation,  i.  e.,  by  the  exclusion  of  oxygen.  As  a  substitute  for 
nitrogen  in  atmospheric  proportions  with  oxygen,  it  has  been  breathed  for 
some  time  without  any  other  effect  than  that  of  producing  a  slight  tendency 
to  sleep.  The  intensity  of  sound  is  greatly  diminished  in  an  atmosphere  of 
hydrogen.  Leslie,  indeed,  found  that  the  sound  was  more  feeble  than  the 
rarity  of  the  gas,  compared  with  air,  would  have  led  him  to  expect.  He 
placed  a  piece  of  clock-work  by  which  a  bell  was  struck  every  half  minute, 
under  the  receiver  of  the  air-pump,  and,  after  exhausting  the  air,  filled  the 
receiver  with  hydrogen  ;  but  the  sound  was  then  even  feebler  than  in  the 
highly  rarefied  atmosphere.  (Ann.  Philos.,  2d  series,  4,  172.)  It  is  stated 
that  sound  moves  at  least  three  times  as  fast  in  hydrogen  as  in  air. 

Hydrogen  gas  is  the  lightest  known  form  of  matter.  It  is  14.4  times 
lighter  than  air,  and  11,000  times  lighter  than  water.  In  consequence  of  its 
extreme  lightness,  it  is  difficult  directly  to  determine  its  weight  with  accu- 
racy by  the  common  process;  but  the  researches  of  Berzelius  and  Dulong, 
and  of  Dr.  Prout,  lead  us  to  infer  that  its  specific  gravity,  compared  with 
oxygen,  is  as  1  to  16  :  100  cubic  inches,  therefore,  of  pure  hydrogen  gas  at 
mean  temperature  and  pressure  weigh  only  2*14  grains,  and,  compared  with 
air,  its  specific  gravity  would  be  nearly  as  7  to  100,  or  more  correctly  as 
0*0691  to  1.  Boussingault  and  Dumas  have  shown  that  the  density  of  hydro- 
gen is  between  0-0671  and  0  0695.  (Ann.  Ch.  et  Phys.,  3d  series,  8,  201.) 
At  a  temperature  of  32°,  100  cubic  inches  weigh  2*22756  grains.  (Thom- 
son.) It  has  the  highest  refracting  power  of  all  the  gases.  Compared  with 
air  it  is  6614  to  1000.  In  relation  to  magnetism,  it  was  found  by  Faraday 
to  be  diamagnetic  ;  a  vacuum  being  0*0,  hydrogen  was  0  1.  In  the  mag- 
netic field,  a  tube  containing  it  assumed  an  equatorial  position,  or  pointed 
east  and  west.  Its  specific  heat,  compared  with  an  equal  weight  of  air,  was 
12'340  to  1000.  In  its  electro-chemical  relations  hydrogen  is  strongly  posi- 
tive, and  in  electrolysis  it  always  appears  at  the  negative  pole.  It  displaces 
the  metals  under  these  circumstances,  and  enters  into  combination  with  the 
oxygen  or  salt  radical.  This  is  one  of  the  facts  which  is  considered  to  favor 
the  hypothesis  that  hydrogen  itself  is  the  gaseous  state  of  a  metal  perma- 
nently volatile  at  the  lowest  temperature. 

The  low  specific  gravity  of  hydrogen  may  be  illustrated  by  substituting 
it  for  common  air,  in  soap-bubbles,  which  then  rapidly  ascend  in  the  atmo- 
sphere, and  may  be  kindled  by  the  flame  of  a  taper.     This  property  led  to 


COMBUSTION    OF    HYDROGEN.  121 

its  employment  formerly  in  the  inflation  of  balloons,  but  of  late  years  coal- 
gas  has  been  substituted.  Small  balloons,  made  of  gold-beater's  skin,  or  of 
collodion,  when  filled  with  pure  hydrogen,  dried  by  passing  it  through  a 
tube  containing  chloride  of  calcium,  rise  in  the  air,  their  specific  gravity 
being  inferior  to  that  of  the  surrounding  atmosphere.  This  gas  has  a  remark- 
able penetrating  power.  It  rapidly  traverses  porous  septa  of  unglazed 
earthenware — animal  membrane  or  caoutchouc,  and  it  will  pass  through  tubes 
of  red-hot  platinum.  A  current  of  hydrogen  issuing  from  a  jet,  traverses 
white  blotting  paper  as  readily  as  if  there  were  no  obstacle  to  its  passage. 
Spongy  platinum  placed  on  the  paper  is  soon  made  red-hot  by  the  gas  which 
passes  through  the  paper. 

Hydrogen  is  itself  inflammable,  but  it  extinguishes  flame.  When  pure,  it 
burns  quietly,  with  a  pale  yellowish  flame  at  the  surface  in  contact  with  air  ; 
but,  if  mixed  with  twice  its  volume  of  air,  it  burns  rapidly  and  with 
detonation. 

The  phenomena  of  its  combustion  vary  according  to  the  mode  in  which 
the  experiment  is  performed,  but  the  product  is  always  water  (HO) — the 
hydrogen  at  a  high  temperature  taking  the  oxygen  from  the  atmosphere.  If, 
by  withdrawing  the  glass  plate  from  a  jar,  a  slight  aperture  only  is  made, 
the  gas  may  be  kindled  without  explosion,  and  by  the  gradual  withdrawal 
of  the  plate  it  will  burn  quietly,  and  with  a  scarcely  visible  flame,  until  all 
is  consumed.  If  the  gas  is  kindled,  as  the  cover  is  suddenly  removed,  it 
always  burns  with  explosion  by  its  rapid  admixture  with  air  in  its  great 
tendency  to  diffuse.  If  the  cover  be  entirely  removed,  and  the  lighted  taper 
be  held  six  or  eight  inches  above  the  mouth  of  ajar,  there  will  be  an  interval 
before  combustion  takes  place,  and  the  gas  will  tlien  burn  with  a  loud  explo- 
sion. The  following  experiment  may  serve  as  another  illustration.  Drop  a 
piece  of  potassium  into  a  stout  jar  containing  hydrogen  gas,  having  a  stratum 
of  an  inch  of  water  at  the  bottom.  The  potassium  at  first  decomposes  the 
water  without  producing  flame  ;  but,  in  a  few  seconds,  the  air  rushes  in  to 
supply  the  place  of  a  portion  of  the  hydrogen  which  has  escaped,  and  the 
mixture  is  then  kindled  by  the  burning  potassium  with  a  loud  detonation. 
This  experiment  may  be  performed  with  perfect  safety  in  a  stout  glass  jar, 
eight  inches  deep  and  two  or  three  inches  wide.  It  illustrates  the  decompo- 
sition of  water  by  a  metal,  and  its  recomposition  by  the  union  of  its  elements 
at  a  high  temperature. 

It  has  been  stated  that  hydrogen  extinguishes  burning  bodies ;  in  other 
words,  that  it  does  not  support  combustion.  To  prove  this,  the  jar  contain- 
ing the  hydrogen  must  be  inverted.  A  large  jar  filled  with  the  gas,  having 
its  open  end  downward,  may  be  brought  over  a  lighted  taper,  supported  on 
a  wire.  The  gas  is  instantly  kindled,  and  burns  at  the  mouth  of  the  jar. 
By  depressing  the  jar  over  the  taper  this  will  become  extinguished,  and  the 
blackened  wick  will  be  seen  in  the  midst  of  the  hydrogen,  which  is  burning 
below.  The  taper  may  be  relighted  by  raising  the  jar,  and  again  extinguished 
by  depressing  it,  an  experiment  which  may  be  repeated  several  times.  There 
are  other  interesting  experiments  which  prove  that  hydrogen  is  not  a  sup- 
porter of  combustion  in  the  ordinary  meaning  of  these  terms.  Place  a  piece 
of  phosphorus  in  a  small  saucer  floating  in  a  vessel  containing  a  thin  stratum 
of  water.  Kindle  the  phosphorus,  and,  when  fully  burning,  cover  it  com- 
pletely with  ajar  of  hydrogen  as  with  an  extinguisher.  The  hydrogen  is 
inflamed  at  the  mouth  of  the  jar,  but,  with  the  flame  of  the  phosphorus,  it  is 
extinguished  when  the  jar  is  plunged  beneath  the  water.  In  place  of  phos- 
phorus, a  piece  of  camphor  may  be  employed  with  like  results.  Paper  im- 
pregnated with  a  solution  of  nitrate  of  potash,  when  dried,  ignited,  and 
introduced  into  ajar  of  hydrogen,  is  extinguished.    A  certain  degree  of  heat 


122  HYDROGEN.   EXPLOSIVE  PROPERTIES. 

is  required  for  the  kindling  of  this  gas  in  air.  It  is  not  inflamed  by  an  iron 
bar  heated  to  dull  redness,  but  is  immediately  kindled  at  a  bright  red  heat. 
Daring  combustion,  hydrogen  combines  with  eight  times  its  weight  of  oxygen, 
producing  a  more  intense  degree  of  heat,  weight  for  weight,  than  any  other 
combustible.     {See  page  106.) 

Hydrogen,  when  mixed  with  air,  and  inflamed  by  a  taper  or  the  electric 
spark,  burns  with  a  loud  explosion.  Cavendish  found  that  the  loudest  ex- 
plosion was  produced  by  mixing  one  volume  of  hydrogen  with  three  of  air, 
or  two  volumes  with  five  of  air.  One  of  hydrogen  with  nine  of  air  burned 
very  feebly,  and  four  of  hydrogen  with  one  of  air  burned  without  explosion. 
{Phil.  Trans. ,  56.)  If,  instead  of  employing  a  mixture  of  hydrogen  and 
atmospheric  air,  two  volumes  of  hydrogen  are  mixed  with  one  of  oxygen, 
and  inflamed  in  a  stout  jar,  the  explosion  is  extremely  violent  ;  but  if  the 
mixture  be  diluted  with  eight  measures  of  hydrogen,  or  with  nine  of  oxygen, 
it  no  longer  explodes.  The  cause  of  this  violent  explosion  is  owing  to  the 
sudden  conversion  of  a  large  volume  of  mixed  gases  into  liquid  w^ater  by  con- 
densation. As  528  cubic  inches  of  mixed  gases  produce  only  0*4  cubic  inch 
of  liquid  water  at  60°,  there  is  a  diminution  in  volume  to  goVuth  part.  A 
vacuum  is  thus  produced,  into  which  the  air  suddenly  rushes,  producing  a 
loud  sound.  There  is,  however,  in  the  first  instance,  expansion  by  the  heat 
of  combustion,  and  this  is  instantly 'followed  by  a  condensation  of  the  pro- 
duced steam  or  aqueous  vapor. 

The  inflammability  and  low  sjDCcific  gravity  of  hydrogen  are  shown  in  the 
following  experiments  :  Let  ajar  filled  with  this  gas  stand  for  a  few  seconds 
with  its  mouth  upwards ;  on  introducing  a  lighted  taper,  the  gas  will  be 
found  to  have  escaped,  and  to  have  been  replaced  by  common  air.  Place 
another  jar  of  the  gas  inverted,  or  with  its  mouth  downward  ;  the  gas  will 
now  be  found  to  remain  a  much  longer  time  in  the  jar,  being  prevented  from 
escaping  upwards  by  the  bottom  and  sides  of  the  vessel.  A  jar  of  this  gas 
may,  for  the  same  reason,  be  removed  with  its  mouth  downwards  from  the 
water-bath  without  a  cover,  and  thus  transported  to  a  considerable  distance. 
It  may  then  be  inflamed  and  burnt,  by  bringing  the  open  mouth  over  a 
lighted  candle.  Place  a  bell-jar  having  a  Harrow  neck  and  containing  hy- 
drogen, so  that  the  wide  open  end  may  rest  on  three  cubes.  The  jar  may  be 
removed  from  the  bath,  as  in  the  previous  experiment,  without  any  cover. 
Remove  the  stopper  and  ignite  the  gas.  It  will  burn  with  a  fierce  flame  as 
the  hydrogen  is  forced  through  the  neck  by  the  pressure  of  the  external  air 
beneath,  and  it  will  finally  produce  an  explosion,  but  without  any  danger, 
owing  to  the  last  portions  of  the  gas  being  mixed  with  the  air  in  explosive 
proportions.  If  a  piece  of  paper  dipped  in  a  solution  of  nitre  and  dried,  is 
burnt  under  the  mouth  of  a  jar  of  hydrogen,  it  will  be  found  that  the  smoke 
produced  will  float  in  a  cloud  below  the  gas,  owing  to  the  lightness  of  the 
hydrogen.  Ajar  of  air  held  over  another  containing  hydrogen,  from  which 
the  cover  is  then  removed,  will  catch  the  hydrogen  as  it  ascends.  The  ap- 
plication of  a  lighted  taper  will  show  its  presence  in  the  upper  jar  and  its 
absence  in  the  lower  jar,  in  which  it  was  originally  contained.  Hydrogen 
may,  in  fact,  be  decanted,  as  it  were,  per  ascensum,  from  one  jar  into  another 
held  above  it.  Thus,  if  a  light  bell-glass  be  suspended  with  its  mouth  down- 
wards to  one  end  of  a  scale-beam,  and  accurately  counterpoised,  it  will  be 
found,  on  placing  a  jar  of  hydrogen  gas  (closed  by  a  plate  of  glass)  under- 
neath it,  that  the  hydrogen,  on  removing  the  glass  plate,  will  ascend  into 
the  bell,  and  by  its  lightness  cause  the  counterpoise  to  sink  ;  the  hydrogen 
may  afterwards  be  inflamed  by  a  taper  introduced  into  the  counterpoised 
bell.  A  large  bell-glass,  suspended,  may  be  filled  with  hydrogen  by  dis- 
placement— I.  e.,  by  opening  one  or  two  large  jars  of  the  gas  beneath  it,  and 


DETECTION    OP    IMPURITIES    IN    THE    GAS.  123 

allowinj;]^  the  hydron^en  to  ascend.  If  a  bell  be  stru(ik  with  a  hammer  in  this 
atmosphere  of  hydrogen,  it  will  be  at  once  perceived  how  much  the  ordinary 
sound  is  reduced.  A  small  shade,  mounted  on  a  handle,  and  introduced  into 
this  atmosphere  of  hydrogen,  with  its  mouth  downwards,  will,  after  a  few 
minutes,  be  filled  with  hydrogen  by  displacement.  This  may  be  transported 
to  a  distance,  and  kindled  over  a  Qame.  The  gas,  owing  to  the  admixture 
of  air,  will  burn  with  a  slight  explosion. 

If  hydrogen  is  generated  in  a  bottle,  provided  with  a  glass  tube  drawn 
out  to  a  capillary  point,  it  may  be  burnt  in  a  jet  at  the  end  of  the  tube  {the 
Philosopher''s  lamp) ;  but  care  should  be  taken  not  to  insert  the  cork  with 
the  jet  until  all  the  air  has  been  removed  from  the  bottle  by  the  free  escape 
of  the  gas.  The  hydrogen  burns  at  first  with  a  long  pointed  yellowish 
flame,  which  may  be  proved  to  be  hollow  like  other  flames  {see  p.  107). 
Although  the  light  is  feeble  the  heat  is  intense.  Fine  platinum  wire  is  made 
white  hot  in  an  instant,  and  sometimes  melted.  Fine  iron  wire  is  rapidly 
consumed  by  combustion  with  the  surrounding  air,  and  glass  is  speedily 
melted.  If  a  cold  glass  vessel  be  brought  over  the  flame,  the  interior  is 
speedily  covered  with  the  condensed  vapor  of  water — the  result  of  combus- 
tion ;  and,  by  a  condensing  tube,  the  water  thus  generated  may  be  easily 
collected  and  tested.  If,  while  the  gas  is  burning,  a  tube  from  half  an  inch 
to  two  inches  in  diameter,  and  twelve  to  twenty  inches  long,  open  at  both 
ends,  be  brought  gradually  over  the  flame,  the  flame  becomes  elongated, 
acquires  a  bluish  tint  at  the  mouth  of  the  jet,  and  a  peculiar  sound  is  heard, 
varying  according  to  the  diameter  of  the  tube.  This  forms  what  has  been 
called  a  chemical  harmonicon  or  hydrogen  music.  It  arises  from  the  vibra- 
tion of  the  column  of  air  within  the  tube,  produced  as  a  result  of  a  rapid 
succession  of  slight  explosions  during  the  combustion  of  the  gas.  The  tone 
varies  in  pitch  with  the  length  and  diameter  of  the  tube;  and  singular  effects 
may  be  produced  by  employing  for  the  experiment  the  tube  of  a  broken 
retort.  If,  while  the  sound  is  issuing,  a  tube  of  larger  size  is  placed  at  dif- 
ferent heights  over  the  tube  in  which  the  hydrogen  is  burning,  there  will  be 
remarkable  modifications  of  the  sound.  A  small  flame  is  better  fitted  for  the 
production  of  this  phenomenon,  but,  if  too  small,  the  flame  may  be  extin- 
guished by  the  strong  current  of  air  passing  through  the  tube. 

We  may  make  use  of  this  flame  for  the  purpose  of  testing  the  purity  of 
the  gas.  If  a  piece  of  cold  glass  or  white  porcelain  be  suddenly  depressed 
on  the  point  of  the  flame,  and  the  gas  is  pure,  there  will  be  no  stain  or  de- 
posit. Nothing  but  a  film  of  water  will  be  perceived.  If  there  be  the 
smallest  trace  of  arsenic  or  antimony  in  the  gas,  there  will  be  a  brown  or 
blackish  stain,  more  distinctly  visible  on  the  surface  of  porcelain  than  on  the 
glass.  By  bending  the  tube  at  a  right  angle,  and  applying  a  strong  red 
heat,  by  means  of  a  spirit-lamp,  to  the  horizontal  portion,  the  presence  of 
any  foreign  matters  will  be  revealed.  All  the  gaseous  compounds  of  hydro- 
gen are  decomposed  at  a  full  red  heat ; — the  gas  passes  off,  and  the  solid 
impurity  is  deposited  in  a  cold  part  of  the  tube.  In  this  way  the  presence 
of  the  minutest  traces  of  sulphur,  arsenic,  antimony,  phosphorus,  or  selenium 
may  be  detected.  A  film  or  ring  of  the  substance,  recognizable  by  its  color 
or  metallic  lustre,  will  be  perceptible.  As  a  proof  of  the  facility  with  which 
hydrogen  combines  with  these  contaminating  substances,  it  may  be  men- 
tioned that  when  the  pure  gas  is  allowed  to  pass  through  a  connecting  piece 
of  vulcanized  rubber  tubing,  it  will  combine  with  a  portion  of  sulphur,  which 
may  be  re-obtained  in  a  solid  state  by  the  method  of  testing  above  described. 

In  discussing  the  nature  of  flame,  and  the  causes  of  its  luminosity  and 
heat,  allusion  has  been  made  to  the  high  temperature  of  that  of  hydrogen. 
Tnis  gas  is  occasionally  employed   for   exciting  intense   heat ;   and,  when 


124  HYDROGEN.       COMPOUNDS. 

mixed  with  oxyf2:en,  and  burned  as  the  mixture  issues  from  a  small  jet,  it 
produces  a  temperature  nearly  equal  to  that  of  the  are  of  flame  in  the  voltaic 
circuit.  A  blow-pipe  upon  this  construction  was  first  made  by  Newman, 
and  afterwards  improved  as  to  its  safety,  by  Professor  Cummin":,  of  Cam- 
bridge. {Journal  of  Science  and  the  Arts,  1,  67,  and  2,  380.)  Hemraing's 
safety-tube  has  also  been  used  in  these  experiments.  (See  Phil  Mag.,  3d 
series,  1,  82.)  An  excellent  mode  of  obtaining  intense  heat  by  the  combus- 
tion of  oxygen  and  hydrogen,  consists  in  propelling  the  two  gases,  in  their 
proper  proportions  to  form  water,  from  separate  air-holders  through  a  burner 
composed  of  two  concentric  tubes :  a  good  form  of  such  a  burner  has  been 
described  by  Daniell.  {Phil.  Mag.,  3d  series,  2,  57.)  The  apparatus  for 
this  purpose  has  been  further  improved  by  Maugham,  especially  as  relates  to 
its  application  to  the  solar  microscope.  {Trans.  Soc.  Arts,  &c. ,  vol.  50.) 
The  gases  are  now  forced  into  a  small  chamber,  terminated  by  a  platinum  jet, 
from  which  they  are  burnt.  The  heat  is  such  that  it  is  capable  of  fusing  and 
even  volatilizing  platinum  ;  it  causes  the  melting  of  rock  crystal,  as  well  as 
alumina  or  clay.  In  this  and  similar  cases  where  the  inflammable  gas  is 
mixed  with  oxygen,  the  nature  of  the  flame  is  materially  altered,  the  com- 
bustion being  entire  throughout  the  body  of  the  flame,  and  not  limited  to 
the  film  in  contact  with  air.  Hence,  under  these  circumstances,  the  quantity 
of  the  combustible  consumed,  and  the  quantity  of  oxygen  combining  with  it  in 
a  given  time,  are  greatly  increased.  Owing  to  this  perfect  mixture  of  oxygen 
and  hydrogen,  the  flame  may  be  described  as  solid,  possessing  an  intensely 
heating  and  penetrating  power.  Although  scarcely  visible  in  itself,  the 
flame,  when  received  on  lime,  asbestos,  or  platinum,  emits  an  intense  light 
(see  page  101). 

Lime  was  first  used  by  Lieutenant  Drummond  as  a  source  of  light,  with 
the  oxyhydrogen  jet,  in  1826.  {Phil.  Trans.  1826,  p.  324.)  By  means  of  it, 
in  the  Triangulation  survey,  he  successfully  connected  the  opposite  shares  of 
England  and  Ireland  at  or  about  Holyhead,  a  distance  of  sixty-four  miles. 
In  Scotland,  he  obtained  a  successful  result  on  the  summits  of  Ben  Lomond 
and  Knock  Layd,  a  distance  of  ninety-five  miles.  {Gas-Lighting  Journal, 
Jan.  1860.)  Dr.  Miller  states  that  the  Druminond  Light  has  been  seen  at  a 
distance  in  a  right  line  of  112  miles.  Coal-gas,  and  other  inflammable  gases 
and  vapors,  when  mixed  with  oxygen  in  their  combining  proportions,  burn, 
for  the  same  reason,  with  what  may  be  described  as  solid  flames.  As  coal- 
gas,  by  being  overheated  in  its  manufacture,  is  converted  in  great  part  into 
hydrogen,  it  is  not  only  substituted  for  this  gas  in  aerostation,  but  also  in 
producing  the  lime-light;  so  that,  except  for  purely  scientific  purposes,  the 
more  costly  oxyhydrogen  flame  need  not  be  employed  as  a  source  of  light. 

Compounds. — The  range  of  combination  of  hydrogen  is  not  so  extensive 
as  that  of  oxygen.  It  forms  with  metallic  and  non-metallic  bodies  the  class 
of  Hydrides.  The  hydrides  of  the  metals  are  few  in  number,  those  of  arsenic 
and  antimony  being  the  principal.  There  are  three  other  metals  which  form 
temporary  combinations  with  hydrogen — namely,  potassium,  tellurium,  and 
zinc.  Among  non-metallic  bodies  it  forms  an  alkali  with  nitrogen  ;  neutral 
compounds  with  carbon  and  phosphorus ;  and  acids  (the  class  of  hydracids) 
with  chlorine,  bromine,  iodine,  sulphur,  selenium,  fluorine,  and  cyanogen. 
These  compounds  are,  for  the  most  part,  products  of  art.  At  a  red  heat, 
hydrogen  is  a  powerful  reducing  agent;  thus  it  readily  decomposes  the 
oxides,  chlorides,  and  sulphides  of  some  of  the  metals,  combining  with  the 
oxygen,  chlorine,  or  sulphur,  and  setting  free  the  metal  in  a  pure  and  finely- 
divided  state.  A  current  of  dry  hydrogen  passed  over  oxide  of  copper,  or 
oxide  of  iron,  heated  to  redness  in  a  tube,  takes  the  oxygen  to  form  water, 


EQUIVALENT.     TESTS.      NASCENT    HYDROGEN.  125 

which  may  be  collected  in  a  condensing  bulb,  or  tube.     The  quantity  of 
oxygen  contained  in  the  dry  oxides  may  be  thus  determined. 

Equivalent. — The  equivalent,  or  combining  weight,  of  hydrogen,  is,  by 
most  English  chemists,  taken  as  unity — 1 :  it  is  the  standard  with  which  the 
atomic  weights  of  all  other  bodies  are  compared.  Its  volume  equivalent  in 
gaseous  combinations  is  double  that  of  oxygen,  and  has  been  variously 
assigned  as  two  volumes  or  one.  We  can  perceive  no  sufficient  reason  for 
departing  from  the  simplicity  of  the  rule  hitherto  received,  that  hydrogen 
shall  be  regarded  as  representing  unity  by  volume  as  well  as  by  weight.  To 
assume  that  there  are  two  standards,  and  that  hydrogen  represents  weight, 
while  oxygen  represents  volume,  presents  no  advantages  in  the  constructioa 
of  chemical  formulae,  or  in  the  explanation  of  chemical  facts. 

Tests.  Special  Characters. — As  a  gas,  hydrogen  is  easily  identified:  1,  by 
its  inflammability,  and  the  production  of  water  as  a  result  of  its  combustion  : 
2,  by  its  lightness  :  3,  by  its  insolubility  in  water,  in  solution  of  potassa, 
and  in  all  liquids  :  4,  when  free  from  oxygen,  by  its  giving  no  red  vapors 
when  mixed  with  deutoxide  of  nitrogen  ;  and  by  the  mixture,  in  equal  parts, 
burning  without  explosion,  with  a  greenish-white  flame  ;  5,  by  its  being 
entirely  converted  into  water  when  mixed  with  half  its  volume  of  pure 
oxygen,  and  the  gases  are  combined  by  the  electric  spark,  by  heat,  or  by  the 
action  of  spongy  platinum.  For  the  detection  of  hydrogen,  when  in  intimate 
combination  with  carbon  and  oxygen  in  organic  compounds,  another  process 
must  be  resorted  to.  Hydrogen,  it  is  well  known,  at  a  red  heat,  decomposes 
oxide  of  copper,  and  is  converted  into  water  {see  p.  128).  The  organic 
substance  (starch)  is  first  deprived  of  water  by  complete  desiccation.  It  is 
then  mixed  with  dry  oxide  of  copper,  placed  in  a  tube,  and  heated  to  redness. 
The  water  produced  is  collected  by  passing  the  products  through  a  balanced 
tube  containing  fused  chloride  of  calcium.  The  increase  of  weight  in  the 
chloride  represents  the  total  amount  of  water  formed  ;  and  one-ninth  part  of 
this  represents  the  amount  of  hydrogen  contained  in  the  substance  under 
examination.  The  process  for  detecting  and  separating  hydrogen  is  incb.ded 
in  that  which  is  employed  for  the  determination  of  water. 

Nascent  or  Allotropic  Hydrogen. — Although  the  existence  of  two  forms  of 
hydrogen  is  unknown,  yet  as  it  is  evolved  from  water  by  electrolysis,  or  as 
it  is  produced  in  the  nascent  state  by  chemical  changes,  the  gas  appears  to 
have  much  greater  energy  in  combining,  than  that  whi(;h  has  been  once  set 
free.  It  has  been  long  known  to  chemists,  that  under  these  circumstances, 
gases  frequently  display  great  chemical  power.  In  1841,  Mr.  Smee  noticed 
that  porous  coke  or  charcoal,  which  had  formed  the  negative  pole  of  a  battery, 
retained  a  portion  of  hydrogen,  and  when  placed  in  a  solution  of  sulphate 
of  copper,  the  coke  or  charcoal  was  covered  with  the  reduced  metal.  Free 
hydrogen  has  no  power  of  decomposing  a  salt  of  copper,  but  in  this  state  it 
was  replaced  by  the  metal.  {Elements  of  Electro- Metallurgy,  1841,  p.  37.) 
Ozann  and  Fremy  have  made  similar  observations  regarding  silver.  If 
hydrogen  is  received  on  platinum  sponge  from  the  negative  electrode  of  a 
battery,  until  bubbles  of  the  gas  begin  to  appear,  it  will  be  absorbed  and 
condensed  by  this  porous  body.  When  the  platinum  sponge  was  washed 
and  placed  in  a  solution  of  sulphate  of  silver,  there  was  immediately  a 
precipitation  of  metallic  silver.  It  was  also  found,  that  if  the  hydrogen 
evolved  from  the  negative  platinum  electrode  in  the  decomposition  of  water, 
was  conveyed  Immediately  into  a  solution  of  sulphate  of  silver,  the  metal  was 
precipitated.  When  the  gas  was  conducted  into  water  containing  perchloride 
of  iron,  with  a  trace  of  ferricyanide  of  potassium,  Prussian  blue  was  formed. 
These  results  could  not  be  obtained  with  hydrogen  gas  in  its  ordinary  stale. 
When  a  current  of  hydrogen  is  passed  into  water  containing  ammouio-chlo- 


126  HYDROGExX    AND    OXYGEN.      WATER. 

ride  of  platinum  diffused  through  it,  there  is  no  change.  If  the  hydrogen  is 
generated  by  zinc  and  sulphuric  acid  in  the  midst  of  the  ammonio-chloride, 
there  is  an  immediate  decomposition,  and  finally  divided  platinum  (platinum 
black)  is  set  free.     (See  Nascent  State,  ante,  p.  125.) 

If  some  granulated  zinc  is  placed  in  diluted  sulphate  of  indigo,  and  sul- 
phuric acid  is  added  in  sufficient  quantity  to  generate  hydrogen  in  small 
bubbles,  the  indigo  is  slowly  bleached.  If  the  bleached  liquid  is  exposed  to 
the  air,  it  will  reacquire  its  blue  color.  If  zinc  is  placed  in  a  mixture  of 
diluted  sulphuric  and  nitric  acids,  few  or  no  bubbles  of  gas  escape;  but 
ammonia  is  produced  by  the  hydrogen,  in  the  nascent  state,  entering  into 
combination  with  the  nitrogen  of  the  nitric  acid.  The  liquid  after  some 
hours  will  contain  nitrate  and  sulphate  of  ammonia.  In  the  rusting  of  iron 
in  a  damp  atmosphere,  in  the  oxidation  of  tin  by  nitric  acid,  in  the  effect 
of  heat  and  of  putrefactive  changes  on  nitrogenous  matter,  ammonia  is 
produced  by  nascent  hydrogen  combining  with  nitrogen,  although  hydrogen, 
when  once  free  as  a  gas,  shows  no  tendency  whatever  to  combine  with 
nitrogen. 

These  results,  if  they  do  not  indicate  an  allotropic  state  of  hydrogen, 
demonstrate  that  the  combining  properties  of  this  element  are  widely  dif- 
ferent in  intensity,  according  to  the  circumstances  under  which  the  observations 
are  made. 

In  the  electrolytic  experiments  above  described,  it  has  been  proved  that 
hydrogen  may  displace  copper,  silver,  and  other  metals.  Hence  it  has  been 
supposed,  that  it  is  itself  the  vapor  of  a  metallic  body.  Carbon  and  phos- 
phorus might,  however,  with  equal  propriety,  be  ranked  among  metals. 
Magnesium  and  zinc  readily  displace  hydrogen  from  its  compound  with 
chlorine,  at  ordinary  temperatures. 


CHAPTER     X. 

WATER    (H0=9).  — AQUEOUS    VAPOR.— ICE. 

History. — Water  is  an  important  constituent  of  the  globe.  As  a  liquid  it 
covers  three-fourths  of  the  earth's  surface,  forming  the  ocean.  In  the  at- 
mosphere it  is  universally  diffused  as  an  invisible  vapor,  sometimes  pre- 
cipitated in  the  solid  state  as  hail  or  snow,  at  others  assuming  the  form  of 
clouds  or  rain.  The  surface  of  the  earth  is  itself  covered  with  large  masses 
of  water,  disposed  in  lakes  and  rivers.  There  is  scarcely  a  rock  or  soil  into 
which  water  does  not  penetrate.  All  the  superficial  strata  contain  it,  and  it 
is  found  in  a  great  number  of  minerals,  in  a  proportion  varying  from  two  to 
twelve  per  cent,  of  their  weight.  It  exists  in  the  three  states  in  which 
matter  is  known  to  us  ;  1,  as  vapor  or  gas;  2,  as  a  liquid;  3,  as  a  solid.  The 
range  of  water  as  a  liquid,  is  well  known  to  be  between  32°  and  212°.  It 
is  so  abundantly  found  that  there  is  no  need  to  prepare  it  artificially  ;  and  it 
is  easily  separated  from  the  foreign  ingredients  with  which  it  is  naturally 
associated,  by  converting  it  into  vapor  and  subsequently  condensing  this 
vapor. 

Water  was  long  regarded  as  an  element,  and  was  supposed  to  be 
convertible  into  earth,  until  Lavoisier,  in  17Y3,  showed  the  fallacy  of  this 
notion.     Cavendish   and  Watt,  in   1781,  demonstrated  the  production  of 


CHEMICAL    COMPOSITION.  121 

water  by  the  combustion  of  oxygen  and  hydrogen  ;  and  the  former,  to  whom 
the  important  discovery  of  its  composition  is  strictly  due,  proved  the  corres- 
pondence in  weight  of  the  resulting  })roduct  with  that  of  the  gases  used  in 
its  formation.  Lavoisier  first  resolved  water  into  its  constituents,  and 
Humboldt  and  Gay-Lussac  proved  that  the  volume  of  the  oxygen  to  the 
hydrogen  was  exactly  as  1  :  2.  The  relative  weights  of  these  gases  were 
carefully  determined  by  Berzelios  and  Dulong,  and  shown  to  be  very  nearly 
as  88-9   :  ll'l,  or  8  to  1. 

Chemical  Composition. — Viewed  in  a  chemical  aspect,  water  is  a  perfectly 
neutral  oxide  of  hydrogen.  The  two  gases  combine  in  certain  proportions 
by  weight  and  volume,  but  only  under  fixed  conditions.  If  placed  in  contact, 
they  simply  mix  or  diffuse  with  each  other.  When,  however,  two  volumes 
of  pure  hydrogen  are  mixed  with  one  volume  of  pure  oxygen,  and  the  mixture 
is  inflamed  in  a  proper  apparatus  by  the  electric  spark,  they  totally  dis- 
appear, and  water,  in  equal  weight  to  the  gases  consumed,  is  formed.  Again, 
if  water  is  exposed  to  electrolytic  action,  it  is  resolved  into  two  volumes  of 
hydrogen,  disengaged  at  the  negative  pole  or  cathode,  and  one  volume  of 
oxygen,  disengaged  at  the  positive  pole  or  anode ;  so  that  water  is  thus 
proved  by  synthesis,  and  by  analysis,  to  consist  of  two  volumes  of  hydrogen 
combined  with  one  volume  of  oxygen.  The  specific  gravity  of  hydrogen, 
compared  with  oxygen,  is  as  1  to  16;  these  numbers,  therefore,  represent 
the  comparative  weights  of  equal  volumes  of  those  gases;  but  as  water  con- 
sists of  one  volume  of  hydrogen  and  half  a  volume  of  oxygen  ;  it  is  obvious 
that  the  relative  weights  of  these  elements  in  that  compound  will  be  as  1 : 8. 
The  accuracy  of  these  numbers  has  been  determined  by  the  elaborate  inves- 
tigations of  Dumas  {Recherches  sur  la  Composition  de  VEau,  Ann.  Ch.  et  Ph., 
Juin,  1843),  Regnault,  and  other  chemists. 

Atoms.        Weights.  Per  cent.  Volumes. 

Hydrogen    .         .         .         ,     1       ...       1       ...       11-09       ...       1-0    2- 
Oxygen        .         .         .         .     1       ...       8       ...       88-91       ...       0-5     1- 


Water  .        .         .         .     1       ...       9       ...     100-00       ...       1-      2- 

These  results  nearly  correspond  to  the  weights  of  the  two  elements,  as 
deduced  from  their  specific  gravities.  Thus  taking  the  specific  gravity  of 
hydrogen  at  0-0691,  and  of  oxygen  at  1*1057,  then  0-0691  x  2  =  0-1382 
+  1-1057  (sp.gr.  of  0)  =  1-2439;  and  1-2439  :  M057  ::  100  :  88*89.  The 
specific  gravities  of  the  constituents  thus  give  for  the  composition  of  water 
88 -89  of  oxygen,  and  11-11  of  hydrogen.  The  specific  gravity  of  aqueous 
vapor,  compared  with  air  as  1,  is  found  to  be  0-622.  This  corresponds  to 
one  volume  of  hydrogen  and  half  a  volume  of  oxygen  in  each  volume  of 
vapor : — 

1  volume  of  hydrogen sp.  gr.  =  0-0691 

^  volume  of  oxygen "       =  0-5528 


1  volume  of  aqueous  vapor "       =  0-6219 

The  volume  of  aqueous  vapor  formed  is  always  equal  to  the  volume  of 
hydrogen  consumed.  At  mean  pressure,  and  at  the  temperature  of  212°, 
the  volume  of  this  vapor  is  1689  times  that  of  the  water  which  produces  it ; 
in  other  words,  a  cubic  inch,  or  rather  more  than  half  an  ounce  of  water  will 
be  converted  at  212°,  into  1689  cubic  inches,  or  about  six  gallons  of 
vapor— nearly  a  cubic  foot.  100  cubic  inches  of  the  vapor  weigh,  at  the 
temperature  of  212°,  and  under  mean  pressure,  14-96  grains,  and  at  60°, 
19-34  grains. 

The  experiments  illustrating  the  composition  of-  water  and  showing  the 


128  SYNTHESIS    OF    WATER. 

proportions  in  which  its  elements  are  united,  may  be  arranged  under  synthesis 
and  analysis. 

Synthesis. — If  a  current  of  hydrogen  is  burnt  under  a  funnel-tube  connected 
with  a  condenser,  the  gas  unites  to  the  oxygen  of  the  air,  producing  aqueous 
vapor,  which  may  be  collected  in  a  receiver.  The  water  thus  condensed 
frequently  has  a  slightly  acid  reaction,  apparently  from  the  simultaneous 
combustion  or  oxidation  of  a  portion  of  the  nitrogen  of  the  atmosphere,  so 
that  nitric  acid  is  produced.  According  to  Saussure,  if  the  hydrogen  is  in 
excess,  the  water  may  contain  ammonia.  {An7i.  de  Chim.,  vol.  71,  p.  282.) 
This  experiment  may  be  modified  by  burning  a  small  jet  of  hydrogen  under 
a  tall  and  capacious  bell-glass  (provided  with  a  stopper),  supplying  below, 
by  another  jet  connected  with  a  gas-holder,  a  stream  of  oxygen  equivalent 
to  half  the  volume  of  hydrogen.  The  bell-glass  may  be  placed  in  a  glass 
dish,  and  the  jets  may  be  passed  through  a  perforated  cork  placed  in  the 
centre  of  the  opening  of  the  bell-glass,  and  so  arranged  that  they  are  nearly 
in  contact.  The  water  produced,  as  a  result  of  combustion,  will  trickle 
down  the  sides  of  the  vessel,  and  may  be  collected  in  the  dish. 

One  of  the  best  synthetical  processes  for  the  production  of  water,  however, 
is  that  which  was  employed  by  Dumas  in  his  experiments  on  its  composition. 
It  consists  in  reducing  a  known  weight  of  dry  oxide  of  copper  by  pure  and 
dry  hydrogen.  The  current  of  hydrogen  is  purified  and  dried  by  the  methods 
already  described.  (Page  119.)  The  oxide  is  placed  in  a  bulb  of  hard 
glass,  which  can  be  maintained  at  a  red  heat  without  fusing,  and  which  is 
exhausted  of  its  air  before  commencing  the  operation.  This  is  connected 
with  another  glass  bulb,  kept  cool  in  order  to  condense  and  collect  the  water 
produced.  When  the  oxide  of  copper  is  heated  to  full  redness,  and  hydrogen 
is  passed  over  it,  only  so  much  oxygen  is  taken  by  the  hydrogen,  as  will 
suffice  to  form  water.  Hence  the  loss  of  weight  in  the  oxide  after  the  experi- 
ment, represents  the  oxygen  consumed,  and  by  deducting  this  from  the  weight 
of  water  condensed,  the  amount  of  hydrogen  combined  with  the  oxygen  may 
be  readily  found.  By  this  arrangement,  Dumas  produced  in  one  operation, 
upwards  of  two  ounces  of  water.  The  results  which  he  obtained  correspond 
as  nearly  as  possible  to  those  already  given — namely,  in  100  parts  by  weight 
— 88888  oxygen,  and  11 '11 2  of  hydrogen. 

If  two  measures  of  pure  hydrogen  are  mixed  with  one  of  pure  oxygen,  and 
the  mixture  is  detonated  by  an  electric  spark,  in  a  graduated  glass  tube, 
standing  over  mercury,  the  gases  will  disappear.  If  there  be  any  excess  of 
either  gas,  the  portion  in  excess  will  remain  unconsumed.  At  the  moment 
the  explosion  takes  place,  the  gaseous  mixture  becomes  greatly  expanded, 
probably  to  fifteen  times  its  original  bulk  (Davy  On  Flame^  p.  90),  and  a  por- 
tion is  apt  to  escape  at  the  bottom  of  the  tube ;  hence  to  prevent  any  loss, 
the  experiment  should  be  performed  over  mercury  in  a  siphon  tube. 

Oxygen  and  hydrogen  have  no  tendency  to  combine  when  mixed  as  gases, 
but  when  they  are  suddenly  submitted  to  violent  mechanical  compression,  the 
heat  of  condensation  causes  them  to  unite  with  combustion,  and  water  is  pro- 
duced. (Biot.)  A  red  heat,  visible  by  daylight,  inflames  the  mixture  ;  but 
a  dull  red  heat  only  causes  the  slow  combination  of  the  gases  without  explo- 
sion. Graham  states  that  if  a  mixture  of  oxygen  and  hydrogen  be  heated 
in  a  vessel  containing  a  quantity  of  pulverized  glass,  or  any  sharp  powder, 
they  begin  to  unite,  in  contact  with  the  foreign  body,  in  a  gradual  manner 
without  explosion,  at  a  temperature  not  exceeding  660°. 

In  the  year  1824,  Dobereiner  found  that  spongy  platinum,  procured  by 
heating  the  dry  ammonio-chloride,  on  platinum  foil,  possessed  the  singular 
property  of  causing  the  immediate  combination  of  hydrogen  and  oxygen,  with 
heat  sufficient  to   render  the  metal  red  hot,  and  to  inflame  the  gases.     If 


ACTION    OF    PLATINUM    ON    OXYGEN    AND    HYDROGEN.  129 

freshly-prepared  spongy  platinum  be  held  on  filtering  paper,  over  a  jet  of 
hydrogen  issuing  from  a  small  tube  into  the  atmosphere,  it  will  soon  become 
hot  enough  to  inflame  the  gas.  If  a  mixture  of  oxygen  and  hydrogen,  or  of 
atmospheric  air  and  hydrogen,  not  in  explosive  proportions,  be  submitted  to 
the  action  of  the  platinum,  the  gases  enter  into  slow  combination,  water  is 
gradually  formed,  and  if  there  is  a  sufficiency  of  oxygen,  the  whole  of  the 
hydrogen  will  disappear  under  its  influence  ;  if,  on  the  other  hand,  there  is 
an  excess  of  hydrogen,  the  oxygen  will  disappear,  and  the  surplus  hydrogen 
remain.  In  the  analysis  of  the  atmosphere  and  certain  gaseous  mixtures, 
platinum,  in  this  peculiar  state  of  mechanical  division,  becomes  a  valuable 
agent.  For  its  more  convenient  application  to  such  purposes,  and  to  prevent 
the  danger  of  explosion,  the  platinum  is  mixed  with  an  equal  weight  of  pure 
clay,  and  moulded  with  a  little  water  into  small  balls,  which,  after  having 
been  slowly  dried,  should  be  gradually  heated  to  a  high  temperature  in  a 
Bunsen's  jet.  For  the  purpose  of  manipulation,  a  small  piece  of  platinum 
wire  may  be  fixed  in  the  balls  while  moist.  These  balls  may  be  conveniently 
introduced  into  gases  standing  over  dry  mercury  ;  their  power  is  not  impaired 
by  use,  for  they  may  always  be  rendered  efficient,  or  their  power  restored,  by 
again  heating  them  red  hot.  The  admixture  with  clay  not  only  gives  cohe- 
sion to  the  platinum,  but  prevents  the  rapid  heating  of  the  metal,  and  there- 
fore the  explosion  of  the  gases.  This  will  be  found  a  convenient  method  of 
analysis.  If  the  gases  are  pure,  and  in  their  proper  portions,  the  whole  will 
disappear,  and  the  mercury  will  rise  and  fill  the  tube.  If  there  should  be  a 
residue,  the  amount  of  oxygen  and  hydrogen  which  have  combined  to  form 
water,  may  be  easily  determined.  Two-thirds  of  the  condensed  gases  will 
represent  the  hydrogen,  and  one-third  the  oxygen. 

Spongy  platinum  effects  the  union  of  oxygen  with  several  other  gases, 
such  as  with  carbonic  oxide,  and,  at  high  temperatures,  with  olefiant  gas  ; 
it  also  causes  the  decomposition  of  deutoxide  of  nitrogen  by  hydrogen, 
producing  ammonia.  (Dulong  and  Thenard,  Ann.  de  Gh.  et  Ph.,  23,  440.) 
It  is  an  essential  condition  in  all  cases  of  the  catalytic  influence  of  platinum, 
that  its  surface  should  be  absolutely  clean,  the  slightest  film  of  foreign 
matter — a  result  of  mere  exposure  to  air — impairing,  or  in  some  instances 
preventing  the  action  :  hence  the  advantage  derived  from  carefully  heating 
in  a  clear  flame,  spongy  platinum  which  has  become  inert.  Some  other 
metals,  such  as  palladium  and  iridium,  operate  in  the  same  manner,  but  less 
perfectly  than  platinum.  Spongy  platinum  placed  in  hydrogen  or  in  oxygen 
gas,  separately,  has  no  influence  on  the  gases,  and  undergoes  no  change.  It 
is  in  the  state  of  mixture,  or  when  one  gas  can  come  freely  in  contact  with 
the  other,  that  any  effect  is  produced.  If  freshly-prepared  spongy  platinum 
is  placed  on  mica,  on  a  stand  so  arranged  that  the  open  mouth  of  ajar  of 
hydrogen  can  be  suddenly  lowered  over  it,  the  platinum  retains  its  usual 
appearance,  and  the  hydrogen  is  not  absorbed.  If,  however,  the  jar  is  raised 
so  that  the  mouth  is  on  a  level  with  the  platinum,  the  metal  will  become  red 
hot,  and  the  hydrogen  will  disappear,  owing  to  its  admixture  with  the  oxygen 
of  the  air  at  this  point.  The  heat  is  sometimes  sufficient  to  kindle  the 
hydrogen  with  a  slight  explosion.  If  this  experiment  is  performed  on  the 
mixed  gases,  they  should  be  in  small  q&antity,  and  contained  in  a  stout 
glass  jar,  as  the  explosion  is  sudden  and  violent.  Spongy  platinum  placed 
on  mica,  or  platinum  foil  or  gauze,  undergoes  no  change  in  air,  but  if  a  jet 
of  dry  hydrogen  be  allowed  to  fall  on  it  from  a  bladder,  it  will  become  red 
hot  and  ignite  the  gas.  In  all  cases  the  platinum  acts  most  efficiently  when 
freshly  prepared,  or  when  it  has  been  heated  before  the  performance  of  the 
experiment. 

Faraday  has  found  that  perfectly  clean  platinum /oi7  or  wire  will  also  cause 
9 


130  VARIETIES    OF    WATER. 

the  combination  of  oxygen  and  hydrogen.  He  refers  this  phenomenon  to  a 
peculiar  attraction  between  the  clean  metallic  surface  and  the  particles  of  the 
gaseous  mixture,  resembling  that  by  which  bodies  become  wetted  by  fluids 
with  which  they  do  not  combine  chemically,  or  in  which  they  do  not  dissolve; 
or  the  attraction  which  renders  certain  bodies  hygroraetric,  although  they 
neither  dissolve  in,  nor  combine  with  water.  By  this  surface- attraction,  the 
particles  of  oxygen  and  hydrogen  are  so  approximated  and  condensed,  as  to 
enter  into  chemical  union  ;  and,  in  so  doing,  to  evolve  suflBcient  heat  to  raise 
the  temperature  of  the  metal.  It  is  calculated  that  platinum  in  the  state  of 
sponge,  will  absorb  250  times  its  volume  of  the  mixed  gases,  and  condense 
them  to  1-lOOOth  of  their  bulk. 

Analysis. — Water  may  be  decomposed,  or  resolved  into  its  elements,  by  a 
variety  of  processes.  One  of  these,  based  on  the  decomposition  of  aqueous 
vapor,  by  passing  it  over  iron  wire  heated  to  redness  in  a  tube,  has  already 
been  referred  to,  as  a  source  of  hydrogen  {see  page  119).  In  a  carefully 
conducted  experiment,  the  iron  will  be  found  to  have  increased  in  weight ; 
and  this  increase,  added  to  the  weight  of  the  hydrogen  collected,  will  be 
equal  to  the  weight  of  the  water  which  has  disappeared. 

Electrolysis  furnishes  the  best  method  of  analyzing  water,  in  order  to 
determine  its  chemical  constitution,  as  well  as  the  volumetric  proportions  of 
its  constituent  gases.  By  a  simple  apparatus,  oxygen  and  hydrogen  are 
separately  collected,  and  it  may  be  observed,  during  the  action  of  the  battery, 
that  for  every  cubic  inch  of  oxygen  given  off  at  the  positive  electrode,  there 
are  two  cubic  inches  of  hydrogen  collected  at  the  negative  electrode.  These 
gases  when  mixed  over  mercury  may  be  recombined  in  the  manner  already 
described  (page  128.)  They  entirely  disappear,  and  are  reconverted  into 
water.  Analytically,  and  synthetically,  therefore,  the  constitution  of  water 
has  been  actually  determined.  Pure  water  is  not  easily  decomposed  by  elec- 
trolysis ;  but  its  decomposition  is  readily  brought  about  by  the  addition  of  a 
tenth  part  of  sulphuric  acid.  The  oxygen  evolved  possesses  some  peculiar 
properties  {see  110). 

Varieties  of  Water. — TTater  in  its  ordinary  state,  such  as  spring  and  river 
water,  is  always  so  contaminated  with  foreign  substances  as  to  render  it 
unfit  for  chemical  purposes.  Rain-water  is  more  pure,  but  it  frequently 
contains  small  quantities  of  sulphuric,  nitric,  and  hydrochloric  acids,  in 
combination  with  ammonia,  lime,  or  other  bases,  as  well  as  organic  matter 
of  animal  or  vegetable  origin.  Rain-water  collected  near  the  sea,  invariably 
shows  traces  of  chlorides  ;  its  impurities  vary  much  with  locality.  In  Paris, 
it  has  been  found  to  contain  traces  of  iodine  and  phosphoric  acid.  Even  if 
collected  in  clean  glass  vessels,  before  it  has  touched  any  roof  or  soil,  it  is 
always  found  impure  in  or  near  inhabited  places. 

Lalce  Water. — Among  the  purest  forms  of  natural  water  may  be  mentioned 
lake-water,  as  it  is  collected  in  deep  lakes  and  in  slaty  and  granite  districts. 
Among  pure  waters  of  this  kind  in  Great  Britain,  is  that  of  Loch  Katrine, 
in  Scotland,  containing  only  two  grains  of  solid  matter  in  the  imperial  gal- 
lon. The  waters  Loch  2s ess,  and  of  Enerdale  Lake  in  Cumberland,  are 
nearly  equally  pure. 

JRiver  Water  is  subject  to  great  Variation  in  quality,  according  to  the  nature 
of  the  soil,  and  other  accidental  circumstances.  It  may  be  regarded  as  rain- 
water holding  dissolved,  substances  derived  from  the  atmosphere  and  the  soil 
over  which  it  has  flowed.  It  is  this  kind  of  water  which  is  now  largely 
employed  for  the  supply  of  towns.  The  properties  of  good  River  water  are 
— (1)  It  should  be  colorless,  tasteless,  and  free  from  smell.  (2)  It  generally 
has  an  alkaline  reaction  from  the  presence  of  carbonate  of  lime,  held  dis- 
solved by  carbonic  acid.      This  is  the  principal  mineral  constituent  of  river 


HARDNESS    OF    WATER.  131 

water  in  the  southern  and  eastern  districts  of  England.  (3)  It  gives  a 
slight  white  precipitate  when  nitrate  of  silver  is  added  to  it ;  this  pre- 
cipitate is  not  entirely  dissolved  by  nitric  acid  (chloride  of  sodium).  (4) 
It  gives  a  primrose  yellow  colored  precipitate,  with  a  solution  of  arsenio- 
nitrate  of  silver.  This  indicates  the  predominance  of  an  alkaline  carbonate, 
generally  bicarbonate  of  lime.  The  presence  of  bicarbonate  of  lime  is  also 
known  by  an  alcoholic  solution  of  logwood  striking  a  violet  color  with  the 
water.  As  the  bicarbonates  of  potassa  and  soda  also  produce  this  change  of 
color,  a  solution  of  chloride  of  calcium  should  be  added.  Bicarbonate  of 
lime  is  not  precipitated  by  this  salt.  (5)  It  gives,  after  a  time,  only  a  slight 
white  precipitate,  when  a  solution  of  nitrate  of  baryta  is  added ;  this  pre- 
cipitate being  insoluble  in  nitric  acid  (sulphuric  acid).  (6)  A  white  pre- 
cipitate when  treated  with  oxalate  of  ammonia,  more  abundant  than  with 
any  of  the  other  tests  (lime).  (Y)  When  boiled,  it  does  not  become  milky- 
looking  or  turbid,  or  it  presents  this  appearance  only  in  a  slight  degree 
(precipitation  of  carbonate  of  lime).  (8)  When  a  standard  diluted  solution 
of  permanganate  of  potassa  is  added  to  a  few  ounces,  the  pink  color  is  not 
discharged  (absence  of  organic  matter). 

In  respect  to  the  last  character,  it  may  be  observed,  that  if  the  color  is 
discharged,  it  indicates  in  the  absence  of  foul  effluvia,  the  presence  of  organic 
matter;  and  the  greater  the  amount  of  permanganate  decolorized  before  the 
water  retains  a  pink  color,  the  larger  the  quantity  of  organic  matter  present. 
If  a  graduated  tube  or  burette  is  employed,  two  waters  may  thus  be  com- 
pared, in  reference  to  the  quantity  of  organic  matter  contained  in  them,  or 
they  may  both  be  compared  with  an  artificial  standard.  At  common  tem- 
peratures, the  organic  matter  acts  very  slowly  on  the  permanganate.  At  a 
high  temperature,  the  permanganate  itself  is  decomposed,  although  no  organic 
matter  is  present.  M.^onnier  found  that  this  change  took  place  at  194° 
F.,  and  that  if  the  water  were  not  heated  above  160°,  a  safe  inference  might 
be  drawn  from  the  results.  In  the  ordinary  employment  of  this  test,  it  is 
not  necessary  to  heat  the  water  or  add  any  acid.  A  proper  solution  for  the 
purpose  of  testing  water  may  be  made  by  adding  one  drachm  of  a  cold  satu- 
rated solution  of  crystals  of  permanganate  to  thirty  ounces  of  fresh  distilled 
water.  One  or  two  drachms  of  the  diluted  solution  may  be  added  to  four 
ounces  of  the  water  to  be  tested.  If  free  from  oxidizable  organic  matter, 
the  pink  color  imparted  to  the  sample  of  water  should  remain  unchanged 
for  an  hour  or  longer.  The  crystals  of  the  permanganate  are  soluble  in 
sixteen  times  their  weight  of  cold  water,  hence  a  drachm  of  the  saturated 
solution  would  contain  about  four  grains,  and  the  standard  solution  above 
mentioned  would  contain  l-3600th  part  of  solid  permanganate.  Even  with 
such  a  dilution  the  coloring  power  is  very  strong. 

In  relying  upon  this  test  as  evidence  of  impurity  in  water,  it  must  be 
remembered  that  sulphurous  acid,  sulphuretted  hydrogen,  protoxide  of  iron, 
as  well  as  other  deoxidizing  compounds,  destroy  the  color  of  permanganate 
of  potash  by  reducing  the  permanganic  acid  to  a  lower  oxide  of  manganese. 
A  solution  of  alum  or  sulphate  of  alumina  produces  in  river  or  spring 
water  a  precipitate  of  alumina.  If  the  water  is  free  from  dissolved  impurity 
this  precipitate  will  be  white  ;  otherwise,  it  will  be  more  or  less  colored. 
Alum  has  been  thus  employed  for  the  purification  of  water. 

These  are  the  principal  chemical  reactions  of  river  water.  They  show  the 
presence  of  chlorine,  carbonic  acid,  sulphuric  acid,  and  lime,  and  generally 
indicate  the  existence  of  common  salt,  bicarbonate  and  sulphate  of  lime,  as 
well  as  of  organic  matter.  Salts  of  magnesia  and  potassa,  with  alkaline 
nitrates,  oxide  of  iron,  silica,  and  phosphoric  acid  are  frequently  contained 


132  ANALYSIS    OP    RIVER-WATER. 

in  river  water,  in  smaller  proportion  ;  and  they  may  be  easily  detected  by 
other  processes  applied  to  the  residue  left  by  the  water  after  evaporation. 

Among  other  properties,  it  may  be  observed,  that  river  water  does  not 
readily  dissolve  soap.  If  a  solution  of  soap  in  alcohol  be  added  to  some 
ounces  of  the  water,  and  the  mixture  is  well  agitated,  a  white  curdy  sub- 
stance is  formed  (a  compound  of  the  fatty  acids  of  soap  with  the  calca- 
reous and  other  bases  of  the  water),  and  the  water  is  rendered  milky-looking ; 
but  there  is  no  persistent  frothiness  as  with  pure  water.  On  this  property 
is  founded  the  process  of  determining  the  hardness  or  softness  of  water,  by 
means  of  the  soap-test.  The  method  of  employing  this  will  be  presently 
explained.  The  larger  the  quantity  of  calcareous  and  magnesian  salts,  the 
harder  the  water ;  while  the  more  free  the  water  is  from  any  saline  matter, 
the  softer  it  is.  River  water,  as  it  is  ordinarily  constituted,  has  so  little 
action  on  the  metal  lead,  that  even  after  keeping  the  water  in  a  leaden  vessel 
for  a  considerable  time,  it  will  either  show  no  trace  of  lead,  or  the  quantity 
is  so  small  that  it  may  be  disregarded.  The  waters  of  English  rivers,  how- 
ever, vary  so  much  in  this  respect,  that  each  water  should  be  submitted  to  a 
separate  trial,  whatever  may  be  its  chemical  composition.  Thus,  river 
waters  which  contain  soluble  nitrates,  or  chlorides  in  unusual  quantity, 
generally  act  upon  lead.  This  chemical  effect  depends  not  merely  on  the 
nature  of  the  salts,  but  on  the  proportion  in  which  they  are  contained  in  the 
water. 

The  solid  residue  left  by  the  evaporation  of  river  water  varies  in  weight 
from  6  to  50  grains,  or  more,  in  the  Imperial  gallon  ;  but  potable  river 
waters  are  generally  comprehended  between  these  two  extremes.  The  nearer 
the  point  from  which  the  water  is  taken  to  the  source  of  a  river,  the  more 
free  from  saline  and  other  impurities  will  it  be  found.  The  Thames  water 
formerly  supplied  to  London,  yielded  from  20  to  2# grains  of  solid  residue, 
from  the  Imperial  gallon  of  tO,000  grains.  That  which  is  now  supplied 
from  the  river,  taken  near  Hampton,  yields  only  from  15  to  17  grains  in 
the  gallon,  varying  a  little  with  the  season  of  the  year,  and  the  amount  of 
rain.  All  foreign  substances  in  water  have  been  described  as  "impurity." 
In  a  chemical  sense  this  is  correct,  but  the  presence  of  carbonate  of  lime 
(chalk)  and  chloride  of  sodium  (common  salt),  in  river  water,  in  the  small 
proportions  in  which  these  substances  are  found  therein,  is  not  injurious  to 
health.  The  salubrity  of  districts  bears  no  relation  to  the  greater  or  smaller 
quantity  of  saline  matter  in  water.  If  distilled  water  could  be  supplied  to  a 
population  in  millions  of  gallons  daily,  it  would  be  neither  agreeable  nor 
wholesome  to  the  general  public.  The  experiments  of  M.  Boussingault 
have  clearly  proved  that  the  calcareous  salts  of  potable  waters,  in  conjunc- 
tion with  those  contained  in  food,  aid  in  the  development  of  the  bony 
skeletons  of  animals.  (Pelouze  and  Fremy,  Traitede  Chimie,  1860.  Yol.  i. 
p.  234.)  Calcareous  waters,  such  as  Carrara  water,  are  usefully  employed 
in  medicine.  The  search  after  non-calcareous  water  therefore  is  based  on  a 
fallacy.  If  lime  were  not  freely  taken  in  our  daily  food,  either  in  solids  or 
liquids,  the  bones  would  be  destitute  of  the  proper  amount  of  mineral  matter 
for  their  normal  development. 

With  respect  to  the  chloride  of  sodium,  which  has  been  wrongly  described 
as  a  result  of  the  presence  of  sewage  in  river  water,  it  may  be  safely  said 
that  no  natural  water  taken  from  the  purest  sources  in  the  world,  has  been 
yet  found  without  it.  All  river  and  spring  waters  contain  it  in  greater  or 
less  proportion. 

The  solid  contents  in  the  imperial  gallon  of  some  principal  river  waters  of 
Europe  have  been  found  to  be  as  follows  :  The  Thames  at  Greenwich,  27 '7 9 
grains,  at  Hampton,  15  grains  ;  the  Seine  in  Paris,  20  grains  ;  the  Rhone  at 


SPRING    WATER.      ARTESIAN    WELL-WATERS.  133 

Lyons,  12-88  grains  (Binean)  ;  the  Rhine  at  Basle,  11-97  grains  (Pagenst); 
the  Garonne  at  Toulouse,  9-56  grains  (Deville) ;  the  Loire  at  Mehung,  9-42 
grains;  the  Scheldt  in  Belgium,  2058  grains;  and  the  Danube,  Vienna, 
1015  grains  (Hauer).  The  principal  salts  in  these  waters  are  the  carbonate 
and  sulphate  of  lime,  with  chloride  of  sodium. 

In  conducting  an  analysis  of  a  potable  water,  the  general  course  to  be 
pursued  is  the  following :  1.  To  determine  the  solid  contents  by  the  slow 
evaporation  of  a  gallon,  or  at  least  half  a  gallon  of  the  water,  filtered  or 
unfiltered,  according  to  circumstances.  In  good  river  water  the  residue 
thus  obtained  is  white,  or  of  a  pale  fawn  tint;  and  it  will  weigh,  when  dry, 
from  6  to  20  grains.  2.  The  organic  or  combustible  matter  is  next  ascer- 
tained by  heating  the  dry  residue  to  a  low  red  heat,  and  noting  the  loss  of 
weight.  When  a  water  contains  only  traces  of  organic  matter,  this  may  be 
detected  by  boiling  a  pint  of  it  with  a  few  drops  of  a  solution  of  chloride  of 
gold,  rendered  feebly  alkaline  by  potash.  If  the  water  is  already  alkaline, 
the  addition  of  potash  is  not  necessary.  After  a  time  the  water  acquires 
more  or  less  of  a  pink  color,  by  reason  of  the  reduction  of  the  gold  by 
organic  matter.  This  change  of  color  is  well  seen  when  the  water  is  boiled 
in  a  white  evaporating  dish.  3.  To  determine,  by  the  usual  modes  of 
analysis,  the  nature  and  proportion  of  the  salts  contained  in  this  residue. 
4.  To  ascertain  whether  the  water  has  any  action  on  lead.  A  clean  bar  of 
this  metal,  exposing  an  area  of  from  8  to  12  square  inches,  should  be  im- 
mersed in  the  water  and  the  vessel  freely  exposed  to  air.  In  48  hours  the 
water  may  present  a  railkiness  or  remain  clear.  In  either  case  it  should  be 
tested  for  lead  by  passing  into  it  a  current  of  washed  sulphuretted  hydrogen 
gas.  5.  To  determine  the  relative  hardness  of  the  water.  A  saturated 
solution  of  Spanish  soap  is  made  in  three  parts  of  rectified  spirit  (0-830) 
and  one  part  of  distilled  water.  After  sufficient  digestion  the  solution  is 
filtered,  and  it  then  serves  as  a  soap  test.  The  solution  is  added  from  a 
graduated  vessel  to  from  four  to  eight  ounces  of  distilled  water  contained  in 
a  bottle  ;  and  the  quantity  required  to  produce  a  permanent  froth  in  the 
water  is  noted.  This  forms  a  standard  for  comparison.  A  similar  quantity 
of  river  water  is  treated  in  another  bottle  with  the  same  solution  of  soap ; 
and  it  will  be  found  to  require  five,  six,  ten,  or  twelve  times  the  quantity  of 
soap-solution  to  produce  an  equal  amount  of  permanent  froth  in  it,  as  in  the 
distilled  water.  The  river  water  may  thus  be  described  as  having  5^,  6°,  10°, 
or  12°  of  hardness,  i.  e.,  it  will  require  these  additional  proportions  of  soap 
to  produce  in  it  the  same  detergent  properties,  as  in  a  like  quantity  of  dis- 
tilled water.  Dr.  Clark's  soap  test  is  based  on  a  different  principle.  He 
makes  an  artificial  solution  of  chloride  of  calcium,  and  uses  a  weak  alcoholic 
solution  of  white  curd-soap.  His  degrees,  therefore,  are  referable  to  a 
different  standard. 

Spring  Water. — Spring  waters  may  be  divided  into  those  which  are  de- 
rived from  shallow  wells,  and  those  which  issue  from  deep  springs,  called 
also  Artesian  wells.  The  former  are  generally  within  thirty  to  fifty  feet  of 
the  surface,  while  the  latter  in  the  London  district  are  from  400  to  600  feet 
in  depth,  and  in  Paris  they  reach  a  depth  of  1800  feet.  The  water  from  the 
shallow  wells  of  London  usually  abounds  in  sulphate  and  carbonate  of  lime, 
containing  generally  but  little  chloride  of  sodium  ;  the  solid  contents  of  the 
gallon  are  very  variable,  but  sometimes  amount  to  130  or  140  grains.  The 
water  is  very  hard,  and  yields  in  some  cases  traces  of  sewage,  gas-liquids, 
or  ammonia  and  alkaline  nitrates,  the  products  of  their  decomposition.  The 
deep  (Artesian)  wells  which  penetrate  the  London  clay,  and  are  carried  to 
different  depths  into  the  underlying  chalk,  vary  in  the  quality  of  their  water 
according  to  the  care  with  which  the  superincumbent  springs  have  been 


134  DISTILLED    WATER. 

excluded  :  they  contain  a  larger  relative  proportion  of  solid  matter  than 
river  water,  but  less  than  that  found  in  the  surface-wells,  and  are  remarkably 
characterized  by  the  abundance  of  soda  salts  and  by  their  alkalinity,  which 
is  derived  from  bicarbonate  of  soda :  like  all  other  spring  waters,  they  hold 
more  or  less  carbonic  acid.  They  generally  contain  from  50.to  TO  grains  of 
saline  matter  in  the  imperial  gallon.  The  water  of  the  Trafalgar-square 
springs,  issuing  from  a  depth  of  510  feet,  contains  68  94  grains  of  saline 
matter  in  the  imperial  gallon,  including  14  grains  of  carbonate  of  soda,  19 
grains  of  sulphate,  and  25  grains  of  chloride  of  sodium.  The  well  at  the 
Royal  Mint  has  a  total  depth  of  426  feet.  It  contains  less  than  38  grains 
of  solid  matter  in  the  gallon  :  including  8-63  grains  of  carbonate  of  soda, 
13  14  grains  of  sulphate  of  soda,  and  10  53  of  chloride  of  sodium.  The 
Artesian  water  supplied  to  Guy's  Hospital  issues  from  the  chalk  stratum  at 
a  depth  of  297  feet,  of  which  100  feet  are  in  chalk.  It  contains  47  grains 
of  solid  matter  in  the  gallon,  consisting  of  1276  carbonate  of  soda,  10  40 
of  sulphate  of  soda,  20-4  of  chloride  of  sodium,  and  3*80  of  carbonate  of 
lime  with  carbonate  of  magnesia,  silica,  &c.  The  organic  matter  is  in  very 
small  proportion:  and  can  be  detected  only  by  boiling  a  pint  of  this  water 
with  a  few  drops  of  chloride  of  gold.  The  water  of  the  well  at  Southampton, 
issuing  from  a  depth  of  1360  feet,  contains  68  grains  of  saline  matter  in  the 
gallon,  of  which  18  grains  consist  of  carbonate  of  soda,  8  grains  of  sulphate, 
and  20  grains  of  chloride  of  sodium.  The  Artesian  well-water  of  the  Paris 
Basin  (Grenelle),  issuing  from  a  depth  of  1794  feet,  is  much  purer  than  the 
London  Artesian  waters.  It  contains  20  grains  of  saline  matter  in  the 
gallon,  of  which  nine  grains  are  carbonate  of  lime,  and  four  grains  are 
bicarbonate  of  potassa — the  principal  saline  ingredients.  The  Artesian 
well-waters  differ  from  those  of  surface  wells  in  containing  generally  a  larger 
quantity  of  phosphates  and  a  smaller  proportion  of  calcareous  salts  and  of 
organic  matter. 

Distilled  Water. — When  spring  or  river  water  is  distilled,  the  solid  con- 
tents are  left  in  the  retort  or  still.  In  the  chalk  district  this  residue  consists 
in  great  part  of  carbonate  of  lime,  with  some  sulphate  of  lime,  of  carbonate 
and  sulphate  of  soda,  with  magnesia,  silica,  alumina,  and  oxide  of  iron.  In 
ordinary  waters,  besides  carbonate  and  sulphate  of  lime,  the  insoluble  matter 
deposited  has  been  found  to  contain  traces  of  lead,  copper,  arsenic,  and  other 
metals.  The  condensed  water  obtained  in  the  receiver,  as  it  is  commonly 
distilled,  always  contains  foreign  matter.  The  first  portions  are  frequently 
impregnated  with  ammonia  ;  these  should  be  rejected,  and,  when  four-fifths 
have  been  distilled,  the  operation  should  be  stopped.  Water  distilled  in 
glass  is  sometimes  alkaline,  owing  to  its  dissolving  a  portion  of  soda  from 
the  glass.  It  can  be  considered  perfectly  pure  only  when  it  has  been  redis- 
tilled at  a  low  temperature  in  silver  or  platinum  vessels. 

Pure  water  is  transparent,  and  without  either  color,  taste,  or  smell.  It 
should  be  quite  neutral.  Its  neutrality  may  be  tested  by  adding  at  least  a 
pint  of  it  to  a  small  quantity  of  a  strong  solution  of  litmus,  reddened  to  a 
port  wine  tint  by  tartaric  acid.  If  the  water  is  neutral,  the  addition  of  it  to 
this  solution  of  litmus  will  not  render  the  liquid  blue  or  more  strongly 
redden  it.  Its  chemical  properties  are  chiefly  negative.  It  should  give  no 
precipitate  with  nitrate  of  silver,  nitrate  of  baryta,  oxalate  of  ammonia,  or 
ammonia.  It  should  undergo  no  change  of  color  on  passing  into  it  a  cur- 
rent of  sulphuretted  hydrogen  gas.  On  adding  to  some  ounces  of  the  water 
a  few  drops  of  a  solution  of  ammonio-nitrate  of  silver  and  exposing  the 
vessel  containing  the  water  to  solar  light,  it  should  undergo  no  discolora- 
tion. The  pink  color  imparted  to  the  water  by  a  weak  solution  of  per- 
manganate of  potassa  should  remain  unchanged  for  some  hours.     These  last 


WATER.      CONDUCTION    OF    HEAT    AND    ELECTRICITY.  135 

mentioned  tests  by  their  negative  results  show  the  absence  of  organic  matter 
and  foul  effluvia.  Half  a  gallon  of  the  water  should  leave  no  ponderable 
residue  on  evaporation.  Acetate  of  lead  frequently  produces  in  distilled 
water  a  white  precipitate  owing  to  the  presence  of  carbonic  acid.  The  pre- 
cipitate is  soluble  in  acetic  acid,  If  a  brown  precipitate  is  produced  by 
this  test,  it  indicates  the  presence  of  sulphuretted  hydrogen.  Among  other 
properties,  a  solution  of  soap  in  alcohol  produces  no  curdiness  or  opacity  in 
pure  water,  but  the  soap  is  readily  dissolved :  on  agitation  the  water 
remains  clear,  and  presents  a  persistent  frothy  stratum  on  its  surface.  If  a 
piece  of  clean  sheet  lead  be  immersed  in  pure  distilled  water,  the  water 
rapidly  becomes  opaque,  from  the  production  of  hydro-carbonate  of  lead. 
Distilled  water,  free  from  impurity,  is  indispensable  to  the  chemist.  The 
water  obtained  by  melting  pure  ice  may  be  occasionally  substituted  for  it. 

In  reference  to  physical  properties,  pure  water  is  a  powerful  refractor  of 
light,  but  it  is  a  very  imperfect  conductor  of  heat  and  electricity.  In  reference 
to  the  latter  force,  pure  water  so  completely  resists  the  passage  of  a  current, 
that  it  has  been  even  doubted  whether  it  was  an  electrolyte.  This  resistance 
becomes,  therefore,  a  test  of  the  purity  of  water.  The  electrolysis  of  com- 
mon water  probably  depends  on  the  saline  matter  which  it  holds  in  solution. 
In  such  experiments  on  distilled  water,  it  is  necessary  to  add  to  it  a  small 
quantity  of  sulphuric  acid.  The  following  experiments  will  prove  that  it  is 
a  very  imperfect  conductor  of  heat:  Fill  a  long  test-tube  with  distilled  water, 
and  freeze  the  lower  three  inches  by  immersing  the  end  of  the  tube  in  a  mix- 
ture of  ice  and  salt.  When  the  lower  part  has  been  thus  frozen,  the  upper 
stratum  of  water  may  be  boiled  over  a  spirit-lamp  and  kept  boiling  for  a 
considerable  time  without  melting  the  ice  below.  Lay  a  thermometer  on 
the  bottom  of  a  shallow  porcelain  dish  ;  cover  it  with  a  thin  layer  of  water — 
pour  on  this  a  stratum  of  ether  and  ignite  it.  When  the  ether  is  consumed, 
although  the  surface  of  the  water  was  heated  far  beyond  its  boiling  point,  it 
will  be  observed  that  the  thermometer  has  scarcely  iDcen  affected.  The  sides 
of  the  vessels  used  in  these  experiments  may,  however,  conduct  heat  down- 
wards. The  experiment  may  be  varied  by  placing  in  a  jar  of  water  an  air- 
thermometer,  containing  colored  fluid  with  the  bulb  upwards  and  nearly 
touching  the  surface  of  the  water.  Float  upon  the  water  a  small  copper 
basin  containing  ether ;  this  may  be  inflamed,  and  during  its  combustion, 
although  the  surface  of  the  water  is  heated  to  a  high  temperature,  the  air- 
thermometer  will  be  but  slightly  affected.  Fill  a  test-glass  to  two-thirds  of 
its  capacity  with  water,  and  place  in  this  a  mercurial  thermometer,  the  bulb 
resting  on  the  bottom  of  the  glass.  Now  pour  carefully  upon  the  cold  water 
some,  boiling  distilled  water  which  has  been  slightly  tinted  with  blue  litmus. 
The  colored  water  will  float  on  the  cold  water  in  the  glass  ;  but,  although  at 
212°,  the  thermometer  will  indicate  no  change  of  temperature  except  by  the 
heat  slowly  transmitted  downwards  by  the  sides  of  the  vessel.  These  facts 
clearly  demonstrate  that  unlike  solids,  this  liquid  cannot  transmit  heat  from 
the  surface  downwards. 

The  only  mode  of  distributing  heat  through  water  and  other  liquids  is  by 
a  kind  of  diffusion,  depending  on  a  change  of  density.  Hot  water  is  lighter 
than  cold,  as  one  of  the  above-mentioned  experiments  proves.  If,  therefore, 
the  bottom  of  a  vessel  containing  water  is  heated,  the  liquid  will  rise  as  its 
specific  gravity  is  diminished,  and  there  will  be  a  series  of  upward  and  down- 
ward currents  until  the  water  has  acquired  a  uniform  temperature.  This 
may  be  shown  by  heating  water  in  which  are  diffused  particles  of  camphor, 
precipitated  from  its  alcoholic  solution.  The  motion  of  these  or  of  any  other 
light  solid  diffused  through  the  liquid,  will  indicate  the  course  of  the 
currents. 


136  PHYSICAL    PROPERTIES    OF    WATER.       ICE. 

Water  is  expanded  by  heat,  but  its  rate  of  expansion  is  cceteris  panbvs 
less  than  that  of  other  liquids,  and  the  ratio  of  increase  is  augmented  by  the 
temperature. 

Distilled  water  is  assumed  as  a  standard  to  which  the  relative  weights  of 
all  solids  and  liquids  may  be  compared — its  specijlc  yravity  being  called 
1.000.  (In  reference  to  this  subject,  the  reader  will  find  in  the  Appendix  a 
description  of  the  methods  by  which  the  specific  gravities  of  all  solids  and 
liquids,  whether  lighter  or  heavier  than  water,  may  be  taken.  The  scale  of 
Baume,  then  used  on  the  Continent,  is  also  given  in  a  comparative  table  ) 

At  the  temperature  of  62°,  which  is  that  to  which  specific  gravities  are 
usually  referred,  a  cubic  inch  of  water  weighs  252-458  grains  ;  or  at  60°,  the 
cubic  inch  weighs  almost  exactly  252'5  grains,  and  the  cubic  foot  998'21t 
ounces  avoirdvpois,  which  is  so  near  1000,  that  the  specific  gravity  of  any 
substance,  in  reference  to  water,  is  very  near  the  absolute  weight  of  one  cubic 
foot  of  such  substance  in  avoirdupois  ounces.  The  specific  gravity  of  gold, 
for  instance,  is  19"3,  in  reference  to  water  as  unity  ;  and,  therefore,  a  cubic 
foot  of  gold  weighs  nearly  19,300  ounces.  Water  is  about  815  times  heavier 
than  atmospheric  air.  At  mean  temperature,  it  is  assumed  as  the  unit  to 
which  the  specific  heats  of  bodies,  especially  of  solids  and  liquids,  are  usually 
referred. 

The  density  of  water  varies  with  the  temperature.  It  attains  its  maximum 
density  at  39°-39,  or  about  40°;  hence  water  expands  from  this  point, 
whether  the  thermometer  falls  from  40°  to  32°,  or  whether  it  rises  from  40° 
to  48.  It  is  a  remarkable  confirmation  of  this  fact,  that  the  temperature  of 
the  deep  sea  in  all  latitudes  has  been  found  to  fluctuate  about  40°. 

Water  is  said  to  be  colorless,  but  when  looked  at  in  a  large  mass,  or  what 
is  better,  a  tall  column,  it  has  a  greenish-blue  color.  This  is  well  seen  in 
the  waters  of  Matlock  and  other  springs,  and  in  the  glaciers  of  Switzerland. 
Most  river  waters  have  a  slightly  yellowish  colpr  from  the  presence  of  organic 
and  ferruginous  substances.  A  small  quantity  may  show  no  color,  but  when 
a  gallon  is  examined  in  a  tall  glass  vessel,  placed  on  a  sheet  of  white  paper, 
the  color  may  be  seen.  The  purest  distilled  water  presents  a  color  if  exam- 
ined in  a  column  of  sufficient  length. 

Water  is  susceptible  of  compression,  as  was  originally  shown  by  Canton. 
Perkins  states  that  a  pressure  of  2000  atmospheres  occasions  a  diminution 
of  only  l-12th  of  its  bulk.  {Phil.  Trans.,  1820.)  According  to  the  experi- 
ments of  Oersted,  and  those  of  Colladon  and  Sturm  {Ann.  Ch.  et  Ph.,  xxxvi. 
140),  its  absolute  diminution  of  bulk  for  each  atmosphere  is  not  more  than 
the  51-OOOOOOth  of  its  volume.  It  is  stated  by  Dessaignes,  that  when  water 
is  submitted  to  very  sudden  compression,  it  becomes  luminous.  (Thenard, 
Traite  de  Chimie,  i.  432.) 

Ice. — At  the  temperature  of  32°  water  congeals  into  ice,  which,  if  slowly 
formed,  produces  needles  crossing  each  other  at  angles  of  60°  and  120° 
forming  stars  or  stellated  crystals.  The  forms  are  various,  but  the  primitive 
figure  is  that  of  a  regular  six-sided  prism,  belonging  to  the  rhorabohedral 
system.  Although  the  freezing  of  water  is  commonly  said  to  take  place  at 
32°,  yet  if  the  water  is  contained  in  a  glass  tube,  one-fourth  of  an  inch  in 
diameter,  it  may  be  cooled  to  23°  without  freezing.  When  cooled  to  21°  it 
freezes  at  once.  In  a  capillary  tube  of  l-200th  of  an  inch  diameter,  Mr. 
Sorby  found  that  water  did  not  freeze  at  3°  ;  when,  however,  it  was  cooled 
to  1°  4,  it  passed  to  the  state  of  ice.   {Phil.  Mag.,  August,  1859,  p.  107.) 

The  specific  gravity  of  ice  varies  from  0*918  to  0  950,  but  the  densest  ice, 
obtained  by  freezing  water  deprived  of  air,  is  always  considerably  lighter 
than  water.  According  to  Bruuner,  the  contraction  of  ice  by  diminution  of 
temperature  exceeds  that  of  any  other  solid  ;  its  density  at  32°  being  0918, 


FREEZING    OF    WATER.      PROPERTIES    OF    ICE.  137 

at  18°  it  is  0-919,  and  at  0°,  0-920,  (Ann.  Gh.  et  Ph.,  July,  1845.)  Ice  is 
a  non-conductor,  or  nearly  so,  of  electricity,  and  under  favorable  circum- 
stances becomes  electric  by  friction.  (Faraday's  Exp.  Researches,  4th  series, 
§§  381  and  419  )  It  is  a  very  bad  conductor  of  heat,  but  it  transmits  radiant 
heat  with  such  facility  that  Faraday  was  able  to  ignite  phosphorus  by  con- 
verging the  solar  rays  through  an  ice-lens.  In  freezing,  w^ater  expands,  and 
with  such  force  as  to  burst  the  thick  and  strong  vessels  in  which  it  is 
confined.  The  rupture  of  iron  and  leaden  pipes  is  a  familiar  instance  of 
this  power  of  expansion.  The  greatest  difference  observed  between  the 
bulk  of  water  before  and  after  congelation  was  found  to  be  in  the  ratio 
of  174  :  184.  Exposed  to  the  air,  ice  loses  considerably  in  weight  by 
evaporation. 

The  manner  in  w^hich  water  frees  itself  of  impurities  in  the  act  of  con- 
gelation, is  very  remarkable  ;  by  careful  freezing,  it  may  be  entirely  deprived, 
not  only  of  common  air,  but  of  those  gases  for  which  it  has  a  strong  affinity, 
as  well  as  of  all  saline  matters.  In  the  common  mode  of  freezing  water, 
the  extricated  air  is  entangled  in  the  ice,  and  renders  it  more  or  less  porous 
and  translucent ;  but  if  means  be  taken  to  remove  the  air  bubbles,  by 
agitation  or  otherwise,  the  resulting  ice  is  dense  and  perfectly  pellucid,  as 
we  sometimes  see  in  icicles,  or,  more  remarkably,  when  a  thin  glass  tube 
or  flask,  containing  water,  is  immersed  in  a  freezing  mixture,  and  constantly 
agitated  by  means  of  a  feather,  so  as  to  brush  off  the  air  and  water  from 
the  layer  of  ice  which  forms  upon  the  sides  of  the  vessel.  The  ice  is  not  only 
perfectly  transparent  and  free  from  air-bubbles,  but  it  is  also  freed  from 
saline  matters,  which  are  therefore  contained  in  excess  in  the  unfrozen  water. 
This  will  be  found  to  be  the  case  with  common  spring  water,  but  a  better 
illustration  consists  in  thus  freezing  water  colored  by  sulphate  of  indigo, 
when  the  ice  will  not  only  be  quite  colorless,  but,  when  rinsed  in  a  little 
distilled  water  so  as  to  cleanse  its  surface  from  the  adhering  mother-liquor, 
it  will  not  contain  a  trace  of  sulphuric  acid.  In  the  same  way  an  aqueous 
solution  of  ammonia,  when  properly  frozen,  yields  ice  which  is  quite  free 
from  all  trace  of  the  alkali.  The  beautiful  masses  of  perfectly  transparent 
ice,  imported  for  the  use  of  the  table  from  Norway  and  from  North  America 
(Wenhara  Lake  ice),  yield  perfectly  pure  water ;  they  are  formed  in  deep 
lakes,  as  a  result  of  slow  and  gradual  cooling,  ending  in  congelation.  It 
has  long  been  known  that  wine  and  other  alcoholic  liquors  are  strengthened 
by  partial  freezing,  and  that  the  ice  which  they  deposit  is  little  else  than 
pure  water,  and  that  lemon-juice  and  vinegar  may  be  similarly  strengthened; 
but  the  fact  of  spring  water  thus  losing  the  whole  of  its  saline  and  aerial 
contents  was  first  pointed  out  by  Faraday,  and  in  these  cases  the  unfrozen 
portion  is  of  course,  rendered  relatively  impure,  so  that  water  may  be 
concentrated  by  freezing  as  it  is  by  evaporation.  In  northern  regions, 
salt  is  obtained  from  sea-water  by  simply  allowing  the  water  to  freeze.  The 
blocks  of  ice,  which  are  nearly  pure  water,  are  removed,  and  the  residuary 
liquid  is  a  comparatively  strong  brine,  from  which  salt  may  be  obtained  by 
evaporation. 

When  ice  is  formed  at  a  temperature  a  few  degrees  below  the  freezing- 
point,  it  has  a  well-marked  crystalline  structure,  as  is  seen  in  water 
frozen  from  a  state  of  vapor,  in  flakes  of  snow,  or  hoar  frost.  But  ice 
formed  in  water  at  32^  is  a  homogeneous  mass,  breaki!ig  with  a  vitreous 
fracture,  and  presenting  no  crystalline  structure  (Graham).  The  changes 
which  it  undergoes  in  the  movement  of  glaciers,  is  a  proof  that  it  possesses 
some  plasticity. 

Ice-water  produced  from  the  melting  of  the  ice  of  deep  lakes  is  one  of  the 
purest  forms  of  natural  water.     We  have  found  in  it  only  minute  traces  of 


138  ICE    WATER.       AQUEOUS    VAPOR. 

alkaline  chloride.  Snow-water  is  less  pure,  the  fine  crystals  of  snow  in  their 
formation  lock  up  many  organic  and  mineral  ingredients  which  were  diffused 
through  the  atmosphere,  especially  when  collected  in  the  neighborhood  of 
towns.  If  frequently  contains  so  much  organic  matter  as  to  show  confervoid 
vegetation  under  exposure  to  light.  The  amount  of  air  in  snow  is  very 
great.  We  have  found  that  sixty  cubic  inches  of  snow,  well  compressed, 
will  produce  only  eight  cubic  inches  of  water.  To  this  diffusion  of  air 
among  it  particles  it  owes  its  whiteness.  The  water  derived  from  melted 
snow  is  generally  too  impure  to  be  employed  for  any  chemical  purposes. 

Steam.  Aqueous  Vapor. — Water  gives  off  a  vapor  at  all  temperatures, 
even  at  32°.  In  its  ordinary  state,  if  exposed  to  heat  in  open  vessels,  it 
boils,  or  is  converted  at  212*^  into  steam,  the  barometer  being  at  30  inches ; 
but  the  boiling  point  of  water  varies  with  the  pressure,  and  is  influenced  by 
the  air  which  the  water  contains,  as  well  as  by  the  vessel  in  which  it  is 
heated.  When  quite  pure  and  deprived  of  air,  water  may  be  heated  to 
about  240°  before  it  reaches  the  boiling  point;  at  this  temperature,  however, 
it  is  suddenly  converted  into  vapor  with  explosive  violence.  If  a  piece  of 
pure  ice  be  heated  in  a  vessel  containing  oil,  the  heat  may  be  continued 
until  the  water  from  the  ice  has  reached  a  temperature  of  240°,  when  the 
whole  is  converted  into  vapor  with  explosion.  The  tranquil  ebullition  of 
ordinary  water  at  212°  appears,  therefore,  to  be  mainly  dependent  on  the 
presence  of  air. 

Water  generally  escapes  in  vapor  unmixed  with  the  solids  which  may  be 
dissolved,  but  during  rapid  boiling,  some  portion  of  the  solids  is  carried 
over  with  the  steam.  Thus  the  vapor  of  a  boiling  saturated  solution  of 
carbonate  of  soda  has  been  observed  to  tinge  of  a  yellow  color,  lights  burn- 
ing in  the  same  apartment.  This  is  owing  to  the  combustion  of  a  portion 
of  sodium  from  the  soda-salt  evolved  in  the  aqueous  vapor.  Even  the  most 
fixed  solids  may  thus  escape  with  steam.  Boracic  acid  is  collected  in  the 
lagoons  of  Tuscany  by  condensing  the  aqueous  vapor  in  which  it  is  dissolved; 
this  vapor,  charged  with  the  acid,  is  continually  issuing  from  the  soil.  Even 
mercury,  one  of  the  heaviest  metals  known,  may  be  carried  over  with  the 
vapor  of  water  at  212°  (Chem.  News,  Aug.  24,  1861). 

Steam,  or  aqueous  vapor,  may  be  exposed  to  a  full  red  heat  (1000°)  by 
passing  it  through  iron  tubes  heated  to  redness,  without  undergoing  any 
decomposition.  That  which  is  now  called  superheated  steam,  we  have 
observed  to  issue  from  a  discharge  pipe  at  a  temperature  of  460°.  In  this 
highly  heated  state,  the  steam  is  put  to  various  industrial  uses  without  any 
danger.  The  only  gas  which  we  have  found  associated  with  the  steam  at 
this  high  temperature,  was  nitrogen.  The  decomposition  of  water  by  iron 
at  a  red  heat  appears  to  be  here  arrested  by  the  production  of  the  magnetic 
oxide  of  iron,  which  lines  the  interior  of  the  tubes,  and  prevents  further  chemical 
action.  Aqueous  vapor  has  been  rendered  incandescent  by  the  heat  of  the 
electric  spark  from  Ruhmkorff's  coil,  and  a  spectralytic  examination  of  the 
light  has  shown  that  in  this  state  it  gives  the  bright  lines  due  to  hydrogen. 

When  water  is  placed,  in  small  quantities  at  a  time,  in  a  platinum  or 
other  vessel,  heated  to  full  redness,  it  does  not  boil,  and  does  not  produce 
any  visible  vapor.  The  liquid  assumes  what  is  called  the  spheroidal  state, 
and  rolls  about  in  a  stratum  which  presents  a  convexity  on  all  sides,  and 
nowhere  touches  the  containing  vessel.  At  this  temperature,  there  appears 
to  be  a  repulsion  between  the  water  and  the  metal.  The  liquid  has  been 
found  by  Boutigny  to  be  a  few  degrees  below  its  boiling  point ;  it  gradually 
diminishes  in  volume,  and  at  last  it  evaporates  entirely,  leaving  only  the 
solid  matters  which  it  may  have  contained.  If  while  the  water  is  in  this 
spheroidal  state,  the  source  of  heat  is  suddenly  withdrawn,  the  metal  becomes 


WATER.       SPECIFIC    HEAT.  139 

cooled,  and  at  a  certain  point  the  water  comes  in  contact  with  the  heated 
surface,  and  a  large  portion  of  it  is  suddenly  converted  into  steam.  The 
spheroidal  state  is  common  to  all  liquids.  It  may  be  well  shown  in  water  by 
first  warming  the  liquid  before  pouring  it,  gradually,  on  the  red  hot  metallic 
surface. 

Water  may  be  entirely  decomposed  into  its  constituent  gases  at  a  full 
white  heat.  Mr.  Grove  has  proved  that  if  a  platinum  ball,  heated  to  white- 
ness, is  plunged  into  water  beneath  a  tube  filled  with  water,  the  mere  contact 
of  the  white  hot  metal  liberates  oxygen  and  hydrogen,  which  may  be  col- 
lected and  exploded  in  the  tube.  Heat,  like  electricity,  has  therefore  not 
only  a  composing,  but  a  decomposing  effect,  on  the  elements  of  water. 


CHAPTEK    XI. 

WATER— PHYSIC  AL    AND    CHEMICAL     PRO  PERTIE  S—H  YD  RA- 
TION—MINERAL   WATERS— PEROXIDE   OF    HYDROGEN. 

Relations  to  Heat. — The  relations  of  water  to  heat  are  in  many  respects 
remarkable.  Its  specific  heat,  or  capacity  for  heat,  is  greater  than  that  of 
all  liquids  and  solids.  By  this  term  we  are  to  understand  the  relative  pro- 
portion of  heat  necessary  to  raise  equal  weights  of  different  substances  from 
some  lower  to  some  higher  temperature,  or  more  generally,  the  relative 
quantity  of  heat  contained  in  equal  weights  of  different  substances  at  the 
same  temperature.  This  difference  was  called  by  Dr.  Black  the  capacity  of 
bodies  for  heat.  Equal  quantities  of  the  same  fluid,  at  different  temperatures, 
give  the  arithmetical  mean  on  mixture.  Equal  measures,  for  instance,  of 
water  at  70°,  and  of  water  at  130°,  will  give  the  mean  temperature  of  100°; 
that  is,  the  hot  water  loses  30°,  and  the  cooler  water  gains  30°.  But  if 
equal  measures  of  different  fluids,  as,  for  instance,  water  at  70°,  and  of  mer- 
cury at  130°,  be  mixed,  the  resulting  temperature  will  not  be  the  mean,  or 
100°,  but  only  90°.  Here,  therefore,  the  mercury  loses  40°,  while  the  water 
only  gains  20°,  hence  the  inference  that  the  quantity  of  heat  required  to  raise 
a  given  measure  of  mercury  100°,  will  only  raise  the  same  measure  of  water 
50°  :  that  is  (speaking  here  of  equal  bulks),  the  capacity  of  mercury  for 
heat  is  only  =  half  that  of  water.  But  the  capacities  of  bodies  for  heat  are 
most  conveniently  referred  to  equal  weights  rather  than  measures  ;  and  if  we 
thus  compare  water  with  mercury,  it  will  be  found  that  a  pound  of  water 
absorbs  thirty  times  more  heat  than  the  same  weight  of  mercury ;  viewed, 
therefore,  in  this  way,  the  capacity  of  water  for  heat  is  to  that  of  mercury 
as  30  to  1,  or  as  1000  to  33,  and  we  generally  thus  express  the  capacities  of 
bodies  for  heat  by  a  series  of  numbers,  having  reference  to  water  as  1000, 
such  numbers  representing  their  specific  heats. 

The  most  accurate  determination  of  specific  heat  appears  to  be  derived 
from  the  process  of  cooling,  the  time  required  for  this  purpose  being  directly 
as  the  specific  heats  of  the  bodies,  provided  they  are  carefully  placed  under 
similar  circumstances :  contained,  for  instance,  in  a  polished  silver  vessel,  in 
a  vacuum.  The  following  capacities  were  thus  determined  by  Dulong  and 
Petit :— 


140  SPECIFIC    HEAT    OF    SOLIDS    Ax\D    LIQUIDS. 


Sp.  Heat. 

Sp.  Heat. 

Water  . 

.    1000 

Zinc        ....       93 

Sulphur 

.      188 

Silver     ....       56 

Glass    . 

.     117 

Mercury          ...       33 

Iron 

.     110 

Platinum        ...       31 

Copper 

.       95 

Lead     .           ...       29 

reference 

to  liquids, 

water  stands 

higher  than  all  others  : — 

Sp.  Heat. 

Sp.  Heat 

Water  . 

. 

.   1000 

Oil  of  turpentine     .         .     462 

Alcohol 

.        , 

.     620 

Sulphuric  acid        (1-84)     350 

Ether    . 

, 

.     520 

Nitric  acid    .           (1'36)     630 

Olive  oil 

. 

.     438 

Hydrochloric  acid  (1-15)     600 

Araon^  liquids,  mercury  is  most  easily  heated  and  cooled:  hence  it  is  well 
adapted  for  thermometrieal  uses  ;  while  water  requires  a  lonp;  time  to  be 
brought  to  a  high  temperature,  and,  when  once  heated,  is  a  long  time  in 
cooling.  It  is  by  this  property  that  large  masses  of  water  exert  an  equal- 
izing influence  on  atmospheric  temperature. 

When  solid  passes  into  liquid  water — in  other  words,  when  ice  melts,  a 
large  amount  of  heat  is  absorbed,  or  rendered  latent.  Ice  and  water  there- 
fore contain  different  quantities  of  heat,  although  each  may  be  at  the  same 
temperature,  namely  32°.  This  may  be  proved  by  a  simple  experiment.  If 
equal  weights  of  water  at  32°  and  172°  respectively,  are  mixed,  the  tempe- 
rature of  the  mixture  will  be  the  mean  of  the  two — namely,  102°.  But  if 
ice  at  32°  be  mixed  with  an  equal  weight  of  water  at  172°,  the  temperature 
of  the  mixture,  instead  of  102°,  will  be  only  32°.  Thus,  in  the  substitution 
of  ice  for  ice-cold  water,  there  is  a  loss  of  heat  to  the  amount  of  140°. 
This  expresses  the  latent  heat  of  water  at  32°,  compared  with  that  of  ice  at 
the  same  temperature  ;  and  it  follows,  that  in  reconverting  the  water  into 
ice,  this  amount  of  heat,  which  was  latent  in  the  water  (^.  e.,  not  appreciable 
by  the  thermometer),  must  be  again  set  free.  Hence,  during  a  thaw,  the 
temperature  of  the  air  near  the  surface  of  the  earth,  is  lowered  ;  while,  on 
the  other  hand,  in  the  act  of  freezing,  water  gives  out  a  large  amount  of 
heat,  which  renders  the  temperature  of  the  air  milder. 

The  production  o^  freezing  mixtures  depends  on  these  principles.  Equal 
parts  of  snow  or  finely-powdered  ice  and  common  salt,  will  lower  the  ther- 
mometer from  32°  to  0°.  Both  solids  tend  to  assume  the  liquid  state  ;  the 
brine  which  results  from  their  union,  remains  liquid  nearly  to  zero.  Two 
parts  of  snow  or  ice  and  three  parts  of  powdered  crystals  of  chloride  of  cal- 
cium, produce  a  mixture  which  will  lower  the  thermometer  to  — 50°,  and 
thus  freeze  mercury.  Solid  carbonic  acid  and  ether  are  now  employed  to 
produce  a  maximum  of  cold  {see  Carbonic  Acid).  Whatever  causes  the 
rapid  liquefaction  of  solidified  water,  produces  great  cold.  Thus,  when  ice 
or  snow  is  mixed  in  equal  weights  with  diluted  sulphuric  and  nitric  acids, 
together  or  separately,  cold  is  produced. 

Water  may  be  cooled  below  32°,  without  consolidating  into  ice ;  but  the 
temperature  of  water  in  which  ice  is  melting  is  always  32°,  and  does  not  rise 
above  that  degree  so  long  as  any  ice  remains  unmelted.  This  is  the  degree 
of  cold  which  is  really  represented  as  32°  by  our  thermometers,  and  as  zero 
on  the  scales  of  Reaumur  and  Centigrade.  Again,  when  water  passes  into 
steam  or  aqueous  vapor,  a  still  larger  amount  of  heat  is  absorbed  or  rendered 
latent,  so  that  a  small  quantity  of  water  in  the  form  of  steam  is  sufficient,  by 
condensation,  to  heat  a  large  quantity  of  cold  water.  If  100  gallons  of  water 
at  50°  be  mixed  with  1  gallon  of  water  at  212°,  the  temperature  of  the  whole 
101  gallons  will  be  raised  by  only  1-5°.  But,  if  a  gallon  of  water  be  con- 
densed from  the  state  of  steam  into  a  vessel  containing  100  gallons  of  water, 


LATENT    HI!AT    OF    VAPORS.  141 

the  water  will  in  that  ease  be  raised  11°.  A  gallon  of  water,  therefore, 
condensed  from  steam,  raises  the  temperature  of  100  gallons  of  cold  water 
9.5°  more  than  the  addition  of  a  gallon  of  boiling  water;  consequently,  if 
the  heat  imparted  to  100  gallons  of  water  by  10  pounds  of  steam  could  be 
condensed  in  1  gallon  of  water,  it  would  raise  it  to  950° ;  and  a  gallon  of 
water,  (?onverted  into  steam  of  ordinary  density,  contains  as  much  heat  as 
would  bring  five  and  a  half  gallons  of  ice-cold  water  to  the  boiling  point. 
The  quantity  of  ice,  which  is  melted  by  steam  of  mean  density,  is  seven  and 
a  half  times  the  weight  of  the  steam. 

The  latent  heat  of  steam  and  other  vapors  has  been  examined  by  Dulong, 
and  on  his  researches  the  following  table  is  based  : — 

Water    ....     9550-8  Ether      ....     1740-6 

Alcohol  ....      374-4  Oil  of  turpentine    .         .      138-6 

Hence  the  vapor  of  water  has  a  greater  amount  of  latent  heat,  or  a  greater 
amount  of  heating  power  in  undergoing  condensation,  than  the  vapors  of 
other  liquids. 

It  is  a  well  known  fact  that  the  conversion  of  water  into  vapor  at  any 
temperature  is  attended  with  the  production  of  cold.  The  instrument  in- 
vented by  Dr.  Wollaston,  under  the  name  of  cryopJiorus  (xpvoj,  ice,  ^i^nv,  to 
bear),  is  constructed  on  this  principle  :  it  establishes  the  fact  that  water  may 
be  solidified,  as  a  result  of  the  cold  produced  by  its  own  vapor.  The  instru- 
ment consists  of  a  tube,  having  a  bulb  at  each  extremity,  one  of  which  is 
half  tilled  with  water  ;  the  interior  of  the  tube  is  perfectly  deprived  of  air 
by  boiling  the  water  in  one  of  the  bulbs,  until  a  jet  of  pure  steam  issues 
through  a  small  opening  left  at  the  bottom  of  the  other,  which  is  then  sealed 
by  fusion  in  the  flame  of  a  lamp  ;  the  consequence  is,  that  the  water  in  the 
other  bulb  is  greatly  disposed  to  evaporate  ;  but  this  evaporation  can  only 
proceed  to  a  certain  extent,  because  the  pressure  of  vapor  within  the  tube 
soon  prevents  its  further  progress.  To  get  rid  of  this,  to  keep  up  the  vacuum, 
and  to  occasion  a  constant  demand  upon  the  water  for  the  fresh  formation  of 
vapor,  the  empty  ball  is  y)lunged  into  a  freezing  mixture,  which  continually 
condenses  the  vapor  within,  and  so  accelerates  the  evaporation  of  the  water 
in  the  other  bulb  as  to  cause  it  ultimately  to  freeze. 

These  peculiar  conditions  of  water  in  reference  to  heat  have  a  manifest 
tendency  to  maintain  it  in  a  liquid  condition,  the  state  in  which  it  is  indis- 
pensable for  animal  and  vegetable  existence. 

Water,  which  has  been  exposed  to  the  atmosphere,  always  contains  a  por- 
tion of  air,  a  fact  which  may  be  proved  by  boiling  it,  or  by  exposing  it 
under  the  exhausted  receiver  of  an  air-pump.  To  separate  the  air,  the  water 
must  be  continuously  boiled  in  vacuo,  for  it  is  obstinately  retained.  (Donny, 
Ann.  Ch.  et  Ph.,  Fev.  1846.)  It  absorbs  oxygen  gas  from  atmospheric  air 
in  preference  to  nitrogen,  and,  when  the  air  is  expelled  by  boiling,  the  last 
portions  contain  more  oxygen  than  those  first  given  off.  (Humboldt  and 
Gay-Lussao,  Journal  de  Physique,  1805.)  The  presence  of  air  or  oxygen 
in  water  is  known  by  the  addition  of  protoferrocyanide  of  iron  {see  page  99). 
If  the  white  compound  be  added  to  recently  boiled  water,  the  rapid  absorp- 
tion of  oxygen  will  be  indicated  by  its  acquiring  a  blue  color. 

Dalton  states,  that  100  cubic  inches  of  spring  water  yield  about  two  inches 
of  air,  which,  after  losing  from  5  to  10  per  cent,  of  carbonic  acid  by  the 
£fction  of  lime-water,  consists  of  38  per  cent,  oxygen,  and  62  nitrogen.  {New 
System,  271.)  Dr.  Henry  obtained  4*76  cubic  inches  of  gas  from  100  of  the 
water  of  a  deep  spring,  of  which  338  were  carbonic  acid  gas,  and  1-38  air, 
of  the  same  standard  as  that  of  the  atmosphere.     There  can,  however,  be  no 


142      INFLUENCE    OP    WATER    ON    THE    PROPERTIES    OF    BODIES. 

doubt  that  the  gaseous  conteuts  of  different  springs  vary  both  in  quantity 
and  quality. 

The  following  table,  based  on  the  experiments  of  various  eminent  authori- 
ties, exhibits  the  quantity  of  different  gases  which  water  is  capable  of  absorb- 
ing or  dissolving  at  a  mean  temperature  and  pressure,  the  water  having  been 
previously  deprived  of  air  by  long  boiling.  , 


100  c.  i.  of 

100  c.  i.  of 

■water  dissolve 

water  dissolve 

Fluoboric  acid   . 

.  70000  c.  i. 

Chlorine  .         .         .         . 

200  c.  i. 

Hydrochloric  acid 

.  50000 

Protoxide  of  nitrogen 

100 

Ammonia  . 

.  48000 

Carbonic  acid  . 

,     100 

Fluosilicic  acid . 

.  35000 

Carburetted  hydrogen 

12-5 

HypocMorous  acid     . 

.  20000 

Deutoxide  of  nitrogen 

5 

Sulphurous  acid 

.     5000 

Oxygen    .         .         .         . 

4-6 

Peroxide  of  chlorine  . 

.     2000 

Phosphuretted  hydrogen . 

2-14 

Cyanogen  . 

.       450 

Carbonic  oxide 

ii'6 

Hydroselenic  acid 

.       300 

Nitrogen  .         .         .         . 

2-5 

Sulphuretted  hydrogen       .       300  Hydrogen         .         .         ,         1*56 

The  quantity  of  each  gas  dissolved  by  water  is  materially  dependent  on 
temperature.  While  in  reference  to  solids  which  are  soluble  in  water,  the 
solubility  generally  increases  with  the  temperature,  that  of  gases  decreases, 
so  that  by  heating  the  water  to  the  boiling  point,  the  gas,  unless  it  has  entered 
into  chemical  combination,  is  expelled.  There  is  an  instance  of  this  exQep- 
tional  condition  in  hydrochloric  acid  gas.  When  a  solution  of  this  gas  is 
boiled,  a  portion  of  the  acid  escapes  ;  but  at  a  certain  point  of  saturation, 
the  water  and  gas  are  distilled  over  together. 

Water  is  decomposed  by  many  substances.  Some,  like  chlorine,  take  the 
hydrogen  and  liberate  the  oxygen;  other  substances,  like  potassium,  take 
the  oxygen  and  set  free  hydrogen.  With  the  exceptional  case  of  the  decom- 
position of  this  liquid  by  electrolysis,  oxygen  is  not  set  free  as  a  gas,  but  as 
it  is  liberated,  it  enters  into  new  combinations. 

Water  plays  a  most  important  part  in  the  organic  kingdom.  It  is  not  only 
the  medium  for  conveying  soluble  matters  from  the  earth  and  air  to  the  vege- 
table structure,  but  it  is  essential  to  the  constitution  of  vegetable  and  animal, 
principles.  Thus,  it  forms  from  30  to  80  per  cent,  of  the  animal  tissues  ; 
and  to  its  presence  the  physical  properties  of  these  tissues  are  mainly  due. 
We  have  found  that  muscular  fibre  contains  from  QQ  to  69  per  cent,  of  water, 
and  that  an  oyster  contains  81  per  cent.  Some  of  the  small  jelly-fish  (acale- 
phce)  contain  99  per  cent,  of  this  liquid.  Of  the  fluids  of  the  body,  blood 
contains  18,  milk  86,  and  bile  90  per  cent  of  water.  Its  presence  in  bodies 
is  often  indispensable  to  chemical  action,  and  the  removal  of  it,  either  modi- 
fies or  arrests  chemical  changes.  Albumen  or  gelatin,  when  deprived  of 
water,  may  remain  unchanged  for  years ;  but  when  containing  only  their 
normal  proportion  of  water,  they  rapidly  undergo  decomposition.  Desicca- 
tion, or  the  deprivation  of  an  organic  substance  of  water,  may  be  regarded  as 
one  of  the  most  powerful  antiseptic  processes.  Its  remarkable  influence  on 
chemical  affinity,  and  on  the  chemical  properties  of  compounds,  has  been 
elsewhere  pointed  out  {see  page  42).  In  addition  to  the  illustrations  there 
given,  we  may  here  notice  a  few  others.  It  is  well  known  that  lime  has  a 
strong  tendency  to  combine  with  carbonic  acid ;  but  unless  water  is  present 
as  an  intermediate  agent,  caustic  lime  does  not  easily  combine  with  carbonic 
acid,  to  form  a  carbonate.  It  is  generally  stated  that  caustic  lime  is  procured 
by  heating  the  carbonate  ;  but  the  aflinity  of  lime  for  carbonic  acid,  when 
they  are  once  combined,  is  so  strong,  that  the  gas  cannot  be  expelled  by 
heat — according  to  Faraday,  not  even  by  a  white  heat,  unless  water  is  present. 
Hence,  water  is  not  only  necessary  to  the  combination  of  acid  and  base,  but 


WATER.   HYDRATES.   HYDRATION.  143 

when  they  are  combined,  its  presence  is  necessary  to  bring  about  their  separa- 
tion. The  combination  between  a  gaseous  body  and  a  metal  does  not  readily 
take  place,  unless  water  is  present  {see  page  42).  Thus,  while  humid  chlorine 
readily  combines  with  pure  silver  leaf,  to  form  chloride  of  silver,  the  com- 
bination takes  place  only  slowly  and  with  great  difficulty,  if  the  metal  and 
the  gas^re  first  thoroughly  dried.  Phosphorus,  it  is  well  known,  has  a  strong 
tendency  to  combine  with  the  oxygen  of  air,  and  to  produce  ozone  at  ordi- 
nary temperatures  ;  but  if  the  air  is  perfectly  dry,  no  ozone  is  formed  ;  and 
it  has  been  observed,  that  dry  oxygen  is  not  ozonized  by  this  metalloid. 
These  facts,  among  numerous  others,  show  the  important  part  which  water 
takes  in  promoting  or  modifying  the  chemical  action  between  bodies,  which 
are  known  to  have  strong  affinities  for  each  other. 

Hydrates.  Hydration. — Water  is  a  general  and  useful  solvent.  In  this 
respect  it  is  indispensable  to  the  chemist,  for  by  its  means  he  cannot  only 
separate  substances,  but  reduce  their  particles  to  that  degree  of  tenuity  as  a 
result  of  solution,  that  they  can  be  brought  within  the  sphere  of  each  other's 
attraction.  Although  a  perfectly  neutral  body,  it  is  capable  of  acting  like 
an  acid  or  a  base,  and  entering  into  a  large  variety  of  combinations.  As  the 
water  is  contained  in  these  compounds  in  definite  proportions  by  weight, 
they  are  called  hydrates  to  distinguish  them  frpra  hydrides,  of  which  the  ele- 
ment hydrogen  is  a  constituent.  In  those  cases  in  which  the  hydrated 
compounds  are  crystalline,  the  water  appears  to  be  essential  to  the  crystal- 
line form,  and  it  is  therefore  called  water  of  crystallization.  {See  p.  32.) 
Those  bodies  which  do  not  contain  combined  water,  or  which  have*  been 
deprived  of  it  by  artificial  processes,  are  said  to  be  anhydrous,  and  are  some- 
times, although  improperly  described  as  anhydrides.  They  are  in  fact  anhy- 
drates.  As  instances  of  its  combination  with  gases  may  be  mentioned — 1, 
the  hydrate  of  chlorine,  a  solid  compound,  consisting  of  Cl-f-lOHO,  which 
crystallizes  at  32°,  and  is  reconverted  to  water  and  chlorine  above  this  tem- 
perature ;  2,  the  crystalline  compound  produced  in  the  manufacture  of  sul- 
phuric acid,  (N04  4-2SOa  +  2HO)  resolvable  by  water  or  steam  into  sulphuric 
acid  water  and  deutoxide  of  nitrogen.  Like  an  alkali  orjj^allj^^xide,  water 
combines  with  an  anhydrous  acid  to  form  a  hydrate.  It  thus  unites  to  anhy- 
drous sulphuric,  nitric  or  phosphoric  acid ;  and  in  reference  to  the  last 
mentioned  acid,  it  produces  a  change  in  its  chemical  properties.  In  this 
state,  acting  like  a  base,  it  is  called  basic  water.  When  the  acid  is  once 
combined  with  it,  the  water  cannot  be  again  separated  by  mere  heat ;  the 
acid  and  the  water  are  distilled  over  together.  The  only  method  of  displacing 
water  in  these  combinations  is  to  substitute  another  oxide,  such  as  that  of 
potassium,  and  then  apply  heat.  Under  these  circumstances  the  water  is 
entirely  expelled,  and  it  is  replaced  by  an  atom  of  metallic  oxide.  This 
replacement  sometimes  occurs  as  a  simple  result  of  chemical  affinity.  Thus 
the  three  atoms  of  water  in  the  terhydrate  of  phosphoric  acid,  may  be  replaced 
by  three  atoms  of  oxide  of  silver,  forming  yellow  phosphate  of  silver.  From 
these  facts  it  was  supposed  that  water  was  essential  to  the  acid  reaction  of  a 
compound,  and  that  none  but  hydrated  acids  could  unite  to  bases,  to  form 
salts.  But  certain  acids  which  can  be  made  completely  anhydrous  by  heat, 
such  as  the  boracic,  silicic,  and  stannic,  readily  decompose  the  carbonates, 
nitrates  and  sulphates  at  a  high  temperature,  displacing  their  acids,  and 
forming  new  salts  with  the  bases,  according  to  the  usual  laws  of  affinity. 
Anhydrous  sulphurous  acid  will  also  displace  carbonic  acid  from  dry  (anhy- 
drous) carbonate  of  soda.  (Pelouze  et  Fremy,  op.  cit,  tom.  2,  p.  78.)  The 
dehydration  of  some  compounds  lessens  or  destroys  their  solubility  in  certain 
liquids.  The  silicic  and  antiraonic  acids,  as  well  as  the  oxides  of  aluminum 
and  zinc  in  the  hydrated  ^tate,  are  easily  dissolved  by  alkalies ;  but  when 


144  WATER.       HYDRATED    SALTS.      BASIC    WATER. 

dehydrated  by  heat,  they  become  almost  insohible,  and  can  tlien  only  be 
united  to  an  alkali  by  fusion  at  a  high  temperature.  Water  combines  with 
alkalies  without  altering  or  affecting  their  properties.  The  hydrate  of  potassa 
is  a  compound  of  water  and  oxide  of  potassium,  and  has  powerful  alkaline 
properties.  At  a  high  temperature  the  hydrate  is  volatile  without  any  loss 
of  water.  In  this  compound  as  in  the  acid  hydrates,  the  water  can  only  be 
displaced  by  adding  an  acid,  snch  as  the  sulphuric  or  phosphoric  acid,  and 
heating  the  compound  to  a  high  temperature.  In  some  hydrates  the  water 
may  be  displaced  by  heat  alone,  as  in  the  case  of  silicic  acid,  linae  and  mag- 
nesia. Water  forms  hydrates  with  nearly  all  the  metallic  oxides,  influencing 
their  color  and  solubility  in  acids.  The  hydrated  oxide  of  copper  is  blue,  and 
the  anhydrous  oxide  is  black.  The  hydrated  oxide  of  this  metal  when  pre- 
cipitated by  potassa  from  a  solution  of  sulphate  of  copper  (and  the  alkali  is 
added  in  some  excess)  is  rendered  anhydrous,  merely  by  boiling  the  liquid. 
The  oxide  falls  down  as  a  blackish-brown  powder.  The  hydrated  suboxide 
of  copper  is  yellow,  and  is  produced  on  warming  a  mixture  of  sulphate  of 
copper,  sugar,  and  potassa.  If,  however,  the  liquid  is  boiled,  the  suboxide 
is  rendered  anhydrous,  and  falls  down  as  an  insoluble  red  powder.  Up  to  a 
temperature  of  Qb^  a  saturated  solution  of  sulphate  of  soda  deposits  on  cool- 
ing hydrated  crystals  of  this  salt.  But  if  heated  to  the  boiling  point  the  salt 
becomes  less  soluble  by  reason  of  the  formation  of  the  anhydrous  sulphate, 
the  salt  being  dehydrated  by  elevation  of  temperature.  In  other  cases  a  heat 
of  212°  appears  to  be  necessary  to  the  production  of  a  hydrate.  Precipitate 
a  solution  of  alum  by  potassa,  and  add  enough  potash  to  redissolve  the  pre- 
cipitated alumina  ;  to  this  alkaline  liquid  add  a  solution  of  silicate  of  potassa. 
There  is  no  apparent  change  until  the  mixture  is  heated,  when  the  whole  of 
it  sets  into  a  nearly  solid  hydrated  silicate  of  alumina. 

Water  combines  with  the  greater  number  of  metallic  salts  in  proportions 
variable  for  each  salt,  and  these  are  not  dependent  on  any  general  law. 
Occasionally  the  same  salt  is  observed  to  combine  with  diff'erent  proportions 
of  water,  according  to  the  temperature  of  the  solution.  (See  p.  32.)  The 
color  of  the  salt  and  its  crystalline  form  are  chiefly  affected,  but  its  chemical 
properties  do  not  appear  to  be  changed.  The  blue  crystals  of  sulphate  of 
copper,  and  the  green  crystals  of  sulphate  of  iron  became  of  a  dingy  white, 
when  digested  in  concentrated  sulphuric  acid.  This  is  simply  the  result  of 
dehydration.  The  color  is  restored  in  each  case  by  the  addition  of  water. 
In  some  salts  the  water  is  combined  only  as  water  of  crystallization,  e.  g.,  the 
sulphates  of  iron  and  copper;  in  other  salts,  besides  this  crystalline  water, 
another  portion  exists  in  a  basic  form,  /.  e.,  intimately  combined  with  the 
acid.  This  is  seen  in  the  rhombic  phosphate  of  soda,  which  contains  two 
atoms  of  soda,  and  one  of  water  as  a  base,  while  there  are  in  addition,  24 
atoms  of  combined  or  crystalline  water.  The  whole  of  this  water  can  be 
expelled  by  heat,  but  the  basic  water  with  more  difficulty  than  the  water  of 
crystallization.  The  loss  of  the  basic  water  completely  changes  the  chemical 
properties  of  this  salt  :  it  converts  it  into  pyrophosphate  of  soda,  which  pro- 
duces a  white,  in  place  of  a  yellow  precipitate,  with  nitrate  of  silver.  It  also 
gives  with  a  solution  of  acetate  of  lead,  a  white  precipitate,  which  is  soluble 
in  an  excess  of  the  pyrophosphate,  while  the  phosphate  of  lead  is  insoluble 
in  the  common  phosphate  of  soda. 

It  has  been  suggested  that  some  double  salts,  such  as  the  bisulphate  of 
potassa,  may  really  be  compounds  of  neutral  sulphates  with  water.  Thus  the 
bisulphate  which  is  commonly  represented  as  KO,2S03,HO  may  beK0,S03 
-fH0,S03.  This,  however,  would  be  inconsistent  with  the  constitution  of 
certain  analogous  compounds  not  containing  water,  such  as  bichromate  of 
potassa,  KO,2Cr03.    Chromic  acid  is  isomorphwus  with  the  sulphuric  ;  and 


COMBINED    WATER.  145 

if  the  latter  can  combine  in  two  equivalents  to  form  a  bichromate,  it  is 
reasonable  to  infer  that  the  former  can  equally  combine  with  two  equivalents 
of  acid  to  form  a  bisulphate  of  the  alkali,  and  not  a  sulphate  of  potassa  and 
basic  water. 

The  phenomena  of  hydration,  as  they  are  witnessed  in  the  combination  of 
water  with  acids,  oxides  and  salts,  are  clearly  due  to  chemical  afSnity.  When 
water  is  poured  on  solid  sulphuric  or  phosphoric  acid,  great  heat  is  evolved, 
and  steam  escapes  almost  with  explosive  violence.  If  a  small  quantity  of 
water  is  poured  on  a  few  pieces  of  dry  hydrate  of  potassa  in  a  glass  tube, 
the  alkali  is  dissolved,  but  so  much  heat  is  extricated  that  a  small  portion  of 
phosphorus  applied  to  the  outside  of  the  vessel  will  melt  and  take  fire.  In 
this  experiment,  a  second  hydrate  of  the  alkaline  oxide  is  produced  by  an 
additional  quantity  of  water  entering  into  combination.  When  one  part  of 
water  at  32^  is  added  to  three  parts  of  fresh  burnt  lime  at  the  same  tempe- 
rature, the  water  disappears,  steam  is  after  a  time  copiously  evolved,  the 
lime  becomes  hot,  falls  to  a  white  powder,  and  is  greatly  increased  in  weight. 
The  heat  given  out  in  the  hydration  of  lime  has  been  estimated  at  more 
than  570° — sufiBciently  high  to  inflame  gunpowder.  Felletier  observed  that 
in  slaking  large  quantities  of  lime  in  the  dark,  light  was  evolved  as  well  as 
heat.  The  water  forms  a  solid  compound  with  the  lime  (slaked  lime).  In 
these  experiments  it  is  considered  that  the  late?it  heat  of  water  (see  page  140) 
is  set  free.  This  can  only  be  attributed  to  a  direct  chemical  union  of  water 
in  a  solid  form  with  the  substance.  Concentrated  sulphuric  acid  (already 
a  liquid  hydrate)  presents  some  remarkable  and  apparently  paradoxical 
results  in  uniting  to  an  additional  proportion  of  water.  If  one  part  of 
ice  is  mixed  with  four  parts  of  concentrated  sulphuric  acid,  the  ice  melts — 
great  heat  is  evolved  as  a  result  of  a  second  hydrate  being  formed,  and 
the  latent  heat  of  the  water  being  set  free.  But  if  one  part  of  sulphuric 
acid  is  rapidly  mixed  with  four  parts  of  ice,  in  the  same  or  in  another 
vessel,  so  intense  a  degree  of  cold  is  produced,  that  water  is  frozen  in  a 
lube  which  is  placed  in  the  mixture.  This  result  is  in  accordance  with 
what  has  been  already  stated,  respecting  the  large  amount  of  heat  absorbed 
or  rendered  latent  in  the  liquefaction  of  ice  (p.  140).  A  hydrate  is  equally 
formed  in  the  latter  case :  but  as  the  ice  greatly  preponderates,  and 
requires  much  heat  for  its  liquefaction,  it  not  only  absorbs  that  which  is 
produced  as  a  result  of  hydration,  but  much  more  from  all  surrounding, 
bodies. 

With  some  acids  and  alkalies  water  appears  to  form  no  hydrates.  Thus 
the  nitrous  (NOJ,  the  fulminic,  hydrocyanic,  and  manganic  acids  form  no- 
definite  compounds  with  water,  although  they  combine  with  certain  bases  to- 
produce  salts.  On  the  other  hand,  the  presence  of  an  atom  of  water  is  es- 
sential to  the  constitution  of  oxalic  acid  (C3O3).  When  deprived  of  it,  the  , 
acid  is  converted  into  carbonic  acid  (COJ  and  carbonic  oxide  (CO.)  This 
atom  of  water  admits  only  of  displacement  without  the  decomposition  of  the 
acid,  by  the  substitution  of  an  atom  of  a  metallic  oxide.  Carbonic  acid  as 
a  gas  does  not  combine  with  water  to  form  a  definite  hydrate ;  and  in  the 
liquefied  state,  carbonic  acid  is  quite  insoluble  in  water.  Liquid  carbonic 
acid  has  no  action  upon  litmus,  but  when  the  gas  is  dissolved  in  water,  it 
changes  it  from  blue  to  red,  like  other  acids.  That  it  forms  no  acid  hydrate 
may  be  inferred  from  the  fact,  that  the  blue  color  of  the  litmus  is  restored 
by  boiling  the  reddened  liquid.  Carbonic  acid,  therefore,  is  in  the  condition 
of  a  gas  temporarily  dissolved  by  water.  Solution  in  water  appears  to  be 
necessary  for  the  manifestation  of  acid  properties  on  vegetable  colors  ;  but 
for  reasons  elsewhere  assigned,  it  is  not  necessary  to  suppose  that  the  water 
undergoes  decomposition,  and  that  a  new  binary  compound  of  hydrogen  and 
10 


146  OSMOSIS    AND    DIALYSIS.      TESTS. 

a  hypothetical  radical  is  prodnced  (p.  94.)  Pyrogallic  acid,  as  a  solid,  has 
DO  action  on  litmus ;  ^hen  dissolved  in  water  it  reddens  litmus  paper,  but 
when  dissolved  in  absolute  ether,  and  not  exposed  to  air,  it  has  no  reddening 
action  on  litmus.  In  this  respect,  it  resembles  liquid  carbonic  acid  dissolved 
in  pure  ether.  Among  bases,  ammonia  is  remarkable  for  forming  no  hydrate 
with  water.  Every  particle  of  water  may  be  removed,  without  altering  the 
properties  of  gaseous  ammonia,  by  simply  desiccating  it  with  lime.  It  has 
been  supposed,  that  a  binary  compound  of  oxygen  and  ammonium  (NHJ  is 
formed  under  these  circumstances ;  but  of  this  there  is  a  total  absence  of 
proof.  (See  Ammonium.)  Such  a  view  assumes,  contrary  to  all  experiments 
regarding  the  relative  affinity  of  bodies,  that  hydrogen  leaves  oxygen  to 
combine  with  the  elements  of  ammonia,  when  it  is  utterly  impossible  to 
cause  these  bodies  to  unite  ;  and  when  placed  in  a  favorable  state  for  union, 
they  are  rapidly  evolved  as  hydrogen  and  ammonia. 

The  phenomena  of  osmosis  have  been  referred  by  Graham  to  the  hydra- 
tion and  dehydration  of  the  membrane  forming  the  septum,  or  partition, 
between  two  liquids.  We  have  elsewhere  referred  to  the  passage  of  liquids 
through  animal  membrane.  The  membrane  becomes  hydrated  on  the  sur- 
face which  is  in  contact  with  the  water,  but  on  the  side  of  the  saline  or 
viscid  liquid,  it  is  not  hydrated.  On  the  contrary,  hydration  here  receives 
a  check,  and  some  of  the  water  imbibed  by  the  membrane  is  actually  trans- 
ferred to  the  saline  liquid,  so  that  there  is  a  continual  current  inwards  or 
outwards,  according  to  the  relative  position  of  the  two  liquids.  {Phil.  Trans. ^ 
June,  1861.)  It  is  a  remarkable  fact,  that  while  certain  bodies  will  easily 
traverse  the  membranous  partition,  others  will  not.  Substances  of  a  viscid, 
adhesive,  or  gelatinous  character,  whether  organic  or  inorganic  {colloid 
bodies),  of  which  animal  membrane  itself  may  be  considered  one,  retain  cer- 
tain ingredients,  and  allow  others  to  pass.  It  was  found  by  Graham  in  using 
parchment-paper,  that  on  placing  urine  in  a  vessel  provided  with  such  a 
septum,  the  urea  and  salts  passed  out,  but  the  animal  principles  were 
retained.  Organic  liquids  containing  small  quantities  of  arsenic,  tartar 
emetic,  and  even  strychnia,  were  found  to  yield  the  respective  poisons  to 
water,  while  the  organic  substances  associated  with  them  did  not  pass.  We 
have  verified  this  statement  by  employing  a  weak  solution  of  arsenic  in  milk; 
these  experiments  show  that  pure  water  iu  hydrating  substances,  may  be 
tern  ployed  as  a  separating  agent. 

7'estsfor  Water. — When  water  is  in  a  state  of  chemical  union,  its  presence 
is  not  indicated  by  any  of  the  usual  physical  properties  of  the  liquid.  Pow- 
dered alum  contains  half  of  its  weight  of  water,  but  presents  no  sign  of 
moisture.  In  these  cases  we  must  resort  to  a  high  temperature,  and  to 
complex  .chemical  processes,  in  order  to  determine  its  presence  and  propor- 
.tion  {see  page  32).  When  water  exists  uncombined  in  bodies,  it  is  called 
hyyrometric  water,  and  it  can  be  easily  detected  by  gently  heating  the  solid 
in  a  test  tube.  The  water  is  expelled,  and  is  condensed  in  globules  on  the 
cold  part  of  the  tube.  It  may  be  entirely  driven  off  by  exposing  the 
substance  to  a  dry  current  of  air.  For  this  purpose  the  material  is  inclosed 
in  a  glass  cylinder,  immersed  in  a  water-bath  at  or  below  the  boiling  point. 
The  desiccating  apparatus  commonly  used  is  connected  at  one  end  of  the 
cylinder  with  a  tube  containing  broken  chloride  of  calcium,  while  the  other 
end  of  the  cylinder  is  placed  in  connection  with  an  aspirator.  When  the 
stopcock  of  this  aspirator  is  opened,  air  may  be  made  to  traverse  the  whole 
of  the  apparatus,  first  passing  through  the  chloride  of  calcium  tube,  in  which 
it  is  dried.  It  is  thus  drawn  over  the  substance  in  a  dry  state,  at  the 
temperature  of  the  hot  water  in  which  it  is  immersed.  When  perfectly 
desiccated,  it  ceases  to  lose  weight.     If  the  quantity  of  water  is  to  be  deter- 


MINERAL    WATERS.      SEA    WATER.  l4t 

mined,  a  TJ  tube  containing  chloride  of  calcium,  accurately  balanced,  should 
be  attached  to  the  other  end  of  the  desiccating  tube,  before  connecting  it 
with  the  aspirator.  The  increase  of  weight  in  this  tube,  when'  the  experi- 
ment is  completed,  indicates  the  weight  of  hygrometric  water  contained  in 
the  substance.  The  chloride  of  calcium  absorbs  and  fixes  the  water  as  it 
passes  over.  In  some  porous  powders  the  proportion  of  hygrometric  water 
is  very  large,  amounting  to  12  or  13  per  cent.  Another  method  of  deter- 
mining the  amount  of  free  water  in  liquids  or  solids,  consists  in  placing  them 
in  a  shallow  vessel  in  vacuo,  over  another  vessel  containing  strong  sulphuric 
acid.  When  the  receiver  is  exhausted  there  is  rapid  evaporation  in  the 
cold,  as  the  aqueous  vapor  is  absorbed  and  retained  by  the  sulphuric  acid. 
The  amount  of  water  in  albumen,  or  white  of  egg,  is  thus  determined,  and 
is  found  to  be  about  80  per  cent. 

The  tenacity  with  which  hygrometric  water  fixes  itself  to  solids  is  remark- 
able. All  fine  powders,  such  as  spongy  platinum,  charcoal,  or  fine  metallic 
wire,  or  gauze,  filagree  silver,  and  articles  of  a  porous  description  are,  gene- 
rally speaking,  strongly  hygrometric,  and  require  a  continued  application  of 
heat  to  drive  off  the  water  which  adheres  to  them. 

Of  the  tests  for  liquid  water,  nothing  need  be  said.  It  resembles  no  other 
liquid,  and  the  means  of  determining  its  purity  have  been  already  described 
(page  135).  The  detection  of  water  in  certain  liquids,  "must  depend  on  the 
nature  of  the  liquid.  In  alcohol,  water  may  be  detected  either  by  its  specific 
gravity,  or  by  adding  to  it,  a  small  quantity  of  white  anhydrous  sulphate  of 
copper.  If  water  is  present,  the  white  powder  is  slowly  rendered  blue. 
Fluosilicic  acid  gas  passed  into  the  liquid,  also  reveals  the  presence  of  water, 
by  the  separation  and  deposit  of  white  gelatinous  silica.  The  existence  of 
water  in  gases,  is  determined  by  passing  the  gas  through  a  vessel  containing 
chloride  of  calcium,  or  if  acid,  through  strong  sulphuric  acid.  Any  increase 
of  weight  in  the  chloride,  or  acid,  is  owing  to  water. 

MINERAL   WATERS.       SEA-WATER. 

When  the  saline  and  gaseous  ingredients  of  water  are  in  such  proportion 
as  to  give  to  the  liquid  taste,  smell,  or  medicinal  properties,  it  is  called  a 
mineral  water. 

Sea-water  is  a  strongly  mineralized  water ;  it  may  be  regarded  as  the  accu- 
mulation of  all  the  surface-drainage  of  the  earth.  It  contains,  on  an  average, 
from  3  to  4  per  cent,  of  saline  matter,  and  this  amount  does  not  seem  to  vary 
to  any  great  extent,  either  with  the  latitude,  or  with  the  depth  from  which 
the  water  is  taken.  Water  collected  from  the  surface  of  the  Gulf  of  Guinea, 
contained  3-5  per  cent.,  and  in  the  same  gulf,  when  taken  from  the  depth  of 
4000  feet,  it  is  stated  to  have  yielded  4-5  per  cent,  of  saline  residue,  showing 
an  increase  of  only  1  per  cent,  at  this  depth.  Sea-water  taken  in  N.  L. 
80^^,  sixty  fathoms  under  ice,  gave  354  per  cent,  and  in  S.  L.  20°,  3-9  per 
cent. 

While  carbonate  of  lime  is  the  principal  ingredient  in  river  waters,  it  exists 
sparingly  in  the  sea.  The  chief  saline  constituent  of  sea-water  is  common 
salt,  or  the  chloride  of  sodium :  this  forms  from  one-half  to  three-fourths  of 
the  solid  ingredients.  The  principal  salts  associated  with  it,  are  chloride 
and  bromide  of  magnesium,  with  sulphate  of  magnesia,  which  give  the 
nauseous  bitterness  and  purgative  qualities  to  the  water.  Chloride  of  potas- 
sium and  sulphate  of  lime  are  also  found :  and  as  a  result  of  prismatic 
analysis,  Bunsen  has  announced  the  presence  of  lithium  and  strontium, 
probably  existing  as  chlorides.  He  detected  lithium  in  less  than  two  ounces 
of  the  waters  of  the  Atlantic,  collected  off  the  Azores.  Iron,  lead,  copper, 
and  silver,  have  also  been  found  in  sea-water.     Silver  was  detected  by  M. 


148  SALINE    CONTENTS    OF    SEA    WATER. 

Malaguti  in  water  taken  off  the  coast  of  St.  Malo,  in  the  proportion  of  1 
part  in  100,000,000  (Quart.  Jour.  Chem.  Soc,  1851,  vol.  3,  p.  69),  and 
Mr.  Field  has  lately  announced  its  presence  in  the  waters  of  the  Pacific 
{Proc.  R.  S.,  vol.  8,  p.  292). 

The  proportion  of  saline  matter  in  the  waters  of  some  inland  seas  is  very 
large.  Thus  we  have  found  the  waters  of  the  Dead  Sea  in  Palestine  to  con- 
tain 24  per  cent,  of  saline  matter,  of  which  three-fourths  were  chloride  of 
sodium.  This  is  six  times  as  great  as  the  quantity  contained  in  the  waters 
of  the  Mediterranean  Sea,  in  the  same  parallel  of  latitude.  The  water  of 
the  river  Jordan,  which  flows  into  this  inland  sea,  we  found  to  contain  no 
more  than  two  grains  of  salt  to  the  Imperial  gallon,  and  only  a  trace  of  sul- 
phate of  lime,  while  the  common  salt  in  the  Dead  Sea  water,  amounted  to 
12,600  grains  in  the  Imperial  gallon.  This  water  had  a  specific  gravity  of 
1-16,  and  left  a  considerable  incrustation  of  deliquescent  saline  matter  on 
spontaneous  evaporation.  Every  part  of  the  human  body,  excepting  bone, 
readily  floated  on  it.  The  water  of  the  great  Salt  Lake  in  the  Rocky 
Mountains,  U.  S.,  is  similar  to  that  of  the  Dead  Sea.  It  has  been  found  to 
contain  22  per  cent,  of  saline  matter,  of  which  20  per  cent,  consists  of  chlo- 
ride of  sodium. 

The  tidal  impregnation  of  river-water  with  sea-water  may  therefore  be 
easily  determined,  by  the  discovery  in  it  of  a  large  proportion  of  the  chlorides 
of  sodium  and  magnesium.  Springs  are  said  to  be  hracJcish  when  they 
acquire  a  taste  from  the  presence  of  these  chlorides.  Such  springs  are  met 
with  in  countries  in  which  there  are  vast  sandy  deserts,  also  in  shallow  wells 
on  the  sea  coast. 

The  mean  specific  gravity  of  the  waters  of  the  Atlantic  was  found  to  be 
r027  ;  of  the  Mediterranean,  between  Gibraltar  and  Malta,  r028,  and  be- 
tween Malta  and  Alexandria,  1-029.  The  waters  of  the  Red  Sea,  at  the 
northern  end  of  the  Gulf  of  Suez,  had  a  specific  gravity  of  1"039  {Proc.  R. 
S.,  Feb.  1855).  Admiral  King  found  the  waters  of  the  Pacific  Ocean  to 
have  a  specific  gravity  of  1*026.  The  influence  of  river-water  on  the  specific 
gravity  and  composition  of  sea-water,  is  very  remarkable.  At  the  estuaries 
of  all  great  rivers,  the  percentage  of  salt  is  considerably  reduced,  and  in 
approaching  the  coasts  of  continents,  or  even  of  small  islands,  there  is  a  great 
diminution  in  the  saltness  of  the  sea.  The  following  summary  contains  the 
proportions  of  saline  matter  and  common  salt  found,  by  analysis,  in  1000 
parts  of  the  waters  of  various  seas  :  in  the  North  Sea  (Heligoland),  of  saline 
matter  30-46  (common  salt  23-58)  ;  British  Channel  (Schweitzer),  saline 
matter  35-25  (common  salt  28  05)  ;  Atlantic,  saline  matter  36-3  (common 
salt  25-18)  ;  the  Mediterranean  (XJsiglio),  saline  matter  4373  (common  salt 
29-42)  ;  the  Black  Sea,  saline  matter  17*66  (common  salt  1401)  ;  the  Sea  of 
Azoff,  saline  matter  11-87  (common  salt  9  65)  ;  the  Caspian  Sea,  saline 
matter  6-29  (common  salt  3  67). — (Gobel.)  The  water  of  the  Mediterranean 
Sea  contains  more  lime  than  that  of  the  Atlantic,  and  the  proportion  of  mag- 
nesian  salts  in  the  Mediterranean  water  diminishes  in  proceeding  from  west 
to  east  (Fremy,  Op.  cit,  torn.  1,  p.  253).  The  waters  of  the  Baltic  Sea  con- 
tain but  a  small  proportion  of  saline  matter  ;  and  the  water  of  the  Gulf  of 
Finland  is  so  free  from  it,  that  it  can  be  used  in  place  of  river-water.  The 
waters  of  the  great  lakes  in  the  plains  of  Tartary,  contain  large  quantities  of 
carbonate  of  soda  and  sulphate  of  soda,  with  common  salt;  while  those  of 
Thibet  contain  common  salt,'  with  borate  of  soda. 

Mineral  Waters  owe  their  qualities  not  merely  to  the  quantity  of  the 
ingredients,  but  to  their  nature  and  their  intermixture  under  conditions 
which  it  is  difiScult  to  imitate  by  artificial  processes.  The  Tunbridge  chaly- 
beate spring  contains  only  seven  grains  of  mineral  matter  to  the  Imperial 


MINERAL   WATERS.  149 

gallon ;  it  owes  its  properties  to  the  presence  of  iron,  the  proportion  of 
which  is  not  more  than  two  grains  in  the  gallon.  On  the  other  hand,  one 
of  the  Yichy  springs  contains  460  grains  of  saline  matter  in  the  gallon,  of 
which  333  grains  consist  of  bicarbonate  of  soda.  There  are,  according  to 
O.  Henry,  soluble  silicates  of  soda  and  alumina  in  this  water,  amounting  to 
forty-four  grains  in  the  gallon.  In  several  of  the  German  waters,  Bunsen 
has  detected  lithium,  strontium,  and  caesium,  in  addition  to  other  well-known 
ingredients.  Mineral  waters  may  vary  in  their  solid  contents,  as  much  as 
from  7  to  500  grains  in  the  gallon.  They  are  hot  or  cold,  the  former  being 
called  thermal.  The  hot  springs  in  Great  Britain  are  few.  They  are — the 
waters  of  Bath,  117°;  of  Buxton,  84°;  of  Matlock,  60° ;  and  in  Ireland 
the  waters  of  Mallow,  which  have  a  temperature  of  72°.  On  the  Conti- 
nent, some  of  these  waters  reach  a  temperature  little  short  of  the  boiling 
point.  One  of  the  most  remarkable  waters  for  its  temperature  and  com- 
position is  that  of  the  Great  Geyser,  in  Iceland.  Examined  in  1846  by 
Bunsen,  at  a  depth  of  sixty-three  feet,  this  water  was  found  to  have  a  tem- 
perature of  260°.  A  sample  of  this  water,  collected  on  the  16th  June, 
1856,  was  observed,  at  the  time  of  collection,  to  have  a  temperature. of  190°, 
the  air  being  47°.  We  fdund  this  water  to  contain  106*6  grains  of  saline 
matter  in  the  gallon.  Of  this  19*53  grains  consisted  of  carbonate  of  soda, 
24'42  of  chloride  of  sodium,  14'65  of  sulphate  of  soda,  m^  48  grains  of  silica 
and  insoluble  matter.  There  is  no  doubt  that  in  this,  as  in  the  Vichy  and 
other  waters,  the  silicic  acid  is  held  dissolved  by  the  alkaline  carbonate. 

Various  classifications  of  mineral  waters  have  been  made.  We  here  give 
four  of  the  principal  varieties,  with  their  special  characters  : — 

1.  Carbonated. — These  abound  in  carbonic  acid  associated  with  variable 
quantities  of  the  alkalies,  soda,  potassa,  or  lime,  or  with  traces  of  oxide  of 
iron.  The  waters  of  Seltzer,  Pyrmont,  and  of  Ilkeston,  near  Nottingham, 
are  of  this  kind.  They  are  sparkling,  and  are  characterized  by  an  acidulous 
taste  and  reaction.  1.  They  redden  an  infusion  of  litmus,  but  the  blue 
color  is  restored  on  boiling.  2.  They  give  a  white  precipitate  with  lime- 
water  (carbonate  of  lime),  but  the  precipitate  is  redissolved  by  an  excess  of 
the  water.  3.  When  a  portion  is  boiled  in  a  retort,  and  the  gaseous  con- 
tents are  passed  into  lime-water,  carbonate  of  lime  is  abundantly  deposited. 
These  waters  may  be  alkaline  from  soda  (Vichy),  or  calcareous  from  lime 
(Bath,  Bristol,  Buxton). 

2.  Saline. — These  are  very  numerous.  They  contain  the  salts  of  soda, 
potassa,  and  magnesia.  Chloride  of  sodium  is  generally  a  predominating 
ingredient,  as  in  some  of  the  Cheltenham  waters.  This  chloride  is  generally 
associated  with  traces  of  bromide  and  iodide  of  sodium.  They  are  charac- 
terized by  their  taste,  and  the  large  quantity  of  saline  matter  left  on  evapo- 
ration. 

3.  Sulphureous. — These  are  known  by  their  having  the  offensive  odor  of 
sulphuretted  hydrogen  gas,  and  by  their  tarnishing  or  discoloring  a  piece  of 
silver-leaf,  or  of  glazed  card,  immersed  in  them,  or  by  their  giving  a  brown 
precipitate  (sulphide  of  lead),  with  any  soluble  salt  of  lead.  (Kilburn, 
Harrowgate,  Aix-la-Chapelle,  Bareges.)  The  sulphuretted  hydrogen  appears 
to  be  derived  from  decomposing  iron-pyrites,  diffused  in  the  strata  through 
which  the  water  flows.  The  waters,  when  fresh,  have  an  acid  reaction  on 
litmus,  but  this  disappears  on  boiling.  After  a  time  they  deposit  a  black 
sediment  (sulphide  of  iron),  and  lose  their  offensive  smell.  We  have 
examined  a  water  of  this  description  from  Vancouver's  Island,  in  British 
Columbia.  These  waters  discharge  the  colors  of  the  permanganate  of 
potash. 

4.  Chalybeate  (;ta^i';3oj,  iron.)— Chalybeate  waters  derive  their  name  from 


150  CHALYBEATE    WATERS. 

the  iron  which  they  hold  dissolved.  There  is  scarcely  a  natural  water  in 
which  traces  of  iron  may  not  be  found,  but  the  quantity  is  so  minute  as  not 
to  affect  the  taste  of  the  water,  although  so  small  a  portion  of  oxide  of  iron 
as  l-35000th  part  of  the  weight  of  the  water,  is  sufficient  to  give  the  strong 
chalybeate  taste  possessed  by  the  Tunbridge  spring.  There  are  two  kinds 
of  chalybeate  water — the  carbonated  and  the  sulphated.  The  Tunbridge 
and  Bath  waters  belong  to  the  carbonated  kind  ;  they  contain  but  a  small 
quantity  of  saline  matter  (the  Tunbridge  Chalybeate  less  than  eight  grains 
in  the  gallon),  and  they  owe  their  chief  property  to  protoxide  of  iron,  held 
dissolved  by  carbonic  acid.  Hence,  although  clear  when  freshly  drawn, 
they  become  turbid  on  exposure  by  the  escape  of  carbonic  acid,  and  they 
de'posit  a  brown  ochreous  sediment  of  hydrated  peroxide  of  iron.  The 
sulphated  chalybeates  contain  a  large  quantity  of  sulphate  of  iron  in  solu- 
tion, derived  from  the  oxidation  of  iron  pyrites  in  the  strata  from  which 
they  issue.  We  have  examined  one  such  spring  from  Horncastle,  in  Lin- 
colnshire, and  found  it  to  contain,  in  the  Imperial  gallon,  263  grains  of  solid 
matter,  of  which  169  grains  consisted  of  the  sulphates  of  iron  and  alumina. 
Chalybeate  waters  abound  in  the  Rhine  district,  and  they  are  also  very 
numerous  in  France.  In  some  of  the  waters  of  Aix-la-Chapelle,  the  iron  is 
combined  with  the  crenic  and  apocrenic  acids.  One  curious  fact  connected 
with  them  is,  that  t)||p  generally  contain  traces  of  arsenic.  This  ingredient 
may  be  found  in  the  mineral  water  itself,  but  more  commonly  in  the  ochreous 
sediment.  In  France,  no  fewer  than  forty-six  waters,  including  the  six 
springs  of  Vichy  and  the  waters  of  Mont  d'Or  and  Plombieres,  are  impreg- 
nated with  arsenic.  The  Vichy  water  is  said  to  contain  the  1 25th  part  of 
a  grain  of  arsenic  in  a  gallon. 

The  tonic  and  other  medicinal  properties  of  these  waters  are  now  con- 
sidered to  be  due,  at  least  in  part,  to  the  arsenic  which  they  contain.  The 
Wiesbaden  water,  according  to  Dr.  Hofmann,  contains  one  grain  of  arsenic 
in  166  gallons  {Chem.  News,  Aug.  11,  1860).  The  waters  of  Spa  and  Kis- 
sengeu  are  also  arsenical.  The  arsenic  is  probably  in  the  state  of  arsenite 
and  arseniate  of  iron,  and  is  held  dissolved  in  minute  proportions  by  the 
carbonic  acid  of  the  water.  It  is  precipitated  in  the  sediment  with  oxide  of 
iron.  The  arsenic  has  been  probably  derived  from  decomposed  iron-pyrites 
in  the  strata,  and  to  this  cause  may  be  ascribed  the  presence  of  arsenic  in 
some  of  the  river  waters  of  this  country.  Mr.  Church  states  that  he  found 
arsenic  in  the  water  of  the  Whitbeck,  in  Cumberland  {Ghem.  News,  Aug.  25, 
1860).  We  have  detected  it  in  the  water  of  the  Mersey,  supplied  to  a  large 
town,  in  the  proportion  of  one  grain  of  arsenic  in  250  gallons,  and  Dr. 
Miller  discovered  arsenic  in  a  potable  water  from  Suffolk.  Mr.  D.  Camp- 
bell and  ourselves  discovered  this  mineral  in  the  sediment  of  some  small 
streams  of  Derbyshire,  and  there  is  but  little  doubt  that  if  waters  traversing 
mineral  districts  were  examined  by  chemists  with  a  view  to  its  detection, 
arsenic  would  frequently  be  found,  either  in  the  water  or  in  the  sediment. 
We  have  detected  arsenic  in  two  ounces  of  dry  Thames  mud.  Its  alleged 
presence  in  the  deposits  of  boilers  may  receive  an  explanation  from  these 
facts.  It  is  not  found  in  all  chalybeate  waters.  We  have  made  two  analyses 
of  50  and  100  grains  respectively  of  the  ochreous  deposit  of  the  Tunbridge 
water  without  detecting  any  trace  of  arsenic,  so  that  carbonated  chalybeate 
waters  do  not  necessarily  contain  this  mineral. 

A  carbonated  chalybeate-water  is  known,  1,  by  its  inky  taste  ;  2,  by  its 
giving,  when  boiled,  a  grayish-green  deposit,  which  becomes  ochreous  on 
standing ;  3,  by  its  acquiring  a  pink  or  purple  tint  when  tincture  of  galls  is 
added  to  it;  4,  by  boiling  it  with  a  hw  drops  of  diluted  sulphuric  acid,  and 
adding  to  it  a  solution  of  ferrocyanide  of  potassium,  when  Prussian  blue  is 


'    PEROXIDE    OP    HYDROGEN.      ITS    PROPERTIES.  ^151 

precipitated;  5,  paper  soaked  in  an  infusion  of  rose  petals,  when  dipped  in 
this  water,  acquires  a  dark  color  (tannate  of  iron).  6.  It  discharges  the 
pink  color  of  a  solution  of  the  permanganate  of  potash,  and  by  means  of 
this  test  the  amount  of  protosalt  of  iron  contained  in  the  water  may  be 
voluraetrically  determined.  A  sulphated  chalybeate  water  does  not  dis- 
charge the  color  of  permanganate  of  potash. 

A  s?/lphurated  chidyheate  water  gives  a  dense  blue  precipitate  with  ferro- 
cyanide  of  potassium  (Prussian  bhie).  It  is  precipitated  by  chloride  of 
barium,  the  precipitate  (sulphate  of  baryta)  being  insoluble  in  nitric  acid. 
It  does  not  discharge  the  pink  color  of  the  permanganate  of  potash. 

Peroxide  op  Hydrogen  (HO^). — This  compound  was  discovered  by  The- 
nard,  in  1818.  It  was  at  one  time  considered  to  be  water,  holding  an 
additional  equivalent  of  oxygen,  and  was  thence  called  oxygenated  water',  or 
oxy-water.  It  is,  however,  a  definite  compound  of  oxygen  and  hydrogen, 
although  resolvable  into  water  and  oxygen  under  some  remarkable  conditions. 
It  has  been  obtained  free  from  water  and  in  solution  in  ether;  hence  it  must 
be  regarded  as  an  independent  oxide. 

Preparation. — Regnault  recommends  the  following  process  for  its  prepara- 
tion :  Peroxide  of  barium  is  rubbed  in  a  mortar,  with  a  sufficient  quantity 
of  distilled  water  to  make  a  liquid  paste;  this  paste  i^  added  by  small  por- 
tions to  a  mixture  of  one  part  of  hydrochloric  acid  and  three  parts  of  water 
placed  in  a  porcelain  vessel  immersed  in  a  freezing  mixture.  The  liquid  must 
be  kept  stirred  during  the  additions.  The  changes  which  ensue  may  be  thus 
represented  (Ba03  +  IICl  =  BaCl  +  H03).  *  When  the  diluted  acid  is  satu- 
rated, a  fresh  quantity  of  concentrated  hydrochloric  acid  is  added,  and  to 
this  another  quantity  of  the  peroxide  of  barium.  The  operation  is  repeated 
until  a  solution  of  chloride  of  barium  is  obtained,  which  is  saturated  for  the 
low  temperature  to  which  the  mixture  is  exposed.  If  the  liquid  is  now  im- 
mersed in  a  mixture  of  ice  and  salt,  the  greater  part  of  the  chloride  of  barium 
is  deposited,  by  reason  of  its  insolubility  in  water  at  a  low  temperature.  The 
small  portion  dissolved  may  be  precipitated  entirely  by  the  cautious  addition 
of  sulphate  of  silver  (BaCl-f  AgO,S03=BaO,SO,+ AgCl).  The  precipi- 
tates are  separated  by  filtration  and  pressed.  The  filtrate  is  concentrated  by 
evaporation  in  vacuo.  For  this  purpose  it  should  be  placed  in  a  shallow 
vessel  over  one  containing  concentrated  sulphuric  acid.  Another  and  less 
complex  method  of  preparing  this  compound  consists  m  adding  the  paste  of 
peroxide  of  barium  in  sufficient  quantity  to  a  strong  solution  of  hydrofluo- 
silicic  acid.  The  baryta  is  precipitated  by  the  acid.  The  liquid  containing 
peroxide  of  hydrogen  may  be  separated  by  filtration,  through  gun-cotton, 
and  concentrated  in  vacuo  by  the  method  above  described.  The  peroxide 
may  be  preserved  by  acidulating  it  with  a  small  quantity  of  hydrochloric 
acid,  which,  in  the  diluted  state,  is  not  decomposed  by  it.  The  peroxide 
should  always  be  kept  in  a  cool  place.  This  compound  may  be  more  readily 
obtained  in  solution,  or  combination  with  water  by  passing  a  current  of  car- 
bonic acid  through  peroxide  of  barium  finely  powdered  and  diffused  in  water. 
Peroxide  of  hydrogen  and  carbonate  of  baryta  result.  (BaOo  +  HO-fCOo^ 
HO,+BaOCO,). 

Properties. — Peroxide  of  hydrogen  is  a  colorless  syrupy  liquid  of  a  sp.^r. 
of  1-452.  When  quite  free  from  water  it  is  not  solidified  at  zero.  At  tempera- 
tures above  60°  it  begins  to  be  decomposed.  If  heated,  the  decomposition 
takes  place  rapidly  and  sometimes  with  explosion,  the  compound  being  con- 
verted into  water  and  oxygen  (HO^=HO  +  0).  It  sinks  in  water,  but  is 
dissolved  by  that  liquid  in  all  proportions,  and  the  aqueous  solution  is  not, 


152  PEROXIDE    OF    HYDROGEN.      ITS    COMPOSITION. 

decomposed  until  it  is  heated  to  above  100^.  It  bleaches  the  skin  and  com- 
pletely destroys  organic  colors  by  its  oxidizintr  powers.  Old  paintinf^s  whicli 
have  become  coated  with  a  layer  of  sulphide  of  lead  may  have  the  dingy 
sulphide  removed  by  this  agent.  In  photography  it  has  been  used  of  late 
for  the  purpose  of  oxidizing  and  destroying  any  traces  of  hyposulphate 
which  may  remain  in  the  tissue  of  the  paper.  As  a  cosmetic  it  has  been 
used  to  render  dark  hair  light  in  color.  As  it  is  sold  for  these  purposes  it 
generally  contains  some  hydrochloric  acid.  It  is  a  powerful  oxidizer.  Potas- 
sium, sodium,  arsenic,  selenium  and  other  simple  bodies  are  rapidly  oxidized 
by  it,  and  the  sulphides  of  copper,  silver,  antimony,  and  lead  are  converted 
by  it  into  sulphates.  It  also  oxidizes  the  hydriodic,  hydrosulphuric  and 
sulphurous  acids.  This  compound  is  resolved  into  water  and  oxygen,  not 
only  by  heat  but  by  contact  with  certain  metals  or  their  oxides.  It  is  decom- 
posed by  platinum,  gold,  and  silver  ;  and,  if  the  metals  are  in  a  finely-divided 
state,  with  explosion.  By  mere  contact  with  the  oxides  of  these  metals,  or 
with  the  peroxidesof  manganese  or  lead,  or  by  simple  admixture  with  a  solution 
of  permanganate  of  potassa,  it  is  resolved  entirely  into  oxygen  and  water. 
It  is,  however,  a  remarkable  fact  that  it  may  remain  in  contact  with  phos- 
phorus and  phosphorous  acid  without  immediately  oxidizing  these  substances. 
It  has  been  elsewhere  stated  (p.  118)  that  peroxide  of  hydrogen  is  con- 
sidered to  be  the  ppsitive  polar  state  of  oxygen  (antozone),  while  the 
oxygen  of  the  peroxides  of  manganese  and  lead  is  ozone,  or  oxygen  in  the 
negative  polar  state.  The  union  of  the  two  is  supposed  to  produce  neutral 
oxygen. 

Peroxide  of  hydrogen  has  been  obtained  in  solution  in  ether  by  Dr.  Storer. 
For  this  purpose  he  employed  peroxide  of  sodium  made  by  heating  sodium 
cleaned  from  naphtha,  in  a  platinum  dish,  and  keeping  the  metal  stirred  with 
an  iron  rod.  The  peroxide  was  introduced  in  small  portions  into  a  mixture 
of  1  part  sulphuric  acid  to  24  water,  kept  cool  by  ice.  After  a  few  additions, 
the  acid  liquid  was  agitated  with  successive  portions  of  ether,  until  the  ether 
ceased  to  produce  a  blue  color,  with  a  diluted  solution  of  chromic  acid.  A 
small  quantity  of  the  peroxide  of  sodium  was  found  to  give  a  large  quantity 

of  the  compound {Ghem.  News,  August,   1861,  p.  57.)     Schonbein  has 

succeeded  in  impregnating  ether  with  the  peroxide  by  simply  introducing  a 
coil  of  red-hot  platinum  wire,  into  a  bottle  of  air,  containing  a  small  quan- 
tity of  ether  mixed  with  water.  If  this  experiment  be  performed  several 
times,  and  the  liquid  sTiaken  each  time,  it  will  be  found  to  have  dissolved 
sufficient  peroxide,  to  give  a  blue  color  to  a  solution  of  chromic  acid,  and  to 
evolve  oxygen  with  a  solution  of  permanganic  acid,  with  peroxide  of  lead, 
or  with  the  hypochlorites.  At  the  same  time  the  ether  is  oxidized  by  another 
portion  of  oxygen  (ozone)  which  escapes. — {lb.,  May,  1860,  p.  254.) 

Composition. — The  analysis  of  peroxide  of  hydrogen  is  easily  made  by 
placing  a  measured  quantity  of  the  liquid  in  a  graduated  tube  over  mercury, 
and  then  introducing  into  it  some  finely-powdered  peroxide  of  manganese, 
wrapped  in  filtering  paper.  The  liberation  of  oxygen  begins  on  contact, 
and  the  greater  the  quantity  evolved,  the  stronger  the  compound.  There  is 
no  substance  known  which  contains  so  large  a  proportion  of  oxygen  as  this. 
It  amounts  to  94  per  cent,  by  weight,  and  according  to  Pelonze,  in  its  maxi- 
mii*n  of  concentration,  it  will  give  off  4t5  times  its  volume  of  oxygen.  Its 
constitution  is  as  follows  : — 

Atoms.        Volumes.       Weights.       In  100  Parts.  Pelonze. 

Hydrogen  H        ...        1       ...       1       ...        1       ...         5-9       ...         5-88 
Oxygen      0.       ...        2       ...       1       ...      16       ...       94-1       ...       94  12 


Peroxide  of  hydrogen  1117  100-0  100-00 


METHODS  OF  PROCURING  NITROGEN.  153 

Tt  is  decomposed  by  electrolysis,  and  the  quantity  of  oxygen  evolved  is 
twice  as  great  as  that  separated  from  water. 

There  is  no  other  compound  of  oxygen  and  hydrogen  known. 


CHAPTER    XII. 

NITROGEN  — (N=14).  — THE    ATMOSPHERE. 

History  — Nitrogen  (from  vlt^ov,  nitre,  and  y$v»/a«,  to  produce)  was  dis- 
covered by  Dr.  Rutherford  in  17T2,  up  to  which  time  it  appears  to  have 
been  confounded  with  carbonic  acid.  It  was  called  Azote  by  Lavoisier,  a 
name  still  retained  by  the  French  chemists.  This  is  derived  from  a,  priv., 
and  Cw>7,  life,  owing  to  the  gas  rapidly  destroying  the  life  of  an  animal  ; 
but  it  is  obvious  that  such  a  name  would  be  equally  applicable  to  all  the 
gases.  The  name  assigned  to  this  element  by  English  chemists,  is  based  on 
the  property  which  it  possesses  of  producing,  with  oxygen,  an  acid  which 
enters  into  the  composition  of  nitre.  Nitrogen,  although  found  abundantly 
in  the  mineral  kingdom,  is  one  of  the  most  important  constituents  of  organic 
substances.  A  large  number  of  animal,  and  many  vegetable  compounds 
contain  it.  It  forms  nearly  four-fifths,  by  weight,  of  the  atmosphere  in  an 
uncombined  or  free  state.  Among  native  mineral  substances,  nitrate  of 
potash  contains  14  per  cent.,  and  nitrate  of  soda  16  per  cent,  of  nitrogen. 
It  is  a  constituent  of  most  fulminating  compounds,  e.  g.,  the  fulminates  of 
mercury,  silver,  and  gold.  Ammonia  and  all  its  salts  contain  it  in  large 
proportion. 

Preparation. — Nitrogen  may  be  obtained  by  burning  phosphorus  in  a 
confined  portion  of  atmospheric  air.  For  this  purpose,  a  tall  glass  jar, 
open  at  the  bottom,  and  provided  with  a  stopc^ock,  should  be  selected  :  a 
small  porcelain  or  metallic  cup,  containing  a  sufficiency  of  inflamed  phos- 
phorus, is  then  set  afloat  in  the  water-trough  and  the  jar  immediately  inverted 
over  it.  A  quantity  of  air  is  at  first  expelled  by  the  heat :  the  stopcock  is 
then  closed  and  the  combustion  goes  on  for  a  few  minutes ;  when  it  has 
ceased,  and  the  apparatus  has  cooled,  the  cup  is  easily  removed  by  agi- 
tating the  jar,  so  as  to  sink  the  phosphorus  through  the  water.  The  resi- 
duary gas,  which  is  in  nitrogen,  should  be  then  thoroughly  washed  with 
lime-water,  or  with  a  weak  solution  of  potassa.  2.  We  may  procure  it  with- 
out combustion  by  placing  a  stick  of  phosphorus  on  a  cork  or  in  a  porcelain 
capsule  on  water,  and  inverting  over  this  a  capacious  jar  of  air.  In  about 
48  hours  the  water  will  have  risen  in  the  jar  to  the  extent  of  one-fifth,  and 
the  residuary  gas,  when  washed  with  a  weak  solution  of  potassa,  will  be  found 
to  be  nitrogen  in  a  pure  state.  3.  Bright  iron  filings  sprinkled  in  a  jar 
wetted  on  the  inside  and  inverted  over  a  water-bath,  will  also  yield  it — the 
oxygen  in  this  case  being  removed  by  the  iron.  The  residuary  gas  (nitro- 
gen) is  not  contaminated  with  any  acid,  but  it  may  contain  a  trace  of  am- 
monia, which  is  easily  removed  by  agitation  with  water.  4.  If,  in  place  of 
iron,  copper  turnings  or  filings  are  used,  the  jar  being  previously  rinsed  out 
with  strong  hydrochloric  acid,  nitrogen  will  be  equally  obtained — the  oxygen 
being  entirely  removed,  while  the  copper  is  converted  into  subchloride. 
The  gas  may  be  decanted  and  well  washed  in  water,  to  remove  any  acid 
vapor.     5.  The  mode  in  which  nitrogen  may  be  procured  perfectly  pure  is 


154  NITROGEN.       CHEMICAL    PROPERTIES. 

the  following  :  Place  in  a  porcelain  capsule,  floating  in  a  water-bath,  some 
pyrogallic  acid,  and  pour  on  the  acid  a  strong  solution  of  potassa.  Invert 
over  the  capsule  a  jar  of  air.  The  oxygen  will  be  more  or  less  rapidly 
removed,  according  to  the  quantity  of  pyrogallic  acid,  and  the  strength  of 
the  solution  of  potassa.  In  this  case,  the  carbonic  acid  as  well  as  oxygen  is 
absorbed  by  the  liquid,  so  that  the  residuary  nitrogen  contains  only  aqueous 
vapor,  which,  if  necessary,  may  be  removed  from  it  by  dry  potash.  Other 
methods  for  procuring  the  gas  have  been  suggested,  e.  g.,  by  passing  air 
through  a  tube  containing  metallic  copper,  heated  to  redness.  In  this  experi- 
njent  the  air  is  deprived  of  its  oxygen,  oxide  of  copper  is  formed,  and  the 
nitrogen  passes  over.  It  has  been  also  recommended  to  procure  the  gas  by 
decomposing  a  strong  solution  of  ammonia  by  a  current. of  chlorine,  but 
this  process  is  attended  with  some  danger.  If  the  nitrogen  is  entirely 
deprived  of  oxygen' by  any  of  the  above  processes,  no  red  fumes  will  appear 
on  mixing  it  with  its  volume  of  deutoxide  of  nitrogen.  It  is  less  pure  when 
produced  by  the  vivid  combustion  of  phosphorus,  than  when  it  results  from 
slow  oxidation  as  in  2. 

Properties. — Nitrogen  is  a  permanently  elastic,  colorless,  neutral  gas,  with 
neither  smell  nor  taste  :  it  has  no  action  upon  vegetable  colors  or  upon  lime- 
water.  It  is  not  dissolved  by  water,  except  that  fluid  has  been  deprived  of 
its  ordinary  portion  of  air  by  long  boiling, w^hen  it  takes  up  about  one  and 
a  half  per  cent.  Its  refractive  power  in  regard  to  light  is  to  that  of  atmos- 
pheric air  as  1"034  to  1000.  It  is  rather  lighter  than  atmospheric  air, 
compared  with  which  its  specific  gravity  is  0967  :  100  cubic  inches  weigh 
at  mean  temperature  and  pressure  29*96  grains.  (Thompson.)  Its  specific 
gravity  in  reference  to  hydrogen  is  as  14  to  1.  The  following  experiments 
will  serve  to' illustrate  the  properties  of  this  gas.  It  does  not  support  com- 
bustion :  1.  A  lighted  taper,  burning  camphor,  or  a  flame  of  ether,  when 
plunged  into  the  gas  is  immediately  extinguished.  2.  If  quite  free  from 
oxygen,  inflamed  phosphorus  will  be  extinguished  in  it.  These  facts  prove 
that,  in  ordinary  language,  it  will  neither  burn  nor  support  the  combustion  of 
other  bodies.  3.  The  neutrality  of  the  gas,  if  deprived  by  washing  of  any 
traces  of  the  vapor  of  phosphorus  or  of  phosphorous  acid,  may  be  proved  by 
pouring  into  it  a  solution  of  litmus ;  the  blue  color  will  remain  unchanged. 
4.  On  shaking  the  liquid  with  the  gas,  its  insolubility  in  water  will  be 
manifested  by  a  lighted  taper  being  as  readily  extinguished  after,  as  before 
the  introduction  of  litmus.  5.  If  into  another  jar  we  introduce  a  solution 
of  chloride  of  lime,  colored  with  litmus,  the  blue  color  will  not  be  discharged 
— a  proof  that  the  gas  is  not  acid.  6.  When  lime-water  is  poured  into  ajar, 
and  the  vessel  is  shaken,  the  lime  is  not  precipitated,  t.  If  a  solution  of 
potassa  is  added  to  another  jar,  the  gas  remains  undissolved.  8.  A  piece  of 
caustic  potassa  moistened  and  placed  in  a  tube  of  nitrogen  over  mercury, 
produces  no  absorption  or  alteration  in  the  volume  of  the  gas.  The 
extinction  of  burning  bodies  is  common  to  nitrogen  and  carbonic  acid  ;  but 
the  experiments  3  to  8  serve  clearly  to  distinguish  the  tw^o  gases,  and  by  8 
they  may  be  separated  when  mixed.  Traces  of  an  acid  of  phosphorus  are 
sometimes  found  in  the  nitrogen  obtained  by  the  use  of  this  substance,  and 
the  gas  if  unwashed  may  thus  appear  to  have  an  acid  reaction,  but  as  it  is 
procured  by  the  oxidation  of  iron,  no  acid  is  produced. 

Potassium  will  not  burn  in  nitrogen.  Allow  a  stratum  of  half  an  inch  of 
water  to  remain  in  a  jar  of  the  gas.  Throvv  into  the  jar  a  piece  of  potas- 
sium ;  it  will  decompose  the  water,  but  without  combustion. 

Although  nitrogen  is  a  necessary  constituent  of  atmospheric  air,  it  cannot 
be  breathed  in  a  pure  state  without  destroying  life.  It  does  not  appear  to 
operate  as  a  poison,  but  when  breathed,  it  simply  induces  suflfocation,  owing 


NITROGEN.      EQUIVALENT.      TESTS.  155 

to  tlie  absence  of  free  oxypcen.  If  it  had  any  directly  noxious  effects  on  the 
body,  it  could  not  be  breathed  by  animals  in  the  large  proportion  in  which 
it  enters  into  the  mixture  of  gases,  known  as  the  atmosphere. 

Nitrogen  is  said  not  to  be  combustible,  but  under  certain  circumstances, 
it  may  be  made  to  undergo  a  kind  of  combustion,  as  when  electric  sparks 
are  passed  through  atmospheric  air,  or  through  a  mixture  of  one  volume  of 
nitrogen  with  two  or  three  of  oxygen  ;  in  this  case  each  spark  will  be 
attended  by  the  production  of  a  trace  of  nitric  acid,  and  after  some  hundred 
sparks,  the  blue  color  of  litmus  will  be  changed  to  red.  Here  combustion 
appears  to  take  place  in  that  portion  of  the  gas  immediately  subject  to  the 
action  of  the  sparks  ;  but  the  temperature  of  the  surrounding  gas  is  not 
thus  sufficiently  elevated  to  enable  the  combustion  to  spread  beyond  the 
immediate  sparks.  This  is  probably  the  source  of  the  nitric  acid,  and  of 
the  nitrates  found  in  rain-water  after  thunderstorms.  The- nitrogen  of  the 
atmosphere  is  also  liable  to  oxidation,  as  a  result  of  the  action  of  ozone. 
{See  page  115.)  Some  of  the  eflfects  ascribed  to  ozone,  have  been  set  down 
to  the  combustion  of  nitrogen. 

If  a  mixture  of  nitrogen  with  twelve  or  fourteen  volumes  of  hydrogen,  be 
kindled  as  it  issues  from  a  small  tube,  and  burned  either  in  common  air  or  in 
oxygen,  water  and  nitric  acid  will  be  formed  ;  so  that  in  this  case  the 
nitrogen  may  be  said  to  undergo  combustion  by  the  aid  of  the  elevated  tem- 
perature of  the  flame  of  hydrogen  ;  but  it  must  be  recollected  that  in  these 
cases  nitric  acid  could  be  produced  without  the  presence  of  water,  and  that 
it  may  tend  to  dispose  a  union  which  would  not  otherwise  take  place.  The 
formation  of  a  trace  of  nitric  acid,  when  hydrogen  is  burned  in  common  air, 
is  referable  to  the  same  cause.  Bunsen  has  found  that,  by  adding  to  the 
mixture  of  oxygen  and  nitrogen  two  volumes  of  detonating  gas  (composed 
of  two  volumes  of  hydrogen  and  one  of  oxygen),  nitrogen  may  be  easily 
oxidized  and  converted  into  nitric  acid.  If  the  detonating,  gas  is  used  in  the 
proportion  of  from  three  to  five  volumes  of  the  mixed  oxygen  and  nitrogen, 
so  much  nitric  acid  is  produced,  that  the  mercury  in  the  tube  is  dissolved 
with  the  evolution  of  deutoxide  of  nitrogen. 

Much  discussion  has  arisen  respecting  the  nature  of  nitrogen  ;  and  the 
question  has  been  agitated,  whether  it  is  or  is  not  a  simple  body ;  but 
although  many  ingenious  surmises  have  been  published  on  the  subject,  and 
many  analogies  suggested  in  favor  of  its  being  a  compound,  no  experimental 
proofs  have  been  hitherto  adduced.  The  production  of  nitrides  by  combi- 
nation with  certain  metals,  and  the  metallization  of  ammonia,  are  considered 
by  some  chemists  to  favor  the  view  of  its  compound  nature. 

Nitrogen  is  one  of  those  elementary  bodies  on  which  the  electric  current 
appears  to  exert  no  influence.  According  to  Faraday's  researches,  nitrogen, 
when  under  the  influence  of  the  current,  has  shown  no  tendency  to  pass  in 
either  direction. 

Equivalent  and  Compounds ^^The  equivalent  weight  of  nitrogen   is   14, 

and  its  volume  equivalent  is  1.  In  the  free  state,  it  is  remarkable  for  its 
neutrality  or  indifiference  to  combination.  In  the  nascent  state  it  readily 
unites  with  hydrogen  and  oxygen,  forming  ammonia,  and,  in  some  cases, 
nitric  acid.  It  forms  also  compounds  with  carbon,  chlorine,  and  iodine,  but 
only  as  a  result  of  complex  chemical  changes.  When  combined,  it  is 
remarkable  for  its  instability,  since  slight  physical  causes  will  lead  to  its 
sudden  separation  with  explosion,  from  many  of  its  combinations.  Fulmi- 
nating substances  frequently  owe  their  properties  to  the  suddenness  with 
which  this  element  is  liberated. 

Tests. — Nitrogen-compounds,  such  as  nitric  acid  and  ammonia,  are  easily 
recognized  by  appropriate  tests.     The  only  difficulty  connected  with  the 


156  ATMOSPHERE.      ITS    PROPERTIES. 

detection  of  nitroo^en,  is  in  reference  to  its  presence  in  organic  substances. 
It  is,  however,  readily  converted  into  ammonia,  and  from  the  production  of 
ammonia,  we  infer  the  existence  of  nitrogen.  For  this  purpose,  the  sub- 
stance dried  and  powdered  is  mixed  with  its  bulk  of  soda-lime  (a  mixture 
consisting  of  two  parts  of  hydrate  of  lime,  and  one  part  of  hydrate  of  soda). 
On  the  application  of  heat  to  the  mixture,  ammonia  is  evolved.  This  is 
known  by  its  odor,  and  its  volatile  alkaline  reaction  on  test-paper,  as  well 
as  by  its  special  chemical  character.  {See  Ammonia.)  Another  method 
consists  in  forming  a  carbon-compound  (cyanogen).  The  substance  in 
powder  is  introduced  into  a  narrow  test-tube,  and  a  portion  of  sodium  is 
introduced,  the  metal  being  completely  covered  with  and  surrounded  by  the 
powder.  Heat  is  then  applied  to  carbonization,  and  cyanide  of  sodium 
(NajCgN)  is  one  of  the  products.  When  cold,  the  dark  residue  is  lixi- 
viated in  water,  and  the  solution  filtered.  It  is  of  a  pale  yellow  color,  and 
generally  alkaline  from  the  presence  of  free  soda.  On  adding  to  it  a  solu- 
tion of  green  sulphate  of  iron,  there  is  a  turbid  dark-green  precipitate. 
When  this  is  treated  with  diluted  sulphuric  acid,  oxide  of  iron  is  dissolved 
and  Prussian  blue  remains.  •  This  is  a  clear  proof  that  nitrogen  was  present 
in  the  substance.  A  small  globule  of  sodium  tied  in  a  portion  of  flannel,  and 
thus  treated,  reveals  the  presence  of  nitrogen  in  the  albumen  of  flannel.  We 
have  thus  obtaiaed  Prussian  blue  from  the  nitrogen  of  the  body  of  a  fly. 

THE   ATMOSPHERE. 

It  will  be  understood  from  the  preceding  remarks,  that  the  atmospheric  air 
is  a  mixture  of  gases,  in  which  nitrogen  predominates.  Besides  nitrogen, 
which  forms  nearly  four-fifths,  the  other  principal  ingredient  is  oxygen, 
constituting  about  one-fifth  ;  and  in  addition  to  these,  there  are  compara- 
tively small  quantities  of  carbonic  acid,  aqueous  vapor,  sulphurous  acid, 
ammonia,  and  other  gases,  as  well  as  organic  matter.  The  term  atmosphere 
(from  afjiioj,  vapor,  and  o^jatpa,  sphere),  is  applied  to  the  great  aerial  ocean 
which  surrounds  the  earth,  and  extends,  in  varying  degrees  of  density,  about 
forty-five  miles  from  its  surface.  Large  as  this  may  appear,  it  represents 
only  1-1 60th  part  of  the  earth's  diameter.  In  a  globe  of  forty  feet  diameter, 
this  would  be  equivalent  to  a  thickness  of  only  three  inches.  The  term 
atmosphere  is  appropriate,  inasmuch  as  it  is  the  receptacle  of  all  the  gases 
and  vapors,  organic  or  inorganic,  which  are  constantly  escaping  from  the 
surface  of  the  earth  and  sea. 

Properties. — The  physical  and  chemical  properties  of  the  air  are  those  of 
its  two  principal  constituents,  oxygen  and  nitrogen  ;  the  active  properties  of 
oxygen  being  modified  by  dilution  with  nitrogen.  Air  is  a  transparent, 
colorless,  elastic,  tasteless  fluid,  and,  as  its  two  constituents  are  permanent 
gases,  it  has  not  yet  been  liquefied  by  cold  or  pressure.  It  has  been  con- 
densed to  a  degree  but  little  inferior  to  that  of  water  (l-6t5th  part  of  its 
original  volume),  without  undergoing  any  change  in  its  physical  condition 
(page  81).  Heat  simply  expands  it  (page  83),  and,  within  certain  tempe- 
ratures, with  great  uniformity.  The  nitrogen  has  no  positive  properties  ; 
oxygen  is  the  principal  chemical  agent,  and  is  largely  consumed  iu  combus- 
tion and  respiration  (page  95).  The  oxygen  thus  consumed  is  replaced  by 
an  equal  volume  of  carbonic  acid,  and  this  in  its  turn  is  absorbed  and 
decomposed  by  the  green  parts  of  vegetables  under  the  influence  of  solar 
light,  so  that  the  carbon  is  fixed  in  the  vegetable  structure,  and  the  oxygen 
is  evolved  either  in  its  common  or  allotropic  state.  The  animal  and  vegetable 
are  thus  proved,  in  reference  to  the  atmosphere,  to  have  a  compensating 
relation  to  each  other.  Air  is  dissolved  by  water,  but  the  oxygen  is  taken 
up  in  larger  proportion  than  nitrogen  (page  141).     It  is  this  which  imparts 


COMBUSTION    IN    AIR.  15*7 

a  fresh  aerated  taste  to  water.  The  proportion  of  air  dissolved,  is  subject 
to  variation,  but  in  natural  spring  waters  it  is  seldom  less  than  two  cubic 
inches  in  one  hundred  of  water.  It  is  expelled  by  boiling,  congelation,  or 
the  removal  of  atmospheric  pressure,  as  by  placing  a  glass  of  spring  water 
under  the  receiver  of  an  air  pump  and  exhausting  the  vessel.  The  air  is 
seen  to  escape  in  small  bubbles.  Owing  to  the  diminution  of  pressure, 
water  at  lofty  elevations  is  less  aerated  than  at  the  level  of  the  sea,  and,  by 
reasons  of  the  deficiency  of  air,  the  lake-water  of  high  mountainous  districts, 
is  not  fitted  to  support  the  existence  of  fish.  Air  adheres  more  or  less  to 
all  solids,  and  it  is  especially  contained  in  porous  solids.  A  stick  of  charcoal 
sunk  in  water  by  a  leaden  weight,  and  placed  in  vacuo^  yields  a  large  quantity 
of  air,  which  issues  in  torrents  from  the  broken  ends.  A  piece  of  pumice, 
or  an  ^^^,  sunk  in  a  vessel  of  water,  presents  a  similar  phenomenon.  Even 
the  smooth  and  polished  surfaces  of  metals  may  thus  be  proved  to  have  a 
film  of  air  adherent  to  them. 

In  comhustion,i\\%  oxygen  alone  is  consumed,  the  nitrogen  is  set  free  and 
mixes  with  the  carbonic  acid  produced  at  the  expense  of  the  oxygen.  Air 
is  therefore  rapidly  contaminated  by  this  process,  and  in  a  confined  space, 
the  nitrogen  and  carbonic  acid,  as  a  result  of  the  heat  of  combustion,  ac- 
cumulate in  the  upper  part  of  the  vessel  or  apartment.  Neither  of  these 
g:ases  is  respirable,  and  neither  will  support  ordinary  combustion.  The 
following  experiments  will  illustrate  the  d*eterioration  of  air  under  these 
circumstances.  Fix  three  wax  tapers  to  a  stout  wire  placed  upright,  and 
about  three  feet  in  height,  so  that  one  is  at  the  upper  part,  one  at  the  lower, 
and  the  third  in  the  middle.  Light  the  tapers,  and  invert  over  them  a  tall 
stoppered  shade,  leaving  a  slight  space  for  the  entrance  of  air  below.  The 
accumulation  of  deoxidized  air  (nitrogen)  and  carbonic  acid  in  the  upper 
part  of  the  shade,  will  be  indicated  by  the  early  extinction  of  the  upper  and 
middle  tapers,  while  the  lower  one  will  continue  to  burn.  If,  when  the 
lower  taper  is  burning  dimly  from  impurity  of  the  air,  the  stopper  is  removed 
from  the  shade,  a  current  of  air  is  immediately  set  up,  the  gaseous  products 
of  combustion  are  carried  off,  and  the  lower  taper  will  burn  with  a  brighter 
flame.  This  experiment  establishes  the  necessity  for  a  rapid  removal  of  the 
products  of  combustion,  and  the  results  are  equally  applicable  to  the  con- 
tamination of  air  by  the  respiration  of  animals.  Fix  in  the  stoppered 
aperture  of  a  bell-jar,  by  means  of  a  closely-fitting  cork,  a  glass  tube,  about 
an  inch  in  diameter.  The  tube  should  rise  several  inches  above  the  level  of 
the  jar,  and  should  reach  on  the  inside  to  within  two  inches  of  its  base. 
Mount  in  a  plate  two  pieces  of  wax  taper,  one  sufiQciently  tall  to  reach  nearly 
to  the  top  of  the  jar  when  placed  over  it,  the  other  so  short,  that  when  ignited, 
the  point  of  the  flame  only  will  be  inclosed  by  the  open  end  of  the  glass  tube 
fixed  in  the  jar.  Light  the  tapers  and  invert  the  jar  over  them,  not  pressing 
it  down  closely  at  the  base.  The  tube  should  be  so  adjusted  to  the  short 
taper,  as  to  act  like  a  chimney  to  it,  care  being  taken  that  it  is  not  touched 
by  the  flame.  In  a  short  time,  if  the  cork  is  well  fitted,  the  tall  taper  will 
be  extinguished,  but  the  short  taper  will  continue  to  burn.  In  the  one  case, 
the  products  of  combustion  are  not  carried  off",  in  the  other  they  are,  and 
the  supply  of  air  is  continually  renewed.  As  a  proof  of  this,  if  we  hold  over 
the  chimney-tube  a  small  gas-jar,  the  deposition  of  water  on  the  glass  will  be 
apparent,  and,  after  a  time,  the  presence  of  carbonic  acid  may  be  proved  by 
pouring  lime-water  into  the  jar.  (The  production  of  carbonate  of  lime  will 
be  indicated  by  a  milky  appearance  of  the  lime-water.)  The  principles  of 
the  ventilation  of  dwellings  are  based  on  a  proper  adjustment  of  the  supply 
of  pure  air  for  combustion  and  respiration,  and  a  provision  for  the  complete 
removal  of  the  products  as  they  are  formed.     In  the  burning  of  coal-gas  the 


158  PRESSURE    OF    THE    ATMOSPHERE. 

production  of  sulphurous  acid  may  be  an  additional  source  of  noxious 
impurity. 

When  combustion  takes  place  in  rarefied  air,  as  when  a  candle  is  placed 
under  a  receiver  from  which  the  air  has  been  partially  removed  by  the  air- 
pump,  the  flame  is  elongated,  becomes  less  luminous,  and  is  soon  extin- 
guished. According  to  observations  made  by  Dr.  Frankland,  in  1859,  on 
the  summit  of  Mont  Blanc,  it  appears  that  at  this  elevation  the  amount  of 
combustible  consumed  is  as  great  as  at  the  level  of  the  sea,  although  the 
light  emitted  by  a  burning  candle  is  considerably  less. 

Air  is  usually  taken  as  the  standard  of  specific  gravity  for  gases,  being, 
for  this  purpose,  I'OOO.  It  is  also  the  standard  for  refraction,  specific  heat, 
and  other  properties  of  gases.  One  hundred  cubic  inches  of  dry  air  at  mean 
temperature  (60°),  and  mean  pressure  (30  inches),  are  considered  to  weigh 
31  grains.  This  nearly  corresponds  to  the  sum  of  the  weights  of  the  consti- 
tuent gases,  having  regard  to  the  proportions  in  which  they  are  mixed.  Air 
is  about  815  times  lighter  than  its  volume  of  water,  at  60°.  Compared  with 
hydrogen  its  density  is  as  14  4  to  1.  The  weights  of  100  cubic  inches  of  any 
gas  or  vapor  may  be  determined  by  multiplying  the  specific  gravity  of  the 
gas  or  vapor  by  31,  the  weight  of  100  cubic  inches  of  air.  Thus  :  nitrogen 
has  asp.  gr.  of  0-967  and  0-967  x  31  =29*98  grains,  the  weight  of  100  cubic 
inches  of  this  gas. 

Pressure  of  the  Atmosphere. -^Omng  to  the  gravitating  force  of  the  atmo- 
sphere and  the  great  elasticity  of  its  constituent  gases,  the  lowest  stratum — 
that  which  is  in  contact  with  the  surface  of  the  earth,  and  in  which  warm- 
blooded animals  live,  is  highly  condensed.  The  pressure  of  the  atmosphere 
at  the  level  of  the  sea,  is  equal  to  15  pounds  on  every  square  inch,  or  about 
2216  pounds  on  each  square  foot.  It  is  calculated  that  one  cubic  inch  at 
the  surface,  would  expand  into  12,000  cubic  inches  at  the  extreme  limit  of 
the  atmosphere  (45  miles).  The  proportionate  increase  in  volume  at  differ- 
ent elevations,  as  the  result  of  the  decrease  of  pressure,  is  given  in  the  sub- 
joined table.  It  will  be  perceived  that  at  a  height  of  only  2705  miles 
(14,282  feet),  the  atmosphere  loses  one-half  of  its  density;  in  other  words, 
one  volume  at  the  surface  would  expand  into  two  volumes  at  this  elevation. 
So  rapid  is  the  decrease  of  density,  that  while  one-half  of  the  mass  of  the 
atmosphere  is  within  three  miles  of  the  surface,  four-fifths  of  it  are  within 
eight  miles,  leaving  only  one-fifth  for  the  thirty-seven  miles  above  this  eleva- 
tion. While  the  height  increases  in  arithmetical  progression,  the  increase 
of  volume  (or  decrease  of  density)  follows  a  geometrical,  ratio  : — 


Height  above  the 

-Volume. 

Height  above  the 

Volumt 

sea  in  miles. 

sea  in  miles. 

0 

.     1 

10-820    '. 

, 

.     16 

2-705     . 

.     2 

13-525     . 

, 

.     32 

5-410     . 

.    4 

16-230     . 

, 

.     64 

8-115     . 

.     8 

18-935     . 

. 

.  128 

The  temperature  of  the  atmosphere  diminishes  about  1°  for  every  350  feet 
of  ascent,  the  cause  of  which  is  partly  referable  to  the  increased  capacity  of 
air  for  heat  in  proportion  as  its  density  diminishes,  and  partly  to  the  cir- 
cumstance thaji  the  atmosphere  is  chiefly  heated  by  contact  with  the  earth. 
The  line  of  perpetual  congelation  gradually  ascends  from  the  equator  to  the 
poles.  At  0°  latitude  it  is  stated  to  be  15*^,200  feet ;  at  60°,  3,818  ;  and  at 
76°,  only  1000  feet. 

If  a  tube  three  feet  long  is  filled  with  mercury,  and  inverted  in  a  mercurial 
bath,  the  metal  will  fall  in  the  tube  until  its  height  from  the  surface  of  the 
bath  is  equal  to  about  30  inches.  If  placed  under  a  receiver  and  the  air  is 
withdrawn,  the  mercury  will  fall  in  the  tube.     On  readmitting  the  air  it  will 


PRESSURE    OF    THE    ATMOSPHERE.  159 

again  rise.  It  is  therefore  obvious  that  this  column  of  mercury  is  supported 
in  the  tube  by  the  pressure  of  the  atmosphere  on  the  surface  of  the  liquid 
metal  in  the  bath.  From  this  experiment  it  will  be  easy  to  calculate  the 
exact  amount  of  pressure  on  the  lowest  stratum  of  air.  This  has  been  already 
stated  to  be  equivalent  (in  round  numbers)  to  15  pounds  avoirdupois  on 
every  square  inch  of  surface.  In  reality,  however,  the  pressure,  assuming 
the  mean  height  of  the  barometer  to  be  30  inches,  is  14*6  pounds  on  the 
square  inch — a  result  which  is  thus  obtained  :  The  weight  or  gravitating 
force  of  the  atmosphere,  is  proved,  by  the  experiment  above  mentioned,  to  be 
exactly  equal  to  the  weight  or  gravitating  force  of  a  column  of  mercury  thirty 
inches  in  height.  A  column  of  this  metal,  the  base  of  which  would  be  equal 
in  area  to  a  square  inch,  would  consist  of  thirty  cubic  inches.  The  specific 
gravity  of  mercury  being  13  5,  the  weight  of  a  column  of  30  cubic  inches 
will  represent  the  gravitating  force  of  the  atmosphere  on  the  area  of  a  square 
inch.  A  cubic  inch  of  mercury  weighs  3408'183  grains  (252-458X  13'5 — 
the  weight  of  a  cubic  inch  of  water  multiplied  by  the  specific  gravity  of 
the  metal),  and  therefore  30  cubic  inches  would  weigh  (3408*138  x  30= 
102245'49  grains  or)  14'6  pounds  avoirdupois.  Hence  this  may  be  taken 
as  the  true  amount  of  atmospheric  pressure  when  the  barometer  is  at  its 
mean  height.  A  column  of  water  33  feet  in  height,  or  a  column  of  air  45 
miles  in  height,  each  having  the  area  of  a  square  inch,  would  be  equal  in 
pressure  to,  a  column  of  mercury  30  inches  in  height.  These  diiferent  heights 
correspond  to  the  respective  specific  gravities  of  the  liquids. 

The  influence  of  this  pressure  on  the  volume  of  gases  may  be  easily  proved. 
Place  a  light  caoutchouc-ball  under  the  receiver  of  an  air-pump  and  with- 
draw the  air.  The  ball  will  increase  in  size  as  the  air  is  withdrawn — the 
air  which  is  confined  within  the  ball  acquiring  a  power  of  expansion  by  the 
diminution  of  pressure.  If  the  mouth  of  a  wide  glass  jar  is  well  secured 
with  a  layer  of  stout  caoutchouc,  and  the  jar  is  placed  under  the  receiver, 
on  the  removal  of  the  air  the  membrane  will  be  enormously  distended  by 
the  expansion  of  air  in  the  jar,  and  may  ultimately  burst.  Invert  in  a  gas- 
jar,  a  graduated  tube  containing  water,  colored  with  sulphate  of  indigo, 
leaving  two  cubic  inches  of  air  at  the  top.  Place  this  under  the  receiver. 
As  the  air  is  withdrawn  from  the  receiver  the  air  in  the  tube  will  expand, 
and,  when  the  barometer  marks  15  inches,  it  will  be  found  that  the  two  cubic 
inches  will  occupy  the  space  of  four,  thus  showing  that  by  the  removal  of  half 
the  pressure  the  air  has  been  doubled  in  volume.  This  experiment  proves 
that  the  density  of  the  air  is  in  a  direct  ratio  to  the  compressing  force.  With 
the  pressure  of  half  an  atmosphere  the  volume  is  doubled,  and  with  a  pres- 
sure of  two  atmospheres  it  is  reduced  to  one-half.  It  is  the  same  for  all* 
gases  and  vapors  above  the  boiling  point  of  their  liquids),  whatever  may  be 
their  respective  specific  gravities. 

A  well-ground  receiver,  when  the  air  is  removed  from  the  interior,  is 
pressed  with  such  force  to  the  air-pump  plate  that  it  is  impossible  to  move 
it.  But  this  pressure  may  be  made  visible  by  th«  following  experiments. 
Close  one  end  of  a  stout  glass-cylinder  four  or  five  inches  in  diameter,  with 
a  strong  layer  of  sheet  India  rubber,  and  apply  the  other  end,  which  should 
be  well  ground  for  this  purpose,  to  the  plate  of  the  air-pump.  As  the  air 
is  gradually  withdrawn,  the  rubber  will  be  pressed  downwards,  filling  the 
interior  of  the  vessel,  and  it  may  ultimately  burst.  If  for  the  rubber  we 
substitute  a  layer  of  wet  bladder,  and  allow  this  to  dry,  on  placing  the  glass 
oil  the  air-pump  plate,  and  rapidly  exhausting  it,  the  bladder  will  be  burst 
with  a  loud  report,  as  the  result  of  the  air  rushing  into  a  partial  vacuum. 
Owing  to  the  great  amount  of  this  pressure,  receivers  and  other  vessels 
intended  for  exhaustion  should  be  made  of  stoat  glass,  and  rounded  at  the 


160  EUDIOMETRY.      DETERMINATION    OF    OXYGEN. 

top.  Fill  a  short  wide  jar  with  carbonic  acid.  Pour  into  the  jar  a  small 
quantity  of  water,  and  add  at  the  same  time,  but  without  agitation,  several 
sticks  of  fused  potash.  Tie  over  the  mouth  of  the  jar  firmly  a  stout  sheet 
of  caoutchouc  stretched  tightly  for  this  purpose.  Now  agitate  the  jar,  and 
as  the  solid  potash  is  dissolved  in  the  water  it  removes  the  carbonic  acid 
contained  in  the  jar.  The  universal  influence  of  atmospheric  pressure  now 
shows  itself  by  rendering  the  caoutchouc  concave,  and  it  is  so  much  depressed 
that  "it  sometimes  bursts. 

As  in  all  fluids,  the  pressure  is  equal  in  all  directions.  The  pressure 
downwards  is  proved  by  the  preceding  experiments.  The  force  of  the  pres- 
sure upwards  may  be  proved  by  the  following  simple  experiment:  Fill  a 
well-ground  glass-jar,  about  twelve  inches  long  and  three  or  four  inches  wide, 
with  water.  Place  over  this  a  square  of  stout  writing-paper,  and,  pressing 
it  firmly  to  the  water,  suddenly  invert  the  jar.  The  heavy  column  of  water 
will  be  for  a  time  supported  by  the  atmospheric  pressure  upwards  on  the 
outer  surface  of  the  paper.  Make  a  chemical  vacuum  by  pouring  into  a 
well-ground  jar,  containing  carbonic  acid,  a  small  quantity  of  a  strong  solu- 
tion of  potash,  and  cover  the  jar  immediately  with  plate-glass.  On  agitating 
the  jar,  the  gaseous  contents  will  be  removed,  and  the  cover  will  be  firmly 
fixed  to  the  jar  by  atmospheric  pressure.  In  whatever  position  the  jar  may 
be  held  the  cover  will  remain  equally  fixed,  showing  equality  of  pressure  in 
every  direction.  From  the  powerful  effects  thus  produced  when  the  air  is 
removed  from  one  surface,  it  may  be  conceived  that  nothing  could  withstand 
this  pressure  unless  it  were  equal  in  all  directions,  and  thus  completely  neu- 
tralized. 

Composition.  Eudiometry. — Numerous  analyses  of  the  air  made  by  chemists 
of  repute,  show  that  the  proportions  of  nitrogen  and  oxygen  are  not  strictly 
uniform,  either  for  the  same  place  or  for  different  localities.  The  proportion 
of  oxygen  varies  from  20  to  21  per  cent.  The  amount  of  oxygen  by  volume 
is  readily  determined,  by  the  adoption  of  any  of  the  methods  for  separating 
it  described  under  nitrogen  (page  153),  provided  care  is  taken  to  employ 
for  this  purpose  an  accurately  graduated  gas  tube  and  a  mercurial  bath. 
Among  these,  the  process  described  under  5,  is  preferable  to  the  others. 
Phosphorus  cast  in  small  balls  is  sometimes  used,  but  unless  the  vapor  of 
phosphorous  acid  (produced  as  a  result  of  oxidation)  is  removed  by  a  ball 
of  potash,  before  the  volume  of  nitrogen  is  read  oft",  there  will  be  a  con- 
siderable error  in  the  results.  Liebig  has  advised,  in  place  of  phosphorus, 
a  ball  of  papier  mache,  saturated  with  a  concentrated  solution  of  pyrogallate 
of  potassa.  The  absorption  takes  place  slowly  but  completely,  particularly 
if  the  ball  be  once  renewed.  After  this  absorption,  the  gas  must  be  dried 
by  a  ball  of  potassa,  containing  as  little  water  as  possible.  (Bunsen,  Gasome- 
try,  p.  79.)  In  this  case  the  pyrogallate  of  potassa,  and  dry  potassa,  remove 
the  oxygen,  carbonic  acid  and  aqueous  vapor,  leaving  nothing  but  nitrogen. 
The  temperature  should  be  noted  both  at  the  beginning  and  end  of  the 
experiment.  # 

The  ordinary  volumetric  method  of  analysis,  is  based  on  the  admixture  of 
a  quantity  of  pure  hydrogen  with  air,  and  its  conversion  into  water,  by 
any  of  the  usual  processes,  at  the  expense  of  the  oxygen  contained  in  the 
air  under  examination.  As  oxygen  represents  one-third  of  the  volume  of 
the  combined  gases  (Water,  page  127),  the  division  of  the  loss  by  3  will 
at  once  give  the  quantity  of  oxygen  present  in  the  air.  The  air  and  hy- 
drogen, in  about  equal  proportions,  are  introduced  into  a  graduated  glass- 
tube  placed  over  mercury,  or  into  a  siphon-tube  containing  mercury,  espe- 
cially constructed  for  this  purpose ;  and  the  gases  are  then  either  detonated 
by  the  electric  spark,  or  are  slowly  combined  by  means  of  a  ball  composed 


DETERMINATION    OF    OXYGEN.  161 

of  spongy  platinum  and  clay,  introduced  through  the  mercury  into  the  tube. 
The  gases  should  be  allowed  to  diffuse  thoroughly,  before  any  attempt  is 
made  to  combine  them.  The  following  experiment  on  the  air  of  London, 
will  illustrate  the  principle  of  this  operation.  The  air  examined  amounted 
to  35  parts  by  volume.  To  this  quantity  42  parts  of  hydrogen  were  added. 
The  mixed  gases,  therefore,  amounted  to  77  parts.  A  ball  of  spongy  pla- 
tinum was  introduced  into  the  mixture,  and  in  two  hours  combination  was 
complete.  It  was  found  that  only  56  parts  of  gas  remained  in  the  graduated 
tube.  The  loss,  therefore,  as  watery  vapor  was  77 — 55  =  22  ;  and  one-third 
of  this  must  have  been  oxygen.  Therefore  22-^3=7■33  for  the  proportion 
of  oxygen  in  the  35  measures  taken  :  and  35  :  7  33  :  :  100 :  20-94  oxygen. 
Deducting  these  figures  from  100,  the  air  examined  had  this  composition  in 
100  parts:  oxygen  2094;  nitrogen  79-06.  The  use  of  spongy  platinum 
for  the  combination  of  the  gases,  appears  to  be  less  liable  to  fallacy,  than 
the  detonation  of  the  mixture  by  the  electric  spark.  Bunsen  has  shown, 
that  unless  great  precautions  are  taken,  so  much  •hitric  acid  may  be  formed 
in  the  presence  of  oxygen  and  hydrogen  by  the  combustion  of  the  nitrogen, 
as  to  lead  to  a  serious  fallacy  in  calculating  the  amount  of  oxygen.  (Gaso- 
metry,  page  60.)  On  the  other  hand,  the  pyrogallate  of  potassa,  as  an 
absorbing  liquid,  was  found  to  give  very  accurate  results. 

To  this  kind  of  analysis  the  term  eudiometry  (d,  8iov,  and  fisrpov,  measure 
of  the  purity  of  the  air)  has  been  applied,  since  the  healthiness  of  localities 
was  erroneously  supposed  to  depend  on  the  proportion  of  oxygen  present. 
Eudiometric  tubes,  finely  graduated  and  connected  with  bottles  containing 
a  liquid  for  the  absorption  of  oxygen,  were  formerly  employed.  The  air 
contained  in  the  tubes  was  exposed  to  the  eudiometric  liquid,  and  the  amount 
of  absorption  was  ascertained  by  opening  the  bottle  under  water.  A  solution 
of  suli)hide  of  potassium,  or  of  y)rotosulphate  of  iron  saturated  with  deut- 
oxide  of  nitrogen,  was  formerly  used  for  this  purpose,  ^uch  methods  of 
analysis  have  been  long  since  abandoned. 

As  errors  frequently  arise  in  reading  and  correcting  the  volumes  of  gases, 
owing  to  the  variable  influence  of  pressure,  temperature,  and  other  causes, 
chemists  have  given  some  attention  to  the  discovery  of  a  method  for  deter- 
mining the  oxygen  and  nitrogen  by  weight,  in  one  operation. 

This  has  been  successfully  accomplished  in  the  analysis  of  air,  performed 
by  Dumas  and  Boussingault.  The  operation  is  very  simple.  Air,  deprived 
of  its  carbonic  acid,  and  aqueous  vapor,  by  causing  it  to  pass  through  a 
series  of  tubes,  some  of  which  contain  concentrated  sulphuric  acid,  and 
others,  a  saturated  solution  of  potassa,  is  finally  made  to  traverse  a  balanced 
tube  containing  metallic  copper,  heated  to  redness.  It  is  here  entirely 
deprived  of  its  oxygen.  By  opening  a  stopcock  communicating  with  a  large 
glass  globe  in  a  state  of  vacuum,  the  deoxidized  air,  or  nitrogen,  is  collected 
in  this  vessel,  which  acts  as  an  aspirator.  When  filled,  the  glass  globe  is 
removed  and  weighed.  It  is  now  brought  to  a  state  of  vacuum,  and  again 
weighed.  The  difference  in  weight  represents  the  amount  of  nitrogen,  while 
the  increase  in  weight  in  the  balanced  tube  containing  the  copper,  gives  the 
amount  of  oxygen.  All  the  other  constituents  of  air,  excepting  oxygen  and 
nitrogen,  are  excluded  by  this  method  of  analysis.  The  results  thus  obtained 
are  in  close  accordance  with  those  determined  by  other  chemists.  Air  is 
thus  found  to  be  constituted  by  volume  and  weight: — 

By  Volume.  By  "Weight. 

Oxygen 20-80  23-10 

Nitrogen 79*20  76-90 

CarhoniCf  acid,  although  in  small  proportion,  is  a  universal  constituent  of 
11 


162  DETERMINATION    OF    CARBONIC    ACID    AND    WATER. 

air.  It  has  been  found  at  all  elevations  at  which  it  has  been  sought  for, 
and  may  be  readily  detected  by  causing  a  large  quantity  of  air  to  pass 
through  a  tube  or  vessel,  containing  a  solution  of  lime  or  baryta;  or  by 
simply  exposing  to  the  atmosphere,  a  solution  of  the  alkaline  earth  in  a 
shallow  glass  dish.  A  white  precipitate,  or  an  incrustation  of  carbonate  of 
lime  or  baryta,  is  obtained  after  some  hours.  The  presence  of  aqueous  vapor 
in  the. air  is  known  by  the  deposition  of  water  on  the  exterior  of  a  glass- 
vessel  in  which  ice  has  been  placed,  or  by  exposing  to  a  current  of  air,  fused 
chloride  of  calcium  in  a  glass  tube.  In  this  case  the  water  is  absorbed,  and 
the  chloride  is  thereby  increased  in  weight. 

Various  methods  have  been  adopted  for  the  purpose  of  determining  the 
proportions  of  carbonic  acid  and  aqueous  vapor.  In  reference  to  the  former, 
M.  Thenard  employed  a  solution  of  baryta ;  and  from  the  amount  of  car- 
bonate of  baryta,  obtained  by  agitating  this  liquid  with  a  measured  volume 
of  air,  he  concluded  that  the  proportion  was  about  l-2000th  part,  or  one 
cubic  inch  in  two  thousand  cubic  inches  of  air.  The  plan  more  recently 
adopted  by  Boussingault,  Regnault,  and  other  chemists,  is  based  on  the 
separation  and  weighing  of  carbonic  acid  and  aqueous  vapor  in  one  opera- 
tion. By  means  of  a  large  aspirator,  the  air  is  made  to  traverse  a  series  of 
balanced  tubes  filled  with  broken  pumice,  impregnated  with  concentrated 
sulphuric  acid,  and  after  having  been  thus  deprived  of  water,  the  air  traverses 
another  series  of  balanced  tubes,  also  filled  with  pumice  strongly  impreg- 
nated with  a  concentrated  solution  of  potassa.  These  tubes  arrest  the  carbonic 
acid.  Any  change  of  temperature  in  the  contents  of  the  aspirator,  during 
the  performance  of  the  analysis,  is  accurately  noted.  It  will  be  obvious,  that 
by  repeatedly  filling  the  aspirator  any  quantity  of  air  may  be  thus  made  to 
pass  through  the  balanced  tubes,  and  the  first  of  the  series  may  have  a  length 
of  vulcanized  tubing  so  adjusted  to  it,  as  to  bring  the  air  from  any  particu- 
lar spot.  After  the  completion  of  the  experiment,  the  amount  of  aqueous 
vapor  is  known  by  the  increase  of  weight  in  the  sulphuric  acid  tubes ;  and 
the  amount  of  carbonic  acid,  by  the  increase  in  the  potassa  tubes.  Reducing 
these  quantities  to  volumes,  and  dividing  the  whole  amount  of  air  by  the 
volumes,  the  proportions  of  both  of  these  constituents  may  be  determined. 

The  quantity  of  carbonic  acid  amounts  to  from  3*7  to  6'2  measures  in 
10,000  :  or  on  an  average  about  l-2000th  part  by  volume.  According  to 
Saussure,  the  proportion  varies  with  the  season.  The  air  in  a  meadow,  in 
August,  contained  0-000713  ;  in  January,  0000479  ;  in  November,  in  rainy 
and  stormy  weather,  0  000425.  Dal  ton  estimates  the  carbonic  acid  at  0  001 ; 
Configliachi,  the  maximum  at  0008  ;  and  Humboldt  (probably  an  excess) 
at  0'005  to  O'OIS.  Saussure  and  Gay-Lussac  found  the  usual  proportion  of 
carbonic  acid  in  the  air  from  the  summit  of  Mont  Blanc,  and  4000  feet 
above  Paris.  Beauvais  found  scarcely  a  trace  of  carbonic  acid  in  the  air 
over  the  sea  off  Dieppe,  but  the  usual  proportion  inland. — (L.  Gmelin.) 

Carbonic  acid  is  in  such  small  proportion  in  air,  that  lime-water  indicates 
no  trace  of  its  presence  in  200  cubic  inches  contained  in  a  closed  bottle. 
In  air  taken  from  low  and  confined  situations,  as  wells  and  cellars,  the  car- 
bonic acid  may  amount  to  from  3  to  10  per  cent.  Air  suspected  to  be 
strongly  impregnated  with  this  gas,  may  be  thus  tested.  Fill  a  long,  narrow 
tube  with  lime-water,  and  invert  it  on  the  water-bath  ;  pass  up  through  the 
lime- water  a  few  cubic  inches  of  the  suspected  air.  If  the  carbonic  acid  is  in 
undue  proportion,  this  will  be  made  evident  by  the  lime-water  acquiring  on 
its  surface  a  milky  appearance,  owing  to  the  production  of  carbonate  of  lime. 
Carbonic  acid  is  stated  to  be  contained  in  air,  in  greater  proportion  in 
summer  than  in  winter— at  night,  than  by  day— in  cloudy,  than  in  fine 
weather— in  dry,  than  in  wet  weather ;  but  there  is  no  doubt  that  the  amount 


AIR,      AQUEOUS    VAPOR    AND    AMMONIA.  163 

of  this  gas  is  kept  down  partly  by  its  great  solubility  in  water  and  its 
removal  by  rain  ;  and  partly  by  vegetation.  In  the  latter  case  the  gas  is 
decomposed,  and  oxygen  is  set  free.  The  great  sources  of  carbonic  acid  are 
combustion,  respiration,  putrefaction,  decay,  and  fermentation. 

The  relative  quantity  of  aqueous  vapoi-  in  the  atmosphere,  is  subject  to 
much  variation.  From  the  experiments  of  Saussure,  Dalton,  and  Ure, 
already  referred  to,  it  appears  that  100  cubic  inches  of  atmospheric  air  at 
57°,  are  capable  of  retaining  0-35  grains  of  watery  vapor;  in  this  state,  the 
air  may  be  considered  at  its  maximum  of  humidity.  It  would  also  appear 
that  all  gases  not  condensable  by  water,  take  up  the  same  quantity  of  water 
when  placed  under  similar  circumstances,  and  that  it  consequently  depends, 
not  npon  the  density  or  composition,  but  upon  the  bulk  of  the  gas.  From 
Dalton's  researches,  it  may  be  concluded  that  the  vapor  forms  an  independent 
atmosphere,  mixed,  but  not  combined  with  air. 

The  proportion  of  water  diffused  as  a  vapor  in  a  gas  depends  upon  tem- 
perature, and  not  upon  the  pressure  of  the  atmosphere.  The  higher  the 
temperature,  and  the  dryer  the  atmosphere,  the  larger  the  quantity  of  vapor 
taken  up.  As  it  is  the  same  at  mean  temperature,  in  all  gases,  the  pro- 
portions have  been  tabulated,  and  will  be  found  in  the  Appendix.  The 
quantity  by  volume  contained  in  air  at  52°,  is  estimated  to  be  1*42  per  cent., 
or  about  5  to  12  grains  in  a  cubic  foot.  In  air  already  saturated  with  it 
there  is  no  evaporation.  The  presence  of  aqueous  vapor  in  air,  is  not  only 
necessary  to  vegetation,  but  is  indispensable  to  the  respiration  of  animals. 
Dry  air  produces  an  irritative  effect  on  the  air  passages  and  lungs. 

Ammonia  is  known  to  be  a  constituent  of  air,  but  in  very  small  propor- 
tion. It  is  detected  by  passing  a  large  quantity  of  air  through  a  vessel 
containing  hydrochloric  acid  diluted  with  water.  After  operating  on  a  con- 
siderable quantity  of  air,  chloride  of  platinum  is  added  to  the  acid  liquid, 
which  is  then  evaporated,  and  the  amraonio-chloride  of  platinum,  after  wash- 
ing with  alcohol  to  remove  any  chloride  of  platinum,  is  collected,  dried,  and 
weighed.  From  this  weight  the  proportion  of  ammonia  in  air  is  deduced. 
M.  Grseger  found  that  the  quantity  was  0-000,000,333  of  the  weight  of  air. 
Kemp  found  a  larger  proportion,  namely,  0 '000,003, 88,  and  Fresenius 
0000,000,133.  Horsford,  of  the  United  States,  has  endeavored  to  de- 
termine the  proportion  in  America,  and  has  arrived  at  the  conclusion  that  a 
million  parts  of  air  by  weight  contain  from  1  to  42  parts  of  ammonia,  the  mini- 
mum amount  being  found  in  December,  and  the  maximum  in  August.  It  is 
probable  that  this  constituent,  although  small,  may  serve  an  important  pur- 
pose in  reference  to  vegetation. 

The  great  variation  in  these  results  shows  that  the  proportion  of  ammonia 
cannot  be  accurately  defined.  It  may  be  described  like  some  acid  vapors, 
as  existing  only  in  traces. 

Organic  matter  is  found  in  the  atmosphere,  especially  in  inhabited  locali- 
ties, or  where  animal  or  vegetable  matter  is  undergoing  decomposition.  It 
is  this  which  gives  the  foul  odor  to  closely  confined  rooms,  in  which  many 
persons  have  breathed  without  due  ventilation.  Dr.  Angus  Smith  has 
endeavored  to  determine  the  proportion  present  in  ^air,  by  noticing  how 
many  measures  of  air  were  required  to  remove  the  color  from  a  weak  stan- 
dard solution  of  the  permanganate  of  soda,  or  potassa.  The  larger  the 
amount  of  organic  matter,  the  smaller  the  quantity  of  air  required  to  cause 
the  permanganate  to  lose  its  characteristic  pink  color.  He  has  called  this 
instrument  the  sepometer.  He  states  that  he  has  found  a  considerable  differ- 
ence in  the  results  of  experiments  on  the  air  of  towns,  of  the  country,  and 
of  the  sea-coast.     The  state  of  ventilation  in  a  room  can,  according  to  him, 


I 


'V"i*" 


164  ORGANIC    MATTER    IN    AIR. 

be  determined  by  it,  and  it  has  enabled  him  to  register  degrees  of  impurity 
in  air,  which  could  not  be  detected  by  the  smell. 

He  found  that  equal  quantities  of  a  standard  solution  of  the  alkaline  per- 
manganate were  decolorized  by  22  measures  of  air,  from  the  high  ground  of 
Lancashire — by  9  from  an  open  street  in  Manchester — by  5-5  from  some 
small  houses  on  the  Medlock — by  2  from  a  railway  carriage  full  of  passen- 
gers, and  by  1  from  the  back  yard  of  a  house  in  a  low  and  ill-ventilated 
neighborhood. 

The  results  of  his  experiments  show  that  on  some  of  the  Swiss  lakes,  and 
on  the  German  Ocean,  sixty  miles  from  land,  the  sepometer  indicated,  in  the 
air,  but  a  small  amount  of  organic  matter,  or  of  matter  capable  of  decolor- 
izing the  test  solution.  The  maximum  effects  were  produced  by  air  from  a 
house  kept  close,  and  from  a  pigstye  recently  uncovered.  In  the  subjoined 
table  we  give  from  Dr.  Smith's  remarks  the  relative  amount  of  organic  and 
oxidizable  matters  diffused  in  air  taken  from  different  localities.  An  equal 
measure  of  air  showed  the  following  relative  quantities  in — 

Manchester  (average  of  131  experiments) 52-9 

"  All  Saints,  E.    wind  (37  experiments         ....     52-4 

"  "  W.  wind,  less  smoky  (33  experiments)    .         .49-1 

"  East  wind,  above  70°  Falir.  (16  experiments)    .         .         .     58*4 

"  "  below        "  (21  experiments)    .         .         .     48-6 

"  In  a  house  kept  rather  close 60-7 

In  a  pigstye  uncovered 109*7 

Thames  at  City,  no  odor  perceived  after  the  warmest  weather  of  1858     58-4 

Thames  at  Lambeth 43*2 

"  Waterloo  Bridge 43-2 

London  in  warm  weather  (six  experiments)         .....     29*2 

"     after  a  thunderstorm .         .12*3 

In  the  fields  S.  of  Manchester 13-7 

"  N.  of  Highgate,  wind  from  London 12-3 

Fields  during  warm  weather  in  N.  Italy 6'6 

Moist  fields  near  Milan 18-1 

Open  sea,  calm  (German,  Ocean  60  miles  from  Yarmouth)  .         .         .       3*3 
Hospice  of  St.  Bernard,  in  a  fog  .         .         .         ,         ,         .         .         .2*8 

N.  Lancashire about  same 

Forest  at  Chamouni     .         .         . 2-8 

Lake  Lucerne      .         . 1*4 

The  operation  of  the  permanganate  clearly  depends  on  the  oxidation  of 
organic  matter,  probably  as  a  result  of  the  ozone  associated  with  this  salt 
(page  112).  There  can  be  no  doubt  that  organic  matter  possesses  the 
property  here  ascribed  to  it,  and  that  in  localities  where  ozone  is  least  to  be 
detected  in  air,  the  largest  amount  of  permanganate  will  be  deprived  of  its 
color.  At  the  same  time,  the  results  are  open  to  the  objection  that  sul- 
phurous acid,  sulphuretted  hydrogen,  and  other  volatile  deoxidizing  com- 
pounds, will  equally  discharge  the  color  of  an  alkaline  permanganate, 
whether  organic  matter  is  or  is  not  present.  Hence  provision  should  be 
made  for  the  removal  of  these  agents  before  the  air  is  submitted  to  this 
method  of  testing. 

The  composition  of  the  air,  excluding  ammonia,  organic  matter,  and  other 
casual  constituents,  may  be  thus  stated,  for  1000  and  100  parts  by  volume 
respectively  : — 

In  1000  vols.  In  100  vols. 

Oxygen 208-0  20-80 

Nitrogen 777-0  77-70 

Aqueous  vapor 14-6  1-46 

Carbonic  acid 0-4  0-04 

1000-0  100-00 


AIR.      UNIFORMITY    OP    COMPOSITION.  165 

Hie  air,  not  a  chemical  compound. — The  proportions  of  oxygen  and  nitro- 
gen nearly  approach  to  1  vol.  or  2  eq.  of  oxygen,  and  4  vol.  or  eq.  of  nitrogen. 
This  ratio,  however,  would  give  a  percentage  of  20  of  oxygen  to  80  of  nitro- 
gen, proportions  that  are  never  found.  The  gases  are  therefore  not  com- 
bined in  equivalents,  either  by  weight  or  volume.  As  an  additional  proof 
that  the  air  is  a  mere  mixture,  the  following  experiments  may  be  adduced. 
Remove  the  oxygen  from  ajar  of  air  by  phosphorus  or  iron-filings,  and  then 
restore  the  loss  by  an  addition  of  pure  oxygen.  The  gases  will  diffuse  or 
enter  into  mixture  without  any  of  the  phenomena  that  accompany  chemical 
union,  and  a  candle  will  burn  in  this  mixture,  as  it  does  in  air.  There  is  no 
alteration  in  volume,  no  evolution  of  heat  or  light,  and  the  specific  gravity, 
magnetism,  refractive  power,  and  solubility  in  water,  of  this  mixture,  cor- 
respond to  the  mean  specific  gravity,  and  other  properties  of  the  constitu- 
ents. The  solvent  power  of  water  is  such  as  would  be  exercised  upon  a 
mixture,  and  not  upon  a  chemical  compound  of  the  two  gases.  Thus  oxygen 
is  dissolved  in  larger  proportion  than  nitrogen,  and  the  difference  nearly 
corresponds  to  the  difference  existing  in  the  solubility  of  the  two  gases,  in 
their  separate  states.  Thus,  according  to  Regnault,  of  100  parts  of  air 
dissolved  by  water,  the  oxygen  is  to  the  nitrogen  as  32  to  68,  instead  of 
20*8  to  792  ;  while  the  solubility  of  each  gas  gives  a  calculated  proportion 
of  31-5  to  68-5.     Thus:— 

Calciilated  Actual 

Solnbility.  Solubility.        Solubility. 

Oxygen  .        .         .     0-046     (0     =     0-0092     or    31-5  32 

Nitrogen        .         .         .     0-025     (t)     =     0-0200     or     68-5  68 


Air  in  water 100-  100 

Lastly,  metals  and  metalloids  act  upon  air  in  the  same  manner  as  if  the 
gases  were  free.  Potassium,  sodium,  lead  in  the  melted  state,  phosphorus, 
and  deutoxide  of  nitrogen,  take  the  oxygen  of  air,  just  as  they  take  oxygen 
in  the  free  or  uncorabined  state. 

It  has  been  supposed  that  the  comparative  uniformity  of  composition  iu 
all  parts  of  the  globe,  and  at  all  elevations  above  the  sea,  could  only  admit 
of  explanation  on  the  theory  that  the  two  gases  were  chemically  combined. 
The  laws  of  diffusion,  however,  sufficiently  account  for  the  uniformity  of 
mixture  (page  85),  while  at  the  same  time,  the  ascertained  differences  in  the 
proportions  of  oxygen  and  nitrogen  are  not  reconcilable  with  the  theory  of 
their  being  chemically  united.  Taking  the  proportion  of  oxygen  by  weight 
elsewhere  given  (page  161),  namely,  23  1  parts  in  100,  the  following  are 
comparative  results  of  the  analysis  of  air  in  different  localities  : — 


Wt.  of  0. 

Wt.ofO. 

per  cent. 

per.  cent. 

Paris  (April  to  Sept.  1841) 

23-07 

Guadaloupe  (W.  I.) 

.     22-97 

"     another  observation 

23-13 

Copenhagen 

.     23-01 

Bern  (Switzerland)  . 

22-95 

Elsinore    . 

.     23-03 

Faulhorn  (18,800  feet)      . 

22-98 

German  Ocean . 

.     22-86 

Other  comparisons  may  be  instituted  in  reference  to  its  composition  by 
volume.  Assuming  the  average  proportion  of  oxygen  by  volume  to  be 
2080,  the  following  results  have  been  obtained  : 

Vol.  of  0.  Vol.  of  0. 

per  cent.  per  cent. 

Paris        ....     20-93  Mont  Blanc  (6000  feet)     .     20-20 

London  level  of  sea  .         .     20-92  "       summit  (16,000  ft.)     20-96 

"       18,000  ft.  elevation     20-88  Simplon  (6000  feet)           .     19-98 

Heidelberg        .         .         .     20-95  Waugen  Alp  (4000  feet)  .     20-45 


166      '  PROTOXIDE  OF  NITROGEN. 


Vol.  of  0. 

Vol.  of  0 

per  cent. 

per  cent. 

Berlin 

.     20-90 

Aerial  ascent  (9000  feet)  . 

.     20-70 

Madrid     . 

.     20-91 

In  Manchester  . 

.     20-88 

Geneva     . 

.     20-90 

In  open  places  . 

.     21-10 

Lyons 

'.     20-91 

In  open  country 

.     21-00 

Helvellyn  (3000  feet) 

.     20-58 

In  crowded  rooms     . 

.     21-42 

Snowdon  (3570  feet) 

.     20-65 

Polar  sea  ... 

.     20-85 

During  the  period  of  about  sixty  years,  within  which  accurate  analyses  of 
the  atmosphere  have  been  made,  there  has  been  no  greater  difference  in  the 
proportions  of  its  constituents,  than  that  which  is  above  shown  to  exist 
between  any  two  localities  at  the  present  time.  There  has  been  no  apparent 
diminution  in  the  amount  of  oxygen  and  nitrogen. 

Tests  for  Air. — These  are  necessarily  included  in  the  tests  for  oxygen  and 
nitrogen.  The  presence  of  nitrogen  so  affects  the  combustion  of  bodies  in 
air,  that  the  burning  of  a  candle  furnishes  a  good  test  of  the  atmospheric 
mixture.  The  red  acid  vapor  produced  by  adding  to  air,  deutoxide  of  nitro- 
gen, and  the  entire  removal  of  oxygen  by  the  pyrogallate  of  potassa,  with  the 
negative  properties  of  the  residuary  gas,  nitrogen,  are  sufficient  to  identify 
the  mixture  under  all  circumstances. 


CHAPTER    XIII. 

COMPOUNDS   OF  NITROGEN    AND    OXYGEN.      NITRIC   ACID. 

There  are  five  compounds  of  nitrogen  and  oxygen — two  neutral  gases 
and  three  acids.  In  these  compounds  the  equivalents  of  oxygen  undergo  a 
regular  arithmetical  increase. 

They  are  as  follow  : — 

Nentral.  Acid. 

Protoxide     NO  Hyponitrous  acid  NO3 

Deutoxide    NOg  Nitrous  acid  NO^ 

Nitric  acid  NO. 

1,  Protoxide  of  Nitrogen.  Nitrous  Oxide  (NO). — This  gaseous  com- 
pound was  discovered  by  Priestley  in  17t6:  but  its  properties  were  not 
fully  known  until  after  the  researches  of  Davy  in  1800. 

Preparation. — The  gas  may  be  procured  by  heating  in  a  glass  retort  the 
crystals  of  pure  nitrate  of  ammonia.  The  temperature  should  not  exceed 
400°,  and  the  salt,  which  speedily  melts,  should  be  kept  in  a  state  of  gentle 
ebullition.  The  gas,  being  very  soluble  in  water,  in  order  to  prevent  loss, 
should  be  collected  in  a  small  water-bath,  containing  tepid  water.  In  this 
case,  however,  it  always  becomes  mixed  with  much  air  on  cooling.  The  salt 
is  entirely  resolved  by  heat  into  water  and  protoxide  (NHj,HO,N05,=2NO 
-f  4H0).  One  ounce  of  the  nitrate  will  give  500  cubic  inches,  or  nearly  two 
gallons  of  the  gas. 

If,  during  the  process,  the  liquefied  salt  should  be  overheated,  the  gas 
comes  over  with  explosive  violence,  sometimes  breaking  the  retort,  or  leading 
to  the  production  of  nitrogen  as  well  as  deutoxide,  and  thereby  rendering  it 
impure.  The  production  of  copious  white  vapors  in  the  retort  is  a  sign 
that  the  proper  heat  has  been  exceeded.  If  the  nitrate  contains  hydro- 
chlorate  of  ammonia,  chlorine  may  be  evolved,  and  impart  to  the  gas  its  pecu- 


PROTOXIDE  OF  NITROGEN.  IGY 

liar  odor  as  well  as  bleaching  properties.  The  presence  of  hydrochl orate  in 
the  nitrate  of  ammonia  may  be  known  by  the  solution  of  this  salt  giving  a 
white  precipitate  with  a  solution  of  nitrate  of  silver.  If  any  deutoxide  of 
nitrogen  is  mixed  with  the  gas,  this  may  be  detected  by  the  production  of 
red  acid  fumes  on  exposing  the  gas  to  the  air,  or  by  the  dark  color  imparted 
to  a  fresh  solution  of  protosnlphate  of  iron  when  added  to  a  jar  of  the  gas. 
If  the  protoxide  is  intended  for  respiration,  it  is  necessary,  in  the  first  in- 
stance, to  test  it  for  these  noxious  impurities.  It  may  be  deprived  of  any 
traces  of  chlorine  and  deutoxide  by  passing  it  through  a  solution  of  potassa 
before  collecting  it. 

Properties. — Protoxide  of  nitrogen  is  not  a  permanently  elastic  gas.  It 
may  be  liquefied  by  great  pressure  (p.  80).  The  liquid  protoxide  mixed 
with  sulphide  of  carbon  produces,  by  rapid  evaporation,  the  greatest  degree 
of  cold  yet  observed  ;  namely,  220°  below  the  zero  of  Fahrenheit  (p.  80). 
The  gas  itself  is  solidified  at  about  150*^  below  zero.  The  cold  produced 
by  the  evaporation  of  the  liquid  protoxide,  placed  in  vacuo,  is  sufficient  to 
solidify  it ;  under  atmospheric  pressure  it  evaporates  slowly.  Liquid  mer- 
cury sinks  in  it  and  is  instantly  frozen  to  a  solid.  A  piece  of  red-hot  char- 
coal will  at  the  same  time  float  on  it,  and  burn  brilliantly  wherever  it  touches 
the  liquid.  The  gas  is  colorless  ;  it  has  a  slight  odor  and  a  sweet  taste.  It 
is  soluble  in  water,  and  this  solubility  leads  to  a  great  loss  of  the  gas  when 
it  is  allowed  to  stand  in  contact  with  water.  Cold  water  will  dissolve  about 
its  own  volume,  but  the  gas  will  be  again  given  out  on  boiling  the  solution. 
Its  admixture  with  air  may  thus  be  known,  as  the  gas  should  be  entirely 
removed  by  its  volume  of  water.  It  is  quite  neutral  when  pure;  it  neither 
reddens  nor  bleaches  litmus. 

As  it  contains  half  its  volume  of  oxygen  it  possesses  some  of  the  proper- 
ties of  that  gas,  modified,  however,  by  the  presence  of  nitrogen.  Thus  it 
supports  combustion.  A  taper  burns  in  it  vividly,  and  is  rapidly  consumed. 
Like  oxygen,  it  kindles  into  flame  a  glowing  wick,  a  glowing  splint  of  wood 
or  ignited  nitre-paper.  Sulphide  of  carbon  or  ether  inflamed  on  tow,  and 
introduced  into  this  gas,  burns  with  great  splendor.  In  these  cases  there  is 
a  halo  of  a  peculiar  reddish  color  around  the  flames,  arising  probably  from 
the  combustion  or  incandescence  of  nitrogen  at  a  high  temperature.  Sulphur 
and  phosphorus  require  to  be  strongly  heated  before  they  will  burn  in  this 
gas.  Iron  does  not  burn  in  it,  and  charcoal  only  glows  in  it  when  intensely 
heated,  producing  carbonic  acid.  It  differs  from  oxygen — 1st,  in  its  great 
solubility  in  water;  and  2d,  when  free  from  air,  in  the  fact  that  it  produces 
no  red  fumes  when  the  deutoxide  of  nitrogen  is  added  to  it.  This  gas  is  a 
narcotic  poison,  and,  when  breathed,  rapidly  destroys  the  life  of  an  animal. 
It  may,  however,  be  taken  by  a  human  being  in  limited  quantity ;  and  if  the 
lungs  be  emptied  before  it  is  inhaled,  it  rapidly  causes  a  peculiar  species  of 
intoxication,  manifested  at  first  by  unsteadiness  of  gait,  and  subsequently  by 
violent  muscular  exertion.  There  is  a  brilliant  flow  of  ideas,  with,  generally 
speaking,  a  great  disposition  to  pugnacity.  From  the  pleasing  kind  of  deli- 
rium which  it  produces  it  has  been  called  "  the  laughing  or  paradise  gas." 
When  breathed,  it  is  rapidly  absorbed  into  the  blood,  and  produces  a  great 
change  in  that  fluid — manifested  by  a  dark-purple  color  of  the  lips,  and  by 
a  livid  or  pallid  appearance  of  the  face.  Some  have  fallen  down  at  once 
powerless,  but  the  greater  number  are  thrown  into  a  state  of  violent  excite- 
ment, running  swiftly  from  the  spot  and  scattering  everything  before  them. 
Some  dance,  others  sing,  and  some  make  speeches  of  an  incoherent  kind, 
evidently  under  the  impression  that  they  are  masters  of  elocution.  An  in- 
stance is  referred  to  by  Sir  David  Brewster,  in  which  the  effects  were  mani- 
fested by  an  uncommon  disposition  for  pleasantry  and  mirth,  and  by  extra- 


I 


168  DEUTOXIDE    OF    NriROGEN. 

ordinary  innscular  power,  in  a  person  of  gloomy  mind.  The  effects  continued 
in  a  greater  or  less  degree  for  more  than  a  week.  In  general  the  exhilarating 
effects  pass  off  in  from  five  to  ten  minutes,  and,  with  the  exception  of  some 
prostration  of  strength  and  slight  headache,  no  injurious  symptoms  have 
followed.  It  is  right  to  state,  however,  that  in  certain  cases,  probably  from 
idiosyncrasy,  the  respiration  of  the  gas  has  been  attended  with  severe  head- 
ache, giddiness,  double  vision,  and  even  some  delirium,  wi^i  a  feeling  of 
weakness  from  exhaustion  lasting  for  several  days.  It  is  not  to  be  regarded 
as  an  anaesthetic,  like  chloroform  or  ether-vapor.  It  is  a  powerful  excitent 
and  stimulant  to  the  nervous  system. 

Composition. — At  a  full  red-heat  this  gas  is  decomposed,  and  two  volumes 
of  it  are  resolved  into  two  volumes  of  nitrogen  and  one  volume  of  oxygen, 
so  that  it  acquires  an  increase  of  bulk.  The  analysis  of  the  gas  may  be 
effected  by  detonation  with  hydrogen.  When  a  mixture  of  one  volume  of 
the  protoxide  and  one  volume  of  hydrogen  is  fired  by  the  electric  spark, 
water  is  produced,  and  one  volume  of  nitrogen  remains  (NO 4-11=110 -j-N). 
Now,  as  one  volume  of  hydrogen  takes  half  a  volume  of  oxygen  to  form  water, 
the  protoxide  must  consist  of  one  volume  or  equivalent  of  nitrogen  and 
half  a  volume  or  an  equivalent  of  oxygen;  these  being  so  condensed,  in  con- 
sequence of  chemical  union,  as  only  to  fill  the  space  of  one  volume.  The 
decomposition  of  one  volume  of  the  gas,  by  heating  in  it  the  metal  potassium, 
gives  the  same  results.     One  volume  of  nitrogen  is  left  as  a  residue. 

Atoms.       Equiv.         Per  cent.  Vol.  Sp.  Gr. 

Nitrogen      .         .        .         .     1     =     14     ...     63-6     ...     1-0     ...     0-97 
Oxygen        .         .         .         .1=8...     36*4     ...     0-5     ...     0-55 


Protoxide  of  nitrogen  .         .     1  22  100-0  1-0  1-52 

The  specific  gravity  and  equivalent  of  this  gas  are  the  same  as  those  of 
carbonic  acid.  One  hundred  cubic  inches  of  it  weigh  47  08  grains.  It  is, 
therefore,  half  again  as  heavy  as  the  atmosphere.  If  a  lighted  taper  be 
placed  at  the  bottom  of  a  tall  jar  of  air,  the  gas  may  be  poured  into  this  jar, 
and  the  fact  that  it  falls  to  the  bottom,  will  be  indicated  by  the  increased 
brilliancy  in  the  combustion  of  the  taper.  If  a  tall  jar  containing  the  gas, 
be  left  uncovered  for  some  time,  it  will  be  found,  by  occasionally  introducing 
a  taper  with  a  glowing  wick,  that  this  will  be  kindled  into  flame,  proving 
that,  by  reason  of  its  density,  the  gas  still  remains  there.  So  if  ignited 
nitre-pajier  be  brought  over  a  jar  of  the  gas,  the  smoke,  instead  of  suddenly 
falling  through  it  as  through  air,  will  float  in  the  form  of  a  dense  cloud  on 
the  top  of  the  gas. 

This  gas  enters  into  no  combinations  which  call  for  remark.  It  has  been 
artificially  produced  by  the  slow  deoxidation  of  nitric  acid,  as  where  one 
part  of  nitric  acid  is  diluted  with  from  12  to  16  parts  of  water,  and  some 
granulated  zinc  is  added  to  the  liquid. 

Tests. — The  properties  already  described  are  sufficient  for  its  identification. 
It  is  known  from  all  other  gases,  excepting  oxygen,  by  its  effects  .on  com- 
bustible bodies,  and  from  oxygen  by  the  negative  action  of  deutoxide  of 
nitrogen  and  its  insolubility  in  a  solution  of  green  sulphate  of  iron. 

Deutoxide  of  Nitrogen  (NOJ. — Binoxide  of  Nitrogen.  Nitric  Oxide. 
Nitrous  Gas. — This  gas  was  first  accurately  described  by  Priestley  in  1772. 
It  may  be  procured  by  putting  some  copper-filings  or  clippings  into  a  gas- 
bottle  with  nitric  acid  diluted  with  two  or  three  parts  of  water  ;  the  acid  is 
decomposed,  red  fumes  are  produced,  and  there  is  a  copious  evolution  of  the 
gas,  which  may  be  collected  and  preserved  over  water.     In  this  mode  of 


PROPERTIES    OF    THE    GAS.  169 

obtainiiip:  the  gas,  3  atoms  of  copper  and  4  of  nitric  acid  produce  3  of  nitrate 
of  copper  and  1  of  nitric  oxide,  4N05  +  3Cu  =  3[CuO,XOJ  +  N02.  The 
first  portions  should  be  rejected,  as  containing  nitrogen  and  nitrous  acid 
vapor.  The  latter  being  soluble  in  water  is  speedily  removed.  Protoxide 
of  nitrogen  is  frequently  present  in  the  gas  when  first  prepared.  This  may 
be  removed  by  allowing  it  to  stand  for  some  hours  over  water. 

Properties. — The  deutoxide  of  nitrogen  is  a  colorless,  neutral,  unliquefiable 
gas;  its  specific  gravity  compared  to  hydrogen  is  as  15  to  1.  100  cubic 
inches  weigh  32-10  grains  ;  and,  compared  with  air,  its  specific  gravity  is  as 
10366  to  1000.  Under  common  circumstances,  it  is  permanent  over  water; 
but  if  agitated  with  water  previously  deprived  of  air  by  long  boiling,  it  is 
dissolved  in  the  proportion  of  about  1  volume  to  20.  This  solution,  when 
long  kept,  is  found  to  contain  nitrate  of  ammonia,  resulting  from  the  joint 
decomposition  of  the  deutoxide  and  the  water. 

It  is  rapidly  fatal  to  animals;  but  as  it  will  always  meet  with  a  sufficiency 
of  oxygen  in  the  lungs,  to  convert  a  part  of  it  into  nitrous  acid,  the  noxious 
effects  observed  may  have  depended  on  this  acid.  When  the  gas  has  been 
well  washed  with  water,  it  is  not  acid,  a  fact  which  may  be  proved  by  the 
color  of  litmus  remaining  unchanged  by  it.  The  experiment  may  be  thus 
performed  :  After  having  washed  the  jar  (which  should  contain  no  water), 
and  the  plate  which  confines  the  gas,  introduce  it  into  a  basin  of  blue  litmus, 
and  withdraw  the  cover.  The  gas  may  thus  remain  in  the  litmus  without 
altering  the  blue  color  ;  but  when  the  jar  is  raised  out  of  the  liquid,  so  as  to 
admit  a  portion  of  air,  red  acid  fumes  are  produced,  and  upon  again  plunging 
it  into  the  litmus,  the  liquor  will  be  reddened  and  the  acid  vapors  absorbed. 
The  red  fumes  which  are  formed  when  the  gas  is  exposed  to  air  are  those  of 
nitrous  acid  (N02  +  20  =  NOJ.  They  have  a  peculiar  suffocating  odor,  and 
are  highly  irritating  and  corrosive.  Care  should  be  taken  that  they  are  not 
breathed,  even  in  a  diluted  state. 

The  gas,  if  free  from  protoxide,  extinguishes  the  flame  of  a  taper,  ignited 
camphor,  and  sulphur.  Phosphorus  readily  burns  in  it  if  introduced  in 
intense  ignition;  but  it  is  extinguished  unless  in  vivid  combustion,  and  it 
may  be  touched  with  a  hot  wire  in  the  gas,  without  taking  fire.  Boiling 
phosphorus  decomposes  the  gas,  nitrogen  is  evolved,  and  phosphoric  acid 
is  formed. 

If  dry  nitre-paper  is  ignited  and  suddenly  plunged  into  this  gas,  it  will 
continue  to  glow,  chiefly  at  the  expense  of  the  oxygen  of  the  nitrous  acid, 
produced  when  the  jar  is  uncovered.  It  is  remarkable  that  this  gas  should 
not  support  the  combustion  of  a  taper,  since  it  contains,  in  equal  volumes, 
as  much  oxygen  as  the  protoxide,  and  only  half  the  quantity  of  nitrogen.  If 
mixed  with  the  protoxide,  it  will  readily  support  combustion.  Potassium 
and  sodium,  when  heated  to  ignition  in  air,  burn  in  this  gas  with  great  splen- 
dor :  sodium  burns  with  a  light  which  rivals  that  of  phosphorus.  The  com- 
bustion may  be  effected  by  throwing  a  portion  of  the  metal  into  a  jar  of  the 
gas  having  at  the  bottom  a  thin  stratum  of  water.  It  is  decomposed  when 
passed  over  charcoal  at  a  red  heat— carbonic  acid  is  formed  and  nitrogen  is 
set  free,  NO^+C^N  +  COa,  but  neither  charcoal  nor  sulphur  will  burn  in 
this  gas.  If  introduced  in  a  state  of  ignition  they  are  extinguished,  but  the 
vapor  of  sulphide  of  carbon  mixed  with  the  deutoxide  and  ignited,  completely 
decomposes  it  with  the  evolution  of  the  most  intense  light,  and  the  produc- 
tion of  carbonic  and  sulphurous  acids  at  the  expense  of  its  oxygen,  (3NO2+ 
CSa=2S03+COa+3X).  For  the  performance  of  this  experiment,  we  may 
employ  a  stout  jar,  holding  200  cubic  inches  of  deutoxide.  About  a  drachm 
of  the  sulphide  should  be  poured  into  the  jar,  which  should  be  agitated,  in 
order  to  promote  the  diffusion  or  the  vapor  before  the  mixture  is  ignited. 


ITO  DEUTOXIDE    OF    NITROGEN.      COMPOSITION. 

Deutoxide  of  nitrogen  is  not  altered  by  a  low  red  heat,  but  it  is  decom- 
posed when  passed  and  repassed  through  small  tubes  heated  to  bright  red- 
ness, especially  if  the  heated  surface  is  increased  by  filling  the  tubes  with 
fragments  of  rock  crystal,  or  by  the  introduction  of  platinum  wire.  It  does 
not  detonate  when  mixed  with  two  volumes  of  hydrogen,  all  subjected  to  the 
electric  spark  ;  a  succession  of  sparks,  however,  passed  through  such  a  mix- 
ture, slowly  effects  the  decomposition  of  a  portion.  The  pure  gas  is  itself 
partially  decomposed  by  a  succession  of  sparks  into  nitric  acid  and  nitrogen. 
When  mixed  in  equal  volumes  with  hydrogen,  and  the  mixture  is  kindled,  it 
burns  with  a  greenish-white  flame  and  a  reddish-colored  halo  :  but  there  is 
no  explosion.  Water  is  produced  and  nitrogen  is  set  free  (N03-f2H  = 
2H04-N)  When  a  mixture  of  2  volumes  of  this  oxide  and  5  of  hydrogen 
are  passed  through  a  tube  containing  spongy  platinum,  and  after  the  expul- 
sion of  the  air,  the  tube  is  heated,  the  platinum  becomes  ignited,  and  water 
and  ammonia  are  formed  (N02,-f  5H  =  NH3,2HO).  An  inflamed  jet  of 
hydrogen  is  extinguished  in  the  gas.  Some  substances  which  have  a  strong 
attraction  for  oxygen,  effect  a  partial  decomposition  of  the  deutoxide,  and 
convert  it,  at  common  temperatures,  into  the  protoxide  of  nitrogen ;  such, 
for  instance,  as  moist  iron-filings,  some  of  the  alkaline  sulphides,  some  of 
the  sulphites,  and  protochloride  of  tin  ;  in  these  cases  two  volumes  of  the 
deutoxide  produce  one  of  the  protoxide.  Deutoxide  of  nitrogen  may  also 
be  decomposed,  at  high  temperatures,  by  the  action  of  some  of  the  metals 
which  absorb  its  oxygen.  Sir  H.  Davy  decomposed  it  by  heated  arsenic 
and  by  the  ignition  of  charcoal.  {Elements,  260.)  Gay-Lussac  decomposed 
100  measures  of  it  by  the  action  of  heated  potassium  ;  50  measures  of  pure 
nitrogen  remained,  and  the  loss  of  weight  corresponded  to  50  measures  of 
oxygen  ;  so  that  two  volumes  of  the  gas  are  resolved  into  one  volume  of 
oxygen  and  one  volume  of  nitrogen.  Similar  results  have  been  obtained 
by  passing  the  gas  over  copper  turnings  heated  to  redness  in  a  tube.  The 
deutoxide  then  is  constituted  of  one  volume  of  nitrogen  and  one  volume  of 
oxygen,  combined  without  change  of  volume ;  and  its  atomic  constitution 
as  well  as  its  specific  gravity  may  be  thus  represented  : — 


Nitrogen 
Oxygen 

Atoms.        Equ. 

.     1    =    14     . 
.     2    =     16     . 

.     1     =    30 

Per  cent. 

..     46-67     . 
..     53-33     . 

100-00 

Vols. 

..   1    .. 
..   1    .. 

2 

Sp.  Gr. 

.     0-4837 
.     0-5528 

Deutoxide  . 

1-0365 

Pliicker  has  submitted  this  gas  to  spectral  analysis,  in  a  quantity  so 
small  as  to  be  scarcely  recognizable  by  the  most  sensitive  balance.  The 
red  band  of  nitrogen  was  obtained  in  great  splendor,  and  near  to  it  was  a 
bright  band  derived  from  the  oxygen  ;  but  the  latter  was  gradually  extin- 
guished.    A  similar  result  was  obtained  with  protoxide  of  nitrogen. 

The  most  characteristic  chemical  property  of  this  gas,  by  which  it  is 
immediately  distinguished  from  all  other  gases,  is  that  of  forming  red  fumes, 
chiefly  of  nitrous  acid  vapor,  when  mixed  with  air  or  oxygen  (^02+20  = 
NO4) ;  hence  these  gases  are  mutually  used  to  detect  each  other's  presence. 
As  nitrous  acid  is  absorbed  by  water,  oxygen  may  be  abstracted  from  any 
gaseous  mixture  containing  it  by  the  addition  of  a  sufficient  quantity  of  the 
deutoxide;  and,  on  the  other  hand,  the  deutoxide  may  be  removed  by  the 
addition  of  oxygen. 

Solutions  of  the  protochloride  and  protosulphate  of  iron  dissolve  this  gas, 
forming  a  deep  greenish-black  liquid,  having,  in  reference  to  the  sulphate, 
the  following  composition,  (4FeO,S03)-|-N03.  These  solutions  speedily 
absorb  oxygen   when  exposed  to,  or  agitated  with  air,  or  other  mixtures 


HYPONITROUS    ACID.  Itl 

containing  it.  {See  page  161.)  This  property  enables  us  to  ascertain  the 
purity  of  the  deutoxide,  which  ought  wholly  to  be  absorbed  by  the  solution 
of  iron  :  some  nitrogen  or  protoxide  is  thus  generally  detected  in  it,  by 
remaining  unabsorbed.  According  to  Peligot  {Aim.  Ch.  et  Ph.,  54, 
17),  the  proportion  of  the  gas  absorbed  by  protosulphate  of  iron  is 
definite,  and  in  the  ratio  of  one  equivalent  to  4  of  the  protoxide  of  iron,  in 
accordance  with  the  formula  above  given.  By  exposure  to  a  vacuum  the 
gas  escapes,  and  the  salt  of  iron  remains  unaltered  ;  but  when  heated,  a 
part  only  of  the  gas  is  evolved,  and  a  part  is  decomposed,  while  peroxide  of 
iron  and  ammonia  are  formed.  When  this  solution  is  exposed  to  air  or 
oxygen,  nitric  acid  is  ultimately  produced. 

If  the  deutoxide  is  perfectly  dry,  chlorine  exerts  no  action  upon  it,  but 
the  presence  of  water  causes  an  immediate  change ;  it  is  decomposed,  and, 
furnishing  oxygen  to  the  nitric  oxide,  and  hydfogen  to  the  chlorine,  hyponi- 
trous  and  hydrochloric  acids  are  generated.  It  was  the  presence  of  water 
which  misled  those  who  thought  that  the  red  fumes  produced  by  mixing 
deutoxide  and  chlorine  over  water,  resulted  from  the  existence  of  oxygen  in 
chlorine.  These  may,  however,  arise  from  the  presence  of  air  as  impurity  in 
the  chlorine. 

Tests. — This  gas  is  known  by  the  red  acid  fumes  which  it  produces  when 
brought  in  contact  with  air,  and  by  its  entire  solubility  in  a  solution  of 
protosulphate  of  iron. 

Hyponitrous  Acid  (NO3).  Azotous  Acid.  Nitrous  Acid.  Nitric  Ter- 
oxide. — This  compound  is  generally  designated  by  continental  chemists. 
Nitrous  acid.  Gay-Lussac  found  by  mixing  deutoxide  of  nitrogen  and 
oxygen  in  tubes  standing  over  mercury,  and  containing  a  little  concentrated 
solution  of  potassa,  that  400  volumes  of  deutoxide  were  condensed  under 
such  circumstances  by  100  of  oxygen.  When,  however,  he  attemped  to 
decompose  the  hyponitrite  of  potassa  thus  obtained,  nitric  oxide  was  evolved, 
aud  nitrous  acid  formed.  Dulong  obtained  hyponitrous  acid  (mixed  with 
nitrous  acid)  by  passiug  a  mixture  of  1  measure  of  oxygen  with  somewhat 
more  than  4  of  deutoxide,  first  through  a  tube  filled  with  fragments  of 
porcelain  to  insure  perfect  mixture,  and  afterwards  through  a  bent  tube, 
cooled  below  zero.  The  acid  collected  in  the  tube  was  a  dark -green  fluid, 
more  volatile  than  nitrous  acid,  and  when  distilled  leaving  a  yellow  liquid, 
which  appeared  to  be  nitrous  acid.  Liebig  obtained  hyponitrous  acid  by 
heating  1  part  of  starch  in  8  of  nitric  acid,  sp.  gr.  1  -25,  and  conducting  the 
evolved  gases  first  through  a  tube  filled  with  fragments  of  chloride  of  calcium, 
and  then  into  a  tube  cooled  down  to  0^  ;  ,a  very  volatile  liquid  was  thus 
condensed,  colorless  at  10^,  but  green  at  common  temperatures.  According 
to  Fritzsche,  hyponitrous  acid  may  be  obtained  by  gradually  adding,  by 
means  of  a  tube  drawn  out  to  a  fine  point,  45  parts  of  water  (5  atoms)  to  92 
parts  of  nitrous  acid  (2  atoms)  cooled  down  to  zero,  and  distilling  into  a 
receiver,  surrounded  by  a  freezing  mixture,  until  the  boiling-point  rises  to 
82°.  The  product  is  of  an  indigo-blue  color.  Its  vapor  is  orange-colored, 
and  its  boiling  point  rises  to  82°  ;  but  when  distilled,  it  is  partially  decom- 
posed into  deutoxide  and  nitrous  acid.  It  is  very  doubtful  whether,  by  any 
of  these  processes,  the  acid  has  been  yet  obtained  in  an  absolutely  pure  state. 
It  appears  to  be  generally  mixed  with  nitrous  or  nitric  acid.  Its"instability 
is  so  great,  that  it  is  decomposed  by  water  (3N03=N054-2N03)  into  nitric 
acid  and  deutoxide.  It  is  better  known  in  combination  with  bases,  and  its 
composition  has  been  determined  by  the  analysis  of  its  compound  with  silver. 
It  consists  of : — 


172  NITROUS    OR    HYPONITRIC    ACID. 

Atoms.       Equiv.  Volumes.  Volumes. 

Nitiocen     .         ..     1     ...     14     ...     36-8     1    or  2 )        Deutoxide  4 


l]= 


Oxygen       .         .         .     3     ...     24     ...     63-2     IJ  or  3  j  ~  Oxygen       1 
Hyponitrous  acid         .     1  38  100-0 

Hyponitrites  {Nitrites). — When  nitrate  of  potassa,  or  nitrate  of  baryta  is 
strongly  heated,  the  acid  loses  two  atoms  of  oxygen,  and  a  hyponitrite  of  the 
base  is  formed  :  KO,NO.=KO,X034-20.  When  properly  prepared,  a  small 
portion  of  the  fused  residue,  will  give  a  dense  white  precipitate,  with  a  solu- 
tion of  nitrate  of  silver.  If  the  salt  has  been  overheated,  the  precipitate  will 
be  brown.  Hyponitrite  of  potassa  thus  obtained,  is  a  white  deliquescent  salt, 
very  soluble  in  water  and  alcohol.  By  its  solubility  in  alcohol,  it  may  be 
separated  from  any  undecomposed  nitrate.  The  white  precipitate  which  it 
produces  with  nitrate  of  silv^,  is  soluble  in  nitric  acid  as  well  as  in  a  large 
quantity  of  water.  It  may  be  obtained  in  crystals  from  a  hot  saturated  solu; 
tion.  By  double  decomposition  with  the  chloride  of  any  alkaline  metal, 
other  hyponitrites  may  be  obtained.  It  is  impossible  to  procure  hyponitrous 
acid  in  a  free  state  from  these  salts.  When  an  acid  is  added  to  a  hyponitrite, 
deutoxide  of  nitrogen  escapes,  and  a  nitrate  is  formed  (3KO,N03-f2S03  = 
KO,N05+2N03+2KO,S03).  If  an  acid  solution  of  a  hyponitrite  is  warmed, 
it  becomes  a  powerful  deoxidizer  ;  thus  it  discharges  the  pink  color  of  the 
permanganate  of  potassa,  peroxide  of  manganese  being  formed.  From  a 
solution  of  chloride  of  gold,  the  metal  is  precipitated;  the  color  of  a  solution 
of  indigo  is  discharged  by  it,  and  a  solution  of  protosulphate  of  iron  acquires 
a  deep  greenish-black  color.  The  hyponitrites  are  thus  easily  distinguished 
from  the  nitrates,  by  the  action  of  acids,  and  by  their  reducing  agency  on 
solutions  of  gold  and  permanganate  of  potassa.  Some  of  the  hyponitrites 
may  be  produced  by  the  action  of  deutoxide  of  nitrogen  on  the  respective 
alkaline  liquids.  Thus  when  this  gas  is  kept  for  some  weeks  in  contact  with 
a  strong  solution  of  potassa,  it  is  converted  into  protoxide,  and  the  potassa- 
solution  yields  on  evaporation  a  hyponitrite  (2N03+KO=KO,N03-f  NO). 
It  was  this  reaction  which  led  Gay-Lussac  to  the  discovery  of  the  acid.  100 
volumes  of  deutoxide  left  25  of  pi'otoxide :  the  acid,  therefore,  which  was 
absorbed,  consisted  of  100  volumes  of  nitrogen  and  150  of  oxygen.  Accord- 
ing to  Berzelius,  several  of  the  hyponitrites  are  best  obtained  by  boiling 
metallic  lead  in  a  solution  of  nitrate  of  lead,  by  which  a  hyponitrite  of  lead 
is  formed :  this  salt  may  then  be  decomposed  by  sulphates,  which  form  sul- 
phate of  lead,  and  the  hyponitrous  acid  unites  to  the  base  of  the  original 
sulphate.  Mitscherlich  prepares  the  hyponitrites  by  the  mutual  action  of 
soluble  chlorides  and  hyponitrite  of  silver.     {See  Silver.) 

Nitrous  Acid  (NO^).  Hyponitric  Acid.  Hypoazotic  Acid.  ,  Peroxide 
of  Nitrogen.  Nitric  Tetroxide. — When  2  volumes  of  deutoxide  of  nitrogen 
and  1  volume  of  oxygen,  dried  by  potash,  are  mixed  in  an  exhausted  glass 
vessel,  the  gases  combine  with  the  evolution  of  heat  consequent  upon  their 
mutual  condensation,  and  form  tiitrous  acid  vapor,  which  is  condensable  into 
a  nearly  colorless  liquid  at  zero,  and  crystallizes  at  a  somewhat  lower  tem- 
perature. The  specific  gravity  of  this  liquid  is  1  45  ;  at  32°  it  is  of  a  pale 
yellow  color;  but  at  60°  deep  orange  :  it  boils  at  82°  (Gay-Lussac)  ;  and 
when  exposed  to  the  air  at  common  temperature,  gradually  evaporates  in 
orange-red  fumes.  When  a  mixture  of  the  gases,  in  the  above  proportions, 
is  propelled  through  a  tube  cooled  to  20°,  the  liquid  acid  is  at  once  obtained  ; 
but  at  16°  it  crystallizes  in  prisms.  If  the  gases  be  mixed  over  water, 
hyponitrous  acid  and  nitric  acid  are  formed  at  low  temperatures,  (2N0.j= 
NOg-fNOJ;  and  at  higher  temperatures  nitric  acid  and  deutoxide  are  the 
results  (3NO^=2N05-f  NOJ.     The  product  of  the  distillation  of  dry  nitrate 


NITROUS    ACID.  113 

of  lead  appears  to  be  nitrons  acid,  nearly,  if  not  qnite,  pure  and  anhydrous 
(PbO,N05=N044-PbO-fO).  The  powdered  nitrate,  previously  well  dried, 
should  be  put  into  a  small  retort,  with  the  beak  drawn  out,  and  introduced 
into  a  small  tube  receiver,  which  should  be  immersed  in  a  freezing  mixture. 
A  strong  heat  is  required  for  the  distillation,  and  when  a  sufficient  quantity 
of  the  liquid  acid  has  been  collected,  the  tube  may  be  sealed  by  applying  the 
flame  of  a  spirit-lamp  to  the  elongated  neck.  It  can  only  be  preserved  in 
sealed  tubes. 

Properties. — Nitrous  acid  vapor  supports  the  combustion  of  phosphorus 
and  of  charcoal,  but  extinguishes  burning  sulphur.  These  experiments  may 
be  performed  on  the  vapor  procured  by  passing  a  jet  of  oxygen  into  a  jar, 
or  bell-glass,  filled  with  deutoxide  of  nitrogen,  until  the  mixture  acquires  an 
orange-red  color.  A  lighted  taper,  as  well  as  ignited  nitre-paper,  glow  in 
this  vapor,  and  continue  to  burn.  The  oxitmiiig  properties  of  the  acid 
vapor,  and  its  power  of  destroying  foul  effluvia,  may  be  shown  by  inverting 
over  a  jar  of  it,  another  containing  sulphuretted  hydrogen  gas.  The  sulphur 
is  separated  with  evolution  of  great  heat  (NO^-f  2HS  =  N03-|-2HO-f  2S). 
A  solution  of  iodide  of  potassium  is  instantly  decomposed  by  it,  an#  the 
iodine  set  free.  A  diluted  solution  of  permanganate  of  potassa  has  its  pink 
color  discharged  by  it  as  a  result  of  deoxidation. 

Its  color,  like  that  of  the  liquid  acid,  varies  with  the  temperature,  becom- 
ing darker  when  heated,  and  paler  when  cooled  ;  it  has  a  peculiar  sufi"ocating 
odor,  which  strongly  adheres  to  the  hair  and  to  woollen  clothing.  The 
anhydrous  liquid  has  no  acid  properties,  and  does  not  apparently  unite  with 
bases,  but  forms  with  them  hyponitrites  and  nitrates  (2N04  +  2KO=KO, 
K05-l-K0,Is03) ;  hence  it  has  been  regarded  as  a  peroxide  of  nitrogen,  or  a 
compound  of  hyponitrous  and  nitric  acids  (2N04=N03+N05).  When 
passed  over  baryta  or  other  bases,  at  a  temperature  of  between  300°  and 
400°,  it  is  rapidly  absorbed  with  the  evolution  of  heat,  and  the  products  are 
a  nitrate  and  a  hyponitrite.   (Gay-Lussac,  Ann.  Ch.  etPh.,  1.) 

Nitrous  acid  vapor  is  constituted  of  1  volume  of  nitrogen,  and  2  volumes 
of  oxygen,  condensed  into  2  volumes,  or,  as  above  stated,  2  volumes  of 
nitric  oxide,  and  1  volume  of  oxygen  (NO^j-f  20=N0J.  Its  specific  gravity, 
therefore,  to  hydrogen,  will  be  as  46  to  1  ;  to  air,  as  1-689  to  1.  It  is 
actually  found  to  be  1*7.     It  is  constituted  of: — 

Atoms.         Equ.        Per  cent.  Vols.  Sp.  Gr. 

Nitrogen  .        .         .         .     1     ...     14     ...     30-4     ...     0-5     ...     0-4837 
Oxjgen    .         .        .         .     4     ...     32     ...     69-6     ...     1-0     ...     1*1057 


Nitrpus  acid     ...     1  46  100-0     ...     1-  1-5894 

Nitrous  acid  vapor  is  not  decomposed  by  a  red  heat,  but  it  is  a  powerful 
oxidizer,  and  parts  with  its  oxygen  readily  to  sulphur,  phosphorus,  and  the 
metals.  When  the  acid  vapor  is  passed  over  metallic  copper  heated  to 
redness,  it  gives  up  its  oxygen  entirely  and  nitrogen  escapes.  By  this  process, 
its  composition  has  been  accurately  determined.  The  acid  is  decomposed  by 
water,  when  this  liquid  is  in  large  proportion,  nitric  acid  being  dissolved 
and  deutoxide  of  nitrogen  escaping  (3N0,-f  2H0  =N02+N05,H0). 
When  the  quantity  of  water  is  small,  although  the  same  products  result, 
the  nitric  acid  holds  the  nitrous  acid  dissolved,  and  acquires,  according  to 
its  specific  gravity,  a  variety  of  colors.  Nitric  acid  of  a  high  specific  gravity 
appears  to  be  the  proper  solvent  of  this  compound,  l^ns  when  saturated 
with  it,  nitric  acid  of  a  specific  gravity  of  1-510  is  of  a  deep  orange  color, 
at  1-410  {aquafortis  of  commerce),  yellow,  at  1*320  greenish -blue,  at  1-150 


174  ANHYDROUS    AND    HYDRATED    NITRIC    ACID. 

colorless.  In  the  latter  case,  the  quantity  of  water  is  so  great  as  to  decom- 
pose the  nitrous  acid  in  solution,  and  to  transform  it  into  colorless  nitric  acid. 

Although  this  acid  does  not  combine  directly  with  alkaline  bases,  it  forms 
a  series  of  remarkable  compounds  with  organic  bases.  M.  Martin's  re- 
searches have  shown  that  some  varieties  of  gun-cotton,  or  pyroxyline,  are 
compounds  of  nitrous  (hyponitric)  acid,  with  this  substance  as  a  base.  The 
fulminating  compound  contains  5  equivalents  of  the  acid,  while  the  photo- 
graphic cotton  contains  4.  The  compound  with  3  equivalents  of  the  acid  is 
of  a  pulverulent  nature,  and  when  dissolved  in  alcoholic  ether,  leaves  an 
opaline  residue  on  evaporation  ;  while  another  compound  with  2  equivalents 
of  acid  is  known  by  its  solubility  in  water.  {Cos7nos,Jmn  28,  1861,  p.  769.) 
The  large  amount  of  oxygen  contained  in  this  acid  accounts  for  the  great 
combustibility  of  the  first  of  these  compounds. 

Nitric  Acid  (NO5)-  NiPic  Pentoxide.  Azotic  Acid. — In  its  monohy- 
drated  state  its  formula  is  H0,N05,  or  H,N06.  The  composition  of  this 
acid  was  first  demonstrated  by  Cavendish,  in  1185.  He  produced  it  by 
passing  a  succession  of  electric  sparks  through  a  mixture  of  1  volumes  of 
oxy^l^  and  3  of  nitrogen.  This  result  has  been  verified*  by  Faraday  {Ex- 
perimental Researches,  3d  series,  §  324),  in  reference  to  the  appearance  of 
minute  quantities  of  nitric  acid  in  the  rain  water  of  thunderstorms.  Nitric 
acid  is  also  formed  when  deutoxide  of  nitrogen  is  slowly  added  to  an  excess 
of  oxygen  gas,  over  water.  In  this  way  4  volumes  of  deutoxide  of  nitrogen 
are  condensed,  and  they  combine  with  3  volumes  of  oxygen.     (N02-4-Og= 

Anhydrous  Nitric  Acid. — Nitric  Anhydride  (NO^)  was  discovered  by 
Deville,  in  1849.  {Ann.  Ch.  et  Ph.,  3me  ser.  vol.  28,  p.  241.)  He  obtained 
it  by  passing  dry  chlorine  over  dry  nitrate  of  silver,  placed  in  a  U-tube,  and 
heated  to  303°.  The  temperature  is  lowered,  when  chemical  action  com- 
mences to  between  136°  and  154°.  The  products  are  chloride  of  silver, 
oxygen,  and  anhydrous  nitric  acid  (AgO,N05+Cl=N05+AgCl-|- 0). 
Some  nitrous  acid  is  at  first  evolved,  but  at  the  low  temperature,  crystalline 
anhydrous  nitric  acid  is  volatilized  and  may  be  condensed  in  a  second  tube, 
surrounded  by  ice.  There  are  many  precautions  requisite  to  insure  the 
success  of  this  operation;  no  organic  matter,  such  as  cork,  &c.,  should  be 
used  in  the  apparatus. 

Anhydrous  nitric  acid  crystallizes  in  colorless  rhombic  prisms.  The  crys- 
tals fuse  at  about  85°:  and  the  liquid  boils  and  is  decomposed  at  113°. 
They  dissolve  in  water,  producing  great  heat,  but  no  gas  is  disengaged. 
The  crystals,  like  those  of  other  anhydrous  acids,  have  no  acid  reaction  until 
dissolved  {see  page  42).  They  are  liable  to  be  decomposed  with  explosion 
at  the  common  temperature,  being  suddenly  converted  into  oxygen  and 
nitrous  acid. 

Hydrated  Nitric  Acid,  Hydric  Nitrate.  Preparation. — (HO,  NO  J  is 
usually  obtained  by  the  distillation  of  purified  nitre  with  sulphuric  acid. 
The  nitric  acid  of  commerce,  which  is  generally  red  and  fuming,  in  conse- 
quence of  the  presence  of  nitrous  acid,  is  procured  by  the  distillation  of  2 
parts  of  nitre  with  1  of  sulphuric  acid ;  these  proportions  yield  about  1  part 
of  orange-colored  nitric  acid  of  the  specific  gravity  of  1-48.  Some  manu- 
facturers employ  3  parts  of  nitre  and  2  sulphuric  acid.  The  British  Phar- 
macopoeia directstwo  pounds  (avoirdupois)  of  nitrate  of  potash,  and  seventeen 
fluidounces  (Imperial  measure)  of  sulphuric  acid.  In  all  cases  the  sulphuric 
acid  should  be  in  l^ge  proportion,  if  we  desire  to  obtain  a  colorless  product, 
and  care  should  be  taken  that  the  distillation  is  carried  on  at  the  lowest 
possible  temperature.  Nitrate  of  soda  being  cheaper  than  nitrate  of  potash, 
is  frequently  resorted  to  as  a  source  of  nitric  acid.      As  nitre  generally 


PROPERTIES    OF    NITRIC    ACID.  1Y5 

contains  a  little  sea  salt,  the  first  portions  of  acid  which  come  over  are  im- 
pure, containing  chlorine  or  hydrochloric  acid  and  nitrous  acid,  but  they  serve 
to  wash  quite  clean  the  neck  of  the  retort,  ou  which  some  sulphuric  acid  is 
commonly  to  be  found,  in  spite  of  all  our  care,  as  well  as  traces  of  powdered 
nitre  ;  it  is  best,  therefore,  to  collect  the  first  portion,  say  one-tenth  of  the 
whole,  in  a  separate  receiver,  and  when  the  liquid  that  drops  is  found  to  be 
free  from  chlorine  (by  the  test  of  nitrate  of  silver),  the  receiver  may  be 
changed,  and  the  rest  of  the  nitric  acid  obtained  quite  pure,  or,  at  most, 
slightly  tinged  by  nitrous  acid.  When  2  equivalents  of  sulphuric  acid  (oil 
of  vitriol)  to  1  of  nitre  are  used,  the  results  are  1  equivalent  of  hydrated 
bisulphate  of  potassa  and  1  of  monohydrated  nitric  acid  ;  KO,N05  +  2[HO, 
SOJ=K6,HO,2S03-f  H0,N05.  When  100  parts  of  nitre,  96-8  of  oil  of 
vitriol,  and  40'45  of  water  are  mixed  and  distilled,  at  2G6°  to  270°,  nitric 
acid,  of  specific  gravity  14,  passes  over  during  the  whole  process.     (Mit- 

BCHERLICH.) 

Oil  of  vitriol  of  the  sp.  gr.  1*84,  contains  one  equivalent  of  dry  sulphuric 
acid  and  one  of  water  ;  whereas  liquid  nitric  acid  usually  contains  one  equiva- 
lent of  dry  acid  and  two  of  water  :  hence  the  requisite  excess  of  oil  of  vitriol, 
when  colorless  and  pure  nitric  acid  is  to  be  obtained ;  hence,  too,  the  red 
color  of  the  acid  of  commerce,  in  consequence  of  the  smaller  quantity  of  oil  of 
vitriol  generally  used  by  the  manufacturer,  the  deficiency  of  water  causing 
the  nitric  acid  to  be  resolved  into  nitrous  acid  and  oxygen. 

The  nitric  acid,  or  aquafortis  of  commerce,  is  always  impure,  and  hydro- 
chloric and  sulphuric  acids  may  generally  be  found  in  it.  The  former  may- 
be detected  by  nitrate  of  silver,  or  by  boiling  in  it  gold  leaf,  when  if  this 
impurity  exists  the  gold  will  be  dissolved.  Sulphuric  acid  may  be  detected 
by  a  diluted  solution  of  nitrate  of  baryta.  If,  however,  pure  nitre  and  pure 
sulphuric  acid  be  employed  in  its  production,  and  the  latter  not  in  excess, 
there  is  little  apprehension  of  impurity  in  the  resulting  acid.  If  the  acid  is 
colored  by  the  presence  of  nitrous  acid,  it  is  rendered  colorless  by  boiling, 
which  is  best  performed  in  a  retort,  with  a  loosely-attached  receiver ;  the 
nitrous  acid  passes  off.  If  it  contain  hydrochloric  acid,  this  is  also  decom- 
posed by  boiling,  and  chlorine  escapes.  Iron  may  generally  be  detected  in 
the  common  acid  by  the  usual  test,  ferrocyanide  of  potassium.  The  acid 
should  be  diluted  and  neutralized  before  applying  the  test.  If  pure,  nitric 
acid  should  leave  no  residue  on  evaporation. 

Properties. — Pure  nitric  acid  is  a  colorless  liquid,  very  acid  and  corrosive, 
acting  powerfully  upon  organic  substances.  Its  specific  gravity,  as  usually 
obtained,  fluctuates  between  1-4  and  1-5.  At  24*7°,  when  of  the  specific 
gravity  1-42,  it  boils  and  distils  over  as  a  hydrate  (N0s,4H0)  without 
change,  but  the  diluted  acid  is  strengthened  by  boiling  ;  and  the  strongest 
acid  boils  at  a  lower  temperature  (184°)  than  that  which  is  of  a  lower  spe- 
cific gravity. 

At— 40°  the  concentrated  acid  is  congealed.  When  diluted  with  half  its 
weight  of  water,  it  freezes  at  about  — 2°.  When  the  acid  of  1-45  is  exposed 
to  the  air,  it  exhales  fumes  of  a  peculiar  odor,  and  gradually  absorbs  water, 
so  that  its  bulk  becomes  increased,  and  its  specific  gravity  diminished.  It 
suffers  a  partial  decomposition  when  exposed  to  light,  becoming  yellow  and 
evolving  oxygen,  so  that  it  should  be  kept  in  a  dark  place,  and  especially 
excluded  from  the  direct  rays  of  the  sun  (NO^-j-O).  Nitric  acid,  of  the 
sp.  gr.  1-5,  mixed  with  one-half  its  bulk  of  water,  occasions  an  elevation  of 
temperature  in  the  mixture=:112° :  58  parts  of  the  acid  with  42  of  water, 
both  at  60°,  give,  on  mixture,  a  temperature  of  140°.  On  diluting  the  red 
fuming  acid,  it  assumes  a  green  color— the  tint  depending  upon  the  quantity 
of  water  added. 


176  NITRIC    ACID.       CHEMICAL    PROPERTIES. 


Anhydrous  nitric  acid  is  composed  of— 

■ 

A  torn. s. 

Nitrogen 1     .. 

Oxygen 5     .. 

Equ. 

.     14 

.     40 

Per  cent. 
..      25  9 

...     74-1 

(Ueville.) 
..     25-4 
..     74-6 

54  100-0  100-0 


The  liquid  nitric  acid  in  its  utmost  state  of  concentration  (sp.  gr.  1*520) 
consists  of  1  equivalent  of  anhydrous  acid  and  1  of  water.  It  is  a  mono- 
hydrate.  According  to  Dr.  lire,  the  acid  of  a  specific  gravity  of  1*486  con- 
tains 1  equivalent  of  real  acid  and  two  of  water  : — 


Sp.  Gr. 
=  1-520. 

Sp.  Gr. 
=  1-50. 

Sp.  Gr. 
=  1.486. 

1  54     75 

2  18     25 

1     72  100 

Sp.  Gr. 

=  1-424. 

1     54    85-72 
1       9     14-28 

1       54        80 
1^     13-5     20 

1       67*5  100 

1     54     60 
4    36    40 

1     63  100-00 

1     90  100 

Water 


The  following  table,  drawn- up  by  Dr.  Ure,  exhibits  the  quantity  of  dry 
anhydrous  acid  in  100  parts  at  different  densities  {Quarterly  Journal,  4,  2^7), 
the  quantity  of  anhydrous  acid  in  the  liquid  acid  of  sp.  gr.  1*50  being 
assumed=797.  The  column  of  dry  acid  shows  the  weight  which  any  salifia- 
ble base  would  gain  by  uniting  so  as  to  form  an  anhydrous  salt,  with  100 
parts  of  the  liquid  acid  of  the  corresponding  specific  gravity. 


Specific     Dry  acid 

Specific     Dry  acid 

Specific     Dry  acid 

Specific 

Dry  acid 

gravity.       in  100. 

gravity.      in  100. 

gravity.        in  100. 

gravity. 

in  100. 

1-5000     79-700 

1*4228     60-572 

1-3056    41-444 

1*1587 

22-316 

1*4790     73-324 

1-3882     54-196 

1-2583     35-068 

1-1109 

15-940 

1-4530     66*948 

1-3477    47*820 

1*2084    28-692 

1*0651 

9-564 

Nitric  acid  may  be  decomposed  by  passing  its  vapor  through  a  red-hot 
porcelain  tube  ;  oxygen  is  given  off,  nitrous  acid  vapor  is  produced,  and  a 
quantity  of  diluted  acid  which  has  escaped  decomposition,  passes  over  into 
the  receiver  ;  it  is  thus  proved  to  consist  of  nitrous  acid,  oxygen,  and  water. 
At  a  white  heat,  oxygen,  nitrogen,  and  water  only  are  evolved.  According 
to  Faraday,  nitric  acid  does  not  undergo  electro-chemical  decomposition,  but 
the  water  only.  The  oxygen  at  the  anode  is  always  a  primary  result,  but  the 
products  at  the  cathode  are  often  secondary,  and  due  to  the  reaction  of  the 
hydrogen  upon  the  acid.     {Phil.  Trans.  1834,  p.  96.) 

When  deuotoxide  of  nitrogen  is  agitated  with  concentrated  nitric  acid,  the 
acid  is  decomposed,  and  nitrous  acid  is  formed,  partly  by  the  acquisition  of 
oxygen  by  the  oxide,  and  partly  by  its  loss  by  the  acid  (N02-f2N05=3N04). 
Hyponitrous  acid  may  also  result  (NOa+N05=N03  +  N04).  Various  colors 
are  thus  imparted  to  nitric  acid,  according  to  its  density  {see  page  173).  If 
to  a  jar  holding  about  150  cubic  inches  of  deutoxide,  an  ounce  of  strong 
colorless  nitric  acid  is  added,  this  undergoes  an  immediate  decomposition. 
Dense  orange  fumes  fill  the  jar,  and  the  liquid  acquires  a  deep  green  or  brown 
color.  Nitric  acid  is  so  frequently  a  mixture  of  the  two  acids,  that  it  has 
been  proposed  to  call  it  the  Acidum  nitrico  nitrosum  (NO^HOjNO^). 

Some  of  the  metals,  such  as  copper,  tin,  and  silver,  are  at  first  without 
action  on  concentrated  nitric  acid,  but  become  vehemently  active  upon  the 
addition  of  a  little  water.  Poured  upon  hot  iron-fillings,  or  melted  bismuth, 
zinc,  or  tin,  nitric  acid  causes  a  combustion  of  the  metals.  In  acting  upon 
those  metals  which  decompose  water,  nitric  acid  gives  rise  to  the  formation 
of  ammonia,  and  nitrate  of  ammonia  may  be  found  by  the  appropriate  tests 
among  the  products.  No  ammonia  is  formed  during  the  action  of  the  nitric 
acid  on  copper,  lead,  antimony,  bismuth,  mercury,  or  silver.     These  metals 


NITRIC   ACID.      CHEMICAL    PROPERTIES.  lit 

remove  three-fifths  of  the  oxygen,  the  deutoxide  of  nitrogen  being  evolved. 
If  the  acid  is  much  diluted,  zinc  and  iron  take  four-fifths,  and  protoxide  of 
nitrogen  is  a  product.  Tin,  which  is  without  action  on  the  concentrated 
ocid,  deoxidizes  it  completely  when  of  lower  strength,  nitrous  acid,  deutoxide 
of  nitrogen,  and  nitrogen  being  set  free.  Nitric  acid  is  without  action  on 
gold  and  platinum  at  any  temperature,  and  it  has  no  action  on  aluminum 
in  the  cold.  This  enables  a  chemist  to  detect  the  common  alloys,  which 
are  intended  to  imitate  gold,  as  nitric  acid  immediately  dissolves  them  with 
the  evolution  of  deutoxide  of  nitrogen.  It  is  hence  called  the  jeweller's 
test.  An  article  of  jewelry,  such  as  a  ring,  may  be  tested  by  rubbing  it 
on  a  surface  of  smooth  porphyry  or  other  hard  stone.  One  or  two  drops  of 
the  strongest  acid  should  be  added. to  the  metallic  film  thus  obtained.  If 
gold  it  will  remain,  but  if  only  a  base  alloy  it  will  disappear.  But  gold  may 
be  alloyed  with  nine  per  cent,  of  copper,  and  the  acid  will  not  afi'ect  it.  The 
action  of  protosulphate  of  iron  upon  this  acid  is  somewhat  remarkable.  If 
a  strong  solution  of  the  protosulphate  be  added  to  a  small  quantity  of  nitric 
acid,  the  liquid  acquires  a  dark,  greenish-black  color.  The  nitric  acid  parts 
with  three-fifths  of  its  oxygen,  and  the  deutoxide  of  nitrogen  which  results, 
is  dissolved  by  the  sulphate  (see  page  1*73).  The  reaction  of  the  oxide  of 
iron  upon  the  acid  may  be  thus  represented,  GFeO-fNO.^NOa-f  SFeaOg. 
The  dark  liquid  has  the  composition  4(FeO,S03)-j-N03. 

The  facility  with  which  nitric  acid  imparts  oxygen,  renders  it  a  valuable 
oxidizing  agent.  Phosphorus  decomposes  it  at  common  temperatures,  and 
sulphur  and  carbon  when  aided  by  heat.  A  piece  of  glowing  charcoal  thrown 
upon  the  surface  of  the  concentrated  acid,  burns  vehemently  with  the  evolu- 
tion of  red  fumes.  It  acts  energetically  (often  when  diluted)  upon  the  greater 
number  of  organic  bodies,  and  mutual  decompositions  ensue.  A  drachm  of 
oil  of  turpentine,  mixed  with  half  a  drachm  of  sulphuric  acid,  instantly  bursts 
into  flame  upon  the  addition  of  a  drachm  of  nitric  acid.  Malic,  oxalic,  and 
carbonic  acids  are  the  common  products  of  the  action  of  diluted  nitric  acid, 
upon  many  vegetable  and  animal  substances  ;  ammonia  and  hydrocyanic  acid 
are  also  sometimes  formed.  It  tinges  many  animal  substances  of  a  yellow 
color,  and  permanently  stains  the  nails  and  skin  ;  it  is  sometimes  employed 
in  the  production  of  yellow  patterns  upon  woollen  goods.  Its  oxidizing 
powers  are  increased  by  the  presence  of  nitrous  acid  (NO^).  Pure  nitric  acid 
has  no  action  on  a  solution  of  permanganate  of  potassa,  but  if  it  contain 
nitrous  or  hyponitrous  acid,  the  red  color  of  the  solution  is  discharged. 

Tests.  Nitrates. — Nitric  acid  is  monobasic.  There  are  no  acid  nitrates  ; 
the  salts  are  neutral,  and  are  represented  by  the  formula  MOjNOg.  Among 
the  metals,  there  are,  however,  some  basic  salts.  As  the  salts  of  nitric  acid 
are  all  soluble  in  water,  neither  its  presence  nor  its  proportion  can  be  deter- 
mined by  precipitation.  When  uncombined,  it  is  recognized  :  1.  By  its 
action  on  copper,  and  the  production  of  deutoxide  of  nitrogen.  2.  By  the 
solution  of  gold  when  mixed  with  boiling  hydrochloric  acid.  3.  By  its 
discharging  the  color  of  sulphate  of  indigo  acidulated  with  sulphuric  acid 
when  the  mixture  is  heated.  4.  By  its  giving  a  dark  olive  green  color  to  a 
crystal  of  green  sulphate  of  iron  when  dropped  into  it. 

Nitric  acid,  when  neutralized  by  potassa,  yields  long  striated  prisms  of 
nitrate  of  potassa,  and  when  neutralized  by  soda,  rhombs.  Other  tests  for 
this  acid  are  included  in  those  which  are  required  for  the  detection  of  a 
nitrate.  1.  On  adding  sulphuric  acid  to  a  nitrate,  colorless  fumes  of  nitric* 
acid  are  given  off.  2.  On  performing  this  experiment  in  a  small  test-tube, 
and  adding  a  few  copper-filings  nitrous  acid  fumes  arc  evolved,  known  by 
their  odor,  their  orange-red  color,  acidity,  and  the  decomposition  of  a  mix- 
ture of  iodide  of  potassium  and  starch.  When  the  quantity  of  nitrate  is 
12 


178  AMMONIA. 

small,  this  experiment  should  be  performed  in  a  Florence  flask — starch  paper 
wetted  with  a  solution  of  the  iodide  of  potassium  being  suspended  in  the 
neck  of  the  flask,  which  should  be  corked.  3.  Add  to  the  nitrate,  dissolved 
in  a  small  quantity  of  water,  its  volume  of  sulphuric  acid,  and  when  nearly 
cool,  add  a  crystal  of  protosulphate  of  iron.  The  crystal  is  encircled  with  a 
pink  or  brownish-colored  layer  of  liquid  {see  page  173).  4.  On  boiling  the 
nitrate  with  a  small  quantity  of  hydrochloric  acid  and  a  fragment  of  leaf- 
gold,  the  metal  is  speedily  dissolved.  If  the  gold  does  not  entirely  disappear, 
the  fact  that  some  portion  has  been  dissolved,  will  be  manifested  by  the  liquid 
acquiring  a  purple  or  dark  color  on  the  addition  of  a  few  drops  of  proto- 
ehloride  of  tin.  The  copper  test  may  fail  to  reveal  the  presence  of  a  nitrate 
when  an  alkaline  chloride  is  present.  In  this  case,  the  gold-test  will  be 
found  serviceable.  The  nitrates  are  frequently  present  in  potable  waters, 
and  their  presence  is  generally  indicative  of  the  infiltration  of  nitrogenous 
matters,  and  their,  subsequent  oxidation.  They  may  be  easily  detected,  with- 
out separating  the  other  salts,  by  the  application  of  the  gold-test  to  the 
residue  left  on  evaporation.  5.  A  solution  of  a  nitrate,  tinted  blue  with 
sulphate  of  indigo,  acidulated  with  sulphuric  acid,  and  heated,  causes  a 
destruction  of  the  color. 


CHAPTER  XIV. 

COMPOUNDS  OF  NITROGEN   AND  HYDROGEN.     AMMONIA 
AND  ITS    SALTS. 

It  is  generally  conceded  by  chemists  that  there  are  three  compounds  of 
these  elements — Amidogen,  NHg;  Ammonia,  NHg ;  and  Ammonium,  NH^; 
Of  these,  only  one  has  been  isolated,  namely,  ammonia,  a  gaseous  alkali ; 
and  as  the  two  hypothetical  compounds  are  derived  from  it,  it  is  this  which 
will  first  claim  attention. 

Ammonia  (NH3=1'7). — This  is  a  compound  alkaline  gas,  long  known 
under  the  name  of  volatile  alkali.  It  derives  its  name  from  the  temple  of 
Jupiter  Ammon,  in  Libya,  in  the  neighborhood  of  which  sal  ammoniac  was 
at  one  time  manufactured.  This  gas  is  found  in  the  atmosphere  of  towns  in 
Tery  small  proportion. 

Preparation When  nitrogen  and  hydrogen  are  mixed  in  the  free  state, 

they  show  no  tendency  to  combine ;  they  diffuse  without  change,  and  each 
is  separable  from  the  other.  It  is  only  in  the  iiascent  state  that  they  com- 
bine to  form  ammonia  {see  page  46).  This  gaseous  compound  may  be 
obtained  from  a  mixture  of  equal  parts  of  dry  quicklime  and  one  of  dry 
hydrochlorate  of  ammonia,  finely  powdered,  introduced  into  a  small  retort, 
and  gently  heated.  It  must  be  collected  over  mercury.  Towards  the  latter 
part  of  the  operation,  a  little  water  goes  over,  which  may  be  arrested  in  the 
neck  of  the  retort  by  the  previous  introduction  of  a  piece  of  blotting-paper, 
or  of  stick  potassa,  or  it  may  be  prevented  passing  over  by  filling  up  the 
*bulb  of  the  retort  with  powdered  lime.  Hydrochlorate  of  ammonia  is  a 
compound  of  hydrochloric  acid  and  ammonia;  by  the  action  of  the  lime 
(which  is  an  oxide  of  calcium)  the  ammonia  is  expelled  in  its  pure  and 
gaseous  form  :  the  hydrochloric  acid  and  the  lime  then  mutually  decompose 


ITS    PRODUCTION.       PROPERTIES.  179 

each  other,  and  water  and  chloride  of  calcium  are  the  results  :  CaO.  +  NHj, 
HCl  =  CaCl,4-HO+NH3.  The  gas  may  likewise  be  procured  by  heating 
in  a  retort,  a  saturated  solution  of  ammonia. 

Properties. — Ammonia  is  gaseous  at  common  temperatures,  but  it  may  be 
liquefied  by  a  cold  of — 40°,  or  at  the  temperature  of  40°  by  a  pressure  of 
6  5  atmospheres  (Faraday,  Phil.  Trans.,  1823,  p.  196).  It  is  most  readily 
obtained  as  a  liquid  by  disengaging  it  by  heat,  in  a  sealed  tube,  from  chlo- 
ride of  silver  which  has  been  previously  saturated  with  the  gas  (page  80). 
It  forms  a  colorless  transparent  liquid,  of  a  specific  gravity  of  ()'76,  and  with 
a  refractive  power  surpassing  that  of  water.  When  free  from  water,  it  does 
not  conduct  electricity.  At  103°  below  0°,  this  liquefied  ammonia  became 
a  white,  translucent,  crystalline  solid,  heavier  than  the  liquid. 

Gaseous  ammonia  has  a  pungent  and  suffocating  odor :  it  irritates  the 
nose,  eyes,  and  throat,  and  is  irrespirable ;  but  when  diluted  by  mixture 
with  common  air  it  is  an  agreeable  stimulant.  It  converts  some  vegetable 
blues  to  green,  yellows  to  red,  and  reds  to  blue  or  green,  properties  which 
belong  to  the  bodies  called  alkalies.  Ammonia,  therefore,  has  been  termed 
volatile  alkali,  and  the  change  of  color  thus  effected  by  it  is  distinguished 
from  that  produced  by  the  fixed  alkalies  by  the  return  of  the  original  tint 
when  the  paper  is  warmed,  or  after  the  ammonia  has  passed  off  by  exposure. 
Dry  ammonia  has  no  action  on  dry  vegetable  colors  (page  43).  (K^ne.) 
As  it  is  collected  in  the  state  of  gas,  it  always  holds  sufficient  water  to  act 
upon  vegetable  colors.  If  a  small  jar  of  the  gas  is  opened  under  a  large 
receiver,  in  which  are  suspended  strips  of  paper  colored  with  tincture  of 
turmeric,  infusion  of  roses,  a  decoction  of  Brazil  wood,  and  litmus  reddened 
by  an  acid,  these  will  speedily  undergo  the  changes  of  color  which  are  char- 
acteristic of  an  alkali.  Paper  stained  with  the  yellow  sulphide  of  arsenic  is 
bleached  in  the  gas,  while  that  which  is  wetted  with  arsenio-nitrate  of  silver 
(mixed  solutions  of  arsenious  acid  and  nitrate  of  silver)  acquires  a  yellow 
color.    It  combines  with  the  acids,  and  produces  an  important  class  of  salts. 

The  specific  gravity  of  arnmonia,  compared  with  hydrogen,  is  as  8'5  to  1  ; 
compared  with  air  it  as  0-5873  to  1  ;  100  cubic  inches  weigh  1819  grains. 
The  gas  extinguishes  flame,  but  it  is  partially  burned  with  a  yellow  flame, 
which  does  not  extend  to  the  other  portions  of  the  gas.  Owing  to  its  light- 
ness, this  experiment  may  be  performed  in  a  jar  inverted.  When  mixed 
with  air,  it  may  be  burned  as  it  issues  from  a  capillary  orifice  in  an  atmo- 
spere  of  oxygen.  When  mixed  with  its  volume  of  oxygen  it  bsrns  with  a 
feeble  explosion.  Ammonia  is  abundantly  absorbed  by  chloride  of  calcium, 
as  well  as  by  several  other  chlorides  (chloride  of  silver),  with  which,  and 
with  the  other  haloids,  it  forms  compounds.  Hence  if  it  be  required  arti- 
ficially to  dry  the  gas,  potassa  or  lime  should  be  used. 

Water,  at  the  temperature  of  60°,  takes  up  480  times  its  volume  of  ammo- 
nia, its  bulk  is  ihcreased  (6  measures  of  water  giving  10  of  the  solution), 
and  its  specific  gravity  is  diminished;  that  of  a  saturated  solution  is  0875, 
water  being  TOOO.  A  saturated  solution  of  ammonia  readily  floats  on  water. 
The  following  table  shows  the  quantity  of  ammonia  in  solutions  of  different 
specific  gravities  (Davy,  Chem.  Phil,  p.  268)  : — 

100  parts  of  Sp.  gr.      Of  ammonia.  100  parts  of  Sp.  gr.      Of  ammonia. 
•8750  contain   32-50  -9435  contain  14-53 

•9000        "         26-00  -9513        "         12-40 

•9166        "        22-07  -9573        "        10-82 

•9326        "        17-52  -9692        "  950 

The  solutions  of  this  gas  commonly  met  with  are  the  three  following :— 


180  SOLUTION    OF    AMMONIA. 


t 


Saturated  solu.         Common,  B.  P. 

S.  G -875     ;.....     -889     -959 

Ammonia         ....     32-3     26     10 

Water 67-5     74     90 

100-               .     100  100 


The  solubility  of  the  gas  in  water  may  be  shown  by  the  following  experi- 
ment. Fill  a  tube  with  dry  ammonia,  and  invert  it  in  a  basin  containing  a 
small  quantity  of  mercury.  Pour  into  the  basin  a  solution  of  litmus  just 
reddened  by  tartaric  acid.  Raise  the  tube  containing  tne  ammonia,  so  that 
the  mouth  may  be  immersed  in  the  colored  liquid.  The  liquid  will  gradually 
rise  in  the  tube,  and  will  ultimately  fill  it  if  the  gas  is  pure.  At  the  same 
time  the  alkaline  nature  of  the  gas  will  be  proved  by  the  red  liquid  being 
turned  blue.  A  lighted  taper  applied  to  a  small  jar  of  the  gas  is  extin- 
guished. If  a  little  water  be  added,  and  the  jar  shaken,  the  solution  of  the 
gas  will  be  proved  by  the  taper  now  burning  in  the  jar. 

The  great  solubility  of  ammonia  in  water  renders  it  easy  to  separate  this 
gas  from  many  others  which  are  insoluble  in  this  liquid.  The  usual  state  in 
which  ammonia  is  employed  is  in  aqueous  solution,  both  in  chemistry  and 
medicine.  This  solution  {Liquor  Ammonice)  may  be  readily  obtained  by 
passing  the  gas  into  water  in  a  proper  apparatus,  or  by  distilling  over  the 
water  and  gas  together.  For  this  process  equal  parts  of  sal-ammoniac  and 
well-burned  quicklime  may  be  employed  :  the  lime  is  slaked  by  the  addition 
of  water,  and,  as  soon  as  it  has  fallen  into  powder,  placed  in  an  earthen 
pan,  and  covered  until  quite  cold,  then  mixed  with  the  powdered  sal-ammo- 
niac and  put  into  a  proper  retort,  and  heated  as  long  as  it  gives  out  gas, 
which  should  be  conducted,  by  means  of  a  safety-tube,  into  a  quantity  of 
distilled  water,  equal  to  the  weight  of  the  salt  employed.  The  specific 
gravity  of  a  solution  of  ammonia  so  obtained  is  -936. 

Liquid  ammonia  (as  this  aqueous  solution  is  sometimes  called)  should  be 
preserved  in  well-stoppered  glass  bottles,  since  it  loses  ammonia  and  absorbs 
carbonic  acid  when  exposed  to  air.  The  gas  is  constantly  evolved,  and, 
when  the  solution  is  heated,  ammonia  is  rapidly  given  off  by  it ;  when  con- 
centrated, it  requires  to  be  cooled  to  — 40°  before  it  congeals,  and  then  it 
is  inodorous,  and  of  a  gelatinous  appearance.  If  a  piece  of  ice  be  intro- 
duced into  a  jar  of  gaseous  ammonia  standing  over  mercury,  it  melts  with 
great  rapidity,  and  liquid  ammonia  is  produced.  This  is  owing  to  the  strong 
affinity  of  this  gas  for  water. 

The  solution,  when  pure,  is  colorless,  and  has  the  pungent  odor  of  the 
gas.  It  is  strongly  alkaline,  irritant,  and  caustic.  It  differs  from  potassa 
and  soda  in  redissolving  the  oxides  of  copper  and  silver,  precipitated  by 
alkalies  from  their  solutions.  It  should  leave  no  residue  op  evaporation.  If 
it  contains  carbonic  acid,  this  may  be  detected  by  the  addition  of  lime-water, 
or  a  solution  of  chloride  of  calcium,  either  of  which  will  then  cause  a  white 
precipitate  of  carbonate  of  lime.  The  presence  of  chlorine  may  be  detected 
by  neutralizing  the  alkaline  solution  with  nitric  acid,  concentrating  it  by 
evaporation,  and  then  adding  nitrate  of  silver :  if  it  contains  chlorine  this 
is  made  evident  by  the^ppearance  of  an  insoluble  white  precipitate  of  chloride 
of  silver. 

Tests. — Ammonia  as  a  gas  is  recognized  by  its  odor  and  volatile  reaction, 
as  well  as  by  its  producing  white  fumes  of  hydrochlorate  of  ammonia,  when 
a  rod  dipped  in  strong  hydrochloric  acid,  is  b.rought  near  to  it.  Its  solution 
is  precipitated,  1st,  by  a  solution  of  tartaric  acid,  when  added  in  large  pro- 
portion (acid  tartrate  of  ammonia)  ;  and  2d,  by  a  solution  of  chloride  of 


COMPOSITION    OF    AMMONIA.  181 

platinum,  forming  a  pale  yellow  ammonio-chloride  of  that  metal,  which  is 
insoluble  in  alcohol.  When  existing  in  solution  in  very  minute  proportion, 
and  the  absence  of  other  alkalies  has  been  proved  by  the  entire  evaporation 
of  a  portion  of  the  liquid,  traces  of  ammonia  may  be  readily  detected  by 
adding  a  few  drops  of  the  mixed  solutions  of  arsenious  acid  and  nitrate  of 
silver.  Yellow  arsenite  of  silver  is  produced  and  precipitated.  The  solution 
of  ammonia  is  an  important  agent  to  the  chemist.  It  enables  him  to  precipi- 
tate many  bodies,  and  as  it  is  volatile,  it  can  be  subsequently  expelled  by 
heat  from  any  mixture  to  which  it  has  been  added. 

Composition. — Dr.  Henry  first  observed  that  a  mixture  of  ammonia  and 
oxygen  might  be  fired  by  an  electric  spark,  and  this  property  furnishes  a 
method  of  analyzing  the  gas.  When  the  spark-current  from  Ruhmkorfif's 
induction-coil  is  discharged  through  ammonia,  the  gas  is  rapidly  decom- 
posed, and  at  the  same  time  the  liberated  gases  evolve  the  light  peculiar  to 
nitrogen  and  hydrogen.  The  spectrum  produced,  results  from  the  super- 
position of  the  spectra  for  hydrogen  and  nitrogen.  When  a  succession  of 
electric  sparks  has  been  passed  through  a  quantity  of  the  gas  contained  in  a 
tube  over  mercury,  it  is  uniformly  observed  to  increase  to  twice  its  original 
volume,  and  at  the  same  time  to  lose  its  alkalinity  and  solubility  in  water. 
If  the  gas  thus  expanded  is  mixed  with  from  one-third  to  one-half  of  its  bulk 
of  oxygen,  and  an  electric  spark  passed  through  the  mixture,  an  explosion 
takes  place,  attended  by  a  considerable  diminution  of  volume.  Assuming 
that  in  the  analysis  4  c.  i.  of  ammonia  are  expanded  to  8  c.  i.  by  the  electric 
spark,  and  that  3  c.  i.  of  oxygen  are  mixed  with  the  8  c.  i.  of  decomposed 
gas,  there  will  be  II  c.  i.  of  mixed  gases.  These  after  detonation  are  reduced 
to  2  c.  i.,  water  being  produced  by  the  oxygen  combining  with  the  hydrogen 
of  the  decomposed  ammonia.  Two-thirds  of  the  loss,  or  6  c.  i.,  represent 
hydrogen  (  Water,  page  128),  and  the  2  c.  i.  of  residuary  gas  may  be  proved 
to  be  nitrogen.  Hence  ammonia  is  constituted  of  one  volume  or  atom  of  nitro- 
gen, and  three  volumes  or  atoms  of  hydrogen,  the  four  volumes  being  reduced 
by  combination  to  two.  The  changes  are  represented  in  the  following  equa- 
tion :  2NH3-|-60^2N'-f  6H0.  This  method  of  analysis  is  open  to  the  ob- 
jection that  some  nitrogen  is  converted  by  the  electric  spark  to  nitric  acid, 
which  may  lead  to  error  in  computing  the  loss  after  detonation.  The  follow- 
ing plan  is  not  attended  with  this  difficulty.  Let  100  c.  i.  of  the  gas  be 
passed  through  a  porcelain  tube  containing  platinum-wire  heated  to  redness  ; 
it  will  be  doubled  in  volume  and  entirely  decomposed.  The  100  c.  i.  of  am- 
monia produce  200  c.  i.  of  mixed  gases,  of  which  50  are  nitrogen  and  150 
may  be  proved  to  be  hydrogen. 

These  results  are  confirmed  by  ascertaining  the  sp.  gr.  of  the  gas  ;  but  as 
the  atom  of  ammonia  represents  two  volumes,  the  sum  of  the  sp.  gr.  of  the 
constituents  must  be  divided  by  2.     Thus  : — 

Specific  gravity  of  nitrogen 
"  hydrogen 


.     =0-9674 
.  0-0691  X  3  =  0-2073 

1-1747 -r-2  = 

•5873 

ind  of 

Atoms.          "Weights.           Per  cent. 
.     1       ...       14       ...       82-35       .. 
3       ...         3       ...       17-65       .. 

Vols. 
1 
.       3 

Ammonia,  therefore,  is  a  compound  of 

Nitrogen      .... 
Hydrogen   .... 

Ammonia 1  17  100-00  2 

Ammonia  is  produced  synthetically  during   the  decomposition  of  many 
animal  and  vegetable  substances,  or  by  simply  heating  nitrogenous  matter  j 


182  SYNTHETICAL    PRODUCTION    OF    AMMONIA. 

•  it  is  also  formed  during  the  action  of  nitric  acid  upon  some  of  the  raetals ; 
and  by  moistened  iron-filings  exposed  to  an  atmosphere  of  nitrogen  of  air. 
In  these  cases  the  nascent  gases  unite  so  as  to  form  a  portion  of  ammonia 
(Fcg-f  4HO  +  N=Fe203,HO+NH3).  Rust  of  iron  formed  by  the  exposure 
of  iron  to  a  damp  atmosphere,  generally  contains  traces  of  ammonia.  When 
^nitric  acid  is  added  to  a  mixture  of  zinc  and  dilute  sulphuric  acid,  its  nitrogen 
'  combines  with  the  hydrogen  as  it  is  evolved,  and  ammonia  is  formed,  NO3+ 
8H=NH3-f  6H0;  when,  however,  the  action  is  violent,  some  deutoxide  of 
nitrogen  is  also  evolved.  If,  after  some  days,  a  portion  of  the  liquid  is  boiled 
with  a  solution  of  potassa,  ammonia  will  be  evolved.  The  production  of  this 
gas  during  the  rusting  of  iron  may  be  thus  proved.  Sprinkle  the  inside  of 
a  large  stoppered  bottle  with  fine  iron-filings,  adding  a  small  quantity  of 
water  to  make  the  metallic  particles  adhere  to  the  sides  of  the  bottle.  Sus- 
pend in  the  interior  from  the  stopper  a  slip  of  litmus-paper,  first  reddened 
by  a  weak  acid.  In  about  twenty-four  hours  the  paper  will  be  rendered  blue, 
by  the  ammonia  produced  in  the  rusting  of  iron.  In  the  action  of  nitric 
acid  upon  tin,  ammonia  is  a  product,  provided  water  is  present.  Add  tin- 
filings  to  nitric  acid,  and  then  dilute  the  acid  until  a  violent  action  com- 
mences. The  acid  and  the  water  are  partially  deoxidized  by  the  metal,  and 
the  hydrogen  of  the  one  unites  to  the  nitrogen  of  the  other,  in  the  nascent 
state,  to  form  ammonia  (N05+3HO-f-4Sn=NH3-l-4SnO.,).  If  the  residu- 
ary oxide  of  tin  be  well  mixed  with  water,  and  some  lime  stirred  into  the 
mixture,  ammonia  is  immediately  evolved.  Ammonia,  as  it  is  diffused  in  air 
-and  water,  is  liable  to  become  oxidized  and  converted  into  nitric  acid,  as  a 
result  of  the  action  of  ordinary  or  allotropic  oxygen,  NHg-f  80(Oz)=N05-f 
3H0.  This  oxidation  is  chiefly  observed  to  occur  when  fixed  bases,  with 
which  the  acids  can  combine,  are  present.  The  presence  of  alkaline  nitrates 
in  large  quantity  in  many  well-waters,  especially  in  the  neighborhood  of 
grave-yards,  is  attributed  to  the  effects  of  oxidation  on  the  ammoniacal  pro- 
ducts of  putrefaction.  On  the  other  hand,  it  is  a  curious  fact  that  the  nitric 
acid  of  alkaline  nitrates  is  reconverted  into  ammonia  by  the  nascent  hydrogen 
evolved  from  an  amalgam  of  sodium  placed  in  a  weak  solution  of  the  nitrate 
(N03+8H=NH3+5HO). 

Ammonia  may  be  synthetically  formed  by  the  action  of  spongy  platinum 
on  a  mixture  of  2  volumes  of  deutoxide  of  nitrogen  and  5  of  hydrogen.  For 
such  experiments  platinated  asbestos,  formed  by  dipping  that  substance 
into  a  solution  of  chloride  of  platinum  and  exposing  it  to  a  red  heat,  may 
be  used  ;  while  the  mixed  gases  are  passing,  the  platinum  should  be  heated 
(x\0,+H,=NH3-f2HO.) 

Amidogen  (NHg). — Amidogen  is  presumed  to  exist  in  combination  with 
certain  metals,  and  in  some  organic  compounds.  When  potassium,  or  sodium, 
is  heated  in  a  current  of  dry  ammonia,  one  equivalent  of  hydrogen  is  expelled, 
and  a  solid  substance  is  obtained  which,  in  the  case  of  potassium,  is  sup- 
posed to  have  the  composition  KNH3 — an  atom  of  hydrogen  having  been 
replaced  by  an  atom  of  the  metal.  This  theory  is  strongly  supported  by 
the  fact,  that  when  the  substance  produced  is  placed  in  water,  the  sole  pro- 
ducts obtained  are  potassa  and  ammonia,  KNH3+H0=K0  +  NH3.  Ami- 
dogen is  therefore  regarded  as  a  hypothetical  radical  Among  the  com- 
pounds into  which  it  is  supposed  to  enter,  may  be  mentioned  those  of  copper, 
CuNHg,  and  mercury,  HgjNHg,  the  last  being  the  ammonio-chloride  of  mer- 
cury or  white  precipitate.  Inferring  from  these  and  other  similar  cases, 
that  in  ammonia  the  third  atom  of  hydrogen  is  less  intimately  combined 
with  nitrogen  than  the  remaining  two.  Sir  Robert  Kane  represents  amidogen, 
NHg  by  the  symbol  Ad,  and  treats  it  as  the  radical  of  ammonia.     Ammonia, 


PRODUCTION    OF    AMMONIUM.  183 

therefore,  on  this  view  of  its  constitution,  is  an  amide  of  hydrogen-='^lS.^,Yl 
or  AdH. 

Ammonium  (NHg  +  II,  or  NHJ. — AVhen  mercary  is  made  the  negative 
electrode  in  an  aqueous  solution  of  ammonia,  it  becomes  spongy,  'and 
assumes  the  character  of  a  soft  amalgam  ;  oxygen  is  given  off  at  the  positive 
electrode,  but  there  is  no  corresponding  evolution  of  hydrogen  on  the  negative 
side  until  the  electric  current  is  interrupted,  when  the  metallic  sponge  begins 
to  collapse,  and  gives  out  hydrogen  and  ammonia,  leaving  a  residue  of  pure 
mercury  ;  but  this  change  may  be  retarded  by  cold,  and  on  cooling  the 
pasty  mass  to  0°,  it  is  said  to  yield  cubic  crystals,  which,  when  decomposed 
over  mercury,  give  out  ammonia  and  hydrogen  in  the  respective  volumes  of 
2  to  1.  The  mercury,  therefore,  appears  to  have  been  combined  with  a  body 
represented  by  NH^,  and  as  the  metallic  characters  of  the  mercury  are  un- 
changed, it  is  presumed  that  NH^  constitutes  temporarily  a  metal  which  has 
been  termed  ammonium.  This  phenomenon  may  be  equally  observed  by 
placing  an  amalgam  of  potassium  or  sodium  and  mercury  upon  a  block  of  sal 
ammoniac,  excavated  in  the  form  of  a  cup  and  containing  a  small  quantity 
of  water;  the  amalgam  soon  increases  in  size,  and  forms  a  soft  solid.  With- 
out water  there  is  no  chemical  action.  It  is  supposed,  in  this  case,  that  the 
potassium-amalgam,  acting  upon  hydrochlorate  of  ammonia,  gives  rise  to 
chloride  of  potassium,  and  the  amalgam  of  ammonium,  KHg  +  NH^HCl 
=KCl  +  HgNH^.  The  production  of  this  amalgam  may  be  more  strikingly 
shown  by  the  following  experiments.  Prepare  an  amalgam  of  sodium  by 
gently  warming  some  mercury  in  a  tube  or  capsule,  and  adding  at  intervals, 
small  portions  of  sodium.  The  amalgam,  which  should  be  fluid  when  cold, 
may  be  preserved  for  some  hours  in  a  well-stoppered  bottle.  Prepare  a  few 
ounces  of  saturated  solution  of  chloride  of  ammonium.  Fill  a  tall  glass  or 
jar  to  about  one-third  with  this  solution  at  the  temperature  of  100°,  then 
pour  into  it  a  quantity  of  the  prepared  sodium-amalgam.  On  contact  with 
the  liquid,  the  amalgam  rlapidly  enlarges  into  a  spongy  mass,  sometimes 
rising  out  of  the  glass  and  forming  a  cauliflower  excrescence.  If  kept  in 
contact  with  the  solution,  it  retains  its  spongy  state  for  a  short  time  ;  but 
the  mass  slowly  collapses  :  hydrogen  and  ammonia  are  evolved,  and  metallic 
mercury  remains  in  the  glass,  which  now  contains  a  solution  of  the  chlorides 
of  ammonium  and  sodium.  There  are  other  methods  of  producing  this 
amalgam.  If  an  alloy  of  potassium  and  sodium  is  made  under  naphtha  by 
pressing  the  two  metals  together,  and  a  globule  of  mercury  is  then  added, 
an  amalgam  is  immediately  formed,  with  combustion.  This  amalgam  placed 
in  contact  with  a  warm  solution  of  chloride  of  ammonium  is  converted  into 
the  light,  spongy  amalgam  of  ammonium. 

In  the  production  of  the  ammonium- amalgam^  while  the  metal  increases 
to  ten  times  its  volume  in  the  cold,  and  probably  to  thirty  times  its  volume 
at  lOO'^,  the  hydrogen  and  ammonia  increase  its  weight  only  by  l*2000th 
part.  When  a  portion  of  the  amalgam  is  placed  in  water  tinted  with  red 
litmus,  it  is  slowly  decomposed,  minute  bubbles  of  hydrogen  escape,  and 
the  solution  of  the  ammonia  is  proved  by  the  red  litmus  slowly  acquiring 
a  blue  color.  If  distilled  water  is  used  in  this  experiment,  it  soon  acquires 
an  impregnation  of  ammonia  and  givet  a  yellow  precipitate  with  arsenio- 
nitrate  of  silver.  The  evolution  of  the  two  gases  may  be  further  proved 
by  filling  a  long  test-tube  to  two-thirds  of  its  depth,  with  blue  infusion  of 
cabbage,  and  the  other  third  with  ether.  If  the  amalgam  is  dropped  to  the 
bottom  of  the  tube,  the  ammonia,  as  it  escapes,  will  be  dissolved  by  the 
water,  and  turn  the  blue  cabbage  green,  while  the  hydrogen  not  being  soluble 
will  be  seen  escaping  in  numerous  minute  bubbles  through  the  floating  layer 
of  colorless  ether. 


134  COMPOUNDS    OF    AMMONIA    AND    AMMONIUM. 

These  facts  simply  show  that  hydrogen  and  ammonia  go  into  the  mercury, 
and  that  they  are  again  evolved  as  such  either  spontaneously  or  by  contact 
with  water.  Although  not, isolated  in  a  combined  state,  it  is  assumed — 1, 
from  the  consistency  given  to  the  mercury  :  2,  from  the  amalgam  crystal- 
lizing in  cubes  at  zero,  that  the  hydrogen  and  ammonia  are  temporarily 
>^nited  in  definite  proportions,  to  form  a  metal  which  is  dissolved  by  mercury 
nike  other  metals.  At  temperatures  above  zero  the  tendency  of  the  com- 
ponents of  this  metal  to  assume  the  elastic  state  appears  to  be  so  great  as 
to  lead  to  their  evolution  under  the  form  of  hydrogen  and  ammonia.  It  is 
remarkable  that  in  the  analysis  and  synthesis  of  this  body  the  elements  are 
never  arranged  as  hydrogen  and  nitrogen,  but  as  hydrogen  and  ammonia. 
There  are  many  difficulties  to  the  admission  of  the  hypothesis  that  hydrogen 
and  ammonia,  under  these  circumstances,  produce  a  metal.  When  the 
amalgam  is  exposed  to  air,  especially  in  a  thin  layer,  it  is  speedily  resolved 
into  ammonia,  hydrogen,  and  metallic  mercury,  and  it  has  been  justly  asked 
why,  if  ammonium  falls  apart  thus  readily  in  the  presence  of  mercury,  should 
it  ever  combine  as  such  with  the  liquid  metal.  It  is  admitted  that  it  is 
decomposed  in  the  act  of  union  and  resolved  into  ammonia  and  hydrogen. 
If  a  liquid  amalgam  of  tin  and  mercury  is  compressed  between  two  glass 
plates,  it  retains  its  metallic  character,  the  amalgam  being  simply  con- 
verted into  a  thin  layer.  Not  so  with  the  amalgam  of  ammonium  ;  it  requires 
bulk  in  order  that  it  should  retain  the  gases,  and  thereby  its  spongy  character. 
Place  a  portion  of  ammonium  amalgam  on  plate-glass,  and  touch  it  with  a 
strong  solution  of  chloride  of  ammonium.  As  soon  as  it  begins  to  enlarge 
in  size,  press  it  with  another  glass  plate.  Instead  of  forming  a  continuous 
layer,  it  is  immediately  split  into  numerous  holes  from  the  escape  of  ammonia 
and  hydrogen  from  all  points.  It  thus  looks  like  a  delicate  network  of  metal. 
The  gases  rapidly  escape,  and  nothing  but  mercury  remains.  So  it  has  been 
found  impossible  to  produce  the  ammonium  amalgam  by  voltaic  electricity, 
when  the  experiment  is  performed  on  a  thin  layer  of  mercury.  The  gases 
escape  as  they  are  produced,  a  fact  which  shows  that  they  do  not  unite  in 
the  mercury  to  form  a  metal. 

The  amalgam  of  ammonium  is  produced  by  acting  with  the  sodium  amalgam 
npon  the  chloride,  carbonate,  or  oxalate,  but  not  readily  on  the  nitrate.  The 
hydrogen  and  ammonia  do  not  in  this  case  appear  to  be  retained  by  the 
mercury.  These  experiments  may  be  performed  by  putting  a  few  drops  of 
the  respective  solutions  (saturated)  upon  the  sodium  amalgam.  As  water  is 
essential  to  this  phenomenon,  and  sodium  amalgam  alone  in  water  causes 
an  evolution  of  hydrogen,  soda  being  at  the  same  time  produced,  the  libe- 
ration of  ammonia  has  been  ascribed  to  the  reaction  of  the  soda  upen  the 
salts  of  ammonia.  The  two  gases  as  they  are  evolved  are  for  a  certain  time 
retained  by  the  liquid  mercury,  instead  of  escaping  through  it.  This  may 
explain  the  consistency  and  lightness  acquired  by  the  mercury,  without 
assuming  that  the  two  gases  are  metallized.  The  assumption  that  nitrogen 
*  and  hydrogen  might  combine  with  mercury  to  form  a  metallic  amalgam,  is 
not  inconsistent  with  chemical  doctrines  ;  but  it  would  be  a  novelty  to  assume 
that  nitrogen  and  hydrogen  first  produce  ammonia,  and  that  this  ammonia 
then  enters  into  combination  with  aliother  portion  of  hydrogen  to  form  the 
metal  ammonium.  There  is  no  fact  to  show  that  the  products  are  ever  any- 
thing more  than  a  mixture  of  ammonia  and  hydrogen. 

Although  this  compound  metal  cannot  be  separated  as  such  from  the 
amalgam,  chemists  have  generally  agreed  to  regard  its  independent  existence 
as  sufficiently  established  to  justify  its  use  in  the  nomenclature  of  the  salts  of 
ammonia,  thereby  assimilating  them  in  some  respects  to  the  salts  of  the  other, 
alkaline  metals.     The  hypothetical  ammonium  is,  therefore,  symbolized  some- 


COMPOUNDS    OF    AMMONIA    AND    AMMONIUM.  185 

times  as  Am,  or  more  commonly  by  the  formula  NH^.     The  salts  will  stand 
thus  upou  the  two  theories  : — 


Potassium  series. 

Ammonium 

series. 

Ammonia  series. 

Metal 

K 

Am 

=  NH, 

NH3-I-H 

Oxide 

KO 

Am,0 

=  NH,0 

NH3,H0 

Chloride 

KCl 

AmCl 

=  NH4C1 

NH3,HG1 

Sulphide 

KS 

AmS 

=  ^K^S 

NH,,HS 

Nitrate 

KO,NOg 

AmO,N05 

=  NH,0,N05 

nh;ho,no5 

Sulphate 

K0,S03 

AmOjSOg 

=:NH,0,S03 

NH,,H0,S03 

From  this  comparative  table  it  appears,  that  while  potassium  is  an  alkali- 
genous  metal,  ^.  e.,  a  metal  producing  an  alkali  by  combination  with  oxygen, 
ammonia  is  a  raetalligenous  alkali,  ^.  e.,  an  alkali  producing  a  metal,  by  com- 
bination with  hydrogen.  While  oxide  of  potassium  (KO)  is  an  independent 
and  well-defined  compound,  which  can  be  readily  obtained  either  with  or 
without  water,  the  so-called  oxide  of  ammonium  has  only  a  hypothetical  ex- 
istence. Dry  ammonia,  like  dry  potassa,  has  no  alkaline  reaction,  the  presence 
of  water  being  required  for  the  manifestation  of  this  property  in  bodies  (p.  43). 
There  is,  however,  no  reason  to  suppose  that  the  water  is  decomposed  by 
either  compound.  In  reference  to  ammonia,  water  acts  simply  as  a  solvent, 
as  it  dees  on  carbonic  acid  and  protoxide  of  nitrogen.  The  properties  of 
the  solution  are  simply  those  of  the  gas,  ^nd  like  other  soluble  gases,  ammo- 
nia may  be  entirely  expelled  by  heat.  There  is  no  hydrate  of  ammonia,  nor 
any  condition  of  this  alkali,  which  shows  a  chemical  union  with  or  reaction 
upon  the  elements  of  water.  Every  attempt  to  extract  an  oxide  has  ended 
in  failure,  and  even  where  circumstances  were  most  favorable  for  its  produc- 
tion— i.  e.,  in  the  nascent  state — nothing  but  ammonia  and  water  result. 

When  perfectly  dry  ammonia  and  hydrochloric  acid  gases  are  brought  in 
contact,  a  solid  white  crystalline  salt  is  formed,  which  may  be  either  hydro- 
chlorate  of  ammonia,  or  chloride  of  ammonium.  On  the  latter  hypothesis, 
the  affinity  of  the  ammonia  for  another  equivalent  of  hydrogen  is  assumed  to 
be  such  as  to  lead  to  its  separation  from  the  chlorine  (NH3-|-HC1=NH4,CI). 
But  the  production  of  this  binary  compound  is  not  reconcilable  with  the  facts 
usually  observed  in  reference  to  the  powerful  affinity  of  chlorine  for  hydrogen. 
Ammonia  itself  is  readily  deprived  of  all  its  hydrogen  by  chlorine,  as  in  one 
of  the  processes  for  obtaining  nitrogen  (NB[3  +  3Cl=N-f  3HC1).  In  refer- 
ence to  the  extraction  of  ammonia  by  lime,  most  chemists  treat  sal-ammo- 
niac as  hydi'ochl orate  of  ammonia,  and  not  as  chloride  of  ammonium.  Oq 
the  former  view  there  is  simply  a  displacement  of  the  ammonia  by  the  lime, 
and  the  production  of  water,  NH3,HCl  +  CaO=NH3-i-CaCl-f  HO ;  on  the 
latter  view,  the  decomposition  would  be,  NH^,Cl  +  Cab=NH3  +  CaCl  + HO. 
Thus  synthetically,  the  ammonia  is  supposed  to  be  changed  into  a  metal  by 
a  reaction  on  the  elements  of  hydrochloric  acid  ;  while  analytically,  the  metal 
is  supposed  to  be  reconverted  into  ammonia  and  water  by  a  reaction  on  the 
constituents  of  lime.  It  will  be  perceived  that  the  oxacid  salts  of  ammonia 
enumerated  in  the  table  cpntain  an  atom  of  water,  and  this  is  supposed  to 
furnish  the  hydrogen  for  the  production  of  the  metal,  and  the  oxygen  neces- 
sary to  constitute  its  oxide. 

While  the  alkaline  metals  manifest  no  basic  properties  until  after  they 
have  entered  into  combination  w^ith  oxygen,  ammonia,  in  a  dry  state,  forms 
saline  compounds  with  dry  sulphurous  and  carbonic  acids,  and  even  with  the 
anhydrous  sulphuric,  and  phosphoric  acids.  These  compounds  have  received 
the  name  of  Ammonides,  to  distinguish  them  from  the  salts  formed  with  the 
hydrated  oxacids.  Ammonia  must  therefore  be  regarded  as  exceptional  in 
this  respect.  The  production  of  a  metal,  or  of  the  oxide  of  a  metal,  is  not 
necessary  for  the  manifestation  of  basic  properties  by  this  alkali. 


186  SALTS    OF    AMMONIA. 

Salts  of  Ammonia.  Nitrate,  NHg.HOjNO.. — It  is  usually  obtained  by 
saturating  pure  nitric  acid  with  carbonate  of  ammonia,  evaporating  and 
crystallizing. 

This  salt  was  formerly  called  nitrum  jtammans,  in  consequence  of  its  rapid 
decomposition  with  a  slight  explosion  when  heated  to  about  600^.  At  228^ 
it  enters  into  perfect  fusion ;  at  356°  it  boils  without  decomposition  ;  at 
about  390°  to  400°  it  is  decomposed,  and  is  entirely  resolved  into  protoxide 
of  nitrogen  and  water  (NH3HO,N05=2NO  +  4HO).  It  is  deliquescent, 
and  soluble  in  less  than  its  weight  of  water  at  60°.  Its  taste  is  acrid  and 
bitter.  It  indicates  free  acid  after  exposure  to  air,  and,  like  other.'  ammo- 
niacal  salts,  it  loses  its  neutrality  and  becomes  acid  when  its  solution  has 
been  boiled. 

Hydrochlorate  of  Ammonia  ;  Muriate  of  Ammonia,  NH3IICI ;  Chloride 
of  Ammonium,  NH^Cl. — This  salt  may  be  produced  directly,  by  mixing 
equal  volumes  of  dry  gaseous  ammonia  and  dry  hydrochloric  acid,  when 
entire  condensation  ensues.  The  experiment  which  beautifully  illustrates 
the  solidification  of  two  gases  by  chemical  union,  may  be  thus  performed. 
Place  within  a  tall,  stoppered  shade,  a  small  jar  containing  ammonia.  When 
the  gas  has  diffused  itself,  which  may  be  known  by  a  change  of  color  in  test- 
paper  placed  at  the  top  of  the  shade — the  stopper  may  be  removed,  and  a 
small  jar  of  hydrochloric  acid  inverted  over  the  aperture.  A  dense  white 
cloud  of  chloride  of  ammonium  will  immediately  descend  from  the  top  to  the 
bottom  of  the  shade.  Under  the  name  of  sal-ammoniac  this  salt  was  formerly 
imported  from  Egypt,  where  it  was  obtained  by  burning  the  dung  of  camels. 
It  is  now  prepared  either  by  saturating  hydrochloric  acid  with  carbonate  of 
ammonia,  or  by  decomposing  sulphate  of  ammonia  by  chloride  of  sodium 
(NH3,S03,HO  +  NaCl=NH3,HCl  +  NaO,S03).  When  obtained  by  evapo- 
ration  from  its  solution  in  water,  it  forms  octahedral  crystals  ;  but,  in 
commerce,  it  usually  occurs,  as  produced  by  sablimation,  in  translucent 
fibrous  cakes,  hard,  somewhat  elastic,  and  slightly  deliquescent.  In  this 
compact  state  it  requires  for  solution  about  an  equal  weight  of  water  at  212°, 
and  nearly  three  times  its  weight  at  60°,  cold  being  produced  during  its 
solution.  It  is  also  sparingly  soluble  in  alcohol.  When  heated  it  sublimes, 
before  it  fuses,  without  decomposition,  in  the  form  of  a  white  vapor,  and  may 
be  even  passed  through  a  red-hot  porcelain  tube  without  change. 

Sal-ammoniac  is  an  anhydrous  salt ;  it  is  not  volatile  at  common  tempera- 
tures, but  when  exposed  to  air  it  becomes  slightly  acid,  in  consequence  of 
the  loss  of  a  little  ammonia ;  the  aqueous  solution,  therefore,  of  the  salt, 
often  reddens  litmus.  It  is  used  in  the  arts  for  a  variety  of  purposes,  especially 
in  certain  metallurgic  operations  ;  it  is  used  in  tinning,  to  prevent  the  oxi- 
dation of  the  surface  of  copper  ;  it  is  also  employed  in  small  quantities  by 
dyers. 

Sesquicarhonate  ofAmmo7iia,  2NH3,3CO^,2HO. — This  salt  is  the  carbonate 
of  ammonia  of  commerce.  It  is  gienerally  met  with  in  translucent  cakes  of  a 
fibrous  fracture,  as  obtained  by  sublimation  from  a  mixture  of  carbonate  of 
lime  and  sulphate  or  hydrochlorate  of  ammonia.  When  carbonate  of  lime 
and  sulphate  of  ammonia  are  used  for  its  production,  the  results  are  sulphate 
of  lime,  hydrated  sesquicarbonate  of  ammonia,  and  free  ammonia  and  water. 
3[CaO,COJ  +  3[NH3,S03,HC)]=3[CaO,S03]  +  [2NH3.3CO,,2HO]  +  NH3, 
HO.  When  sal-ammoniac  is  substituted  for  the  sulphate  we  have  3[CaO, 
COJ  +  3[NH3,HCl]=3CaCl4-[2HN3,3CO„2HO]  +  NH„HO. 

This  salt  has  a  pungent  odor,  a  hot  and  saline  taste,  and  a  powerful 
alkaline  reaction.  It  may  be  obtained  in  an  impure  state  by  the  destructive 
distillation  of  nitrogenous  matter,  constituting  salts  of  hartshorn  ;  but  this 
and  other  salts  of  ammonia  are  now  chiefly  procured  from  the  distillation  of 


SALTS    OF    AMMONIA.  18t 

coal,  in  the  manufacture  of  gas.  Four  parts  of  water  at  60°  dissolve  about 
one  of  this  salt,  forming  the  liquor  ammonicB  sesqnicarhonatis.  When 
exposed  to  air,  especially  in  the  state  of  powder,  it  effloresces  into  bicar- 
bonate of  ammonia,  and  carbonate  of  ammonia  is  volatilized.  When  its 
aqueous  solution  is  heated,  carbonic  acid  and  a  little  ammonia  is  evolved, 
and  the  single  carbonate  remains  dissolved.  There  is  a  bicarbonate  of 
ammonia  (NH32CO^MO)  on  the  ammonia  theory ;  to  satisfy  the  ammo- 
nium hypothesis,  this  must  be  regarded  as  a  carbonate  of  ammonia  and 
carbonate  of  basic  water  [HO,C03+NH40,COJ.  This  difficulty  applies 
to  all  the  acid  salts  of  ammonia. 

Snlphide  of  Ammonium  (NPI^S). — As  ammonia  is  not  a  metallic  oxide,  it 
is  assumed  that  when  hydrosulphuric  acid  meets  with  this  alkaline  gas,  the 
hydrogen  is  at  once  transferred  to  the  ammonia,  producing  ammonium,  with 
which  the  sulphur  remains  combined.  If  the  dry  gases  are  placed  in  contact, 
a  volatile  anhydrous  crystalline  compound  is  produced,  which  has  the  com- 
position NH3  +  2HS,  or,  as  it  is  frequently  represented,  NH^S-fHS.  The 
crystals  are  soluble  in  water.  The  sulphide  of  ammonium,  commonly  used 
as  a  test,  is  really  the  hydrosulphate  of  the  sulphide,  and  has  the  composition 
above  given.  The  ordinary  solution  is  made  by  saturating  with  sulphuretted 
hydrogen  one-half  of  a  measured  quan^ty  of  a  solution  of  ammonia,  and 
then  adding  to  it  the  other  half.  At  first  the  liquid  is  pale,  but  after  some 
time,  and  as  a  result  of  exposure  to  air,  it  acquires  a  deep  yellow  color, 
owing  to  the  liberation  of  sulphur  and  the  production  of  bisulphide  of  ammo- 
nium (NII4S2).  A  portion  of  the  hydrogen  combines  with  the  oxygen  of 
the  air.  It  is  ultimately  converted  into  hyposulphite  of  ammonia,  and  sul- 
phur is  precipitated.  If  the  solution  of  sulphide  is  properly  prepared,  it 
should  give  no  precipitate  with  a  solution  of  sulphate  of  magnesia.  The 
liquid,  when  concentrated,  evolves  an  irritating  vapor,  which  is  strongly 
alkaline,  and  has  a  very  offensive  odor.  It  is  a  convenient  test  for  the 
precipitation  of  numerous  metals  as  sulphides.  With  some  of  these  it  enters 
into  combination,  forming  double  sulphides. 

Persulphide  of  Ammonium. — This  is  a  compound  of  sulphuretted  hydro- 
gen and  ammonia,  with  excess  of  sulphur.  It  is  probably  a  bisulphide.  It 
is  obtained  by  distilling  a  mixture  of  about  4  parts  of  slaked  lime,  2  of 
hydrochlorate  of  ammonia,  and  one  of  sulphur.  In  its  concentrated  state, 
this  compound  exhales  white  fumes ;  hence  it  was  formerly  called  BoyWs 
fumi^ig  liquor.  It  is  a  deep  yellow  liquid,  smelling  like  a  mixture  of 
sulphuretted  hydrogen  and  ammonia.     It  dissolves  sulphur. 

Characters  of  the  Salts  of  Ammonia. — They  are  white,  soluble  in  water, 
and  are  volatilized  when  heated.  With  the  exception  of  the  carbonate, 
they  have  no  odor  of  ammonia.  The  solutions  are  rendered  acid  by  boiling. 
In  the  dry  state,  a  salt  of  ammonia  is  known  by  heating  it  in  powder  with 
its  bulk  of  quicklime,  and  in  a  state  of  concentrated  solution,  by  boiling  it 
with  a  solution  of  potassa.  Ammonia,  recognizable  by  its  odor  and  other 
properties,  is  evolved  in  both  cases. 


18S  CHLORINE 


CHAPTER    XV. 

CHLORINE    (Cl  =  36).  — COMPOUNDS    WITH    OXYGEN  AND 
HYDROGEN.     HYDROCHLORIC    ACID. 

History. — Chlorine  is  an  elementary  gas,  which  was  discovered  by  Scheele 
in  1774.  For  a  long  time  it  was  supposed,  on  the  authority  of  Lavoisier, 
to  be  a  compound  of  oxygen  and  muriatic  acid,  and  it  was  thence  called 
Oxymurialic  acid  gas  ;  but  in  the  year  1810  it  was  examined  by  Davy,  and 
proved  by  him  to  be  a  simple  undecomposable  body  of  highly  negative  pro- 
perties, like  oxygen.  It  derives  its  name,  chlorine,  from  its  greenish-yellow 
color  (;t^wp6j,  green).  The  alleged  presence  of  oxygen  and  muriatic  acid  in 
the  gas,  was  explained  by  its  reaction  under  the  influence  of  light,  on  the 
elements  of  water — the  gas  having  been  examined  in  the  humid  state.  Under 
these  circumstances  the  hydrogen  was  taken  by  the  chlorine  foruiing  hydro- 
chloric acid  and  the  oxygen  was  evolved.  It  is  not  found  free  in  nature  ;  its 
combining  tendencies  are  so  strong,  that  it  could  not  long  exist  in  the  free 
state.  It  is  a  most  abundant  element,  and  is  the  great  constituent  of  the  sea, 
as  oxygen  is  of  the  earth.  It  is  hence  called  a  halogen  (ajij,  salt).  One 
pound  of  common  salt  (chloride  of  sodium)  contains  more  than  half  a  pound 
of  chlorine.  This  is  equivalent  to  rather  more  than  five  gallons  of  the  gas, 
for  each  gallon  of  sea-water. 

Preparaiion Chlorine  may  be  procured  by  acting  on  a  mixture  of  sea 

salt  and  black  oxide  of  manganese  with  sulphuric  acid ;  but  it  will  be  found 
more  convenient  to  obtain  it  directly  from  hydrochloric  acid,  which  contains 
97  per  cent,  of  this  gas.  The  peroxide  of  manganese,  in  coarse  powder,  is 
mixed  with  four  parts,  by  weight,  of  hydrochloric  acid,  to  which  a  little  water 
is  added  to  check  the  fumes.  A  flask  or  retort  may  be  used,  but  two-thirds 
of  the  capacity  of  the  vessel  should  be  left  free,  as  the  mixture  swells  up 
when  heated.  By  the  application  of  a  gentle  heat  the  gas  will  come  over 
freely.  It  should  be  collected  in  a  bath  containing  but  a  small  quantify  of 
tepid  water.  It  is  very  soluble  in  water,  and  much  is  lost  by  collecting  it  in 
cold  water.  If  hot  water  is  used  there  is  less  of  the  chlorine  dissolved,  but 
on  cooling,  the  gas  is  liable  to  become  mixed  with  a  large  proportion  of  air. 
It  must  not  be  allowed  to  stand  over  water,  or  it  will  entirely  disappear. 
The  jars  should  stand  on  accurately  fitted  glass-plates,  and  the  vessels  which 
are  not  ground  may  be  placed  in  plates  containing  a  small  quantity  of  a 
saturated  solution  of  chlorine.  The  decomposition  which  ensues  in  the 
above-mentioned  process,  may  be  thus  represented  :  2HCl4-MnO^=Cl4-Mn 
CI  -f  2H0.  From  this  it  will  be  perceived,  that  only  one-half  of  the  chlorine 
is  obtained.  It  may  be  procured  from  common  salt  by  heating  a  mixture  of 
four  parts  of  chloride  of  sodium,  and  three  parts  of  peroxide  of  manganese, 
with  seven  of  sulphuric  acid  and  four  of  water  (NaCH-Mn03-f2S03H0  = 
NaO,S034-MnO,S03-fCl  +  2HO). 

The  gas  may  be  procured  quite  pure  and  dry,  by  passing  it  first  through 
a  wash-bottle  containing  some  distilled  water,  and  afterwards  through  a 
glass  tube  containing  broken  chloride  of  calcium  or  concentrated  sulphuric 
acid.  As  the  respiration  of  even  a  small  quantity  of  chlorine  is  highly 
injurious  to  the  lungs,  the  gas  should  be  made  only  where  there  is  a  free 


PROPERTIES    OF    CHLORINE.  189 

current  of  air.  The  first  portions  (containing  air)  should  be  collected  in 
jars,  and  these  may  be  opened  under  a  flue.  The  gas  should  not  be  col- 
lected for  experiments,  until  it  appears  of  a  rich  greenish-yellow  color.  As 
it  is  very  heavy,  it  may  be  obtained  by  displacement.  For  this  purpose  the 
gas,  dried  by  the  process  above  described,  should  be  conducted  by  a  delivery- 
tube  to  the  bottom  of  a  clean  dry  jar,  and  when  the  colored  gas  is  seen  to 
overflow,  the  jar  may  be  covered  and  removed.  For  common  purposes, 
chlorine  may  be  speedily  dried  by  placing  some  strong  sulphuric  acid  at  the 
bottom  of  the  jar  in  which  it  is  to  be  collected,  and  causing  the  delivery- 
tube  to  dip  into  this.  The  chlorine  in  passing  through  the  sulphuric  acid  is 
deprived  of  its  water,  and  if  the  jar,  when  filled,  is  closely  covered,  and  is 
allowed  to  stand  for  a  short  time,  the  gas  will  be  perfectly  desiccated. 

Properties. — Chlorine  gas  is  of  a  greenish-yellow  color,  has  a  pungent 
and  suffocating  odor,  a  peculiar  and  somewhat  astringent  taste,  is  highly 
irritating  when  respired,  exciting  cough  and  great  irritation  of  the  lungs, 
even  when  considerably  diluted  with  atmospheric  air.  When  dry  and  pure, 
it  is  not  affected  by  light,  neither  is  it  altered  by  a  high  temperature.  But 
when  the  gas  in  a  humid  state  is  passed  through  a  red-hot  porcelain  tube,  it 
decomposes  the  watery  vapor,  combining  with  the  hydrogen  to  form  hydro- 
chloric acid,  and  liberates  oxygen.  Although  a  gas  at  the  ordinary  tem- 
perature and  pressure,  chlorine  admits  of  liquefaction  by  cooling  to — 106°, 
or  by  a  pressure  of  four  atmospheres  at  60°,  forming  a  yellow  liquid  which 
has  not  been  yet  solidified.  Chlorine  readily  combines  with  aqueous  vapor 
to  form  a  crystalline  hydrate  of  a  pale  yellowish-green  color.  A  jar  of  the 
gas  containing  the  ordinary  amount  of  vapor,  readily  yields  this  hydrate 
when  exposed  to  a  temperature  of  32°.  If  the  temperature  rises,  the  crystals 
melt,  and  the  jar  will  be  again  filled  with  the  gas,  which  is  set  free  with 
effervescence.  This  hydrate  of  chlorine  consists  of  one  atom  of  the  gas  to 
ten  atoms  of  water  (Cl  +  IOHO);  it  may  be  obtained  in  a  pure  state,  by 
placing  a  small  quantity  of  water  in  a  large  bottle  containing  chlorine,  and 
keeping  the  bottle  in  a  dark  place  at  or  near  the  freezing  point.  If  these 
crystals  are  introduced  into  a  small  bent  tube,  and  the  tube  is  sealed,  they 
will  serve  as  a  source  for  obtaining  the  gas  in  the  liquefied  state  {see  page  80.) 
On  heating  the  end  containing  the  crystals,  and  keeping  the  other  end  of 
the  tube  cool,  a  yellow  vapor  is  evolved  which  is  condensed  into  two  distinct 
fluids,  the  upper  and  lighter  being  an  aqueous  solution  of  chlorine,  while 
the  lower  and  heavier,  which  is  of  a  yellow  color,  is  the  liquefied  gas.  When 
the  tube  is  broken,  the  liquid  is  immediately  converted  to  gaseous  chlorine. 
The  sp.  gr.  of  the  liquid  gas  is  1-33.     It  is  a  non-conductor  of  electricity. 

The  specific  gravity  of  gaseous  chlorine  compared  with  air  is  2*4876, 
which  gives  77 '04  grains  as  the  weight  of  100  cubic  inches  at  mean  tem- 
perature and  pressure.  Its  specific  gravity,  in  reference  to  hydrogen,  may 
be  considered  as  36  to  1.  In  the  electrolysis  of  its  compounds,  chlorine, 
like  oxygen,  appears  at  the  positive  pole  or  anode. 

At  the  temperature  of  60°,  water  dissolves  twice  its  volume  of  the  gas. 
The  solution,  saturated  at  42°,  has  a  specific  gravity  of  1-003  ;  it  is  of  a 
pale  greenish-yellow  color,  has  an  astringent,  nauseous  taste,  and  destroys 
vegetable  colors ;  hence  its  use  in  bleaching.  The  bleaching  agency  is 
explained  by  the  evolution  of  nascent  oxygen,  resulting  from  the  decom- 
position of  aqueous  vapor  or  water.  Chlorine  itself,  when  perfectly  free 
from  moisture,  has  no  such  action.  Thus  if  a  strip  of  dry  litmus-paper  be 
placed  in  a  jar  of  chlorine  collected  by  displacement  through  sulphuric  acid 
in  the  manner  already  described,  it  will  be  found  that  that  portion  of  the 
paper  which  is  in  the  jar  retains  its  blue  color,  while  that  which  hangs  oat 
of  the  jar  will  be  bleached.     The  mouth  of  the  jar  should  be  closely  covered 


190  COMBUSTION    IN    CHLORINE. 

by  a  glass  plate,  or  the  moisture  in  the  air  wil^cause  a  bleaching  of  the 
whole  of  the  litmus-paper.  The  general  effect  of  the  humid  gas  on  organic 
colors  may  be  thus  represented  (Cl  +  HO  =  HCl  +  0).  Indigo,  litmus, 
cochineal,  aniline-purple,  and  other  colors,  are  thus  so  completely  destroyed, 
that  they  cannot  be  artificially  restored. 

The  bleaching  properties  of  the  gas  may  be  shown  by  passing  a  few  cubic 
inches  of  it  into  a  jar  filled  with  diluted  sulphate  of  indigo,  and  inverted  in 
the  water-bath.  The  color  of  the  indigo  is  destroyed  on  agitation.  Let 
some  artificial  flowers  and  a  bunch  of  parsley  be  suspended  in  a  tall  shade 
filled  with  water  and  inverted  in  the  bath.  On  decanting  into  the  shade 
chlorine  gas,  so  as  to  fill  the  upper  part  of  it,  the  colors  depending  on  organic 
compounds  will  be  destroyed,  while  mineral  colors,  including  those  depend- 
ing on  carbon,  will  remain. 

The  aqueous  solution  of  chlorine  was  formerly  known  as  oxymuriatic  acid. 
It  is  now  called  liquor  chlori  or  oqua  chlorinii.  It  has  no  acid  reaction, 
unless  it  has  been  exposed  to  light.  It  is  a  powerful  astringent,  and  pos- 
sesses all  the  bleaching  and  oxidizing  properties  of  the  gas.  It  converts 
sulphurous  into  sulphuric  acid  (Cl-f  S03+2HO=HCl-f  SO3HO),  and  the 
protoxides  of  iron  and  manganese  into  peroxides.  The  ferrocyanide  of 
potassium  is  changed  to  ferricyanide  by  chlorine.  This  solution  gives  a 
white  precipitate  with  nitrate  of  silver  (AgCl),  in  nitric  acid.  When  ex- 
posed to  a  temperature  of  32*^,  the  aqueous  solution  freezes,  forming  the 
crystalline  hydrate  (page  189),  and  ice  which  is  free  from  chlorine.  The 
aqueous  solution  of  chlorine  dissolves  gold  by  the  aid  of  a  gentle  heat. 
When  this  solution  is  exposed  to  the  direct  rays  of  the  sun,  oxygen  is 
evolved  in  consequence  of  the  decomposition  of  the  water,  the  hydrogen  of 
which  unites  to  the  chlorine,  and  forms  hydrochloric  acid  (Cl-fHO  =  HCl-f- 
O).  The  same  change  ensues  more  slowly  in  common  daylight,  but  in  the 
dark,  there  is  no  such  decomposition  ;  so  that  as  gaseous  chlorine  generally 
contains  aqueous  vapor,  the  bottles  in  which  it  is  preserved  should  be  care- 
fully excluded  from  light. 

Chlorine,  and  its  aqueous  solution,  are  powerful  antiseptics,  and  destroyers 
of  foul  arid  noxious  efl9uvia.  This  property  depends  on  its  power  of  decom- 
posing the  noxious  compounds,  which  generally  contain  hydrogen,  and 
resolving  them  into  others  which  are  harmless.  For  the  purposes  of  fumiga- 
tion, chlorine  liberated  at  common  temperatures,  from  black  oxide  of  man- 
ganese and  hydrochloric  acid,  or  from  manganese,  salt,  and  sulphuric  acid, 
may  be  diffused  through  the  foul  atmosphere.  In  the  same  way  the  offensive 
odor  of  decomposing  animal  matter,  may  be  removed  by  sprinkling  it  with 
a  solution  of  chlorine. 

When  a  burning  taper  is  immersed  in  a  jar  of  this  gas,  the  flame  becomes 
red,  throws  oS"  dense,  black  fumes,  and  is  soon  extinguished.  If  a  green 
wax  taper  with  a  glowing  wick  is  suddenly  introduced  into  ajar  of  the  gas, 
the  flame  will  be  rekindled,  and  it  will  continue  to  burn  with  the  evolution 
of  much  carbonaceous  smoke.  Tow  or  cotton,  impregnated  with  ettier,  and 
introduced  in  a  state  of  flame  into  the  gas,  burns  with  a  dense  smoke,  chiefly 
of  carbon.  Bibulous  paper  soaked  in  hot  oil  of  turpentine  suddenly  plunged 
into  a  jar  of  the  gas  (kept  partially  covered)  frequently  bursts  into  flame,  a 
large  quantity  of  carbon  being  given  off  during  the  combustion.  In  all  these 
cases,  chlorine  supports  combustion,  by  taking  only  the  hydrogen  of  the 
combustible,  and  setting  free  the  carbon.  That  hydrochloric  acid  is  a  pro- 
duct, may  be  proved  by  introducing  litmus-paper,  which  will  be  reddened — 
as  well. as  a  glass  rod  dipped  in  strong  ammonia,  which  will  cause  the  evolu- 
tion of  copious  ^^ite  fumes  of  hydrochlorate  of  ammonia.  Some  bodies — 
Buch  as  sulphide  of  carbon,  which  burn  with  great  splendor  in  oxygen — are 


EQUIVALENT.      TESTS    FOR    CHLORINE.  191 

immediately  extinguished  in  this  gas.  There  are,  however,  many  substances, 
such  as  phosphorus  and  several  of  the  metals,  which  are  spontaneously  in- 
flamed by  chlorine,  and  burn  in  it  with  much  energy  Phosphorus  burns 
in  the  gas  at  all  temperatures  (see  page  102).  In  these  cases,  binary  com- 
pounds result,  some  of  which,  like  those  of  oxygen,  are  possessed  of  acid 
properties  :  others  are  not  acid,  and  are  termed  chlorides.  Brass  or  copper 
leaf,  and  powdered  antimony,  serve  well  to  show  the  intense  action  of 
chlorine  upon  certain  metals.  When  introduced  into  the  gas,  they  enter 
into  immediate  combustion,  and  chloride  of  copper  and  chloride  of  antimony 
art  formed. 

Fill  a  dry  jar  with  some  leaves  of  Dutch  gold,  and  invert  over  it  a  jar  of 
pure  chlorine ;  as  the  gas  descends,  the  metal  will  undergo  combustion, 
acquiring  a  red  heat  without  flame,  and  the  whole  will  disappear.  The  com- 
bustion of  antimony  may  be  shown  by  sifting  the  freshly-powdered  metal 
into  ajar  of  the  gas  on  partially  removing  the  cover.  If  a  piece  of  sodium, 
heated  to  ignition  in  air,  be  introduced  into  a  bell-jar  of  the  gas,  it  will  burn 
with  great  splendor.  If  a  coil  of  fine  iron-wire  is  made  red  hot  and  plunged 
into  the  gas,  it  will  burn  with  a  deep  lurid-red  flame,  evolving  copious  brown 
vapors  of  sesquichloride  of  iron.  When  fine  copper  or  brass  wire  ignited  is 
employed,  it  burns  in  chlorine  with  splendid  scintillations.  Arsenic  and 
mercury  at  a  high  temperature  burn  in  the  gas,  producing  highly  noxious 
fumes.  These  experiments  should  only  be  performed  where  there  is  a  free 
current  of  air  to  carry  off  the  volatile  products. 

Chlorine  displaces  bromine  and  iodine  from  their  metallic  and  non-metallic 
combinations.  Paper  wetted  with  a  solution  of  bromide  of  potassium,  and 
introduced  into  chlorine,  acquires  a  yellow  color  from  the  liberated  bromine. 
If  iodide  of  potassium  is  used,  iodine  is  abundantly  set  free. 

There  is  no  body  for  which  chlorine  manifests  so  strong  an  afiinity  as  for 
hydrogen.  All  the  hydrogen  compounds  of  carbon,  sulphur,  phosphorus, 
nitrogen,  antimony,  and  arsenic,  are  decomposed  by  it:  hydrochloric  acid  is 
produced,  and  the  metal  or  metalloid  is  liberated.  If  a  jar  of  chlorine  is  in- 
verted over  one  containing  sulphuretted  hydrogen,  this  gas  is  decomposed, 
sulphur  is  precipitated,  and  hydrochloric  acid  is  formed.  This  may  serve  as 
an  illustration  of  its  operation  in  deodorizing  foul  and  offensive  effluvia.  The 
decomposition  of  ammonia  by  this  gas  has  been  already  referred  to.  The 
whole  of  the  hydrogen  is  taken  and  the  nitrogen  is  liberated  (3Cl-f  4NH3  = 
3(NH.,IICl-f-N)  (page  185).  The  results  may  be  shown  in  another  mode. 
Introduce  into  ajar  of  chlorine  bibulous  paper  saturated  with  a  strong  solu- 
tion of  ammonia.  There  is  violent  combustion  with  a  pale  reddish  flame 
(chloride  of  nitrogen  ?),  and  dense  white  fumes  of  hydrochlorate  of  ammonia 
escape  (6Cl-f  4NH3=3(NH3HCl)-f  NCI3).  Ammonia  may  be  regarded  as 
the  most  effectual  agent  for  the  removal  or  neutralization  of  gaseous  chlorine. 
Solutions  of  potassa  and  soda  absorb  the  gas,  producing  salts  which  vary 
according  to  circumstances.  A  current  of  the  gas  passed  into  a  hot  and 
concentrated  solution  of  potassa,  produces  chloride  of  potassium  and  chlorate 
of  potassa,  which  may  be  obtained  by  evaporation  (6KO  +  6Cl=5KCl-h 
KOCIO5).  If  t,he  alkaline  solution  is  cold  and  much  diluted,  then  a  chloride 
and  hypochlorite  are  produced.     (See  Hypochlorous  Acid.) 

Equivalent  and  Compounds. — The  atomic  weight  of  chlorine  is  usually 
taken  at  36  (page  66),  and  its  combining  volume  1.  Like  hydrogen,  it  is 
a  monatomic  gas.  Its  range  of  combination  is  as  great  as  that  of  oxygen. 
It  combines  with  all  the  metals,  and  with  the  greater  number  of  metalloids. 
These  binary  compounds  are  called  Chlorides.  It  forms  only  acid  compounds 
with  oxygen  and  hydrogen. 

Tests. — The  color,  odor,  and  bleaching  properties  of  this  gas  are  in  all 


192  HYPOCHLOROUS    ACID. 

cases  sufficient  for  its  identiflcation.  In  solution  \i  may  be  known  by  these 
properties,  and  by  the  white  curdy  precipitate  which  it  gives  wth  a  solution 
of  nitrate  of  silver,  as  well  as  by  its  power  of  decomposing  iodide  of  potas- 
sium, and  producing  a  deep-blue-colored  compound  when  the  iodide  is  mixed 
with  a  solution  of  starck     An  excess  of  chlorine  destroys  this  color. 

Compounds  of  Chlorine  and  Oxygen. — These  elementary  bodies  do  not 
combine  directly.  They  have  but  a  feeble  affinity  for  each  other,  and,  when 
combined,  are  readily  separated  by  slight  causes.  There  are  five  compounds 
of  these  elements,  four  of  which  are  acids  : —  • 

1.  Hypochlorous  acid,  CIO  3.  Peroxide  of  chlorine,  CIO4 

2.  Chlorous  acid,  CIO3  4.  Chloric  acid,  CIO. 

5.  Perchloric  acid,  CIO7. 

1.  Hypo  chlorous  Acid  (C10=44) When  a  small  quantity  of  hydrate  of 

lime  is  placed  in  ajar  of  chlorine,  the  gas  soon  disappears,  and  a  compound 
of  hypochlorite  of  lime  and  chloride  of  calcium  is  formed  (2CaO-f2Cl  = 
CaO,C10  +  CaCl).  This  is  well  known  as  bleaching  powder  {see  Chloride 
OF  Lime).  When  a  current  of  chlorine  is  passed  into  a  cold  weak  solution 
•of  soda  or  potassa,  a  similar  reaction  takes  place,  and  an  alkaline  hypo- 
chlorite is  formed  (2K0  +  2C1=K0,C10  +  KC1).  If  these  compounds  are 
acted  upon  by  acids,  they  evolve  chlorine,  and  not  hypochlorous  acid.  If, 
however,  diluted  sulphuric  acid  is  added  very  gradually  to  chloride  of  lime, 
diffused  in  water  and  the  mixture  is  kept  stirred,  hypochlorous  acid  is  liber- 
ated and  may  be  distilled  over  as  a  weak  solution  of  the  acid  in  water. 
Balard  first  suggested  a  method  of  obtaining  pure  hypochlorous  acid.  His 
process  consists  in  agitating  a  mixture  of  one  part  of  precipitated  red  oxide 
of  mercury  with  twelve  of  distilled  water,  in  a  bottle  filled  with  chlorine  ; 
the  gas  is  rapidly  absorbed.  If  the  proportion  of  the  oxide  is  insufficient, 
the  deposited  powder  is  white,  and  some  of  the  chlorine  remains  unabsorbed; 
but  the  oxide  should  be  in  slight  excess,  so  as  to  remain  red,  and  entirely 
absorb  the  gas.  (2HgO  +  2Cl  =  C10-fHgCl,HgO.)— (6  drachms  of  red 
oxide  mixed  in  .fine  powder  with  an  ounce  and  a  half  of  water,  and  shaken 
in  a  quart  bottle  of  chlorine,  are  proportions  recommended  by  Graham)* 
When  the  absorption  is  complete,  the  contents  of  the  bottle  are  poured  upon 
a  filter,  and  the  filtered  liquor  subjected  to  distillation  in  vacuo,  by  which  a 
diluted  solution  of  hypochlorous  acid  is  obtained,  and  this  may  be  concen- 
trated by  a  second  distillation. 

Tlie  gaseous,  is  obtained  from  the  aqueous  acid,  by  introducing  into  an 
inverted  jar  of  mercury,  a  quantity  of  the  concentrated  liquid,  and  then  pass- 
ing into  it,  through  the  mercury,  small  fragments  of  fused  nitrate  of  lime. 
The  nitrate  abstracts  the  water  and  liberates  pure  hypochlorous  acid  in  the 
state  of  a  gas,  a  little  deeper-colored  than  chlorine,  of  a  strong  penetrating 
odor,  and  absorbable  by  mercury,  forming  oxychloride,  from  the  contact  of 
which  it  is  preserved  in  the  above  mode  of  obtaining  it,  by  the  layer  of  solu- 
tion of  nitrate  of  lime.  A  slight  elevation  of  temperature,  even  the  warmth 
of  the  hand,  is  sufficient  to  decompose  this  gas  with  explosion  and  evolution 
of  heat  and  light,  so  that  it  requires  careful  management.  It  is  not  changed 
by  some  hours'  exposure  to  diffused  daylight,  but  direct  solar  rays  decom- 
pose it  in  a  few  minutes  without  explosion  ;  when  mixed  with  hydrogen  and 
inflamed,  it  detonates  violently,  but  at  common  temperatures,  the  mixture 
remains  unchanged.  Bromine  and  iodine  slowly  decompose  it;  sulphur, 
selenium,  phosphorus,  arsenic,  and  antimony,  decompose  it  with  sudden  and 
violent  detonation  ;  charcoal  also  causes  it  to  explode,  apparently  in  con- 
sequence of  the  condensation  which  the  gas  suffers  in  its  pores.     In  these 


PEROXIDE    OF    CHLORINE.  193 

cases  the  elements  are  pejyjxidized  and  converted  into  the  higher  class  of 
acids.  When  placed  in  contact  with  iron-61ings,  the  iron  is  oxidized,  and 
chlorine  is  evolved  ;  but  when  silver  is  substituted  for  iron,  chloride  of  silver 
is  formed,  and  oxygen  is  evolved.  Hypochlorous  acid  gas  may  be  procured 
as  a  yellow  gas,  by  passing  a  current  of  dry  chlorine  over  well-dried  oxide 
of  mercury.  The  gas  must  be  condensed  in  a  receiver,  kept  cool  by  a  freez- 
ing mixture.  In  this  reaction,  the  oxygen  is  simply  displaced  by  the 
chlorine  (HgO  +  SCl  — C10  +  ITgCl),.and  corrosive  sublimate  as  well  as  hypo- 
chlorous  acid  results.  In  performing  this  experiment,  unless  the  temperature 
is  kept  low,  oxygen  only  will  be  liberated.  The  gas  is  formed  of  a  volume 
of  chlorine  united  to  half  a  volume  of  of  oxygen,  these  being  condensed  into 
one  volume  of  the  compound.  The  specific  gravity  of  the  gas  is  in  accord- 
ance with  this  constitution  ;  for  one  half  volume  of  oxygen  =0-5528+2'48'76 
sp.  gr.  of  chlorine  =3'0404.  Its  specific  gravity  is,  therefore,  3*04,  and  100 
c.  i.  weigh  94*16  grains. 

According  to  Regnault,  water  dissolves  at  least  two  hundred  times  its 
volume  of  this  gas,  forming  a  pale  yellow-colored  liquid.  The  solution  pos- 
sesses powerfully  bleaching  properties  ;  twice  as  great  in  proportion  as  those 
of  chlorine.  This  is  probably  owing  to  the  nascent  oxygen  which  is  evolved 
in  its  decomposition.  It  is  contained  with  hydrochloric  acid  in  a  solution  of 
chlorine  which  has  undergone  chemical  changes,  and  it  adds  to  its  bleaching 
power.  It  is  decomposed  by  the  non-metallic  substances,  which  act  upon 
the  gas,  and  is  a  most  powerful  oxidizing  agent.  It  will  even  oxidize  the 
chloride  of  potassium,  and  convert  it  into  chlorate  of  potassa.  It  throws 
down  peroxide  of  lead  from  a  solution  of  the  chloride  of  that  metal,  and 
sesquioxide  of  manganese  from  the  chloride.  A  solution  of  chlorine  pro- 
duces these  effects  only  under  the  agency  of  light.  (Regnault.)  Chloride 
of  silver  exerts  upon  it  a  catalytic  action,  resolving  it  into  its  elements 
without  undergoing  any  change.  A  concentrated  solution  of  the  gas  is 
decomposed  by  hydrochloric  acid,  and  chlorine  is  evolved  (HCl-fC10  = 
H0  =  2C1).  If  the  liquids  are  mixed  at  a  low  temperature,  a  solid  crys- 
talline hydrate  of  chlorine  is  obtained. 

2.  Chlorous  Acid  (ClOg=60).— This  is  a  gaseous  acid  of  a  greenish- 
yellow  color,  not  easily  liquefied  by  cold.  It  may  be  procured  by  mixing  3 
parts  of  arsenious  acid  with  4  parts  of  chlorate  of  potassa  and  sufficient 
water  to  make  a  paste,  and  adding  to  the  mixture  in  a  retort  12  parts  of 
nitric  acid  diluted  with  4  parts  of  water.  This  mixture,  distilled  in  a  water- 
bath,  yields  a  greenish-yellow  colored  gas  (chlorous  acid)  of  a  specific  gravity 
of  2  64 6.  (Regnault.)  Water  dissolves  five  or  six  times  its  volume  :  the 
solution  has  a  golden-yellow  color.  The  chloric  acid  is  deoxidized  by  the 
arsenious  acid,  which  is  converted  during  the  process  into  arsenic  acid.  The 
gas  can  be  collected  only  in  the  dry  way,  as  it  is  very  soluble  in  water,  and 
is  decomposed  by  mercury.  It  is  converted  by  explosion  at  about  130° 
into  chlorine  and  oxygen.  Like  hypochlorous  acid,  it  oxidizes  with  explo- 
sion many  of  the  non-metallic  bodies.  It  re  a  powerful  bleaching  agent, 
and  is  a  monobasic  acid,  forming  chlorites  with  bases.  The  specific  gravity 
of  the  gaseous  acid  shows  that  it  must  contain  in  each  volume  one  volume  of 
oxygen  and  two-thirds  of  a  volume  of  chlorine— 1 -1057 +  1-6584=2 '764, 
which  does  not  widely  differ  from  the  specific  gravity  actually  determined. 
In  reference  to  its  constitution  by  volume,  it  is  usually  considered  that  two 
volumes  of  chlorine  (two  atoms),  and  three  volumes  of  oxygen  (six  atoms), 
are  condensed  into  three  volumes  or  atoms  of  the  compound. 
^  3.  Peroxide  of  Chlorine  (010^=68). — This  compound,  which  is  some- 
times called  hypochloric  acid,  was  discovered  by  Davy,  in  1815.  It  may  be 
procured  by  acting  on  fused  chlorate  of  potassa  by  concentrated  sulphuric 

Id 


194  CHLORIC    ACID. 

acid,  in  the  proportion  of  one  part  of  the  salt  to  three  parts  of  acid.  The 
materials  in  small  quantity  may  be  heated  in  a  tube-retort  by  a  water-bath, 
at  a  temperature  not  exceeding  100°.  The  gas  is  soluble  in  water,  which 
will  take  up  twenty  times  its  volume  ;  and  it  is  decomposed  by  mercury, 
hence  it  can  be  collected  only  by  displacement.  The  gas  is  of  a  yellowish 
color,  and  has  a  peculiar  odor  resembling  chlorine ;  it  is  not  acid  in  reac- 
tion, but  it  has  strong  bleaching  properties.  It  is  decomposed  with  explo- 
sion at  about  140°.  Phosphorus  produces  with  it  violent  combustion  even 
under  water.  This  experiment  may  be  performed  by  placing  the  powdered 
chlorate  in  a  tall  conical  glass  with  a  small  quantity  of  phosphorus,  and 
covering  the  mixture  with  cold  water.  On  pouring  concentrated  sulphuric 
acid  into  the  mixture  by  a  long  funnel  the  peroxide  is  set  free,  and  the 
phosphorus  burns  with  bright  scintillations,  producing  phosphoric  acid. 
The  gas  may  be  readily  liquefied  by  cold  and  pressure.  Although  not  acid, 
it  is  dissolved  by  alkaline  liquids,  but  it  forms  no  saline  combinations  :  on 
evaporating  the  alkaline  solution,  a  chlorite  and  chlorate  of  the  alkali  are 
obtained  (2010^=0103 -I-CIO5).  The  specific  gravity  of  the  gas  is  233. 
This  nearly  corresponds  to  half  a  volume  of  chlorine  and  one  volume  of 
oxygen  in  each  volume  (r2438  +  1105t  =  2*3495),  or  in  two  volumes 
there  would  be  one  volume  of  chlorine  and  two  volumes  of  oxygen. 

4.  Chloric  Acid  (0105=16). — This  acid  was  discovered  by  Gay-Lussac 
{Ann.  de  Chim.,  xci.  108).  It  cannot  exist  independently  of  an  atom  of 
water,  or  of  some  base,  so  that  it  has  not  been  obtained  anhydrous  ;  the 
hydrated  acid,  in  its  state  of  extreme  concentration,  being  HO,C10,=85. 
In  depriving  it  of  water  it  is  converted  into  peroxide  of  chlorine  and  oxygen. 
Hydrated  chloric  acid  may  be  prepared  by  adding  diluted  sulphuric  acid  to 
a  solution  of  chlorate  of  baryta,  as  long  as  it  occasions  a  precipitate.  The 
baryta  is  thus  separated  in  the  form  of  an  insoluble  sulphr^e,  and  the  chloric 
acid  remains  in  aqueous  solution.  Oare  must  be  taken  to  add  no  more  sul- 
phuric acid  than  is  requisite,  for  any  excess  contaminates  the  chloric  acid. 
If  the  exact  proportion  has  been  used,  the  chloric  acid  is  neither  rendered 
turbid  by  diluted  sulphuric  acid  nor  by  chlorate  of  baryta.  If  either  of  these 
occasions  a  precipitate,  the  solution  must  be  carefully  added  till  the  efl'ect 
ceases ;  the  clear  liquid  may  then  be  decanted  or  filtered  off.  It  may  be 
concentrated  by  evaporation  in  vacuo  until  it  acquires  a  syrupy  consistency. 
It  may  also  be  procured  by  the  action  of  fluosilicic  acid  on  chlorate  of  potassa. 
A  hot  aqueous  solution  of  ciilorate  of  potassa  is  mixed  with  excess  of 
fluosilicic  acid  ;  the  acid  liquid,  when  cold,  is  filtered,  evaporated  below  80°, 
and,  after  two  days,  filtered  through  powdered  glass. 

Hydrated  chloric  acid  is  a  sour  liquid,  and  of  a  yellowish  tint  when  highly 
concentrated.  It  deoxidizes  permanganate  of  potassa  and  destroys  its  color. 
It  reddens  vegetable  blues,  and  then  bleaches  them.  When  added  to  a 
strong  solution  of  potassa,  crystals  of  chlorate  of  potassa  are  deposited. 
When  concentrated,  it  acts  powerfully,  and  even  to  ignition,  upon  paper, 
cotton,  and  some  other  dry  organic  bodies;  it  decomposes  alcohol,  with  the 
formation  of  acetic  acid.  The  most  remarkable  of  its  salts,  which  are  now 
termed  chlorates,  were  formerly  known  under  the  name  of  oxymuriates,  or 
hyperoxymuriates.  When  distilled  at  a  higher  temperature  than  100°,  it 
suffers  decomposition,  and  a  portion  of  chlorine  and  oxygen  are  liberated, 
perchloric  acid  passing  over,  but  no  chloric  acid.  It  is  decomposed  by 
hydrochloric  acid  into  chlorine  and  water,  5H01  +  C105=5HO  +  6C1.  This 
mixture  dissolves  gold,  and  is  sometimes  employed  for  the  oxidation  and 
destruction  of  organic  matter  in  toxicological  researches.  By  excess  of  sul- 
phurous acid,  it  produces  sulphuric  and  hydrochloric  acids;  6SOa-fC105,HO 
«6S03-fHCl:   and  by  excess  of  sulphuretted  hydrogen  it  forms  water, 


PERCHLORIC    ACID.  195 

hydrochloric  acid,  and  sulphur;    6HS4-C105=5II0,  +  HC1  +  6S.      Those 
acids  which  are  already  saturated  with  oxygen,  do  not  act  upon  it. 

Chlorates. — These  salts  are  MO-f-ClO^.  They  deflagrate  powerfully  with 
combustible  matter,  and  often  by  mere  friction.  {See  Chlorate  of  Potassa.) 
They  are  all  soluble  in  water.  By  heat  they  are  mostly  resolved  into  chlo- 
rides and  evolve  oxygen.  The  electrolysis  of  the  chlorate,  when  in  igneous 
fusion,  has  been  found  by  M.  Gerardin  to  present  an  exception  to  the  general 
results  of  the  decomposition  of  salts  by  current  electricity.  Thus,  in  refer- 
ence to  the  salts  of  potassa  and  soda,  in  igneous  fusion,  it  was  observed  that 
the  oxygen  only  was  set  free  at  the  positive  pole,  the  radicals  of  both  acid 
and  base  appearing  at  the  negative  pole.  In  thus  decomposing  the  fused 
chlorate  of  potassa,  however,  it  was  found  that  the  oxygen  and  chlorine 
appeared  at  the  positive  pole  in  a  state  of  mixture,  and  the  potassium  at  the 
negative.  This  apparent  anomaly  is  probably  due  to  the  simultaneous  de- 
composition of  the  chloride  of  potassium  produced  by  the  eifect  of  heat  on 
the  chlorate  {Cosmos,  Oct.  25,  1861,  p.  471.) 

A  chlorate  is  easily  identified  by  adding  to  a  small  portion  in  powder  a 
drop  of  sulphuric  acid.  The  odor  of  peroxide  of  chlorine  is  immediately 
perceived.  If  a  grain  or  two  of  white  sugar  be  added  to  the  mixture,  there 
will  be  immediate  combustion.  A  solution  of  a  chlorate  colored  with  indigo 
has  the  color  discharged  in  the  cold,  by  the  addition  of  sulphurous  acid. 
When  indigo  is  mixed  with  the  solution  of  a  nitrate,  and  sulphurous  acid  is 
added,  the  color  is  not  discharged  until  the  mixture  has  been  heated. 

The  euchlorine  of  Davy,  which  was  produced  by  the  reaction  of  hydro- 
chloric acid  on  chlorate  of  potassa,  was  probably  a  compound  of  chlorous 
acid  and  chlorine. 

5.  Perchloric  Add,  ClOy,  or  as  hydrate=H0,C107,  was  discovered  by 
Count  Stadion.  It  is  unknown  in  the  anhydrous  state,  but  it  may  be  pro- 
cured as  hydrate  by  distilling  perchlorate  of  potassa  with  its  own  weight  of 
sulphuric  acid,  diluted  with  about  a  fourth  part  of  water.  At  a  temperature 
of  about  280^,  white  vapors  pass  off,  which  condense  in  the  form  of  a  color- 
less liquid. 

Another  method  consists  in  decomposing  a  hot  solution  of  chlorate  of 
potassa  with  fluosilicic  acid,  concentrating  the  chloric  acid  by  boiling,  and 
subsequently  distilling  the  residue.  Dr.  Roscoe  found  that  one  atom  of  per- 
chlorate of  potassa,  distilled  with  four  atoms  of  concentrated  sulphuric  acid, 
also  yielded  the  concentrated  hydrate.  It  is  considered  to  be  a  more  stable 
compound  than  the  preceding,  as  it  is  not  decomposed  by  sulphuric  or 
hydrochloric  acid.  When  concentrated,  its  specific  gravity  is  16,  and  it 
boils  at  392°.  By  distillation  with  strong  sulphuric  acid,  it  may  be  obtained 
in  the  solid  form  and  crystallized. 

The  properties  of  the  concentrated  acid  have  been  lately  examined  by  Dr. 
Roscoe  {Proc.  of  Brit.  Assoc,  Sept.  1861).  He  procured  it  as  a  colorlessj 
heavy  (sp.  gr.  1782),  oily-looking  liquid,  fuming,  highly  corrosive,  and 
giving  off,  when  heated  in  air,  dense  white  vapors.  It  is  one  of  the  most 
powerful  oxidizing  agents  known  ;  a  single  drop  brought  into  contact  with 
charcoal,  paper,  wood,  alcohol,  ether,  and  other  combustibles,  caused  ex- 
plosive combustion  resembling  that  of  the  chloride  of  nitrogen.  It  could 
not  be  kept  long,  even  in  sealed  glass  tubes  placed  in  the  dark.  It  under- 
went spontaneous  decomposition,  blowing  the  glass  vessel  to  pieces.  When 
mixed  with  water,  it  produced  a  hissing  noise,  with  the  evolution  of  great 
heat  forming  a  crystalline  hydrate.  It  could  not  be  distilled  without  decom- 
position. The  acid  contains  61  per  cent,  of  oxygen.  The  solution  has  a 
strongly  acid  reaction,  but  no  bleaching  properties. 

Perchlorates.     Oxy chlorates.— -These  salts  have  the  formula  MO  +  CIO^ 


196  nYDROCHLORIC    ACID. 

Although  more  abundant  in  oxygen,  they  are  of  less  explosive  tendency,  and 
less  easily  decomposed  by  heat  than  the  chlorates,  like  which  they  are 
resolved  either  into  chlorides  and  oxygen  gas,  or  into  lower  oxides,  oxygen, 
and  chlorine  :  they  are  all  soluble  in  boiling  water,  but  the  perchlorate  of 
potassa  requires  150  parts  of  cold  water  to  dissolve  it.  A  perchlorate  is 
known  from  a  chlorate  by  the  non-production  of  peroxide  of  chlorine  when 
strong  sulphuric  acid  is  added  to  it. 

Chlorine  and  Hydrogen. — There  is  only  one  compound  of  these  elements 
— an  anhydrous  gaseous  hydracid,  known  as  hydrochloric  or  muriatic  acid 
gas.     It  was  discovered  by  Priestley  in  1172. 

Hydrochloric  Acid  (HC1=37).  Cfdorhydric  ov  Muriatic  Acid.  Spirit 
of  Salt. — Chlorine  and  hydrogen,  when  mixed  in  equal  volumes,  combine 
directly  to  produce  hydrochloric  acid  gas.  If  a  lighted  taper  is  applied  to 
the  mixture,  or  the  electric  spark  is  discharged  into  it,  there  is  immediate 
combination,  with  a  violent  explosion.  This  also  happens  when  the  mixed 
gases  are  exposed  to  the  direct  rays  of  the  sun,  the  lime-light,  or  the  light  of 
burning  phosphorus.  The  combination  takes  place  more  slowly  and  gradu- 
ally in  diffused  daylight,  and  is  totally  arrested  in  the  dark.  A  mixture  of 
the  two  gases  placed  in  a  graduated  vessel  over  water  may  be  employed  for 
photometrical  purposes,  the  amount  of  absorption  as  a  result  of  combination, 
indicating  the  intensity  of  light. 

Preparation. — The  gas  is  generally  procured  by  acting  upon  common  salt 
with  sulphuric  acid  ;  it  must  be  collected  over  mercury.  The  proportions 
are  one  part  of  salt  to  two  parts  of  acid.  The  salt  should  be  fused,  coarsely 
powdered,  and  put  into  a  tubulated  retort,  which  may  be  one  fourth  filled 
with  it :  the  sulphuric  acid  should  barely  cover  the  salt ;  the  gas  is  instantly 
extricated,  and  when  its  evolution  slackens,  it  may  be  quickened  by  the 
gentle  heat  of  a  lamp.  It  is  convenient  to  put  a  long  strip  of  blotting- 
paper  into  the  neck  of  .the  retort,  which  absorbs  any  liquid  that  may  chance 
to  go  over,  and  prevents  its  soiling  the  mercury.  Clean  and  dry  bottles  may 
be  filled  with  this  gas  by  displacement,  as  it  has  a  high  specific  gravity. 
The  chemical  changes  may  be  thus  represented:  NaCl-j-S0„,H0=HCl4- 
NaCSOg. 

Properties. — Although  permanently  gaseous  at  common  temperatures  and 
pressures,  Mr.  Faraday  liquefied  this  gas  by  generating  it  in  a  sealed  tube, 
so  as  to  expose  it  to  a  pressure  of  about  forty  atmospheres  at  50°.  It  was 
colorless,  and  possessed  a  refractive  power  inferior  to  that  of  water.  He 
could  not  succeed  in  solidifying  it.  {Phil.  Trans.,  1823;  and  1845,  p.  163.) 
Hydrochloric  acid  gas  is  perfectly  irrespirable  :  it  extinguishes  the  flame  of 
a  taper,  and  of  all  combustible  bodies,  and  is  itself  uninflammable.  It  irri- 
tates the  skin  ;  has  a  strong  attraction  for  water  ;  and  when  it  escapes  into 
the  air,  it  forms  visible  fumes,  arising  from  its  combination  with  aqueous 
vapor.  A  piece  of  ice  introduced  into  the  gas  over  mercury,  is  immediately 
liquefied  and  the  gas  is  absorbed  by  the  liquid.  If  a  tall  jar  of  the  gas  be 
carefully  transferred,  with  its  mouth  downwards,  from  the  mercurial  to  the 
water-trough,  the  water  instantly  rushes  in  with  violence,  and  fills  it.  The 
gas  has  no  bleaching  properties,  but  it  strongly  reddens  litmus-paper.  In 
the  dry  state,  it  undergoes  no  change  by  exposure  to  heat ;  but  when  mixed 
with  air  and  passed  over  broken  pumice,  heated  to  redness,  aqueous  vapor 
and  chlorine  result.     (Pelouze.) 

Water  takes  up  480  to  500  times  its  bulk  of  hydrochloric  acid  gas,  at  40°, 
and  has  its  specific  gravity  increased  from  1  to  1*210.  (H.  Davy.)  This 
may  be  shown  by  throwing  up  a  few  drops  of  water  into  a  tall  jar  of  the  gas 
standing  over  mercury  j  the  gas  disappears,  and  the  mercury  fills  the  vessel. 


SOLUTION    OF    HYDROCHLORIC    ACID.  197 

There  is  considerable  elevation  of  temperature  during  this  condensation  of 
the  gas.  The  experiment  maybe  performed  like  that  described  at  page  209, 
using  a  solution  of  blue  in  place  of  red  litmus.  Entire  absorption  is  a  proof 
of  the  purity  of  the  gas. 

For  saturating  water  with  the  acid  gas,  we  may  employ  a  tubulated  retort 
or  flask,  connected  with  a  globe  receiver  from  which  issues  a  bent  tube  at  a 
right  angle,  and  just  dipping  below  the  surface  of  distilled  water  contained 
in  a  bottle.  The  bottle  should  be  closed  and  the  water  kept  cool,  as  much 
heat  is  given  out  during  the  condensation  of  the  gas.  The  different  joints 
of  the  apparatus  may  be  secured  either  by  grinding,  or  by  well-cut  corks 
rendered  tight  by  a  mixture  of  drying-oil  and  pipe-clay.  The  retort  or  flask 
may  be  gently  heated  by  a  sand-bath.  The  bottle  should  be  only  half  filled 
with  water,  as,  in  dissolving  the  gas,  it  increases  from  one- third  to  two-thirds 
in  volume. 

Solution. — When  gaseous  hydrochloric  acid  is  thus  dissolved  in  water,  it 
forms  the  liquid  hydrochloric  acid,  commonly  called  muriatic  acid  or  spirit 
of  salt,  which  was  discovered  by  Glauber  about  the  middle  of  the  seventeenth 
century.  It  is  generally  procured  by  distilling  a  mixture  of  dilute  sulphuric 
acid  and  common  salt.  The  proportions  directed  in  the  "  London  Pharma- 
copoeia" are  two  pounds  of  salt  and  twenty  ounces  of  sulphuric  acid,  diluted 
with  twelve  ounces  of  water.  The  retort  containing  these  ingredients  may 
be  luted  on  to  a  receiver,  containing  the  same  quantity  of  water  used  in 
diluting  the  sulphuric  acid,  and  the  distillation  carried  on  in  a  sand-bath. 
The  specific  gravity  of  the  product  is  stated  to  be  1-160,  and  100  grains  of 
it  should  be  saturated  by  132  grains  of  crystallized  carbonate  of  soda.  The 
following  will  be  found  convenient  proportions  for  procuring  the  acid — 6 
ounces  of  salt,  previously  fused,  8|  ounces  by  measure  of  sulphuric  acid  (sp. 
gr.  r65),  and  4  ounces  of  water.  An  acid  of  1-15  sp.  gr.  is  obtained.  In 
order  to  procure  the  acid  of  greater  strength  (1 '21)  we  may  employ  the 
weak  acid  in  place  of  water  and  sulphuric  acid,  in  a  second  distillation  with 
fused  salt.  (Gregory.)  The  quantity  of  real  acid  in  hydrochloric  acid  of 
different  densities  may  be  ascertained  by  the  quantity  of  pure  carbonate  of 
lime  (Carrara  marble)  which  a  given  weight  of  the  acid  will  dissolve.  Every 
fifty  grains  of  the  carbonate  are  equivalent  to  thirty-seven  of  real  acid. 

When  this  acid  is  pure  and  concentrated,  it  should  be  colorless,  but  it  has 
generally  a  pale  yellow  hue  arising  from  particles  of  cork  or  lute  that  may 
have  accidentally  fallen  into  it,  or  sometimes  from  a  little  iron.  The  acid  of 
commerce  almost  always  contains  iron,  sulphuric  acid,  and  sometimes  nitric 
acid,  as  well  as  common  salt.  The  iron  may  be  detected  by  the  black  tint 
produced  by  tincture  of  galls,  in  the  acid  previously  diluted  and  neutralized 
by  carbonate  of  soda.  If  a  solution  of  chloride  of  barium,  dropped  into 
the  diluted  acid,  occasion  a  white  cloud  or  precipitate,  it  announces  sulphuric 
acid.  The  presence  of  nitric  acid  (and  of  free  chlorine  and  bromine?)  is 
shown  by  boiling  some  gold-leaf  in  the  suspected  hydrochloric  acid,  and 
then  dropping  into  it  a  solution  of  protochloride  of  tin.  If  nitric  acid  be 
present,  this  will  produce  a  purplish  tint,  showing  the  gold  to  have  been 
dissolved,  while  pure  hydrochloric  acid  has  no  action  upon  it.  Common 
salt  and  other  saline  substances  may  be  detected  in  it  by  evaporating  the 
acid  to  dryness ;  when  pure,  it  leaves  no  residue.  Traces  of  arsenic  also 
frequently  exist  in  hydrochloric  acid.  This  impurity  is  derived  from  the 
sulphuric  acid  used  in  its  formation.  It  may  be  deprived  of  arsenic  by  dis- 
tilling it  over  a  small  quantity  of  sulphide  of  barium.  The  presence  of 
arsenic  in  this  acid  may  be  detected  by  boiling  in  the  acid  diluted  with  four 
parts  of  water,  a  small  slip  of  pure  copper  foil.  If  the  acid  contains  arsenic, 
this  is  indicated  by  a  dark  metallic  deposit  on  the  copper.     (See  Arsenic.) 


198  HYDROCHLORIC    ACID.      CHEMICAL    PROPERTIES. 

The  highly  concentrated  liquid  acid  (sp.  gr.  1  -20)  is  very  corrosive,  emits 
copious  fumes  when  exposed  to  air,  and  boils,  according  to  Dalton,  at  a 
temperature  of  about  112^;  it  freezes  at  — 60°  The  boiling-point  varies 
with  the  density  of  the  acid  ;  it  is  highest  (230*^)  when  it  contains  between 
19  and  20  per  cent,  of  the  dry  gas.  (sp.  gr.  r094.)  The  strong  acid  becomes 
weaker,  and  the  weak  acid  stronger  by  boiling.  It  is  impossible  to  expel  the 
whole  of  the  gas  by  boiling.  At  a  sp.  gr.  of  r096,  acid  and  water  are  dis- 
tilled over  together.  When  mixed  with  water,  there  is  a  slight  elevation  of 
temperature.  It  is  decomposed  by  many  oxacids,  such  as  the  chloric,  iodic, 
and  bromic  acids,  and  several  of  the  metallic  peroxides.  Its  decomposition 
by  peroxide  of  manganese,  for  the  production  of  gaseous  chlorine,  has  already 
been  referred  to  (page  188).  This  may  be  regarded  as  a  good  test  for  the 
presence  of  the  acid. 

When  metallic  zinc  is  put  into  strong  liquid  hydrochloric  acid,  it  is  rapidly 
decomposed,  and  hydrogen  is  copiously  evolved.  Some  peroxide  of  lead 
added  to  another  portion  of  the  acid  immediately  disengages  chlorine,  which 
may  be  shown  by  its  bleaching  power  upon  litmus  paper;  these  experiments 
well  illustrate  the  separation  of  the  two  elements  of  the  acid.  On  the  other 
hand,  the  production  of  the  acid  by  synthesis  may  be  well  illustrated  by 
bringing  a  small  jar  of  chlorine  over  the  flame  of  hydrogen  burning  from  a 
jet.  The  color  of  the  flame  is  changed  to  a  pale  greenish-white,  and  acid 
fumes  of  hydrochloric  acid  are  copiously  formed.  Hydrogen  may  be  thus 
perfectly  burnt  in  an  atmosphere  of  chlorine.  In  the  voltaic  circuit  the  chlorine 
is  evolved  at  the  positive  electrode  or  anode,  and  the  hydrogen  at  the  negative 
electrode  or  cathode,  so  that  when  thus  electrolyzed  and  tinged  with  indigo, 
a  bleaching  effect  is  produced  at  the  anode.  Uncombined  hydrochloric  acid 
is  not  found  in  nature  except  in  an  occasional  volcanic  product.  The  acid 
is  an  irritant  poison  to  animals,  and  its  vapors  are  extremely  injurious  to 
vegetation  ;  when  mixed  with  20,000  times  its  volume  of  atmospheric  air, 
it  proved  fatal  to  plants,  shrivelling  and  killing  all  the  leaves  in  twenty-four 
hours. 

The  following  table,  by  Mr.  E.  Davy,  calculated  for  40°  and  a  pressure  of 
30  inches,  shows  the  strength  of  hydrochloric  acid  of  different  densities  : — 

Sroccific  firavitv  ^^  grains  contain  of  gnpHflc  Gravitv  ^^^  grains  contain  of 

bpeciflc  bravity.  Hydrochloric  Gas.  bpeciflc  Orarity.  Hydrochloric  Gas. 

1-21  42-43  1-15  30-30 

1-20  40-80  1-14  28-28 

1-19  38-38  1-13  26-26 

1.18  36-36  1-12  24-24 

1-17  34-34  1-05  10-10 

1-16  32-32  1-01  2-02 

According  to  Dr.  Thompson,  the  strongest  liquid  hydrochloric  acid  (sp. 
gr.  1-208)  contains  one  atom  of  real  acid  -j-  6  atoms  of  water;  when  this  is 
evaporated  in  the  air,  hydrochloric  acid  escapes,  and  it  is  ultimately  reduced 
to  1  atom  of  acid -f  12  of  water  (sp.  gr.  11 19).  This  hydrate  is  said  to 
have  a  sp.  gr.  of  1-128  at  58°,  and  it  boils  at  223°.  When  a  solution  of 
hydrochloric  acid  is  distilled,  a  quantity  of  gas  escapes  in  the  first  instance  ; 
but  acid  and  water  soon  begin  to  be  distilled  together,  and  the  boiling 
point  remains  fixed  at  230°.  This  new  hydrate  has  a  sp.  gr.  of  r094,  and 
it  is  found  to  contain  16  atoms  of  water.  There  are  therefore,  according 
to  Bineau,  three  hydrates  of  this  acid— HC1,6H0:  HCU2H0  :  and  HCl, 
16H0.  Pure  hydrochloric  acid  of  convenient  strength  for  use  in  the  labo- 
ratory may  be  obtained  by  diluting  the  strongest  acid  with  about  its  volume 
of  water,  so  as  to  reduce  its  density  to  about  Tl,  and  then  distilling  it  over 
a  little  chloride  of  barium.     The  acid  carries  over  a  sufficiency  of  water  for 


EQUIVALENT.      COMPOSITION.  199 

condensation,  which  may  be  effected  by  Liebig's  condenser.  Acid  of  this 
strength  does  not  fume  on  exposure  to  air. 

The  concentrated  acid,  at  a  high  temperature,  carbonizes  and  destroys 
organic  matter.  It  has,  generally  speaking,  no  action  on  non-metallic 
bodies;  and  among  metals  it  is  not  decomposed  by  gold,  platinum,  mercury, 
or  silver.  If  pure,  it  may  be  boiled  on  these  metals  without  change.  Its 
chlorine  is  taken  by  lead,  tin,  zinc,  magnesium,  aluminum,  and  iron,  hydrogen 
being  set  free.  Its  action  on  copper  is  peculiar.  In  the  concentrated 
state  and  under  a  free  access  of  oxygen  or  air,  the  acid  loses  its  hydrogen, 
which  forms  water,  and  oxychloride  of  copper  is  produced.  By  means 
of  copper  and  hydrochloric  acid,  the  whole  of  the  oxygen  may  be  removed 
from  a  confined  volume  of  air.  {See  Nitrogen,  p.  154.)  It  is  decomposed 
by  the  alkaline  metals,  chlorides  being  formed,  and  the  hydrogen  liberated. 
Metallic  oxides,  including  the  alkalies,  decompose  it,  producing  water  and 
a  chloride  (K0-fHCl=H04-KCl.)  Some  bases,  however,  appear  to  enter 
into  direct  combination  with  it — among  these  may  be  mentioned  magnesia, 
alumina,  and,  according  to  some  chemists,  the  oxides  of  chromium  and  cobalt. 
These  appear  to  form  both  hydrochlorates  as  well  as  chlorides.  Morphia 
and  the  vegetable  alkaloids  form  hydrochlorates  only. 

Equivalent  and  Composition. — When  equal  volumes  of  chlorine  and  hydro- 
gen are  mixed,  and  the  electric  spark  is  passed  through  the  mixture,  the 
gases  unite,  without  change  of  volume,  to  produce  hydrochloric  acid,  which 
is  entirely  absorbed  by  water.  If  exposed  to  diffused  light  over  water,  they 
combine  and  slowly  disappear — the  water  dissolving  the  compound  as  it  is 
produced.  By  heating  potassium  in  a  measured  quantity  of  the  gas,  the 
chlorine  is  removed  and  the  volume  of  the  gas  is  reduced  to  one-half — the 
residue  being  pure  hydrtbgen.  The  specific  gravity  of  the  gas  is  1*2783. 
This  is  equivalent  to  one-half  of  the  sp,  gr.  of  chlorine,  plus  one-half  of  the 
sp.  gr.  of  hydrogen.     Hence  it  is  thus  constituted : — 


Hydrogen    . 
Chloriue 

Atoms. 
.      1      .. 
.      1      .. 

.      1 

Weight. 
.        1      .. 

.     36     .. 
37 

Per  cent. 

.      2-7 
.    97-3 

Volumes. 
...      1      ... 
...     1      ... 

2 

Sp.  Gr. 
0-0691 
2-4876 

Hydrochloric  acid 

100-0 

2-5567 

and  2-556Y-^ 2  =  1-2783.    Compared  with  hydrogen,  its  sp.  gr.  is  1-85  ;  100 
cubic  inches  weigh  39-59  grains. 

Tests. — The  gas  is  known  by  its  acid  reaction,  great  solubility  in  water, 
the  dense  fumes  which  it  produces  in  a  humid  atmosphere,  and  the  white 
fumes  of  hydrochlorate  of  ailimonia  which  are  evolved  when  a  glass  rod, 
dipped  in  a  strong  solution  of  ammonia,  is  brought  near  to  it.  The  produc- 
tion of  a  solid  compound  by  the  combination  of  the  two  gases,  may  be  well 
illustrated  by  placing  a  small  jar  of  dry  ammonia  within  a  tall  stoppered 
jar.  When  the  ammonia  is  proved,  by  its  reaction  on  test-paper,  to  have 
reached,  by  diffusion,  the  top  of  the  bell-jar,  the  stopper  may  be  removed 
and  a  jar  of  hydrochloric  acid  gas  placed  over  the  opening.  The  gases 
immediately  combine,  and  the  hydrochlorate  of  ammonia  formed  descends  in 
a  dense  white  cloud.  A  solution  of  hydrochloric  acid  in  the  concentrated 
state,  may  be  identified  by  its  evolving  chlorine  when  boiled  with  peroxide 
of  magnesia.  In  the  diluted  state,  it  is  recognized  by  giving  a  white-clotted 
precipitate  with  a  solution  of  nitrate  of  silver  (AgCl)  which  is  insoluble  in 
nitric  acid,  and  becomes  slate-colored  and  ultimately  blackens  by  exposure 
to  light. 

"NiTRO- HYDROCHLORIC  AciT).  NiTRO-MURiATic  AciD. — This  term  has  been 
applied  to  the  Aqua  Regia  of  the  alchemists.      When  nitric  and  hydrochloric 


200  NITRO-HYDROCHLORIC    ACID. 

acids  are  mixed,  they  become  yellow,  and  acquire  the  power  of  dissolving 
gold  and  platinum,  which  neither  of  the  acids  possesses  separately.  This 
mixture,  when  heated,  evolves  chlorine,  a  partial  decomposition  of  both  acids 
taking  place.  Three  parts  of  hydrochloric  and  one  of  nitric  acid  furnish  the 
most  effective  mixture ;  but  a  solution  having  the  same  general  properties, 
is  obtained  by  adding  nitre  to  hydrochloric  acid,  or  common  salt  to  nitric 
acid.  In  the  mutual  decomposition  of  the  two  acids  by  heat,  chlorine  is 
evolved  until  one  of  the  acids  is  entirely  decomposed.  When  a  metal  is  put 
into  nitro-hydrochloric  acid,  it  is  not  dissolved  by  either  of  these  acids,  but 
by  the  nascent  chlorine,  the  metal  combining  with  it  as  fast  as  it  is  evolved. 
The  application  of  heat  greatly  accelerates  this  action,  but  much  chlorine 
may  be  lost  by  employing  too  high  a  temperature.  The  red  vapors  which 
escape  on  heating  the  mixture  may  be  condensed  by  distillation.  The  con- 
densed liquid  is  known  as  Chlo7'onitnc  Sicid,  and  has  the  composition  N02Cla. 
The  reaction  by  which  it  is  produced  may  be  thus  represented:  (NO5HO  + 
3HCl=N02Cl3+Cl  +  4HO).  Towards  the  end  of  the  distillation,  another 
compound,  called  Chloro-nitrous  acid,  is  produced.  This  has  the  compo- 
sition NO^Cl,  and  is  thus  formed  :  (N05,II0  +  3HC1=N02C1  +  2C1  +  4H0). 
This  is  a  gaseous  acid  of  a  deep  orange-red  color;  it  may  be  procured  by  the 
direct  union  of  deutoxide  of  nitrogen  with  one-half  of  its  volume  of  chlorine. 
During  the  solution  of  metals  in  this  acid,  the  production  of  a  metallic  chlo- 
ride and  of  deutoxide  of  nitrogen  may  be  thus  represented:  (3M-fN05+ 
3HCl=3MCl-f  NOa-fSHO).  Nitro-hydrochloric  acid  is  the  common  solvent 
of  gold  and  platinum,  and  may,  with  proper  precautions,  be  used  in  the 
separation  of  these  metals  from  silver,  which  remains  as  an  insoluble  chloride. 
It  furnishes  a  useful  solution  of  tin;  and  is  employed  in  the  analysis  of  mine- 
rals containing  sulphur,  to  separate  and  acidify  that  substance. 

Nitrogen  and  Chlorine.  Chloride  of  Nitrogen;  Ter-chloride  of 
Nitrogen.  NCI3. — The  gases  do  not  unite  directly,  but  the  compound  may 
be  obtained  by  exposing  a  solution  of  nitrate  of  hydrochlorate  of  ammonia 
to  the  action  of  chlorine,  at  a  temperature  of  60°  or  70°,  The  chlorine 
must  be  in  excess,  otherwise  nitrogen  may  be  evolved.  The  gas  is  absorbed, 
and  a  yellow  oil-like  fluid,  heavier  than  water,  is  produced  by  the  union 
of  the  nascent  nitrogen  (evolved  in  the  decomposition  of  the  ammonia 
bf  the  salt)  with  the  chlorine.  NH3,HCl-f  6Cl  =  4HCl  +  NCl3.  It  was  dis- 
covered by  Dulong,  in  1812,  and  its  properties  were  afterwards  investigated 
by  Davy. 

The  simplest  mode  of  obtaining  this  compound  consists  in  filling  a  per- 
fectly clean  glass  basin  with  a  solution  of  1  part  of  sal-ammoniac  in  12  or  15 
of  water,  and  inverting  in  it  a  tall  jar  of  chlorine.  The  saline  solution  is 
gradually  absorbed  and  rises  into  the  jar,  a  film  forms  upon  its  surface,  and 
it  acquires  a  yellow  color ;  at  length  small  globules  of  the  pure  chloride  of 
nitrogen,  looking  like  a  yellow  oil,  collect  upon  its  surface,  and  successively 
fall  into  the  basin  beneath.  Balard  obtained  this  compound  by  suspending 
a  piece  of  sulphate  of  ammonia  in  a  strong  solution  of  hypochlorous  acid. 

The  specific  gravity  of  chloride  of  nitrogen  is  1*65  ;  it  is  not  congealed  by 
cold.  Its  odor  is  irritating  and  peculiar  ;  it  very  soon  evaporates  when  ex- 
posed to  air.  It  is  apparently  a  non-conductor  of  electricity.  It  is  danger- 
ously explosive,  and  is  decomposed  with  violent  detonation  by  mere  contact 
with  many  combustibles,  especially  phosphorus,  oil  of  turpentine,  and  the 
fixed  oils.  In  making  these  experiments,  great  caution  is  required.  Dulong 
lost  an  eye  and  the  use  of  a  finger,  and  Sir  H.  Davy  was  wounded  in  the  face, 
by  the  effects  of  its  detonation.  The  explosion  takes  place  with  a  flash  of 
light,  and  the  vessel  containing  the  substance  is  shattered.     A  leaden  basin 


BROMINE.  201 

should  therefore  be  used  for  the  experiment.  At  160°  it  distils  without 
chauf^e,  but  at  212°  it  explodes,  and  is  decomposed. 

The  production  of  light  and  heat  in  the  decomposition  of  this  compound 
does  not  admit  of  explanation  on  any  of  the  ordinary  theories  of  combus- 
tion. In  combustion  bodies  unite,  and  light  and  heat  are  the  products  of 
their  union  and  condensation.  In  reference  to  this  chloride,  however,  as 
well  as  the  oxides  of  chlorine  and  the  iodide  of  nitrogen,  the  light  and  heat 
are  the  results  of  the  separation  of  the  elements. 

The  composition  of  this  chloride,  although  given  as  NClg,  is  by  some  con- 
sidered to  be  NCI4.  Its  true  constitution  is  not  accurately  known.  From 
the  researches  of  Millon  it  probably  contains  hydrogen.  When  mixed  with 
concentrated  hydrochloric  acid  it  forms  ammonia,  and  chlorine  is  evolved. 
It  is  slowly  decomposed  by  diluted  solution  of  ammonia — hydrochlorate  of 
ammonia  is  formed,  and  nitrogen  is  evolved.  Even  when  kept  in  water  in 
a  stoppered  bottle  it  slowly  disappears,  while  nitric  and  hydrochloric  acids 
are  formed. 

Chlorine  and  carbon  form  several  compounds,  but  these  belong  to  organic 
chemistry. 


CHAPTER    XVI. 

BROMINE  — IODINE  — FLUORINE;    AND   THEIR   COMPOUNDS. 
BROMINE     (Br  =  78). 

History  and  Preparation. — Bromine  was  discovered,  in  1826,  by  M.  Balard, 
of  Montpelier,  in  the  uncrystallizable  residue  of  sea-water,  commonly  called 
bittern.  A  current  of  chlorine,  passed  through  this  liquid,  gives  to  it  an 
orange  tint,  in  consequence  of  the  evolution  of  bromine  from  its  combina- 
tions (MgBr+Cl=Br4-MgCl).  A  portion  of  sulphuric  ether  is  then  shaken 
up  with  the  colored  liquid ;  this  abstracts  the  bromine,  acquires  a  reddish- 
brown  tint,  and  rises  to  the  surface.  The  ethereal  solution  is  drawn  off  and 
agitated  with  a  strong  solution  of  potassa,  by  which  a  solution  of  bromate 
of  potassa  and  bromide  of  potassium  is  formed  :  the  ether  floating  upon  the 
surface  may  be  separated  and  used  again;  the  denser  liquid  is  then  evapo- 
rated to  dryness,  and  the  residue,  exposed  to  a  dull-red  heat,  leaves  bromide 
of  potassium.  Purified  bromide  of  potassium  is  usually  employed  for  pro- 
curing bromine ;  but  the  bromide  of  barium  is  preferable,  as  this  salt  may 
be  obtained  entirely  free  from  chloride.  The  bromide  in  fine  powder  is 
mixed  with  half  its  weight  of  peroxide  of  manganese,  and  its  weight  of  sul- 
phuric acid  previously  diluted  with  half  its  weight  of  water  ;  and  the  mix- 
ture is  distilled  into  a  cold  receiver  containing  water,  and  into  which  the 
beak  of  the  retort  or  condenser  just  dips.  The  deep  orange-colored  vapor 
of  bromine  is  condensed,  and  the  liquid  bromine,  which  falls  to  the  bottom 
of  the  vessel,  is  separated  from  the  water,  and  is  afterwards  dehydrated,  if 
necessary,  by  distilling  it  over  chloride  of  calcium  [2(S03HO)  +  KBr-f  MnOa 
=K0,S03-f  MnO,S03  +  Br  +  2HO].  Should  the  liquid  from  which  bro- 
mine is  to  be  obtained  contain  iodine,  this  must  be  first  separated  in  the 
form  of  subiodide  of  copper  (CuJ),  by  the  addition  of  a  solution  of  1  part 
of  sulphate  of  copper,  and  2J  parts  of  sulphate  of  iron. 

Bromine  probably  exists  in  sea-water  in  the  state  of  bromide  of  magne- 
sium, but  its  relative  proportion  is  exceedingly  minute.  One  hundred  pounds 
of  sea- water,  at  Trieste,  aflforded  only  5  grains  of  bromide  of  sodium  =  3  3 


BROMINE        CHEMICAL    PROPERTIES 

grains  of  bromine  :  it  is  there  unaccompanied  by  iodine ;  and  the  same  is  the 
case,  according  to  Hermbstadt,  in  the  waters  of  the  Dead  Sea.  In  the 
Mediterranean,  on  the  contrary,  iodine  accompanies  it.  Schweitzer  found 
bromide  of  magnesium  in  the  waters  of  the  British  Channel.  Sea-water 
sometimes  contains  as  much  as  one  grain  of  bromine  in  a  gallon.  Bromine 
is  found  in  the  mineral  kingdom  combined  with  silver. 

The  presence  of  bromine  is  recognized  either  in  sea-water  or  in  mineral 
springs,  by  evaporating  the  water  so  as  to  separate  its  more  crystallizable 
contents,  reducing  the  remainder  to  a  small  bulk,  and  dropping  into  it  a  con- 
centrated solution  of  chlorine.  In  the  absence  of  iodine,  which  may  be 
detected  by  starch,  the  appearance  of  a  yellow  tint  announces  bromine.  It 
has  been  thus  discovered  in  many  saline  springs,  in  the  ashes  of  marine 
plants,  and  in  those  of  some  marine  animals.  Among  the  saline  springs 
most  abundant  in  bromine  are  those  of  Theodorshal,  near  Kreutznach,  in 
Germany ;  these  are  now  the  chief  scource  of  bromine  as  an  article  of  com- 
merce. 

Properties. — At  common  temperatures  and  pressures  bromine  is  a  deep 
reddish-brown  liquid,  of  a  pungent  disagreeable  odor,  something  resembling 
that  of  oxide  of  chlorine,  whence*  its  name  (ppw^oj,  fetor)  :  its  specific 
gravity  is  about  3  (2'96  to  2-99).  It  emits  a  heavy  brownish-red  vapor  of 
an  offensive  and  irritating  nature  at  common  temperatures.  This  vapor  has 
a  specific  gravity  of  5-3898,  and  compared  with  hydrogen,  T8;  100  cubic 
inches  of  it  weigh  166*92  grains.  It  has  the  color  of  nitrous  or  hyponitric 
acid.  If  respired  in  a  diluted  state,  it  causes  a  sense  of  suffocation  and  great 
irritation  in  the  nose  and  throat,  producing  all  the  effects  of  a  severe  cold, 
sometimes  lasting  for  several  days.  The  vapor  is  so  heavy,  that  it  may  be 
readily  poured  into  and  collected  in  dry  jars  ;  it  then  appears  like  an  orange- 
colored  gas.  It  bleaches  litmus-paper  as  well  as  solutions  of  organic  colors 
(litmus,  aniline-red,  indigo,  and  ink)  with  the  same  power  as  chlorine.  The 
dry  vapor,  like  dry  chlorine,  does  not  bleach ;  hence  the  bleaching  probably 
depends  on  the  decomposition  of  aqueous  vapor  and  the  effect  of  nascent 
oxygen.  Its  affinity  for  hydrogen  is  not  so  great  as  that  of  chlorine.  If 
the  air  has  been  entirely  displaced  by  the  vapor,  a  lighted  taper,  inOamed 
camphor,  or  ether,  introduced  into  a  jar  of  it,  is  instantly  extinguished. 
Bromine  vapor,  therefore,  is  a  non-supporter  of  ordinary  combustion.  The 
vapor  produces  with  ammonia  dense  white  fumes  of  bromide  of  ammonium. 
It  decomposes  hydriodic  acid  gas,  setting  free  the  purple  vapor  of  iodine 
when  a  small  quantity  of  it  is  poured  into  a  jar  containing  that  gas.  It  also 
decomposes  the  solutions  of  the  alkaline  iodides  ;  bromides  are  formed,  and 
iodine  is  separated.  Place  in  a  large  shallow  dish  a  thin  solution  of  starch, 
to  which  a  solution  of  iodide  of  potassium  has  been  added.  Allow  the  vapor 
of  bromine  to  fall  from  a  bottle  containing  this  liquid,  upon  the  starch  ;  the 
blue  iodide  of  starch  will  be  immediately  produced.  This  experiment,  at  the 
same  time,  serves  to  illustrate  the  great  density  of  the  vapor. 

If  a  jar  containing  bromine  vapor  is  inverted  over  another  containing 
sulpharetted  hydrogen,  the  sulphur  is  precipitated,  and  hydrobromic  acid  is 
formed.  It  is  almost  as  effectual  as  chlorine  in  destroying  foul  effluvia,  but 
its  vapor  is  too  noxious  and  irritating  to  render  it  practically  useful  for 
this  purpose. 

As  a  liquid,  bromine  boils  at  145°.  It  is  solidified  when  cooled  to  — 1-6, 
and  retains  this  condition  up  to  104.  (Pelouze.)  Its  vapor,  in  spite  of 
its  density,  is  so  diffusive,  that  one  drop  of  the  liquid  placed  in  a  large  globe 
receiver,  or  jar,  will  speedily  give  a  color  to  the  whole  of  the  gaseous  con- 
tents. Bromine  is  a  non-conductor  of  electricity,  and  appears  in  the  voltaic 
circuit  at  the  positive  electrode.     It  suffers  no  change  by  transmission  through 


HYDROBROMTC    ACID.  203 

red-hot  tubes.  It  dissolves  sparingly  in  water  (1  part  in  33),  forming  an 
amber-colored  solution  of  an  astringent,  but  not  sour  taste,  from  which  the 
bromine  escapes  by  exposure,  and  rapidly  by  boiling  :  when  long  kept, 
especially  if  exposed  to  light,  it  becomes  acid  from  the  formation  of  hydro- 
bromic  acid.  It  forms,  under  certain  circumstances,  a  definite  hydrate, 
which  may  be  obtained  by  exposing  bromine  with  a  small  quantity  of  water 
to  a  temperature  of  32^  ;  red  octohedral  crystals  of  the  hydrate  of  bromine 
are  then  deposited,  which  continue  permanent  at  the  temperature  of  50^, 
and  contain  10  equivalents  of  water.  At  a  higher  temperature  they  are 
decomposed  into  liquid  bromine  and  an  aqueous  solution  of  it.  The  hydrate 
is  also  obtained  by  passing  the  vapor  of  bromine  through  a  moistened  tube 
cooled  nearly  to  the  freezing-point.  Bromine  dissolves  in  alcohol,  and  more 
abundantly  in  ether  and  chloroform  : — these  two  liquids  readily  separate  it 
from  its  aqueous  solution.  It  communicates  an  orange  tint  to  a  solution  of 
starch.  Antimony  burns  in  it ;  and  it  combines  with  potassium  and  phos- 
phorus with  explosive  violence.  Its  action  on  alkaline  solutions  is  analo- 
gous to  that  of  chlorine  and  iodine.  It  stains  the  skin  of  a  yellow  color, 
and  irritates  it;  it  acts  as  a  corrosive  upon  most  vegetable  and  animal 
substances,  and  is  fatal  to  animal  life  ;  a  single  drop  placed  in  the  beak  of  a 
bird  will  kill  it. 

Bromio  Acid  (BrO,). — This  is  the  only  known  compound  of  bromine  and 
oxygen.  Bromic  acid  is  obtained  by  the  decomposition  of  a  solution  of 
bromate  of  baryta  by  diluted  sulphuric  acid :  sulphate  of  baryta  is  precipi- 
tated, and  a  solution  of  bromic  acid  is  obtained,  which  may  be  concentrated 
by  slow  evaporation  ;  at  a  high  temperature  it  is  partly  decomposed,  and 
cannot  be  obtained  anhydrous.  It  is  colorless,  acid,  inodorous,  and  first 
reddens,  and  then  destroys  the  blue  of  litmus.  It  is  partially  decomposed 
by  concentrated  sulphuric  acid,  but  not  by  nitric  acid.  It  is  decomposed  by 
sulphurous  acid,  by  sulphuretted  hydrogen,  and  by  hydriodic  and  hydrochloric 
acids.  From  the  analysis  of  bromate  of  potassa,  there  can  be  no  doubt 
that  the  bromic  acid  is  analogous  in  composition  and  chemical  properties 
to  the  chloric  and  iodic  acids.  As  it  is  always  in  the  state  of  hydrate,  its 
proper  formula  is  BrOa.HO. 

Bromates. — These  salts  are  represented  by  MO+BrOg)  they  are  resolved 
at  a  red  heat,  either  into  bromides  and  6  atoms  of  oxygen,  or  into  5  atoms 
of  oxygen  and  1  of  bromine,  a  metallic  oxide  being  left :  they  deflagrate  with 
combustibles  like  the  chlorates.  They  are  recognized  by  evolving  bromine, 
when  heated  with  strong  sulphuric  acid. 

Hydrogen  and  Bromine.  Hydrobromic  Acid  (HBr=Y9). — Bromine 
vapor  and  hydrogen  do  not  combine  with  each  other,  either  under  the  influ- 
ence of  the  sun's  rays,  or  by  the  application  of  a  lighted  taper  or  the  electric 
spark ;  but  when  they  are  passed  through  a  tube  heated  to  redness,  the 
vapor  and  gas  combine,  and  hydrobromic  acid  is  produced.  This  gaseous 
acid  may  be  procured  by  gently  heating  a  mixture  of  1  part  of  phosphorus. 
12  5  of  bromine,  and  T'8  of  bromide  of  potassium,  with  a  little  water, 
(MiLLON.)  Hydrobromic  acid  is  evolved  in  dense  white  fumes  when  bro- 
mide of  potassium  is  decomposed  by  sulphuric  acid;  KBr-fS03,H0  = 
HBr+K0,S03;  but  in  this  case  a  portion  of  it  is  decomposed  and  bromine 
vapor  escapes;  KBr  +  2S0,H0=Br+S0,-f KO,S03+2HO.  Phosphoric 
acid  is  not  liable  to  this  objection,  hence  a  strong  solution  of  this  acid  may 
be  mixed  with  the  bromide  of  potassium  in  place  of  the  sulphuric,  and  the 
mixture  distilled. 

This  compound,  although  gaseous  at  common  temperatures  and  pressures, 


204  HYDROBROMIC    ACID. 

condenses  into  a  clear,  colorless  liquid  at  100°  below  0° :  at  124°  below  0°, 
it  is  a  transparent  crystalline  solid.  As  a  gas  it  is  colorless,  of  a  pungent 
and  highly  irritating  odor,  and  yields  dense  acid  vapors  when  mixed  with 
humid  air.  It  undergoes  no  change  when  passed  through  a  red-hot  tube, 
either  alone  or  mixed  with  oxygen  or  iodine ;  but  chlorine  decomposes  it, 
producing  the  vapor  and  drops  of  liquid  bromine,  which,  being  absorbed  by 
mercury,  leaves  hydrochloric  acid.  The  attraction  of  oxygen  and  of  bromine 
for  hydrogen,  is  probably  nearly  equal ;  for  bromine  does  not  decompose 
water  at  common  temperatures,  nor  does  oxygen  decompose  hydrobromic 
acid  ;  but  at  a  red  heat  bromine  decomposes  aqueous  vapor,  hydrobromic 
acid  is  formed,  and  oxygen  is  liberated.  Hydrobromic  acid  gas  is  not  altered 
by  mercury,  but  tin  and  potassium  entirely  decompose  it :  the  former  requires 
the  aid  of  heat ;  but  potassium  acts  at  common  temperatures,  reducing  the 
gas  to  half  its  bulk,  and  forming  bromide  of  potassium.  Hence  it  appears 
that  the  constitution  of  hydrobromic  acid  is  analogous  to  that  of  hydrochloric 
acid,  and  that  it  consists  of  equal  volumes  of  hydrogen  and  bromine  vapor 
combined  without  condensation.  The  weight,  therefore,  of  100  cubic  inches 
of  hydrobromic  acid  is  84 '53  grains,  and  the  gas  consists  of — 

Atoms.  Weights.  Per  cent.  Volumes.  Sp.  Gr. 
Hydrogen  '.  .  .  1  ...  1  ...  1-266  ...  1  ...  0-069 
Bromine    .         .         .        .     1     ...     78     ...     98-734     ...     1     ...     5-389 


Hydrobromic  acid     .         .     1  79  100-000  2  5.458 

And  5 '458-:- 2=2 -729  sp.  gr. ;  compared  with  hydrogen,  its  sp.  gr.  is  39*5. 

Hydrobromic  acid  gas  is  rapidly  absorbed  by  water ;  heat  is  evolved,  and 
a  fuming  liquid  acid  is  obtained,  which  is  colorless  when  pure,  but  which 
readily  dissolves  bromine,  and  acquires  a  yellow  color.  The  specific  gravity 
of  the  densest  aqueous  hydrobromic  acid  is  1-486.  It  boils  at  258°*8  and 
may  be  distilled  at  this  temperature.  The  concentrated  acid  has  the  formula 
HBr,10HO.  The  solution  is  instantly  decomposed  by  chlorine,  acquiring  a 
yellow  color  from  the  liberation  of  bromine.  ^Nitric  acid  also  decomposes  it, 
evolving  bromine,  and  .forming  water  and  nitric  acid.  This  mixture  may  be 
considered  a  sort  of  aqua  regia,  as  it  dissolves  gold  and  platinum.  An 
aqueous  solution  of  the  acid  may  be  obtained  by  passing  a  current  of  sul- 
phuretted hydrogen  gas  into  a  mixture  of  bromine  and  water;  but  more 
conveniently  by  decomposing  a  strong  solution  of  bromide  of  barium  with 
sulphuric  acid  diluted  with  its  weight  of  water.  On  distilling  the  mixture, 
hydrobromic  acid  is  procured  in  the  receiver. 

"When  heated  with  any  of  the  peroxides  of  metals,  the  acid  is  decomposed, 
water  is  formed,  and  bromine  escapes  in  vapor.  In  its  reaction  on  alkalies, 
a  bromide  and  water  result  (KO  +  HBr=KBr  +  HO,)  except  in  the  case  of 
ammonia,  in  which  it  is  supposed  that  bromide  of  ammonium  is  produced  : 
NH,+HBr=NH,Br. 

Bromides — These  salts  are  readily  identified,  1st.  By  heating  them  with 
sulphuric  acid  and  peroxide  of  manganese,  when  bromine  escapes.  2d. 
When  dissolved  in  water — by  the  solution  acquiring  a  yellow  color,  and  the 
odor  of  bromine  when  a  solution  of  chlorine  is  poured  into  it.  Ether  or 
chloroform  may  then  be  used  to  separate  the  bromine.  3d.  The  solution 
gives  a  yellowish-white  precipitate  with  nitrate  of  silver,  insoluble  in  nitric 
acid,  and  requiring  a  large  quantity  of  ammonia  to' dissolve  it.  4th.  It  gives 
an  insoluble  white  precipitate  with  a  salt  of  lead  but  no  precipitate  with  a 
solution  of  corrosive  sublimate.  The  insoluble  bromides  are  decomposed  by 
chlorine  and  strong  sulphuric  acid,  bromine  being  set  free. 

Chloride  of  Bromine. — By  passing  chlorine  through  bromine,  and  con- 


IODINE.      PREPARATION.      PROPERTIES.  205 

densing  the  resulting  vapors  at  a  low  temperature,  a  reddish-yellow  liquid  is 
obtained,  having  a  penetrating  odor  and  disagreeable  taste.  It  is  very  vola- 
tile, emitting  a  yellow  vapor  j  it  is  dissolved  by  water,  and  the  solution 
destroys  vegetable  colors. 

IODINE.      (1=126.) 

History. — ToDiNE  was  discovered  in  1811  by  M.  Courtois,  a  chemical 
manufacturer  at  Paris.  It  derives  its  name  from  the  Greek  labri^  (violet- 
colored),  from  the  color  of  its  vapor. 

It  is  chiefly  prepared  at  Glasgow  from  help,  which  is  the  fused  ash  obtained 
by  burning  sea-weeds,  and  is  principally  manufactured  on  the  west  coast  of 
Ireland,  and  the  Western  Islands  of  Scotland.  The  long  stems  of  the  Fucus 
palmatus  are  most  productive  of  iodine.  Traces  of  iodine,  in  the  form  of 
iodide  of  sodium,  have  been  discovered  in  plants  growing  near  the  sea,  iu 
sea-water,  in  sponge,  in  many  saline  springs,  in  certain  kinds  of  coal,  and  in 
the  coarser  varieties  of  common  salt.  Yauquelin  detected  it  in  some  silver 
ores  from  Mexico.  It  has  also  been  found  iu  cod-liver  oil,  and  in  the  oil  of 
the  liver  of  the  skate,  as  well  as  in  the  common  oyster.  The  commercial 
source  of  iodine  is  sea-weed. 

Preparation. — For  commercial  purposes,  a  lixivium  of  kelp,  containing 
chiefly  iodide  of  sodium,  is  employed  for  the  extraction  of  iodine.  It  may 
be  readily  procured  by  mixing  iodide  of  potassium  with  half  its  weight  of 
peroxide  of  manganese,  and  its  weight  of  sulphuric  acid,  previously  diluted 
with  half  its  weight  of  water.  The  materials  may  be  heated  in  a  short-necked 
retort  or  flask  connected  with  a  large  globular  receiver  which  must  be  kept 
cool.  The  changes  which  ensue  may  be  thus  represented  :  (2S03HO-f  KI  + 
MnO,=KO,S03+MnOS03  +  2HOH-L)  The  iodine  is  sublimed,  and  is  de- 
posited in  a  crystalline  form  in  the  cool  parts  of  the  receiver.  The  crystals 
may  be  washed  out  of  the  receiver  by  a  solution  of  iodine  in  water,  the  liquid 
poured  off,  and  the  deposit  rapidly  dried  between  folds  of  blotting-paper. 
It  may  be  purified  by  resubliraation  at  a  gentle  heat.  If  the  alkaline  iodide 
in  kelp  be  associated  with  a  large  proportion  of  chloride,  the  iodine  may  be 
conveniently  precipitated  as  snbiodide  of  copper  (CuJ),  by  the  addition  of 
a  mixed  solution  of  sulphate  of  copper  (one  part)  and  of  sulphate  of  iron 
(two  and  a  half  parts.)  The  insolu))le  subiodide  of  copper,  when  heated 
with  peroxide  of  manganese,  yields  iodine  by  sublimation. 

Properties — Iodine  has  a  gray  or  bluish-black  color,  resembling  plumbago  ; 
its  lustre  is  metallic,  and  its  fracture  when  in  a  mass,  is  greasy  and  lamellar. 
It  is  a  non-conductor  of  electricity.  It  is  not  changed  by  passing  its  vapor 
through  a  red-hot  tube,  either  alone  or  over  charcoal.  It  is  soft  and  friable. 
Its  specific  gravity,  as  a  solid,  is  4*946.  It  produces  a  yellow  stain  upon 
paper  and  on  the  skin,  without  corroding  it.  Its  smell  somewhat  resembles 
that  of  diluted  chlorine  ;  its  taste  is  acrid.  It  is  extremely  volatile,  and  pro- 
duces a  pale  violet  vapor  at  a  temperature  of  between  60°  and  80°.  This 
vapor  may  be  well  brought  out  by  dropping  a  few  grains  of  iodine  into  a 
large  globular  glass  vessel  previously  heated.  At  120°  or  130°  it  rises  more 
rapidly  in  vapor ;  at  220°  it  fuses  ;  and  at  350°  it  boils  and  produces  dense 
violet-colored  fumes,  which  are  condensed  in  brilliant  rhombic  plates  and 
octahedra.  It  may  be  entirely  volatilized  by  heating  it  on  writing  paper. 
One  hundred  cubic  inches  of  iodine  vapor  weigh  269  64  grains.  Its  specific 
gavity,  compared  with  air,  is  8-'7066,  and  with  hydrogen,  126.  Like  chlo- 
rine and  oxygen,  it  is  evolved  from  its  combinations  at  the  positive  electrode  ; 
it  is  very  sparingly  soluble  in  water,  this  liquid  not  holding  more  than  one 
7000th  of  its  weight  in  solution.  The  color  of  this  solution  is  pale  brown  ; 
it  gives  out  no  oxygen  by  exposure  to  sunshine  ;  it,  however,  slowly  loses 


206  IODINE.      PROPERTIES. 

its  color,  and  gives  rise  to  the  formation  of  iodic  and  hydriodic  acids. 
Iodine  is  very  soluble  in  alcohol  and  ether,  forming  deep  brown  solutions. 
It  is  soluble  in  sulphide  of  carbon,  forming  a  rich  crimson-colored  liquid. 
If  in  a  free  state,  it  may  be  thus  detected  and  removed  from  strongly  colored 
organic  liquids.  Chloroform  also  dissolves  and  separates  it  from  its  aqueous 
solution,  acquiring  a  rich  purple  color. 

It  is  said  to  be  destitute  of  bleaching  properties,  but  this  arises  from  the 
small  amount  of  iodine  dissolved  by  water.  One  ounce  of  a  saturated  solu- 
tion contains  only  about  one-sixteenth  of  a  grain.  If  a  few  grains  of  iodide 
of  potassium  are  dissolved  in  the  water,  a  much  larger  amount  of  iodine  is 
taken  up.  This  aqueous  solution  has  a  dark  brown  color,  and  slowly  acts 
upon  litmus  and  indigo  w^hen  added  in  sufficient  quantity  so  as  to  give  them 
a  light  greenish  tint.  Iodine  is  very  soluble  in  water  containing  chloride  of 
ammonium,  nitrate  of  ammonia,  or  hydriodic  acid.  Either  as  a  solid,  or  in 
solution,  iodine  is  an  irritant  poison. 

The  violet  color  of  the  vapor  of  iodine,  as  well  as  its  peculiar  odor,  is  in 
many  cases  a  sufficient  evidence  of  its  presence ;  a  more  delicate  test,  how- 
ever, is  furnished  by  its  property  of  forming  a  deep  blue  compound  with 
starch.  According  to  Stromeyer,  a  liquid  containing  only  one  450,000th  of 
its  weight  of  iodine,  receives  a  reddish-blue  tinge  when  a  solution  of  starch 
is  added  to  it,  provided  too  much  starch  is  not  present.  To  insure  success, 
the  iodine  should  be  in  a  free  state,  and  the  solution  cold,  for  heat  destroys 
the  color.  When  the  proportion  of  iodine  is  very  minute,  a  few  minutes  may 
elapse  before  the  discoloration  ensues.  When  a  very  minute  quantity  of 
iodide  of  sodium  or  potassium  is  present  in  a  solution,  the  addition  of  chlo- 
rine is  necessary  ;  and  if  a  solution  of  starch  be  then  added,  the  iodine,  set 
free  by  the  chlorine,  is  detected  by  the  blue  color.  If  too  much  chlorine  or 
starch  is  added,  the  blue  color  of  the  iodide  is  destroyed.  One  or  two  drops 
of  strong  nitric  acid  may  be  employed  as  a  substitute  for  chlorine.  Any 
compound  containing  common  salt  and  an  alkaline  iodide,  mixed  with  a  solu- 
tion of  starch,  and  exposed  to  voltaic  action,  yields  a  blue  color  at  the  posi- 
tive electrode. 

The  starch-test  may  be  equally  applied  for  the  detection  of  the  vapor. 
Place  a  few  grains  of  iodine  in  a  jar  of  200  c.  i.  capacity ,  previously  warmed, 
and  allow  the  vapor  to  diffuse  by  agitation.  Now  introduce  into  the  jar,  in 
which  the  vapor  is  scarcely  visible  by  color,  a  slip  of  paper  which  has  been 
dipped  in  a  solution  of  starch.  The  blue  color  will  speedily  appear,  and 
become  stronger  as  the  paper  is  lowered  into  the  jar.  The  slow  diffusion  of 
the  vapor  from  the  solid  may  be  thus  proved.  Suspend  within  a  tall  bell-jar 
a  slip  of  bibulous  paper  soaked  in  a  solution  of  starch.  Invert  the  bell-jar 
over  a  saucer  containing  a  few  crystals  of  iodine.  After  some  minutes,  the 
diffusion  of  the  vapor  will  be  manifested  by  the  blue  color  acquired  by  the 
paper,  the  change  proceeding  from  below  upwards. 

The  blue  compound  obtained  by  adding  a  solution  of  iodine  to  starch  is 
not  permanently  destroyed  by  heat.  Unless  the  solution  has  been  so  long 
boiled  that  the  whole  of  the  iodine  has  been  expelled,  the  blue  color  will 
return  as  the  liquid  cools.  Iodine  acts  upon  iron,  zinc,  silver,  and  some 
other  metals,  by  direct  contact.  It  has  no  solvent  power  on  gold.  When 
placed  on  phosphorus,  so  much  heat  is  evolved  that  the  phosphorus  takes 
tire  and  burns.  In  vapor  as  well  as  in  solution  in  water,  it  decomposes  sul- 
phuretted hydrogen,  and  sulphur  is  precipitated. 

Iodine  is  sometimes  adulterated  with  plumbago,  sulphide  of  antimony,  or 
peroxide  of  manganese  ;  but  these  adulterations  are  easily  detected  by  their 
insolubility  in  alcohol,  or  by  the  residue  left  on  heating  the  iodine  on  mica, 
so  as  to  volatilize  it.     The  relative  quantity  of  moisture  in  iodine  may  be 


PERIODIC    AOID.  20t 

ascertained  by  heating  it  in  a  tube,  with  twice  its  weight  of  fused  chloride  of 
caleliim,  at  a  temperature  not  exceeding  the  boiling-point  of  the  iodine  ;  the 
iodine  may  be  expelled  by  a  current  of  air,  and  the  increase  of  weight  sus- 
tained by  the  chloride  gives  the  quantity  of  water. 

Iodine  and  Oxygen. — Of  the  compounds  of  these  elements  only  two  have 
undergone  a  complete  examination,  namely,  the  Iodic  and  Periodic  acids. 

Iodic  Acid  (IO5). — This  compound  cannot  be  obtained  by  the  direct 
action  of  oxygen  on  iodine  ;  it  may  be  procured  by  boiling  iodine  for  many 
hours  with  about  five  times  its  weight  of  the  strongest  nitric  acid.  The 
mixture  should  be  introduced  into  a  flask  having  a  long  neck,  or  into  a 
retort,  in  order  that  the  iodine,  as  it  sublimes  to  the  upper  part,  may  be 
returned  into  the  acid,  until  it  disappears  entirely  :  on  carefully  driving  off 
the  nitric  acid  by  heat,  the  iodic  acid  remains  as  a  white  uncrystalline  solid. 
It  may  be  dissolved  in  water,  and  obtained  as  a  crystalline  hydrate.  By  this 
process  four  parts  of  iodine  yield  four  and  a  half  parts  of  iodic  acid. 

The  aqueous  solution  of  this  acid,  when  concentrated  by  evaporation, 
yields  a  pasty  mass,  which  is  hydrated  iodic  acid,  lO^jHO.  This  may  be 
crystallized  in  hexagonal  plates,  from  which  some  of  the  water  may  be  driven 
off  by  the  careful  application  of  a  higher  temperature.  It  then  becomes 
HO.SlOj  (360*^).  At  about  100^  it  fuses,  and  is  decomposed  into  oxygen 
and  iodine.  Iodic  acid  acts  powerfully  upon  the  metals,  and  with  the  oxides 
forms  a  class  of  salts  called  iodates.  Nitric,  sulphuric, -phosphoric,  and 
boracic  acids  do  not  decompose  it ;  but  it  is  decomposed  by  hydrochloric, 
hydrofluoric,  hydriodic,  oxalic,  sulphurous,  arsenious,  hydrosulphuric,  and 
other  acids. 

When  it  is  mixed  with  charcoal,  sulphur,  and  some  other  combustibles,  it 
forms  compounds  which  deflagrate  when  heated.  The  solution  of  iodic  acid 
is  decomposed  by  several  organic  substances,  as  by  morphia,  narcotine,  gallic, 
and  pyrogallic  acids  ;  and  among  salts  by  the  sulphocyanides  and  hyposul- 
phites, as  well  as  by  sulphate  of  iron.  Zinc  and  magnesium  liberate  iodine. 
Iodic  acid  is  analogous  to  the  chloric  :  it  is  composed  of : — 

Iodine   .... 
Oxygen 


oms. 

Weights. 

Per  cent. 

1 

126 

75-9 

5 

40 

24-1 

Iodic  acid       ....     1         ...         166        ...       100-0 

Iodates. — The  salts  are  represented  by  the  general  formula  MOjIOs.  By 
heat,  they  either  become  iodides,  losing  six  atoms  of  oxygen,  or  they  lose 
iodine  and  five  atoms  of  oxygen,  leaving  a  metallic  oxide.  Their  deflagration 
with  combustibles  is  less  powerful  than  that  of  the  chlorates,  but  they  are 
decomposed  when  heated  with  charcoal  leaving  metallic  iodides.  They  are 
not  very  soluble  in  water,  and  their  solutions  are  decomposed  by  sulphurous 
acid,  iodine  being  set  free.     This  is  the  best  test  for  their  presence. 

Periodic  Acid  (I0,H0).— When  a  solution  of  iodate  of  soda,  mixed  with 
pure  soda,  is  saturated  by  chlorine,  and  concentrated  by  evaporation,  a 
sparingly  soluble  white  salt  is  obtained,  which  is  a  periodate  of  soda.  This 
is  dissolved  in  the  smallest  possible  quantity  of  diluted  nitric  acid,  and  mixed 
with  nitrate  of  lead  ;  a  precipitate  of  periodate  of  lead  is  thrown  down. 
This  is  collected  and  decomposed  by  a  small  quantity  of  diluted  sulphuric 
acid.  Periodic  acid  is  not  known  in  the  anhydrous  state  ;  it  may  be  obtained 
as  a  crystalline  hydrate  by  filtering  the  liquid  and  evaporating  it.     The 


208  HYDRIODIC    ACID. 

periodaies  are  less  soluble  than   the  iodates,  but  like  them  they  are  decom- 
posed at  a  red  heat  and  evolve  oxygen. 

Hydriodio  Acid  (HI). — Hydrogen  and  iodine  do  not  readily  combine 
directly  ;  but  when  they  are  passed  through  a  red-hot  tube  hydriodic  acid 
gas  is  produced  by  their  union.  The  gas  may  be  produced  by  the  following 
process  suggested  by  Millon  :  10  parts  of  iodide  of  potassium  are  dissolved 
in  5  parts  of  water,  and  20  parts  of  iodine  are  added  to  ^the  solution  in  a 
retort.  One  part  of  phosphorus  in  small  portions  is  then  added  and  a  gentle 
heat  is  applied  (2KI-fl3+P  +  8HO=HO,2KO,(P05)  +  THI).  Hydriodic 
acid  passes  over,  and  phosphate  of  potassa  remains  in  the  retort.  As  it  is  a 
very  heavy  gas,  it  may  be  collected  by  displacement  in  dry  jars.  It  is  decom- 
posed by  mercury,  and  hydrogen  is  evolved,  so  that  it  cannot  be  be  collected 
over  that  metal.  • 

Hydriodic  acid  gas  is  colorless,  but  fumes  strongly  in  the  air,  and  smells 
like  hydrochloric  acid.  It  reddens  vegetable  blues.  Its  specific  gravity, 
compared  with  air,  is  as  4'3878  to  1 ;  100  cubic  inches  weigh  about  135*89 
grains.  Compared  with  hydrogen,  its  specific  gravity  is  as  63-5  to  1.  It 
extinguishes  flame,  and  is  not  itself  inflammable.  It  is  liquefiable  under 
pressure,  and  becomes  a  transparent  colorless  solid  at  about  — 60°.  It  is 
not  permanent  at  a  red  heat,  for,  when  passed  through  a  red-hot  porcelain 
tube,  it  is  partially  resolved  into  iodine  and  hydrogem 

Hydriodic  acid  gas  is  not  decomposed  by  dry  air,  but  when  water  is  present 
the  oxygen  of  the  air  unites  to  the  hydrogen,  and  iodine  is  eliminated  and 
dissolved.  The  gas  is  very  soluble  in  water,  but  in  what  proportion  has  not 
been  determined.  The  saturated  solution,  exposed  to  a  temperature  below 
260°,  becomes  concentrated  by  loss  of  water ;  at  about  260°  it  boils,  and 
may  be  distilled.  The  specific  gravity  of  the  strongest  liquid  acid  is  11.  It 
dissolves  iodine.  It  becomes  dark-colored  when  kept  in  contact  with  air, 
in  consequence  of  a  partial  separation  of  iodine,  which  colors  the  liquid.  The 
aqueous  hydriodic  acid  is  best  prepared  by  passing  sulphuretted  hydrogen 
through  a  mixture  of  iodine  and  water  :  sulphur  is  deposited,  and,  on  heat- 
ing and  filtering  the  liquid,  a  solution  of  hydriodic  acid  is  obtained,  which 
may  be  concentrated  by  evaporation.  The  solution  is  decomposed  by  chlorine, 
by  nitric,  sulphuric,  arsenic,  iodic,  and  sulphurous  acids,  and  by  the  proto- 
sulphate  of  iron,  the  iodine  being  separated. 

When  hydriodic  acid  gas  is  mixed  with  oxygen,  and  is  passed  through  a 
red-hot  tube,  it  is  resolved  into  iodine  and  water.  Its  decomposition  by 
chlorine  produces  hydrochloric  acid,  sometimes  with  explosion,  and  the 
purple  vapor  of  iodine  is  rendered  evident,  but  rapidly  disappears  in  conse- 
quence of  the  formation  of  chloride  of  iodine.  This  decomposition  is 
beautifully  shown  by  causing  hydriodic  acid  gas  to  pass  into  a  jar  of 
atmospheric  air,  mixed  with  about  a  twelfth  of  its  bulk  of  chlorine;  the 
violet  fumes  are  then  more  permanent.  On  the  other  hand,  mercury  takes 
the  iodine  and  sets  free  hydrogen.  A  little  strong  nitric  acid  dropped  into 
hydriodic  acid  gas  energetically  decomposes  it,  with  the  evolution  of  so  much 
heat  that  the  gas  is  occasionally  inflamed. 

The  composition  of  hydriodic  acid  gas  is  analogous  to  that  of  the  hydro- 
chloric. It  consists  of  1  volume  of  the  vapor  of  iodine  and  1  of  hydrogen  ; 
these  produce  2  volumes  of  the  acid.  When  potassium  is  heated  in. the  gas 
it  is  reduced  to  half  its  volume,  which  consists  of  pure  hydrogen.  It  is 
therefore  thus  constituted  : — 


Hydrogen   . 
Iodine 

Atoms. 
.      1      . 
.      1      . 

Weiglits. 
1      . 
..     126     . 

127 

Per  cent, 
..        0-8 
..      99-2 

100-0 

Volumes. 
...      1      ... 
...      1      ... 

2 

Sp.  Gr. 
0-0345 
4-3533 

Hydriodic  acid   . 

.      1 

4-3878 

IODIDES.      SEPARATION    OF    IODINE.  209 

Iodides. — These  salts  may  be  thus  identified:  1.  When  heated  with  sul- 
phuric acid  and  peroxide  of  manganese,  iodine  is  evolved.  2.  When  dissolved 
in  water,  the  iodide  (of  potassium)  is  neutral,  and  has  no  action  on  starch. 
On  adding  to  the  mixture  a  solution  of  chlorine,  or  some  nitric  acid,  a  deep 
blue  color  is  produced.  3.  The  solution  gives  a  pale  yellow  precipitate 
with  nitrate  of  silver,  insoluble  in  ammonia:  4,  a  bright  yellow  precipitate 
with  a  salt  of  lead  (iodide  of  lead);  and  5,  a  bright  scarlet  precipitate  with  a 
solution  of  corrosive  sublimate  (iodide  of  mercury).  The  presence  of  an 
iodate  is  detected  by  adding  a  solution  of  tartaric  acid  :  the  solution  becomes 
colored  by  iodine  being  set  free,  as  a  result  of  the  reaction  of  iodic  oa 
hydriodic  acid. 

The  relative  insolubility  of  the  silver  compounds  of  chlorine,  bromine,  and 
iodine  is  indicated  by  the  following  experiments.  A  solution  of  chloride  of 
silver  in  ammonia  is  precipitated  by  bromide  and  iodide  of  potassium,  while 
a  solution  of  bromide  of  silver  in  ammonia  is  precipitated  by  a  solution  of 
iodide  of  potassium. 

Iodide  of  Nitrogen  (NHIJ. — This  compound  has  been  shown  to  contain 
hydrogen,  as  well  as  nitrogen  and  iodine.  It  may  be  prepared  by  placing 
finely-powered  iodine  for  hfflf  an  hour  in  a  solution  of  ammonia.  The 
liquid  portion  is  poured  from  the  insoluble  dark  brown  powder,  which  is  the 
iodide.  It  should  be  well  washed  in  water.  The  compound  is  dangerously 
explosive  when  dry;  hence  it  should  be  put  in  small  quantities,  while  moist, 
on  filtering  paper,  and  allowed  to  dry  spontaneously  on  sheet  lead.  The 
slightest  contact  of  a  body,  or  merely  dropping  the  powder  through  the  air 
or  on  the  surface  of  water,  causes  a  sudden  and  violent  explosion,  with  a 
flash  of  light  and  the  escape  of  iodine  in  vapor.  Even  under  water  it  will 
explode  by  friction.  It  is  slowly  decomposed  when  moist  by  exposure  to 
air.  Boiling  water  and  solutions  of  potassa  and  soda  decompose  it  rapidly. 
It  is  converted  into  nitrogen,  iodic,  and  hydriodic  acids.  It  is  decomposed 
by  sulphuretted  hydrogen,  and  it  loses  its  detonating  properties  in  the  pre- 
sence of  an  excess  of  ammonia.  By  numerous  experiments,  M.  Bineau  has 
proved  that  its  true  formula  is  NHIg. 

Chlorine  forms  two  volatile  and  unstable  compounds  with  iodine,  ICl 
(liquid)  and  ICI3  (solid).^ 

Chlorine,  iodine,  and  bromine  are  occasionally  so  associated  as  to  require 
separation  in  analyses.  To  ascertain  the  quantity  of  iodine  in  the  mixed 
chlorides  and  iodides  of  mineral  waters,  Rose  recommends  precipitation  by 
nitrate  of  silver;  the  mixed  chloride  and  iodide  of  silver  thus  thrown  down 
is  fused,  weighed,  and  afterwards  heated  in  a  tube,  and  a  stream  of  chlorine 
passed  over  it;  the  iodine  is  thus  expelled,  and  the  whole  converted  ioto 
chloride  of  silver;  this  is  weighed  again,  and  a  loss  is  found  to  have  taken 
place  in  consequence  of  the  equivalent  of  the  expelled  iodine  being  greater 
than  that  of  the  expelling  chlorine;  this  loss,  multiplied  by  1'4,  gives  the 
quantity  of  iodine,  originally  present,  which  has  been  replaced  by  chlorine 
for  (126— 36  =  90,  and  126 -^"90= 1-4)  .Schweitzer  recommends  the  adoption 
of  a  similar  method  for  estimating  the  quantity  of  iodine  when  mixed  with 
bromine  ;  in  this  case  the  mixed  iodide  and  bromide  of  silver  is  to  be  heated 
in  an  atmosphere  of  bromine  vapor,  by  which  the  iodine  is  expelled.  The 
presence  of  an  iodide,  in  mixture  with  a  chloride  and  bromide,  may  be 
detected  by  considerably  diluting  the  solution  with  water,  and  adding  to  it  a 
solution  of  chloride  of  palladium.  Iodine  gives  with  this  salt  a  dense  purple 
black  precipitate  of  iodide  of  palladium  (Pdl).  A  diluted  chloride  or 
bromide  is  not  thrown  down  by  this  reagent.  The  mixed  sulphates  of  iron 
and  copper  {see  page  205)  precipitate  the  iodine  of  an  iodide  in  an  insoluble 
14 


210  FLUORINE.      HYDROFLUORIC    ACID. 

form.     A  chloride  is  not  affected,  and  a  bromide  only  when  the  solution  is 
moderately  strong. 

Fluorine  (F=19). 

History  and  Properties. — Fluorine  is  a  simple  body  concerning  which,  in 
its  pure  state,  but  little  is  known.  It  is  most  abundantly  met  with  in  the 
mineral  known  as  fluor  or  fltior- spar,  which  is  a  fluoride  of  calcium  (CaF). 
Hence  the  name  Jiuo7^ine.  In  its  pure  state  the  fluoride  of  calcium  contains 
49  per  cent,  of  fluorine.  This  mineral  is  found  abundantly  in  Derbyshire, 
Cornwall,  and  Cumberland.  It  is  well  known  by  its  cubic  crystals,  sometimes 
colorless,  but  more  commonly  colored  purple,  yellow,  or  green.  The  mineral 
cryolite,  from  which  aluminum  is  extracted,  is  a  compound  fluoride  of  alum- 
inum and  sodium  (AlgFgjSNaF).  It  is  a  white  translucent  fusible  substance 
found  in  Greenland.  It  contains  about  42  per  cent,  of  fluorine.  Fluorine 
is  a  constituent  of  the  topaz :  it  is  found  in  some  kinds  of  mica,  in  fossil 
bones  and  coprolites.  It  exists  in  traces  in  sedimentary  rocks,  in  river, 
spring,  and  sea-water,  in  recent  bones,  in  teeth,  and  in  many  organic  substances. 

Davy  and  other  chemists  have  attempted  to  isolate  fluorine  by  heating  dry 
fluoride  of  silver  in  a  current  of  chlorine.  In  operating  in  glass  or  platinum 
vessels,  the  fluorine  instantly  entered  into  combination  with  the  silicon  or 
platinum,  and  fluorides  of  silicon  and  platinum  alone  were  obtained.  It  is 
stated  that  fluorine  has  been  procured  by  the  substitution  of  vessels  of  fluor- 
spar for  those  of  glass  and  platinum ;  but  the  description  of  the  properties 
of  the  body  thus  obtained,  shows  that  it  was  probably  a  mixture  of  clilorine 
and  hydrofluoric  acid.  One  fact,  however,  has  been  elicited  as  a  result  of 
these  experiments.  When  an  anhydrous  fluoride  in  a  state  of  fusion  is 
submitted  to  electrolysis,  there  is  evolved  at  the  positive  electrode  a  body 
which  decomposes  glass  and  forms  with  platinum  a  fluoride  which  is  decom- 
posed by  heat.  Hence  it  may  be  assumed  that  fluorine,  whether  gaseous, 
liquid,  or  solid,  is  an  electro-negative  metalloid,  bearing  some  analogy  to 
chlorine,  bromine,  anfl  iodine.  It  forms  no  known  compounds  with  these 
elements,  with,  oxygen,  or  carbon.  It  unites  readily  to  metals  forming 
fluorides,  and  to  three  non-metallic  bodies — namely,  hydrogen,  boron,  and 
silicon.  The  principal  compound  of  fluorine,  is  that  which  it  forms  with 
hydrogen — hydrofluoric  acid. 

Hydrofluoric  Acid  (HF). — This  was  formerly  called  fluoric  acid,  from 
the  supposition  that  it  was  a  compound  of  fluorine  and  oxygen.  It  is  a 
gaseous  anhydrous  acid  analogous  to  the  hydrochloric.  The  existence  of 
this  acid  was  first  made  known  by  Scheele,  although  as  he  employed  vessels 
of  glass,  he  did  not  obtain  it  in  a  pure  state.  Its  properties  were  examined 
by  Gay-Lussac  and  Thenard  in  1810  {JRecherches  Physico-chemiques),  and 
by  Davy(PM.  Trans.  1809-1813).  When  finely-powdered /zfont/e  of  cal- 
cium Qv  Jiuor-spar,  as  it  is  usually  called  (carefully  selected  for  its  purity  and 
freedom  from  silica),  is  distilled  with  twice  its  weight  of  sulphuric  acid,  a 
highly  volatile  and  corrosive  liquid,  which  is  hydrated  hydrofluoric  acid,  is 
obtained:  CaF-}-S03,HO  =  CaO,S03-j-HF.  It  acts  powerfully  on  glass 
and  on  most  of  metals :  the  retort  employed  in  the  experiment  may  be  of 
lead,  with  a  tube  and  receiver  of  platinum  ;  the  receiver  must  be  immersed 
in  a  mixture  of  ice  and  salt.  The  product  may  be  preserved  in  a  platinum 
bottle,  with  a  well-fitted  stopper  of  the  same  metal,  but  gutta-percha  bottles 
are  now  commonly  employed.  In  this  concentrated  state  it  is  a  clear, 
colorless  liquid ;  it  fumes  when  exposed  to  air ;  boils  at  68°,  and  flies  off  in 
vapor.  Its  specific  gravity  in  this  state  is  10609.  It  has  not  been  con- 
gealed. By  the  gradual  addition  of  a  certain  proportion  of  water  it  acquires 
a  considerable  increase  of  density,  the  mixture  having  a  specific  gravity  of 


PROPERTIES    OF    HYDROFLUORIC    ACID.  211 

l'15(HF,4HO).  Its  attraction  for  water  exceeds  that  of  oil  of  vitriol ;  and 
when  dropped  into  water  it  causes  a  hissing  noise,  and  great  heat  is  evolved. 
Its  vapor  it  dangerously  pungent  and  irritating,  and  the  liquid  acid  is 
eminently  active  upon  organic  substances;  a  minute  drop  of  it  upon  the  skin 
produces  a  painful  sore,  and  in  larger  quantities  malignant  ulceration  :  hence 
the  vessels  containing  it  require  to  be  handled  with  great  caution.  Its  most 
characteristic  property  is  the  energy  with  which  it  acts  upon  glass :  its 
vapors  soon  destroy  the  polish  and  transparency  of  all  neighboring  glass- 
vessels,  and  when  dropped  upon  glass,  great  heat  and  effervescence  are  pro- 
duced, and  dense  fumes  are  evolved,  consisting  of  hydrofiuosilicic  acid. 
Diluted  with  about  six  parts  of  water,  the  acid  may  be  used  for  etching 
upon  glass,  which  it  effectually  accomplishes  in  a  few  minutes.  For  this 
purpose  the  surface  is  covered  with  a  thin  layer  of  wax  and  tallow,  and  this 
is  removed  from  those  parts  on  which  it  is  intended  the  acid  should  act. 
The  diluted  acid  is  then  poured  on  the  glass,  and  after  a  short  time  it  is 
removed.  The  layer  of  wax  is  melted  off,  and  the  pattern  then  appears 
corroded  on  the  glass.  If  a  prepared  plate  is  exposed  to  the  acid  vapors,  a 
dull  surface  is  given  to  the  corroded  portions. 

When  the  concentrated  acid  is  submitted  to  electrolysis,  hydrogen  is 
evolved  at  the  negative  electrode,  and  the  positive  platinum  wire  is  corroded 
and  converted  into  a  brown  compound,  probably  of  fluorine  and  platinum. 
All  the  metals  excepting  mercury,  gold,  silver,  platinum,  and  lead,  decom- 
pose it  with  the  evolution  of  hydrogen  ;  and  peculiar  compounds  result, 
Jluorides,  consisting  of  the  metal  in  combination  with  fluorine.  The  action 
of  potassium  upon  the  concentrated  acid  is  very  energetic  ;  it  is  attended 
by  explosion,  by  the  liberation  of  hydrogen,  and  by  the  formation  of  a 
peculiar  soluble  saline  compound  which  is  considered  as  a  fluoride  of 
potassium. 

The  only  metalloids  on  which  it  acts  are  boron  and  silicon.  It  has  no 
action  on  carbon  hence  it  enables  a  chemist  to  distinguish  the  true  from  the 
false  diamonds.  Like  hydrochloric  acid,  it  acts  violently  upon  zinc,  mag- 
nesium, and  aluminum,  setting  free  hydrogen  ;  but  it  has  very  little  action 
on  copper.  When  added  to  solutions  of  lime,  baryta,  strontia,  magnesia, 
and  alumina,  it  throws  down  insoluble  fluorides  of  the  metals.  In  this 
respect  it  differs  from  the  hydracids  of  chlorine,  bromine,  and  iodine,  which 
form  soluble  compounds  with  these  bases.  Nitrate  of  silver  produces  with 
this  acid  a  white  compound,  which  is  soluble  in  water,  which  is  not  affected 
by  light,  and  easily  decomposed  by  heat.  The  chloride,  bromide,  and  iodide 
of  silver  are  entirely  different  in  their  properties.  Its  most  remarkable 
property  is  that  of  acting  upon  silica  and  all  its  combinations,  even  upon 
glass — a  substance  which  is  not  attacked  or  dissolved  by  any  other  acid.  A 
small  quantity  of  the  acid  poured  upon  glass  produces  immediately  an 
opaque  spot  or  streak  (SiO,+3HF=3HO-f  SiFg).  The  fluoride  of  silicon 
produced  when  in  contact  with  water  undergoes  a  change  by  which  hydrated 
silicic  acid  or  silica  is  precipitated. 

This  acid,  when  mixed  with  strong  nitric  acid,  and  the  mixture  is  heated, 
does  not  dissolve  gold  or  platinum.  It  forms  no  aqua  regia,  like  the  hydro- 
chloric acid. 

Composition — Kuhlman's  experiments  have  proved  that  this  is  a  hydracid  ; 
he  found  that  pure  fluor-spar  (fluoride  of  calcium)  was  not  in  the  least  acted 
upon,  even  at  a  red  heat,  by  anhydrous  sulphuric  acid,  and  that  when  hydro- 
chloric acid  was  transmitted  over  fluor-spar  at  a  red  lieat,  hydrofluoric  acid 
was  disengaged  and  chloride  of  calcium  formed.  It  cannot  therefore  be 
doubted  that  the  hydrofluoric,  like  the  hydrochloric  acid,  is  composed  of  one 


212  SULPHUR.      ITS    PRODUCTION. 

atom  or  volume  of  each  of  its  elements,  and  it  may  be  assumed  that  they  are 
united  without  auj  condensation. 


Atoms. 

Weights. 

Per  cent. 

Volumes. 

Hydrogen 

. 

.      1 

= 

1 

5 

1 

Fluorine. 

, 

*      1 

= 

19 

95 

1 

1  20  100  2, 

Its  atomic  weight  is  derived  from  the  proportion  of  sulphate  of  lime 
obtained  by  the  decomposition  of  a  known  weight  of  pure  fluoride  of  calcium. 

Fluorides. — A  soluble  fluoride  is  known  by  its  action  on  glass.  An  inso- 
luble fluoride  may  be  powdered  and  covered  with  sulphuric  acid  in  a  platinum 
crucible.  If  the  substance  is  a  fluoride,  or  if  any  fluoride  be  present,  the 
vapor  set  free  will  produce  a  visible  change  on  a  glass  plate  placed  over  the 
crucible. 


CHAPTEE    XVII. 

SULPHUR   AND    ITS    C  OMPO  U  N  D  S  — SE  LENIUM    AND    ITS 
COMPOUNDS. 

Sulphur  (S=16). 

This  important  substance  is  found  native,  chiefly  in  volcanic  districts, 
either  crystallized  or  amorphous.  The  Island  of  Sicily,  and  the  Solfatara, 
near  Naples  are  the  principal  sources  of  supply.  There  are  large  deposits 
of  sulphur  in  Spain,  also  around  Hecla,  in  Iceland,  and  it  occurs  more 
sparingly  in  certain  gypsum  beds  in  Europe.  The  well-known  mineral,  iron- 
pyrites,  contains  about  54  per  cent,  of  sulphur,  and  readily  yields  this  sub- 
stance by  distillation.  The  sulphur  thus  obtained  is,  however,  less  pure  than 
native  volcanic  sulphur,  and  is  generally  contaminated  with  arsenic.  Although 
commonly  described  as  a  mineral  body,  sulphur  enters  into  the  composition 
of  certain  animal  and  vegetable  substances.  Associated  with  nitrogen,  it  is 
a  constituent  of  albumen,  fibrin,  and  casein  ;  it  enters  into  the  composition 
of  silk,  hair,  horn,  nail,  and  feathers.  It  is  found  in  gluten,  and  certain 
essential  oils — e.g.,  those  of  mustard  and  horseradish. 

Preparation. — The  native  mineral,  on  which  the  sulphur  is  deposited,  is 
broken  up  and  submitted  to  distillation  in  fireclay  pots,  connected  with  re- 
ceivers. The  mineral  contains  from  30  to  50  per  cent,  of  sulphur.  The 
greater  part  of  this  is  separated  by  the  first  distillation,  the  sulphur  thus 
obtained  containing  rarely  more  than  5  or  6  per  cent,  of  earthy  impurities. 
By  a  second  distillation,  the  sulphur  is  obtained  pure  ;  and  while  in  a  liquid 
state  it  is  poured  into  wooden  moulds  of  a  slightly  conical  shape.  The 
sulphur,  when  cooled,  is  removed,  and  it  then  forms  the  well-known  rolU 
sulphur  of  commerce.  By  conveying  the  vapor  during  distillation  into  a 
large  chamber,  kept  cool,  the  sulphur  is  deposited  in  a  pulverulent  state, 
and  is  then  known  as  flowers  of  sulphur.  Owing  to  the  combustion  of  a 
portion  some  sulphurous  acid  is  produced,  and  thus  the  powder  occasionally 
has  an  acid  reaction  from  this  cause.  Sublimed  sulphur  may  be  purified  by 
washing  it  in  hot  water.  Sulphur  is  obtained  from  pyrites,  by  simply  dis- 
tilling the  broken  mineral  in  fireclay,  or  cast-iron  retorts,  connected  with 
receivers.     The  mineral  yields  readily  from  20  to  25  per  cent,  of  sulphur, 


SULPHUR.      PHYSICAL    AND    CHEMICAL    PROPERTIES.  213 

which  frequently  has  a  greenish  tint,  from  the  presence  of  some  sulphide  of 
iron.     Sulphur  in  its  purest  form  generally  contains  a  trace  of  hydrogen. 

Properties. — Sulphur,  or  brimstone,  is  a  brittle  substance,  of  a  pale  yellow 
color,  insipid,  and  inodorous,  but  exhaling  a  peculiar  odor  when  rubbed  or 
heated.  Its  specific  gravity  is  1-970  to  2080.  According  to  Regnault, 
the  specific  heat  of  crystallized  native  sulphur  is  O'lTTG,  and  of  sulphur 
recently  fused,  0*1844.  It  becomes  negatively  electrical  by  heat  and  by 
friction,  and  is  a  non-conductor  of  heat  and  electricity.  *  Sulphur,  as  a 
mineral  product,  occurs  crystallized,  its  primitive  form  being  an  acute  octa- 
hedron with  a  rhombic  base.  In  this  state  its  sp.  gr.  is  2  045,  and  the 
crystals  are  in  a  high  degree  doubly  refractive.  Crystals  of  native  sulphur, 
which  have  been  formed  by  the  condensation  of  sulphur  vapor,  as  well  as 
those  which  are  deposited  from  a  solution  of  sulphur  in  any  menstruum, 
possess  forms  which  are  either  identical  or  connected  by  being  referable  to 
the  same  crystalline  axes.  Such,  on  the  contrary,  as  are  produced  by  the 
cooling  of  fused  sulphur,  belong  to  a  different  system  of  crystallization.  One 
of  the  conditions  determining  the  form,  is  temperature  :  if  the  crystal  be 
formed  below  232°  it  belongs  to  the  right  prismatic  system  ;  if  at  that  point, 
to  the  oblique  prismatic.  This  is  proved  by  the  influence  of  temperature  on 
a  crystal  of  either  system  ;  a  crystal  of  fusion,  when  first  formed,  is  perfectly 
clear  and  transparent,  but  kept  at  common  temperatures  it  soon  becomes 
opaque,  and  presents  the  appearance  of  the  roll  sulphur  of  commerce  ;  the 
same  change  occurs  when  a  native  crystal  is  placed  in  a  solution  of  salt  which 
boils  at  232°.  The  opacity  is  in  both  cases  produced  by  a  new  arrangement 
of  the  particles  of  sulphur,  by  which,  without  any  change  in  the  external 
form,  the  internal  structure  of  the  crystal  is  altered.  Sulphur,  therefore,  is 
dimorphous.     {See  p.  38.) 

Sulphur  has  no  injurious  action  on  the  body  :  it  is  insoluble  in  water,  and 
snfiFers  no  change  by  exposure  to  air.  An  invisible  vapor  is  constantly 
escaping  from  it  at  common  temperatures.  If  leaf-silver  be  suspended  in 
the  upper  part  of  a  bottle  containing  sulphur,  it  will,  after  a  few  weeks, 
become  blackened  by  conversion  into  sulphide  of  silver.  At  about  180^ 
sulphur  is  volatilized,  and  its  peculiar  odor  is  strong  and  disagreeable  ;  at 
about  220^^  it  begins  to  fuse,  and  between  230°  and  2t0^  it  is  perfectly 
liquid,  and  of  a  bright  amber-yellow  color.  It  may  be  readily  melted  by 
heating  it  on  writing-paper  over  a  candle.  On  cooling  it  sets  into  a  group  , 
of  prismatic  crystals.  If  melted  on  a  glass-slide,  and  examined  by  an  inch- 
power  of  the  microscope,  the  phenomena  of  prismatic  crystallization  are 
beautifully  seen.  When  sulphur  is  heated  to  between  300°  and  500°,  it 
becomes  viscid,  and  of  a  dark  brown  color,  but  regains  its  fluidity  When 
cooled  to  230°.  At  a  higher  temperature  (out  of  contact  of  air)  it  again 
becomes  more  liquid,  and  at  about  800°  it  boils,  producing  an  amber-colored 
vapor,  which  may  be  condensed  either  in  a  solid  or  pulverulent  state,  accord- 
ing to  the  rapidity  of  the  process  and  the  size  of  the  condensing  vessels. 
The  residue  is  the  sulphur  vivum  of  old  pharmacy.  If  sulphur  is  heated  to 
about  450°,  and  while  still  viscid,  is  poured  into  cold  water,  it  acquires  and 
retains  a  certain  flexibility  and  elasticity,  having  at  the  same  time  a  dark 
color  :  it  hardens  slowly.  In  this  state,  it  is  sometimes  used  to  take  impres- 
sions of  gems  and  medals,  or  plaster  medallions.  For  this  purpose,  the 
surface  of  the  mould  should  be  oiled  before  the  sulphur  is  poured  on  it. 
When  cold,  it  has  a  reddish-brown  color,  and  a  specific  gravity  of  2'3. 
When  slowly  cooled  after  fusion,  sulphur  forms  a  fibrous  crystalline  mass  ; 
but  it  so*raetiraes  retains  its  fluidity,  and  does  not  concrete  till  touched  by 
some  solid  body.  This  state  appears  somewhat  analogous  to  that  of  water 
cooled  in  a  quiescent  state  below  its  freezing-point.     (Faraday,  Quarterly 


214  SULPHUR.   ALLOTROPIC  STATES. 

Journal,  21,  392.)  (For  the  method  of  procuring  crystals  of  sulphur  by 
fusion,  see  page  26.)  The  following  table  shows  the  results  of  Dumas's 
experiments  on  the  influence  of  temperature  upon  the  color  and  properties 
of  sulphur : — 

Temperature.  Hot  Sulphnr.  Sulphnr  suddenly  cooled  by  immersion  in  water. 

230°  .         .  Very  liquid  :  yellow  .  .  Very  brittle  :  usual  color. 

284   .         .  Liquid :  deep  yellow  .  .             Do.                   do. . 

338   .         .  Thick :  orange  yellow  .  Brittle  :    '              do. 

374.         .  Thicker:  orange         .  .      5  ^t  first  soft  and  transparent,  then  brittle 

^  ^     and  opaque  :  usual  color. 

428    .         .  Viscid  :  reddish          .  .  Soft :  transparent :  amber  color. 

464  to  500  Very  viscid  :  brown-red  .  Very  soft :  transparent :  reddish. 

800  boiling  Less  viscid :  brown-red  .            Do.  *            do.           brown-red. 

In  order  that  sulphur  may  retain  its  soft  or  viscid  state,  it  is  not  necessary, 
as  sometimes  directed,  to  keep  it  long  in  a  fused  state,  but  merely  to  take 
care  that  it  has  been  raised  to  a  due  temperature,  and  then  suddenly  cooled 
by  dropping  it  into  cold  water;  if  poured  into  the  water  in  mass,  the 
interior  cools  slowly  and  reverts  to  its  brittle  state.  Here,  therefore,  the 
effect  of  what  may  be  called  tempering,  is  the  reverse  of  that  produced 
upon  steel,  and  somewhat  corresponds  with  the  phenomena  presented  by 
bronze. 

The  researches  of  Deville,  Berthelot,  Magnus,  and  other  chemists,  have 
shown  that  sulphur,  according  to  the  effect  of  heat  and  sudden  cooling,  may 
assume  various  allotropic  conditions.  Deville  assigns  four  varieties,  and 
Magnus  six.  These  are  based  chiefly  on  crystalline  form,  color,  and  solu- 
bility. The  hlach  sulphur  of  Magnus  is  obtained  by  heating  sulphur 
repeatedly  to  near  its  boiling-point,  and  then  suddenly  cooling  it  in  water. 
It  is  characterized  not  only  by  its  color,  but  by  its  insolubility  in  sulphide 
of  carbon,  and  the  usual  solvents  of  sulphur.  (Pelouze  and  Fremy,  Traite 
de  Chimie,  1,  200.)  The  sulphur  of  commerce  occurs  in  three  prevailing 
colors,  namely,  lemon  yellow,  verging  on  ^reen,  dark  yellow,  and  brown 
yellow.;  these  shades  result,  partly  at  least,  as  the  above  table  shows, 
from  the  different  degrees  of  heat  to  which  it  has  been  exposed  during  its 
fusion  or  extraction  on  the  great  scale — the  palest  variety  having  been  the 
least  heated. 

For  some  pharmaceutical  purposes,  sulphur  is  precipitated  from  a  solu- 
*tion  of  tersulphide  of  potassium  or  pentasulphide  of  calcium,  by  hydrochloric 
acid,  and,  when  washed  and  dried,  it  forms  a  pale  yellowish-gray  impalpable 
powder;  this  is  the  milk  of  sulphur  Qlw^  precipitated  sulphur  of  the  Pharma- 
copoaia.  Thomson  considers  it  to  be  a  compound  of  sulphur  and  water — a 
hydrate.  {System  of  Chemistry,  vol.  1,  p.  285.)  When  dried  it  gives  out  no 
water,  but  fuses  into  common  sulphur,  always,  however,  evolving  a  little 
hydrogen. 

The  purity  of  sulphur  may  be  judged  of  by  heating  it  gradually  upon  a 
piece  of  mica  or  platinum-foil  ;  if  free  from  earthy  substances,  it  should 
evaporate  and  leave  no  residue.  It  should  also  be  soluble  in  benzole  or 
boiling  oil  of  turpentine.  According  to  Ure,  sulphur  is  soluble  in  ten  times 
its  weight  of  boiling  oil  of  turpentine  at  316°,  forming  a  red-colored  solu- 
tion which  remains  clear  at  180°.  When  the  solution  cools  rapidly,  or  is 
rapidly  evaporated,  prismatic  cijstals  are  deposited.  If,  however,  it  is 
allowed  to  evaporate  spontaneously,  octahedral  crystals  are  formed.  The 
same  phenomena  is  observed  in  reference  to  the  solution  of  sulphur  in  ben- 
zole. The  employment  of  either  of  these  liquids  enables  a  chemist  #o  deter- 
mine whether  sulphur  is  contaminated  with  its  usual  impurities,  namely, 


SULPHUR.       COMPOUNDS.      TESTS.  215 

carbonate  and  sulphate  of  zinc,  oxide  and  sulphide  of  iron,  sulphide  of 
arsenic  and  silica.     These  remain  undissolved. 

The  sp.  gr.  of  sulphur-vapor  is  theoretically  6  "6336,  and,  supposing  it  to 
exist  ^s  vapor  at  mean  temperature  and  pressure,  100  cubic  inches  would 
weigh  205-44  grains.  From  the  experiments  of  Dumas  and  Mitscherlich,  at 
a  temperature  of  932°,  the  sp.  gr.  of  the  vapor  is  6  •654.  According  to 
Bineau,  when  taken  at  a  temperature  of  1832°,  the  sp.  gr.  is  2-218.  Cora- 
pared  with  hydrogen,  the  sp.'gr.  of  sulphur-vapor  is  as  96  to  1. 

Sulphur  is  not  readily  dissolved  by  alcohol,  ether,  or  chloroform.  Anhy- 
drous alcohol  when  boiled  with  it  dissolves  it  in  small  quantities.  The 
vapors  of  these  liquids  also  combine  with  it.  It  is  very  soluble  in  sulphide 
of  carbon  ;  100  parts  of  this  liquid  will  dissolve  38  parts  of  sulphur  at  the 
common  temperature,  and  73  parts  when  heated.  The  sulphide  may  be  use- 
fully employed  for  the  separation  of  sulphur  from  vulcanized  rubber,  gun- 
powder, &c.  If  recently  fused  sulphur  is  dissolved  in  the  sulphide,  and  it  is 
spontaneously  evaporated,  crystals  belonging  to  the  two  systems  are  de- 
posited, namely,  transparent  octahedra,  and  oblique  rhombic  prisms,  which 
are  opaque.  It  is  probable  that  by  heat  the  sulphur  has  partially  undergone 
an  allotropic  change.  Among  other  solvents  of  sulphur  may  be  mentioned 
chloride  of  sulphur  and  the  alkaline  sulphites.  The  latter  are  commonly 
used  for  devulcanizing  caoutchouc. 

When  heated  in  the  atmosphere  to  about  560°  sulphur  inflames  and  burns 
with  a  peculiar  blue  light;  at  a  higher  temperature  its  vapor  kindles  with  a 
purple  flame ;  and  in  oxygen  it  burns  vividly,  with  a  large  lilac-colored 
flame.  The  comparatively  low  temperature  at  which  sulphur  is  kindled,  is 
an  important  circumstance  in  reference  to  its  use  for  the  manufacture  of  gun- 
powder, matches,  &c.  It  may  be  well  illustrated  by  propelling  powdered 
sulphur  into  the  hot  air  issuing  from  an  argand  lamp-glass;  it  takes  fire  at 
a  great  height  above  the  flame.  The  product  of  combustion  is  sulphurous 
acid,  known  by  its  peculiar  odor. 

Equivalent  and  Compounds. — Sulphur  combines  with  the  metalloids  and 
metals,  forming  the  class  oi sulphides  or  sulphurets.  The  metallic  sulphides 
generally  correspond  to  the  oxides.  The  range  of  combination  of  sulphur 
is  very  great ;  it  frequently  displaces  oxygen,  converting  oxides  into  sul- 
phides, while  many  sulphides,  by  simple  exposure  to  air,  are  converted  into 
oxides.  Its  atomic  weight,  as  deduced  from  its  compound  with  hydrogen,  is 
16.  Hence  as  sulphur-vapor  has  a  sp.  gr.  of  96,  compared  with  hydrogen, 
each  volume  of  the  vapor  will  correspond  to  six  atoms,  or  the  atomic  volume 
of  sulphur-vapor  will  be  one-sixth  of  a  volume.  If  the  atomic  volume  of 
hydrogen  be  two,  then  that  of  sulphur  will  be  one-third  of  a  volume. 

Tests. — The  color,  fusibility,  and  combustion  with  a  blue  flame,  as  well  as 
the  odor  of  the  vapor,  are  sufficient  tests  for  sulphur  in  a  solid  state.  Its 
solubility  in  sulphide  of  carbon,  and  the  production  of  octahedral  crystals  as 
a  result  of  the  spontaneous  evaporation  of  the  solution,  are  also  characteristic 
of  the  presence  of  this  substance.  In  many  organic  solids  its  existence  is 
revealed  by  applying  heat,  when  sulphuretted  hydrogen  escapes.  If  sulphur, 
or  any  substance  containing  traces  of  it  (quill  or  gluten),  be  boiled  in  a  solu- 
tion of  potassa,  holding  dissolved  a  small  quantity  of  oxide  of  lead,  the  liquid 
or  the  solid  acquires  a  brown-black  color  from  the  production  of  sulphide  of 
lead.  The  test  is  prepared  by  adding  to  a  solution  of  potassa  a  few  drops 
of  a  solution  of  acetate  of  lead,  and  then  adding  a  sufficient  quantity  of  po- 
tassa to  dissolve  the  white  precipitate  which  is  first  formed. 

SuLPHua  AND  Oxygen. — Sulphur  forms  no  oxide ;  but  there  are  seven 
compounds  of  sulphur  and  oxygen,  all  of  which  rank  among  the  acids.     The 


216  SULPHUR    AND    OXYGEN.      SULPHUROUS    ACID. 

most  important  of  these  are,  1.  Sulphurous  acid  ;  2.  Sulphuric  acid  ;  and  3. 
Hyposulphurous  acid. 


Sulphurous  acid 

.     SO, 

Hvposulphuric  (dithionic)  acid     S^Og 

Sulphuric  acid    . 

.     SO3 

Trithionic  acid         .     ,    .         .     S3O5 

Hyposulphurous  acid  ) 

.    s,o, 

Tetrathionic  acid      .         .         .     S^Og 

Dithiouous  acid           / 

Pentathionic  acid     .         .         .     S5O5 

In  the  four  last  compounds,  the  atoms  of  oxygen  being  5,  there  is  aa 
increase  of  one  atom  of  sulphur  in  each.  Of  the  seven  oxy-compounds  here 
enumerated,  the  first  three  have  a  special  importance  to  the  chemist,  and  as 
they  are  produced  by  a  conversion  or  reaction  of  sulphurous  acid,  it  is  this 
compound  which  will  first  claim  our  consideration. 

Sulphurous  Acid  (SOg) This  is  an  anhydrous  gaseous  acid  produced  by 

the  burning  of  sulphur  in  oxygen.  In  1Y74,  Scheele  pointed  out  a  method 
of  obtaining  it :  and  about  the  same  time  Priestley  procured  it  in  the  gaseous 
form,  and  ascertained  its  leading  properties.  Its  atomic  composition  was 
first  accurately  investigated  by  Davy,  Gay-Lussac,  and  Berzelius. 

Sulphurous  acid  may  be  obtained  by  several  processes.  It  may  be  pro- 
cured directly,  by  burning  sulphur  in  dry  oxygen  gas  ;  or  indirectly,  by 
boiling  one  part  of  copper  filings  or  of  mercury  in  three  of  sulphuric  acid 
(Cu-fi^[S03,HO]  =  CuO,S03+2HO  +  S02):  or  by  heating  in  a  retort  a 
mixture  of  three  parts  of  black  oxide  of  manganese  in  powder  and  one  of 
sulphur,  S3-HMn02=S03  4-MnS.  Charcoal  or  sulphur  boiled  with  sulphuric 
acid,  also  yields  this  gas.  As  water  dissolves  about  fifty  times  its  bulk  of 
the  gas,  it  should  be  collected  and  preserved  over  mercury.  For  all  the 
common  purpose  of  experiment,  it  may  be  collected  by  displacement  in  dry 
jars  or  bottles.  When  generated  by  the  action  of  charcoal,  wood,  and  various 
organic  matters,  upon  sulphuric  acid,  it  is  mixed  with  carbonic  acid.  Sul- 
phurous acid  may  be  procured  by  the  combustion  of  sulphur  or  sulphide  of 
carbon  in  a  confined  volume  of  air.  Under  these  circumstances,  it  is  mixed 
with  nitrogen  or  carbonic  acid. 

Properties. — The  gas  is  without  color,  but  it  has  the  suffocating  odor  of 
burning  sulphur,  and  a  sour  taste.  If  breathed  in  a  diluted  state,  it  causes 
cough  and  headache ;  and  in  a  concentrated  form  it  is  fatal  to  life.  It  is 
highly  destructive  to  all  animals.  It  is  very  heavy,  being  more  than  twice 
the  weight  of  air.  Its  sp.  gr.  is  2-2112,  and  compared  with  hydrogen,  32 
to  1  ;  100  cubic  inches  weigh  68'48  grains.  It  is  one  of  the  most  easily 
liquefiable  of  the  gases  (p.  80).  By  mere  cooling  to  14°,  it  becomes  aa 
anhydrous  limpid  liquid. 

In  the  liquefied  state  it  has  asp.  gr.  of  1-45,  evaporating  with  such  rapidity 
at  common  temperatures  as  to  generate  a  great  degree  of  cold,  so  that  by 
its  aid  mercury  may  be  frozen,  and  chlorine,  ammonia,  and  cyanogen  liquefied. 
The  liquid  acid  is  not  an  electrolyte.  When  it  is  allowed  to  evaporate  in 
vacuo,  the  cold  produced  is  so  intense,  that  the  liquid  acid  is  congealed  ;  it 
solidifies  at  — 105°  ;  it  may  also  be  frozen  by  the  aid  of  a  mixture  of  solid 
carbonic  acid  and  ether  ;  it  then  forms  a  white  crystalline  mass,  denser  than 
the  liquid  acid. 

When  sulphur  is  burned  in  pure  and  perfectly  dry  oxygen,  sulphurous 
acid  only  is  produced,  without  any  change  in  the  volume  of  oxygen,  so  that 
its  composition  is  learned  by  the  increase  of  weight.  Oxygen,  when  saturated, 
is  exactly  double  in  weight;  hence  sulphurous  acid  consists  of  equal  weights 
of  sulphur  and  oxygen.  According  to  Mitscherlich's  estimate  of  the  specific 
gravity  of  sulphur-vapor,  sulphurous  acid  consists  of  100  volumes  of  oxygen 
gas,  and  16  of  the  vapor  of  sulphur,  condensed  into  100  volumes;  or  one 
volume  of  oxygen  combined  with  one-sixth  of  a  volume  of  sulphur-vapor 
constitute  one  volume  of  sulphurous  acid. 


SULPHUROUS    ACID.      COMPOSITION.  21T 

Atoms,    Weights.    Per  cent.    Volume.  Sp.  Gr. 

Sulphur.         .         .         .     1     ...     16     ...     50     ...     ^     ...  1-1055 

Oxygen  .         .         .         .     2     ...     16     ...     50     ...     1     ...  1-1057 


Sulphurous  acid      .         .     1  32  100  1  2-2112 

As  oxyp^en  undergoes  no  chanpje  of  volume  in  forming  this  gas,  the  num- 
ber of  volumes  of  sulphurous  acid  are  indicated  by  the  quantity  of  oxygen 
consumed  in  the  combustion  of  sulphur. 

The  gas  has  a  strongly  acid  reaction.  It  extinguishes  most  combustibles 
when  they  are  immersed  in  it  in  an  inflamed  state ;.  hence  burning  soot  in  a 
chimney  may  be  extinguished  by  throwing  a  handful  of  sulphur  into  the  fire. 
The  upper  part  of  the  flue  should  be  stopped,  and  no  air  allowed  to  pass 
into  the  chimney  except  that  which  traverses  the  burning  sulphur.  Air  con- 
taining only  one-third  of  its  volume  of  this  gas  does  not  support  ordinary 
combustion.  The  gas  vividly  maintains  the  combustion  of  potassium  and 
sodium.  At  mean  temperature  and  pressure,  recently  boiled  water  takes  up 
about  50  volumes  of  sulphurous  acid  gas.  This  solution  {aqueous  sulphurous 
acid),  which  may  be  procured  by  passing  the  gas  into  distilled  water,  has  a 
sulphurous  and  somewhat  astringent  taste,  and  it  bleaches  some  vegetable 
colors.  If  long  kept,  sulphuric  acid  is  formed;  it  acquires  a  sour  flavor, 
and  reddens  vegetable  blues.  Some  coloring  matters,  such  as  those  of 
litmus  and  cochineal,  are  not  readily  bleached  by  sulphurous  acid  ;  while 
those  which  are  bleached  may  have  their  colors  restored  by  an  acid  or  an 
alkali.  If  a  solution  of  sulphurous  acid  is  added  to  infusion  of  roses  or  blue 
infusion  of  cabbage,  it  will  redden  these  liquids,  owing  to  the  presence  of 
free  sulphuric  acid.  By  carefully  neutralizing  this  acid  with  potassa,  the 
color  will  entirely  disappear.  If  the  liquid  thus  bleached  be  now  treated 
with  a  strong  solution  of  potassa,  it  will  acquire  a  green  color,  while  another 
portion  will  be  intensely  reddened  by  sulphuric  acid.  If  added  to  a  solu- 
tion of  azuline  there  is  no  change  of  color,  but  when  a  solution  of  potash  is 
added  to  neutralize  the  sulphuric  acid  present,  the  blue  liquid  becomes  color- 
less. On  adding  strong  sulphuric  acid  to  this  liquid,  the  blue  color  is 
restored.  The  bleaching,  therefore,  depends  upon  a  temporary  production 
of  colorless  sulphites.  Cotton  goods,  as  well  as  those  of  silk,  woollen,  and 
straw,  which  would  be  injured  by  chlorine,  are  bleached  by  this  acid.  The 
articles,  wetted,  are  exposed  in  a  close  chamber  to  the  fumes  of  burning 
sulphur.  They  are  then  well  washed,  to  remove  the  colorless  sulphites,  and 
are  thus  eff'ectually  bleached.  Hops  are  also  bleached  by  exposure  to  the 
vapor  of  burning  sulphur.  Sulphurous  acid  by  its  removal  of  free  oxygen 
arrests  fermentation  and  putrefaction.  When  the  aqueous  solution  of  sul- 
phurous acid  is  boiled,  a  great  part  of  the  gas  escapes,  but  not  when  it  is 
frozen.  The  specific  gravity  of  the  solution  at  60°,  when  it  contains  50 
volumes  of  the  gas,  is  1-04.  At  a  low  temperature  the  concentrated  aqueous 
solution  deposits  a  crystalline  hydrate  consisting  of  SOg+OHO.  Alcohol 
dissolves  sulphurous  acid  more  copiously  than  water ;  one  volume  taking  up 
at  60°,  115  volumes  of  the  gas. 

Sulphurous  acid  gas  suffers  no  change  at  a  red  heat;  but  if  mixed  with 
hydrogen,  and  passed  through  a  red-hot  tube,  water  is  formed  and  sulphur 
deposited  (2H  +  S0a=S-f  2H0).  Under  the  same  circumstances,  it  is  de- 
composed by  charcoal,  by  potassium,  and  sodium,  and  probably  by  several 
other  metals.  It  undergoes  no  change  when  mixed  with  oxygen,  unless 
humidity  or  water  be  present,  in  which  case  a  portion  of  sulphuric  acid  is 
slowly  formed.  But  a  mixture  of  the  dried  gases  passed  over  heated  spongy 
platinum  produces  anhydrous  sulphuric  acid.  When  mixed  with  chlorine, 
and  in  contact  with  water,  sulphurous  acid  produces  sulphuric  and  hydro- 


218  TESTS    FOR    SULPHUROUS    ACID    AND    SULPHITES. 

chloric  acids  (SOa+HO  +  Cl^SOg  +  HCl) ;  but  the  perfectly  dry  gases 
have  no  mutual  action,  except  under  the  influence  of  bright  summer  sun- 
shine, when  a  mixture  of  equal  volumes  of  chlorine  and  sulphurous  acid 
yields  a  liquid  of  the  specific  gravity  of  1-659  at  68°,  which  boils  at  170°, 
the  specific  gravity  of  the  vapor  being  4-67.  Its  formula  is  S0^,C1.  It 
may  be  compared  to  sulphuric  acid,  in  which  one  atom  of  oxygen  has  been 
replaced  by  one  of  chlorine.  With  water,  it  evolves  heat  and  yields  hydro- 
chloric and  sulphuric  acids.  Iodine  and  bromine  are  without  action  on 
sulphurous  acid  unless  water  is  present,  when  sulphuric  acid,  and  hydriodic 
and  hydrobromic  acids  are  formed  (S034-H04-I=HI-|-S03).  The  chloric, 
bromic,  and  iodic  acids  are  decomposed  by  sulphurous  acid,  with  the  evolu- 
tion of  chlorine,  bromine,  and  iodine,  and  the  formation  of  sulphuric  acid. 
When  gaseous  sulphurous  acid  is  mixed  with  hydrochloric,  hydriodic,  or 
hydrobromic  acid  gases,  they  mutually  decompose  each  other  ;  water,  with 
chloride,  iodide  or  bromide  of  sulphur  is  formed  ;  but  when  these  acids  are 
in  aqueous  solution,  they  do  not  decompose  each  other.  In  the  dry  state, 
sulphurous  acid  has  no  action  on  hydrosulphuric  acid  :  but  when  water  is 
present,  or  the  aqueous  sohitions  of  the  two  gases  are  mixed,  water  is  pro- 
duced and  sulphur  is  thrown  down  (S02-i-2HS  =  2B[0  +  3S).  Sulphur  and 
pentathionic  acid  are  sometimes  products  of  this  mixture.  It  is  probably 
by  a  reaction  of  this  kind  that  sulphur  is  naturally  deposited  at  the  Sol- 
fatara,  and  in  other  volcanic  districts.  Sulphurous  acid  deoxidizes  the 
oxacid  compounds  of  nitrogen.  Thus,  in  contact  with  nitric  acid,  sulphuric 
acid  and  deutoxide  of  nitrogen  are  produced  (3S02-fN05,HO=3S03+ 
NOg+HO).  Two  atoms  of  sulphurous  acid  produce  hyponitrous  acid,  and 
one  atom  produces  nitrous  acid,  both  of  which  are  dissolved  in  the  unde- 
composed  nitric  acid,  giving  to  it  a  bluish  green  or  green  color.  An  excess 
of  sulphurous  acid  therefore  entirely  decomposes  the  acid  compounds  of 
nitrogen  and  oxygen.  On  evaporation  of  the  mixture,  nothing  but  sulphuric 
acid  is  obtained  :  the  deutoxide  of  nitrogen  escaping  as  a  gas.  Iodic  acid 
undergoes  a  similar  deoxidation,  (5SO^+IO,=l4-5S03).  Iodine  is  set 
free,  and  may  be  detected  by  its  odor,  or  by  its  action  on  a  solution  of 
starch.  Sulphurous  acid  gas  is  entirely  absorbed  and  removed  by  peroxide 
of  lead,  Pb03  +  S03=PbO,S03.  In  the  presence  of  water  or  of  certain 
bases,  sulphuric  acid  and  deutoxide  of  nitrogen  combine  to  form  crystalline 
compounds.  Peroxide  of  lead,  or  of  manganese,  added  to  the  aqueous  solu- 
tion of  sulphurous  acid,  converts  it  into  sulphuric  acid,  and  destroys  its 
odor. 

Tests. — The  best  test  for  sulphurous  acid  gas  is  its  odor,  and  acid  reaction. 
Paper  wetted  with  a  solution  of  protonitrate  of  mercury  is  blackened  by  it. 
A  mixture  of  iodic  acid  and  starch  in  solution,  or  paper  immersed  in  this 
liquid,  reveals  the  presence  of  the  smallest  quantity  of  the  acid  by  the  pro- 
duction of  blue  iodide  of  starch.  Zinc  is  dissolved  by  the  aqueous  acid 
without  any  evolution  of  hydrogen  (2Zn  +  3S03=ZnO,S,0,+  ZnO,S02). 
If  hydrochloric  acid  is  added  to  the  mixture,  sulphuretted  hydrogen  is  pro- 
duced and  evolved.  Traces  of  sulphurous  acid  may  thus  be  found  in  hydro- 
chloric acid.  Sulphurous  acid  may  be  detected  in  the  smoke  of  coke  and 
coal,  and  it  is  thus  imparted  to  the  atmosphere  of  places  where  coal  is  burnt. 

Sulphites  and  Bisulphites  (MO.SO^  and  MO,2S03).— The  sulphites  of  the 
alkalies  when  exposed  in  a  moist  state  to  the  air,  pass  gradually,  by  absorp- 
tion of  oxygen,  into  sulphates.  Chlorine,  nitric  acid,  and  several  other 
oxidizing  agents,  produce  a  similar  change.  Sulphites  destroy  the  color  of 
a  solution  of  permanganate  of  potassa,  and  reduce  the  persalts  of  iron  to  the 
state  of  protosalts ;  added  to  nitrate  of  silver  they  form  a  white  precipitate 
of  sulphite  of  silver  ;.  which  is  soluble  in  nitric  acid  at  a  boiling  temperature. 


SULPHURIC    ACID.      OIL    OP    VITRIOL.  219 

The  precipitate  given  by  nitrate  of  baryta  in  the  solution  of  a  sulphite  (free 
from  sulphate),  is  also  soluble  in  nitric  acid.  When  an  alkaline  sulphite  is 
boiled  with  nitric  acid,  fumes  of  sulphurous  acid  and  nitrous  acid  are  evolved, 
and  nitrate  of  baryta  will  now  produce  in  the  liquid  a  white  precipitate  of 
sulphate  of  baryta,  which  is  insoluble  in  nitric  acid.  A  sulphite  reduces  the 
chloride  of  gold  from  its  acid  solution  slowly  in  the  cold,  but  rapidly  by  heat. 
Arsenic  acid  is  converted  into  arsenious  acid  by  boiling  it  with  a  sulphite  or 
with  sulphurous  acid.  Bisulphite  of  soda  is  occasionally  used  in  analysis  for 
the  removal  of  chlorine  from  liquids.  The  solid  sulphites  evolve  sulphurous 
acid,  when  concentrated  sulphuric  acid  is  poured  on  them.  This  may  be 
detected  by  iodic  acid  and  starch. 

Sulphuric  Acid  (SO3).     Oil  of  Vitriol  (HOjSOg). 

Production. — This  acid  was  first  obtained  by  the  distillation  of  sulphate  of 
iron,  or  green  vitriol,  and  was  termed  from  its  appearance  and  consistency, 
oil  of  vitriol.  It  was  formerly  procured  by  the  combustion  of  a  mixture  of 
eight  parts  of  sulphur  and  one  part  of  nitrate  of  potassa  or  soda  in  a  furnace. 
During  this  combustion  sulphurous  acid  and  nitric  as  well  as  nitrous  acid 
were  evolved.  It  is  now  found  more  convenient  to  produce  the  sulphurous 
acid  by  burning  sulphur  or  iron-pyrites  under  a  regulated  current  of  air  in 
a  furnace,  and  to  decompose  the  nitrate  of  potassa  or  soda  by  means  of  sul- 
phuric acid,  in  vessels  or  pots  exposed  to  the  heat  of  the  burning  sulphur — 
or  in  a  separate  chamber.  The  vapors  are  carried  by  the  flues  into  capacious 
leaden  chambers,  which  are  sometimes  100  feet  long,  20  to  30  feet  wide,  and 
10  to  16  feet  high.  On  the  floor  of  these  chambers  there  is  a  stratum  of 
water;  and  the  decomposition  of  the  gases  by  which  sulphuric  acid  is  pro- 
duced, is  effected  by  the  occasional  introduction  of  jets  of  steam.  The  water 
on  the  floor  of  the  chamber  dissolves  the  products,  and  gradually  becomes 
more  and  more  acid  :  it  is  converted  into  diluted  sulphuric  acid.  When  it 
has  thus  acquired  a  specific  gravity  of  1*2  to  13,  it  is  drawn  off  into  shallow 
leaden  boilers,  where  it  is  evaporated  until  it  reaches  a  specific  gravity  of 
]  'to.  In  addition  to  the  loss  of  water  by  evaporation,  any  traces  of  sulphur- 
ous or  nitric  acid,  are  then  expelled.  L%  this  density  the  acid  would  begin 
to  act  upon  lead,  and  the  heat  required  for  its  further  evaporation  would 
endanger  the  softening  of  the  metal.  At  this  degree  of  concentration,  there- 
fore, the  acid  is  run  off  into  boilers,  or  into  stills  of  platinum,  which  are  set 
upon  cast  iron,  and  in  which  the  further  boiling  down  of  the  acid  is  continued 
until  vapors  of  sulphuric  acid  begin  to  appear,  or  it  has  attained  the  specific 
gravity  of  r84.  It  is  then  drawn  off  by  a  siphon  into  a  platinum  cistern  or 
cooler,  and  is  thence  transferred  into  carboys,  or  large  bottles  protected  by 
basket  work,  each  holding  about  100  pounds  of  the  acid.  Before  the  intro- 
duction of  platinum  vessels,  the  evaporation  was  finished  in  glass  retorts. 

In  this  process  the  sulphurous  acid  derived  from  the  combustion  of  sulphur 
or  pyrites  is  oxidized  and  converted  into  sulphuric  acid  by  the  agency  of 
deutoxide  of  nitrogen  and  water.  The  nitric  and  nitrous  acids,  set  free  from 
the  nitre,  are  deprived  of  three  and  two  equivalents  of  oxygen  respectively 
apd  sulphuric  acid  and  deutoxide  of  nitrogen  result  (5SOa+N05  +  N04= 
5SO3  +  2NO3).  As  there  is  air  in  the  chamber,  the  deutoxide  of  nitrogen 
is  immediately  converted  to  nitrous  acid  (2N0.3+04=2NOJ  and  thenitrous 
acid  thus  produced  is  again  decomposed  by  the  sulphurous  acid.  It  will  be 
perceived  from  this  statement,  that  the  deutoxide  of  nitrogen,  once  formed, 
serves  as  a  medium  for  transferring  the  oxygen  of  air  in  the  chamber  to  the 
sulphurous  acid  ;  and  the  operation  is  made  continuous  by  allowing  a  certain 
quantity  of  air  to  pass  into  the  chamber  with  the  sulphurous  acid.     The 


290  SULPHURIC    ACID.      CHEMICAL    PROPERTIES. 

amount  of  sulphuric  acid  produced,  depends  on  the  supply  of  sulphurous 
acid.  Only  a  comparatively  small  proportion  of  deutoxide  is  needed  for  the 
chang:e. 

Dry  sulphurous  and  nitrous  acids  have  no  action  on  each  other.  The 
presence  of  a  small  quantity  of  aqueous  vapor  brings  about  their  combina- 
tion, and  a  white  crystalline  solid  is  produced.  This  is  decomposed  by 
water  or  steam,  and  while  deutoxide  of  nitrogen  is  evolved,  sulphuric  acid  is 
dissolved  in  the  liquid.  The  composition  of  these  crystals  is  viewed  differ- 
ently by  different  chemists,  but  the  following  equation  indicates  the  changes  : 
2SO,+NO„  +  2HO=2(SO„HO)-fNO,. 

The  phenomena  connected  with  the  production  of  sulphuric  acid  may  be 
easily  witnessed  by  introducing  sulphurous  acid  with  nitrous  acid  vapor  into 
a  large  glass  globe,  and  adding  water  in  a  small  quantity  to  produce  the 
crystals,  and  afterwards  in  larger  quantity  to  decompose  them.  On  a  small 
scale,  the  reaction  of  these  gases  upon  each  other  may  be  illustrated  by 
inverting  a  small  jar  of  moist  deutoxide  of  nitrogen  over  a  jar  of  sulphurous 
acid.  A  deposit  of  a  white  crystalline  substance  over  the  interior  speedily 
takes  place.  In  the  working  chamber,  the  crystals  are  not  commonly  pro- 
duced, as  the  jets  of  steam  introduced  and  the  abundance  of  water  prevent 
their  formation.  Other  methods  of  forming  sulphuric  acid  have  been  pro- 
posed, but  they  have  not  been  hitherto  applied  on  a  large  scale. 

Properties. — Monohydrated  sulphuric  acid  is  a  heavy  oily-looking  liquid 
— limpid,  colorless,  and  inodorous.  It  gives  off  no  vapor  at  common  tem- 
peratures. The  specific  gravity  of  the  pure  acid  is  1'842  at  60^  (Pelouze). 
Dr.  Ure  states  that  he  has  met  with  it  as  high  as  1'845,  and  Dr.  Lyon 
Playfair  has  procured  it  as  high  as  1*8479.  Sulphuric  acid  boils  at  a  tem- 
perature of  about  650°,  which,  therefore,  approaches  a  red-heat,  and  it  may 
be  distilled  over  without  decomposition.  Its  boiling-point  diminishes  with 
its  dilution;  when  of  the  specific  gravity  of  I'YS  it  boils  at  435°  ;  and  at 
348°  when  its  specific  gravity  is  1*63.  Owing  to  the  small  amount  of  heat 
rendered  latent  by  the  vapor  of  sulphuric  acid,  it  boils  with  explosive  vio- 
lence, and  gives  off  sudden  jets  of  vapor.  This  may  be  obviated  by  intro- 
ducing into  the  liquid,  broken  glass  or  portions  of  platinum  foil  or  wire. 
The  vapor  is  readily  condensed  by  mere  cooling:  it  is  not  necessary  to  place 
the  receiver  in  cold  water.  The  concentrated  acid  freezes  at  — 30°  ;  and  at 
the  same  time  contracts  considerably  in  its  volume.  When  once  frozen,  it 
retains  its  solid  state  until  the  temperature  rises  to  about  the  freezing-point 
of  water.  Sulphuric  acid  of  the  specific  gravity  of  1*78  (which  is  a  definite 
hydrate,  containing  one  atom  of  anhydrous  sulphuric  acid,  and  2  atoms  of 
water),  freezes  at  40°,  but  if  the  density  of  the  liquid  be  either  increased  or 
diminished,  a  greater  cold  is  required  for  its  congelation. 

Sulphuric  acid  is  intensely  acrid  and  corrosive  ;  it  acts  speedily  upon  the 
skin,  occasioning  a  biting  sensation,  and  a  soapy  feel  of  the  part,  in  conse- 
quence of  its  chemical  action  on  the  cuticle  ;  its  taste,  even  when  very  largely 
diluted,  is  extremely  acid,  and  it  powerfully  reddens  litmus.  It  has  a  strong 
attraction  for  water,  so  that  it  absorbs  aqueous  vapor  from  the  atmosphere 
and  increases  rapidly  in  bulk  ;  in  moist  weather  three  parts  increase  to  four 
in  the  course  of  24  hours,  and  by  longer  exposure  a  larger  quantity  of  water 
is  taken  up,  so  that  it  requires  to  be  preserved  in  well-closed  vessels.  It  is 
this  property  which  renders  it  applicable  to  the  drying  of  certain  gases,  and 
to  the  purposes  of  evaporation  and  desiccation  under  the  exhausted  receiver 
of  the  air-pump.  When  sulphuric  acid  is  suddenly  mixed  with  water,  mutual 
condensation  ensues,  and  much  heat  is  evolved.  Four  parts  by  weight  of 
acid,  specific  gravity  1*84,  and  one  of  water  at  60^  produce,  when  thus 
mixed,  a  temperature  =300°.     According  to  Dr.  Ure,  the  greatest  heat  is 


SULPHURIC    ACID.       CHEMICAL    PROPERTIES.  221 

evolved  by  mixing  13  of  acid  with  21  of  water.  Even  a  boiling  temperature 
does  not  prevent  sulphuric  acid  taking  up  moisture  from  the  air;  hence  it 
cannot  be  concentrated  so  well  in  an  open  as  in  a  close  vessel ;  on  which 
account  retorts,  or  large  platinum  stills,  are  used  for  the  last  stage  of  its  con- 
centration, by  manufacturers.  The  mixture  of  sulphuric  acid  with  ice  or 
snow  causes  its  immediate  liquefaction,  and  as  this  liquefaction,  consistently 
with  the  theory  of  latent  heat,  produces  cold,  while  on  the  other  hand  the 
union  of  the  acid  with  the  water  evolves  heat,  the  resulting  temperature  of 
such  a  mixture  depends  upon  the  relative  proportions  of  the  substances 
mixed.  Four  parts  of  acid  and  one  of  pounded  ice,  evolve  heat ;  but  four 
parts  of  ice  and  one  of  acid,  generate  cold.  Its  affinity  for  water  is  so  great 
that  it  will  dehydrate  and  render  colorless,  crystals  of  sulphate  of  iron  and 
sulphate  of  copper.  At  the  boiling-point  it  will  decolorize  Prussian  blue  ; 
but  the  color  is  restored  on  adding  water. 

Sulphuric  acid,  under  ordinary  circumstances,  displaces  the  greater  number 
of  other  acids  fro'm  their  combinations  ;  thus,  in  the  humid  way,  it  decom- 
poses the  phosphates  and  the  borates  ;  at  a  red  heat,  however,  the  phosphoric 
and  the  boracic  acids,  which  are  comparatively  fixed  in  the  fire,  expel  sul- 
phuric acid  from  its  salts.  A  solution  of  sulphate  of  lime  is  decomposed  by 
oxalic  acid,  which  forms  an  insoluble  oxalate  of  lime  ;  and  the  tartaric, 
racemic,  perchloric,  and  picric  acids  decompose  sulphate  of  potassa  in  solu- 
tion. In  consequence  of  its  strong  affinity  for  water,  sulphuric  acid  chars 
most  organic  substances ;  it  acquires  a  brown  tinge  from  the  smallest  par- 
ticles of  straw,  cement,  or  dust,  that  accidentally  fall  into  it;  it  appears 
capable  of  dissolving  small  portions  of  charcoal,  and  also  of  sulphur,  tellu- 
rium, and  selenium  ;  these  substances  give  to  it  various  tints  of  brown,  red, 
and  green,  or  blue,  and  are  precipitated  when  the  acid  is  diluted  with  water  ; 
but  if  heat  be  applied,  they  are  oxidized  at  the  expense  of  the  acid,  and 
sulphurous  acid  and  carbonic  acid  are  evolved. 

When  heated  with  charcoal,  sulphuric  acid  gives  rise  to  the  production 
of  carbonic  and  sulphurous  acids  (C  +  2S03=C02+2S03)  :  with  sulphur, 
sulphurous  acid  is  the  only  product  (8  +  2803=3803).  It  is  decomposed 
by  several  of  the  metals,  which  become  oxidized  and  evolve  sulphurous  acid, 
as  shown  in  the  production  of  this  acid  by  boiling  sulphuric  acid  with  copper, 
silver,  mercury,  tin,  or  lead.  Gold  and  platinum  are  not  affected  by  the 
acid  even  at  the  boiling-point.  When  metals,  such  as  magnesium,  zinc,  and 
iron,  are  acted  on  in  the  cold  by  diluted  sulphuric  acid,  the  water  only  is 
decomposed,  its  oxygen,  being  transferred  to  the  metal,  forms  a  metallic 
oxide,  which  unites  to  the  undecomposed  sulphuric  acid  to  form  a  sulphate 
of  the  oxide,  whilst  the  hydrogen  is  evolved  in  the  gaseous  form. 

The  strength  of  sulphuric  acid  is  generally  determined  by  its  specific 
gravity,  after  its  freedom  from  any  solid  impurities  has  been  determined  by 
evaporation.  According  to  Dr.  TJre,  the  proportion  of  dry  acid  contained 
in  100  parts  of  liquid  acid  at  different  specific  gravities  is  as  follows  :• — 


Specific    Dry  acid 

Specific     Dry  acid 

Specific    Dry  acid 

Specific    Dry  acid 

gravity,    in  100. 

gravity,     in  100. 

gravity,     in  100. 

gravity,      in  100. 

1-8460     81-54 

1-6630     61-97 

1-4073    42-40 

1-2032    22-83 

1-8233     75-02  ' 

1-5760    55-45 

1-3345     35-88 

1-1410     16-31 

1-7570    68-49 

1-4860    48-92 

1-2645     29-35 

1-0809       9-78 

In  ascertaining  the  specific  gravity  of  sulphuric  acid,  the  temperature 
requires  attention,  because  from  the  small  specific  heat  of  the  acid  it  is  easily 
affected,  and  because  it  greatly  influences  the  density.  When  accuracy  is 
required,  the  strength  of  the  acid  may  be  determined  by  its  saturating  power. 
For  this  purpose,  a  given  weight  of  the  acid  is  diluted  with  six  or  eight  parts 
of  water,  and  a  solution  (of  known  strength)  of  pure  carbonate  of  soda  added 


222  ANHYDROUS    SULPHURIC    ACID.      PROPERTIES. 

until  the  solution  is  exactly  neutral  (see  Alkalimetry).  Every  54  parts  of 
anhydrous  carbonate  of  soda  are  equivalent  to  40  parts  of  the  anhydrous 
acid,  or  to  49  of  the  liquid  sulphuric  acid,  or  oil  of  vitriol,  of  the  specific 
gravity  of  1*84.  Besides  lead  and  potassa,  tin  and  arsenic  are  sometimes 
found  in  sulphuric  acid  :  the  tin  and  lead  are  derived  from  the  leaden  cham- 
bers, and  the  arsenic  from  the  sulphur  or  pyrites.  The  methods  of  detecting 
these  impurities  will  be  described  under  the  respective  metals. 

Tests. — The  concentrated  acid. — 1.  It  carbonizes  a  splint  of  wood  intro- 
duced into  it.  2.  It  evolves  sulphurous  acid  when  boiled  with  metallic  cop- 
per. 3.  Diluted  with  its  volume  of  water,  heat  is  evolved.  The  diluted  acid. 
— In  the  most  diluted  state  a  salt  of  baryta,  added  to  the  liquid,  throws 
down  a  white  precipitate  of  sulphate  of  baryta,  which  is  insoluble  in  acids 
and  alkalies.  Diluted  sulphuric  acid  does  not  carbonize  organic  matter 
until  the  water  has  been  driven  off  by  heat,  and  the  acid  is  thus  concentrated. 
A  streak  of  the  diluted  acid  on  paper,  when  heated,  produces  a  black  mark 
by  carbonizing  the  paper.  Pure  sulphuric  acid  should  leave  no  residue  on 
evaporation. 

The  presence  of  nitric  or  nitrous  acid  is  indicated  in  sulphuric  acid  by  the 
change  of  color  produced  on  adding  a  few  drops  of  a  concentrated  solution 
(or  a  crystal)  of  protosulphate  of  iron  ;  a  solution  of  narcotine  is  also  red- 
dened by  sulphuric  acid  containing  nitrous  acid.  Sulphurous  acid  is  detected 
by  its  odor  and  by  discharging  the  color  of  permanganate  of  potassa. 

Anhydrous  Sulphuric  Acid  {Sidphuric  Anhydride). — When  crystallized 
green  vitriol,  or  protosulphate  of  iron,  is  exposed  to  a  dull  red  heat,  it 
crumbles  into  a  white  powder,  and  loses  the  greater  part  of  its  water  of 
crystallization.  In  this  state,  if  put  into  a  coated  earthen  or  green  glass 
retort,  and  gradually  exposed  to  a  full  red  heat,  a  dark-colored  liquid  is 
distilled  over,  of  a  specific  gravity  of  about  1-89.  This  has  been  called 
Nordhausen,  or  Saxon  sidphuric  acid :  it  evolves  a  vapor  when  exposed  to 
air,  owing  to  the  escape  of  the  highly  volatile  dry  sulphuric  acid,  which  is 
united  in  the  brown  liquid  to  a  portion  of  hydrated  acid.  The  brown, 
fuming  acid  is  a  ready  and  perfect  solvent  of  indigo.  It  is  resolved  by  heat 
into  the  common  and  the  anhydrous  acid.  The  changes  which  take  place 
in  its  production  may  be  thus  represented:  2(FeO,S03)==S03+S03-{- 
FegOg ;  but  the  sulphate  of  iron  is  not  entirely  dehydrated,  so  that  a  portion 
of  hydrated  acid  is  distilled  over  at  the  same  time.  The  Saxon  acid  is 
generally  supposed  to  be  thus  constituted  :  SOg+SOg.HO  ;  but  the  propor- 
tion of  hydrated  acid  is  subject  to  variation. 

The  dry  or  anhydrous  sulphuric  acid  may  be  separated  from  this  brown 
(or  Nordhausen)  acid,  by  a  careful  distillation  from  a  retort  into'  a  dry  and 
cold  receiver ;  it  passes  over  in  drops,  which  concrete,  on  cooling,  into  a 
tenacious  crystalline  mass  resembling  asbestos.  The  acid  is  liquid  at  tem- 
peratures above  66°;  and  at  78°  its  specific  gravity  is  1  9t.  When  it  has 
once  congealed,  it  is  difficult  to  fuse  it,  because  the  first  portions  heated 
become  vapor,  and  propel  the  rest  forward  ;  by  slight  pressure,  however, 
this  may  be  prevented.  When  kept  at  a  temperature  between  75°  and  80°, 
it  gradually  liquefies.  At  a  temperature  of  .110°,  it  boils  and  evolves  a 
colorless  vapor,  the  density  of  which,  according  to  Mitscherlich,  is  3.  The 
calculated  density  is  2-77,  so  that  100  cubic  inches  would  weigh  85'969 
grains.  In  the  absence  of  all  moisture,  it  has  no  action  upon  litmus-paper. 
Passed  through  a  red  hot  porcelain  tube,  anhydrous  sulphuric  acid  is 
resolved  into  one  volume  of  oxygen  and  two  of  sulphurous  acid.  Caustic 
lime  or  baryta,  heated  in  its  vapor,  becomes  ignited,  and  is  converted  into 
sulphate.  The  attraction  of  this  anhydrous  acid  for  water  is  such  as  to 
produce  intense  heat  and  a  hissing  noise  when  small  portions  of  it  are  thrown 


ANHYDROUS    SULPHURIC    ACID  223 

into  that  liquid  ;  and  if  a  sufficient  quantity  of  it  be  added  to  such  a  propor- 
tion of  water  as  is  required  to  convert  it  into  hydrated  acid,  they  combine 
with  heat,  light,  and  explosion.  • 

Anhydrous  sulphuric  acid  may  also  be  obtained  by  the  action  of  anhy- 
drous phosphoric  acid  upon  monohydrated  sulphuric  acid.  (Barreswill.) 
The  phosphoric  acid  is  put  into  a  stoppered  retort  surrounded  by  ice  and 
salt,  and  the  oil  of  vitriol  gradually  added  so  as  to  prevent  arise  of  tempera- 
ture, to  the  amount  of  two-thirds  of  the  weight  of  the  phosphoric  acid  ;  the 
retort  is  then  removed  from  the  freezing  mixture,  and  a  receiver  placed  there, 
to  which  the  retort  is  adapted ;  on  applying  a  gentle  heat,  the  anhydrous 
sulphuric  acid  is  distilled  over,  and  is  condensed  in  white  silky  crystals  in 
the  cooled  receiver.  The  principal  requisite  precaution  in  this  process,  is  to 
keep  the  acids  sufficiently  cool,  whilst  mixing  them  in  the  retort  {Pharm. 
Journ.^  8,  12T.)  It  has  also  been  procured  by  distilling  at  a  high  tempera- 
ture the  dry  bisulphate  of  soda. 

It  appears,  then,  that  this  extraordinary  substance,  which  is  thus  volatile 
and  easy  of  congelation,  forms,  by  combining  with  water,  the  fixed  and  with 
difficulty  cojigealable  oil  of  vitriol^  and  that  it  contains  sulphur  and  oxygen 
in  the  same  proportions  as  they  exist  in  the  acid  of  the  dry  sulphates.  From 
its  resolution  when  passed  through  a  red  hot  tube,  into  one  volume  of  sul- 
phurous acid  and  half  a  volume  of  oxygen,  and  likewise  from  the  experiments 
of  Berzelius  upon  the  direct  acidification  of  sulphur,  it  appears  that  the  anhy' 
drous  sulphuric  acid  consists  of: — 

Sulphur      .... 
Oxygen       .... 


jms. 

Weights. 

Per  cent. 

1 

16 

40 

3 

24 

60 

Anhydrous  sulphuric  acid .         .     1  40  100 

The  sp.  gr.  of  the  vapor  is  found  to  be  3*01.  Assuming  that  one  volume 
of  sulphurous  acid  and  half  a  volume  of  oxygen  are  condense^  into  one 
volume  of  vapor,  the  sp.  gr.  would  be  2-T64. 

The  liquid  hydrated  sidphuric  acid,  or  oil  of  vitriol,  when  of  the  sp.  gr. 
1*846,  consists  of: — 

Atoms.  Weights.  Per  cent. 

Dry  sulphuric  acid         .         .1         ...         40         ...         81-64 
Water 1         ...  9         ...         18-36 


Monohydrated  sulphuric  acid     1  49  100-00 

The  compound  of  sulphuric  acid  and  water  of  the  specific  gravity  l'T8, 
which  has  been  above  stated  to  congeal  at  40°,  remains  solid  until  the  tem- 
perature rises  to  45°  :  it  is  a  definite  combination  of  1  atom  of  anhydrous 
acid  +2  atoms  of  water.  The  acid  of  specific  gravity  1*632,  appears  also 
to  be  a  hydrate  containing  1  atom  of  anhydrous  acid  and  3  atoms  of  water, 
for  it  is  to  this  strength  that  a  diluted  sulphuric^^cid,  evaporated  in  vacuo 
at  212°,  is  reduced  ;  and  it  is  also  in  these  proportions,  that  sulphuric  acid 
and  water  suffer  the  greatest  diminution  of  bulk  in  combining.  It  would 
appear,  therefore,  that  there  are  three  definite  hydrates  of  sulphuric  acid,  of 
which  the  following  are  the  formulae,  specific  gravities,  and  boiling-points : — 

Monohydrate    . 
Bihydate  . 
Terhydrate 

Each  of  these  hydrates  contains  in  100  parts,  the  following  proportions 
of  dry  acid  and  water : — 


Formula;. 

Sp.  Gr. 

Boils  at 

Congeals  at 

SO3,  HO      . 

..     1-846     . 

..      650°     . 

...     —30° 

S03,2HO     . 

..     1-780     . 

..     435      . 

40 

S0„3H0     . 

..     1-632     . 

..     348      . 

... 

224  HYPOSULPHUROUS    ACID.      HYPOSULPHITES. 

Monohyd.  Bihyd.  Terhyd. 

Anhydrous  acid       .         .  •      .         .     81-64     ...     70-94     ...     61-16 
Water 18-36     ...     29-06     ...     38-84 

According  to  Dr.  L.  Playfair,  the  variation  in  the  sp.  gr.  of  the  monohy- 
drated  acid,  as  given  by  Bineau  and  Marignac — namely,  r842  to  1-845 — 
may  depend  upon  the  temperature  at  which  it  has  been  distilled.  Dr.  Play- 
fair  found  that  from  an  acid  of  asp.  gr.  of  r848  (81  62  per  cent,  of  anhy- 
drous acid),  he  obtained  a  distillate  of  a  sp.  gr.  of  1840  (80  12  per  cent). 
This  acid,  therefore,  lost  by  distillation  one  and  a  half  per  cent,  of  anhydrous 
acid.  The  weak  acid  thus  obtained,  was  heated  for  half  an  hour  to  550*^ ; 
and  after  cooling,  it  gave  an  acid  of  1847 9  (81*61  per  cent,  of  anhydrous 
acid).  Hence  it  follows,  that  there  is  a  monobydrate  which  loses  anhydrous 
acid  above  550°,  and  water  below  this  temperature  ;  so  that  a  strong  acid 
is  weakened  by  being  heated  above  550*^,  and  a  weak  acid  is  strengthened 
by  heating  it  to  a  temperature  not  exceeding  550°.  The  different  tempera- 
tures at  which  the  acid  has  been  concentrated,  may  thus  explain  the  varia- 
tions recorded  in  its  specific  gravity  and  strength.  {Cheni.  News,  vol.  3, 
p.  21.) 

Sulphates. — These  salts  in  the  anhydrous  state  are  represented  by  the 
formula  MOjSOg.  Among  the  alkalies,  there  are  some  which  form  acid  sul- 
phates, such  as  potassa  and  soda,  in  which  two  equivalents  of  acid  are  united 
to  one  of  oxide.  These  are  called  hisulphates  (MO,2S03).  These  salts 
resist  a  high  temperature,  but  are  readily  decomposed  when  heated  with  two 
or  three  parts  of  charcoal,  sulphides  of  the  metals  being  produced.  They 
are  converted  into  sulphides  at  a  still  lower  temperature,  when  heated  in  a 
close  vessel  with  cyanide  of  potassium.  An  insoluble  sulphate,  such  as  that 
of  baryta,  is  thus  easily  recognized  by  its  conversion  into  a  soluble  sulphide 
of  barium.  A  slight  trace  of  any  soluble  sulphate,  may  be  detected  by  the 
addition  of  a  salt  of  baryta  to  the  liquid.  If  a  soluble  sulphate  is  present,  a 
white  precipitate  of  sulphate  of  baryta,  insoluble  in  nitric  acid,  will  be  pro- 
duced. 

Hyposulphurous  Acid  {Dithionotis  Acid),  {^fi^. — This  acid  is  only 
known  in  the  combined  state.  Its  salts,  now  called  Hyposulphites,  were 
originally  described  by  Gay-Lussac  {Ann.  de  Chim.,  85),  under  the  name  of 
sulphuretted  sulphites.  Thomson  first  suggested  the  term  hyposulphurous  for 
the  peculiar  acid  of  sulphur  contained  in  these  compounds  {Syst.  of  Chem., 
1817),  and  they  were  afterwards  examined  by  Herschel.  {Edin.  Phil.  Journ.) 
When  an  attempt  is  made  to  separate  the  acid  from  its  salts  by  adding  an 
acid  to  the  solution,  sulphurous  acid  escapes,  and  sulphur  is  precipitated. 

(SA=s-fSoj 

Hyposulphites. — These  salts  are  formed,  1.  "When  sulphur  is  digested,  at 
a  high  temperature  but  without  ebullition,  in  a  solution  of  a  sulphite;  in 
which  case  the  oxygen  of  the  sulphurous  acid  divides  itself  between  the 
original  and  the  newly-adoed  sulphur :  thus  we  obtain  hyposulphite  of  soda 
by  digesting  finely-powdered  sulphur  in  a  hot  solution  of  sulphite  of  soda, 
KaO,S03,-f  S,  becoming  NaO^SgOg.  2.  When  sulphurous  acid  gas  is  passed 
through  a  solution  of  an  alkaline  sulphide,  until  it  no  longer  precipitates  sul- 
phur ;  thus,  we  obtain  hyposulphite  of  soda  by  passing  sulphurous  acid  gas 
through  a  solution  of  sulphide  of  sodium  ;  in  which  case  2XaS,  and  SSOg, 
become  2NaO,2S02,-|-S.  The  properties  of  the  acid  may  be  studied  in  its 
salts,  and  for  this  purpose  the  hyposulphite  of  soda  may  be  selected.  This 
compound  is  now  manufactured  on  a  large  scale  for  the  purposes  of  photo- 
graphy. Hyposulphite  of  soda  dissolves  every  compound  of  silver  excepting 
the  sulphide,  and  that  portion  of  a  silver  salt  which  has  been  decomposed  by 


HYPOSULPHURIC    ACID.      HYPOSULPHATES,  225 

light.  Even  the  insoluble  chloride  is  easily  taken  up  by  it,  and  the  solution 
has  a  sweetish  taste.  The  acid  forms  soluble  double  salts  with  silver  and 
gold.  A  hyposulphite  precipitates  a  solution  of  lead,  but  redissolves  the 
precipitate  when  added  in  excess.  Hyposulphurous  acid  forms  soluble  com- 
pounds with  all  the  alkalies  and  alkaline  earths,  excepting  baryta,  the  salts 
of  which  are  precipitated  by  a  hyposulphite.  The  admixture  of  a  sulphate 
is  thus  easily  known  :  a  salt  of  strontia,  which  does  not  precipitate  a  pure 
hyposulphite,  throws  down  any  sulphate  which  may  exist  in  it  as  impurity. 
A  hyposulphite  dissolves  iodine,  destroys  the  blue  color  of  iodide  of  starch, 
and  decomposes  iodic  acid,  setting  iodine  free  ;  but  it  has  no  action  on  iodide 
of  potassium.     It  also  decomposes  the  permanganate  of  potash. 

I'ests. — A  hyposulphite  may  be  recognized,  1.  By  the  separation  of  sul- 
phur and  sulphurous  acid,  when  its  solution  is  treated  with  an  acid  :  2.  By 
its  giving  at  first  a  white  precipitate  with  a  solution  of  nitrate  of  silver,  solu- 
ble in  an  excess  of  the  hyposulphite.  It  dissolves  readily  the  chloride  of 
silver  ;  the  bromide,  iodide  and  cyanide  are  also  dissolved  by  it.  If  nitrate 
of  silver  is  added  in  excess  to  a  solution  of  a  hyposulphite,  the  white  precipi- 
tate which  is  at  first  formed  rapidly  undergoes  various  changes  of  color,  to 
yellow,  brown,  and  black — sulphide  of  silver  being  ultimately  produced  ; 
3.  By  its  yielding  a  black  precipitate  with  protonitrate  of  mercury  ;  4.  it 
gives  a  white  precipitate  with  a  salt  of  lead  (hyposulphite)  which  is  soluble 
in  an  excess  of  the  solution. 

It  has  been  shown  by  Rose  {Poggendorffh  Annalen,  21),  that  although 
the  ratio  of  the  sulphur  to  the  oxygen  in  this  acid  is  as  16  to  8,  its  equiva- 
lent, or  combining  proportion,«is  not  24,  but  48,  hence  it  must  be  considered 
as  a  compound  of 

Sulphur      .         .         .     2     32     66-67 )_/ Sulphur     .         .     1     16     33-33      '. 
Oxygen       .         .         .     2    16    33-33  J  ~"  \  Sulphurous  acid     1     32     66-67 


Hyposulphurous  acid .     1     48  100-00  1     48  100-00 

HYPOSULPHURIC  Acid  {DitMonic  Acid)  (S^OJ  was  discovered  by  Gay- 
Lussac  and  Welther.  It  is  obtained  by  passing  a  current  of  sulphurous  acid 
through  a  cold  mixture  of  finely-powdered  and  pure  peroxide  of  manganese 
and  water:  2S02H-Mn03=MnO,S205.  A  solution  is  obtained,  which  is 
filtered  and  thoroughly  agitated  and  digested  with  hydrated  baryta,  which 
must  be  added  in  small  excess.  The  sulphuric  acid  and  the  greater  part  of 
the  oxide  of  manganese  are  thus  precipitated.  The  solution  is  again  filtered 
and  evaporated  until  it  crystallizes,  and  the  crystals  of  hyposulphate  of  baryta 
are  a  second  time  dissolved  and  obtained  by  evaporation,  in  order  to  pro- 
cure them  free  from  manganese  ;  they  are  then  dried,  powdered,  weighed, 
and  dissolved  in  water ;  and  to  every  hundred  parts  of  the  dissolved  salt, 
18'78  parts  of  sulphuric  acid,  of  the  specific  gravity  of  184,  diluted  with 
four  parts  of  water,  are  added.  The  baryta  is  thus  thrown  down  in  the 
state  of  sulphate,  and  the  new  acid  remains  in  solution.  Having  been  fil- 
tered, it  is  to  be  concentrated  by  exposure  under  the  exhausted  receiver  of 
an  air-pump,  including  a  vessel  of  sulphuric  acid,  until  it  acquires  a  density 
of  1'347.  If  the  exposure  and  evaporation  be  continued  beyond  this  point, 
it  is  resolved  into  sulphuric  and  sulphurous  acids  (8^05=803  +  803).  A 
temperature  of  212°  effects  the  same  change  in  its  composition.  It  is  an 
inodorous  acid,  and  reddens  vegetable  blues.  It  has  not  been  obtained  in 
an  anhydrous  state. 

Hyposulphates. — These  salts  are  remarkable  for  their  solubility.  When 
heated,  they  are  resolved  into  sulphates,  and  sulphurous  acid  escapes.  In 
the  cold,  sulphuric  acid  does  not  so  act  upon  them  as  to  set  free  sulphurous 
15 


226  HYDROSULPHURIC    ACID. 

acid  ;  but  this  acid  is  evolved  on  boiling.     They  do  not  give  a  deposit  of 
sulphur  when  an  acid  is  added  to  their  solutions. 

Trithionic  Acid  (S.,0.). — If  three  atoms  of  bisulphite  of  potassa  in  a 
saturated  solution  in  water,  are  digested  with  two  atoms  of  sulphur,  hypo- 
sulphite and  trlthionate  of  potassa  are  produced,  as  in  the  following  equa- 
tion (3[KO,2SOJ  +  2S  =  2[KOS303]  +  [KO,S,OJ).  The  acid  may  be  ob- 
tained from  the  trithionate  by  adding  tartaric  acid  to  the  solution,  but  it  soon 
undergoes  decomposition.  It  gives  no  precipitate  with  the  salts  of  baryta 
or  lead.  When  a  trithionate  is  heated,  sulphur  and  sulphurous  acid  are 
given  off,  and  a  sulphate  of  the  alkali  remains. 

Tetrathionic  Acid  (S^OJ. — This  acid  was  obtained  by  Fordos  and  G^lis 
(Ann.  de  Ch.  et  Ph.,  Dec.  1842)  by  carefully  decomposing  its  combination 
with  baryta  by  sulphuric  acid,  so  diluted  as  to  avoid  elevation  of  temperature. 
The  tetrathionate  of  baryta  may  be  procured  by  the  reaction  of  iodine  on 
hyposulphite  of  baryta  2(BaO,S20j-f  I  =  Bal4-BaO,S^05.  The  diluted 
acid  may  be  boiled  without  decomposition,  but  as  it  becomes  concentrated, 
it  deposits  sulphur,  evolves  sulphurous  acid,  and  the  liquid  contains  sulphuric 
atfid.  The  acid  is  not  affected  by  dilute  hydrochloric  or  sulphuric  acids,  but 
nitric  acid  throws  down  sulphur. 

Pentathionic  Acid  (S5O5). — This  compound  is  produced  by  the  reaction 
of  sulphuretted  hydrogen  on  a  solution  of  sulphurous  acid.  Sulphur  is 
deposited  and  the  two  preceding  acids  are  simultaneously  produced. 

Sulphur  and  Hydrogen.  Hydrosulphuric  Acid  (HS).  Sulphydric 
acid.  Sulphuretted  Hydrogen  Gas. — This  compound  was  discoved  by  Scheele 
in  1777:  The  two  elements  cannot  be  made  to  combine  directly  under  ordi- 
nary circumstances  ;  but  when  hydrogen  is  set  free  in  the  nascent  state,  in 
contact  with  a  sulphur  compound,  this  gas  is  immediately  produced,  and  is 
recognized  by  its  disagreeable  odor.  Sulphuretted  hydrogen  is  thus  evolved 
in  the  decomposition  of  many  organic  substances  and  in  the  action  of  water  on 
the  alkaline  sulphides,  on  iron  pyrites,  as  well  as  in  the  decomposition  of 
water  by  heated  coke  containing  sulphur. 

Preparation. — Protosulphide  of  iron  may  be  prepared  by  rubbing  a  roll 
of  sulphur  on  a  bar  of  wrought-iron  heated  to  a  full  red  heat,  and  collecting 
the  compound  as  it  melts  in  a  pail  of  cold  water.  One  part  of  this  sulphide 
broken  into  small  fragments  may  be  placed  in  a  retort  with  four  or  five  parts 
of  water  and  one  part  of  sulphuric  acid.  The  heat  produced  by  the  mixture 
of  acid  and  water  is  sufficient  to  liberate  the  gas  copiously.  It  is  dissolved 
by  water,  and  acts  chemically  upon  mercury.  It  should  be  collected  over 
a  bath  holding  a  small  quantity  of  water,  placed  near  to  or  under  a  flue. 
The  chemical  changes  which  ensue  in  its  production,  may  be  thus  repre- 
sented :  FeS4-S03,HO  =  HS  +  FeO,S03.  The  gas,  as  it  is  thus  produced, 
generally  contains  a  portion  of  free  hydrogen.  A  mixture  of  sulphide  of 
antimony  and  of  hydrochloric  acid  also  evolves,  when  heated,  hydrosulphuric 
acid  gas. 

Properties. — Hydrosulphuric  acid  is  a  colorless  gas  at  common  tempera- 
tures and  pressures.  Under  a  pressure  of  about  seventeen  atmospheres  at 
50",  it  assumes  the  liquid  form  :  it  is  then  limpid,  and  apparently  possessed 
of  a  refractive  power  exceeding  that  of  water ;  its  specific  gravity  is  about 
09.  When  a  tube  containing  it  was  opened  under  water,  it  instantly  and 
violently  rushed  forth  under  the  form  of  gas  (Faraday,  Phil.  Trans.,  1823, 
p.  92.)  When  cooled  to  122°  below  0°,  it  solidifies,  and  it  is  then  a  white 
crystalline  translucent  substance,  heavier  than  the  liquid. 


CHEMICAL   PROPERTIES.      COMPOSITION.  22t 

The  gas  has  a  peculiarly  nauseous,  fetid  odor,  resembling  that  of  rotten 
eggs,  and  so  diffusible,  that  a  single  cubic  inch  escaping  into  the  atmosphere 
of  a  large  room,  is  soon  perceptible  by  its  smell  in  every  part.  100  cubic 
inches  weigh  36*38  grains.  Its  specific  gravity  compared  with  air  is  as 
1-1747  to  1  :  and  compared  with  hydrogen  as  17  to  1.  It  is  inflammable, 
burning  with  a  pale  blue  flame,  evolving  the  odor  of  burning  sulphur. 
During  its  slow  combustion,  sulphur  is  deposited,  and  water  and  sulphurous 
acid  are  formed  (HS-f  03=S0^-|-H0).  It  extinguishes  the  flame  of  a  taper. 
When  respired,  it  proves  fatal ;  and  it  is  very  deleterious,  even  though 
largely  diluted  with  atmospheric  air.  Nausea,  giddiness,  headache,  and  a 
peculiar  faintness,  with  loss  of  appetite,  are  the  usual  symptoms  produced, 
when  an  atmosphere  even  slightly  contaminated  by  sulphuretted  hydrogen 
has  been  breathed  for  any  length  of  time.  When  its  escape  into  the  labora- 
tory cannot  be  prevented,  its  effect  may  be  counteracted  by  the  diffusion  of 
a  little  chlorine,  or  by  sprinkling  the  room  with  an  aqueous  solution  of 
chlorine  or  ozonized  ether.  The  gas  exists  in  some  mineral  waters,  which 
are  thence  called  sulphureous,  such  as  those  of  Harrogate.  It  is  also  found 
in  the  air  and  water  of  foul  sewers,  and  in  putrescent  animal  matter. 

Water  dissolves  three  times  its  volume  of  this  gas  at  60°.  The  aqueous 
solution  is  transparent  and  colorless  when  recently  prepared,  but  gradually 
becomes  opalescent,  and  if  exposed  to  air  it  deposits  sulphur,  while  the 
hydrogen  combines  with  the  oxygen  of  air  to  form  water.  The  whole  of 
the  gas  is  evolved  by  heat.  It  is  an  exceedingly  delicate  test  of  the  presence 
of  most  of  the  metals,  with  which  it  forms  colored  precipitates.  The  colors 
of  the  sulphides  produced,  when  accurately  observed,  serve  to  identify  the 
respective  metals.  Thus  arsenic'  and  cadmium  give  a  yellow,  silver,  lead, 
and  bismuth  a  black,  antimony  an  orange,  and  zinc  a  white  sulphide.  The 
symbols  of  the  different  metals  may  be  printed  on  paper  in  the  respective 
metallic  solutions,  and  the  paper  exposed  in  ajar  containing  the  gas.  The 
colors  produced  by  the  different  metals,  are  at  once  indicated  by  the  symbols. 
One  measure  of  sulphuretted  hydrogen  mixed  with  200,000  measures  of 
hydrogen,  carburetted  hydrogen,  or  atmospheric  air,  produces  a  sensible 
discoloration  of  white  lead,  mixed  with  water,  and  spread  upon  a  piece  of 
card,  or  on  test-paper  impregnated  with  salt  of  lead.  Cards  which  have 
been  glazed  with  white  lead  are  useful  as  a  test  for  this  gas.  In  this  way 
we  may  ascertain  the  presence  of  extremely  small  quantities  of  sulphuretted 
hydrogen  in  coal-gas  or  air.  The  card  or  paper  acquires  a  color  varying 
from  a  pale  brown  to  black,  according  to  the  quantity  of  the  gas  present  in 
the  mixture,  or  the  length  of  exposure.  The  gas  is  entirely  dissolved  by  a 
solution  of  potassa  and  ammonia. 

Sulphuretted  hydrogen  reddens  infusion  of  litmus  and  moist  litmus-paper, 
but  the  blue  color  is  destroyed  on  boiling  the  infusion  ;  it  is  generally 
classed  among  the  hydracids,  and  is  not,  therefore,  considered  to  unite 
directly  with  the  basic  oxides,  a  metallic  sulphide  and  water  being  the 
usual  results  of  their  mutual  reaction  (HS,MO  =  MS,HO)  ;  it  combines 
certain  sulphides  (basic  sulphides),  and  forms  a  class  of  sulphur  salts; 
compounds  which  are  analogous  to  the  hydrated  oxides,  if  we  substitute 
sulphur  for  oxygen. 

When  hydrogen  becomes  sulphuretted  hydrogen,  its  volume  is  unchanged: 
and  when  one  volume  of  sulphuretted  hydrogen  is  detonated  with  half  its 
volume  of  oxygen,  water  is  formed  and  sulphur  is  precipitated  (HS-f  0  = 
HO  -f  S),  the  whole  of  the  mixed  gases  being  condensed.  But  when  a  volume 
of  sulphuretted  hydrogen  and  a  volume  and  a  half  of  oxygen  are  inflamed  in 
a  deto!iating  tube,  one  volume  of  sulphurous  acid  is  produced,  and  water  is 
condensed.     Thus  the  sulphur  is  transferred  to  one  volume  of  the  oxygen. 


228  HYDROSULPHURIC    ACID.      DECOMPOSITION. 

and  the  hydrogen  to  the  half  volume.  This  gas,  therefore,  consists  of  its 
volume  of  hydrogen  pins  one-sixth  of  its  volume  of  sulphur,  or  16  parts  by 
weight. 

Atoms.      Weights,      Per  cent.         Vols.  Sp.  Gr. 

Sulphur     .         .         .         .     1     ...     16     ...     94-1     ...       i     ...     1-1056 
Hydrogen  .         .         .         .     1     ...       1     ...       5-9     ...     1       ...     0-0691 


Sulphuretted  hydrogen     .     1  17  100-0  1-00         1-1747 

It  will  be  observed  that  this  compound  differs  from  the  other  hydracid 
gases  in  undergoing  condensation  :  hence  its  atomic  volume,  which  is  always 
equal  to  the  hydrogen  present,  is  represented  by  1.  The  hydrochloric, 
hydriodic,  and  hydrobromic  acids  have  an  atomic  volume  represented  by  2, 
the  hydrogen  being  equal  to  only  one-half  of  the  volume  of  the  gas. 
Whether  sulphur  be  considered  as  representing  one-sixth,  one-third,  or  a 
whole  volume  of  vapor,  the  result  is  the  same  ;  it  adds  nothing  to  the  volume 
of  this  gas.  In  constitution  this  gas  resembles  water,  if  we  suppose  sulphur 
to  be  substituted  for  oxygen,  rather  than  the  hydracid  gases  of  the  halogeuous 
elements.  When  a  current  of  the  gas  is  heated  to  full  redness  in  a  glass 
tube,  it  is  decomposed,  and  sulphur  is  deposited.  Spongy  platinum  does 
not  effect  the  combustion  of  a  mixture  of  sulphuretted  hydrogen  and  oxygen 
unless  free  hydrogen  be  also  present. 

Chlorine,  iodine,  and  bromine,  in  vapor,  instantly  decompose  hydrosul- 
phuric  acid  gas  ;  when  they  are  not  in  excess,  sulphur  is  deposited,  and 
hydrochloric,  hydriodic,  and  hydrobromic  acids  are  formed.  Strong  nitric 
acid  poured  into  the  gas  occasions  a  deposition  of  sulphur,  and  nitrous  acid 
and  water  are  formed,  with  a  considerable  elevation  of  temperature,  and 
occasionally  flame.  A  fold  of  bibulous  paper  dipped  in  the  acid  may  be 
safely  introduced.  An  aqueous  solution  of  the  gas  is  also  decomposed  by 
these  reagents.  When  two  volumes  of  this  gas  are  mixed  in  an  exhausted 
vessel  with  one  of  sulphurous  acid,  they  mutually  decompose  each  other, 
occasioning  the  production  of  water,  and  the  deposition  of  sulphur  (2HS-|- 
S02=2HO-f-3S).  If  the  gases  are  perfectly  dry,  the  action  is  slow.  Strong 
sulphuric  acid  also  decomposes  hydrosulphuric  acid;  the  results  are  water, 
sulphurous  acid,  and  sulphur(HS-f-S03=HO-f-S03-f  S):  but  if  the  acid  be 
diluted  with  four  or  five  parts  of  water,  it  has  no  action,  and  if  in  that  case 
it  is  rendered  turbid  by  the  gas,  the  presence  of  sulphurous  or  arsenious 
acid  may  be  suspected.  Hydrosulphuric  acid  decomposes  chromic  as  well 
as  iodic  acid,  and  in  the  latter  case  sets  free  iodine.  Sulphur  is  in  these 
cases  precipitated.  Hydrochloric  acid  has  no  action  on  it.  It  is  completely 
oxidized  and  the  odor  is  removed  by  an  alkaline  permanganate.  Chloride 
of  zinc  decomposes  it,  and  sulphide  of  zinc  is  formed.  The  gas  is  rapidly 
absorbed  by  charcoal,  the  hydrogen  is  oxidized  and  sulphur  is  deposited. 
If  a  weak  solution  of  sulphuretted  hydrogen  is  shaken  with  powdered  char- 
coal, the  smell  of  the  gas  rapidly  disappears,  and  on  filtering  the  liquid  it 
no  longer  acquires  a  brown  color  by  the  addition  of  a  salt  of  lead.  Owing 
to  this  property.  Dr.  Stenhouse  has  recommended  the  use  of  a  charcoal- 
respirator  for  persons  who  may  breathe  the  exhalations  of  sewers. 

One  of  the  most  efficient  metallic  compounds  for  the  removal  of  sulphu- 
retted hydrogen  either  in  the  gaseous  or  dissolved  form,  is  the  hydrated 
peroxide  of  iron.  The  substance  is  now  largely  employed  for  the  separation 
of  sulphuretted  hydrogen  from  coal-gas.  Black  sulphide  of  iron  and  water 
are  formed,  and  sulphur  is  set  free  (Fe203  4-3HS=3HO-f  2FeS-f  S).  The 
change  takes  place  on  contact,  but  more  rapidly  when  aided  by  heat  and 
moisture.     The  sulphide  of  iron  is  reconverted  into  oxide  on  exposure  to 


SULPHIDES.      CHLORIDES    OF    SULPHUR.'  2!5$ 

air  [2FeS4-03(air)=Fea03  +  S2].      This  fact  illustrates  the  facility  with 
which  sulphur  and  oxygen  may  replace  each  other  in  metallic  combinations. 

When  potassium  or  sodium  is  heated  in  hydrosulphuric  acid  gas,  a 
sulphur-salt  of  the  metal  is  formed  with  vivid  combustion,  and  pure  hydro- 
gen is  liberated  (K4-2HS=KS,HS  +  H).  When  tin  or  lead  is  heated  in 
the  gas,  they  all  decompose  it,  and  absorb  the  sulphur,  leaving  a  volume  of 
hydrogen  equal  to  that  of  the  original  gas.  Passed  over  metallic  oxides, 
water  and  metallic  sulphides  are  the  results  :  the  different  oxides  effect  this 
decomposition  at  very  different  temperatures. 

Tests. — 1.  The  odor  of  the  gas  is  sufiBcient  to  reveal  its  presence,  even 
when  it  forms  only  1-200, 000th  part  of  the  atmosphere.  2.  Paper  wetted 
with  a  solution  of  acetate  of  lead  and  dried,  or  a  glazed  card,  will  indicate, 
by  the  appearance  of  a  brown  color,  the  presence  of  the  gas,  even  when  the 
proportion  is  infinitesimal.  The  same  tests  apply  to  the  presence  of  sulphu- 
retted hydrogen  in  water.  In  addition,  a  portion  of  leaf-silver  may  be 
allowed  to  remain  in  the  water  for  some  hours.  If  the  gas  is  present,  the 
silver  will  be  sooner  or  later  tarnished. 

Persulphide  of  Hydrogen. — This  is  a  liquid  compound,  the  composition  of 
which  is  not  accurately  known,  but  it  is  supposed  to  be  HSg.  It  is  pro- 
cured by  adding  a  solution  of  persulphide  of  calcium  to  diluted  hydrochloric 
acid.  Under  these  circumstances,  sulphuretted  hydrogen  is  not  produced, 
but  the  greater  part  of  the  sulphur  remains  united  to  it,  producing  a  heavy 
yellow  liquid,  which  subsides  to  the  bottom  of  the  glass.  It  has  a  sp.  gr. 
of  1-76  ;  it  is  inflammable,  and  is  rapidly  decomposed  in  water  or  by  expo- 
sure to  air. 

Sulphides. — The  soluble  monosulphides  are  easily  recognized  :  1.  By  the 
odor  of  sulphuretted  hydrogen  when  wetted,  or  when  an  acid  .is  added.  2. 
In  solution,  by  the  deep  brown  or  black  precipitate,  which  is  produced  on 
adding  a  salt  of  lead.  3.  By  the  rich  purple  or  crimson  color  produced  on 
the  addition  of  a  few  drops  of  a  fresh  solution  of  nitroprusside  of  sodium. 
The  color  produced  in  this  reaction  is  of  a  blue  or  splendid  purple  tint,  when 
the  alkaline  sulphide  is  in  small  quantity;  and  of  a  rich  crimson,  in  stronger 
solutions.  The  color  is  slow  in  appearing  in  a  weak  solution  of  sulphide, 
and  sooner  or  later  fades.  As  the  nitro-prusside  produces  no  change  of 
color,  in  a  solution  of  sulphuretted  hydrogen,  this  reaction  enables  a  chemist 
to  say  whether  the  solution  is  or  is  not  mixed  with  any  traces  of  sulphide. 
The  monosulphides  may  be  represented  by  MS,  the  sulphuretted  sulphides 
by  MS.HS,  and  a  polysulphide  by  MS^.  Solutions  of  pure  monosulphides 
are  pale,  and  evolve  sulphuretted  hydrogen  without  yielding  a  precipitate  of 
sulphur,  when  hydrochloric  acid  is  added  to  them.  Solutions  of  persulphides 
have  a  deep  orange  or  amber  color,  and  .when  treated  with  an  acid,  not  only 
evolve  sulphuretted  hydrogen,  but  give  an  abundant  precipitate  of  sulphur  of 
a  pale  lemon-white  color  {precipitated  sulphur). 

Chloride  of  Sulphur  (SCI). — When  sulphur  is  heated  in  an  excess  of 
dry  chlorine,  it  absorbs  rather  more  than  twice  its  weight  of  this  gas.  Ten 
grains  of  sulphur  absorb  30  cubic  inches  of  chlorine,  and  produce  a  liquid 
of  a  greenish-yellow  color  by  transmitted  light,  but  orange-red  by  reflected 
light.  The  combination  also  takes  place  at  common  temperatures,  and  may 
e  effected  by  passing  an  excess  of  dry  chlorine  through  a  tube  containing 
powdered  sulphur.  Chloride  of  sulphur  exhales  suffocating  and  irritating 
fumes  when  exposed  to  the  air.  Its  specific  gravity  is  1"60.  It  boils  at  146^, 
yielding  a  vapor  of  the  density  of  3io. 

DiCHLORIDE  OF  SuLPHUR  ;    SUBCHLORIDE  OF  SULPHUR  (S^Cl). — When  the 

preceding  liquid  is  saturated  with  sulphur,  it  deposits  a  portion,  often  la 
crystals,  but  retains  an  additional  atom  of  sulphur,  forming  a  yellow-brown 


230  SELENIUM.      ITS    PROPERTIES. 

liquid  of  the  specific  gravity  of  1  686.  It  boils  at  282°.  The  density  of 
its  vapor  is  4  70.  It  is  a  powerful  solvent  of  sulphur,  and  is  used  in  the 
cold  vulcanization  of  caoutchouc.  It  also  dissolves  phosphorus.  Tetra- 
hedral  crystals  of  sulphur  may  be  obtained  from  this  liquid,  the  deposition 
of  which  is  much  influenced  by  light.  According  to  Rose  {Poggendorffh 
Ann.,  xxxi.),  this  is  the  only  chloride  of  sulphur,  and  the  preceding  com- 
pound is  merely  a  solution  of  chlorine  in  this  dichloride.  When  dropped 
into  water,  it  gradually  yields  hydrochloric  acid,  sulphur,  and  hyposulphurous 
acid,  the  latter  resolving  itself  into  sulphurous  acid  and  sulphur:  2S,C1, 
2HO=2HCl,SO„3S. 

Sulphur  forms  compounds  with  bromine,  SBr;  with  iodine,  SI;  and  nitro- 
gen, SgN  ;  but  these  present  no  features  of  interest. 

Selenium  (Se=40). 

Selenium  was  discovered  in  ISlt  by  Berzelius,  during  an  examination  of 
certain  substances,  found  in  the  sulphuric  acid,  manufactured  at  Gripsolm, 
in  Sweden.  {Ann.  Ch.  et  Fh.,\x.  160)  The  sulphur  used  in  these  works 
is  procured  from  the  iron  pyrites  of  Fahlun,  and  the  acid  obtained  from  it 
deposits  a  red  matter,  which  was  supposed  to  contain  tellurium,  but  which 
was  proved  to  be  a  distinct  substance,  to  which  its  discoverer  gave  the  name 
of  Selenium,  from  as%rjv^,  the  moon.  It  resembles  sulphur,  and  is  generally 
placed  next  to  it  among  the  non-metallic  bodies. 

Preparation. — Selenium  may  be  obtained  by  the  decomposition  of  selenic 
acid,  which  may  be  effected  by  adding  hydrochloric  acid  to  its  solution  in 
water,  and  immersing  a  plate  of  zinc  in  the  mixture  :  a  gray  or  reddish-brown 
flocculent  precipitate  of  selenium  is  then  deposited.  Selenium  may  also  be 
extracted  from  the  native  sulphide  of  iron  which  contains  it,  by  mixing  the 
powdered  sulphide  with  eight  parts  of  peroxide  of  manganese,  and  exposing 
the  mixture  to  a  low  red  heat  in  a  glass  retort,  the  beak  of  which  dips  into 
water.  The  sulphur,  oxidized  at  the  expense  of  the  manganese,  escapes  in 
the  form  of  sulphurous  acid  gas,  while  the  selenium  is  either  sublimed  ia 
vapor  or  in  the  state  of  selenious  acid  :  should  any  of  the  latter  go  over  into 
the  water  it  would  there  be  reduced  to  selenium  by  the  sulphurous  acid. 

Properties — Selenium,  when  cooled  after  fusion,  has  a  reddish-brown 
color,  and  a  dim  metallic  lustre;  it  is  very  brittle,  and  its  fracture  is  of  a  lead- 
gray  color.  Its  specific  gravity  is  4-32,  Specific  heat=0-083t.  Obtained 
from  its  solutions  by  precipitation  upon  zinc,  it  is  red,  but  becomes  black 
when  boiled  in  water.  It  has  neither  taste  nor  smell.  When  fused,  and 
very  slowly  cooled,  its  surface  is  granular,  without  lustre  ;  and  its  fracture 
dull,  like  that  of  metallic  cobalt.  It  is  easily  reduced  to  a  powder,  which  is 
red.  It  is  a  non-conductor  of  heat  and  electricity.  Selenium  is  softened 
by  heat,  becoming  semifluid  at  212°,  and  melting  at  a  temperature  some- 
what higher :  it  remains  for  some  time  soft  on  cooling,  and  may  be  drawn 
out  into  filaments  like  sealing-wax,  which  are  of  a  gray  metallic  lustre  by 
reflected  light,  but  by  transmitted  light  of  a  clear  ruby-red.  Heated  in  a 
tube  to  about  650°,  it  boils,  and  is  converted  into  a  yellow  vapor,  which 
condenses  into  black  drops  that  run  together  like  quicksilver.  It  is  entirely 
volatile.  It  does  not,  like  sulphur,  assume  a  crystalline  state  on"  cooling. 
Heated  in  the  open  air  it  rises  into  vapor,  which  may  be  condensed  into  a 
red  powder.  It  is  characterized  by  tinging  flame  of  a  light  blue  color,  and 
by  exhaling,  when  strongly  heated,  a  peculiarly  offensive  odor.  It  is  com- 
bustible, but  when  ignited  it  does  not  continue  to  burn,  like  sulphur.  It 
evolves  no  acid  vapor  resembling  sulphurous  acid.  It  is  insoluble  in  water, 
and  scarcely  dissolved  by  benzole,  except  at  the  boiling-point.  Its  best 
solvent  is  boiling  sulphide  of  carbon,  but  it  is  taken  up  in  very  small  pro- 


COMPOUNDS    OF    SELENIUM.  231 

portion,  and  is  left  as  a  red  powder  by  spontaneous  evaporation.  Powdered 
selenium  when  heated  in  liquids,  even  in  solutions  of  alkalies,  has  a  tendency 
to  agglutinate,  forming  a  mass  which  the  solvent  scarcely  attacks.  Selenium 
is  considered  to  exist  in  two  different  states — the  one  vitreous  and  the  other 
metallic-looking.  The  vitreous  condition  is  obtained  by  the  slow  cooling  of 
the  melted  substance.  In  this  allotroi)ic  state,  it  is  insoluble  in  sulphide  of 
carbon,  while  in  the  other  form,  it  is  soluble. 

When  sulphur  is  mixed  with  selenium,  they  may  be  separated  by  defla- 
grating the  mixture  with  nitrate  and  carbonate  of  potash.  Sulphate  and 
seleniate  of  potassa  are  obtained,  which  may  be  separated  by  the  process 
described  under  Seleniates. 

Assuming  the  combining  volume  of  the  vapor  of  selenium  to  be  the  same 
as  that  of  sulphur,  and  that  one  volume  of  selenious  acid  includes  one 
volume  of  oxygen,  and  one-sixth  of  a  volume  of  selenium  vapor,  then  the 
density  of  the  latter  would  be  by  calculation  16  6392  (air==l),  and  com- 
pared with  hydrogen  240;  100  cubic  inches  would  weigh  515*8  grains. 
Selenium  forms  three  compounds  with  oxygen — one  oxide  and  two  acids. 
These  compounds  are  thus  constituted  : — 


Oxide  (SeO). 

Selenious  Acid  (SeO,). 

Selenic  Acid  (SeO,). 

Selenium    . 

, 

.     83-33 

71-06 

62-07 

Oxygen 

. 

.     16-67 

28-94 

37-93 

This  body  differs  from  sulphur  in  forming  an  oxide. 

Oxide  of  Selenium  (SeO)  is  formed  by  heating  selenium  in  a  limited 
quantity  of  atmospheric  air,  and  washing  the  product  to  separate  a  portion 
of  selenious  acid  which  is  at  the  same  time  formed.  The  oxide  is  sparingly 
soluble  in  water,  but  it  does  not  redden  litmus  or  combine  with  alkalies.  It 
appears  to  be  the  source  of  the  peculiar  odor,  emitted  during  the  oxidation 
of  selenium. 

Selenious  Acid  (SeOg). — This  acid  may  be  obtained  in  a  solid  state  by 
digesting  selenium  in  nitric  or  nitrohydrochloric  acid  until  entirely  dissolved, 
and  then  evaporating  to  dryness.  Its  taste  is  sour  and  hot  :  its  odor,  when 
sublimed,  acid,  but  not  like  that  of  the  oxide.  It  is  very  soluble  in  warm 
water,  and  the  solution  furnishes  crystals  of  the  hydrated  acid.  The  selenious 
acid  and  its  salts  are  decomposed  by  sulphurous  acid — selenium  being  slowly 
separated  in  red  flocculi  (SeO,-|-2SO,=Se 4-2803). 

Selenic  Acid  (SeOg). — This  acid  is  obtained  by  fusing  selenium  or 
selenious  acid,  or  any  of  its  salts,  with  nitrate  of  potassa  or  soda  ;  an  alkaline 
seleniate  is  thus  obtained.  This  may  be  dissolved  in  water  and  decomposed 
by  nitrate  of  lead.  The  insoluble  seleniate  of  lead  thus  obtained,  is  diffused 
through  water,  into  which  a  current  of  sulphuretted  hydrogen  is  passed  to 
precipitate  the  lead ;  the  liquid  is  boiled,  to  expel  any  excess  of  sulphuretted 
hydrogen,  and  is  now  diluted  selenic  acid  ;  it  may  be  concentrated  by  careful 
evaporation,  but  the  acid  cannot  be  entirely  deprived  of  water  without  being 
decomposed. 

Selenic  acia,  as  thus  procured,  is  a  colorless  liquid,  which  may  be  heated 
to  about  536°  without  change;  but  it  is  partially  decomposed  at  higher 
temperatures ;  and  at  554°,  is  rapidly  resolved  into  selenious  acid  and 
oxygen  (Se03  =  SeOa-|-0).  When  concentrated,  by  exposure  to  a  tempera- 
ture of  about  329°,  it  acquires  a  specific  gravity  of  2-524  ;  at  513°,  it  is 
2'6  :  it  may  be  rendered  somewat  denser  by  exposing  it  to  a  higher  tem- 
perature ;  but  in  this  case  a  portion  of  selenious  acid  is  formed  in  it.  It  is 
unknown  in  an  anhydrous  state.  The  hydrated  acid  may  be  represented  by 
HOjSeOg.     When  boiled  with  hydrochloric  acid,  selenious  acid  and  chlorine 


232  COMPOUNDS    OP    SELENIUM.      SELENIATES. 

* 

are  produced,  so  that  the  selenio-hydrochloric  acid  dissolves  gold  like  the 
nitro-hydrochloric  (HO,Se03  +  HCl  =  HO,SeO,+HO  +  Cl).  It  dissolves 
zinc  and  iron  with  the  evolution  of  hydrogen  ;  and  copper,  with  the  produc- 
tion of  seleuious  acid.  Sulphurous  acid,  which  decomposes  selenious  acid, 
has  no  action  on  selenic  acid  ;  so  that  to  decompose  selenic  acid,  it  must 
first  be  boiled  with  hydrochloric  acid,  which  converts  it  into  selenious  acid ; 
and  sulphurous  acid,  or  a  sulphite,  then  effects  the  separation  of  selenium. 
The  affinity  of  selenic  acid  for  bases  is  little  inferior  to  that  of  sulphuric  acid. 
Seleniates. — The  selenic  and  sulphuric  acids  are  isomorphous,  as  are  the 
seleniates  and  sulphates,  as  well  as  the  chromates  and  mangauates.  The 
seleniates  mostly  withstand  a  red  heat :  they  are  more  easily  reduced  at 
high  temperatures  by  hydrogen,  than  the  sulphates.  Heated  with  sal- 
ammoniac,  they  are  decomposed  with  the  separation  of  selenium.  The 
seleniates  of  baryta,  strontia,  and  lead,  are  insoluble  in  water,  and  in  dilute 
nitric  acid.  A  seleniate  boiled  with  hydrochloric  acid  dissolves  gold.  It  is 
thus  distinguished  from  a  sulphate.  When  a  sulphate  is  mixed  with  a 
seleniate,  they  may  be  separated  by  passing  into  the  solution  after  boiling, 
it  with  hydrochloric  acid,  a  current  of  sulphurous  acid  gas.  Selenium  is 
thrown  down  in  red  flocculi,  while  the  alkaline  sulphate  remains  in  the 
solution. 

Seleniuretted  Hydrogen  ;  Hydroselenic  Acid  (HSe). — This  is  a  color- 
less gaseous  compound  which  may  be  obtained  by  the  action  of  hydrochloric 
acid  upon  selenide  of  potassium  or  of  iron.  It  is  readily  dissolved  by  water, 
forming  a  solution  at  first  colorless,  but  after  a  time  acquiring  a  reddish  hue  ; 
the  solution  smells  and  tastes  somewhat  like  that  of  sulphuretted  hydrogen  ; 
it  reddens  litmus,  and  tinges  the  skin  of  a  reddish-brown  color.  Nitric  acid 
dropped  into  it  occasions  no  change,  and  the  gas  does  not  readily  escapes 
from  the  water;  but,  when  exposed  to  air,  the  solution  is  gradually  red- 
dened, and  deposits  selenium,  the  hydrogen  combining  with  the  oxygen  of 
air.  It  occasions  black  or  dark  brown  precipitates  in  all  solutions  of  neutral 
metallic  salts,  with  the  exception  of  those  of  zinc,  manganese,  and  cerium, 
which  are  flesh-colored.  Heated  with  tin,  one  volume  yields  one  volume  of 
hydrogen  and  selenide  of  tin.  It  is  decomposed  by  the  joint  action  of  air 
and  water  ;  it  is  absorbed  by  moist  substances,  and  soon  communicates  to 
them  a  red  color.  The  selenium  is  thus  remarkably  deposited  throughout 
the  texture  of  organic  bodies.  A  piece  of  moist  paper  is  penetrated  by  the 
red  color.  It  exerts  a  noxious  action  upon  the  trachea  and  organs  of  respi- 
ration ;  it  inflames  the  eyes,  and  painfully  stimulates  the  nasal  membrane, 
destroying  for  some  hours  the  sense  of  smell.  The  gas  is  inflammable.  By 
combustion  it  produces  water,  and  in  close  vessels  leaves  a  reddish-colored 
deposit  of  selenium. 

The  specific  gravity  of  seleniuretted  hydrogen  is  2 '7 95.  It  contains  one 
volume  of  hydrogen  and  one-sixth  of  a  volume  of  selenium  condensed  into 
one  volume  of  the  compound.  Its  equivalent  or  atomic  weight  is  41.  The 
gas  contains  97*52  per  cent,  of  selenium.  Although  considered  to  be  a 
hydracid  gas,  it  shares  the  peculiarity  of  hydrosulphuric  acid.  Its  atomic 
volume  is  equal  to  the  amount  of  hydrogen,  and  is  not  affected  by  the  large 
amount  of  the  metalloid  which  enters  into  combination  with  it.  Two  volumes 
of  this  gas  contain  two  of  hydrogen,  but  two  volumes  of  hydrochloric  acid 
contain  only  one  of  hydrogen. 


PHOSPHORUS.      PRODUCTION.  ^|^ 


% 


CHAPTER    XVIII. 

PHOSPHORUS  (P=32).    ITS   COMPOUNDS   WITH   OXYGEN   AND 

HYDROGEN. 

History. — Phosphorus,  so  termed  from  its  property  of  shining  in  the  dark 
(from  4)wj,  light,  and  ^i^^Biv,  to  bear),  occurs  in  the  three  kingdoms  of  nature, 
but  most  abundantly  as  a  component  of  the  bones  and  urine  of  animals  :  it  is 
generally  present  as  phosphoric  acid,  combined  with  various  bases.  Although 
phosphorus  is  found  in  certain  phosphates  in  the  mineral  kingdom,  it  is,  like 
carbon  and  sulphur,  a  most  important  constituent  of  organic  matter.  It 
exists  in  albumen,  fibrin,  and  gelatine,  in  the  brain,  blood,  milk,  and  other 
secretions.  It  is  found  in  combination  with  oxygen,  united  to  lime  and 
magnesia,  in  the  seeds  and  husks  of  the  cerealia,  and  in  numerous  esculent 
roots.  There  is  no  substance  which  yields  it  so  abundantly  as  bone.  The 
subphosphate  of  lime  forms  about  eighty  per  cent,  of  calcined  bone,  and 
from  this  source  it  is  now  exclusively  obtained. 

Phosphorus  was  discovered  in  1669,  by  Brandt,  a  merchant  of  Hamburg, 
in  the  solid  residue  of  urine,  but  no  practical  use  was  made  of  the  discovery 
until  a  century  later,  when  a  process  for  preparing  this  substance  from  bone, 
was  first  made  public  by  Scheele  and  Gahn. 

Preparation. — On  twenty  parts  of  calcined  bone,  ground  to  a  fine  powder, 
pour  forty  of  water  (by  weight)  and  eight  parts  of  sulphuric  acid,  previously 
diluted  with  an  equal  weight  of  water.  These  materials  are  well  stirred 
together  by  means  of  a  revolving  wooden  stirrer,  for  about  six  hours,  steam 
being  let  into  the  mixture  to  promote  the  chemical  changes.  The  whole  is 
then  put  into  a  conical  bag  of  linen  to  separate  the  clear  liquor,  and  the 
residuum  is  washed  and  pressed  until  the  water  ceases  to  taste  acid.  Evapo- 
rate the  strained  liquor,  and  when  reduced  to  about  half  its  bulk,  let  it 
cool.  A  white  sediment  will  form,  which  must  be  allowed  to  subside ;  the 
clear  solution  (superphosphate  of  lime)  must  be  decanted  and  boiled  to 
dryness  in  a  glass  vessel.  A  white  mass  will  remain,  which  may  be  fused  in  a 
platinum  crucible,  and  poured  out  into  a  clean  copper  dish.  A  transparent 
substance  is  thus  obtained,  consisting  of  phosphoric  acid,  with  phosphate, 
and  a  little  sulphate  of  lime,  commonly  known  under  the  name  of  glass  of 
phosphorus.  It  yields  phosphorus  when  distilled  at  a  white  heat  with  one- 
fourth  of  its  weight  of  charcoal.  The  retort,  which  is  made  of  the  most 
refractory  fire-clay,  should  be  well  and  carefully  luted,  and  should  have  a 
wide  neck  terminating  in  a  copper  tube,  so  bent  as  to  dip  perpendicularly 
into  a  bottle  of  hot  water,  otherwise  it  is  apt  to  become  plugged  up  by  con- 
gealed phosphorus.  When  cold,  it  is  cut  into  small  pieces,  which  are  put, 
with  water,  into  a  slightly  conical  glass  tube,  and  fused  by  immersion  in  hot 
water  :  on  cooling,  the  phosphorus  is  withdrawn  in  the  shape  of  a  stick. 

The  changes  which  take  place  in  the  various  stages  of  this  process,  may 
be  thus  described.  The  subphosphate  of  lime  in  bone  is  3(CaO),P05.  Sul- 
phuric acid  transforms  this  salt  into  acid  phosphate  (superphosphate)  and 
sulphate  of  lime,  3(CaO)P03+2SO,=CaO,2HO,P05+2(CaO,SO,).  The 
acid  phosphate  when  heated  with  charcoal  is  converted  into  pyrophosphate 
(which  is  not  decomposed  by  carbon)  carbonic  oxide  and   phosphorus,  a 


234  PHOSPHORUS.   CHEMICAL  PROPERTIES, 

portion  of  the  phosphoric  acid  being  set  free  and  deoxidized  by  the  charcoal 
at  a  white  heat,  2(CaO,PO,) -f  Cs=5CO  +  2CaO,P05  +  P.  Phosphuretted 
hydrogen  also  escapes  during  the  process  as  a  result  of  the  reaction  of  the 
vapor  of  phosphorus  on  water. 

The  phosphorus  obtained  by  the  first  distillation  is  commonly  of  a  dirty 
red  or  brown  color,  owing  to  the  presence  of  impurities.  It  is  melted  in  a 
solution  of  ammonia,  and  is  bleached  by  heating  it  in  a  mixture  of  bichro- 
mate of  potassa  and  sulphuric  acid.  After  this  it  is  again  melted,  and  wliile 
liquid  is  strained  through  chamois-leather.  The  mechanical  impurities  are 
thus  separated,  and  it  is  recast  into  sticks  in  the  manner  above  described. 
This  substance  is  now  manufactured  in  tons,  chiefly  for  the  purpose  of 
making  lucifer  matches.  According  to  Mr.  Gore,  about  six  tons  are  annu- 
ally consumed  in  Great  Britain  in  the  match  manufacture — and  one  pound 
will  suflfice  for  600,000  matches.  This  manufacture  is,  however,  conducted 
on  a  larger  scale  abroad.  There  are  two  manufactories  on  the  continent, 
which  consume  twenty  tons  of  phosphorus  annually. 

Properties. — When  pure,  solid  phosphorus  is  tasteless,  but  when  in  solu- 
tion, it  has  a  sharp  nauseous  taste :  it  is  colorless,  or  of  a  pale  yellow  color, 
translucent,  sectile,  and  flexible  at  common  temperatures,  but  at  32°  vitreous 
and  brittle.  Exposed  to  air,  it  exhales  luminous  fumes,  having  a  peculiar 
odor,  distantly  resembling  that  of  garlic,  and  ozone  is  produced  {see  page 
110).  Its  specific  gravity  is  1'826  at  50°.  Its  specific  heat  is  0188T 
(Regnault).  It  is  a  non-conductor  of  electricity,  both  in  its  solid  and  fluid 
state.  Phosphorus  is  insoluble  in  water,  but  it  is  dissolved  sparingly  by 
absolute  alcohol,  ether,  the  oils,  naphtha,  benzole  (and  other  liquid  hydro- 
carbons, but  most  abundantly  by  sulphide  of  carbon.  The  chlorides  of 
sulphur  and  of  phosphorus  also  dissolve  it.  When  water  is  added  to  the 
alcoholic  solution,  phosphorus  is  separated  as  a  milk-white  substance,  probably 
in  the  state  of  hydrate.  If  the  alcoholic  solution  be  poured  on  hot  water 
in  the  dark,  there  is  an  evolution  of  light  arising  from  the  slow  combustion 
of  phosphorus.  The  solution  in  ether  presents  similar  phenomena.  If  this 
is  rubbed  over  the  skin  or  any  warm  surface,  in  the  dark,  the  luminosity  of 
phosphorus  is  seen  in  a  pale,  bluish-colored,  lambent  flame,  which  pro- 
duces no  sense  of  warmth.  The  ethereal  solution  is  decomposed  by  exposure 
to  light,  and  red  oxide  of  phosphorus  or  red  phosphorus  is  deposited.  The 
saturated  solution  in  sulphide  of  carbon,  if  allowed  to  evaporate  spon- 
taneously on  paper,  leaves  a  finely-divided  residue  of  phosphorus,  which, 
when  dry,  instantly  takes  fire,  and  burns  in  air  with  a  brilliant  white  light 
peculiar  to  this  body.  Although  phosphorus  is  not  soluble  in  water,  it  is 
slowly  oxidized  in  this  liquid,  which  is  soon  found  to  acquire  an  acid  reac- 
tion, and  to  have  the  mixed  properties  of  phosphorous  and  phosphoric  acids. 
As  no  hydrogen  escapes,  it  is  probable  that  the  air  diffused  through  the 
water,  furnishes  oxygen.  Under  exposure  to  light,  phosphorus  acquires  a 
reddish  color.  This  was  supposed  to  be  caused  by  oxidation,  but  as  it  takes 
place  in  vacuo  it  is  probably  owing  to  a  molecular  change  in  phosphorus 
itself,  a  superficial  layer  of  the  metalloid  being  changed  into  amorphous 
phosphorus.  The  white  layer  which  forms  on  the  surface,  when  phosphorus 
is  kept  in  the  dark,  has  been  also  ascribed  to  molecular  changes.  The 
phosphorus  in  which  this  change  has  taken  place  is  very  fusible  and  inflam- 
mable. 

Phosphorus  cannot  be  readily  crystallized  by  fusion,  but  it  may  be  crys- 
tallized by  solution.  By  slowly  cooling  some  of  its  hot  saturated  solutions, 
phosphorus  has  been  procured  in  crystals,  having  the  form  of  rhombic  dode- 
cahedra.  Crystals  of  this  substance  have  also  been  obtained,  by  melting 
under  water  two  parts  of  phosphorus  with  one  of  sulphur :  a  portion  of  the 


PHOSPHORUS.   CHEMICAL  PROPERTIES.  235 

phosphorus  is  deposited  in  regular  crystals  on  cooling.  (See  Sulphide  of 
Phosphorus.)  Phosphorus  melts  at  about  115°,  undergoing  an  increase  of 
volume.  If  suddenly  cooled  to  32°,  after  having  been  heated  to  140°,  it 
sometimes  becomes  black  (Thbnard)  ;  but  if  slowly  cooled,  it  remains  color- 
less. When  fused  and  left  undisturbed,  it  may  remain  liquid  for  hours  at 
the  usual  temperature,  particularly  when  covered  by  an  alkaline  liquid.  At 
from  550°  to  570°  in  close  vessels,  it  boils  and  evaporates  in  the  form  of  a 
colorless  vapor,  the  density  of  which,  according  to  Dumas,  is  4*3o5  ;  4  326 
(Regnault)  ;  100  c.  i.  weigh  13696  grains.  But  phosphorus  evaporates, 
especially  if  in  contact  with  moisture,  at  a  much  lower  temperature.  The 
volatility  of  phosphorus  in  conjunction  with  aqueous  vapor,  may  be  shown 
by  boiling  a  flask  of  water  containing  a  piece  of  phosphorus,  over  a  lamp; 
the  vapor,  as  it  issues  from  the  flask,  is  luminous  in  a  dark  room.  Owing  to 
its  great  inflammability,  it  should  always  be  preserved  in  water,  in  a  dark 
place,  and,  when  required,  cut  under  water. 

Phosphorus  is  a  formidable  poison  ;  a  few  grains  of  this  substance  are 
sufficient  to  destroy  life.  Even  the  vapors  when  breathed  (as  in  lucifer- 
match  making)  produce  caries  and  necrosis  of  the  jaws,  with  wasting  disease. 

There  are  some  peculiar  circumstances  connected  with  the  luminosity  and 
inflammability  of  phosphorus.  When  exposed  to  humid  air  at  temperatures 
above  the  freezing-point,  it  shines  in  the  dark  with  a  pale  blue  light,  which 
increases  in  intensity  with  the  temperature.  This  arises  from  slow  combus- 
tion, attended  by  the  production  of  phosphorous  acid  (PO3)  and  ozone.  If 
a  streak  is  drawn  on  litmus-paper  with  a  stick  of  dry  phosphorus,  the  paper 
is  slowly  reddened.  The  luminosity  ceases  in  close  vessels  as  soon  as  the 
oxygen  has  been  absorbed,  and  it  does  not  take  place  when  the  air  has  been 
artificially  dried  :  in  this  case  the  formation  of  phosphorous  acid  seems  to  be 
prevented.  In  pure  oxygen,  phosphorus  is  not  luminous  until  heated  to 
between  70°  and  80°,  above  which  temperature  it  becomes  strongly  luminous, 
and  soon  inflames.  Gases,  in  which  phosphorus  has  been  immersed,  acquire 
its  odor,  and  when  mixed  with  air,  they  become  slightly  luminous.  If  a 
piece  of  phosphorus  be  introduced  into  a  vessel  of  pure  and  dry  oxygen  gas 
over  mercury,  at  a  temperature  not  exceeding  80°,  no  perceptible  absorption 
will  happen  in  twenty-four  hours  ;  but  if,  the  temperature  remaining  the 
same,  the  pressure  be  diminished  to  one-eighth  or  one-tenth  of  that  of  the 
atmosphere,  the  phosphorus  will  be  surrounded  with  white  vapors,  will 
become  luminous  in  the  dark,  and  will  absorb  oxygen.  Graham  has  shown 
that  the  slow  combustion  of  phosphorus  in  air  is  prevented  by  small  addi- 
tions of  certain  gases  and  vapors.  Thus  at  the  temperature  of  66°,  and 
even  above  this,  oxidation  is  entirely  prevented  by  the  presence  of  small 
quantities  of  sulphurous  acid,  sulphuretted  hydrogen,  and  of  oleflant  gas,  as 
well  as  by  the  vapors  of  sulphide  of  carbon,  ether,  creasote,  naphtha,  and  oil 
of  turpentine.  This  is  probably  owing  to  the  oxidation  of  these  vapors, 
since  it  has  been  noticed  that  when  two  oxidable  bodies  are  in  contact,  one 
of  them  often  takes  precedence  in  combining  with  oxygen,  to  the  entire 
exclusion  of  the  other.  Potassium  is  defended  from  oxidation  in  air  by  the 
same  vapors,  though  to  a  less  degree.  When  these  oxidable  vapors  are 
absent,  there  is  no  better  test  of  the  presence  of  free  oxygen,  than  that 
furnished  by  the  luminosity  of  phosphorus  in  the  dark. 

When  dry  phosphorus  is  sprinkled  with  lamp-black,  or  powdered  animal 
charcoal,  it  is  apt  to  inflame  ;  and,  when  very  thin  slices  of  dry  phosphorus 
are  placed  upon  dry  wood,  flannel,  wool,  lint,  fine  feathers,  or  other  non-con- 
ducting substances,  they  speedily  melt  and  readily  inflame  upon  the  gentlest 
friction.  It  seems  as  if  the  slow  combustion  of  the  phosphorus  produced 
heat  enough  to  melt  it  whilst  lying  upon  a  very  bad  conductor.     If  several 


236  COMBUSTION    OF    PHOSPHORUS. 

pieces  of  phosphorus  be  placed  upon  or  near  to  each  other,  they  are  also  apt 
to  inflame. 

The  actual  temperature  at  which  phosphorus  inflames  has  been  variously 
stated  ;  but  it  is  generally  a  little  above  its  melting  point.  We  Kave  noticed 
that  phosphorus  coated  with  a  white  layer,  has  melted  in  air  below  tO^,  and 
burst  into  flame  on  being  touched.  Phosphorus  easily  takes  fire  by  the  heat 
of  the  hand  and  by  slight  friction,  as  when  rubbed  upon  a  piece  of  coarse 
paper  :  it  requires,  therefore,  to  be  handled  with  the  utmost  caution.  Owing 
to  the  superficial  formation  of  phosphorus  and  phosphoric  acids,  when  it  burns 
imperfectly  at  low  temperatures,  its  further  combustion  is  often  prevented  : 
thus,  in  rubbing  a  fragment  of  phosphorus  between  two  pieces  of  brown 
paper,  a  momentary  combustion  ensues,  and  it  often  requires  considerable 
friction  to  cause  it  again  to  inflame.  For  the  same  reason  it  is  diSicult  to 
light  a  piece  of  paper  by  the  flame  of  phosphorus,  the  paper  becoming 
covered  and  protected  by  the  acid  produced.  So  also  a  small  piece  of 
phosphorus  may  be  fused  by  the  gradual  application  of  heat,  but  it  will  not 
inflame  until  the  surface  is  disturbed  by  touching  it  with  a  wire.  A  frag- 
ment gently  heated  on  writing-paper,  may  be  melted  and  consumed  without 
igniting  the  paper.  Paper  or  linen  soaked  in  phosphate  of  ammonia,  is, 
for  a  similar  reason,  rendered  uninflammable  by  the  application  of  heat; 
ammonia  is  volatilized,  and  the  phosphoric  acid  liberated,  glazes  over  and 
protects  the  material  from  combustion. 

When  in  brilliant  combustion  in  the  air,  phosphorus  evolves  copious  fumes 
of  phosphoric  acid  (PO.)  :  its  flame  is  intensely  luminous,  and  nearly  white. 
If  phosphorus  be  heated  in  a  confined  portion  of  air,  it  enters  into  less  per- 
fect combustion,  and  an  oxide,  a  red  solid,  less  fusible  than  phosphorus,  is 
produced.  The  difi*erent  products  of  the  combustion  of  phosphorus  are 
well  shown  by  heating  a  fragment  of  it  placed  near  the  centre  of  a  thin  glass 
tube  of  about  a  fourth  of  an  inch  diameter,  and  three  or  four  feet  long,  and 
then  gently  driving  a  current  of  air  through  the  tube  ;  the  fixed  and  volatile 
acids,  and  the  red  oxide,  are  in  this  way  distincly  separated. 

The  vapor  of  phosphorus  explodes  with  oxygen,  and  burns  violently  where 
it  meets  with  air.  It  may  be  safely  produced  and  burnt  at  the  mouth  of  a 
test-tube,  by  heating  a  piece  of  phosphorus  in  a  small  quantity  of  ether. 
The  tube  becomes  filled  with  ether-vapor,  and  the  phosphorus-vapor  burns 
only  as  it  issues  from  the  mouth  of  the  tube.  Gases  in  which  oxygen  is  in 
a  combined  state,  do  not  readily  part  with  it  to  phosphorus,  even  at  the 
temperature  of  combustion.  Thus  burning  phosphorus  is  extinguished  in 
pure  carbonic  acid.  It  may  be  melted  in  deutoxide  of  nitrogen  by  a  heated 
wire  without  being  inflamed  ;  but  when  introduced  into  this  gas  in  a  boiling 
state,  it  decomposes  it,  and  unites  to  the  oxygen,  producing  a  vivid  com- 
bustion. It  takes  fire  spontaneously  in  chlorine,  burning  with  a  pale  flame; 
and  on  contact  with  iodine,  the  heat  of  combination  is  such  as  to  kindle  the 
phosphorus  immediately. 

Its  great  affinity  for  oxygen  is  manifested  not  only  by  its  luminosity  in  air 
at  a  low  temperature,  but  by  its  decomposition  of  the  oxides  of  certain 
metallic  salts.  Small  portions  of  fresh-cut  phosphorus  suspended  in  weak 
solutions  of  sulphate  of  copper,  nitrate  of  silver,  chloride  of  gold,  and  chlo- 
ride of  platinum,  are  speedily  coated  with  layers  of  the  respective  metals, 
sometimes  deposited  in  a  beautifully  crystalline  state.  Phosphorus  here  acts 
as  a  powerful  deoxidizer,  and  is  converted  into  phosphoric  acid  P-f5(AgO, 
NO,)=5Ag  +  P05+5NO„  and  5  (CuO,S03)  +  P=5Cu  +  P05-f5S03.  If 
some  thin  slices  of  phosphorus  be  placed  on  a  very  diluted  solution  of  chlo- 
ride of  gold  (a  grain  of  chloride  to  4000  of  water),  and  covered  over,  they 
will  soon  be  surrounded  by  thin  transparent  films  of  reduced  gold,  which 


ALLOTROPIC,    OR    AMORPHOUS    PHOSPHORUS.  231 

may  be  raised  from  the  fluid  by  clean  and  dry  plates  of  glass.  There  is  no 
instance  in  which  metallic  gold  is  brought  to  a  finer  state  of  tenuity  than  in 
this  experiment.  Advantage  is  taken  of  this  property  in  the  electrotype 
art,  for  coating  vegetable  and  animal  substances,  insects,  seeds,  &c.,  with  a 
layer  of  metal,  and  thus  making  them  conductors.  The  substance  is  brushed 
over  with  a  small  quantity  of  a  weak  solution  of  any  salt  of  gold,  silver,  or 
platinum,  and  it  is  then  exposed  to  the  vapor  of  a  solution  of  phosphorus  in 
alcohol  or  ether.  A  thin  film  of  metal  is  deposited,  and  this  serves  as  a 
conducting  surface  for  a  further  deposit  by  the  battery.  An  alcoliolic  solu- 
tion of  phosphorus  throws  down  the  metals  from  solutions  of  gold  and  silver. 
Phosphorus  decomposes  solid  nitrate  of  silver  and  chlorate  of  potassa  with 
a  violent  explosion,  when  a  mixture  of  the  two  substances  is  suddenly  struck 
with  a  hammer. 

Equivalent. — The  atomic  weight  of  phosphorus  is  in  round  numbers  32. 
As  the  specific  gravity  of  its  vapor,  compared  with  hydrogen  is  63  71,  it 
follows  that  its  atomic  volume  must  be  0'5,  or  half  a  volume,  so  that  each 
volume  of  vapor,  like  that  of  oxygen,  will  necessarily  contain  two  atoms. 
{See  p.  69.)  It  is  diatomic.  The  hypothesis  of  Gerhardt,  that  the  atomic 
weights  of  elements  in  the  gaseous  or  vaporous  condition,  correspond  to 
single  volumes  of  their  vapors,  is  therefore  wholly  inconsistent  with  the  facts 
which  are  known  regarding  the  vapor  of  phosphorus.  Deville  did  not  find 
that  a  heat  of  1900°  in  any  way  affected  the  relative  volumes  of  the  specific 
gravities  of  phosphorus  and  oxygen. 

Tests. — The  smallest  fragment  of  phosphorus,  even  when  mixed  with 
Other  substances,  may  be  sometimes  identified  by  its  garlic  odor,. and  in  all 
cases  by  its  luminosity  in  the  dark.  If  the  substance  suspected  to  contain 
phosphorus  is  dried  and  heated  in  the  dark,  in  a  thin  layer  spread  on  a 
metallic  plate,  the  minutest  fragment  of  phosphorus  will  appear  luminous, 
or  will  burn  with  a  puff  of  white  vapor.  The  contents  of  the  stomach  and 
intestines  of  persons  poisoned  by  phosphorus  have  been,  in  some  instances, 
quite  luminous  in  the  dark.  If  the  test  of  luminosity  should  fail  under  these 
circumstances,  the  dried  substance  should  be  digested  in  its  volume  of 
sulphide  of  carbon  for  twenty-four  hours.  The  liquid  strained  off  should 
be  poured  into  a  watch-glass,  floating  on  a  surface  of  hot  water  in  the 
dark,  when,  if  phosphorus  be  present,  there  will  be  a  luminosity,  as  the 
sulphide  evaporates.  By  evaporation,  at  ordinary  temperatures,  small 
particles  of  phosphorus  are  left  as  a  residue,  which  may  be  ignited  by  a 
heated  wire. 

Allotropic,  or  Amorphous  Phosphorus. — It  has  been  already  remarked  that 
phosphorus,  when  suddenly  cooled  from  a  state  of  fusion,  undergoes  certain 
changes  in  its  physical  properties.  As  a  result  of  exposure  to  heat  or  light, 
it  acquires  a  red  color,  and  this  red  substance,  which  is  allotropic  or  amor- 
phous phosphorus,  is  possessed  of  peculiar  properties,  which  have  been  fully 
described  by  Schrotter  and  others.  {Ann.  Ch.  et  Ph.,  3eme  ser.,  24,  p. 
406.)  Schrotter  made  the  discovery  of  this  variety  of  phosphorus  in  1848. 
He  obtained  it  by  distilling  phosphorus  in  an  atmosphere  of  nitrogen  or 
carbonic  acid,  at  a  temperature  between  460°  and  480°.  In  this  case,  a 
part  of  the  phosphorus  assumes  the  amorphous  or  red  condition,  while  the 
unchanged  portion  acquires  the  property,  after  repeated  distillations,  of 
remaining  for  a  long  time  liquid,  and  even  sustaining  considerable  agitation 
without  congealing.  To  separate  the  common,  from  the  amorphous  kind, 
sulphide  of  carbon  is  employed.  This  dissolves  common  phosphorus  only, 
and  leaves  the  allotropic  variety,  -after  having  been  well  purified  by  washing 
with  the  sulphide,  in  the  form  of  a  red  or  brownish-red  powder.  For 
commercial  purposes,  allotropic  phosphorus  is  made  by  heating  phosphorus 


238         PROPERTIES  OF  ALLOTROPIC  .  PHOSPHORUS. 

under  water,  in  an  air-tight  cast-iron  boiler  to  a  temperature  of  450°.  A 
quantity  of  about  200  pounds  of  ordinary  phosphorus  is  thus  kept  heated, 
for  three  or  four  weeks.  When  the  vessel  is  opened,  the  phosphorus 
presents  itself  as  a  hard,  red,  briek-like-looking  substance,  as  brittle  as 
glass.  It  is  broken  into  small  pieces  under  water,  and  ground  between 
mill-stones  in  a  vessel  supplied  with  a  small  stream  of  water,  which  washes 
the  finer  particles  into  a  tank,  in  which  they  subside.  Any  unchanged 
phosphorus  is  then  removed  by  sulphide  of  carbon.  (Gore.)  For  the 
purpose  of  experiment,  this  change  may  be  shown  by  heating  a  small  portion 
of  phosphorus  to  a  proper  temperature,  in  a  tube  filled  with  dry  carbonic 
acid  gas.  The  change  of  color  produced  by  heat,  and  the  volatility  of 
phosphorus  at  a. still  higher  temperature,  may  thus  be  proved.  One  end  of 
the  tube  should  be  sealed,  and  the  other  end  should  be  plunged  into  mercury 
or  water. 

Properties. — The  color  of  amorphous  phosphorus  varies  according  to  the 
temperature  to  which  it  has  been  exposed,  from  nearly  black  (with  a  metallic 
lustre)  to  iron-gray,  brick-red,  crimson,  and  scarlet.  It  has  no  odor.  Its 
specific  gravity  at  50°  is  1  964  to  214.  When  dry,  it  undergoes  no  change 
in  air :  when  moist  it  is  slowly  oxidized,  but  it  is  not  luminous  in  the  dark, 
and  it  produces  no  ozone.  It  does  not  remove  oxygen  from  air,  and  will 
not  combine  with  this  gas  to  produce  the  phenomenon  of  combustion  under  a 
temperature  of  500°;  but  it  requires  to  be  heated  to  570°  for  its  entire 
combustion.  In  vessels  filled  with  carbonic  acid  or  nitrogen,  it  may  be 
distilled  over  as  ordinary  phosphorus  at  this  temperature.  Chlorine  acts 
upon  it,  producing  heat,  but  no  evolution  of  light.  Chloride  of  phosphorus 
is  formed.  Iodine  has  no  action  upon  it;  and  although  it  is  only  phos- 
phorus in  an  altered  molecular  condition,  it  has  no  poisonous  properties. 
In  addition  to  the  characters  above  described,  allotropic  phosphorus  is  quite 
opaque,  hard,  and  brittle,  and  without  crystalline  structure.  It  is  insoluble 
in  sulphide  of  carbon,  ether,  and  all  the  liquids  which  dissolve  common 
phospliorus.  It  is  slightly  dissolved  by  a  solution  of  chlorine.  Although  it 
is  considered  to  be  less  energetic  in  its  affinities  than  common  phosphorus, 
yet  when  mixed  in  equal  parts  with  chlorate  of  potassa,  it  explodes  with 
tremendous  violence,  and  with  the  slightest  friction. 

From  this  description  it  will  be  perceived  that  although  the  two  varieties 
are  easily  convertible  into  each  other,  they  differ  as  much  in  properties  as 
any  two  metalloids,  or  metals.  The  amorphous  phosphorus  is  used  in  the 
manufacture  of  lucifer-matches,  and  in  some  cases  a  surface  of  amorphous 
phosphorus  is  employed,  on  which  matches,  properly  prepared,  may  be 
rubbed. 

Phosphorus  and  Oxygen. — Phosphorus  combines  with  oxygen  to  form 
four  different  compounds  : — 

Oxide  of  phosphorus    .     PjO  Phosphorous  acid  .     PO3 

Hypophosphorous   acid     P  0  Phosphoric  acid   .         .     PO5 

Oxide  OF  Phosphorus  (PgO) When  phosphorus  is  burnt  in  air,  there 

is  generally  a  red  residue,  which  consists  in  great  part  of  this  oxide.  If  a 
large  quantity  of  phosphorus  is  burned  in  a  confined  volume  of  air,  the 
oxide  is  abundantly  produced.  It  may  be  prepared  in  quantity,  by  melting 
phosphorus  in  a  conical  glass  under  hot  water,  and  then  passing  upon  it,  in 
the  melted  state,  a  current  of  oxygen.  The  phosphorus  burns  under  water, 
producing  phosphoric  acid,  which  is  dissolved,  and  the  red  oxide,  which  is 
diffused  as  an  insoluble  red  powder  through  the  liquid  (3P  +  60  =  PO^-f 
PgO).     When  it  has  subsided,  and  the  vessel  is  cool,  the  water  is  poured  off, 


OXIDE    OF    PHOSPHORUS.      HYPOPHOSPHOROUS    ACID.  239 

and  the  red  compound  is  digested  in  snlphide  of  carbon.  This  removes  any 
uncombined  phosphorus,  and  leaves  the  oxide.  The  oxide  is  an  insoluble 
red  solid,  not  inflammable  in  air  unless  mixed  with  phosphorus,  when,  if 
dry,  it  will  take  fire  spontaneously.  It  burns  on  contact  with  nitric  acid, 
and  explodes  when  mixed  with  powdered  chlorate  of  potassa.  It  is  un- 
changed by  dry  air  or  oxygen  ;  but  in  damp  air,  it  is  slowly  oxidized.  It  is 
not  luminous  in  the  dark ;  it  is  not  very  inflammable  when  heated  in  air ; 
but  at  a  red  heat,  it  is  converted  into  phosphoric  acid  and  phosphorus 
(5P.^O=P05-f  Pg).  Like  allotropic  phosphorus,  it  is  insoluble  in  sulphide 
of  carbon,  and  in  all  liquids  which  dissolve  phosphorus.  It  is  neutral,  and 
enters  into  no  combinations. 

HYPOPHOSPHOROUS  AciD  (P0,2H0,  or  3H0)  is  prepared  as  follows : — 
Upon  one  part  of  phosphide  of  barium  pour  four  parts  of  water,  and  when 
the  evolution  of  phosphuretted  hydrogen  gas  has  ceased,  pour  the  whole 
upon  a  filter.  To  the  filtered  liquid  add  sulphuric  acid,  as  long  as  any 
precipitate  falls:  separate  the  precipitate,  which  is  sulphate  of  baryta,  and 
the  clear  liquor  now  contains  hypophosphorous  acid  in  solution.  When 
concentrated  by  evaporation,  a  sour  viscid  liquid  is  obtained,  incapable  of 
crystallization,  and  eagerly  attractive  of  oxygen.  The  concentrated  acid  is 
of  the  consistency  of  syrup  ;  it  has  not  been  obtained  free  from  water,  with 
two,  or,  according  to  some,  with  three  equivalents  of  which,  it  is  always 
combined. 

In  place  of  the  phosphide  of  barium,  bisulphide  of  barium  and  phosphorus 
may  be  employed.  When  these  are  boiled  in  water,  sulphuretted  hydrogen 
escapes,  and  ahypophosphite  of  baryta  is  formed  (BaS^-f  P  +  2HO=2HS  + 
BaO,PO).  When  potassa,  soda,  or  lime  is  boiled  with  phosphorus  in  water, 
phosphuretted  hydrogen  escapes,  and  ahypophosphite  of  the  alkali  is  formed 
and  dissolved.  The  salt  may  be  obtained  on  careful  evaporation,  although 
there  is  a  liability  to  explosion  if  it  is  carried  to  dryness. 

When  hydrated  hypophosphorous  acid  is  heated,  it  is  decomposed  with 
the  evolution  of  phosphuretted  hydrogen,  and  the  production  of  phosphoric 
acid:  2PO  +  3HO  =  PH3+POs.  It  is  a  powerful  deoxidizing  agent.  It 
reduces  the  salts  of  gold,  silver,  mercury,  and  copper  to  the  metallic  state 
(PO  +  4AgO=Ag4+P03).  When  boiled  with  sulphuric  acid,  it  decora- 
poses  it ;  sulphurous  acid  is  evolved,  and  sulphur  is  deposited.  An  acid 
solution  of  permanganate  of  potassa  is  deoxidized  in  the  cold,  and  the  color 
is  discharged  by  this  acid.  In  combination  with  bases  it  forms  hypophos- 
phites ;  they  are  soluble  in  water,  and  many  of  them  in  alcohol;  they  are 
decomposed  by  a  red  heat ;  they  are  mostly  deliquescent,  and  uncrystallizable, 
but  some  are  inflammable  and  even  explosive  when  heated. 

Phosphorous  Acid  (PO3). — The  volatile  white  substance  which  has  been 
mentioned  as  one  of  the  products  of  the  combustion  of  phosphorus  in  rarefied 
air,  consists  chiefly  of  this  acid  in  a  dry  state.  By  burning  phosphorus  in  a 
tube  with  a  limited  access  of  dry  air,  and  caution  as  to  temperature — as,  for 
instance,  by  placing  a  piece  of  phosphorus  near  one  end  of  a  tube  two  or 
three  feet  long,  drawn  out  at  the  ends,  inflaming  it,  and  gently  propelling 
dry  air  through  the  tube — this  acid  may  be  collected  in  the  form  of  a  white 
volatile  powder.  It  has  the  odor  of  garlic,  and  when  exposed  to  air,  rapidly 
absorbs  moisture  as  well  as  oxygen,  and  is  converted  into  phosphoric  acid. 
The  solid  acid  may  be  volatilized  by  heat  in  carbonic  acid  or  nitrogen,  but 
when  moderately  heated  in  air,  it  takes  fire  and  burns,  producing  phosphoric 
acid  (5POj,=3P05-|-p2).  The  slow  combustion  of  phosphorus  in  air  at  a 
low  temperature  is  attended  with  the  production  of  this  acid  (PO3).  If 
sticks  of  phosphorus  be  placed  in  glass  tubes,  open  at  both  ends,  and 


240  ANHYDROUS    PHOSPHORIC    ACID. 

arranged  round  a  glass  funnel  inserted  in  the  neck  of  a  bottle,  the  phosphorus 
will  slowly  disappear,  as  if  by  deliquescence,  and  the  liquid  colleeied  in  a 
bottle  will  be  chiefly  a  solution  of  this  acid,  mixed  with  some  phosphoric 
acid.  It  was  formerly  called  phosphatic  acid.  When  the  hydrated  acid  is 
heated,  or  when  its  solution  is  evaporated  to  dryness,  phosphuretted  hydro- 
gen is  evolved,  and  it  is  converted  into  phosphoric  acid  (4P03+3HO  = 
PHg  +  SPOg).  It  may  be  obtained  hy  evaporation  in  vacuo,  as  a  crystalline 
hydrate  (POgSHO).  The  solution  in  water  is  not  corrosive,  but  powerfully 
acid.  When  heated  with  zinc  or  iron,  phosphuretted  hydrogen  is  evolved, 
and  phosphates  of  the  metals  are  formed.  The  solution  absorbs  oxygen  when 
exposed  to  air,  and  phosphoric  acid  is  produced.  It  is  a  powerful  deoxidiz- 
ing agent.  It  reduces  at  a  boiling  temperature  the  oxide  of  mercury,  per- 
manganate of  potassa,  and  the  salts  of  gold  and  silver.  In  reference  to  the 
salts  of  silver  the  following  changes  take  place  :  P054-2AgON03=2Ag  + 
PO5+XO5.  It  deoxidizes  sulphuric  acid,  converting  it  into  sulphurous  acid, 
and  this  again  is  decomposed  and  sulphur  is  deposited.  It  also  deoxidizes 
nitric  and  arsenic  acids,  converting  the  latter  into  arsenious  acid.  In  these 
reactions  it  is  changed  into  phosphoric  acid.  The  solution  of  this  acid  does 
not  precipitate  albumen.  Chlorine  converts  it  into  phosphoric  acid  (PO3-I- 
2C14-2H0=P034-2HC1). 

Phosphites. — The  phosphites  contain,  according  to  Graham,  three  atoms 
of  base  to  one  of  acid,  the  hydrated  acid  being  the  tribasic  phosphite  of 
water.  Others  regard  the  acid  as  dibasic — one  atom  of  water  being  retained 
in  its  combination  with  two  atoms  of  a  metallic  oxide.  The  afQnity  of  the 
phosphorous  acid  for  bases  is  but  feeble.  All  the  phosphites  include  water, 
and  when  sufficiently  heated,  are  resolved  into  hydrogen  and  phosphates, 
often  with  combustion.  At  common  temperatures  they  do  not  absorb  oxygen 
from  the  air,  but  they  are  easily  convertible  into  phosphates  by  nitric  acid, 
chlorine,  and  other  oxidizers.  They  have  the  characters  assigned  to  phos- 
phorous acid. 

Phosphoric  Acid  (POg). — Anhydrous  phosphoric  acid  can  only  be  ob- 
tained by  the  direct  combustion  of  phosphorus  in  an  excess  of  dry  oxygen  ; 
intense  heat  and  light  are  evolved,  and  white  deliquescent  flocculi  line  the 
interior  of  the  receiver.  The  acid  may  be  produced  by  burning  phosphorus 
under  a  tall  receiver  in  atmospheric  air,  the  air  having  been  previously 'well 
dried  by  placing  under  the  receiver  a  saucer  containing  sulphuric  acid.  The 
receiver  should  be  placed  in  a  glass  dish,  and  should  rest  upon  some  thick 
pieces  of  plate-glass.  A  piece  of  phosphorus  in. a  platinum  or  porcelain 
capsule,  may  be  ignited  and  covered  over  with  the  receiver.  The  phosphorus 
burns  at  first  furiously,  but  the  combustion  gradually  subsides  for  want  of 
oxygen,  and  may  be  renewed  by  gently  lifting  the  receiver  oflf  the  glass 
plates :  thus  the  whole  of  the  phosphorus  may  be  gradually  consumed,  and  it 
forms  a  quantity  of  dense  vapor,  which  subsides  in  the  form  of  white  flakes 
like  snow,  some  portions  adhering  to  the  sides  of  the  glass.  A  convenient 
apparatus  has  been  constructed  for  burning  phosphorus  in  oxygen,  so  as  to 
produce  this  acid  in  large  quantity.  The  solid  phosphoric  acid  obtained  by 
this  process,  should  be  transferred  as  quickly  as  possible  into  a  dry  stopper- 
bottle,  in  which  it  may  be  pressed  down  ;  and  the  portions  of  acid  which 
remain  adhering  to  the  receiver  and  dish,  may  be  washed  out,  and  they  will 
yield  a  solution  of  the  acid. 

In  the  anhydrous  state,  phosphoric  acid  is  an  extremely  deliquescent  un- 
crystalline  white  powder,  fusible  into  a  vitreous  substance,  and  volatile  at 
a  full  red  heat.  It  is  inodorous,  not  acid  in  the  dry  state,  and  not  corrosive. 
A  small  quantity  of  water  poured  upon  the  solid  acid,  dissolves  it  with  a 


HYDRATES    OF    PHOSPHORIC    ACID.  241 

hissing  noise,  and  great  heat  is  evolved.  A  solution  of  the  protohydrate  of 
phosphoric  acid  is  thus  obtained.  The  liquid  is  sour  to  the  taste,  and 
powerfully  acid  in  reaction.  Chloroform  and  ether  dissolve  it,  but  acquire 
no  acid  reaction  on  litmus  until  water  is  added.  Anhydrous  phosphoric 
acid  is  occasionally  employed  in  chemistry  for  the  purpose  of  dehydrating 
liquids  by  distillation.  At  high  temperatures  it  is  decomposed  by  charcoal, 
and  by  several  of  the  metals.  It  combines  with  hydrate  of  lime  to  form  a 
hard  cement,  which  has  been  used  for  stopping  teeth.     The  acid  consists  of: — 

Phosphorus 

Oxygen   .... 


Atoms. 

Equiv. 

Per  cent. 

.     1 

32 

44-4 

.     5 

40 

55-6 

Phosphoric  acid       ...     1  72  100-0 

Mr.  Graham  has  shown  that  phosphoric  acid  occurs  in  three  peculiar  or 
isomeric  conditions,  which  may  be  designated,  1.  Metaphosphoric  acid,  or 
a  phosphoric  acid  ;  aPO^ :  2.  Pyrophosphoric  acid,  or  h  phosphoric  acid  ; 
6PO5 :  3.  Common  phosphoric  acid,  or  c  phosphoric  acid  ;  cVO^  The  first 
combines  with  one,  the  second  with  two,  and  the  third  with  three  atoms  of 
water  or  base.  The  acid  is  regarded,  by  Graham,  as  the  same  in  all  these 
modifications,  which  are  supposed  to  depend  upon  the  proportion  of  water 
or  base  with  which  it  is  in  union  :  so  that  c<PO,  may  become  iPOg  by  the 
acquisition  of  a  second  atom  of  water  or  of  base,  and  cPO,  by  a  third  ;  and 
inversely  cPOgby  losing  an  atom  of  base  or  of  water,  becomes  hVO^,  and  this 
by  the  further  abstraction  of  base  or  basic  water,  passes  into  aPOg,  and 
aPOg  losing  its  single  equivalent  of  water  or  base  reverts  to  PO5.  In  ac- 
cordance with  this  view,  phosphoric  acid  intimately  combined  with  one  atom 
of  water,  only  allows  of  the  replacement,  by  substitution,  of  that  atom  of 
water  by  one  atom  of  base  :  but  if  the  original  acid  be  similarly  united  with 
two  or  three  atoms  of  water,  these  are  then  replaced  by  two  or  three  atoms 
of  base. 

PO5HO.  Protohydrate  or  Monobasic  Phosphoric  Acid;  Metaphosphoric 
Acid. — Aqueous  solutions  of  any  of  the  modifications  of  phosphoric  acid, 
when  evaporated  and  heated  until  they  cease  to  lose  water,  yield  the  proto- 
hydrate, in  the  form  of  what  has  been  termed  glacial  phosphoric  acid.  In 
this  state  it  contains  11-2  per  cent,  of  water,  which  cannot  be  expelled  by 
heat.  When  the  acid  is  kept  in  solution  in  water,  ^t  slowly  combines  with  two 
additional  atoms  and  becomes  a  terhydrate.  When  phosphate  of  ammonia, 
is  heated  to  expel  the  alkaline  base,  this  acid  remains  as  a  glassy-looking 
residue.  The  white  anhydrous  phosphoric  acid  procured  by  burning  phos- 
phorus in  dry  air  or  oxygen,  when  dissolved  in  water  forms  a  solution  of  the 
protohydrate.  It  is  characterized  by  producing  a  white  precipitate  in  a, 
solution  of  albumen  ;  and  in  solutions  of  baryta,  lime,  and  oxide  of  silver,  it 
gives  peculiar  white  precipitates  like  soft  solids,  without  crystallization. 
These  compounds  contain  one  atom  of  base  to  one  of  acid. 

P05,2HO.  Bihydrate  or  Bibasic  Phosphoric  Acid.  Pyrophosphoric 
Acid. — When  a  solution  of  pyrophosphate  of  soda  (obtained  by  heating  the 
phosphate  to  full  redness)  is  precipitated  by  acetate  of  lead,  and  the  insoluble 
salt  of  lead  is  washed  and  decomposed  by  sulphuretted  hydrogen,  an  acid 
liquid  is  obtained,  which  must  be  left  in  a  shallow  basin  until  the  sulphuretted 
hydrogen  has  escaped ;  it  is  then  an  aqueous  solution  of  pyrophosphoric 
acid.  It  yields  the  pyrophosphate,  when  neutralized  by  carbonate  of  soda  ; 
gives  a  white  precipitate  with  nitrate  of  silver  ;  and  forms  salts,  all  of  which 
have  two  atoms  of  base.  The  acid,  before  neutralization,  does  not  pre- 
cipitate solutions  of  nitrate  of  silver  or  of  baryta,  and  it  does  not  precipitate 
16 


242  PHOSPHORIC    AOID.      CHEMICAL    PROPERTIES. 

albumen.  A  diluted  solution  of  this  bihydrate  of  phosphoric  acid  may  be 
preserved  without  change  ;  but  when  it  is  boiled  for  some  time,  it  passes 
into  the  terhydrate.  Graham  and  Peligot  obtained  this  acid,  not  however 
quite  free  from  terhydrate,  by  evaporating  the  solution  of  the  terhydrate  in 
a  platinum  flask,  until  its  temperature  attained  416°.  It  appeared  as  a  soft 
glass.  Peligot  obtained  it  in  opaque  imperfect  crystals  resembling  grape 
sugar. 

POgjSHO.  Terhydrate  or  Trihasic  Phosphoric  Acid.  Common  Phosphoric 
Acid. — The  common  phosphate  of  soda  yields  this  acid,  when  a  solution  of 
the  salt  is  precipitated  by  acetate  of  lead,  and  the  phosphate  of  lead  is 
decomposed  by  sulphuretted  hydrogen  ;  but  it  is  generally  procured  by 
oxidizing  phosphorus  with  nitric  acid.  The  acid  must  be  diluted  with 
three  parts  of  water  in  order  to  prevent  too  violent  an  action.  Portions  of 
phosphorus  are  introduced  into  a  Florence  flask  and  covered  with  the  acid 
and  water.  The  mixture  is  heated  carefully,  and  as  soon  as  red  fumes 
appear,  the  heat  is  reduced,  and  the  action  is  allowed  to  proceed  (3P-f 
5N05=3P05-i-6N02).  When  the  acid  is  saturated,  the  liquid  is  evapo- 
rated, and  the  surplus  nitric  acid  is  expelled.  It  is  finally  concentrated  to 
a  syrupy  state  in  a  platinum  dish.  When  dissolved  in  water,  it  forms  the 
ordinary  solution  of  phosphoric  acid,  A  solution  of  the  terhydrate  may  be 
prepared  by  boiling  the  monohydrate  in  diluted  nitric  acid.  The  conversion 
is  rapid  in  a  diluted  solution,  and  no  bihydrate  appears  to  be  formed.  The 
nitric  acid  in  this  case  appears  to  act  by  catalysis  (page  58). 

In  solution,  it  is  very  acid,  but  not  corrosive,  so  that  when  heated  on 
paper,  the  paper  is  not  carbonized.  It  gives  no  precipitate  with  a  solution 
of  albumen  or  nitrate  of  baryta,  or  with  a  solution  of  nitrate  of  silver ;  but 
when  united  with  a  base,  it  gives  with  the  latter  salt,  a  yellow  precipitate. 
It  precipitates  a  solution  of  pure  lime,  but  readily  dissolves  the  precipitate, 
if  the  acid  is  added  in  excess.  When  heated  to  400°  it  loses  water,  and 
becomes  a  mixture  of  proto  and  bihydrate  ;  but  it  cannot  be  made  anhydrous 
by  heat,  as  it  is  volatilized  in  the  state  of  protohydrate  below  *a  red  heat. 
If  kept  below  this  temperature,  it  is  entirely  converted  into  protohydrate. 
Conversely,  the  proto  and  bihydrate,  when  kept  for  some  time  in  solution  in 
water,  take  one  and  two  equivalents  of  water,  and  are  ultimately  converted 
into  the  terhydrate.  This  change  is  rapid  when  the  aqueous  solutions  are 
weak  and  submitted  to  a  boiling  temperature,  or  when  a  little  nitric  acid  is 
added.  The  acid  liquid 'will  no  longer  precipitate  albumen,  and  when 
neutralized  by  an  alkali,  it  will  give  a  yellow  precipitate  with  nitrate  of 
silver.  In  general,  water  in  combining  wuth  anhydrous  acids  in  more  than 
one  equivalent,  does  not  alter  the  properties  of  the  acid.  Thus  there  are 
three  hydrates  of  sulphuric  acid,  but  all  have  similar  properties.  In  reference 
to  phosphoric  acid,  the  protohydrate,  in  its  reactions  on  albumen  and  on  a 
solution  of  nitrate  of  silver,  is  wholly  different  from  the  terhydrate  ;  and  the 
bihydrate  difl'ers  from  both. 

The  only  impurity  likely  to  be  found  in  this  acid,  when  made  according  to 
the  method  above  described,  is  nitric  acid.  This  may  be  detected  by  the 
usual  tests  (page  177).  If  any  phosphorous  acid  is  present,  it  may  be 
detected  by  warming  a  portion  with  a  solution  of  sulphurous  acid.  In  this 
case,  there  will  be  a  precipitation  of  sulphur  ;  and  if  arsenic  is  present,  it  will 
be  under  similar  circumstances  thrown  down  as  yellow  sulphide  of  arsenic. 

The  constitution  of  the  three  hydrates  of  phosphoric  acid  may  be  thus 
represented : — 


TESTS    FOR    SOLUBLE    PHOSPHATES.  243 

Mouobasic.  Bibasic.  Tribasic. 


Atoms.    Weights.  Per  cent.  Atoms.     Weights.     Per  cent.    Atoms.   Weights.   Per  cent. 

Phosphoric  acid  1  72        88-8        1  72  80  1  72        72-72 

Water      .         .    1  9        11-2        2  18  20  3  27        27-2^ 


1  81       100-0        1  90  100  1  99       100-00 

Phosphoric  acid  has  less  aflfinity  for  bases  than  the  sulphuric,  at  ordinary 
temperatures,  but  as  it  is  more  fixed,  it  will  expel  the  sulphuric  acid  from 
the  sulphates  at  a  high  temperature. 

Phosphates. — Each  of  the  above  hydrates  of  phosphoric  acid  forms  a 
distinct  class  of  salts,  namely,  metaphos^. hates,  which  are  monobasic  ;  pyro- 
phosphates, which  are  bibasic  :  and  common  phosphates,  which  are  tribasic  ; 
so  that  the  proportion  of  fixed  base  with  which  the  acid  unites  in  the  humid 
way,  is  dependent  upon  the  proportion  of  water  which  the  fixed  base 
replaces.  Thus,  the  metaphosphoric  acid,  or  protohydrate,  will  only  combine 
with  one,  and  the  pyrophosphoric  or  deutohydrate  with  two  equivalents  of 
soda ;  and  if  in  either  case  a  larger  quantity  of  base  be  added,  it  remains 
uncombined  :  so  also  in  regard  to  the  terhydrate  ;  if  to  one  equivalent  of  it 
in  solution,  one  equivalent  of  soda  is  added,  one  equivalent  only  of  its  water 
isdisplacedandtwoare retained:  3(HO)P05  +  NaO=NaO,2(HO)P05  +  HO. 
On  the  addition  of  a  second  equivalent  of  soda,  a  second  atom  of  basic  water 
is  displaced,  the  salt  therefore  still  remaining  characteristically  tribasic  ;  for 
in  this  case,  NaO,2(HO)P03+NaO,  becomes  2(NaO)HO,P05+HO  ;  and 
lastly,  the  addition  of  a  third  equivalent  of  soda  displaces  the  remaining  atom 
of  water,  and  we  have  an  anhydrous  tribasic  phosphate  of  soda  :  2(NaO)HO, 
POg  +  NaO  =  3(NaO)P05+HO.  So  also  in  regard  to  the  insoluble  phos- 
phates formed  by  precipitation  :  the  monobasic,  or  metaphosphate  of  soda, 
decomposes  one  equivalent  of  nitrate  of  silver,  and  a  white  monobasic  phos- 
phate of  silver  is  thrown  down:  NaO,P05-f-AgO,NOs=AgO,P05-fNaO, 
KO5.  On  the  other  hand,  the  bibasic  salt,  or  pyrophosphate  of  soda,  decom- 
poses two  equivalents  of  nitrate  of  silver  to  form  a  white  bibasic  phosphate 
of  silver  :  2(NaO)P03+2[AgO,N03]  =  2(AgO)P05+2[NaO,N03].  And, 
lastly,  one  equivalent  of  the  tribasic  phosphate  of  soda  decomposes  three 
equivalents  of  nitrate  of  silver,  forming  one  equivalent  of  the  yellow  or  common 
phosphate  of  silver,  and  three  of  nitrate  of  soda.  3(NaO)P05-f  SfAgO, 
NOJ=3(AgO)P03+3[NaO,NO,]. 

^  The  phosphates  which  are  soluble  are  easily  recognized  by  the  addition  of 
nitrate  of  silver.  A  yellow  precipitate  is  thrown  down.  When  acetate  of 
lead  is  added  to  the  solution,  a  white  precipitate  of  phosphate  of  lead  is 
formed,  and  this  is  not  soluble  in  an  excess  of  the  phosphate.  For  neutral 
solutions  the  following  plan  may  be  adopted  :  Precipitate  a  solution  of  sul- 
phate of  magnesia,  and  add  sufficient  chloride  of  ammonium  to  redissolve 
the  magnesian  precipitate.  This  liquid  added  to  the  solution  of  a  phos- 
phate, even  when  much  diluted,  produces  a  white  crystalline  precipitate  of 
phosphate  of  ammonia  and  magnesia,  insoluble  in  ammonia  and  chloride 
of  ammonium,  but  soluble  in  nitric  and  acetic  acids.  This  precipitate, 
when  collected,  dried,  and  calcined,  is  thus  constituted :  2(MgO)P05.  In 
the  absence  of  arsenic  acid,  it  serves  for  the  detection  and  estimation  of 
phosphoric  acid.  In  an  acid  solution  of  a  phosphate  the  perchloride  of  iron 
is  a  useful  reagent,  not  merely  for  the  detection,  but  for  the  separation  of 
phosphoric  acid.  Add  to  the  diluted  solution  of  a  phosphate,  acetate  of 
soda  and  a  few  drops  of  a  solution  of  perchloride  of  iron — a  pale  reddish- 
brown  precipitate  of  phosphate  of  iron  is  thrown  down.  This  precipitate  is 
not  soluble  in  acetic  acid,  but  is  dissolved  by  the  hydrochloric  and  some 
othef  acids,  hence,  before  the  test  is  employed,  it  is  advisable  to  nearly 


244  COMPOUNDS    OF    PHOSPHORUS    AND    HYDROGEN. 

neutralize  the  solutioD.  The  precipitation  is  rendered  more  complete  by 
boiling  the  liquid. 

An  insoluble  phosphate  (lime)  should  be  first  dissolved  in  diluted  nitric 
acid.  The  acid  solution  gives  a  gelatinous  or  flocculent  white  precipitate  of 
phosphate  of  lime,  when  the  acid  is  neutralized  by  ammonia.  It  is  insoluble 
in  alkalies.  If  nitrate  of  silver  is  added  to  another  portion  of  the  acid 
liquid,  and  then  a  few  drops  of  a  weak  solution  of  ammonia,  the  presence  of 
phosphoric  acid  is  indicated  by  the  production  of  a  yellow  precipitate  of  phos- 
phate of  silver.  The  whole  of  the  phosphoric  acid  may  be  obtained  from  an 
insoluble  phosphate,  by  dissolving  it  in  diluted  hydrochloric  acid,  nearly 
neutralizing  the  solution  with  ammonia,  and  then  adding  to  it  acetate  of 
soda  with  a  suffijcient quantity  of  perchloride  of  iron  to  give  a  reddish  color 
to  the  liquid.  On  boiling  the  liquid,  the  whole  of  the  phosphoric  acid  is 
precipitated  in  combination  with  the  oxide  of  iron. 

The  Pyrophosphates  give  white  precipitates  with  solutions  of  nitrate  of 
silver  and  acetate  of  lead.  The  lead-precipitate  is  dissolved  by  an  excess  of 
the  Solution  of  pyro-phosphate.  When  a  pyrophosphate  is  added  to  a  solu- 
tion of  albumen,  and  the  liquid  is  acidulated  with  acetic  acid,  there  is  no 
precipitate.  The  metaphosphates  have  the  characters  assigned  to  metaphos- 
phoric  acid  (page  241).  They  precipitate  the  salts  of  baryta,  lead,  and 
silver.  The  white  salt  of  silver  is  soluble  in  an  excess  of  metaphosphate, 
in  which  respect  it  differs  from  the  pyrophosphate. 

Phosphorus  and  Hydrogen.  {Phosphide  of  Hydrogen). — Phosphorus 
forms  three  compounds  with  hydrogen,  one  gaseous,  PH3 ;  one  liquid,  PHg ; 
and  one  solid,  P3H.  The  gaseous  compound  is  that  which  is  best  known  as 
%  highly  combustible,  and  in  some  cases  spontaneously  inflammable  gas. 
This  spontaneous  inflammability  is  not,  however,  a  property  of  the  pure  gas; 
but  it  depends  on  the  admixture  of  the  vapor  of  the  liquid  compound,  which 
is  generated  at  the  same  time.  It  is  the  spontaneous  combustion  of  this 
vapor  in  air,  which  renders  the  phosphuretted  hydrogen,  associated  with  it, 
inflammable. 

The  pure  phosphuretted  hydrogen  may  be  procured  by  acting  on  phosphide 
of  calcium  with  strong  hydrochloric  acid.  As  thus  procured,  it  is  a  colorless 
gas,  having  a  fetid  odor  resembling  that  of  onions  or  garlic.  Some  have 
compared  it  to  the  small  of  putrid  fish.  It  is  soluble  in  water  and  alcohol. 
Water  will  take  up  about  one-eighth  of  its  volume.  The  gas  has  no  alkaline 
reaction.  Although  combustible  at  a  comparatively  low  temperature,  212° 
(Regnault),  it  does  not  burn  spontaneously  in  air,  unless  it  is  mixed  with 
the  vapor  of  the  second  compound.  In  this  case,  it  burns  with  a  bright 
white  light,  producing  solid  phosphoric  acid  and  water. 

The  mixed  compound,  containing  the  inflammable  vapor,  was  for  a  long 
time  considered  to  be  the  true  phosphuretted  hydrogen  gas.  It  was  dis- 
covered by  Gengembre,  in  1783,  while  the  uninflammable  variety  was  first 
made  known  by  Davy,  in  1812.  The  spontaneously  inflammable  gas  is  pre- 
pared by  heating  phosphorus  in  a  very  strong  solution  of  potassa,  a  little 
ether  being  placed  in  the  retort,  to  prevent  an  accident  from  explosion,  when 
the  gas  is  first  produced.  The  gas  does  not  burn  in  the  vapor  of  ether.  The 
changes  which  take  place  in  its  production  may  be  thus  represented  :  3K0-f 
4P  +  3HO=PH3-f-3(KO,PO).  It  may  be  collected  over  water,  and  pre- 
served in  bottles  in  a  dark  place  for  more  than  a  week,  still  retaining  its 
property  of  spontaneous  inflammability.  If  exposed  to  light,  the  vapor  of 
the  liquid  PH3  undergoes  decomposition,  and  it  is  resolved  into  a  solid 
phosphide  of  a  yellowish  color,  and  into  the  non-inflammable  gas.  This 
vapor  may  be  separated  from  the  gas,  by  passing  it  through  a  freezing  mix- 


INFLAMMABLE    PHOSPHURETTED    HYDROGEN.  245 

ture.  Tt  is  also  decomposed  by  hydrochloric  acid,  and  in  these  cases,  the 
gas  loses  the  property  of  spontaneous  inflammability. 

When  a  bubble  of  this  gas  escapes  into  the  air,  it  bursts  and  burns  with 
the  bright  white  light  of  phosphorus,  producing  an  expanding  wreath  of 
white  phosphoric  acid  vapor,  which,  as  it  slowly  dissolves  in  the  air,  may  be 
seen  to  be  composed  of  numerous  smaller  wreaths,  each  rapidly  revolving 
around  a  central  axis,  and  at  right  angles  to  the  expanding  horizontal 
wreath.  This  motion  appears  to  be  dependent  on  the  heated  currents  of  air 
carrying  the  solid  particles  of  phosphoric  acid  in  their  course.  PH3,PH3+ 
0^5=2P05+5HO.  Bubbles  passed  into  ajar  of  oxygen  or  of  protoxide  of 
nitrogen,  burn  with  a  brilliant  light.  In  chlorine,  they  burn  with  a  pale 
bluish  light  forming  perchloride  of  phosphorus.  In  nitrogen,  deutoxide  of 
nitrogen,  and  carbonic  acid  there  is  no  combustion.  When  the  gas  is  passed 
into  a  solution  of  ammonio-nitrate  of  silver  it  is  absorbed,  and  the  solution 
blackened  from  the  reduction  of  the  silver. 

A  quantity  of  this  gas  suddenly  exposed,  explodes  with  oxygen  or  air, 
and  in  the  absence  of  sufBcient  oxygen  for  perfect  combustion,  red  oxide  of 
phosphorus  is  deposited  in  the  vessel.  The  gas  is  frequently  mixed  with 
free  hydrogen.  This  may  be  detected  by  a  solution  of  sulphate  of  copper, 
which  dissolves  the  phosphuretted  hydrogen  only.  It  is  also  absorbed  by  a 
solution  of  chloride  of  lime. 

It  has  been  long  known  that  whether  spontaneously  inflammable  or  not, 
the  gas  had  the  same  composition,  a  fact  which  is  now  intelligible,  as  the 
property  is  an  accidental  result  of  the  admixture  of  another  phosphide  in 
vapor.  Gay-Lussac  and  Thenard  found  that  one  volume  of  this  gas,  when 
decomposed  by  chlorine,  gave  three  volumes  of  hydrochloric  acid.  This 
proved  that  each  volume  contained  one  and  a  half  volumes  of  hydrogen,  or 
two  volumes  of  the  compound  contained  three  of  hydrogen.  The  removal 
of  the  phosphorus  from  the  gas  by  copper  and  potassium,  establishes  the 
accuracy  of  these  volumetric  proportions.  The  weight  of  phosphorus  in  each 
volume  is  found  by  deducting  one  and  a  half  times  the  specific  gravity  of 
hydrogen  from  the  ascertained  specific  gravity  of  the  gas.  This  is  as  nearly 
as  possible  equal  to  one-fourth  the  specific  gravity  of  phosphorus- vapor ; 
hence  one  quarter  of  a  volume  of  phosphorus-vapor  is  combined  v/ith  one 
and  a  half  volume  of  hydrogen,  in  each  volume  of  phosphuretted  hydrogen  : 
or  one  half  volume  with  three  of  hydrogen,  in  two  volumes  of  the  gas. 
Some  chemists  prefer  doubling  the  volumes — thus  making  one  volume  of 
phosphorus-vapor  to  be  associated  with  six  volumes  of  hydrogen — the 
seven  volumes  being  condensed  into  four.  Its  composition  will,  therefore, 
stand  thus : — 

Atoms.       Equiv.         Per  cent.  Vol.  Sp.  Gr. 

Phosphorus        .    1     ...     32     ...     91-43     ...      J     ...     2-1777 
Hydrogen  .         .     3     ...       3     ...       8-57     ...     3       ...     0-2073 


1  35  100-00  2  2-3850 

The  sum  of  the  sp.  gr.  divided  by  2  gives  1*1925.  The  specific  gravity 
of  the  gas  is  commonly  represented  to  be  1*1850  compared  with  air;  and 
com.pared  with  hydrogen  17 '5.  It  will  be  perceived  that  the  gas  has  some 
analogy  in  its  volumetric  constitution  to  ammonia,  but  it  has  not  the  alka- 
line properties.  It  forms,  however,  solid  crystalline  compounds  with  the 
hydriodic  and  hydrobromic  acids.  The  constitution  of  this  gas  shows  that 
the  atoms  of  elements  are  not  necessarily  represented  by  single  volumes  ; 
and  those  of  compounds  by  two  volumes.  On  the  former  view,  the  atomic 
volume  of  phosphuretted  hydrogen  would  be  equal  to  four  volumes  of  the 


246      COMPOUNDS    OF    PHOSPHORUS    WITH    NITROGEN,    CHLORINE, 

compound  ;  and  on  the  latter  view,  the  atom  of  phosphorus  must  necessarily 
be  represented  by  half  a  volume  {see  page  68). 

Phosphuretted  hydrogen  does  not  change  the  color  of  paper  impregnated 
with  a  salt  of  lead ;  but  it  immediately  decomposes  solutions  of  silver  and 
gold,  the  metals  being  reduced  by  it  to  the  metallic  state.  The  gas  is  ab- 
sorbed and  decomposed  by  these  solutions.  Thus  the  nitrate  of  silver 
forms  a  good  test  for  the  presence  of  this  compound.  When  passed  through 
a  tube  heated  to  redness,  the  gas  is  decomposed. 

Liquid  Phosphide  of  Hydrogen  (PHg). — This  is  procured  by  distilling 
fragments  of  phosphide  of  calcium  with  water  only,  and  collecting  the  pro- 
duct in  a  receiver,  kept  cool  by  a  freezing  mixture.  The  phosphide  thus 
procured  is  a  most  inflammable  liquid.  It  takes  fire  in  air,  and  burns  with 
a  brilliant  light.  It  is  colorless,  highly  refracting,  and  insoluble  in  water. 
It  remains  liquid  at  — 4^  ;  is  destroyed  by  a  temperature  of  86°,  and  when 
exposed  to  light  is  resolved  into  solid  phosphide  and  non-inflammable  phos- 
phuretted hydrogen  :  5PH2=P2H-f  3PH3.  When  its  vapor  is  mixed  with 
hydrogen  it  renders  this  gas  spontaneously  inflammable  in  air.  It  is  decora- 
posed  by  strong  hydrochloric  acid,  and  by  oil  of  turpentine.  When  phos- 
phide of  calcium  is  put  into  water,  gaseous  phosphuretted  hydrogen,  with 
the  vapor  of  liquid  phosphide,  escapes,  and  burns  in  the  air  with  great 
brilliancy.  The  bubbles  of  gas  are  similar  to  those  which  are  evolved,  by 
boiling  phosphorus  in  a  strong  solution  of  potassa. 

Solid  Phosphide  0/ Hydrogen  (F 2^). — This  is  analogous  in  constitution 
to  the  oxide,  hydrogen  being  substituted  for  oxygen.  It  may  be  procured 
by  exposing  to  light  the  liquid  compound,  or  the  spontaneously  inflammable 
gas.  It  is  of  a  yellow  color,  has  an  odor  of  phosphorus,  but  is  not  luminous 
in  the  dark.  It  is  reddened  by  light.  It  is  insoluble  in  water  and  alcohol. 
It  is  not  inflamed  in  air  under  a  temperature  of  320°. 

Phosphorus  and  Nitrogen. — A  compound  of  these  metalloids  was  an- 
nounced by  Rose  under  the  formula  N^P.  He  procured  it  by  saturating 
the  pure  terchloride  of  phosphorus  at  a  low  temperature  with  ammonia. 
The  white  substance  thus  obtained,  when  heated  to  redness  out  of  contact  of 
air,  left  a  light  white  powder  insoluble  in  water,  alcohol,  and  ether.  When 
excluded  from  air  and  moisture,  it  is  fixed  and  infusible  at  a  red  heat, 
although  its  constituents  are  volatile.  When  heated  in  contact  with  air  and 
moisture,  it  evolves  white  fumes  of  phosphoric  acid,  and  becomes  slowly 
oxidized  without  inflaming.  Heated  on  platinum,  it  corrodes  the  metal,  and 
converts  it  into  a  phosphide.  According  to  Gerhardt,  it  contains  hydrogen, 
and  is  in  reality  an  amide  of  phosphorus,  NH^P,  or  Phosphamide. 

Phosphorus  and  Chlorine. — There  are  two  compounds  of  these  ele- 
ments, a  terchloride  corresponding  to  phosphorous  acid  j  and  a  pentachloride 
corresponding  to  phosphoric  acid. 

Terchloride  of  Phosphorus  (PCI3). — This  compound,  which  is  liquid, 
is  procured  by  distilling  a  mixture  of  phosphorus  and  chloride  of  mercury  ; 
or,  by  passing  the  vapor  of  phosphorus  over  chloride  of  mercury  heated  in 
a  glass  tube,  terminating  in  a  cool  receiver.  This  liquid  dissolves  phos- 
phorus, and  generally  holds  a  little  in  solution,  which  gives  to  it  a  reddish 
color.  When  purified  by  slow  distillation,  it  becomes  limpid  and  colorless  ; 
it  requires  to  be  cautiously  excluded  from  the  action  of  the  air.  It  has  a 
suff'ocating  odor.  Its  specific  gravity  is  1*45.  Exposed  to  the  air  it  is  vola- 
tile, and  exhales  acid  fumes  :  it  does  not  change  the  color  of  dry  vegetable 
blues,  but  becomes  powerfully  acid  upon  the  least  acquisition  of  moisture. 


BROMINE,   IODINE,    AND    SULPHUR.  24T 

Its  vapor  is  combustible.  It  has  a  sp.  ^r.  of  4*742  ;  3  vols,  of  chlorine  are 
combined  with  5  vol.  of  phosphorus  to  form  2  vols,  of  the  vapor.  Chlorine 
converts  it  into  pentachloride  of  phosphorus.  It  acts  upon  water  with  j]rreat 
energy,  and  produces  phosphorous  and  hydrochloric  acids,  PCl34-3HO  = 
PO3  +  3HCI. 

Pentachloride  of  Phosphorus  (PCI5). — When  dry  phosphorus  is  sub- 
mitted to  the  action  of  chlorine  in  excess,  it  burns  with  a  pale  yellow  flame, 
and  produces  a  white,  flaky,  volatile  and  deliquescent  compound,  which 
attaches  itself  to  the  interior  of  the  vessel,  and  which  is  i\iQ  pentachloride 
of  phosphorus.  It  may  be  conveniently  formed  in  an  exhausted  retort,  con- 
taining phosphorus,  to  which  chlorine  is  admitted  until  the  phosphorus  is 
saturated.  It  was  formerly  mistaken  for  phosphoric  acid,  but  its  easy 
volatility  is  alone  a  sufficient  distinction,  for  it  rises  in  vapor  at  200^.  It  is 
fusible  under  pressure,  and  crystallizable  in  transparent  prisms;  it  is  a  non- 
conductor of  electricity;  it  reddens  dry  litmus-paper,  in  consequence,  as 
Berzelius  supposes,  of  its  acquiring  hydrogen  and  oxygen  from  the  decom- 
position of  the  paper.  It  fumes  in  the  air,  and  when  brought  into  contact 
with  water,  a  mutual  decomposition  immediately  takes  place,  and  phosphoric 
and  hydrochloric  acids  result.  PClg-f  5H0  =  P05+5HC1.  It  is  combustible, 
and  produces  chlorine  and  phosphoric  acid  by  its  combustion.  When  passed 
through  a  red-hot  porcelain  tube  with  oxygen,  phosphoric  acid  is  produced, 
and  chlorine  is  evolved ;  these  facts  show  that  oxygen,  at  a  red  heat,  has  a 
stronger  attraction  for  phosphorus  than  chlorine.  Potassium,  heated  in  its 
vapor,  burns  with  great  brilliancy:  with  dry  sulphuretted  hydrogen  it  yields 
hydrochloric  acid  and  chloro-sulphide  of  phosphorus;  PCl5+2HS=PS2Cl3 
-i- 2HCI.  Metallic  oxides  decompose  it  with  the  production  of  metallic 
chlorides  and  phosphates.  The  vapor  has  a  sp.  gr.  of  3 '66.  It  consists  of 
one-half  vol.  of  phosphorus  and  5  vols,  of  chlorine  condensed  into  4  vols,  of 
the  compound. 

There  is  an  oxychloride,  PCI3O3,  which  requires  no  particular  notice. 

Phosphorus  and  Bromine. — There  are  two  bromides  of  phosphorus — a 
liquid  and  a  solid — corresponding  to  the  two  chlorides  (PBr3,PBr5).  The 
elements  combine  on  contact  with  explosive  violence,  hence  great  caution 
should  be  used  in  preparing  these  compounds. 

Phosphorus  and  Iodine. — Iodine  combines  with  phosphorus  on  contact, 
producing  combustion  when  the  mixture  is  exposed  to  air.  There  are  two 
iodides,  a  biniodide,  PI3,  and  a  teriodide,  PI3.  They  are  both  solid  and 
crystalline  ;  they  may  be  procured  by  dissolving  the  constituents  in  their 
equivalent  proportions  in  sulphide  of  carbon,  and  cooling  the  solutions. 

Phosphorus  and  Sulphur. — These  elements  combine,  according  to 
Pelouze  and  Fremy,  to  form  five  diflferent  compounds,  four  of  them  corres- 
ponding to  the  four  oxygen-compounds  of  phosphorus — sulphur  being 
substituted  for  oxygen.  Besides  these,  there  is  the  persulphide  PS^,  to 
which  there  is  no  analogous  oxygen  compound.  Sulphur  and  phosphorus 
may  be  combined  by  fusion  in  an  atmosphere  of  carbonic  acid,  but  great 
caution  should  be  used,  as  with  common  phosphorus  a  violent  explosion 
may  occur.  The  phosphorus  should  be  melted  under  water,  and  the  sulphur 
gradually  added  in  small  fragments.  Phosphorus  will  thus  combine  with  a 
large  quantity  of  sulphur  without  losing  its  liquid  state.  Sulphur  or  phos- 
phorus may  be  obtained  in  crystals  from  this  mixture  on  cooling,  according 


248  CARBON. 

to  whether  one  or  the  other  happens  to  be  in  excess.  Amorphous  phos- 
phorus may  be  fused  with  sulphur  under  these  circumstances,  without  giving 
rise  to  an  explosion,  although  there  is  a  violent  action  when  fusion  takes 
place.     (Kekule.) 


CHAPTEH  XIX. 

CARBON    AND    ITS   COMPOUNDS    WITH    OXYGEN.     CARBONIC 
OXIDE.     CARBONIC  ACID. 

The  carbon  group  of  metalloids  comprises  three  bodies — carbon,  boron, 
and  silicon.  Carbon  is  the  great  constituent  of  the  organic,  and  silicon  of 
the  inorganic  kingdom.  Boron  is  not  found  among  organic  products,  and 
is  only  sparingly  diffused  in  the  mineral  kingdom.  These  bodies  do  not 
enter  into  combination  with  each  other  ;  but  they  have  certain  characters  in 
common.  They  exist  either  in  a  crystalline  or  amorphous  state  ;  in  the 
latter  state,  they  assume  the  form  of  black  or  dark-colored  solids,  which  may 
be  heated  in  close  vessels  without  change,  but  undergo  combustion  and  oxi- 
dation when  heated  in  the  air.  Carbon  entirely  disappears  as  a-  gaseous 
acid  (carbonic  acid),  while  boron  and  silicon  are  converted  into  white 
fusible  solids  (boracic  and  silicic  acids).  These  three  bodies  cannot  be  made 
to  assume  the  vaporous  condition,  although  they  readily  combine  with  other 
metalloids  to  form  gaseous  compounds.  As  a  summary  of  their  characters, 
they  are  chiefly  remarkable  for  being  in  the  crystalline  state  intensely  hard ; 
and  in  the  amorphous  state,  insoluble,  and  fixed  at  the  highest  temperatures. 
Carbon  is  infusible,  but  boron  and  silicon  may  be  fused  at  a  very  high 
temperature. 

Carbon  (C=6). 

History. — Carbon  is  found  in  various  states  which  are  considered  to  be 
allotropic  modifications  of  the  same  elementary  substance,  but  widely 
differing  from  each  other  in  appearance  and  physical  properties.  In  its 
purest  form,  it  constitutes — 1,  diamond,  which  is  crystallized  carbon.  In 
a  less  pure  state,  it  is  seen  in — 2,  plumbago,  or  graphite;  3,  as  anthracite  ; 
and  4,  as  coke,  the  carbon  of  coal.  The  state  in  which  it  is  most 
commonly  seen  is — 5,  as  charcoal,  derived  either  from  animal  or  vegetable 
matter. 

All  these  varieties  agree  in  the  fact  that  when  heated  to  a  high  tempe- 
rature in  oxygen  or  air,  they  undergo  combustion  and  are  converted  into 
carbonic  acid.  The  combustibility,  however,  varies  greatly  with  the  molecular 
condition  of  the  carbon.  Tinder,  the  carbon  of  linen  or  cotton,  is  easily 
ignitable,  and  when  once  ignited,  combustion  spreads  readily  throughout  the 
mass  ;  but  a  piece  of  wood  charcoal  or  coke,  if  ignited,  is  soon  extinguished 
on  exposure  to  air.  Animal  charcoal,  in  consequence  of  its  hardness,  and 
the  very  large  quantity  of  mineral  matter  associated  with  it,  burns  with 
difficulty.  Plumbago  and  diamond,  owing  to  their  compact  texture,  require 
to  be  heated  to  a  very  high  temperature  in  pure  oxygen,  before  they  will 
readily  undergo  combustion.  The  diamond  finely  powdered,  may,  however, 
be  burnt  by  heating  it  on  red-hot  platinum  ;  diamond  dust  heated  with 
sulphuric  acid  and  bichromate  of  potassa,  is  said  to  be  completely  converted 
into  carbonic  acid.     (Rogers.) 


DIFFUSION    OF    CARBON.      PROPERTIES    OF    DIAMOND.  249 

Carbon  is  essentially  the  element  of  the  organic  kingdom.  All  organic 
substances,  or  those  which  have  been  produced  under  the  influence  of  life, 
contain  it.  It  constitutes  nearly  half  the  weight  of  the  dried  animal  or 
vegetable  substance.  In  the  vegetable  kingdom,  it  forms  the  skeleton  of  the 
plant  or  tree — a  fact  which  is  made  evident  to  us  by  the  perfect  preservation 
of  form,  when  the  substance  has  been  heated  out  of  contact  with  air.  The 
detection  of  carbon  in  the  residues  of  substances  heated  to  redness  in  close 
vessels,  is  properly  relied  upon  as  the  best  evidence  of  the  presence  of 
organic  matter.  Carbon  is,  however,  an  important  constituent  of  the  mineral 
kingdom.  Apart  from  its  crystalline  forms  in  diamond  and  plumbago,  it  is 
found  as  anthracite,  bituminous  coal,  and  lignite,  in  vast  deposits  in  the 
earth.  Limestone,  marble,  chalk,  and  coral  contain  carbon  (in  a  combined 
state  as  carbonic  acid)  in  the  proportion  of  about  twelve  per  cent,  of  their 
weight ;  and  in  the  atmosphere,  carbonic  acid  (which  contains  twenty-seven 
per  cent,  by  weight  of  carbon)  is  universally  found.  There  is  reason  to 
believe  that  it  is  through  this  medium  that  carbon  finds  its  way  into  the 
vegetable  structure ;  and  that  the  oxygen  associated  with  it  is  restored  to 
the  atmosphere  to  be  again  converted  by  animals  into  carbonic  acid.  Carbon 
is  also  present,  as  carbonic  acid,  in  rain,  spring,  and  river-water. 

Diamond  (d5a/*aj,  signifying  hardness). — This  substance  has  been  found 
in  India,  Borneo,  the  Brazils,  and  Siberia.  Diamonds  have  hitherto  been 
met  with  in  detached  crystals,  in  alluvial  soils,  associated  with  rolled  quartz- 
pebbles,  sand,  and  a  ferruginous  clay.  They  are  obtained  by  simply  washing 
the  soil ;  their  great  specific  gravity  facilitating  their  separation  from  the 
light  sand  and  clay.  Diamonds  are  now  chiefly  procured  from  the  district  of 
Serra  do  Frio,  in  the  province  of  Minas  Geraes,  in  the  Brazils. 

The  primitive  form  of  the  diamond  is  a  regular  octahedron,  each  triangular 
facet  of  which  is  sometimes  replaced  by  six  secondary  triangles,  bounded  by 
curved  lines  ;  so  that  the  crystal  becomes  spheroidal,  and  presents  forty-eight 
facets.  Diamonds,  with  twelve  and  twenty-four  facets,  are  not  uncommon. 
The  diamond  has  been  found  of  various  colors;  those  which  are  colorless  are 
most  esteemed  ;  then  those  of  a  decided  red,  blue,  yellow,  pink,  or  green 
tint.  Those  which  are  brown  are  least  valuable.  Three-fourths  of  the 
stones  found  are  tinged  with  some  color,  mostly  pale  yellow  or  yellow 
brown. 

The  fracture  of  the  diamond  is  foliated,  its  laminae  being  parallel  to  the 
sides  of  a  regular  octahedron.  Although  the  hardest  of  bodies,  it  is  brittle, 
and  is  easily  broken  when  struck  in  its  planes  of  cleavage,  which  are  four, 
corresponding  to  the  octahedral  sides.  Its  specific  gravity  varies  from  3 '5 
to  3'6  :  it  is  most  commonly  3'52.  Its  specific  heat  is  O'l  192.  Itis  a  non- 
conductor of  electricity,  and  acquires  positive  electricity  by  friction.  It  con- 
ducts heat  so  much  better  than  glass,  that  this  property  is  sometimes  employed 
as  a  test,  to  distinguish  the  diamond  from  substances  which  resemble  it. 
It  exerts  a  highly  refractive  power  on  light :  compared  with  glass  or  rock- 
crystal  it  is  2 '47  to  I'Q.  When  exposed  for  some  time  to  strong  sunshine, 
it  becomes,  by  insolation,  luminous  in  the  dark.  The  strongest  alkalies  and 
acids,  including  the  fluoric  acid,  whether  singly  or  in  mixture,  have  no  effect 
upon  it.  The  fluoric  acid,  however,  dissolves  and  destroys  artificial  or  paste 
diamonds.  With  the  exception  of  oxygen  the  metalloids,  including  fluorine, 
have  no  action  upon  it ;  and  oxygen  will  only  combine  with  it  at  a  very  high 
temperature.  Its  combustibility  was  first  proved  in  1694.  It  requires  a 
most  intense  heat  to  effect  this.  It  may  be  burnt  in  a  vessel  of  pure  oxygen 
by  concentrating  upon  it  the  solar  rays,  or  by  heating  it  in  the  flame  of  the 
oxy-hydrogea  blowpipe,  and  then   introducing  it   into  a  bell-jar  of  pure 


250      PHYSICAL    AND    CHEMICAL    PROPERTIES    OP    THE    DIAMOND. 

oxygen.  In  the  atmosphere,  however  heated,  it  will  cease  to  burn  so  soon 
as  the  current  of  air  is  withdrawn.  It  has  been  clearly  proved  that  carbonic 
acid  is  the  sole  product  of  this  combustion,  and  that  equal  weights  of  pure 
carbon  and  diamond  yield  the  same  quantity.  The  diamond,  like  other  kinds 
of  carbon,  deflagrates  with  melted  nitrate  of  potassa,  and  produces  carbonate 
of  potassa  During  its  combustion  in  oxygen,  it  evolves,  without  flame,  a 
bright  light,  which  is  even  visible  in  sunshine  ;  and  it  occasionally  leaves  a 
slight  incombustible  residue.  Some  diamonds  have  been  entirely  consumed 
in  oxygen ;  others  have  left  a  residue  of  silica  and  oxide  of  iron,  varying 
from  0"15  to  0*2  per  cent,  of  their  weight — a  quantity  so  small,  that  it  may 
be  regarded  as  an  accidental  impurity.  The  black,  or  carbonic  diamond 
{carbona),  found  at  Bahia,  in  Brazil,  in  1843,  when  burnt,  leaves  a  larger 
residue.  Three  samples  left  respectively  residues  weighing  0-24,  027,  and 
3  03  per  cent,  of  their  weight.  (Dumas.)  The  sp.  gr.  of  this  variety  of 
diamond,  which  is  chiefly  used  for  making  polishing  powder,  is  from  3"1  to 
3 "43.  It  is  the  diamond  in  an  amorphous  state,  quite  opaque,  and  varying 
in  color  from  iron-gray  to  reddish-black.  In  two  years,  four  thousand  ounces 
were  extracted  in  Bahia. 

When  a  diamond  is  heated  on  charcoal  in  the  arc  of  fire  from  a  powerful 
voltaic  battery,  it  softens,  cracks,  increases  in  size,  becomes  black,  and  assumes 
the  appearance  of  coke.  Its  sp.  gr.  is  reduced  from  3  3  to  2*6.  In  this 
state  it  is  a  conductor  of  electricity  :  it  scratches  glass,  but  is  so  brittle  that 
it  can  be  broken  between  the  fingers.  The  effect  of  intense  heat  in  thus 
destroying  the  transparency  and  completely  changing  the  molecular  condition 
of  the  diamond,  appears  to  show  that  this  substance,  as  it  is  found  in  nature, 
has  not  been  exposed  to  a  high  temperature  in  its  production.  All  attempts 
to  fuse  or  crystallize  carbon,  or  to  form  diamonds  artificially,  have  hitherto 
failed.  Some  suppose  that  the  carbon  of  diamond  is  of  organic  origin  ;  but 
all  that  we  can  surmise  is,  that  it  has  been  crystallized  from  some  unknown 
solvent,  defiant  gas,  sulphide  of  carbon  and  chloroform  are  colorless  com- 
pounds of  this  element,  and  it  is  remarkable  that  the  two  latter,  which  are 
liquid,  have  great  weight  and  have  a  high  refracting  power  with  the  lustre  of 
diamond.  The  sulphide  of  carbon  contains  one-sixth  of  its  weight,  and 
chloroform  one-tenth  of  its  weight  in  combination.  The  sulphide  readily 
dissolves  sulphur,  which  may  be  obtained  crystallized  from  it,  but  it  has  no 
solvent  action  on  carbon.  If  sulphur  and  chlorine  could  be  slowly  removed 
from  these  compounds,  the  carbon  might  be  deposited  in  crystals.  As  it  is, 
when  these  or  other  gaseous  and  liquid  compounds  are  decomposed  the  car- 
bon always  assumes  the  black  or  amorphous  condition  of  finely-divided  char- 
coal. There  is  reason  to  believe  that  all  crystallized  diamonds  found  native 
have  been  deposited  from  a  state  of  solution.  According  to  Mr.  Lionnet,  by 
the  decomposition  of  sulphide  of  carbon  by  a  weak  voltaic  current  in  which 
platinum  and  tin  were  the  metals  used,  he  obtained  carbon  in  crystals  at  the 
bottom  of  the  vessel  while  the  sulphur  combined  with  the  tin.  The  diamond 
is  not  always  found  crystallized  in  a  regular  form.  Sometimes  the  substance 
has  presented  only  a  crystalline  structure,  at  others,  as  in  the  black  diamond, 
it  has  been  found  amorphous,  having  the  appearance  of  intensely  hard  black 
charcoal. 

The  art  of  cutting  and  polishing  diamonds,  though  probably  of  remote 
antiquity  in  Asia,  was  first  introduced  into  Europe  in  1456,  by  Louis  van 
Berquen,  of  Bruges,  who  accidentally  discovered  that,  by  rubbing  two 
diamonds  together,  a  new  surface  or  facet  was  produced.  The  forms  which 
are  given  to  the  polished  diamond  are  the  brilliant  and  the  rose.  The  bril- 
liant form,  which  has  from  56  to  64  facets,  was  first  introduced  by  Cardinal 
Mazarin,  in  1650.     It  is  especially  calculated  to  bring  out  the  lustre  and 


PLUMBAGO.       GRAPHITE.      BLACK    LEAD.  251 

refractive  powers  of  the  p^em.  Thus  a  well-cut  brilliant,  held  in  a  beam  of 
light,  reflects  nearly  the  whole  of  the  light  which  falls  upon  it,  throwing  it 
out  and  refracting  it  in  colored  rays  through  the  facets  in  front.  With  the 
exception  of  one  small  point  of  light  through  the  collet,  the  brilliant  forms 
an  opaque  shadow  on  a  screen. 

The  diamond  appears  to  be  unchangeable,  and  the  most  indestructible  of 
substances.  The  Koh-i-Noor,  said  to  have  been  discovered  in  1550,  and  now 
among  the  British  crown  jewels,  had  undergone  no  apparent  alteration  in 
brilliancy  or  polish  after  the  lapse  of  three  hundred  years.  The  weight  and 
value  of  diamonds  is  usually  estimated  in  carats,  of  which  150  are  about 
equal  to  one  ounce  troy,  or  480  grains ;  ^.  e.,  each  carat  is  equivalent  to  32 
grains.  The  Koh-i-Noor,  when  first  discovered,  is  stated  to  have  weighed 
900  carats.  It  lost  by  the  first  cutting  279  carats,  and  it  has  been  consider- 
ably reduced  by  its  having  been  recently  cut  into  the  shape  of  a  brilliant. 
Its  weight  is  now  said  to  be  102  carats.  The  Russian  diamond,  the  Koh-i- 
Toor,  weighs  193  carats,  but  in  consequence  of  its  irregular  shape,  its  value 
is  small  in  proportion  to  its  weight.  Probably  the  finest  diamond  in  the 
world,  for  its  water,  shape,  and  size,  is  the  Pitt  diamond,  now  among  the 
crown  jewels  of  France.  It  was  discovered  in  1702,  and  was  purchased  in 
the  rough  state  by  Mr.  Pitt,  governor  of  Bencoolen.  In  1717,  it  was  sold 
to  the  Regent  Duke  of  Orleans,  during  the  minority  of  Louis  XV.,  for  the 
Bum  of  135,000/.  It  was  cut  into  the  form  of  a  perfect  brilliant,  and  proved 
to  be  of  the  finest  water,  without  color  or  flaw.  It  weighed,  before  cutting, 
410  carats,  and  after  cutting,  136.  The  chips  and  dust  obtained  from  it 
were  valued  at  8000^.  In  1791  a  commission  of  jewellers  assigned  its  value 
at  480,000/.  It  is  remarkable  that  these  three  large  diamonds  were  found  in 
the  same  district  of  Central  India.  The  cutting  and  polishing  of  diamonds 
is  chiefly  carried  on  at  Amsterdam. 

Apart  from  its  use  in  ornamental  jewelry,  the  diamond  is  employed  in 
the  arts.  Owing  to  its  hardness,  it  is  found  a  useful  substance  for  the  pivot- 
holes  of  watches.  It  has  been  employed  for  microscopic  lenses,  and  it  is 
extensively  used  for  cutting  glass.  The  edge  of  one  of  the  small  curvilinear 
crystals  is  selected  for  this  purpose,  as  the  edges  of  the  crystals  formed  by 
flat  planes,  only  scratch  the  surface  without  producing  that  peculiar  fissure 
by  which  the  glass  can  be  smoothly  cut. 

The  diamond  possesses  none  of  the  ordinary  properties  of  carbon,  as  they 
are  known  in  charcoal.  This,  no  doubt,  depends  on  the  different  molecular 
states  of  the  two  bodies. 

Plumbago,  Graphite.  Black  Lead. — This  substance  is  well  known 
in  the  manufacture  of  pencils,  for  which  purpose  it  is  almost  exclusively 
obtained  from  the  mine  of  Borrowdale,  at  the  west  end  of  Derwent  Lake, 
in  Cumberland,  where  it  was  first  wrought  during  the  reign  of  Elizabeth. 
In  a  less  pure  state,  it  is  not  an  uncommon  mineral,  occurring  in  detached 
masses,  generally  in  primitive  rocks.  It  is  thus  found  in  Germany,  France, 
India,  Ceylon,  and  North  and  South  America.  It  is  of  an  iron-gray  color, 
metallic  lustre,  and  soft  and  greasy  to  the  touch,  producing  a  leaden  mark 
on  paper.  Its  specific  gravity  varies  from  19  to  25  ;  it  occasionally  occurs 
crystallized  in  hexagonal  plates ;  it  conducts  electricity,  and,  for  this 
purpose,  is  much  used  in  the  electrotype  process.  It  is  infusible,  very 
difficult  of  combustion,  and,  when  mixed  with  fire-clay,  is  a  useful  ingredient 
in  the  manufacture  of  crucibles  and  melting-pots  intended  to  withstand  high 
temperatures.  It  undergoes  no  change  in  air,  and  is  used  to  cover  articles 
of  iron  to  prevent  them  from  rusting.  When  it  is  burned  in  a  stream  of 
oxygen  gas,  it  leaves  a  small  quantity  of  yellow  ash,  composed    chiefly  of 


252  VARIETIES    OF    COAL.      COKE. 

oxide  of  iron,  with  silica  and  titanic  acid,  but  varying  in  quantity  in  different 
specimens.  In  good  plumbago,  the  carbon  amounts  to  96  per  cent.  Some 
specimens  from  Brazil  leave  scarcely  any  residue  when  burnt.  The  oxide  of 
iron  is  an  incidental  ingredient,  and  is  not  in  chemical  combination  with 
carbon.  It  exists  in  no  definite  proportion.  The  late  Mr.  Brockedon  found 
that  the  dust  of  plumbago  might  be  forced,  under  great  pressure  (like  spongy 
platinum),  into  a  coherent  mass,  which  might  be  cut  and  applied  to  the  same 
uses  as  the  pure  native  substance. 

Cast-iron,  after  corrosion,  as  a  result  of  long  immersion  in  sea-water, 
acquires  the  softness,  greasiness,  and  some  other  physical  characters  of  plum- 
bago. The  cannon-balls  and  cast-iron  guns  of  the  Royal  George,  sunk 
at  Spithead,  presented  this  condition  after  many  years'  submersion  in  sea- 
water.  A  mass  of  cast-iron,  which  had  been  immersed  some  years  in  a 
brewer's  vat,  had  a  loose  and  spongy  structure,  and  was  so  soft  that  it  could 
be  cut  with  a  knife.  It  appears  from  analysis  that,  in  this  transformation, 
the  greater  portion  of  the  iron  is  removed,  and  the  carbon  largely  predomi- 
nates. The  durability  of  cast-iron  piers,  sunk  in  sea-water,  may  be  affected 
by  this  change. 

Mr.  Brodie  has  found  that  plumbago  is  remarkably  altered  in  its  chemical 
and  physical  properties,  when  it  is  heated  with  sulphuric  acid  and  chlorate 
of  potassa. 

Carbon  op  Coal. — The  principal  constituent  of  coal  is  carbon,  associated 
with  variable  proportions  of  oxygen  and  hydrogen,  as  well  as  with  small 
quantities  of  sulphur  and  nitrogen.  The  British  caking  or  bituminous  coals, 
including  those  of  Northumberland,  Nottinghamshire,  and  South  Wales, 
have  a  sp.  gr'.  of  about  1*2  ;  and  according  to  Dr.  Percy,  they  contain  from 
"IT  to  83"44  per  cent,  of  carbon.  The  British  non-caking  coals  contain  from 
72  to  80  per  cent,  of  carbon  ;  while  cannel  coals  contain  78  to  84  per 
cent.  (Percy,  Metallurgy,  p.  99.)  All  kinds  of  coal  yield  an  ash  consisting 
of  silica,  oxide  of  iron,  and  lime.  In  good  coal  this  varies  from  one  to  three 
per  cent,  of  its  weight.  In  the  bituminous  schists,  such  as  the  Torbane 
mineral,  miscalled  coal,  the  ash  amounts  to  25  per  cent  of  the  weight  of  the 
substance. 

The  chief  characters  of  good  coal  are  that  it  is  a  black,  brittle,  combustible 
substance,  containing  a  large  amount  of  carbon,  of  which  it  will  yield  about 
half  of  its  weight,  under  the  form  of  coke,  when  it  is  heated  out  of  contact 
of  air.  The  amount  of  mineral  ash  which  is  left,  after  perfect  combustion, 
is  small,  and  does  not  interfere  with  the  use  of  the  substance  for  heating 
purposes. 

In  Lignite,  or  wood  coal,  which  forms  one  end  of  the  coal  series,  the 
shape  and  structure  of  the  wood  are  preserved.  In  Bituminous,  or  pit-coal, 
the  vegetable  structure  is  in  great  part  lost,  probably  as  a  result  of  heat  and 
compression.  Anthracite,  or  stone-coal,  called  also  mineral  charcoal,  contains 
a  larger  proportion  of  carbon  than  the  other  varieties.  It  is  very  heavy, 
having  a  specific  gravity  of  1-4  to  1"8,  and  has  no  resemblance  whatever  to 
wood.  It  is  well  known  as  the  culm  of  Wales,  and  the  Kilkenny  coal  of 
Ireland.  It  has  a  slight  metallic  lustre,  is  very  difficult  of  combustion,  so 
that  it  will  burn  only  in  a  strong  current  of  air  ;  and  when  ignited  it  is 
consumed  without  flame,  smell,  or  smoke.  We  have  found  good  Kilkenny 
anthracite,  to  leave  only  4*4  per  cent,  of  a  reddish-brown  ash,  consisting 
chiefly  of  oxide  of  iron  and  silica,  so  that  this  coal  might  be  considered  as 
mineral  carbon  in  a  state  nearly  pure.  It  constitutes  the  other  extreme  of 
the  coal  series. 

Coke. — This  is  the  carbonaceous  residue  of  the  distillation  of  pit-coal. 


PREPARATION    OF    CHARCOAL.  253 

It  is  manufactured  on  a  large  scale  in  ovens  constructed  for  the  purpose 
The  bituminous  coal  of  Northumberland  yields  66  per  cent.  ;  and  that  of 
Nottinghamshire,  63  per  cent,  of  coke.  Non-caking  and  cannel  coals  yield 
rather  less.  Coke  has  a  sp.  gr.  of  r6  to  2,  but  in  equal  bulks  it  is  about 
one-half  the  weight  of  coal.  It  has  a  porous  texture,  and  sometimes  a 
metallic  lustre.  This  is  owing  to  the  glazing  or  fusion  of  the  ashes  upon  the 
surface.  It  is  difficult  of  combustion  except  in  large  masses,  and  under  a 
rapid  current  of  air.  Small  pieces,  when  removed  from  the  fire  red-hot,  are 
soon  extinguished.  It  contains  sulphur,  and  yields,  by  combustion,  sul- 
phurous acid.  If  quenched  with  water  while  red-hot,  sulphuretted  hydrogen 
is  produced  by  the  decomposition  of  the  water.  It  exceeds  all  fuels  in  the 
amount  of  heat  which  it  evolves  by  combustion.  Next  to  hydrogen,  there 
is  no  body  which  consumes  so  large  an  amount  of  oxygen  as  carbon ;  but 
coke  gives  a  more  powerful  and  steady  heat  than  wood-charcoal,  hence  it  is 
largely  employed  as  a  fuel  in  furnaces.  It  will  evaporate  14  times  its 
weight  of  water.  The  harder  the  coke,  the  greater  is  its  value  as  fuel. 
Dry  coke  does  not  absorb  aqueous  vapor  like  charcoal.  It  will  not  take  up 
more  than  from  1  to  2^  per  cent,  in  a  humid  atmosphere  ;  but  perfectly  dry 
coke,  placed  in  water,  will  absorb  this  liquid  to  the  extent  of  half  of  its 
weight.  1000  parts  of  dry  coke,  according  to  Berthier,  consists  of  carbon, 
^8;  ashes,  115  ;  volatile  matters,  -027.  Good  coke  should  not  yield  more 
than  4  or  5  per  cent,  of  ash.  Certain  hard  kinds  will  yield  from  10  to  15 
per  cent,  of  their  weight. 

Charcoal. — Preparation. — Charcoal  may  be  obtained  either  from  vege- 
table or  animal  substances.  In  order  to  procure  it,  it  is  necessary  that  the 
organic  matter  should  be  heated  to  a  high  temperature  out  of  contact  of  air. 
If  an  ordinary  splint  of  wood  be  burnt  in  air,  the  carbon  is  entirely  con- 
sumed, and  a  white  alkaline  ash  remains.  If  a  similar  splint  ignited,  is  gradually 
lowered  into  a  narrow  test-tube,  allowing  only  a  slow  combustion  to  go  on 
at  the  mouth  of  the  tube,  a  skeleton  of  the  wood  in  charcoal  will  be  obtained. 
Introduce  between  two  layers  of  mica  a  slip  of  paper,  and  place  a  similar 
slip  on  the  outside  of  the  mica.  When  heat  is  applied  beneath,  the  piece 
of  paper  which  is  protected  from  air  will  be  converted  into  charcoal,  while 
that  which  is  exposed  will  be  consumed,  leaving  only  a  slight  ash.  If  a 
sheet  of  paper,  or  a  portion  of  lace,  impregnated  with  a  solution  of  phosphate 
of  ammonia  is  dried  and  burnt  in  air,  the  carbon  of  the  vegetable  matter  is 
obtained,  retaining  its  perfect  form  {see  page  236).  Charcoal  may  be  pre- 
pared for  chemical  purposes,  by  heating  to  redness,  in  a  crucible,  pieces  of 
boxwood,  covered  with  sand,  and  keeping  them  in  that  state  for  about  an 
hour,  or  until  all  volatile  matters  are  expelled.  They  are  thus  converted 
into  a  black,  brittle,  porous  substance,  which  appears  to  be  essentially  the 
same,  from  whatever  kind  of  wood  it  has  been  procured.  The  stick  of  char- 
coal, when  broken,  should  be  equally  black  throughout.  Sugar  and  certain 
other  substances,  which  neither  contain  nitrogen  nor  leave  any  residue  after 
combustion,  when  intensely  heated  in  closed  vessels,  yield  a  pure  charcoal ; 
it  always  retains,  however,  traces  of  oxygen  and  hydrogen ;  thus,  Erdmann 
and  Marchand  found  in  the  carbon  of  sugar  obtained  at  a  white  heat,  3'1 
per  cent,  of  oxyygen,  and  0*6  of  hydrogen,  and  even  after  it  had  been  sub- 
jected for  three  hours  to  the  highest  temperature  of  a  blast-furnace,  it  retained 
0*5  per  cent,  oxygen,  and  0*2  hydrogen.  In  passing  the  vapors  of  certain 
hydrocarbons,  and  of  oils,  alcohol,  and  ether,  through  white-hot  porcelain 
tubes,  pure  carbon  is  deposited.  A  variety  of  pure  carbon  is  occasionally 
found  in  coal-gas  retorts,  and  in  the  tubes  connected  with  them,  resulting 
from  the  decomposition  of  the  first  products  of  the  distillation  of  coal.  It 
has  a  gray  color,  and  often  exhibits  a  laminated  texture  ;  its  streak  is  black, 


264  INFLUENCE  OF  TEMPERATURE. 

and  it  breaks  with  an  earthy  fracture  :  its  specific  gravity  is  about  IS.  It 
sometimes  happens  that  the  gas  escapes  through  a  crack  in  the  retort,  in 
which  case  a  peculiar  carbonaceous  deposit  is  forming  upon  the  surrounding 
brickwork,  of  a  stalactitic  character,  an  iron-gray  color,  and  considerable 
lustre  ;  it  does  not  easily  burn,  nor  does  it  soil  the  fingers.  Some  specimens, 
from  their  appearance,  might  be  considered  to  be  metallic  ;  its  specific  gravity 
is  about  1-75. 

Common  charcoal,  employed  as  fuel,  is  usually  made  of  oak,  chestnut,  elm, 
beech,  or  ash-wood,  the  resinous  woods  being  seldom  used.  Young  wood 
afifords  a  better  charcoal  than  large  timber,  which  is  also  too  valuable  to  be 
thus  employed.  The  billets  are  formed  into  a  conical  pile,  which,  being 
covered  with  earth  or  clay,  is  suffered  to  burn  with  a  limited  access  of  atmo- 
spheric air,  by  which  its  complete  combustion,  or  reduction  to  ashes,  is  pre- 
vented. Another,  and  a  more  perfect  mode  of  preparing  charcoal,  consists 
in  submitting  the  wood  to  a  red  heat  in  a  kind  of  distillatory  apparatus, 
consisting  of  cast-iron  cylinders,  from  which  issue  one  or  more  tubes  for  the 
escape  of  gaseous  matters  and  vapors.  This  kind  of  charcoal  is  preferred 
for  the  manufacture  of  gunpowder.  A  third  method  of  charring  wood  con- 
sists in  exposing  it  to  the  action  of  highly  heated  steam,  by  which,  according 
to  Violette  {Ann.  Ck.  et  Ph.^  3me  ser.,  xxiii.  475),  different  modifications 
of  charcoal  may  be  obtained,  especially  adapted  for  the  manufacture  of  gun- 
powder. In  another  memoir  upon  the  same  subject  {Ibid.,  xxxii.  346),  M. 
Yiolette  arrives  at  the  following  conclusions :  1.  That  the  quantity  of  char- 
coal obtained  from  wood  decreases  in  proportion  as  the  temperature  in- 
creases. At  482^  the  average  product  of  charcoal  is  50  per  cent.  ;  at  572^ 
33  per  cent. ;  at  752°,  about  20  per  cent.  ;  and  at  the  temperature  of  fusing 
platinum  about  15  per  cent.  2.  The  quantity  of  charcoal  varies  with  the 
duration  of  the  process  of  carbonization,  and  is  greatest  when  the  process  is 
slowly  carried  on.  3.  The  normal  carbon  of  the  wood  is  divided  during 
carbonization  into  two  parts,  one  of  which  remains  in  the  charcoal,  and  the 
other  escapes  with  the  volatile  products.  This  division  varies  with  the  tem- 
perature of  carbonization  ;  thus,  at  482°  the  carbon  remaining  in  the  char- 
coal is  double  that  which  escapes :  between  572°  and  662°  the  two  portions 
are  equal,  and  at  a  high  temperature  the  quantity  which  escapes  is  double 
that  which  remains.  4.  The  charcoal  retains  a  quantity  of  carbon  propor- 
tionate to  the  temperature  of  carbonization ,  at  482°  it  includes  65  per  cent, 
of  carbon  ;  at  572°,  73  per  cent. ;  at  752°,  80  per  cent.  ;  and  carbonized  at 
a  higher  temperature  it  contains  96  per  cent,  of  carbon,  but  at  no  tempera- 
ture is  the  product,  carbon,  in  a  state  of  purity.  5.  Charcoal,  however  pre- 
pared, always  retains  gaseous  matter,  varying  with  the  temperature  of  its 
preparation  ;  when  made  at  482°  it  amounts  to  half  the  weight  of  the  char- 
coal ;  at  572°  to  one-third  ;  at  662°  to  one-fourth  ;  at  752°  to  one-twentieth  ; 
and  at  the  highest  temperatures  to  about  one  one-hundredth.  The  preceding 
facts  show  the  great  influence  of  temperature,  and  of  the  duration  of  the 
carbonizing  process,  upon  the  produce  of  charcoal  from  the  same  wood. 
6.  When  wood  is  carbonized  in  perfectly  close  vessels,  the  resulting  charcoal 
retains  nearly  the  whole  amount  of  carbon ;  when  thus  charred,  at  between 
300°  and  660°,  the  percentage  of  carbon  in  the  charcoal  is  about  80,  which 
is  thrice  that  contained  in  charcoal  prepared  in  the  usual  way.  7.  In  ordi- 
nary carbonization,  the  so-called  brown  charcoal  {Charbon  ronx)  is  not  ob- 
tained under  518°,  and  the  quantity  amounts  to  about  40  per  cent ;  but  in 
a  perfectly  air-tight  vessel  the  quantity  obtained  is  90  per  cent.,  and  the 
temperature  at  which  it  is  formed  is  356°.  8.  Wood,  inclosed  in  a  perfectly 
air-tight  vessel,  and  subjected  to  a  temperature  of  from  572°  to  752°,  under- 
goes a  species  of  fusion  ;  it  agglutinates  and  adheres  to  the  vessel  j  on  cool- 


PROPERTIES    OP    CHARCOAL 


255 


ing,  it  has  lost  all  organic  texture,  and  is  a  black,  shining,  porous,  fused 
mass,  exactly  resembling  pit-coal  which  has  undergone  serai-fusion.  This 
seems  to  explain  the  formation  of  coal.  9.  Charcoal  made  in  perfectly  close 
vessels  contains  ten  times  more  ash  than  common  charcoal,  so  that  the  vola- 
tile matters  which  escape  during  the  ordinary  process  of  carbonization  or 
distillation,  carry  with  them,  either  blended  or  combined,  a  large  proportion 
of  the  mineral  substances  which  constitute  the  ashes.  10.  Charcoal,  pre- 
pared in  the  ordinary  way,  varies  much  in  quality  and  composition,  in  con- 
sequence of  the  variation  in  temperature  and  time  consumed  in  the  process 
of  charring.  The  position  of  the  pieces  of  wood  in  the  cylinders,  namely, 
whether  central  or  external,  in  reference  to  their  contents,  affects  its  quality, 
a  matter  of  much  inconvenience  in  the  manufacture  of  gunpowder.  Char- 
coal obtained  by  the  action  of  highly  heated  steam,  is  of  a  more  uniform 
character  than  that  which  is  produced  as  a  result  of  partial  combustion  in  a 
stack. 

The  quantity  and  quality  of  charcoal  obtained  from  different  kinds  of  wood 
are  liable  to  much  variation,  according  to  the  temperature  and  mode  of 
charring.  The  following  table  shows  the  produce  of  charcoal  fronii  1000  parts 
of  several  varieties  of  dense  and  light  woods  after  exposure  to  a  very  high 
temperature  out  of  contact  of  air. 


Ebony  . 

Botany  Bay-wood 
Brazil-wood  . 
Eveoas-wood 
King-wood  . 
Tulip-wood  . 
Satin-wood  . 


305 

281 
260 
225 
220 
208 
207 


Box      .        .        . 

202 

Fir        .         .         . 

181 

Lignum-vitae 

175 

Oak      . 

174 

Mahogany     . 

157 

Beech  .         .         .         , 

150 

The  ashes  left  by  charcoal  after  complete  combustion,  vary  in  quantity 
with  the  kind  of  wood  from  which  it  has  been  procured.  Ordinary  charcoal 
used  as  fuel  leaves,  on  an  average,  2  per  cent,  of  ashes,  consisting  chiefly  of 
carbonate  of  potash,  silica,  lime,  and  oxide  of  iron.  The  results  of  experi- 
ments on  this  subject  have  shown  that  1000  parts  of  charcoal  from  the  wood 
of  the  lime-tree  yield  of  ashes  50  parts  ;  the  charcoal  of  the  oak,  25  ;  of  the 
birch,  10  ;  of  the  fir-tree,  8 ;  of  the  hornbeam,  26 ;  and  of  the  beech,  30 
parts.  There  is  a  great  loss  of  carbon  in  the  ordinary  methods  of  preparing 
charcoal.  Thus,  assuming  that  green  wood  contains  38 '5  per  cent,  of  this 
element,  the  most  perfect  processes  of  carbonization  do  not  give  a  product 
greater  than  27  or  28  per  cent.,  and  the  common  plan  adopted  in  forests  is 
so  wasteful  that  not  more  than  17  to  18  per  cent,  are  obtained.  The  loss 
is  occasioned  partly  by  the  production  of  carburetted  hydrogen,  and,  as  a 
result  of  combustion,  carbonic  acid  ;  and  partly  by  the  formation  of  tar  and 
acetic  acid. 

Properties. — Wood-charcoal  is  a  black,  amorphous,  insoluble,  inodorous, 
insipid,  opaque,  and  brittle  substance.  It  preserves  the  form  of  the  wood, 
is  very  porous,  containing  much  air,  and  has  a  ringing  metallic  sound.  Its 
pores  may  be  injected  and  made  visible  by  cooling  it  when  red-hot  under 
mercury.  Unlike  the  diamond,  it  is  a  good  conductor  of  electricity,  but  a 
bad  conductor  of  heat,  especially  when  in  the  state  of  powder.  It  is 
unchanged  by  the  combined  action  of  air  and  moisture  at  common  tempe- 
ratures. It  is  easily  combustible  in  oxygen  gas.  Its  specific  heat,  as 
estimated  by  Regnault,  is  0  2411.  When  pure  it  is  perfectly  infusible  at 
all  known  temperatures;  in  the  cases  in  which  it  was  supposed  to  have  been 
fused,  the  fusion  was  owing  to  the  presence  of  silicates  in  the  ashes.  Under 
common  circumstances  of  ignition,  it  does  not  appear  to  volatilize,  but  it  is 
not  improbable  that  in  the  process  of  steel-making  the  penetration  of  iron 


256  ABSORPTION    OF    GASES    AND    VAPORS    BY    CHARCOAL. 

by  carbon  may  be  partly  due  to  its  volatility  ;  and  in  the  voltaic  ignition  of 
charcoal-points,  carbon  passes  from  the  positive  to  the  negative  side  in  the 
arc  of  flame  :  so  that  a  concavity  is  formed  upon  the  surface,  when  the  4- 
electricity  emanates,  and  a  deposit  of  carbon  upon  the  opposite  pole.  The 
intense  white  light  produced  in  the  passage  of  the  electric  fluid,  is  owing  to 
the  incandescence  of  the  minute  particles  of  carbon,  transferred  from  one 
pole  to  the  other.  In  air,  there  is  combustion,  but  when  the  experiment  is 
performed,  invacuo,  the  light  is  just  as  brilliant,  and  in  this  case,  it  must  be 
exclusively  due  to  incandescence.  The  speciflc  gravity  of  charcoal  is  about 
I'T.  It  readily  floats  on  water,  owing  to  the  large  quantity  of  air  within  its 
pores.  If  a  piece  of  charcoal,  after  having  been  heated  to  full  redness  for 
some  time,  is  suddenly  cooled  under  water,  it  will  acquire  its  proper  density 
and  sink.  Ordinary  charcoal,  sunk  in  a  jar  of  water  by  attaching  to  it 
sheet-lead,  will  be  found  to  yield,  in  vacuo,  a  large  quantity  of  air,  chiefly 
from  the  broken  ends.  Pieces  of  charcoal  placed  in  a  jar  full  of  water, 
inverted  in  a  basin,  will  give  out  a  large  portion  of  the  air  which  they  contain. 
When  strongly  heated  out  of  contact  of  air,  it  becomes  harder  and  closer  in 
texture,  and  is  rendered  a  better  conductor  of  heat  and  electricity.  AYhea 
heated  in  a  current  of  air,  it  is  consumed,  leaving  a  white  or  reddish-white 
ash  {see  p.  255).  Water,  alcohol,  ether,  hydrochloric  acid,  and  solutions  of 
chlorine  and  hydrofluoric  acid,  have  no  action  upon  it.  It  is  slightly 
dissolved  by  strong  sulphuric  acid,  giving  to  it  a  brownish  color  ;  and  by  the 
aid  of  heat  it  decomposes  njtric  acid.  It  is  this  indifference  to  chemical 
agents,  which  renders  charred  wood,  such  as  piles  sunk  in  the  earth,  inde- 
structible. Some  of  these  have  been  found  entire  after  the  lapse  of  many 
centuries. 

Newly-raade  charcoal  has  the  property  of  ahsorhing  and  fixing  gases  and 
vapors,  including  aqueous  vapor.  We  have  found  that  box-wood  charcoal 
increased  in  weight  14  per  cent,  within  24  hours.  The  average  increase 
from  this  absorption  is  from  10  to  12  per  cent.  The  researches  of  Saussure 
have  proved  that  different  gases  are  absorbed  by  charcoal  in  different  pro- 
portions, and  that  the  absorption  attains  its  maximum  in  24  hours.  Damp 
charcoal  does  not  absorb  gases  so  readily  as  that  which  is  dry.  If  charcoal 
is  heated  red-hot,  cooled  under  mercury,  and  then  introduced  into  a  graduated 
tube  containing  a  gas,  the  results  may  be  easily  observed  and  compared. 
Assuming  that  one  cubic  inch  of  charcoal  is  employed  in  the  experiment, 
then,  according  to  Saussure,  the  number  of  cubic  inches  of  each  gas  absorbed 
will  be  represented  by  the  figures  in  the  following  table  : — 


Ammonia 

.     90 

defiant  gas        .         .         .35- 

Hydrochloric  acid 

.     85 

Carbonic  oxide  .         .         .9-42 

Sulphurous  acid    . 

.     65 

Oxygen       .         .         .         .9-25 

Sulphuretted  hydrogen 

.     55 

Nitrogen     .         .         .         .     7'5 

Protoxide  of  nitrogen    . 

.     40 

Light  carburetted  hydrogen     5  • 

Carbonic  acid 

.     35 

Hydrogen  .         .        .         .1-75 

Saussure  appears  to  have  employed  in  his  experiments  boxwood  char- 
coal, and  charcoals  made  from  hard  and  dense  woods  appear  to  have  the 
greater  absorbing  powers.  Mr.  Hunter  experimented  with  charcoal  from 
logwood,  ebony,  boxwood,  and  the  hard-shell  of  the  cocoa-nut.  He  found 
the  latter  to  have  the  greatest  absorbing  power.  The  charcoal  is  very  dense 
and  brittle,  the  pores  are  quite  invisible,  and  when  broken  the  edges  present 
a  semi-metallic  lustre.  Vapors  are  also  absorbed,  but  the  absorption  power 
of  charcoal  ceases  sooner  in  them  than  in  the  true  gases. 

It  has  been  observed  that  the  temperature  of  the  charcoal  rises  as  a  gas 
is  condensed  within  its  pores.     When  charcoal,  already  saturated  with  any 


ABSORBING    POWER    OF    CHARCOAL.  251 

one  g:as,  is  put  into  another,  it  p:ives  out  a  portion  of  the  pras  already  ab- 
sorbed, and  takes  up  a  portion  of  the  new  gas.  It  would  also  appear  that 
this  absorptive  quality  partly  depends  upon  the  mechanical  texture  of  the 
charcoal,  and  consequently  varies  in  the  charcoals  of  different  woods.  Ac- 
cording to  Vogel,  when  recently-ignited  charcoal,  which  has  been  cooled 
under  mercury,  is  put  into  a  jar  of  atmospheric  air,  it  absorbs  the  oxygen  of 
the  air  to  a  greater  extent  than  the  nitrogen.  A  piece  of  well-burned  char- 
coal, cooled  under  sand,  and  then  introduced  into  a  mixture  of  oxygen  and 
sulphuretted  hydrogen  gases,  rapidly  absorbed  them  ;  it  then  became  ignited, 
and  caused  a  violent  explosion  which  shattered  the  bell-jar.  In  this  experi- 
ment, which  nearly  led  to  a  serious  accident,  a  yellow  vapor  appeared  to 
issue  from  the  pores  of  the  charcoal,  jnst  before  the  explosion  took  place. 
This  was  owing  to  the  separation  of  sulphur.  It  is  probable  that  the  sul- 
phuretted hydrogen  employed  w^as  mixed  with  some  free  hydrogen.  Thenard 
observed,  that  when  fresh  made  and  dry  charcoal  was  saturated  with  sul- 
phuretted hydrogen,  and  introduced  into  oxygen,  the  gases  combined,  with 
explosion,  and  water  and  sulphurous  acid  were  produced.  When  the  oxygen 
was  mixed  with  nitrogen,  the  effect  took  place  more  slowly,  and  the  hydrogen 
alone  was  consumed  ;  there  was  at  the  same  time  a  deposit  of  sulphur. 

This  property  of  charcoal  is  referred  to  catalysis  (p.  58).  It  resembles 
the  action  of  spongy  platinum  on  certain  mixtures  of  gases:  but  there  is 
this  difference  between  the  two  substances  :  Platinum  has  not  the  absorbent 
powers  on  gases  which  is  manifested  by  charcoal,  but  it  has  a  greater  com- 
bininff  power.  If  coarsely-powdered  wood-charcoal  is  boiled  in  a  solution 
of  chloride  of  platinum,  until  it  is  thoroughly  impregnated  with  the  liquid, 
and  is  then  heated  to  redness  in  a  covered  crucible,  it  will  retain  within  its 
pores  a  residue  of  platinum  :  this  substance  is  remarkable  for  its  powers  of 
absorption  and  combination. 

To  this  property  may  be  ascribed  the  power  which  charcoal  possesses  of 
absorbing  and  removing  foul  effluvia  {see  p.  229).  A  small  quantity  of 
powdered  charcoal  shaken  in  a  jar  of  air  containing  sulphuretted  hydrogen 
gas,  soon  removes  the  smell.  If  water,  containing  sul})huretted  hydrogen, 
is  filtered  through  charcoal,  it  is  speedily  deodorized.  The  gas  is  first 
absorbed,  and  by  a  catalytic  action,  the  oxygen  of  the  air  unites  to  the 
hydrogen,  while  sjilphur  is  deposited.  The  charring  of  the  interior  of  a 
cask,  intended  to  hold  water  for  use  at  sea,  has  a  similar  influence  on  foul 
water  put  into  it.  Sulphuretted  hydrogen  is  so  completely  removed,  that 
the  usual  tests  for  the  gas  will  fail  to  indicate  its  presence.  Pans  of  pow- 
dered charcoal  placed  about  a  room  in  which  there  are  foul  effluvia,  are  thus 
efficacious  in  removing  them.  Putrescent  animal  matter  is  deprived  of  its- 
offensiveness  by  covering  it  with  powdered  charcoal.  If  the  charcoal  should 
lose  its  power  by  long  use,  it  may  be  easily  restored  by  again  heating  it. 

Experiments  on  a  large  scale  have  been  performed  by  Dr.  Letheby  and 
Mr.  Haywood,  in  order  to  determine  how  far  charcoal  could  be  practically 
employed  for  destroying  the  effluvia  of  public  sewers.  Well-dried  charcoal, 
broken  to  the  size  of  a  filbert,  was  placed  in  trays  in  the  current  of  air  pro- 
ceeding from  a  sewer — it  thus  acted  as  an  air-filter.  The  result  was  most 
satisfactory ;  the  foul  effluvia  were  arrested  and  destroyed,  and  the  charcoal, 
after  from  nine  to  twenty  months'  use,  when  treated  with  water,  yielded  an 
abundance  of  alkaline  nitrate,  a  fact  which  proved  that  it  had  caused  the 
oxidation  of  nitrogen  in  ammonia  and  other  nitrogenous  compounds.  The 
absorbing  and  oxidizing  powers  of  charcoal  were  greatly  diminished  when 
it  was  saturated  with  water,  hence,  owing  to  the  absorption  of  moisture, 
the  sieves  required  changing  once  in  three  months.  If  the  charcoal  is  kept 
dry,  there  appears  to  be  no  limit  to  the  oxidizing  action,  of  this  substauce. 
17 


258  DEODORIZING    POWER    OF    CHARCOAL. 

There  can  be  no  doubt  from  these  experiments,  that,  by  a  proper  use  of 
powdered  charcoal,  the  noxious  effluvia  of  drains  and  sewers — the  vehicles 
of  typhoid  fever — may  be  prevented  from  entering  our  dwelling.  {Report 
to  Commissioners  of  Sewers,  Feb.  1862.) 

But  charcoal  has  not  only  the  power  of  removing  smells ;  it  will  also 
remove  colors,  and  even,  in  some  cases,  the  taste  of  liquids,  where  this 
depends  on  the  presence  of  certain  organic  substances.  Introduce  into  four 
bottles  containing  powdered  charcoal,  solutions  of  diluted  sulphate  of  indigo, 
of  cochineal,  of  the  blue  iodide  of  starch,  and  of  the  red  permanganate  of 
potassa.  Agitate  these  liquids  for  a  short  time  with  the  charcoal,  and  on 
filtration,  it  will  be  found  that  the  colors  are  entirely  removed.  Port-wine 
may  be  rendered  tawny  or  light  colored  by  a  similar  process,  thus  giving  to 
it  the  appearance  of  age.  Impure  solutions  of  sugar  and  of  nitre  lose  their 
colors  by  filtration  through  beds  of  charcoal — animal  charcoal  being  preferred 
for  this  purpose.  Other  impurities  which  interfere  with  the  crystallization 
of  these  substances  are  also  removed.  The  crystallizable  vegetable  acids 
and  alkaloids  are  thus  brought  to  a  high  state  of  purity,  but  not  always 
without  loss.  Mr.  Warington  observed  that  the  sulphate  of  quinia  was 
removed  from  its  solution  by  charcoal,  and  that  the  bitterness  of  the  hop 
may  be  entirely  removed  from  ale  by  this  substance,  in  the  attempt,  to  make 
dark-colored  ale  pale.  Strychnia  is  so  completely  removed  under  these 
circumstances,  that  Mr.  Graham  has  recommended  it  as  the  basis  of  a  process 
for  the  detection  of  strychnia  in  liquids  containing  organic  matter.  As  a 
medium  of  filtration,  therefore,  charcoal  is  eminently  qualified  to  purify  water. 
It  removes  color,  taste,  and  smell.  Charcoal  obtained  by  the  distillation  of 
peat,  or  of  spent  oak-bark,  used  in  tanning,  possesses  these  properties  in  an 
eminent  degree. 

Charcoal  has  a  great  deoxidizing  power,  even  at  low  temperatures.  Por- 
tions of  fresh-burnt  boxwood  charcoal,  free  from  ashes,  introduced  into 
nearly  neutral  and  very  diluted  solutions  of  gold,  platinum,  palladium,  silver, 
and  copper,  separate  the  respective  metals,  which  are  deposited  on  the  char- 
coal in  thin  films.  The  deposit  of  copper,  if  allowed  to  remain  in  the  liquid, 
soon  disappears.  At  a  red  heat,  charcoal  deoxidizes  many  fixed  and  volatile 
imetallic  oxides  (arsenious  acid),  reducing  them  to  the  metallic  state.  It  U 
tin  fact,  the  great  reducing  agent  of  metallurgists.  At  a  white  heat,  owing 
ito  its  fixedness,  it  deoxidizes  even  potassa,  soda,  and  phosphoric  acid,  setting 
free  in  vapor,  potassium,  sodium,  and  phosphorus.  It  also  decomposes 
water,  producing  carbonic  oxide  and  hydrogen  (water  gas).  When  the 
vvapor  of  water  is  passed  slowly  over  charcoal  heated  to  full  redness  in  a 
porcelain  tube,  or  when  an  incandescent  piece  of  charcoal  is  plunged  under 
a  jar  in  a  water-bath,  these  gases  are  evolved,  and  may  be  collected  :  (HO 
-4-C  =  H4-CO).  But  carburetted  hydrogen  and  carbonic  acid  are  also  pro- 
ducts of  this  decomposition.  Bunsen  found  that  in  100  parts  of  this  water- 
gas,  there  were  5603  hydrogen;  29'15  carbonic  oxide;  14*65  carbonic 
acid;  and  017  of  carburetted  hydrogen. 

Charcoal  produces  in  the  cold  a  violent  explosion  with  perchloric  acid  ; 
at  a  red  heat,  it  deoxidizes  the  chlorates,  perchlorates,  iodates,  and  nitrates 
with  deflagration,  producing  carbonates  with  the  respective  alkaline  bases. 
At  a  full  read  heat  it  converts  most  of  the  sulphates  to  sulphides.  It  has  no 
action  on  the  haloid  salts — namely,  the  chlorides,  bromides,  iodides,  and 
.fluorides,  and  it  does  not  decompose  at  a  high  temperature  silica,  magnesia  or 
alumina.  Its  combinations  with  metals  are  called  Carbides,  or  carburets. 
There  is  only  one  of  these  well  known — namely,  its  compound  with  iron  as 
cast-iron.  Carbon  is  found  as  an  impurity  in  aluminum,  and  in  some  other 
.metals.     Among  the  metalloids,  it  enters  into  direct  union  only  with  oxygen 


ANIMAL    CHARCOAL.  259 

and  sulphur,  and  even  in  reference  to  these  bodies  a  very  high  temperature 
is  required  to  bring  about  chemical  combination. 

Equivalent.      Tests The   atomic    weight  of  carbon   is  fixed,  by  some 

chemists,  at  6,  and  by  others  at  12.  As  it  is  unknown  in  the  vaporous  con- 
dition, its  volume  is  of  course  hypothetical.  For  convenience,  it  is  assumed 
to  be  the  same  as  that  of  hydrogen,  and  is  therefore  taken  as  one  or  two 
volumes,  according  to  the  assumed  volume-equivalent  of  that  element.  When 
carbon,  as  charcoal,  is  in  a  free  state,  it  may  be  identified  by  its  color,  inso- 
lubility in  all  menstrua,  its  fixedness  in  close  vessels,  and  its  combustion  and 
entire  conversion  into  gaseous  matter  when  heated  in  air.  It  may  be  also 
known  when  existing  in  any  state,  by  its  combustion,  as  a  result  of  deflagra- 
tion in  melted  nitre  or  chlorate  of  potassa,  and  by  the  production  of  car- 
bonate of  potassa.  Carbon  may,  however,  exist  in  such  a  form,  in  organic 
compounds,  that  with  the  exception  of  deflagration,  these  tests  are  no  longer 
applicable  for  its  detection.  The  substance  suspected  to  contain  it,  should 
be  well  dried  and  mixed  with  four  parts  of  dried  black  oxide  of  copper,  or 
dry  chromate  of  lead.  The  mixture  inclosed  in  a  small  reduction-tube,  bent 
at  an  angle,  should  be  then  gradually  heated  to  redness — the  mouth  of  the 
tube  being  immersed  in  lime-water,  contained  in  a  watch-glass.  The  pro- 
duction of  a  white  deposit  of  carbonate  of  lime  will  prove  that  the  substance 
under  examination  contained  carbon.  The  oxjrgen  of  the  oxide  of  copper, 
or  chromic  acid,  here  serves  as  the  medium  for  converting  the  carbon,  present 
in  the  organic  matter,  into  carbonic  acid.  If  the  quantity  is  required  to  be 
determined,  then  it  will  be  necessary  to  connect  the  tube  containing  the  mix- 
ture, with  another  tube,  in  which  is  placed  powdered  chloride  of  calcium 
(for  the  purpose  of  drying  the  carbonic  acid),  and  conduct  the  products  of 
combustion  into  a  balanced  vessel  containing  a  saturated  solution  of  potassa. 
{See  Analysis  of  Organic  Substances.)  The  amount  of  carbonic  acid, 
and,  by  calculation,  the  amount  of  carbon,  present,  may  be  thereby  de- 
termined. 

Two  other  forms  of  carbon  require  a  brief  notice. 

Animal  Charcoal. — Charcoal  obtained  by  the  carbonization  of  animal 
substances,  such  as  muscle,  horn,  or  hoof,  resembles  wood-charcoal  in  its 
general  characters ;  but  instead  of  retaining  the  form  of  the  matter  from 
which  it  is  produced,  it  appears  as  if  it  had  undergone  fusion,  and  often  has 
a  peculiar  lustre  and  sponginess.  In  all  animal  charcoals,  we  discover  traces 
of  nitrogen,  derived  probably  from  the  presence  of  paracyanogen,  or  of 
mellone  ;  they  also  contain  the  fixed  saline  and  other  bodies  which  existed 
in  their  respective  sources.  The  charcoal  obtained  by  the  distillation  of 
bone,  is  called  bone-black  and  ivory-black  in  commerce,  and  is  mixed  with  a 
large  proportion  of  phosphate  of  lime  and  other  earthy  salts  contained  in 
the  bone,  so  that  for  some  purposes  it  requires  to  be  freed  from  these  salts  by- 
digesting  it  in  diluted  hydrochloric  acid,  and  then  washing  and  drying  it. 
The  special  properties  of  animal  charcoal  in  reference  to  the  destruction  of 
odors  and  colors,  have  already  been  mentioned.  They  are  due  to  its  mole- 
cular state,  and  not  to  difference  of  composition,  charcoal  being  essentially 
the  same  under  all  its  various  forms.  Of  the  different  kinds  of  charcoal 
used  for  decoloration,  bone  charcoal  or  ivory-black  is  comparatively  feeble, 
although  it  is  superior  to  wood-charcoal.  Its  decolorizing  properties  are 
nearly  doubled  by  washing  it  with  diluted  hydrochloric  acid,  to  remove  the 
mineral  matter,  and  afterwards  with  water.  For  perfect  decoloration,  the 
charcoal,  finely  powdered,  should  be  allowed  to  remain  for  some  hours  in 
contact  with  the  colored  liquid,  and  in  certain  cases  warmed.  The  charcoal 
employed  should  contain  no  substances  soluble  in  water  or  in  alcohol.  After 
a  time,  animal  charcoal  loses  its  efficacy,  the  surface  being  covered  with  the 


260  COMPOUNDS    OF    CARBON    AND    OXYGEN. 

coloring  matter  and  other  impurities,  but  the  property  may  be  restored  by 
reheating  it  in  close  cylinders.  This  renovation  is  a  necessary  process  in 
large  sugar-refineries.  We  have  found  that  a  sample  of  good  animal  char- 
coal contained  only  18  per  cent,  of  carbon,  leaving  as  a  residue  after  com- 
bustion, 82  per  cent,  of  phosphate  and  carbonate  of  lime. 

Lamp-hlack  is  prepared  principally  by  the  combustion  of  refuse  and  resi- 
duary resin,  left  by  the  distillation  of  turpentine,  as  well  as  of  the  tarry  oils 
obtained  in  the  distillation  of  coal.  These  are  burned  in  a  furnace,  so  con- 
structed that  the  dense  smoke  arising  from  it  may  pass  into  chambers  hung 
with  old  sacking,  where  the  soot  is  deposited,  and  from  time  to  time  swept 
off  and  sold  without  any  further  preparation.  When  lamp-black  has  been 
thus  procured  and  heated  red-hot,  it  may  be  regarded  as  a  pure  form  of 
charcoal,  for  it  burns  entirely  away,  and  leaves  no  residuary  ash,  but,  it  is 
found  to  contain  traces  of  oxygen  and  hydrogen.  A  pure  form  of  lamp- 
black for  chemical  purposes,  may  be  obtained  by  burning  camphor,  and  re- 
ceiving the  carbon  of  the  smoke  in  a  saucer  or  basin.  When  washed  with 
alcohol  this  is  pure  carbon.  A  substance  analogous  to  lamp-black  is  obtained 
by  passing  the  vapor  of  certain  oils,  and  of  hydrocarbonous  compounds, 
through  red-hot  tubes ;  at  that  high  temperature  they  are  more  or  less  per- 
fectly decomposed,  and  deposit  a  quantity  of  impalpable  charcoal,  in  which, 
however,  as  in  lamp-black,  traces  of  hydrogen  may  be  detected.  Pure  lamp- 
black, as  it  is  procured  from  the  carbonaceous  smoke  of  the  tarry  oils  from 
coal,  is  a  very  light  flocculent  substance.  We  found  a  sample  of  this  carbon 
to  yield  only  one  per  cent,  of  a  white  ash,  whereas  the  substance  ordinarily 
sold  as  lamp-black,  yields  an  ash  containing  iron  and  silica,  amounting  to  9 
per  cent,  of  its  weight.  It  is  close  and  heavy,  and  appears  to  be  a  mixture 
of  soot  and  finely-powdered  charcoal.  One  of  the  principal  uses  of  lamp- 
black is  in  the  manufacture  of  printers'  ink.  Spanish-black  is  the  carbon  of 
cork  ;  Vine-black,  that  which  results  from  vine-tendrils,  and  Peach-black  from 
peach  kernels  ;  the  two  former  have  a  brownish  tint,  and  the  latter  a  bluish 
tint.  German  or  Frankfort-black,  is  said  to  be  obtained  by  the  carboniza- 
tion of  a  mixture  of  grape  and  wine  lees,  peach  kernels,  and  bone-shavings, 
and  to  be  especially  fit  for  copper-plate  printing. 

Carbon  and  Oxygen Although  a  powerful  affinity  exists  between  these 

bodies,  they  have  no  tendency  to  combine  at  ordinary  temperatures.  Carbon 
as  it  exists  in  certain  organic  compounds,  exposed  to  the  conditions  of  decay 
or  putrefaction,  will,  however,  unite  with  the  oxygen  of  the  air  to  form  car- 
bonic acid.  Thus  if  damp  and  decaying  woody  fibre  (sawdust)  be  kept  in  a 
closed  vessel  of  air  for  some  weeks,  it  will  be  found  that  the  air  will  no 
longer  support  combustion,  and  that  oxygen  has  been  to  a  greater  or  less 
extent  replaced  by  carbonic  acid.  It  is  probable  that  the  union  of  carbon 
and  oxygen  here  takes  place  as  a  result  of  evolution  in  the  nascent  state. 
When  carbon  is  in  a  free  state,  it  will  not  combine  with  oxygen  below  a  red 
heat. 

Chemists  have  enumerated  eight  compounds  of  these  elements,  two  of 
which  are  gaseous,  and  are  well  known  under  the  name  of — 1,  Carbonic 
oxide  (CO)  ;  and  2,  Carbonic  acid  (COg).  The  other  compounds  are — 3, 
Oxalic  acid  (CaOg.SHO),  a  crystallizable  vegetable  acid,  which  will  be  de- 
scribed hereafter,  and  its  derivative,  4,  the  Mesoxalic  acid  (CgOJ.  In  addi- 
tion to  these,  there  are  four  other  compounds,  possessing  at  present  but 
little  chemical  interest,  and  therefore  requiring  only  a  brief  notice.  These 
are  only  known  in  the  hydrated  or  combined  state.  They  are — 5,  the  Rho- 
dizonic  acid  (C^Oy.SHO),  so  named  from  the  red  color  of  its  salts.  The 
rhodizonate  of  potassa  is  procured  by  digesting  in  water  the  compound  of 


CARBONIC    OXIDE.  261 

potassium  and  carbonic,  oxide,  produced  in  the  manufacture  of  potassium, 
or  as  a  result  of  heating  potassium  in  the  gas.  The  acid  may  be  procured 
^  from  this  salt ;  it  is  a  solid  crystalline  acid  forming  colored  salts.  6,  Cro- 
conic  acid  (CjO^.HO).  Croconate  of  potassa  is  a  product  of  the  decompo- 
sition of  the  rhodizonate  of  potassa,  when  this  salt  is  boiled  in  water ;  the 
acid  may  be  obtained  from  the  solution  of  the  croconate,  by  the  addition  of 
fluosilicic  acid.  It  is  a  solid  crystalline  substance,  of  a  yellow  color,  whence 
its  name.  7,  MeUitic  acid  (C^Og.HO).  This  is  obtained  by  a  complex 
process,  from  a  mineral  known  as  mellilite  (honeystone),  a  mellitate  of 
alumina.  It  is  a  solid  colorless  acid,  crystallizing  in  prisms,  and  yielding 
by  dry  distillation,  8,  Pyromellitic  acid  (C5O3) ;  also  a  crystalline  body, 
remarkable  for  its  solubility  in  strong  nitric  and  sulphuric  acids,  without 
change. 

Carbonic  Oxide.  Oxide  of  Carbon  (CO). — This  gas  was  discovered  by 
Priestley,  but  its  real  nature  was  first  made  known  by  Cruickshank,  in  1802. 
It  may  be  procured  by  gently  heating  oxalic  acid  with  three  times  its  weight 
of  strong  sulphuric  acid,  or  a  sufficient  quantity  of  the  acid  to  drench  the 
crystals;  the  mixture  effervesces  in  consequence  of  the  evolution  of  carbonic 
oxide  and  carbonic  acid  gases  :  the  latter  may  be  separated  by  a  strong  solu- 
tion of  potassa,  and  pure  carbonic  oxide  will  remain.  If  the  experiment  be 
performed  in  a  test-tube,  the  carbonic  oxide  may  be  burnt  at  the  mouth  of 
the  tube.  In  this  case  the  evolution  of  gases  is  caused  by  the  abstraction  of 
water  from  oxalic  acid,  which  contains,  in  its  anhydrous  state,  the  elements 
of  one  atom  of  carbonic  oxide  and  one  atom  of  carbonic  acid ;  but  these 
can  only  exist  as  oxalic  acid  when  in  union  with  water,  or  with  a  base. 
Crystallized  oxalic  acid  is  =  C303,3HO,  which  acted  upon  by  three  atoms  of 
oil  of  vitriol  =:3[S03,HO]  become  3[S03,2HO]-f  CO^-f  CO  ;  the  hydrated 
sulphuric  acid,  darkened  in  color,  remains  in  the  retort.  It  may  also  be  pro- 
cured by  heating,  in  an  iron  or  earthen  retort,  a  mixture  of  carbonate  of 
lime  (chalk)  or  baryta,  with  its  weight  of  iron  or  zinc  tilings.  The  changes 
are  as  follows:  3BaO,CO,-f 2Fe=3CO  +  3BaO  +  Fe,03»  and  CaO.CO^-f 
Zn  =  CO  +  CaO  +  ZnO.  Chalk  mixed  with  finely-powdered  charcoal,  and 
heated  to  full  redness,  also  yields  this  gas  (CaO,C03-f-C=2CO-i-CaO). 
The  first  portions  of  gas  being  mixed  with  air,  should  be  rejected.  In  all 
cases  carbonic  acid  is  also  evolved ;  this  may  be  separated  by  causing  the 
gases  to  traverse  a  strong  solution  of  potassa,  or  a  tube  containing  broken 
pumice  soaked  in  potassa.  Carbonic  oxide  is  not  very  soluble  in  water; 
hence  it  may  be  collected  and  preserved  over  water.  The  tests  of  its  purity 
are  that  it  should  not  give  any  precipitate  with  lime-water,  or  red  fumes  with 
deutoxide  of  nitrogen.  This  gas  is  a  product  of  the  combustion  of  carbon 
when  the  latter  element  preponderates,  or  the  supply  of  oxygen  is  inade- 
quate to  the  production  of  carbonic  acid.  The  lambent  blue  flame  which 
sometimes  plays  upon  a  coke  or  charcoal  fire,  or  is  seen  to  issue  from  certain 
furnaces,  is  carbonic  oxide,  produced  by  the  passage  of  carbonic  acid  over 
red-hot  charcoal,  COg+C  being  converted  into  2C0. 

Properties. — The  specific  gravity  of  this  gas  compared  to  hydrogen  is  as 
14  to  1;  and  to  atmospheric  air  as  0  9674  to  I'OOO;  100  cubic  inches 
weigh  29*96  grains.  Carbonic  oxide  is  a  powerful  narcotic  poison.  When 
breathed  it  is  speedily  fatal  to  animals  :  it  produces  before  death  giddiness 
and  insensibility,  followed  by  profound  coma.  According  to  Bernard,  it  has 
the  peculiar  property  of  reddening  the  blood.  There  can  be  but  little  doubt 
that  some  of  the  noxious  effects  hitherto  attributed  to  carbonic  acid,  have 
been  due  to  the  action  of  this  gas.  It  is  produced  during  the  combustion 
of  any  form  of  carbon  when  this  element  is  in  excess,  and  it  may  escape 


262  PROPERTIES  OF  CARBONIC  OXIDE. 

through  leaks  in  stoves  or  flues.  Leblanc  found  that  an  atmosphere  con- 
taining only  1-lOOth  of  carbonic  oxide  was  as  fatal  to  a  bird  as  one  contain- 
ing l-25th  part  of  carbonic  acid.  Boussingault  has  lately  made  the  discovery, 
that  this  gas,  with  light  carburetted  hydrogen,  in  the  proportion  together 
of  3  or  4  per  cent.,  is  eliminated  by  the  green  parts  of  vegetables  under  the 
influence  of  water,  light,  and  heat.  This  may  arise  from  the  decomposition 
of  carbonic  acid  in  vegetation,  not  being  so  complete  as  it  has  been  hitherto 
supposed  to  be.  If  this  observation  be  confirmed,  it  will  show  that  while 
vegetation  aids  in  purifying  the  air,  it  leads  to  the  evolution  of  small  quan- 
titTes  of  one  of  the  most  deadly  gases  known  to  chemists  ;  and  difi'ering  from 
some  other  noxious  gases  in  the  fact  that  it  cannot  be  recognized  by  its 
odor,  or,  in  fhe  small  proportion  in  which  it  exists,  by  any  other  sensible 
properties.  Aquatic  plants  and  those  growing  in  swampy  places,  evolve  it 
in  greater  proportion  than  those  growing  on  a  dry  soil  {Cosmos,  Nov.  22, 
1861).  Is  this  gaseous  poison  the  secret  cause  of  the  unhealthiness  of  such 
localities  ? 

Carbonic  oxide  extinguishes  flame  and  burns  with  a  peculiar  blue  light 
when  mixed  with,  or  exposed  to,  atmospheric  air.  Thus,  then,  it  is  a  com- 
bustible gas,  but  a  non-supporter  of  combustion.  When  consumed  in  air  it 
emits  no  odor,  and  there  is  no  deposit  of  solid  matter.  Its  volume  is  also 
unchanged ;  each  cubic  inch  of  carbonic  oxide  being  converted  into  a  cubic 
inch  of  carbonic  acid  (C0  +  0  =  C03).  Its  conversion  into  carbonic  acid  by 
combustion,  may  be  proved  by  adding  lime-water  to  a  jar  of  the  gas  while  it 
is  in  the  act  of  burning.  Sir  H.  Davy  found  that  the  temperature  of  an  iron 
wire  heated  to  dull  redness  was  sufficient  to  inflame  it.  It  has  no  taste,  and 
little  odor,  and  when  pure,  it  occasions  no  precipitate  in  lime-water  and 
does  not  redden  a  solution  of  litmus.  If  burned  under  a  dry  bell-glass  of 
air  or  oxygen,  no  moisture  whatever  is  deposited,  showing  that  it  contains 
no  hydrogen. 

Carbonic  oxide  suffers  no  change  by  being  passed  and  repassed  through  a 
red-hot  porcelain  tube  ;  it  is  not  decomposed  at  high  temperatures  by  phos- 
phorus, sulphur,  nor  even,  according  to  the  experiments  of  Saussure,  by  hy- 
drogen (Journal  de  Physique,  Iv.),  although  it  is  stated,  upon  other  authori- 
ties, that  at  high  temperatures,  hydrogen  does  decompose  it.  When  one 
volume  of  carbonic  oxide  is  detonated  with  one  of  protoxide  of  nitrogen, 
there  result  one  volume  of  carbonic  acid  and  one  of  nitrogen  (CO-|-NO  = 
COg-l-N).  None  of  the  metals  exert  any  action  upon  this  gas,  except  potas- 
sium and  sodium,  which,  at  a  red  heat,  burn  in  it  by  abstracting  its  oxygen, 
and  carbon  is  deposited.  In  the  nascent  state,  itYorms  a  solid  compound 
with  potassium,  from  which  rhodizonic  and  croconic  acids  may  be  obtained 
(p.  260).  It  appears  to  combine  with  this  metal  at  a  temperature  not  ex- 
ceeding 176°.  At  the  melting-point  of  potassium  the  gas  is  absorbed  form- 
ing a  black  mass,  which  is  spontaneously  inflammable  in  air  (Liebig). 

Carbonic  oxide  is  one  of  the  few  compound  gases  which  has  not  yet  been 
liquefied  by  the  most  intense  cold  and  pressure  (p.  81).  The  gas  is  a  per- 
fectly neutral  oxide.  If  pure,  it  neither  reddens  nor  turns  green,  the  blue 
infusion  of  cabbage.  Water  dissolves  about  6  per  cent,  of  the  gas  by 
volume  :  it  is  not  soluble  in  a  strong  solution  of  potassa.  Berthelot  found 
that  the  gas  was  slowly  dissolved  by  hydrochloric  acid,  or  by  ammonia  hold- 
ing in  solution  subchloride  of  copper.  Carbonic  oxide  is  a  powerful  deoxi- 
dizing agent,  inasmuch  as  it  always  has  a  tendency,  at  a  high  temperature, 
to  be  converted  into  carbonic  acid.  It  thus  plays  an  impoi'tant  part  in  blast- 
furnaces in  the  smelting  of  iron.  At  a  red  heat,  it  converts  the  alkaline  and 
alkaline-earthy  sulphates  to  sulphides,  CaO,S03  +  4CO  =  4C03-f  CaS.'  Le- 
vol  has  recommended  a  solution  of  chloride  of  gold  as  a  test  for  the  gas, 


CARBONIC    ACID.  263 

inasmuch  as  it  reduces  this  metallic  compound  at  common  temperatures ; 
bat  sulphurous  acid  has  also  this  property.  Oxalate  of  lime,  for  a  similar 
reason,  serves  as  a  flux  for  the  reduction  of  arsenious  acid.  When  carbonic 
oxide  is  added  in  an  equal  volume,  to  a  mixture  of  hydrogen  and  oxygen 
gases  in  explosive  proportions,  it  prevents  spongy  platinum  from  causing 
detonation  ;  but  the  gases  slowly  react  upon  each  other,  and  form  water  and 
carbonic  acid. 

Coynposition. — The  composition  of  carbonic  oxide  is  determined  by  the 
result  of  its  combustion  with  oxygen,  with  which  it  forms  carbonic  acid. 
When  two  volumes  of  carbonic  oxide  and  one  of  oxygen  are  acted  on  by  the 
electric  spark,  detonation  ensues,  and  two  volumes  of  carbonic  acid  are  pro- 
duced :  hence  it  follows,  that  carbonic  oxide  is  unchanged  in  volume  by  this 
conversion,  and  that  it  contains  half  as  much  oxygen,  and  the  same  quantity 
of  carbon,  as  carbonic  acid.  Hence,  assuming  carbonic  oxide  to  be  a  prot- 
oxide of  carbon,  it  will  consist  of — 

Atoms.    Weights.      Per  cent.  Vols.  Sp.  Gr. 

Carbon         .         .     1     ...     6     ...     42-85     ...     1       ...     0-4146 
Oxygen        .         .     1     ...     8     ...     57-15     ...     ^       ...     0-5528 

1  14  100-00  1  0-9674 

The  volume  of  carbon-vapor  which  has  not  been  determined  experiment- 
ally, is  here  assumed  to  be  equal  to  that  of  hydrogen.  As  carbonic  oxide 
has  a  sp.  gr.  of  0*9674,  and  it  contains  half  its  volume  of  oxygen,  then,  0  9674 
— 0-5528(l-1057H-2)  =  0-4146,  the  hypothetical  sp.  gr.  of  carbon-vapor. 
From  this  result,  the  percentage  of  carbon  and  oxygen  contained  in  the  gas, 
may  be  easily  deduced;  for  0*9674  :  0  4146  :  :  100  :  4285  per  cent,  of  car- 
bon. The  difference  will  represent  the  oxygen.  Carbonic  oxide  has  the 
sp.  gr.  and  equivalent  of  nitrogen. 

Chlorocarbonic  Acid;  Phosgene  Gas{CO,(j\). — This  gas  may  be  obtained 
by  exposing  to  solar  light  a  mixture  of  equal  volumes  of  chlorine  and  car- 
bonic oxide  :  hence  its  name  (^w?,  light,  y? fi-aw,  to  produce).  It  is  also  formed 
by  exposing  the  mixed  gases  to  ordinary  daylight,  but  several  hours  are 
required  for  the  purpose.  When  perfectly  excluded  from  light,  the  gases 
have  no  tendency  to  combine.  In  the  sunshine  the  mixture  diminishes  in 
bulk  to  one-half  of  its  original  volume,  and  forms  a  compound  of  a  peculiar 
and  pungent  odor,  but  not  disagreeable  when  considerably  diluted.  It  red- 
dens litmus,  and  is  resolved  by  water  into  carbonic  and  hydrochloric  acid 
gases.  Alcohol  and  pyroxylic  spirit  absorb  it,  and  form  ethereal  compounds. 
The  specific  gravity  of  chlorocarbonic  acid  compared  with  hydrogen  is  as 
50  to  1,  and  with  common  air  as  3  425  to  1.  In  reference  to  the  theory  of 
substitutions  this  compound  has  been  regarded  as  carbonic  acid,  in  which  1 
equivalent  of  oxygen  has  been  replaced  by  I  of  chlorine. 

Carbonic  Acid.  Fixed  Air  ;  Aerial  Acid;  Garhonic  Anhydride  (COj. — 
This  compound  was  first  described  by  Dr.  Black,  in  1757,  under  the  name 
of  fixed  air,  a  name  which  it  derives  from  its  being  a  constituent  of  limestone. 
Its  composition  was  first  determined  by  Lavoisier.  It  is  produced  by  burn- 
ing carbon,  either  pure  charcoal,  graphite,  or  the  diamond,  in  oxygen  gas ; 
the  oxygen,  in  thus  becoming  converted  into  carbonic  acid  gas,  suffers  no 
change  of  volume.  When  charcoal  is  burned  in  a  jar  of  oxygen  gas  the 
phenomena  of  combustion  depend  upon  the  nature  of  the  charcoal,  which,  if 
well  made,  and  of  a  dense  wood,  glows  with  intense  heat  without  flame,  and 
gradually  disappears  ;  but  if  of  a  lighter  wood,  and  especially  if  covered  with 
portions  of  the  bark,  it  throws  off  jets  of  brilliant  sparks.  These  scintilla- 
tions are  especially  brilliant  and  beautiful,  when  a  small  piece  of  the  charred 


264  CARBONIC    ACID.      PREPARATION.      PROPERTIES. 

bark  of  oak  or  elm  is  used;  it  should  be  attached  to  a  copper  wire,  and  in- 
troduced into  a  sufficiently  capacious  air-jar  filled  with  pure  oxygen  ;  the 
combustion  may  thus  be  made  to  last  for  some  minutes.  If  only  the  quiet 
combustion  of  charcoal  is  required  for  the  purpose  of  showing  the  conversion 
of  oxygen  into  carbonic  acid,  the  best  kind  of  carbon  which  can  be  used  for 
this  purpose  is  that  obtained  from  box,  lignum  vitae,  or  other  hard  and 
dense  woods. 

Carbonic  acid  is,  like  sulphurous  acid,  an  anhydrous  oxacid  gas  producing 
no  hydrate  acid,  having  less  affinity  for  bases  than  sulphurous  acid,  so  that 
it  may  be  expelled  from  the  dry  alkaline  carbonates  by  means  of  this  gas.  It 
is  a  natural  constituent  of  the  atmosphere,  of  which  it  forms  from  ^^Vo^^  to 
^^i__th  part :  it  is  a  result  of  the  decomposition  of  animal  and  vegetable  sub- 
stances, and  is  the  chief  gaseous  product  of  combustion,  respiration,  and  the 
vinous  fermentation. 

Preparation. — Carbonic  acid  constitutes  about  half  the  weight  of  carbonate 
of  lime  or  marble.  It  is  readily  procured  by  adding  to  one  part  of  broken 
marble  one  part  of  hydrochloric  acid  diluted  with  three  parts  of  water.  The 
gas  is  instantly  evolved,  producing  the  phenomenon  known  as  effervescence 
(CaO,CO,+HCl  =  CO,+CaCl-|-HO).  A  flask  or  retort  may  be  used  in 
the  experiment.  The  gas  should  not  be  collected  until  a  few  bubbles  of  it, 
thrown  into  a  jar  containing  deutoxide  of  nitrogen,  cease  to  produce  ruddy 
fumes.  It  may  be  collected  in  a  water-bath,  although,  owing  to  the  solu- 
bility of  the  gas  in  water,  there  is  considerable  loss.  One  grain  of  pure 
marble  will  give  nearly  a  cubic  inch  of  the  gas. 

Properties. — This  gas  is  colorless,  of  a  slightly  sour  taste,  and  much  heavier 
than  atmospheric  air,  its  specific  gravity  being  about  152.  Compared  with 
hydrogen,  its  sp.  gr.  is  as  22  to  1.  100  cubic  inches  weigh  47 '087  grs.  at 
mean  temperature  and  pressure.  When  so  far  diluted  with  air  as  to  admit 
of  being  received  into  the  lungs,  carbonic  acid  operates  as  a  narcotic  poison, 
producing  drowsiness,  entire  loss  of  muscular  power,  rapidly  followed  by 
insensibility  and  coma.  When  the  gas  is  respired  into  the  lowest  poisonous 
proportion,  the  symptoms  come  on  very  gradually,  and  the  transition  from 
life  to  death  is  usually  tranquil.  This  gas  is  the  fatal  chohe-damp  of  coal 
mines.  It  is  a  product  of  the  combustion  of  light  carburetted  hydrogen 
(fire-damp),  and  is  the  common  cause  of  death  to  miners  who  are  not  at  once 
killed  by  the  explosion. 

It  is  not  combustible,  and  immediately  extirrguishes  other  bodies  which 
are  in  a  state  of  combustion.  This  may  be  proved  by  successively  introducing 
into  ajar  of  the  gas  a  burning  taper,  ignited  camphor,  and  a  large  flame  of 
ether,  on  cotton  or  tow.  The  flames  of  these  substances  are  instantly  extin- 
guished. We  have  found  that  a  candle  will  burn  in  mixtures  of  carbonic 
acid  and  air  until  the  proportion  of  the  gas  reaches  20  per  cent. ;  but  such 
mixtures  would  be  noxious  to  breathe  :  hence,  although  the  extinction  of  a 
candle  in  wells  or  cellars  is  a  proof  of  danger,  the  fact  that  it  continues  to 
burn  must  not  be  regarded  as  an  indication  of  safety.  We  have  also  found 
that  the  presence  of  a  large  proportion  of  oxygen  completely  counteracts 
this  effect  of  carbonic  acid.  In  a  mixture  of  equal  parts  of  oxygen  and  car- 
bonic acid  a  taper  burns  as  brilliantly  as  in  oxygen  ;  and  the  presence  of 
carbonic  acid  would  not  be  suspected  in  the  mixture  but  for  the  effect  pro- 
duced by  the  addition  of  lime-water  and  other  tests.  Carbonic  acid  cannot, 
however,  replace  nitrogen  in  air.  When  it  forms  four-fifths  of  the  mix'ture, 
combustion  is  no  longer  supported,  and  animals  are  killed. 

This  gas  possesses  well-marked  acid  properties.  If  blue  infusion  of 
litmus  is  added  to  ajar  of  the  gas,  it  is  speedily  reddened.  If  the  red'liquid 
is  boiled,  the  blue  color  will  be  restored,  thus  showing  that  the  reaction 


I 


CARBONIC    ACID    A    PRODUCT    OF    COMBUSTION.  265 

depended  on  a  gaseous  acid.  If  to  jars  of  the  gas,  solutions  of  lime, 
baryta,  or  subacetate  of  lead,  are  separately  added,  dense  white  precipitates 
of  the  respective  carbonates  of  these  bases  will  be  produced.  Lime-water 
is  the  usual  test  for  this  gas,  but  a  solution  of  the  subacetate  of  lead  is  more 
delicate  in  its  reaction.  Lime-water  will  be  found  to  be  alkaline  to  test- 
paper  before  pouring  it  into  the  gas,  but  it  will  entirely  lose  its  alkalinity 
afterwards.  Air  containing  one  per  cent,  of  carbonic  acid  produces  a  white 
precipitate  in  lime-water,  hence  in  an  atmosphere  containing  a  noxious 
proportion  of  carbonic  acid,  lime-water  is  instantly  rendered  turbid,  even  by 
a  small  portion  of  the  air  collected  in  a  bottle.  If  the  precipitated  carbonate 
of  lime  be  transferred  to  another  jar  of  carbonic  acid,  it  will  be  found  after 
a  time  to  be  re-dissolved.  Carbonic  acid  is  absorbed  by  alkalies.  If  a 
saturated  solution  of  potassa  is  put  into  a  jar  of  the  gas,  and  well  shaken, 
the  plate-glass  cover  of  the  jar  is  fixed  as  if  by  a  vacuum.  On  removing 
the  cover  and  introducing  a  lighted  taper,  this  will  be  found  to  burn  as  in 
air.  Introduce  into  a  wide  jar,  containing  carbonic  acid,  some  solid  hydrate 
of  potassa  with  a  small  quantity  of  water.  Cover  quickly  the  mouth  of  the 
vessel  with  a  stout  layer  of  caoutchouc,  and  then  agitate  the  liquid.  As  the 
carbonic  acid  is  absorbed  by  the  dissolved  potassa,  the  atmospheric  pressure 
forces  down  the  elastic  caoutchouc  cover,  just  as  in  a  vessel  exposed  to  the 
vacuum  of  an  air-pump.  The  most  perfect  vacua  known,  are  now  produced 
by  gently  heating  hydrate  of  potassa  in  tubes  filled  with  pure  carbonic  acid, 
hermetically  sealed. 

Solution. — Water  takes  up  its  own  volume  of  the  gas  at  common  tempera- 
ture and  pressure,  and  acquires  a  slight  increase  of  specific  gravity  (about 
r0018).  Under  increased  pressure  a  much  larger  quantity  is  absorbed. 
Thus,  water  may  be  made  to  take  up  five  or  six  times  its  volume  by  pressure. 
It  then  becomes  brisk  and  acid,  and  reddens  vegetable  blues.  If  litmus- 
paper,  thus  reddened,  be  exposed  to  the  air,  the  blue  color  returns  as  the 
acid  evaporates.  By  freezing,  boiling,  or  exposure  to  the  vacuum  of  an  air- 
pump,  the  gas  is  given  off,  and  it  gradually  makes  its  escape  when  exposed 
to  air,  collecting  in  small  bubbles  upon  the  sides  of  the  containing  vessel, 
and  passing  off  with  especial  rapidity  when  any  foreign  substances  are 
thrown  in,  or  when  any  substance  is  dissolved  in  the  water ;  thus  it  is,  that 
sugar  added  to  soda-water,  cider,  champagne,  or  other  similar  carbonated 
liquors,  occasions  in  them  an  immediate  and  abundant  effervescence.  The 
effervescent  qualities  of  many  mineral  waters,  as  well  as  of  fermented  liquids, 
are  referable  to  the  presence  of  this  gas.  Artificially  aerated  waters  are 
prepared  on  a  large  scale  by  condensing  carbonic  acid  under  pressure,  into 
water  holding  dissolved  alkaline  or  saline  substances.  Carbonic  acid  may 
be  thus  made  to  dissolve  lime,  magnesia,  and  the  protoxide  of  iron.  A  solu- 
tion of  carbonic  acid  in  water,  precipitates  lime-water,  but  re-dissolves  the 
precipitate  when  added  in  larger  quantity. 

Carbonic  acid  forms  no  hydrate  with  water ;  and  when  liquefied,  or  solidi- 
fied by  cold,  it  will  not  combine  with  water.  Some  English  chemists  have 
given  to  it  the  name  of  Carbonic  anhydride.  As  this  term  is  applied  to 
acids  which  are  capable  of  forming  definite  hydrates  with  water,  in  order  to 
distinguish  the  anhydrous  from  the  hydrated  state,  it  is  singularly  inappro- 
priate to  apply  it  to  an  acid  which  forms  no  hydrate  whatever.  The  words, 
too,  imply,  not  the  absence  of  water,  but  the  absence  of  hydrogen.  Nitrogen 
and  carbonic  oxide  would,  in  either  point  of  view,  have  an  equal  claim  to  be 
called  anhydrides.  Long  established  usage  has  fixed  the  name  of  carbonic 
acid  in  chemical  nomenclature,  and  no  sufficient  reason  has  been  adduced  for 
the  adoption  of  this  innovation. 

As  all  common  combustibles,  such  as  coal,  wood,  oil,  wax,  and  tallow, 


266  CARBONIC    ACID    OF    RESPIRATION. 

contain  carbon  as  one  of  their  component  parts,  so  the  comhustion  of  these 
bodies  is  always  attended  by  the  production  of  carbonic  acid.  Float  a  lighted 
taper,  fixed  in  a  cork,  on  lime-water,  contained  in  a  glass  dish  ;  and  invert 
over  the  taper  a  bell-glass  of  air  or  exygen.  After  a  time  tlie  tai)er  will  be 
extinguished,  and  the  surface  of  the  lime-water  will  be  covered  with  a  white 
film  of  carbonate  of  lime.  Hold  a  large  jar  so  that  its  mouth  shall  be 
slightly  above  a  jet  of  burning  gas,  or  the  flame  of  a  spirit-lamp.  After  a 
few  minutes  remove  it,  and  pour  lime-water  into  the  jar.  This  will  be 
rendered  milky  by  the  carbonic  acid  which  has  resulted  from  combustion. 

This  gas  is  also  produced  by  respiration ;  hence  it  is  detected,  often  in 
considerable  proportion,  in  crowded  and  illuminated  rooms  which  are  ill- 
ventilated.  The  symptoms  produced  by  the  respiration  of  such  a  con- 
taminated atmosphere,  are  difficulty  of  breathing,  giddiness,  and  faintness. 
Its  expiration  from  the  lungs  is  easily  shown,  by  blowing  the  expired  air 
through  lime-water  by  means  of  a  small  tube ;  the  liquid  becomes  milky  and 
soon  deposits  carbonate  of  lime.  The  same  fact  is  also  strikingly  shown  by 
allowing  expired  air  to  pass  into  a  solution  of  chloride  of  lime,  colored  blue 
by  litmus.  The  color  is  soon  destroyed  by  the  carbonic  acid  discharged 
from  the  lungs  decomposing  the  chloride,  and  setting  free  chlorine.  An 
apparatus  has  been  contrived,  by  which  the  air  inspired,  is  made  to  traverse 
lime-water  without  producing  any  change  in  it,  while  the  air  expired 
through  the  same  liquid  produces  carbonate  of  lime.  If  lime-water  is 
placed  in  a  large  jar,  and  the  air  of  the  jar  is  breathed  two  or  three  times, 
taking  care  that  the  air,  as  it  is  expired,  is  returned  into  the  jar,  the  lime 
water,  which  was  unaffected  by  the  air  contained  in  the  vessel,  will  be 
rendered  milky  from  the  production  of  carbonate  of  lime.  Inspired  air 
contains  only  from  l-2000th  to  l-2500th  part  of  carbonic  acid,  but  expired 
air  contains  (on  the  assumption  that  3  per  cent,  only  are  present)  sixty  times 
as  much  carbonic  acid,  or  l-33d  part  by  volume.  Dr.  Prout  assigns  the 
proportion  of  carbonic  acid  in  expired  air  at  from  3*3  to  4-1  per  cent.,  and  the 
average  at  3  43  per  cent.  It  varies  at  different  periods  of  the  day,  according 
to  the  state  of  health,  and  other  conditions.  On  this  estimate,  however,  16 
cubic  inches,  representing  4  grains  of  solid  carbon,  are  thrown  out  of  the 
lungs  of  an  adult  every  minute — a  quantity  amounting  to  about  12  ounces  of 
carbon  in  24  hours  1  According  to  Dr.  Brinton  {Food  and  its  Digestion), 
the  carbonic  acid  daily  given  off  from  the  adult  healthy  body  may' be  esti- 
mated at  n  cubic  feet,  or  about  two  pounds  in  weight.  Allowing  that  half 
a  cubic  foot  (about  an  ounce)  is  eliminated  through  the  skin,  the  remainder 
is  exhaled  from  the  lungs.  The  quantity  of  carbon  or  charcoal  by  weight,  to 
which  this  amount  of  carbonic  acid  would  correspond,  is  nine  ounces.  In 
making  this  estimate  Dr.  Brinton  assumes  l-2500th  part  of  carbonic  acid  as 
the  proportion  present  in  inspired,  and  l-25th  part  as  the  proportion  con- 
tained in  expired  air. 

Carbonic  acid  retards  the  putrefaction  of  animal  substances.  It  favors  the 
growth  and  development  of  vegetables  in  air  and  water.  Most  plants  thrive 
in  an  atmosphere  containing  as  much  as  a  tenth  or  twelfth  part  of  carbonic 
acid ;  and  under  certain  circumstances  they  decompose  it,  appropriate  the 
carbon,  and  evolve  the  oxygen. 

At  high  temperatures,  carbonic  acid  is  decomposed  by  carbon  and  several 
of  the  metals,  and  is  converted  into  carbonic  oxide.  The  influence  of  ignited 
carbon  in  effecting  this  decomposition  is  seen  in  an  ordinary  coal-fire.  The 
oxygen  of  the  air  in  passing  between  the  bars  below,  produces  carbonic 
acid  :  and  this  is  deoxidized  by  the  red-hot  coke  (CO,-f  C=2C0)  the  car- 
bonic oxide  thus  produced,  burning  at  the  top  of  the  fire  with  a  flickering 
blue  flame.     Potassium  and  sodium,  when  heated  intensely,  burn  in  the  gas, 


CARBONIC    ACID.      COMPOSITION.  267 

and  are  converted  into  potassa  and  soda,  whilst  the  carbon  of  the  gas  is 
separated  in  the  form  of  charcoal.  There  are  some  other  substances,  which, 
at  hipjh  temperatures,  are  capable  of  decomposing  carbonic  acid,  and  ab- 
stracting part  of  its  oxygen  ;  thus,  if  a  mixture  of  2  parts  of  hydrogen  and 
1  of  carbonic  acid  by  volume,  be  passed  through  a  red-hot  tube,  water  and 
carbonic  oxide,  with  the  excess  of  hydrogen,  escape. 

Carbonic  acid  is  not  affected  by  heat  alone :  it  may  be  passed  through  a 
red-hot  porcelain  tube  unchanged ;  but  it  is  partially  converted  by  a  succes- 
sion of  electric  sparks  into  carbonic  oxide  and  oxygen.  It  is  worthy  of 
remark,  as  illustrative  of  the  variable  effects  of  the  electric  spark,  that  by 
means  of  it,  a  mixture  of  carbonic  oxide  and  oxygen  may  be  suddenly  con- 
verted into  carbonic  acid.  Iron,  zinc,  and  manganese,  at  a  high  temperature, 
deprive  the  gas  of  half  of  its  oxygen,  and  convert  it  into  carbonic  oxide. 

Equivalent  and  Tests. — The  equivalent  or  atomic  weight  of  carbonic  acid 
is  22,  and  its  volume-equivalent  is  I.  The  tests  for  its  presence  are — 1,  the 
extinction  of  a  burning  taper;  2,  the  production  of  a  milky  precipitate  of 
carbonate  of  lime,  when  lime-water  is  added  to  a  jar  containing  the  gas  ; 
3,  entire  absorption  and  removal  by  potassa.  For  this  purpose,  the  carbonic 
acid  should  be  collected  in  a  tube  over  mercury,  and  some  portions  of  solid 
potassa,  with  a  small  quantity  of  water,  introduced.  The  carbonic  acid 
slowly  disappears,  and  if  the  gas  is  pure,  there  will  be  no  residue.  A 
strong  solution  of  potassa,  or  portions  of  alkali,  moistened,  and  placed  in  an 
appropriate  apparatus,  previously  balanced,  will  separate  carbonic  acid  from 
most  neutral  gases  ;  and  by  the  increase  in  the  weight  of  the  potassa,  a 
chemist  will  be  enabled  to  determine  the  weight  or  volume  of  carbonic  acid 
present. 

Composition. — As  oxygen,  in  being  converted  into  carbonic  acid  by  the 
combustion  of  carbon,  undergoes  no  change  of  volume,  it  is  evident  that 
the  weight  of  carbon  present  must  be  equal  to  the  difference  between  the 
specific  gravities  of  carbonic  acid  and  oxygen  =0-4145  (1'5202 — 1"1057). 
Assuming  that  this  represents  one  volume  of  carbon-vapor,  then  the  weight 
of  carbon  in  100  parts  of  carbonic  acid  is  equal  to  27  22  (I  520  :  0*4145  :  : 
100  :  27*22),  and  the  oxygen  will  be,  72-78.  These  elements  are  obviously 
in  the  proportions  of  3  to  8,  or  6  to  16,  as  found  by  Stas  and  Dumas  in  the 
burning  of  pure  carbon  in  oxygen,  and  in  taking  directly  the  weight  of  the 
resulting  carbonic  acid.  The  composition  of  this  gas  will  therefore  stand  as 
follows : — 

Atoms.     Weights.      Per  cent.         Vols.  Sp.  Gr. 

Carbon         .        .     1     ...       6     ...     27-22     ...     1     ...     0-4145 
Oxygen        .         .     2     ...     16     ...     72-78     ...     1     ...     1-1057 


1  22  100-00  1  1-5202 

As  the  weight  of  carbon  is  added  to  that  of  the  oxygen  without  altering 
its  bulk,  this  gas  is  very  heavy ;  hence  it  accumulates  temporarily  in  wells, 
cellars,  or  other  excavations  in  the  soil  :  but  unless  constantly  produced,  it 
will  soon  disappear  by  the  law  of  diffusion  (p.  86).  The  following  experi- 
ments will  serve  to  prove  how  much  denser  it  is  than  air.  Balance  a  glass 
shade  in  a  scale  pan,  allow  a  current  of  carbonic  acid  gas  to  pass  into  it  from 
a  bottle,  taking  care  that  the  tube  conveying  the  gas  reaches  nearly  to  the 
bottom  of  the  shade.  It  will  collect  and  displace  the  air,  and  the  shade  will 
now  preponderate  by  reason  of  the  greater  weight  of  the  gas,  A  lighted 
taper  lowered  within  the  shade  is  extinguished.  Dry  nitre  paper  ignited, 
will  also  be  extinguished  when  introduced,  but  the  smoke  produced  as  a 
result  of  its  combustion  will  float  upon  the  heavy  stratum  of  carbonic  acid. 
A  soap-bubble,  or  a  small  collodion  balloon  of  air,  will  also  float  upon  the  gas. 


268  LIQUID    AND    SOLID    CARBONIC    ACID. 

If  a  small  jar  or  glass-beaker  is  lowered  into  the  shade,  it  will,  in  a  few 
minutes,  be  filled  (by  displacement)  with  carbonic  acid,  which  may  be 
removed  to  a  distance  and  tested  by  a  lighted  taper,  as  well  as  by  lime-water. 
Remove  the  covers  from  two  small  jars  containing  the  gas,  taking  care  that 
one  is  placed  with  its  mouth  upwards  and  the  other  with  its  mouth  down- 
wards. After  a  few  minutes,  a  lighted  taper  may  be  applied  to  the  two.  It 
will  be  found  that  the  gas  has  fallen  out  of  the  jar  with  its  mouth  downwards, 
and  that  the  taper  will  burn  brightly  in  it ;  whereas  it  will  be  immediately 
extinguished  in  the  other  jar,  and  will  not  entirely  escape  from  it  for  a  quarter 
of  an  hour,  or  longer.  Smoke  produced  by  the  combustion  of  nitre-paper 
at  the  mouth  of  the  jar,  will  float  like  a  cloud  upon  it.  The  falling  of  the 
gas  from  one  vessel  to  another  may  be  easily  demonstrated  by  allowfng  a 
taper  to  burn  at  the  bottom  of  a  jar  of  air,  and  then  gradually  inverting 
over  it  another  jar  containing  carbonic  acid  :  the  taper  will  be  extinguished 
in  the  jar  which  contained  air,  while  in  that  which  contained  the  carbonic 
acid  it  will  now  continue  to  burn.  This  experiment  may  be  varied  by  placing 
three  lighted  tapers  at  dififerent  levels  in  a  glass  basin  about  eight  inches 
wide,  and  five  or  six  inches  deep.  If  a  large  jar  of  carbonic  acid  is  brought 
over  the  mouth  of  the  basin,  at  the  part  corresponding  to  the  lowest  taper, 
and  the  cover  gradually  raised,  the  gas  will  fall  through  the  air  in  the  basin, 
and  as  it  rises  it  will  successively  extinguish  the  three  tapers.  The  Grotta 
del  Cane,  near  Naples,  is  an  excavation  on  the  side  of  a  hill,  in  which  carbonic 
acid  collects,  owing  to  the  basin-like  form  of  the  floor  of  the  grotto.  The 
gas  is  always  issuing  from  fissures  in  the  soil,  and  thus  the  accumulation  goes 
on  faster  than  the  diffusion.  Dogs  are  asphyxiated  by  being  held  within 
the  stratum  of  gas,  which  rises  to  about  the  height  of  the  knee.  On  gra- 
dually lowering  burning  straw  and  phosphorus  in  this  grotto,  we  found  that 
the  level  of  the  gas  was  accurately  determined  by  the  extinction  of  the  flame 
and  the  floating  of  the  smoke.  These  well-known  facts  regarding  the  specific 
gravity  of  carbonic  acid,  have  led  to  the  erroneous  supposition  that,  under 
all  circumstances,  the  gas  will  accumulate,  and  remain  on  the  floor  or  soil. 
The  law  of  diffusion,  however,  prevents  such  accumulation,  unless  there  is 
a  constant  source  from  which  the  gas  can  proceed. 

Liquid  and  solid  Carbonic  Acid. — Carbonic  acid  may  be  liquefied  by 
great  pressure,  aided  by  a  low  temperature  (page  80).  It  is  usually  liquefied 
by  its  own  pressure — i.  e.,  by  liberating  it  in  a  wrought-iron  vessel,  the 
capacity  of  which  is  very  small  compared  with  the  amount  of  gas  which  can 
be  set  free  by  the  action  of  an  acid  on  bicarbonate  of  soda.  It  may  be 
Uquefied  by  mere  cooling  to  106^  without  pressure.  The  liquid  is  colorless, 
very  soluble  in  alcohol,  ether,  and  essential  oils.  It  will  not  mix  or  combine 
with  water,  but  floats  on  that  liquid.  It  does  not  redden  the  solid  extract 
of  litmus.  It  dissolves  camphor  and  iodine.  Although  it  has  no  solvent 
action  on  gutta-percha  or  caoutchouc,  it  penetrates  into  these  substances, 
and  whitens  them.  It  is  a  strong  insulator  of  electricity,  and  is  deoxidized 
only  by  the  alkaline  metals.    (Oore,  Proc.  R.  S.,  1861,  No.  43,  page  85.) 

By  allowing  liquefied  carbonic  acid  to  escape  through  a  perforated  metallic 
box,  the  cold  produced  is  so  intense  that  a  portion  of  the  gas  is  solidified, 
and  presents  the  appearance  of  a  snowy-looking  mass.  Solid  carbonic  acid 
has  a  temperature  of  at  least  100°  below  zero,  but  it  is  surrounded  in  the  air 
with  a  gaseous  atmosphere,  which  prevents  immediate  contact  with  bodies, 
and  it  rapidly  disappears  as  gas,  when  exposed.  This  solid  acid  may  be 
borne  in  the  hand  without  any  particular  sensation  of  coldness  or  pain ;  but 
when  mixed  with  ether,  it  produces  an  intense  degree  of  cold,  which  would 
destroy  at  once  the  vitality  of  any  part  of  the  body  with  which  it  was  in 
contact.     A  small  portion  placed  on  stout  plate-glass  produced  no  effect 


CARBON    AND    HYDROGEN.  209 

until  ether  was  poured  upon  it,  when,  owing  to  the  intense  cold  suddenly 
produced,  the  glass  was  broken  to  pieces.  A  sheet  of  paper  was  folded  so 
as  to  make  a  long  trough,  or  cavity,  into  which  liquid  mercury  was  poured  ; 
the  metal  was  then  covered  with  solid  carbonic  acid,  and  ether  was  poured 
upon  it.  The  mercury  was  instantly  frozen  into  a  long  bar  of  metal,  the 
temperature  of  the  air  being  at  the  time  above  60°  Medals  of  mercury 
have  thus  been  made,  and  preserved  for  some  time  in  the  cold  bath  of  car- 
bonic acid  and  ether.  Gases  may  be  liquefied  and  solidified  by  means  of  this 
bath.  In  vacuo  the  cold  produced  by  it  has  been  calculated  by  Faraday 
to  reach  to  — 166°,  or  198°  below  the  freezing-point  of  water.  From  the 
experiments  of  Tyndal  it  appears  that  ice  contains  sufficient  heat  to  liquefy 
and  boil  solid  carbonic  acid. 

Carhonates, — These  salts  are  represented  by  the  formula  MO, COg,  and  the 
bicarbonates  by  MO.SCOa.  Among  the  alkaline  carbonates  those  of  potassa, 
soda,  ammonia,  and  iithia,  are  alone  soluble  in  water,  and  have  an  alkaline 
reaction.  Those  of  lime,  magnesia,  protoxide  of  iron,  and  manganese,  are 
dissolved  by  water  containing  much  carbonic  acid.  A  soluble  carbonate  gives 
a  white  precipitate  with  the  solutions  of  lime,  or  baryta,  or  with  their  salts. 
This  precipitate  is  dissolved  with  effervescence  (escape  of  carbonic  acid)  by 
the  acetic  and  other  acids.  The  precipitate  given  by  sulphate  of  magnesia 
is  soluble  in  hydrochlorate  of  ammonia,  containing  free  ammonia  ;  that  given 
by  lime  is  not.  A  soluble  bicarbonate  gives  no  precipitate  with  sulphate  of 
magnesia,  and  a  yellowish  (becoming  slowly  a  red)  precipitate,  with  a  solu- 
tion of  corrosive  sublimate.  This  test  at  once  precipitates  a  soluble  car- 
bonate, excepting  that  of  Iithia,  of  a  deep-red  color.  A  solution  of  a 
carbonate  added  to  a  strong  acid,  effervesces  strongly,  /^so/wi/e  carbonates 
are  identified  by  their  dissolving  with  effervescence  in  nitric  acid.  The  gas 
which  escapes  is  invisible,  and  without  smell.     It  precipitates  lime-water. 


CHAPTER    XX. 

CARBON.     COMPOUNDS    OF    CARBON    WITH    HYDROGEN, 
NITROGEN,    CHLORINE,    AND     SULPHUR. 

Carbon  and  Hydrogen. — These  elements,  although  they  form  a  large 
number  of  compounds  chiefly  belonging  to  the  organic  kingdom,  cannot  be 
easily  made  to  unite  directly.  When  a  voltaic  current  of  a  very  powerful 
kind  is  established  in  an  atmosphere  of  hydrogen  by  means  of  charcoal  points, 
a  peculiar  hydrocarbon  is,  however,  formed  as  a  result  of  direct  combination. 
This  is  called  (Mtyllne.  It  is  represented  by  the  formula  C^HgOr  CgH.  Carbon 
and  hydrogen  form  gaseous,  liquid,  and  solid  compounds,  among  which  it  is 
sometimes  difficult  to  distinguish  those  which  ought  to  be  considered  as  defi- 
nite, from  others  which  are  mere  mixtures.  These  compounds  are  generally 
termed  hydrocarbons,  or  carbo-hydrogens.  Amongst  them  are  some  striking 
illustrations  of  that  species  of  isomerism,  which  has  been  called  polymerism 
(page  19) — that  is,  of  compounds  differing,  often  essentially,  in  their  physical 
or  chemical  properties,  or  both,  and  yet  apparently  produced  by  the  union 
of  the  same  elements  in  similar  proportions.  Among  these  compounds  may 
be  mentioned  the  oils  of  lemon,  turpentine,  juniper,  and  savin  ;  naphtha, 
naphthaline,  and  benzole ;  all  remarkable  for  their  inflammability  and  their 
combustion  with  a  yellowish-white  smoky  flame.  As  these  hydrocarbons  are 
of  a  complex  nature,  and  are  for  the  most  part  educts,  or  products,  of  organic 


2Y0      LIGHT  CARBURETTED  HYDROGEN.   PROPERTIES. 

substances,  they  will  be  the  subject  af  consideration  hereafter.  The  three 
which  now  require  notice  are,  the  light  carburetted  hydrogen,  CHg,  olefiant 
gas,  CgH^,  and  oil  gas,  C.H^. 

Light  Carburetted  Hydrogen  (CH.J.     Marsh-gas.     Fire-damp This 

gas  is  considered  to  be  diffused  in  very  small  proportion  in  the  atmosphere. 
It  is  the  well-known  Fire-damp  of  coal-mines,  rushing  out  occasionally  in 
enormous  quantities  in  "  blowers"  from  seams  of  coal,  owing  to  its  being 
probably  contained  in  the  strata  under  high  pressure.  It  derives  its  synonym 
of  marsh-gas  from  the  fact  that  it  is  formed  in  stagnant  pools  in  hot  wither, 
during  the  spontaneous  decomposition  of  vegetable  matter.  It  may  be  pro- 
cured by  stirring  the  mud,  and  collecting  the  gas  as  it  rises  in  bubbles,  in  a 
glass-jar  filled  with  water  and  inverted.  In  this  state  it  is  mixed  with  nitro- 
gen and  carbonic  acid  ;  the  latter  may  be  separated  by  washing  the  gas  in 
lime-water  or  in  a  solution  of  caustic  potassa.  The  gas  procured  from  a 
Mower  in  a  coal  mine,  after  having  been  washed  with  lime-water,  furnishes 
tljis  compound  in  a  pure  state.  It  may  also  be  obtained  by  the  decomposi- 
tion of  certain  acetates,  when  heated  in  a  retort  with  an  excess  of  alkali. 
Dumas  recommends  for  this  purpose  40  parts  of  crystallized  acetate  of  soda, 
40  of  caustic  potassa,  and  60  of  powdered  quick-lime.  They  should  be 
strongly  mixed  and  well  heated,  the  use  of  the  lime  being  to  prevent  the 
action  of  the  alkali  upon  the  glass.  At  a  heat  approaching  to  dull  redness, 
the  gas  is  evolved,  and  may  be  collected  over  water ;  the  action  is  determined 
by  the  affinity  of  the  alkaline  bases  for  carbonic  acid,  and  the  instability  of 
the  acetic  acid  at  high  temperatures  ;  an  atom  of  acetic  acid  and  an  atom  of 
water  produce  carbonic  acid,  which  combines  with  the  soda  and  potassa  ; 
while  light  carburetted  hydrogen  passes  off;  (C^HgOg-f  HO)  yielding  2CO2, 
and  2CH2. 

Properties. — The  specific  gravity  of  this  gas  is  0*552,  and  compared  with 
hydrogen  it  is  as  8  to  1.  It  is  the  lightest  known  body  next  to  hydrogen, 
and  like  that  gas  it  has  resisted  all  attempts  to  liquefy  it  by  cold  and  pres- 
sure. 100  cubic  inches  weigh  17*12  grains.  It  is  a  colorless  gas.  Its  re- 
fractive power  is  2097,  air  being  1*000.  When  breathed  in  a  pure  state,  it 
is  fatal  to  life,  but  it  is  not  very  noxious  when  mixed  with  air,  even  when  it 
forms  from  8  to  10  per  cent,  of  the  mixture.  It  is  sparingly  soluble  in  water, 
and  is  not  dissolved  by  fuming  sulphuric  acid.  It  does  not  support  combus- 
tion, but  is  inflammable,  burning  with  a  pale  yellowish  flame,  and  producing 
carbonic  acid  and  water  CH^-f  0,==CO,-f  2H0  ;  it  has,  when  quite  pure, 
neither  odor  nor  taste.  It  is  decomposed  Iby  a  succession  of  electric  sparks, 
the  carbon  being  deposited  and  hydrogen  left  in  double  the  volume  of  the 
original  gas.  When  passed  through  a  white-hot  tube,  it  deposits  a  portion 
of  its  carbon,  CH2=C  +  H2.  When  chlorine  is  mixed  with  the  pure  gas, 
there  is  no  immediate  action  ;  but  when  1  volume  of  the  gas  and  3  of  chlorine 
are  mixed  and  exposed  to  diffused  light,  a  violent  explosi«p  soon  ensues, 
hydrochloric  acid  is  formed,  and  carbon  is  deposited.  One'  volume  of  the 
gas  with  two  volumes  of  chlorine,  produce  the  strongest  effect  (CH^-f  2C1  = 
2HC1  +  C),  and  the  combination  is  immediately  effected  by  the  electric  spark. 
When  the  gas  is  previously  mixed  with,  its  volume  of  carbonic  acid,  the 
chlorine  may  be  added  without  danger.  If  exposed  to  light,  carbonic  acid 
is  produced,  and  an  oily  liquid  is  deposited,  which  is  chiefly  bichloride  of 
carbon  (C,Cl2).  In  the  dark,  there  is  no  combination.  When  the  gas  is 
passed  with  chlorine  through  a  red-hot  tube,  carbon  is  deposited,  and  hydro- 
chloric acid  is  formed.  When  mixed  with  twice  its  volume  of  oxygen,  and 
the  mixture  is  detonated,  it  produces  its  volume  of  carbonic  acid,  and  water 
IS  at  the  same  time  condensed.  From  these  results,  its  constitution  may  be 
determined.     One  volume  of  oxygen  is  contained  in  each  volume  of  carbonic 


COAL    GAS. 


211 


acid  ;  and  as  two  volumes  are  required  for  the  perfect  combustion  of  the  gas, 
the  other  volume  of  oxygen  must  combine  with  two  volumes  of  hydrogen  to 
form  water,  or 


1  vol. 


O4 

2  vols. 


=         CO, 


1  vol. 


+ 


2H0 


2  vols. 


hence  one  volume  of  carbon-vapor  and  two  volumes  of  hydrogen  must  be 
contained  in  each  volume  of  the  light  carburetted  hydrogen.  Its  specific 
gravity  is  in  accordance  with  this  constitution  : — 


Carbon 
Hydrogen  . 


Atoms. 

1  . 

2  . 

Weights. 
..     6     .. 
..     2     .. 

Per  cent. 
.      75      .. 
.     25     .. 

Vol. 
.      1      .. 
.     2     .. 

Sp.  Gr, 
.     0-4146 
.     0-1382 

100 


0-5528 


The  ascertained  specific  gravity  is  very  nearly  in  accordance  with  this  view, 
being  0556. 

The  production  of  the  gas  in  marshy  localities,  is  owing  to  the  decay  of 
vegetable  matter,  and  the  decomposition  of  woody  fibre,  in  contact  with  the 
elements  of  water.  The  water  simply  furnishes  hydrogen  and  oxygen  to  the 
carbon  of  the  decaying  vegetables. 

Coal  Gas. — Gas  procured  by  the  distillation  of  bituminous  coal  in  iron 
retorts  is  a  mixture  of  gases  and  vapors,  but  consists  chiefly  of  light  carbu- 
retted hydrogen.  100  parts  of  coal,  distilled  at  a  high  temperature,  yield 
the  following  solid,  liquid,  and  gaseous  products  by  weight : — 


Coke. 

68-93 

defiant  gas          .         .     0-78 

Tar    . 

12-23 

Sulphuretted  hydrogen     0-75 

Water 

7-40 

Hydrogen    .         .         .     0-50 

Liglit  carb.  hydrogen 

7-04 

Ammonia    .         .         .     0-17 

Carbonic  oxide  . 

1-18 

Nitrogen      .         .         .     0-03 

Carbonic  acid     . 

1-07 

(BUNSEN  AND  PlAYFAIR.) 

The  more  bituminous  the  coal  the  larger  the  amounts  of  gas  yielded  by- 
distillation.  A  ton  of  ordinary  coal  yields  from  8000  to  11,000  cubic  feet  of 
gas,  but  a  ton  of  cannel  coal  will  yield  15,000  cubic  feet.  The  liquid  and 
watery  products  are  condensed  :  the  carbonic  acid  is  removed  from  the 
gaseous  mixture  by  passing  it  through  lime,  and  the  sulphuretted  hydrogen 
by  causing  it  to  traverse  beds  of  hydrated  oxide  of  iron  and  sawdust  (page 
228),  and  the  ammonia  by  water.  The  purified  coal  gas,  thus  obtained, 
when  not  overheated,  was  found  to  consist  in  100  parts  of  825  parts  of  light 
carburetted  hydrogen  and  13  of  olefiant  gas,  with  3'2  parts  of  carbonic  oxide 
and  0  8  of  nitrogen.  Its  sp.  gr.  was  0"65.  These  were  the  proportions  in 
the  early  stage  of  the  process.  The  gaseous  mixture  collected  after  five 
hours'  working;  when  the  tubes  had  become  strongly  heated,  contained  a 
larger  proportion  of  free  hydrogen,  derived  from  the  decomposition  of  the 
light  carburetted  hydrogen.  It  then  consisted  in  100  parts,  of  56  parts  of 
light  carburetted  hydrogen  and  7  of  olefiant  gas,  11  of  carbonic  oxide,  to  7 
of  nitrogen  and  21-3  of  hydrogen.  Its  sp.  gr.  was  050.  After  ten  hours' 
distillation,  the  olefiant  gas  had  entirely  disappeared — the  light  carburetted 
hydrogen  amounted  to  only  20  parts,  carbonic  oxide  10,  nitrogen  10,  and 
hydrogen  60,  the  sp.  gr.  being  as  low  as  0345.  (MiTSCHERLicn.)  The  con- 
stitution of  the  coal  gas  varies,  therefore,  greatly  with  the  temperature  of 
distillation. 

Coal  gas  is  colorless,  and  has  commonly  a  strong  odor  of  naphtha  vapor. 
A  taper  plunged  to  the  bottom  of  a  jar  containing  it  is  extinguished  ;  but 


2Y2  COAL    GAS.      PROPERTIES. 

the  gas  burns,  where  it  -meets  with  air,  with  a  yellowish  flame.  Aqueous 
vapor  is  condensed  on  the  sides  of  the  jar,  and  carbonic  acid  may  be  proved 
to  be  a  product  of  its  combustion,  by  pouring  lime-water  into  the  jar,  while 
the  gas  is  burning  ;  or  by  holding  the  mouth  of  a  clean  jar  of  air  over  a  jet 
of  gas  in  combustion,  and  then  adding  lime-water :  the  presence  of  carbonic 
acid  will  be  indicated  by  a  white  precipitate.  This  gas  may  be  kindled  ia 
air  by  a  full  red  heat  without  flame.  Apply  a  red-hot  bar  of  iron  tS  a  jar  of 
the  gas,  or  to  a  current  of  gas,  as  it  issues  from  a  jet,  and  it  will  be  found 
that  the  iron,  although  visibly  red,  will  not  inflame  the  gas  unless  the  metal 
is  heated  to  bright  redness.  If  fine  platinum  wire  is  made  red-hot  in  a  gas- 
flame,  as  it  is  burnt  with  air  from  a  wire-gauze  burner,  and  the  flame  is  sud- 
denly extinguished,  the  wire  will  continue  to  glow  in  the  current  of  unignited 
gas,  causing  the  slow  combustion  of  the  gas  and  air  without  inflaming  the 
mixture,  until  some  portions  of  the  wire  acquire  a  white  heat:  the  mixture  is 
then  suddenly  kindled  with  a  slight  explosion.  This  gas  is  so  light  that  the 
series  of  experiments  described  under  hydrogen  (page  121)  may  be  readily 
performed  with  it.  A  jar  of  the  gas  may  be  removed  from  the  water-bath, 
with  its  mouth  downwards,  without  a  cover,  to  a  distance,  and  there  ignited. 
It  rapidly  escapes  from  jars  which  are  open  with  their  mouths  upwards.  A 
jar  of  air  held  over  ajar  of  the  gas,  suddenly  uncovered,  will  thus  receive  it 
in  the  act  of  ascending.  The  contents  may  be  exploded,  while  the  jar  which 
originally  contained  the  gas,  will  contain  air.  Nitre-paper  burnt  at  the 
mouth  of  an  inverted  jar  of  the  gas  will  produce  smoke,  which  will  remain  at 
the  lowest  level,  the  gas  floating  on  the  top  of  it.  A  jar  opened  under  a 
balanced  shade,  inverted,  will  cause  the  opposite  scale  to  preponderate,  the 
air  being  displaced  by  the  light  gas  which  rises  to  the  upper  part  of  the 
shade.  Soap-bubbles  blown  with  this  gas,  on  collecting  it  by  pressure  from 
an  ordinary  jet,  will  ascend  in  air,  and  balloons  of  goldbeater's  skin  filled 
with  it  acquire  great  buoyancy,  thus  illustrating  the  principles  of  aerosta- 
tion. As  this  gas  is  only  half  the  weight  of  air,  and  only  one-third  the 
weight  when  partially  decomposed  by  overheating,  it  is  now  exclusively 
employed  for  the  purposes  of  aerostation — the  larger  size  of  the  balloon  com- 
pensating for  the  higher  specific  gravity  of  the  gas  compared  with  hydrogen. 
Coal  gas  should  have  no  acid  reaction  on  infusion  of  blue  litmus.  If  it  con- 
tains sulphuretted  hydrogen,  it  will  give  a  brown  discoloration  to  paper 
wetted  with  a  salt  of  lead  :  if  ammonia  is  present,  this  will  be  indicated  by 
its  restoring  the  color  of  faintly  reddened  litmus-paper.  When  these  im- 
purities coexist,  the  gas  will  give  a  bluish  or  pinkish  red  color  to  a  solution 
of  nitro-prusside  of  sodium.  In  spite  of  all  ordinary  methods  of  purifica- 
tion, coal  gas,  in  burning,  evolves  an  acid  vapor,  which  is  found  to  be  sul- 
phurous acid.  This  proceeds  from  a  minute  portion  of  sulphide  of  carbon 
vapor,  which  the  common  purifiers  do  not  remove. 

The  illuminating  power  of  coal  gas  is  increased  by  saturating  it  with  coal 
naphtha.  The  gas  is  simply  passed  through  a  box  in  which  the  vapor  of 
naphtha  is  diffused,  and  it  is  speedily  saturated  with  it. 

The  effect  produced  by  the  presence  of  this  vapor  may  be  illustrated  by 
generating  hydrogen  in  a  two-necked  vessel  provided  with  glass  tubes  which 
can  be  fixed  into  the  necks  by  corks.  One  of  these  tubes  should  have  in  it  a 
few  fibres  of  asbestos  soaked  in  naphtha  or  benzole.  The  gas  may  be  then 
ignited  as  it  issues  from  the  two  jets.  In  one  the  flame  will  be  scarcely 
visible ;  in  the  other  there  will  be  a  luminous  smoky  flame.  The  effect  on 
coal  gas  may  also  be  illustrated  by  burning  it  from  a  tube  in  which  asbestos 
with  naphtha  is  placed. 

Acetylene  CjHaC^H,.  This  is  usually  found  in  coal  gas.  It  is  a  gaseous 
body  having  a  disagreeable  odor,  and  burning  with  a  luminous  smoky  flame. 


EXPLOSIONS    IN    COAL    MINES.      SAFETY    LAMP.  273 

Light  carburetted  hydrogen  and  the  vapor  of  alcohol,  when  passed  through 
a  red-hot  tube,  yield  acetylene  as  a  product.  It  appears  to  be  produced  in 
all  cases  in  which  there  is  an  incomplete  combustion  of  carbon  compounds. 
It  is  characterized  by  giving  a  red  precipitate  with  an  aramoniacal  solution 
of  subchloride  of  copper.     It  combines  directly  with  chlorine  and  bromine. 

In  reference  to  explosions  in  coal-mines,  two  important  chemical  questions 
present  themselves  for  consideration — 1st,  the  proportion  per  cent,  of  light 
carburetted  hydrogen,  which  forms  the  most  dangerous  explosive  mixture 
with  air;  and  2d,  the  temperature  at  which  such  a  mixture  is  liable  to  be 
kindled.  It  is  here  assumed  that  the  gas  is  pure,  and  that  it  contains  no 
admixture  of  olefiant  gas  or  carbonic  oxide.  In  the  experiments  which 
Davy  performed  on  this  subject,  he  found  that  the  greatest  explosive  power 
was  manifested  when  the  gas  v^as  in  the  proportion  of  one  volume  to  seven 
or  eight  volumes  of  air,  or  when  it  formed  from  12  to  14  per  cent,  of  the 
mixture.  As  two  volumes  of  oxygen  are  theoretically  required,  and  these 
correspond  to  ten  volumes  of  air,  it  will  be  seen  that  the  maximum  explosive 
effect  takes  place  with  a  smaller  proportion  of  oxygen  than  theory  indicates. 
When  the  gas  was  in  the  proportion  of  20  per  cent,  of  the  mixture,  there 
was  combustion  without  explosion.  When  it  amounted  to  rather  less  than 
T  per  cent.,  there  was  no  explosion,  but  an  enlargement  of  the  flame  of  a 
candle;  and  this  enlargement,  but  in  a  diminishing  ratio,  was  observed  in 
mixtures  gradually  reduced  to  3  or  4  per  cent,  of  the  gas.  From  these 
results,  which  have  been  since  confirmed  by  the  observations  of  others,  it  is 
obvious  that  long  before  the  point  of  danger  is  reached,  a  warning  is  given 
by  an  elongation  of  the  flame  of  a  lamp  or  candle. 

As  to  the  temperature  required  for  the  explosion  of  a  mixture  of  fire- 
damp and  air,  Davy  observed  that  well-burned  charcoal,  ignited  to  the 
strongest  red  heat,  did  not  explode  any  mixture  of  air  and  of  the  fire-damp; 
and  a  fire  made  of  well-burned  charcoal,  i.  e.,  charcoal  that  burned  without 
flame,  was  blown  up  to  full  redness  by  an  explosive  mixture  containing  the 
fire-damp,  without  producing  its  inflammation.  An  iron  rod  at  the  highest 
degree  of  red-heat,  and  even  at  the  common  degree  of  white-heat,  did  not 
inflame  explosive  mixtures  of  fire-damp  ;  but,  when  in  brilliant  combustion, 
it  produced  this  efl'ect.  Flame  of  any  kind  exploded  a  mixture  of  fire-damp 
and  air.  In  reference  to  combustibility,  therefore,  this  compound  difl'ers 
from  the  other  common  inflammable  gases.  Davy  found  that  olefiant  gas 
which  explodes  when  mixed  in  the  same  proportion  with  air,  is  fired  by 
both  charcoal  and  iron  heated  to  redness.  Carbonic  oxide,  which  explodes 
when  mixed  with  two  parts  of  air,  is  likewise  inflamed  by  red-hot  iron  and 
charcoal ;  and  hydrogen,  which  explodes  when  mixed  with  three-sevenths  of 
its  volume  of  air,  takes  fire  at  the  lowest  visible  heat  of  iron  and  charcoal ; 
this  also  occurs  with  a  mixture  of  air  and  sulphuretted  hydrogen. 

The  safety-lamp  contrived  by  Davy  for  the  prevention  of  accidents  by 
explosion  in  coal-mines,  consists  of  a  cylinder  of  metallic  wire-gauze  con- 
taining from  700  to  900  meshes  in  the  square  inch.  This  presents  a  large 
metallic  surface  favorable  for  the  cooling  of  flame,  and  of  reducing  its 
temperature  below  that  required  for  kindling  explosive  mixtures.  The 
principle  of  its  qperation  may  be  illustrated  by  various  experiments.  Flame 
is  nothing  more  than  gaseous  or  vaporous  matter,  heated  to  a  very  high 
temperature,  and  requiring  a  high  temperature  for  its  continuance.  {See 
page  107.)  The  following  experiments  will  serve  as  illustrations:  Place 
a  lump  of  camphor  on  a  sheet  of  wire-gauze  like  that  which  is  used  for  the 
safety-lamp.  The  camphor  may  be  inflamed  from  beneath,  and  it  will  there 
be  consumed,  but  the  inflammable  vapor  of  the  camphor  will  not  be  ignited 
above  the  gauze — the  heat  conducted  by  the  metal  having  lowered  the  tem- 
18 


5lt4  CONSTRUCTION    OP    THE    SAFETY    LAMP. 

peratnre  far  below  that  required  for  its  combustion.  Tow  or  cotton  soaked 
in  ether  or  alcohol  may  be  substituted  for  the  camphor  with  like  results. 
There  will  be  no  ijrnition  of  the  vapor  of  either  liquid  above  the  gauze,  while 
it  will  burn  readily  below.  Into  a  small  cylinder  of  wire-gauze  (closed  at 
the  bottom  with  a  layer  of  gauze,  but  open  at  the  top)  throw  a  miss  of  tow 
soaked  in  alcohol  and  inOamed.  The  cylinder  may  now  be  placed  in  a  saucer 
containing  alcohol.  The  whole  of  the  spirit  will  be  drawn  in  and  consumed 
within  the  cylinder  ;  but  there  will  be  no  communication  of  flame  to  that 
which  is  on  the  outside.  Let  the  same  cylinder  be  fitted  closely  to  a  wire- 
stand  supporting  a  wax  taper,  so  that  when  the  taper  is  kindled,  it  may  be 
completely  enclosed  by  the  gauze  cylinder.  If  a  jar  of  hydrogen  or  coal-gas, 
or  a  mixture  of  either  with  air,  is  brought  over  the  cylinder  inverted,  and 
very  gradually  lowered,  the  inflammable  gas  will  traverse  the  gauze  and  burn 
with  flame,  but  without  explosion,  in  the  interior  of  the  cylinder,  and  there 
will  be  no  kindling  of  the  explosive  mixture  on  the  outside  of  the  cylinder. 
In  this  manner  the  whole  of  the  inflammable  gas  may  be  consumed  without 
being  inflamed  in  the  jar  ;  whereas,  if  any  such  mixtures  were  brought  over 
the  lighted  taper,  not  covered  by  the  gauze  cylinder,  there  would  be  instanta- 
neous inflammation  and  explosion. 

The  safety-lamp  consists  of  an  ordinary  oil-lamp,  to  which  a  gauze  cylinder 
is  so  secured  as  to  allow  of  combustion  only  by  the  air  which  traverses  the 
meshes  of  the  gauze.  As  a  test  of  the  eflBcacy  of  the  lamp,  it  may  be  lighted 
and  suspended  within  a  large  gas-jar,  to  the  bottom  of  which,  a  current  of 
coal-gas  is  conducted  by  a  vulcanized  rubber  tube.  The  efl'ects  produced 
by  mixtures  of  coal-gas  and  air,  in  various  proportions,  can  thus  be  ob- 
served. If  there  is  a  deficiency  of  oxygen,  the  lamp  will  be  extinguished; 
if  the  quantity  of  gas  is  in  very  small  proportion,  combustion  will  be  con- 
tinued with  an  elongated  flame.  In  explosive  proportions,  the  mixture  will 
penetrate  the  lamp  and  burn  in  the  interior  of  the  gauze-cylinder,  tempo- 
rarily extinguishing  the  flame.  If  suddenly  raised  into  the  air,  the  flame  will 
sometimes  be  re-kindled  ;  but  in  no  case,  if  the  wire-gauze  is  in  a  sound 
condition,  wil-l  the  flame  be  communicated  to  the  gaseous  contents  of  the  jar. 
If  a  full  stream  of  coal-gas  mixed  with  air  is  allowed  to  play  at  diflerent 
distances  upon  the  flames  of  a  Davy  lamp,  all  the  phenomena  described  will 
be  witnessed.  According  to  the  proportions  of  gas  and  air  the  flame 
will  be  lengthened  or  the  gas  burnt  inside,  but  if  the  lamp  is  sound,  there 
will  not  be  any  kindling  of  the  gas  on  the  outside  as  it  issues  from  the  jets. 
The  wick  of  the  lamp  is  frequently  re-kindled  when  the  jet  of  gas  is  with- 
drawn.^ If  the  jet  is  brought  close  to  the  wire,  there  is  so  much'gas  and  so 
little  air  that  combustion  can  no  longer  go  on,  and  the  lamp  is  extinguished. 

In  the  use  of  this  lamp  in  coal  mines  the  cylinder  should  be  locked  or 
securely  fastened  to  the  lamp,  and  on  no  pretence  removed  while  it  is  em- 
ployed for  mining  purposes.  The  real  object  of  this  invention  has  been,  to 
a  great  extent,  defeated  by  ignorance  and  carelessness.  Davy's  experiments 
have  shown  that  the  state  of  the  flame  will  alwavs  give  warning  of  danger. 
The  lamp  is  admirably  adapted  to  test  with  safety  the  condition  of  the  air  in 
the  shafts  and  galleries  of  coal  mines,  and  to  warn  the  miner  of  the  spots 
where  it  would  be  unsafe  to  commence,  or  continue  work,  until  the  fire-damp 
had  been  removed  by  proper  ventilation.  As  the  explosive  mixture  is  not 
noxious  to  breathe,  miners  continue  to  use  the  lamp  long  after  it  has  indi- 
cated danger.  The  gauze  may  become  red-hot  by  the  continued  combustion 
of  the  mixture  within  the  lamp  ;  the  flame  may  be  driven  through  the  meshes 
by  a  strong  current  of  the  gas  from  Mowers,  or  a  small  particle  of  coal-dust 
may  strike  upon  the  outside  of  the  red-hot  wire  and  be  kindled  into  flame, 
when  the  whole  mixture  will  be  exploded,  with  a  great  destruction  of  life, 


OLEFIANT    GAS,      PREPARATION.  216 

arising  from  burning,  from  serious  mechanical  injury,  or  from  suffocation  as 
a  result  of  the  carbonic  acid  produced  in  the  explosion.  The  accidents  which 
have  almost  annually  led  to  a  great  destruction  of  life  in  coal  mines  have 
been  wrongly  attributed  to  the  use  of  the  lamp.  They  have  been  rather  due 
to  its  abuse.  The  removal  of  the  gauze-cylinder — or,  when  locked,  the  per- 
foration of  it  for  obtaining  more  light — the  use  of  tobacco,  lucifer  matches, 
and  gunpowder  in  coal  mines,  are  the  principal  causes  of  these  accidents, 
when  it  has  been  possible  to  trace  them.  In  the  late  fatal  accidents,  1866-t, 
lucifer  matches  and  pipes  were  found  in  the  pockets  of  some  of  the  miners 
who  had  been  killed  by  the  explosion. 

The  fire-damp,  being  very  light,  ascends  and  collects  in  hollows  or  recesses 
at  the  upper  parts  of  the  workings ;  so  that  while  the  lower  part  or  floor 
may  be  ventilated  and  free  from  danger,  a  light  brought  near  to  the  roof 
might  lead  to  a  dangerous  explosion.  For  the  prevention  of  accidents  a 
better  system  of  ventilation  is  required,  and  a  more  strict  supervision  of  the 
modein  which  safety-lamps  are  used  by  miners.  A  very  ingenious  instru- 
ment has  been  lately  devised  by  Mr.  Ansell,  called  the  Fire-damp  Indicator, 
the  object  of  which  is  to  show  when  there  is  an  undue  accumulation  of  gas 
in  coal  mines.  Its  action  depends  on  the  law  of  diffusion  and  on  the  great 
diffusive  powers  of  coal-gas.  If  a  vessel  covered  with  a  porous  membrane  or 
with  unglazed  porcelain,  containing  air  is  brought  into  a  mixture  of  light 
carburetted  hydrogen  and  air,  the  gas  penetrates  rapidly  into  the  interior, 
and  either  distends  the  elastic  membrane,  or,  if  unglazed  porcelain  is  used, 
causes  a  pressure  upon  a  column  of  mercury  which  immediately  begins  to 
rise.  By  movements  thus  obtained  the  wires  of  a  voltaic  battery  may  be 
brought  into  communication  and  a  signal  given,  or,  where  the  instrument  is 
in  the  form  of  an  aneroid  barometer  the  degree  of  mixture  may  be  read  by  an 
index  affixed.  The  presence  of  one  or  two  per  cent,  of  the  gas  in  air  is  said 
to  be  indicated  by  some  of  these  instruments.  (See  Chem.  News,  1867,  v.  15, 
p.  13.) 

Explosions  in  houses  from  an  accumulation  of  coal-gas  and  its  admixture 
with  air  are  equally  formidable,  and  depend  on  similar  chemical  principles. 
There  is,  however,  always  ample  warning  in  these  cases  by  the  powerful 
odor  which  announces  the  escape  of  coal-gas,  long  before  it  has  reached  its 
explosive  proportion.  Instead  of  opening  doors  and  windows,  and  keeping 
at  a  distance  all  lights,  until  the  smell  has  disappeared,  the  ordinary  practice 
is  to  ap[)ly  a  light  for  the  purpose  of  ascertaining  where  the  leakage  has 
occurred.  The  whole  of  the  air  in  a  room  may  be  in  an  explosive  state,  but 
the  coal-gas  has  a  great  tendency  to  accumulate  at  the  upper  part.  Hence 
it  is  this  part  which  should  be  thoroughly  ventilated.  A  lighted  candle  may 
burn  on  the  floor  of  a  room,  but,  if  raised  a  few  feet  above  it,  it  may  cause 
a  violent  explosion.  In  no  case,  however,  can  this  accumulation  occur  with- 
out full  warning  being  given  by  the  odor  of  the  gas,  which  is  perceptible 
when  mixed  with  500  times  its  volume  of  air.  {See,  on  the  subject  of  gas- 
explosions  in  houses,  a  paper  in  the  Medical  Gazette,  vol.  xlii.  p.  343.) 

Olefiant  Gas.  Elayle.  Elhelene.  Carburet  of  Hydrogen.  Bicarhu' 
retted  Hydrogen  (CallJ. — This  gas  was  discovered  in  1796,  by  the  Dutch 
chemists,  who  gave  to  it  the  name  which  it  commonly  bears,  owing  to  the 
property  which  it  possesses  of  forming  an  oily  compound  with  chlorine. 

It  is  usually  obtained  by  the  decomposition  of  alcohol  by  concentrated 
sulphuric  acid.  For  this  purpose,  about  two  parts  of  the  acid  and  one  of 
alcohol  (by  measure)  are  put  into  a  capacious  retort,  and  heated  by  a  lamp  ; 
when  the  mixture  boils,  the  gas  is  evolved  with  sulphurous  and  carbonic 
acids  J  and  a  carbonized  mass  remains  in  the  retort.     It  may  be  collected 


276  CHEMICAL    PROPERTIES.       COMPOSITION. 

over  water,  and  should  be  well  washed  with  lime-water,  or  with  a  solution  of 
potassa,  in  order  to  remove  carbonic  and  sulphurous  acids  ;  it  also  retains 
a  little  ethereal  vapor,  which  may  be  remove  by  agitating  it  with  vteak  alcohol 
and  afterwards  with  water.  During  the  distillation,  the  black  carbonaceous 
mass  is  apt  to  fill  the  retort  and  pass  over  into  the  bath.  To  prevent  an 
accident  of  this  kind,  the  heat  should  be  applied  around  the  body  of  the 
retort  by  a  circular  jet  of  gas,  and  sand  or  broken  glass  may  be  mixed  with 
the  liquids  before  the  heat  is  applied. 

The  changes  which  take  place  in  the  production  of  this  gas  may  be  thus 
represented  :  Alcohol  is  C^HgO^,,  a  constitution  which  is  equivalent  to  two 
volumes  of  olefiant  gas  2(C2,H2)  and  two  volumes  of  aqueous  vapor  2(H0). 
By  the  action  of  sulphuric  acid,  at  a  temperature  of  about  320°  the  alcohol 
is  resolved,  by  a  catalytic  action  (p.  58),  into  these  compounds,  while  the 
water  is  retained  by  the  acid  in  the  receiver  (C4Hg02+ 803X10  =  2C2H2-f 
S03,3HO).  There  are  other  and  more  complicated  changes  in  the  latter 
stage  of  the  distillation,  as  the  carbon  of  the  alcohol  then  decomposes  part 
of  the  sulphuric  acid,  forming  the  two  gaseous  acid  products  which  contami- 
nate the  gas  :  these  changes  will  be  considered  at  another  time. 

Properties. — Olefiant  gas  is  colorless,  and  neutral  in  reaction.  It  has  been 
liquefied  by  pressure,  and  cooling  to  — 166°,  but  not  solidified.  Even  when 
purified,  it  retains  a  slight  ethereal  odor.  It  acts  like  a  narcotic  poison 
when  breathed.  Water  dissolves  about  12*5  per  cent,  of  its  volume.  It  is 
dissolved  more  freely  by  fuming  sulphuric  acid,  and  by  the  ammoniacal  solu- 
tion of  the  subchloride  of  copper.  It  extinguishes  all  burning  bodies,  but 
is  itself  highly  combustible,  burning  with  a  bright  white  flame,  similar  to 
that  of  burning  oil,  tallow,  wax,  or  a  coal-fire.  It  evolves  much  light  during 
combustion  :  the  particles  of  carbon,  of  which  it  contains  a  large  quantity, 
being  rendered  incandescent  by  the  combustion  of  the  hydrogen.  A  portion 
of  this  carbon  is  deposited  on  any  cold  surface  introduced  into  the  flame. 
When  mixed  with  a  large  proportion  of  air  it  burns  with  a  pale  flame,  the 
carbon  being  then  entirely  consumed  as  well  as  the  hydrogen.  If  a  taper  is 
suddenly  plunged  to  the  bottom  of  a  jar  of  the  gas  it  will  kindle  the  gas,  but 
be  itself  extinguished.  If  the  taper  is  withdrawn,  and  a  quantity  of  water 
is  poured  through  the  burning  gas  so  as  gradually  to  fill  the  jar,  the  gas  will 
be  brought  to  the  surface,  and  burnt  in  a  large  sheet  of  flame.  If  lime-water 
is  "added  to  another  jar,  during  its  combustion,  this  liquid  will  be  rendered 
milky,  showing  the  production  of  carbonic  acid.  This  may  also  be  proved 
by  burning  the  gas  from  a  jet  under  a  jar  of  air,  and  afterwards  testing  the 
contents  of  the  jar  with  lime-water. 

When  mixed  with  three  times  its  volume  of  oxygen,  and  the  mixture  is 
exploded,  either  by  flame  or  the  electric  spark,  it  is  converted,  with  a  violent 
detonation,  into  carbonic  acid  and  water : 

C2H2    4-    Og     (15  vols,  air)  =  2CO2    -f     2H0 

1  vol.       3  vols.  2  vols.        2  vols. 

Its  composition  may  be  deduced  from  these  results  :— the  2  vols,  of  car- 
bonic acid  represent  2  vols,  or  equivalents  of  carbon,  with  2  vols,  of  oxy- 
gen ;  while  2  vols,  of  aqueous  vapor  represent  2  vols,  of  hydrogen,  and  1 
vol.  of  oxygen  : — 

Atoms.    Weights.      Per  cent.        Vols.  Sp.  Gr. 

Carbon.        .        .     2     ...     12     ...     85-7     ...     2     ...     0-8292 
Hydrogen      .        .    2     ...       2     ...     14-3     ...     2     ...     0-1382 


14  100-0  1  0-9674 


CARBON    AND    NITROGEN.  2*77 

The  specific  gravity  of  olefiant  gas  is  therefore  about  0'96*74,  and,  com- 
pared with  hydrogen,  it  is  14  to  1.  100  cubic  inches  weigh  29-96  grains. 
Its  refractive  power  is  1818,  air  being  =1000: — its  specific  heat,  com- 
pared with  that  of  air,  1-53  (Dulong),  being  greater  than  that  of  any 
other  gas.  As  it  is  usually  prepared,  it  is  often  associated  with  other  hydro- 
carbon vapors,  which  may  affect  its  physical  properties.  A  mixture  of  this 
gas  with  oxygen  is  converted  into  acetic  acid  by  spongy  platinum,  and  its 
solution  in  sulphuric  acid  has,  by  agitation  in  water  and  mercury,  produced 
alcohol.  (Berthelot).  When  passed  through  a  tube  heated  to  redness, 
it  deposits  one-half  of  its  carbon,  and  is  changed  into  light  carburetted 
hydrogen.  If,  however,  the  tube  is  heated  to  whiteness,  all  the  carbon  is 
deposited,  and  each  volume  of  the  gas  yields  two  volumes  of  hydrogen. 

The  action  of  chlorine  on  olefiant  gas  is  remarkable.  When  the  gas  is 
mixed  with  chlorine,  in  the  proportion  of  1  to  2  by  volume,  the  mixture, 
when  inflamed,  produces,  without  explosion,  hydrochloric  acid,  and  black 
amorphous  carbon  is  abundantly  deposited.  If  the  gases  be  well  mixed, 
and  then  inflamed  in  a  tall  and  narrow  glass  jar  (about  2  feet  high  and  4 
inches  in  diameter),  placed  with  its  mouth  upwards,  the  experiment  is  very 
striking ;  a  deep-red  flame  gradually  descends  through  the  mixture,  and  a 
dense  black  cloud  of  carbon  rise's  into  the  atmosphere  ;  fumes  of  hydrochloric 
acid  are  at  the  same  time  formed,  and  a  peculiar  aromatic  odor  is  evolved 
(C3H2+2C1=2HCI  +  2C).  The  hydrochloric  acid  maybe  detected  by  its 
effect  on  litmus-paper,  and  the  production  of  white  fumes  with  ammonia. 

Chloride  of  Olefiant  Gas  (CgHj^Cl)  ;  Dutch  Liquid ;  Chloric  Ether. — 
If  chlorine  and  olefiant  gases  be  merely  mixed,  in  equal  volumes,  over  water, 
or  in  a  clean  and  dry  glass  globe,  exhausted  of  air,  they  act  slowly  upon 
each  other,  and  a  peculiar  liquid  is  formed,  which  appears  like  a  heavy  yel- 
low oil  :  hence  the  term  olefiant  gas,  applied  to  this  hydrocarbon  by  the 
Dutch  chemists,  and  Elayle  (from  l-Kauov,  and  v-kri,  the  source  of  an  oil)  by 
Berzelius.  It  may  also  be  formed  by  allowing  a  current  of  each  gas  to  meet 
in  a  proper  receiver ;  but  there  should  always  be  an  excess  of  olefiant  gas, 
for  if  the  chlorine  is  in  excess,  the  liquid  will  absorb  it.  To  purify  it,  it 
should  be  washed  in  water,  and  then  carefully  distilled  over  fused  chloride 
of  calcium. 

This  compound  is  a  transparent  and  colorlcvss  liquid ;  its  taste  is  sweet, 
and  somewhat  acrid  ;  its  odor  fragrant.  Its  specific  gravity  is  1-2.  It  boils 
at  180°.  According  to  Gay-Lussac,  the  specific  gravity  of  its  vapor  is  3-45. 
It  burns  with  a  green  flame,  evolving  hydrochloric  acid,  and  depositing  car- 
bon. It  is  decomposed  when  passed  through  a  red-hot  tube,  and  is  converted 
into  acetylene  and  hydrochloric  acid.  It  has  been  employed  as  an  anaesthetic, 
but  has  been  found  too  stimulating.  Olefiant  gas  forms  a  similar  compound 
with  the  vapor  of  bromine. 

Oil  Gas  (C4HJ. — This  is  a  gaseous  compound,  containing  in  each  volume, 
as  its  vapor  density  proves,  double  the  proportions  of  carbon  and  hydrogen 
existing  in  olefiant  gas.  It  was  obtained  by  Faraday  as  one  of  the  products 
of  the  destructive  distillation  of  oil.  He  called  it  bicarburetted  hydrogen. 
As  a  gas,  it  has  a  sp.  gr.  of  1-9264 ;  it  burns  with  a  brilliant,  white,  smoky 
flame.  It  is  not  dissolved  by  water,  but  is  soluble  in  alcohol  and  the  oils. 
When  cooled  to  zero,  it  is  condensed  into  a  colorless,  light  liquid,  having  a 
sp.  gr.  of  0-627. 

Carbon  and  Nitrogen. — These  elements  cannot  be  made  to  combine 
directly,  but  they  form  three  different  compounds  ;  a  gaseous  body,  cyano- 
gen, NCa)  and  two  solids,  paracyanogen,  N^C^,  and  mellone,  N^Cg. 


2Y8  CYANOGEN.      CHEMICAL    PROPERTIES. 

Cyanogen  (NCg,  or  Cy=26).  Bicarhuret  of  Nitrogen. — This  gaseous 
componnd  was  discovered,  in  1815,  by  Gay-Lussac,  and  terml^d  cyanogen 
(from  xvaroj,  blue,  and  yiwdoi,  to  generate),  in  consequence  of  its  being  essen- 
tial to  the  production  of  Prussian  blue.  It  is  sometimes  formed  by  the 
direct  action  of  nitrogen  upon  carbon  in  the  presence  of  bases,  as  where 
nitrogen  or  air  is  passed  over  a  mixture  of  charcoal  and  carbonate  of  potassa, 
heated  to  redness.  Under  these  circumstances,  cyanogen  is  produced,  and 
enters  into  combination  with  the  metal  potassium  (KOjCO^  +  C^-f  N=K,NCg 
-f  SCO).  Cyanide  of  potassium  is  thus  sometimes  produced  and  deposited 
in  the  crevices  of  the  walls  of  blast-furnaces.  When  an  organic  substance 
containing  nitrogen  and  carbon  is  heated,  these  elements  will  not  unite 
directly;  but  if  heated  with  the  alkaline  metals,  potassium  or  sodium,  in  a 
glass  tube,  out  of  contact  of  air,  they  instantly  combine  to  form  cyanogen, 
and  this  body  unites  with  the  metal,  to  produce  a  metallic  cyanide.  This 
conversion  has  already  been  described  as  one  of  the  best  methods  of  detect- 
ing nitrogen  in  organic  matter  (p.  156).  In  the  destructive  distillation  of 
coal,  the  nitrogen  and  carbon  combine  to  form  cyanogen,  which  is  found  in 
the  solid  products  in  combination  with  ammonia  and  lime.  Sulphocyanogen 
is  also  produced  under  these  circumstances,  as  the  cyanogen  combines  with 
a  portion  of  the  sulphur  of  coal. 

Preparation. — Cyanogen  may  be  obtained  in  the  gaseous  state  by  heating 
well-dried  cyanide  of  mercury  in  a  small  retort  to  dull  redness.  The  gas 
readily  comes  over,  and,  as  it  is  dissolved  by  water,  it  should  be  collected, 
and  preserved  over  mercury.  Although  cyanogen  and  mercury  are  both 
volatile  bodies,  it  is  impossible  to  obtain  more  than  one-third  of  the  cyano- 
gen present  in  the  cyanide  [3HgCy=NC2(cyanogen)4-N4C4(paracyanogen) 
H-3Hg].  Mercury  sublimes,  but  there  remains  in  the  retort  a  brownish- 
black,  spongy-looking  solid,  which  from  its  composition  has  been  called />«m- 
cyanogen.  It  is  equivalent  to  two  atoms  of  cyanogen,  and  is  polymeric  with 
it  (2NC3=N2C4).  When  strongly  heated  in  air,  this  residue  yields  carbonic 
acid,  and  leaves  CN  ;  but  it  is  very  difBcult  of  combustion.  Cyanogen  is  so 
easily  decomposed  by  the  elements  of  water,  that  great  care  should  be  taken 
to  dry  the  cyanide  of  mercury  thoroughly  before  it  is  submitted  to  heat ;  and 
no  moisture  should  be  present  in  the  jars  in  which  the  gas  is  collected. 

Properties. — Cyanogen  is  a  colorless  neutral  gas,  of  a  pungent  odor,  irri- 
tating to  the  eyes,  and  highly  poisonous  if  breathed  even  in  a  diluted  state. 
Its  specific  gravity  when  compared  with  hydrogen  is  as  26  to  1  ;  and  with 
common  air,  as  1-796  to  1;  100  cubic  inches  weigh  55-64  grains.  It  sustains 
a  high  temperature  in  porcelain  tubes  without  decomposition.  Under  a 
pressure  of  between  three  and  four  atmospheres  at  the  temperature  of 
45°,  Faraday  condensed  cyanogen  into  a  limpid  colorless  liquid,  of  a  specific 
gravity  of  about  0  9,  and  a  refractive  power  rather  less  than  that  of  water. 
When  a  tube  containing  it  was  opened,  the  expansion  within  appeared  incon- 
siderable, and  the  liquid  slowly  evaporated,  producing  intense  cold.  It 
does  not  conduct  electricity.  At  temperatures  below  —30°,  it  becomes  a 
transparent  crystalline  solid. 

It  extinguishes  a  lighted  taper,  but  takes  fire  and  burns  with  an  inner 
rose-red  flame,  surrounded  by  a  blue  flame.  As  it  is  very  heavy,  the  jar 
Bhould  be  slightly  inclined  for  its  complete  condensation,  or  water  should  be 
poured  into  the  jar  while  it  is  burning.  Carbonic  acid  and  nitrogen  are  the 
sole  products  of  this  combustion.  Four  equivalents  or  two  volumes  of 
oxygen  are  required  for  its  entire  combustion  (NC3  +  0,=2CO,-fN).  In 
these  proportions  the  mixture  is  explosive  by  heat  or  electricity.  '  A  red-hot 
platinum  wire,  or  the  electric  spark,  will  kindle  the  gases  instantly.  The 
production  of  carbonic  acid  as  a  result  of  its  combustion,  may  be  proved  by 


COMPOUNDS  OF  CYANOGEN.  279 

burning  the  gas  from  a  jet  under  a  jar  of  air,  and  subsequently  adding  lime- 
water  to  the  contents  of  the  jar.  All  ordinary  combustibles  are  extin(z;uished 
in  it.  Alkaline  metals  may,  however,  be  burnt  in  it  as  readily  as  in  chlorine. 
Potassium  or  sodium  heated  to  ignition  and  introduced  into  the  gas,  under- 
goes vivid  combustion,  and  the  cyanogen  combines  directly  with  the  metal  to 
form  a  metallic  cyanide.  It  is  this  property  of  entering  into  combination 
like  an  element,  and  the  fact  that  with  hydrogen  it  forms  a  hydracid  in  every 
respect  analogous  to  those  produced  by  the  halogens,  which  have  induced 
chemists  to  designate  cyanogen  as  a  compound  radical,  and  to  associate  it 
with  chlorine,  bromine,  and  iodine.  Its  existence  shows  that  a  body  may 
have  all  the  ordinary  chemical  properties  assigned  to  an  element,  and  yet  be 
of  a  compound  nature. 

Cyanogen  does  not  bleach  organic  colors.  Water  will  dissolve  4*5  volumes 
of  the  gas;  alcohol  will  dissolve  23  volumes;  and  it  is  also  taken  up  by 
ether  and  oil  of  turpentine.  Its  aqueous  solution  is  rapidly  decomposed 
by  exposure  to  light ;  it  acquires  at  first  acid  and  afterwards  alkaline  pro- 
perties, cyanic  acid  and  ammonia  being  products  of  this  reaction.  Oxalate 
and  carbonate  of  ammonia,  formate  of  ammonia,  urea,  and  paracyanogen,  are 
also  products,  in  different  stages  of  decomposition,  of  the  aqueous  solution. 
Iodine,  sulphur,  and  pliosphorus  may  be  sublimed  in  the  gas  without  change. 
Dry  chlorine  has  no  action  on  dry  cyanogen  ;  but  when  moist  and  exposed 
to  light,  a  yellow  oil  is  produced,  which  appears  to  be  a  mixture  of  chloride 
of  carbon  and  chloride  of  nitrogen  (Serullas),  furnishes  another  proof  of 
the  importance  of  water  to  bring  about  chemical  changes  in  bodies  {see  pages 
42  and  145). 

The  gas  is  readily  dissolved  by  alkaline  liquids  ;  and,  as  with  the  halogens, 
a  cyanate  of  the  alkali  and  cyanide  of  the  metal  are  produced.  Oxide  of 
mercury  in  a  humid  state,  also  absorbs  the  gas,  forming  a  soluble  cyanide. 

Composition. — Cyanogen  may  be  passed  through  a  porcelain  tube  intensely 
heated  without  undergoing  any  change  ;  but  if  passed  through  a  red-hot  iron 
tube,  carbon  is  deposited,  and  a  volume  of  nitrogen*,  equivalent  to  the  cyanogen 
employed,  is  set  free.  If  one  volume  of  this  gas  is  mixed  with  two  volumes 
of  oxygen,  and  the  mixture  is  detonated  by  the  electric  spark  over  mercury, 
two  volumes  of  carbonic  acid  and  one  volume  of  nitrogen  result;  hence, 
deducting  the  oxygen  employed,  each  volume  of  this  gas  must  consist  of  two 
volumes  of  carbon  vapor,  and  one  volume  of  nitrogen  condensed  into  a  single 
volume  of  the  gas. 

Atoms.     Weights.       Per  cent.  Vols.  Sp.  Gr. 

Nitrogen      .         .     1     ...     14     ...     53-85     ...     1     ...     0-9G74 
Carbon         .         .     2     ...     12     ...     46-15     ...     2     ...     0-8292 


1  26  100-00  1  1-7966 

Test. — The  colored  flame  of  the  gas  during  combustion,  and  an  examina- 
tion of  the  products,  carbonic  acid  and  nitrogen,  are  sufficient  to  identify  it. 

Compounds. — Cyanogen  combines  directly  with  metals,  like  an  element, 
forming  cyanides  of  metals  analogous  to  oxides  and  chlorides  ;  it  forms  acids 
with  oxygen  and  hydrogen,  and  compound  radicals  with  sulphur  and  iron, 
which  also  combine  with  hydrogen  to  form  acids,  and  with  metals  to  form 
peculiar  classes  of  salts.  The  metallic  cyanides  are  remarkable  for  the  readi- 
ness with  which  they  produce  double  salts.  The  subjoined  list  comprises  the 
principal  derivative  compounds  of  cyanogen  : — 


280  CYANIC    ACID.      CHEMICAL    PROPERTIES. 

Cyanogen  Cy  Cyanide  MCy 

Cyanic  acid  Cy,  0  Cyanate  ^^^'^^?..^ 

Fulminic  acid  Cy2,02  Fulminate  S^202,2MO 

Cyanuric  acid  Cyg.Og  Cyanurates  Cy.Og.SMO 

Hydrocyanic  acid       HCy  +  MO  =  Cyanide  MCy, (HO) 

f  H    Hvdrosulphocyanic  acid 
Sulphocyanogen         bgf^y  |  j£    Sulphocyanide 

j  H,  Hydroferrocyanic  acid 
Ferrocyanogen  teLy^  \  Mg  Ferrocyanide 

f  H3  Hydroferricvanic  acid 
Femcyanogen  i^e^Ly^  \  M3  Ferricyanide 

„    „    „^  f  H,  Nitroliydrocyanic  acid 

Nitroferricyanogen     Fe^CygNO^  JmJ  Nitroprusside 

Mellone  (N^Cfi). — The  third  compound  of  carbon  and  nitro^jen  is  a  solid 
substance  of  a  yellow  color,  produced  in  the  destructive  distillation  of  sul- 
phocyanogen. It  may  be  heated  to  dull  redness  without  change,  but  at  a 
higher  temperature  it  is  resolved  into  three  volumes  of  cyanogen  and  one  of 
nitrogen  (N4C6=3NC24-N).  It  is  a  compound  radical,  and  combines  directly 
with  metals  to  form  Mellonides.  According  to  Gerhardt,  it  always  contains 
hydrogen. 

Cyanogen  and  Oxygen. — These  bodies  form  three  homologous  acids, 
the  cyanic  (CyO),  the  fulminic  (CygOJ,  and  the  cyanuric  (CygOg).  They 
are  monobasic,  bibasic,  and  tribasic,  respectively. 

Cyanic  Acid  (CyO). — When  cyanogen  is  passed  into  an  alkaline  solution, 
a  cyanide  and  a  cyanate  are  formed  (2BaO  +  2Cy  =  BaCy-fBaO,CyO),  and 
so  far  the  action  of  cyanogen  corresponds  to  that  of  chlorine  :  but  the  ex- 
treme tendency  of  the  cyanates  so  formed,  to  decomposition,  prevents  their 
separation.  A  permanent  cyanate  may  be  obtained  by  the  following  process: 
six  parts  of  ferrocyanide  of  potassium  and  two  of  carbonate  of  potassa, 
both  carefully  dried  (anhydrous),  are  intimately  mixed  in  fine  powder  with 
eight  parts  of  pure  and  dry  peroxide  of  manganese:  this  mixture  is  heated 
for  some  time  to  dull  redness,  until  a  portion  cooled  and  dissolved  in  water, 
does  not  give  a  blue  precipitate  with  a  persalt  of  iron.  The  contents  of  the 
crucible  are  then  allowed  to  cool,  reduced  to  powder,  and  boiled  for  fifteen 
minutes  in  alcohol,  sp.gr.  'SSO.  The  liquid  is  filtered  while  hot,  and  on  cooling 
it  deposits  crystals  of  cyanate  of  potassa.  The  alcohol  is  poured  from  the 
salt  and  again  boiled  with  the  residue,  so  long  as  further  portions  of  cyanate 
can  be  thus  obtained.  The  salt  should  be  well  dried  by  pressure  in  filtering 
paper,  and  afterwards  in  vacuo  over  sulphuric  acid;  it  must  be  preserved  out 
of  contact  of  air  and  moisture,  otherwise  it  will  soon  pass  into  ammonia  and 
carbonate  of  potassa.  Although  the  cyanic  acid  may  thus  be  obtained  in 
union  with  a  base,  any  attempt  to  set  it  free  by  means  of  another  acid,  is 
attended  by  its  immediate  decomposition  into  carbonic  acid  and  ammonia. 
Wohler  endeavored  to  procure  the  acid  in  a  pure  state,  by  decomposing 
cyanate  of  silver  by  dry  hydrochloric  acid.  The  product,  however,  was  hy- 
drated  cyanic  acid  with  one  equivalent  of  hydrochloric  acid  gas ;  hence, 
when  brought  into  contact  with  water,  it  was  immediately  resolved  into 
hydrochlorate  of  ammonia  and  carbonic  acid.  Cyanic  acid,  in  the  presence 
of  water,  cannot  be  separated  from  its  salts  without  undergoing  immediate 
decomposition.  Liebig  found  that  it  might  be  procured  in  a  concentrated 
form  as  hydrate,  by  heating  cyanuric  acid  in  an  air-tight  retort,  connected 
with  a  receiver  surrounded  by  ice.  These  acids  contain  the  same  elements, 
and  are  mutually  convertible  the  one  into  the  other  ;  but  cyanic  acid  is  a 
simple  atom,  while  cyanuric  acid  is  a  complex  atom. 

Properties.— "Yhx^  acid  in  its  concentrated  state  (HO, CyO)  is  a  limpid 
colorless  liquid.     It  is  intensely  corrosive  and  strongly  acid.     Its  vapor  is 


FULMINIC    ACID.  281 

very  pungent,  like  that  of  the  stronp^est  acetic  acid,  and  It  is  very  irritating 
to  the  eyes  and  nose  ;  but  it  is  not  inflammable.  Wiien  diluted  with  a  little 
water  and  retained  at  32°,  its  odor  is  like  that  of  acetic  acid,  but  it  soorf 
begins  to  change  ;  carbonic  acid  is  evolved,  carbonate  and  cyanate  of  ammo- 
nia are  formed,  and,  by  evaporation,  crystals  of  urea  may  be  obtained.  In 
this  case  one  atom  of  cyanic  acid  and  three  of  water,  at  first  yield  one  atom 
of  bicarbonate  of  ammonia;  C2N,0  +  3HO=NH3,2C03 :  but  the  cyanic, 
being  a  stronger  acid  than  the  carbonic,  the  undecomposed  cyanic  acid  com- 
bines with  the  ammonia  and  expels  carbonic  acid  ;  and,  on  evaporation,  the 
cyanate  of  ammonia  combines  with  an  atom  of  water  to  form  urea ;  NH3, 
HO,C,NO  =  C,H,OA. 

Hydrated  cyanic  acid,  as  obtained  by  the  method  above  described,  when 
it  has  cooled  to  60°,  becomes  turbid  and  milky-looking  ;  it  acquires  heat 
spontaneously,  begins  to  boil,  and  then  passes  into  a  pasty-looking  solid, 
while  there  are  sudden  evolutions  of  gas  with  explosions,  from  the  unchanged 
portion  of  the  acid.  It  is  ultimately  converted  into  a  dry,  solid,  uncrystal- 
line  white  substance,  which  is  called  Gyamelide  (Liebig).  These  remarkable 
changes  take  place  rapidly  at  the  common  temperature,  and  quite  independ- 
ently of  air  and  moisture.  They  also  take  place  at  the  freezing-point,  but 
more  slowly,  and  no  gas  is  evolved  under  these  circumstances. 

Cyamelide  is  insoluble  in  water,  nitric  acid,  and  hydrochloric  acid,  either 
separately  or  mixed  as  aqua  regia.  It  is  dissolved  by  potassa  with  evolution 
of  ammonia,  and  cyanurate  of  potassa  is  obtained  by  evaporation.  Concen- 
trated sulphuric  acid  dissolves  it  when  the  mixture  is  moderately  heated,  with 
escape  of  carbonic  acid  and  the  production  of  sulphate  of  ammonia.  The 
products  of  its  decomposition  are  therefore  the  same  as  those  of  cyanic  acid 
in  water,  and  when  cyamelide  is  distilled  by  itself  it  is  reconverted  into  hy- 
drated cyanic  acid.     It  is  therefore  an  isomeric  solid  condition  of  this  acid. 

Cyanates. — The  cyanates  of  the  alkalies  alone  are  soluble  in  water,  and 
are  not  decomposed  by  a  red  heat.  When  an  aqueous  solution  of  an  alkaline 
cyanate  is  heated,  carbonic  acid  and  ammonia  are  produced  (NC.30  +  3HO  = 
NH3+2COij).  The  nitrates  of  lead,  silver,  and  mercury  give  with  the  solu- 
tion of  a  cyanate  white  precipitates.  When  mixed  with  sulphate  of  ammonia, 
and  evaporated  to  dryness,  a  solution  of  a  cyanate  yields  urea.  When  hy- 
drated cyanate  of  ammonia  is  gently  heated  either  in  the  dry  state  or  in  solu- 
tion, it  is  converted  into  urea  (Wohler).  These  substances  are  metameric 
(seepage  19).  When  an  acid  is  added  to  a  cyanate,  either  solid  or  in  solu- 
tion, there  is  eflfervescence,  owing  to  the  production  and  escape  of  carbonic 
acid.  The  strong  pungent  odor  of  hydrated  cyanic  acid  will  be  perceptible, 
and  a  salt  of  ammonia  is  formed  in  the  liquid.  Hence  a  cyanate  cannot  be 
mistaken  for  a  carbonate. 

FuLMiNio  Acid  2(C3N)03  or  {(^yfi^. — Under  the  articles  Mercury  and 
Silver,  the  process  for  preparing  detonating  compounds  of  these  metals,  by 
acting  upon  their  nitric  solutions  by  alcohol,  will  be  described.  The  oxides 
are  united  to  an  acid  containing  the  same  elements,  and  in  the  same  relative 
proportions,  as  the  cyanic  acid,  to  which,  in  that  particular  state  of  combi- 
nation, the  term  Falminic  Acid  has  been  applied  ;  but  the  equivalent  of  the 
fulminic  acid  is  exactly  double  that  of  the  cyanic.  This  acid  has  not  been 
isolated  :  it  is  known  only  in  combination  with  bases. 

Fulminic  acid,  therefore,  cannot  be  obtained  as  such  from  the  bases  with 
which  it  is  combined  ;  at  the  moment  of  its  separation  by  a  stronger  acid, 
it  is  resolved  into  hydrocyanic  acid  and  other  products.  Hence  we  have  ia 
this  compound  an  acid  in  which  the  metal  cannot  be  replaced  by  hydrogen 
{see  page  75). 

Fulminates. — These  are  bibasic  salts  containing  either  two  atoms  of  fixed 


282      CYANOGEN  AND  HYDROGEN.   HYDROCYANIC  ACID. 

base  (neutral  fulmitiates),  or  one  atom  of  fixed  base  and  one  atom  of  water. 
The  two  atoms  of  fixed  base  may  be  represented  by  two  atoms  of  the  oxide 
of  an  easily  reducible  metal,  or  by  two  atoms  of  the  oxides  of  two  different 
metals,  also  easily  reducible.  There  are  no  fulminates  of  two  alkaline  bases. 
The  fulminates  explode  by  concussion,  friction,  heat,  or  contact  with  concen- 
trated sulphuric  acid.  They  evolve  hydrocyanic  acid  when  treated  v/ith 
hydrochloric  acid. 

Cyanuric  Acid  (CgNgOa  or  CygO.). — This  acid  may  be  obtained  in  com- 
bination with  three  atoms  of  water,  as  SHO  +  Cy^Og.  Scheele  first  described 
it  under  the  name  of  pyro-uric  acid.  He  procured  it  by  the  destructive  dis- 
tillation of  uric  acid.  It  exists  in  the  hydrated  and  anhydrous  states.  It 
is  dissolved  by  strong  sulphuric  or  nitric  acid  without  change,  and  is  pre- 
cipitated by  water.  The  alkaline  cyanurates  evolve,  when  heated,  hydrated 
cyanic  acid,  cyanate  of  ammonia,  carbonic  acid,  and  nitrogen,  leaving  a 
residue  of  cyanate. 

The  cyanic,  fulminic,  and  cyanuric  acids,  although  composed  of  similar 
proportions  of  the  same  elements,  are  widely  different  in  properties — a  fact 
which  appears  to  show  that,  in  compounds  of  a  quasi-organic  character,  the 
properties  of  bodies  are  more  dependent  on  molecular  arrangement  than  on 
atomatic  constitution.  The  cyanuric  acid  alone  can  exist  in  the  anhydrous 
state,  and  remain  unchanged  in  contact  with  water  and  other  acids.  This 
acid  alone  is  soluble  in  alkalies  without  change,  and  may  be  separated  from 
its  alkaline  solution  by  acids  in  an  unaltered  state.  Cyanurate  of  silver  will 
bear  a  temperature  of  300°,  without  undergoing  decomposition.  At  this 
temperature,  cyanate  of  silver  is  decomposed  with  ignition  and  evolution  of 
carbonic  acid  and  nitrogen  (Liebig),  while  fulminate  of  silver  under  the 
same  circumstances  is  decomposed  with  detonation,  a  double  amount  of  car- 
bonic acid  and  nitrogen  being  produced.  Although  fulminic  acid  is  the 
intermediate  compound,  it  cannot  be  procured  either  by  the  intermixture  of 
the  cyanic  and  cyanuric  acids,  or  by  the  action  of  any  chemical  reagents 
upon  them.  In  this  respect  these  three  compounds  somewhat  resemble  the 
hydrates  of  phosphoric  acid,  the  first  being  converted  at  once  into  the  third, 
without  the  production  of  the  second  hydrate  (p.  242).  In  phosphoric  acid, 
the  difference  arises  from  an  increase  in  the  atoms  of  water  of  hydration  :  in 
these  acid  compounds  of  cyanogen,  the  first  and  last  members  of  the  series 
only  are  hydrated  ;  and  there  is  an  increase  in  the  proportion  of  the  elements 
as  well  as  of  the  atoms  of  water.  In  reference  to  fulminic  acid,  it  is  worthy 
of  note  that,  as  in  an  isolated  state,  it  will  not  combine  with  the  elements  of 
water,  its  existence  proves,  among  other  facts,  that  acids  are  not  necessarily 
salts  of  hydrogen  {see  p.  94). 

Cyanogen  and  Hydrogen.  Hydrocyanic  Acid.  Oyanhydric  Acid, 
Prussic  Acid.—{R,^G,  or  HCy) — This  compound  was  first  obtained  by 
Scheele  in  1782.  It  was  not,  however,  until  the  discovery  of  cyanogen  by 
Gay-Lussae,  in  1815,  that  its  real  nature  was  understood,  and  its  compo- 
nents accurately  determined.  Cyanogen  and  hydrogen  have  no  tendency 
to  direct  combination,  but  by  the  action  of  certain  acids  on  metallic  cyan- 
ides, hydrocyanic  acid  is  produced  by  double  decomposition  :  in  this  way  it 
is  obtained  by  the  action  of  hydrochloric  acid  on  dry  cyanide  of  mercury  or 
silver  (AgCy  +  HCl=AgCl4-HCy).  The  mixture  may  be  distilled  in  a 
sand-bath,  and  the  product  collected  in  a  receiver  kept  cool  by  a  freezing 
mixture.  In  order  to  obtain  anhydrous  hvdroeyanic  acid,  the  following  pro- 
cess 18  preferable.  Introduce  the  dry  cyanide  of  mercury  into  a  long  glass 
tube,  terminating  at  one  extremity  in  a  receiver  immersed  in  a  freezing  mix- 
ture, and  then,  from  a  proper  apparatus,  pass  over  it  a  stream  of  pure  and 


COMPOSITION    OF    HYDROCYANIC    ACID.  283 

well  dried  sulphuretted  hydrogen,  the  sulphur  of  which  combines  with  the 
mercury  to  form  sulphide  of  mercury,  while  the  hydrogen  unites  to  the 
cyanogeu  to  form  hydrocyanic  acid  (HgCy  +  HS  =  HgS  +  HCy).  The  vapor 
of  the  acid  may  be  driven,  by  the  application  of  a  gentle  heat,  into  the  cold 
receiver,  and  there  condensed.  The  ordinary  process  of  obtaining  this  acid, 
consists  in  distilling  by  a  gentle  heat  10  parts  of  6nely  powdered  ferrocyanide 
of  potassium,  with  a  mixture  of  5  parts  of  sulphuric  acid  and  14  of  water: 
the  product  should  be  collected  in  a  well  cooled  receiver.  The  acid  may  be 
concentrated  by  digesting  it  with  chloride  of  calcium.  Any  Prussian  blue 
may  be  separated  from  it  by  re-distillation.  The  hydrocyanic  acid  thus  pro- 
cured, should  be  preserved  in  a  well-stopped  phial.  In  this  process,  the 
cyanide  of  potassium  of  the  ferrocyanide,  is  decomposed  by  the  hydrated 
sulphuric  acid.  KCy-f  HO,S03=KO,S03-f  HCy.  Cyanide  of  potassium 
may  be  substituted  for  the  ferrocyanide.  Hydrocyanic  acid  forms  no  definite 
hydrate  with  water:  hence,  according  to  Millon,  it  may  be  obtained  anhy- 
drous from  the  most  diluted  solution  with  as  little  trouble  as  absolute  alcohol. 
He  submits  the  diluted  acid  to  fractional  distillation,  collecting  the  distillate 
between  120°  and  212°.  After  two  or  three  distillations,  he  passes  the 
vapor  through  two  Woulfe's  bottles,  containing  dry  chloride  of  calcium,  and 
condenses  it  in  a  receiver,  placed  in  a  freezing  mixture.  The  heat  of  distilla- 
tion in  the  last  stage  is  not  allowed  to  exceed  ITG^. 

Properties. — Anhydrous  hydrocyanic  acid  is  a  colorless  liquid  :  its  vapor 
when  diffused  in  air  has  an  odor  resembling  that  of  bitter  almonds.  Its 
taste,  when  diluted  with  water,  is  warm  and  acrid,  and  it  is  highly  poisonous, 
so  that  the  utmost  care  should  be  taken  to  avoid  the  inhalation  of  its  vapor. 
The  respiration  of  a  small  quantity  of  this  vapor,  even  in  a  diluted  state, 
produces  an  acrid  sensation  in  the  nose  and  throat,  dizziness,  sense  of  weight 
in  the  head,  and  insensibility.  It  is  irritating  to  the  eyes.  The  vapor 
readily  traverses  by  osmosis,  paper,  animal  membrane,  and  even  caoutchouc. 
The  anhydrous  acid  is  the  most  powerful  poison  known,  whether  we  regard 
the  smallness  of  the  dose  or  the  rapidity  of  its  operation.  Less  than  a  grain 
of  the  acid  has  destroyed  the  life  of  an  adult  in  twenty  minutes.  The  anhy- 
drous acid  volatilizes  so  rapidly  as  to  freeze  itself,  when  a  drop  of  it  is  placed 
on  a  glass  plate.  Its  specific  gravity  at  64°  is  0*696  :  and  the  specific 
gravity  of  its  vapor,  as  experimentally  determined  by  Gay-Lussac,  is  09476  ; 
it  boils  at  80°,  and  congeals  at  3°,  or  4°  above  0°  in  its  ordinary  state  ;  but 
when  it  is  perfectly  anhydrous,  it  remains  liquid  according  to  Schultz  at 
— 40°.  It  burns  with  a  bright  flame.  It  scarcely  affects  the  blue  of  litmus. 
It  is  very  liable  to  spontaneous  decomposition,  especially  under  the  influence 
of  light,  becoming  brown,  evolving  ammonia,  and  depositing  paracyanogen, 
changes  which  are  prevented  by  the  presence  of  minute  portions  of  other 
acids,  but  are  accelerated  by  traces  of  ammonia  or  other  bases.  The  pure 
anhydrous  acid  is  decomposed  spontaneously,  whether  kept  in  the  light  or 
dark,  whether  in  open  or  closed  vessels.  If  highly  concentrated,  it  solidifies 
into  a  brownish-black  jelly-like  mass.  When  mixed  with  strong  hydro- 
chloric acid,  it  soon  solidifies  into  a  pure  crystalline  mass  of  hydrochlorate 
o*f  ammonia.  Millon  found  that  the  anhydrous  acid  forms  other  compounds, 
which  are  only  stable,  so  long  as  water  is  excluded.  Moisture  destroys 
them,  and  formate  of  ammonia  is  produced.  The  effect  of  ammonia  upon 
this  liquid  is  remarkable  :  a  few  bubbles  of  the  gas  were  found  to  solidify 
several  ounces  of  the  anhydrous  acid.  Dilution  with  water  delayed,  but  did 
not  prevent  this  result.  The  preservative  effects  of  acids,  appear  to  depend 
on  the  neutralization  of  ammonia  or  the  prevention  of  its  production.  When 
water  is  present,  the  concentrated  inorganic  acids  resolve  it  into  ammonia 
and  formic  acid :  3  atoms  of  water  and  1  of  hydrocyanic  acid   include  the 


284  DILUTED    HYDROCYANIC    ACID^ 

elements  of  1  atom  of  formate  of  ammonia;  3H0-f  H,NC3=H,NC3  +  XH3. 
It  is  resolved  by  dry  chlorine,  under  the  influence  of  the  sun's  rays,  into 
hydrochloric  acid  and  chloride  of  cyanogen.  The  changes  produced  by  acids 
in  the  constitution  of  hydrocyanic  acid,  show  that  an  excess  of  hydrochloric 
or  sulphuric  acid  employed  in  its  preparation  may  lead  to  its  decomposition 
and  contamination  with  formic  acid.  As  a  singular  fact  connected  with  this 
conversion,  Leibig  has  noticed  that  when  formate  of  ammonia  is  transmitted 
through  a  glass  tube,  heated  to  dull  redness,  it  is  decomposed  and  is  recoa- 
verted  into  hydrocyanic  acid  and  water. 

CgH    -I-     N      =     1  atom  of  hydrocyanic  acid. 
O3  -j-     H3    =    3  atoms  of  water 

1  atom  of  formic  acid.     1  atom  of  ammonia. 

The  easily  reducible  oxides  (of  mercury  and  silver)  decompose  hydrocyanic 
acid,  and  yield  water  and  a  metallic  cyanide.  When  lime  or  baryta  is  heated 
to  redness  in  hydrocyanic  acid  vapor,  they  afford  cyanides  and  cyanates, 
and  hydrogen  is  evolved. 

In  the  voltaic  circuit,  hydrocyanic  acid  yields  hydrogen  at  the  negative, 
and  cyanogen  at  the  positive  electrode,  but  the  aqueous  solution  of  this 
acid,  when  pure,  is  a  very  bad  conductor  of  electricity.  When  its  vapor 
is  mixed  with  oxygen  it  may  be  exploded  by  the  electric  spark,  in  which 
case  2  volumes  of  hydrocyanic  acid  vapor  require  for  perfect  combustion  2 
volumes  and  a  half  of  oxygen  :  the  results  are  water,  2  volumes  of  carbonic 
acid,  and  1  volume  of  nitrogen  (H,NC3-f05=2C03-f-HO  +  ^^).  When 
potassium  is  heated  in  its  vapor,  cyanide  of  potassium  is  formed,  and 
hydrogen,  equal  to  half  the  volume  of  the  acid  is  liberated:  it  appears, 
therefore,  that  there  is  the  strictest  analogy  between  the  hydrocyanic  and 
the  other  hydracids,  and  that  1  volume  of  cyanogen  and  1  of  hydrogen  form 
2  volumes  of  the  vapor  of  hydrocyanic  acid.  It  contains  in  each  volume, 
half  a  volume  of  hydrogen  and  half  a  volume  of  cyanogen. 

Atoms.     Weights.      Per  cent.  Vols.  Sp.  Gr. 

Hydrogen     .         .     1     ...       1     ...       3-70     ...     1     ...     0-0691 
Cyanogen     .         .     1     ...     26     ...     96*30     ...     1     ...     1-7966 


1  27  100-00  2  1-8657 

And  1 -8657 -^2=0-9328,  the  sp.  gr.  of  hydrocyanic  acid  vapor.  The  ex- 
perimental result  of  Gay-Lussac  makes  it  rather  higher.  100  cubic  inches 
of  the  vapor  weigh  2889  grains;  compared  with  hydrogen,  hydrocyanic 
acid  vapor  has  a  sp.  gr.  of  13-5.  The  anhydrous  acid  is  miscible  in  all  pro- 
portions with  water,  alcohol,  and  ether. 

This  acid  forms  no  definite  hydrate,  but  in  various  states  of  dilution  it  is 
used  in  medicines  as  a  sedative,  and  certain  processes  are  recommended  for 
at  once  obtaining  it  of  a  convenient  strength  for  pharmaceutical  purposes. 
The  Pharmacopoeial  hydrocyanic  acid  contains  2  per  cent,  of  anhydrous  acid, 
while  that  which  is  sold  under  the  name  of  Scheele^s  acid  contains  from  4  t9 
6  per  cent.  A  dose  of  Scheele's  acid  exceeding  20  drops,  and  an  equivalent 
portion  of  any  of  the  other  solutions  of  the  acid,  would  generally  suffice  to 
destroy  life.  Diluted  hydrocyanic  acid  of  the  sp.  gr.  0*982  at  54°,  con- 
tains 10-53  per  cent,  of  anhydrous  acid  (Trautwein).  The  process  for 
preparing  diluted  hydrocyanic  acid  for  officinal  purposes,  consists  in  the 
decomposition  of  ferrocyanide  of  potassium  (FeCy,2KCy),  by  diluted  sul- 
phuric acid.  The  proportions  are  somewhat  different  from  those  above 
described,  but  the  process  is  similar. 

Liebig  recommends  for  obtaining  dilated  hydrocyanic  acid,  the  distillation 


DILUTED    HYDROCYANIC    ACID.  285 

of  a  mixture  of  equal  parts  of  cyanide  of  potassium  and  sulphuric  acid  ;  the 
cyanide  being  dissolved  in  twice  its  weigiit  of  water,  and  the  acid  diluted 
with  three  times  its  weight  of  water  ;  these  solutions  are  to  be  gradually 
mixed,  and  the  mixture  cautiously  distilled.  This  acid  is  a  product  of  the 
distillation  of  the  bitter  almond,  the  kernels  of  the  peach,  nectarine,  and 
other  seeds  of  the  like  nature.  It  may  also  be  procured  by  distilling  the 
young  shoots  of  laurel. 

As  pure  hydrocyanic  acid,  even  in  a  diluted  state,  is  still  liable  to  decom- 
position, it  should  be  prepared  in  small  quantities,  and  preserved  in  well- 
stopped  phials  out  of  the  presence  of  light :  or  a  very  minute  addition  of 
diluted  sulphuric  or  hydrochloric  acid  may  be  made  to  it,  by  which  its  ten- 
dency to  change  is  prevented. 

When  diluted  hydrocyanic  acid  is  pure,  it  leaves  no  residue  on  evapora- 
tion, and  only  slightly  and  transiently  reddens  litmus  :  if  it  contains  any  of 
the  stronger  acids,  its  action  on  vegetable  blues  is  very  decided.  Under 
these  circumstances,  also,  it  throws  down  red  iodide  of  mercury  from  the 
solution  of  the  double  salt  of  iodide  of  potassium  and  cyanide  of  mercury ; 
but  in  using  this  test  no  alcohol  must  be  present,  as  it  would  retain  the 
cyanide  of  mercury  in  solution.  (Geoghegan,  Ph,  Mag.  and  Journ.,  vii. 
400.) 

Officinal  hydrocyanic  acid  may  contain,  as  impurity,  hydrochloric  or  sul- 
phuric acid,  and  occasionally  Prussian  blue.  The  latter  substance  is  de- 
posited on  standing,  or  readily  separated  by  careful  distillation.  In  order  to 
detect  hydrochloric  acid,  ammonia  is  added,  and  the  liquid  is  concentrated 
by  evaporation.  The  hydrocyanate  of  ammonia  is  volatilized,  while  the 
hydrochlorate  of  ammonia  remains  in  prismatic  crystals.  A  solution  of  these 
crystals  may  be  tested  by  the  addition  of  nitrate  of  silver.  The  chloride  of 
silver  with  its  characteristic  property  of  insolubility  in  nitric  acid,  is  thrown 
down.  A  solution  of  borax,  free  from  chloride  of  sodium,  may  be  employed 
instead  of  ammonia.  This  fixes  the  hydrochloric  acid  alone.  Sulphuric 
acid  may  be  detected  by  the  addition  of  nitrate  of  baryta  ;  if  present,  a  white 
precipitate  of  sulphate  of  baryta,  insoluble  in  nitric  acid,  is  deposited. 

Hydrocyanic  acid  is  a  weak  acid  :  it  will  not  decompose  the  alkaline  car- 
bonates, or  set  free  carbonic  acid  from  these  salts ;  but  it  separates  silicic 
acid  from  the  soluble  alkaline  silicates.  It  dissolves  the  oxide  of  mercury, 
and  this  solution  is  not  precipitated  by  alkalies  (Hg04-HCy=--HgCy  +  H0). 
It  decomposes  a  solution  of  subnitrate  of  mercury,  giving  a  gray  precipitate 
of  the  reduced  metal  (HCy  +  Hg30=HgCy  +  Hg+H0).  It  has  no  action 
on  solutions  of  the  chloride  and  nitrate  of  mercury.  Among  other  chemical 
properties,  it  gives  a  white  cyanide,  insoluble  in  cold  nitric  acid,  with  a 
solution  of  nitrate  of  silver  (AgO,N054-HCy=AgCy-fHO,N05).  Unless 
it  contains  sulphuric  acid,  it  does  not  precipitate  a  salt  of  baryta.  It  does 
not  affect  a  persalt  of  iron,  and  it  does  produce  with  it  Prussian  blue  when 
an  alkali  is  added  to  precipitate  the  oxide.  It  does  not  precipitate  a  solu- 
tion of  the  green  sulphate  of  iron,  but  produces  Prussian  blue  on  the  addition 
of  an  alkali,  by  a  reaction  of  its  elements  on  the  mixed  oxides  of  iron  which 
are  precipitated.  This  may  be  proved  by  adding  diluted  hydrochloric  acid 
to  the  mixture  :  the  oxide  of  iron  is  dissolved,  and  Prussian  blue  remains. 
It  does  not  affect  a  solution  of  copper  until  potassa  is  added,  when  white 
subcyanide  of  copper,  insoluble  in  hydrochloric  acid,  is  produced.  When 
the  sulphate  of  copper  is  previously  mixed  with  a  small  quantity  of  sulphurous 
acid,  the  white  subcyanide  of  copper  (CugCy)  is  formed,  and  slowly  deposited. 
Hydrocyanic  acid  destroys  the  color  of  iodine  in  aqueous  solution,  as  well  as 
the  blile  color  of  iodide  of  starch. 

However  carefully  diluted  hydrocyanic  acid  may  have  been  prepared,  its 


286  TESTS    FOR    HYDROCYANIC    ACID. 

real  strength  should  always  be  determined  by  experiment,  for  the  specific 
gravity  is  no  adequate  criterion.  Neither  the  proportions  of  materials  used, 
nor  the  specific  gravity  of  the  product,  can  convey  any  accurate  knowledge 
of  the  strength  of  the  acid.  The  strength  of  the  medicinal  acid  may  be  ob- 
tained by  precipitating  a  given  weight  of  it  by  nitrate  of  silver,  v^^liich  throws 
down  an  insoluble  cyanide  of  silver,  of  which  134  parts  are  equivalent  to  27 
of  anhydrous  hydrocyanic  acid  ;  so  that  if  the  weight  of  the  precipitated 
cyanide  of  silver  (well  washed,  and  carefully  and  perfectly  dried,)  be  divided 
by  5,  or  multiplied  by  0-2015  (2t-M34)  the  product  will  almost  exactly 
represent  the  quantity  of  real  acid.  One  hundred  grains  of  officinal  acid,  of 
'a  strength  of  2  per  cent.,  should  therefore  give  10  grains  of  dry  cyanide  of 
silver  ;  and  100  grains  of  Scheele's  acid  should  give  from  20  to  25  grains  of 
dry  cyanide.  From  the  result  of  such  an  analysis  it  is  easy,  by  the  addition 
of  water,  to  reduce  a  strong  acid  to  any  assignable  strength. 

Tests  for  Hydrocyanic  Acid.  Analysis  in  cases  of  Poisoning. — The  pecu- 
liar odor  of  the  acid  is  perceptible  in  liquids,  unless  other  strong  odors  are 
present.  1.  Nitrate  of  Silver.  This  throws  down  a  heavy  white  precipitate 
(cyanide  of  silver)  unchanged  by  exposure  to  light.  It  is  insoluble  in  cold 
nitric  acid.  When  well  dried  and  heated  in  a  small  reduction-tube  it  melts, 
and  evolves  a  gas  which  burns  with  the  rose-red  and  blue-colored  flame  of 
cyanogen. — 2.  Sulphate  of  Iron.  Add  to  the  liquid  a  few  drops  of  a  solu- 
tion of  green  vitriol,  followed  by  a  solution  of  potassa,  and  agitate  the  mix- 
ture. It  will  acquire  a  dark  bluish-green  color.  After  a  short  time  add 
diluted  hydrochloric  or  sulphuric  acid  ;  oxide  of  iron  will  be  dissolved,  and 
Prussian  blue  (having  a  greenish  tint  if  much  iron  is  present)  will  be  left. 
Prussian  blue  is  known  by  its  color  and  insolubility  in  diluted  acids.  This 
test  will  reveal  the  presence  of  prussic  acid  even  when  mixed  with  alkaline 
chlorides  and  other  salts. — 3.  Sulphide  of  Ammonium.  Add  to  the  liquid 
one  or  two  drops  of  yellow  or  bisulphide  of  ammonium,  and  evaporate  to 
dryness  on  a  sand-bath.  The  hydrocyanic  acid  is  converted  into  sulpho- 
cyanide  of  ammonium  (NH.S^-f  HCy  +  0(air)=NH,S,Cy-f  HO).  And  this 
is  at  once  proved  by  the  deep  red  color  imparted  to  the  white  residue  by  the 
addition  of  a  persalt  of  iron.     {London  Medical  Gazette,  vol.  xxxix.  p.  765.) 

These  tests  may  be  applied  to  detect  the  vapor  of  hydrocyanic  acid,  as  it 
escapes  from  any  simple  or  complex  liquid  which  contains  it.  The  suspected 
liquid  is  placed  in  a  small  jar,  or  beaker,  the  top  of  which  admits  of  being 
covered  by  a  watch-glass.  A  drop  of  nitrate  of  silver  in  the  hollow  of  the 
glass,  when  inverted  over  a  liquid  containing  prussic  acid,  will  be  whitened, 
owing  to  the  production  of  cyanide  of  silver:  if  slowly  formed,  the  deposit 
will  be  found  under  the  microscope  to  consist  of  well-defined  oblique  rhombic 
prisms.  A  drop  of  a  solution  of  bisulphide  of  ammonium  may  be  added  to 
the  deposited  cyanide  of  silver,  and  the  mixture  warmed.  Persulphate  of 
iron  will  produce  a  red  color  in  the  liquid  notwithstanding  the  presence  of 
black  sulphide  of  silver.  This  will  prove  the  presence  of  cyanogen,  if  the 
cyanide  is  in  too  small  a  quantity  to  yield  evidence  by  combustion.  In  em- 
ploying the  iron-test  for  the  detection  of  the  vapor,  a  solution  of  potassa 
should  be  placed  in  the  watch-glass,  and,  after  sufficient  exposure  of  the 
alkali  to  the  vapor,  the  sulphate  of  iron,  followed  by  diluted  hydrochloric 
acid,  should  be  added  to  the  alkaline  liquid.  These  tests  will  fail  if  the  liquid 
contains  sulphuretted  hydrogen;  but  in  this  case,  the  sulphur-test  will  be 
available.  The  bisulphide  of  ammonium,  placed  in  a  watch-glass,  absorbs 
the  vapor  completely,  and,  on  evaporation  to  drvness,  the  residue  will  be 
found  to  contain  sulphocyanide  of  ammonium  by  th*e  iron-test.  These  vapor- 
tests  may  be  thus  readily  applied  to  the  detection  of  the  poison  in  food',  in  the 


ANALYSIS    OF    THE    CYANIDES.  28T 

contents  or  coats  of  the  stomach  or  intestines,  in  blood,  and  in  the  substance 
of  the  heart  and  liver. 

In  order  to  obtain  the  acid  from  the  coats  of  the  stomach,  or  its  contents, 
in  cases  of  poisoning,  the  substance,  cut  in  small  pieces,  should  be  mixed 
with  cold  distilled  water,  and  distilled  by  a  water-bath  at  a  low  temperature 
(170°),  the  distillate  being  collected  in  a  cooled  receiver.  If  the  liquid 
suspected  to  contain  the  poison  is  alkaline,  a  small  quantity  of  tartaric  acid 
may  be  added  to  neutralize  it.  The  colorless  distillate  in  the  receiver  may 
then  be  examined  for  its  odor,  and  tested  by  the  action  of  the  three  tests 
above  described.  If  the  liquid  of  the  stomach  is  acid,  it  should  be  neu- 
tralized; as,  if  ferrocyanide  of  potassium  was  present,  any  excess  of  acid, 
would  produce  hydrocyanic  acid  from  this  salt.  In  the  dead  body,  hydro- 
cyanic acid  is  converted  by  putrefaction  into  sulphocyanide  of  ammonium, 
which  may  be  dissolved  out  by  alcohol,  and  tested.   {See  Sulphocyanides.) 

Cyanides. — The  salts  formed  by  hydrocyanic  acid  are  similar  to  those  of 
the  halogens.  Thus,  in  contact  with  diluted  alkaline  solutions,  water  and  a 
cyanide  are  produced  (KO-f  HCy=H04-KCy).  If  the  alkaline  solution  is 
concentrated,  then  as  with  the  concentrated  acid  in  the  presence  of  water, 
hydrocyanic  acid  is  resolved  into  formic  acid  and  ammonia  {see  page  284). 
The  cyanides  of  the  alkaline  and  alkaline  earthy  metals  are  very  soluble, 
producing  strongly  alkaline  solutions,  which  evolve  an  odor  of  hydrocyanic 
acid  from  the  action  of  the  carbonic  acid  of  the  air.  They  are  powerful 
poisons.  They  are  readily  distinguished  from  other  salts  by  the  fact  that  the 
weakest  acid  decomposes  them,  and  sets  hydrocyanic  acid  at  liberty.  This 
may  be  detected  by  the  vapor-tests.  The  metallic  cyanides,  excepting  that 
of  mercury,  are  insoluble  in  water,  and  are  not  readily  decomposed  by  oxacids. 
Hydrochloric  and  hydrosulphuric  acids  decompose  them,  and  liberate  hydro- 
cyanic acid.  Many  of  the  metallic  cyanides  are  soluble  in,  and  form  double 
salts  with,  cyanide  of  potassium.  Nitrate  of  silver  throws  down  from  solu- 
tions of  the  cyanides,  white  cyanide  of  silver,  possessing  the  characters 
above  described.  A  solution  of  green  sulphate  of  iron  followed  by  a  diluted 
acid,  produces  with  a  soluble  cyanide,  Prussian  blue.  When  heated  to 
redness,  out  of  contact  of  air,  the  cyanides  of  potassium  and  sodium  undergo 
no  change,  but  if  heated  with  exposure  to  air,  or  in  contact  with  sub- 
stances containing  oxygen,  cyanates  of  the  alkalies  are  produced.  They 
are  powerful  deoxidizers.  Cyanide  of  potassium,  owing  to  its  fusility,  and 
its  deoxidizing  action,  has  been  usefully  employed  in  the  arts  for  the  soldering 
of  metals.  It  removes  every  particle  of  oxide,  and  produces  a  clean  surface 
for  the  solder. 

Cyanogen  and  Chlorine. — These  bodies  unite  to  form  gaseous,  liquid 
and  solid  compounds,  which  are  isomeric.  The  gaseous  compound  (Cy.Cl) 
may  be  obtained  by  placing  a  small  quantity  of  powdered  cyanide  of  mercury, 
moistened  with  water,  in  a  vessel  of  chlorine,  taking  care  that  it  is  kept  la 
the  dark.  In  a  few  days  the  chlorine  will  be  replaced  by  the  gaseous  chlo- 
ride. On  cooling  the  vessel  to  zero,  the  chloride  is  desposited  in  crystals, 
which  are  soluble  in  water.  (Serullas.)  The  odor  of  this  gas  is  pungent 
and  irritating.  It  does  not  redden  litmus,  or  precipitate  a  solution  of  nitrate 
of  silver.  (Pelouze.)  After  some  time  it  is  spontaneously  decomposed  into 
carbonic  acid  and  hydrochlorate  of  ammonia.  This  gas  is  composed  of  a 
volume  of  each  of  its  constituents,  which  unite  without  condensation.  The 
specific  gravity  is  2'1244,  which  nearly  corresponds  to  the  sum  of  the  specific 
gravities  of  chlorine  and  cyanogen,  2*4876+1  "7966 -r-2  =  2'l 421. 

Liquid  Chloride  (CygClJ. — This  is  obtained  from  the  same  substances  as 
the  previous  compound  j  but  in  this  case  the  vessel  must  be  exposed  to  sun- 


288  SULPHOCYANIC    ACID. 

light.  This  chloride  is  a  heavy,  yellow,  oily-looking  liquid,  insoluble  in 
water,  but  soluble  in  alcohol. 

Solid  Chloride  (CygClg). — This  is  a  white  solid  crystalline  substance  at 
common  temperatures.  It  is  not  very  soluble  in  cold  water,  and  is  decom- 
posed by  boiling  water  into  hydrochloric  and  cyanuric  acids.  It  may  be 
procured  by  adding  a  small  quantity  of  hydrocyanic  acid  to  a  vessel  of  dry 
chlorine,  and  exposing  it  to  the  solar  rays.  These  compounds  are  deadly 
poisons. 

Bromide  of  Cyanogen  (CyBr)  is  a  colorlevSS  solid  of  a  pungent  odor,  ob- 
tained by  the  reaction  of  bromine  on  cyanide  of  mercury. 

Iodide  of  Cyanogen  (Cyl)  is  a  volatile  solid  resembling  the  bromide.  It 
is  obtained  by  the  action  of  iodine  on  the  cyanide  of  mercury.  Both  are 
poisonous. 

Cyanogen  and  Sulphur.  Sulphocyanogen  (NC3S2=CyS3). — Liebig 
obtained  this  compound  radical  by  saturating  a  concentrated  solution  of 
sulphocyanide  of  potassium  with  chlorine,  as  well  as  by  boiling  a  soluble 
metallic  sulphocyanide  in  diluted  nitric  acid.  It  falls  in  the  form  of  a 
yellow  precipitate,  which  preserves  its  color  when  dry  ;  it  is  insoluble  in 
water,  alcohol,  and  ether,  but  soluble  in  hot  sulphuric  acid,  from  which  it  is 
again  thrown  down  by  water.  It  is  decomposed  by  concentrated  nitric  acid  ; 
when  heated  with  potassium — sulphide,  cyanide,  and  sulphocyanide  of  po- 
tassium are  formed;  subjected  to  dry  distillation,  it  yields  sulphide  of  carbon, 
and  ultimately  nitrogen  and  cyanogen. 

SuLPHOCYANio  AciD.  JTydrosiilpJiocyanic  Acid  (CyS^,!!). — The  aqueous 
solntion  of  this  acid  may  be  obtained  by  decomposing  basic  sulphocyanide 
of  lead  by  diluted  sulphuric  acid,  taking  cace  to  leave  an  excess  of  the  salt  of 
lead,  which  may  be  afterwards  removed  by  sulphuretted  hydrogen.  It  is 
also  formed  when  sulphocyanide  of  lead  or  of  silver,  diffused  through  water, 
is  decomposed  by  a  current  of  sulphuretted  hydrogen  gas. 

The  hydrated  hydrosulphocyanic  acid  is  colorless,  easily  decomposed  by 
exposure  to  air  or  heat,  yielding,  among  other  products,  a  peculiar  yellow 
insoluble  powder  {Mellotie,  see  page  280).  Chlorine  and  nitric  acid  abstract 
its  hydrogen,  and  evolve  sulphocyanogen  ;  by  their  prolonged  action,  cyanic 
and  sulphuric  acids  are  formed,  and  ultimately  ammonia.  It  reddens  the 
solutions  of  persalts  of  iron.  It  exists  in  a  combined  state  in  the  seeds  of 
certain  cruciferous  plants  (mustard),  and  in  the  saliva  of  man  and  the  sheep. 

Sulphocyanides. — This  is  a  monobasic,  and  the  salts  are  procured  by  neu- 
tralizing sulphocyanic  acid  with  the  respective  bases,  or  by  the  action  of 
hydrocyanic  acid  on  polysulphides.  The  alkaline  compounds  are  soluble  in 
water  and  alcohol.  They  are  identified  by  the  deep  red  color  which  is  pro- 
duced, when  a  persalt  of  iron  is  added  to  their  aqueous  solutions.  This 
reaction  is  employed  for  the  detection  of  hydrocyanic  acid  (p.  286).  The 
red  color  is  destroyed  by  solutions  of  corrosive  sublimate  and  chloride  of 
gold.  They  give  white  precipitates  with  the  salts  of  silver,  and  lead,  and  a 
gray  precipitate  with  subsalts  of  mercury.  The  sulphocyanide  of  silver 
readily  changes  by  light;  it  is  not  soluble  in  nitric  acid,  which  gives  a  reddish 
color  to  the  liquid,  but  it  is  dissolved  by  an  excess  of  the  alkaline  sulpho- 
cyanide. Chloride  of  sodium  produces  no  precipitate  in  this  solution.  The 
sulphocyanide  of  lead  is  soluble  in  nitric  and  acetic  acids.  With  a  salt  of 
copper,  a  concentrated  sulphocyanide  gives  a  black  precipitate  :  when  diluted 
a  white  sulphocyanide  of  the  metal  is  slowly  formed.  When  heated  to  a  high 
temperature,  a  sulphocyanide  is  decomposed,  yielding  nitrogen,  sulphide  of 
carbon,  and  a  metallic  sulphide.     The  sulphocyanide   of  mercury  undergoes 


FERROCYANOGEN.      BISULPHIDE    OF    CARBON.  289 

combustion  producing  a  bulky  porous  residue  of  a  smoke-like  form  and  color 
{Pharaoh's  serpents).  • 

FERROCYANOGEN  (FeCy3=Cfy)  and  Ferricyanogen  (FegCyn.ssCfdy)  are 
compound  radicals,  in  which  metallic  iron  is  an  important  constituent. 
These  will  he  again  referred  to  in  the  description  of  that  metal.  Ferrocij- 
anides. — The  compounds  formed  with  the  alkalies  are  soluble  in  water,  the 
others  are  insoluble.  The  soluble  salts  are  yellow  in  the  hydrated,  and  while 
in  the  dehydrated  state.  The  persalts  of  iron  give,  with  the  soluble  ferro- 
cyanides,  a  deep  blue  precipitate  (Prussian  blue)  3Cfy,4Fe.  The  pure  pro- 
tosalts  of  iron  give  a  white  precipitate  (protoferrocyaoide  of  iron)  becoming 
blue  by  exposure  to  air,  oxygen,  or  chlorine.  This  has  already  been  described 
as  a  valuable  test  for  oxygen  in  water  (page  99).  Sulphate  of  copper  gives, 
with  a  ferrocyanide,  even  in  an  extremely  diluted  state,  a  reddish-colored 
precipitate,  ferrocyanide  of  copper  (Cfy2Cu).  The  alkaline/em  oy  ferrid- 
cyanides  are  crystalline  salts  of  a  ruby-red  color.  They  are  recognized  by 
the  action  of  a  protosalt  of  iron,  which  produces  with  them  a  blue  precipitate 
(2Cdfy,3Fe).  A  persalt  of  iron  darkens  the  solution,  but  there  is  no  pre- 
cipitate of  Prussian  blue.  A  crystal  of  an  alkaline  ferricyanide  produces, 
with  a  mixture  of  strychnia  and  concentrated  sulphuric  acid,  a  splendid 
blue,  passing  to  a  purple  and  red  color.  No  such  results  are  produced 
when  a  portion  of  an  alkaline  ferrocyanide  is  employed. 

Nitroprussides. — By  the  action  of  nitric  acid  on  ferrocyanide  of  potas- 
sium, among  other  products,  salts  known  as  the  nitroprussides  are  formed. 
This  acid,  like  the  ferrocyanic,  is  bibasic  {see  page  280.)  The  salt  of  sodium 
(NagFeaCysjNOg)  crystallizes  in  long  red-colored  prisms.  It  is  soluble  in 
water,  but  the  solution  is  decomposed  by  light,  Prussian  blue  being  deposited. 
The  test  for  a  nitro-prusside,  is  a  soluble  alkaline  sulphide,  the  smallest 
quantity  of  which  produces  a  rich  purple  or  crimson  color,  which,  however, 
is  not  permanent  (p.  ^9).  The  solution,  although  decomposed,  is  not 
colored  by  sulphuretted  hydrogen  alone. 

Melam  (CiaNi^HJ  is  a  product  of  the  decomposition  of  sulphocyanide  of 
ammonium. 

Melamin  (CgN(.H(,),  Ammelin  (CgNgH^Og),  and  Ammelid  (CigNgHgOg)  are 
products  of  the  decomposition  of  melam.  They  possess  but  little  chemical 
interest. 

Carbon  and  Sulphur.  Bisulphide  of  Carbon.  Sulphocarbonio  Acid 
(CSJ. — This  is  a  liquid  compound  which  was  discovered  in  1796  by  Lam- 
padius,  while  distilling  a  mixture  of  pyrites  and  charcoal  ;  he  termed  it  alco- 
hol of  sulphur.  It  may  be  obtained  either  by  passing  the  vapor  of  sulphur 
over  red-hot  charcoal  in  a  porcelain  tube,  or  by  distilling  about  six  parts  of 
yellow  iron  pyrites  (bisulphide  of  iron)  with  one  of  charcoal.  The  charcoal 
should  be  in  small  fragments  heated  to  full  redness — the  sulphur  vapor 
slowly  passed  through  it,  and  the  refrigerator  and  receiver  should  be  cooled 
to  32°,  or  even  below.  Vessels  of  porcelain  and  coated  earthenware  answer 
best,  although  it  is  difficult  to  prevent  loss  by  the  escape  of  the  vapor ;  iron, 
at  the  high  temperature  which  is  required,  too  easily  combines  with  the  sul- 
phur to  render  it  conveniently  available.  The  product  is  sometimes  con- 
veyed by  a  glass  tube  into  ice-cold  water. 

When  purified  by  redistillation  at  a  low  temperature  with  chloride  of  cal- 
cium, the  bisulphide  is  a  transparent,  colorless  liquid,  insoluble  in  water, 
but  soluble  in  alcohol  and  ether.  It  should  leave  no  residue  on  evaporation, 
its  refractive  and  dispersive  powers  on  light  are  very  considerable.  Inclosed 
in  a  prismatic  bottle  it  serves  for  the  spectral  analyses  of  the  alkaline  and 
19 


290  CARBON    AND    SULPHUR.       SULPHOCARBONIC    ACID. 

Other  metals.     Its  specific  gravity  is  1-272.     It  boils  at  110°  and  does  not 

freeze  at 60^.     It  is  very  volatile  and  inflammable,  and  has   a   pungent 

taste  and  peculiarly  fetid  odor.  The  liquid  poured  on  paper  and  inflamed, 
commonly  burns  with  a  blue  flame  without  igniting  the  paper.  When  poured 
on  water,  a  portion  sinks  in  globules  like  a  heavy  oil,  while  another  portion 
floats.  This  may  be  ignited,  and  in  the  pale  flame,  iron-wire  burns  with 
great  brilliancy.  If  burnt  on  blue  infusion  of  litmus,  this  liquid  is  reddened. 
The  cold  which  it  produces  during  evaporation  is  so  intense,  that  by  exposing 
a  thermometer  bulb,  covered  with  fine  lint,  and  moistened  with  it,  in  the 
receiver  of  an  air-pump,  the  temperature  sank,  after  exhaustion,  to  80^. 
When  a  mercurial  thermometer  was  used  the  metal  froze.  The  intensity  of 
the  cold  is  such  that  it  appears  to  have  the  power  of  freezing  a  portion  of  the 
liquid  {see  page  75).  Asbestos  or  filtering  paper  placed  in  the  liquid,  soon 
acquires  as  a  result  of  capillary  attraction,  a  deposit  of  the  solidified  vapor. 
It  is  soluble  in  fixed  and  volatile  oils,  and  it  dissolves  camphor,  sulphur, 
phosphorus,  and  iodine.  The  readiness  with  which  phosphorus  dissolv'es  in 
the  bisulphide  of  carbon  is  remarkable,  and  the  amount  considerable — one 
part  of  the  bisulphide  taking  up  twenty  parts  of  phosphorus.  The  solution 
is  occasionally  used  to  give  a  thin  film  of  phosphorus  to  delicate  articles 
intended  to  be  coated  with  metals :  they  are  dipped  into  it,  and  then  into  a 
solution  of  silver  or  copper,  by  which  a  film  of  the  metal  is  reduced  upon 
the  surface  :  upon  this  other  metals  may  be  precipitated  by  the  electric  cur- 
rent. The  solution  of  phosphorus  is  a  powerful  and  often  useful  deoxidizer 
(page  236).  When  the  vapor  of  bisulphide  of  carbon  is  passed  over  heated 
lime  or  baryta,  it  produces  ignition,  and  carbonates  of  these  bases,  together 
with  sulphides  of  calcium  and  barium  are  formed.  It  is  also  decomposed  by 
copper,  and  iron.  At  a  red  heat  potassium  and  sodium  float  on  it  without 
decomposing  it  at  ordinary  temperatures.  If  while  the  sodium  is  floating  on 
the  sulphide,  in  a  test-tube,  a  few  drops  of  water  are  added,  hydrogen  is 
evolved,  and  after  a  time  the  sodium  takes  fire  tnd  burns  with  explosive 
violence,  a  cloud  of  yellow  vapor  at  the  same  time  escaping.  Sulphide  of 
sodium  is  found  in  the  liquid  residue.  Under  the  influence  of  dry  chlorine, 
it  yields  chloride  of  sulphur  and  perchloride  of  carbon. 

The  vapor  of  this  liquid  is  very  heavy,  and  may  be  decanted  from  one 
vessel  into  another.  Pour  the  vapor  into  a  small  jar  containing  a  solution 
of  blue  litmus,  and  ignite  it :  it  will  burn  with  a  pale  blue  flame,  producing 
sulphurous  acid — known  by  its  peculiar  odor — and  the  litmus  will  be  reddened. 
If  a  mixture  of  starch  and  iodic  acid  is  placed  in  another  jar,  into  which 
the  vapor  is  poured  and  ignited,  blue  iodide  of  starch  will  be  produced  (page 
218).^  The  vapor  is  not  decomposed  by  mere  heat,  but  at  a  temperature  of 
600°  it  takes  fire  in  air,  and  burns  with  explosion.  Pour  a  small  quantity 
of  the  liquid  sulphide  into  ajar  of  200  c.  i.  capacity,  and  after  a  few  minutes, 
when  the  vapor  is  diffused,  apply  a  lighted  taper  to  it :  the  vapor  will  burn 
with  a  slight  explosion,  producing  a  deposit  of  sulphur.  It  requires  three 
volumes  of  oxygen  for  its  perfect  combustion  ;  and  sulphurous  and  carbonic 
acids  are  the  only  products  (CS^-f  60  =  COa-j-2SO,).  As  it  is  burnt  in  a 
jar,  sulphur  is  deposited,  the  air  not  being  in  sufficient  quantity  to  consume 
it.  Lead  water  indicates  the  production  of  carbonic  acid,  and  iodic  acid 
and  starch  the  presence  of  sulphurous  acid. 

Bisulphide  of  carbon  appears  to  be  frequently  formed  during  the  produc- 
tion of  gas  from  coal,  and  to  be  retained  in  the  state  of  vapor  by  the  coal-gas 
after  its  purification  by  lime.  This  impurity  gives  a  sulphurous  smell  to  the 
gas  when  burned,  although  so  perfectly  deprived  of  sulphuretted  hydrogen 
as  not  to  discolor  carbonate  of  lead.  The  Rev.  Mr.  Bowditch  has  found 
that  when  coal-gas  containing  this  vapor  is   passed   over  hydrate  of  lime. 


BISULPHIDE    OP    CARBON.      COMPOSITION.  291 

heated  below  the  melting-point  of  lead,  sulphide  of  calcium  is  produced,  and 
sulphuretted  hydrogen  is  set  free;  this  gas  maybe  subsequently  separated 
by  the  hydrated  oxide  of  iron.  When  the  vapor  of  the  bisulphide  is  burned 
with  pure  oxygen,  it  forms  carbonic  and  sulphurous  acids.     It  consists  of 

Atoms.      Weights.      Per  cent.  Vols.  Sp.  Gr. 

Carbon     .         .   '     .         .     1     ...       6     ...     15-79     ...     1       ...     0*4145 
Sulphur  .         .         .         .     2     ...     32     ...     84-21     ...       ^     ...     2-2112 


Bisulphide  of  carbon       .     1  38  100-00  1  2-6257 

The  specific  gravity  of  the  vapor  was  found  by  Mitscherlich  to  be  2 '640, 
which  does  not  difi'er  widely  from  that  above  given  as  the  sum  of  the  calcu- 
lated specific  grnvities  of  its  constituents.  Compared  with  hydrogen,  the 
vapor  has  a  specific  gravity  of  38.  It  is  analogous  to  carbonic  acid,  the 
two  atoms  of  oxygen  being  replaced  by  two  atoms  of  sulphur.  Mr.  Gore, 
who  has  compared  the  properties  of  the  bisulphide  with  those  of  liquid  car- 
bonic acid,  finds  that  in  solvent  powers  and  general  properties  they  are 
analogous.  *  The  bisulphide  is  a  more  powerful  solvent  of  fatty  substances. 
The  chemical  constitution  of  this  compound  may  be  easily  determined  by 
evaporating  a  portion  to  dryness,  with  sodium  in  a  test-tube,  and  afterwards 
igniting  the  residue.  On  digesting  this  in  water,  and  throwing  it  on  a  filter, 
the  carbon  is  left  in  the  filter  as  a  black  powder,  and  the  sulphur,  combined 
with  sodium,  will  be  found  by  the  usual  tests  in  the  filtrate. 

The  vapor  has  been  employed  as  an  anaesthetic,  but  unsuccessfully.  It  is 
a  narcotic  poison.  The  liquid  sulphide  is  manufactured  on  a  large  scale, 
and  is  extensively  employed  as  a  solvent  of  sulphur  and  caoutchouc,  in  the 
manufacture  of  vulcanized  rubber.  It  is  also  used  for  the  separation  of 
phosphorus  and  iodine  from  organic  substances  in  cases  of  poisoning.  It 
will  not  combine  with  alkalies,  but  it  forms  a  class  of  salts  with  the  alkaline 
sulphides  known  as  suJphocarhojuites,  represented  by  MS,CS3.  These  re- 
semble the  carbonates  which  are  MO,COa.  It  is  obvious  that  if,  according 
to  the  views  of  certain  writers,  a  carbonate  should  be  represented  as  MjCOg, 
the  sulphocarbonate  would  stand  as  M,CS3,  a  change  for  which  no  suflBcient 
reason  has  been  offered.  The  vapor  of  this  liquid  furnishes  a  most  powerful 
means  of  sulphuration.  At  a  red  heat,  nearly  all  oxides  are  converted  by  it 
into  sulphides  (Fremy). 

Tests. — The  odor  of  the  liquid,  and  the  inflammability  of  the  vapor,  with 
the  nature  of  the  products  of  combustion,  are  sufficient  to  identify  it.  If 
pure,  it  should  evaporate  without  leaving  any  residue.  When  the  liquid  is 
boiled  with  potassa  containing  oxide  of  lead  dissolved,  the  presence  of  sulphur 
is  indicated  by  the  copious  formation  of  brown  sulphide  of  lead.  It  thus 
serves  as  a  test  for  detecting  the  presence  of  oxide  of  lead  as  an  impurity  in 
a  solution  of  potassa. 


PREPARATION    OF    BORON. 


CHAPTEE     XXI. 

BORON    AND    SILICON.      BORACIC    AND    SILICIC    ACIDS. 
BORON   (B  =  ll). 

Boron  is  a  solid  metalloid  found  only  in  combination  with  oxygen,  as 
boracic  acid.  It  was  discovered  by  Davy  as  a  constituent  of  this  acid  in 
1807.  Unlike  carbon,  it  is  an  element  which  is  but  sparingly  dij0fused,  and 
is  only  found  in  the  mineral  kingdom.  In  the  Lipari  Islands  and  Tuscany 
it  is  deposited  in  the  form  of  boracic  acid;  but  in  most  cases  it  is  associated 
with  alkaline  or  alkaline  earthy  bases,  either  in  mineral  deposits  or  as  a  con- 
stituent of  the  waters  of  lakes  and  springs.  Borate  of  soda  or  tincal  is  found 
in  the  waters  of  certain  lakes  in  Ceylon,  Thibet,  and  Tartary.  Borate  of 
lime,  or  datholite,  is  found  in  Norway,  Sweden,  and  in  South  America,  while 
borate  of  magnesia,  or  horacite,  is  met  with  in  Holstein.  The  South  Ameri- 
can mineral  is  a  compound  borate,  being  a  mixture  of  borate  of  soda  and 
borate  of  lime  (NaO,2BO3+2CaO,3BO3  4-10HO).  It  is  found  in  Peru  in 
white  kidney-shaped  masses,  called  tiza,  associated  with  the  deposits  of 
nitrate  of  soda.  Borax  has  lately  been  discovered  in  certain  lakes  in  Cali- 
fornia. 

Preparation. — Boron  may  be  procured  in  an  amorphous  state  by  heating 
anhydrous  boracic  acid  finely  powdered,  to  a  temperature  of  about  300°, 
with  twice  its  weight  of  potassium  or  sodium.  The  experiment  may  be  per- 
formed in  a  copper  or  iron  tube  (B03  +  3K=3KO-f  B).  This  substance  is 
also  obtained  by  melting  in  a  cast-iron  crucible,  a  mixture  of  10  parts  of 
anhydrous  boracic  acid,  with  6  parts  of  sodium,  and  4  or  5  parts  of  common 
salt.  The  salt  aids  the  chemical  changes,  and  forms  an  easily  removable 
flux.  The  fused  matter  is  washed  out  of  the  tube  or  crucible  with  water, 
and  the  whole  put  upon  a  filter.  The  boron  remains  in  the  form  of  a  dark- 
colored,  insipid,  insoluble  powder.  The  product  is  at  first  washed  with 
diluted  hydrochloric  acid  and  then  with  water.  Berzelius  obtained  boron  by 
decomposing  the  borofluoride  of  potassium.  This  compound,  in  the  state  of 
dry  powder,  may  be  heated  in  a  porcelain  crucible  with  potassium;  the  re- 
duction goes  on  quietly,  and  the  fused  mass  may  be  triturated  with  water, 
by  which  the  boron  is  separated.  It  is  then  washed  upon  a  filter  with  a 
solution  of  hydrochlorate  of  ammonia,  and  afterwards  with  alcohol. 

Wohler  and  Deville  obtained  boron  in  a  crystallized  state,  by  heating,  to 
a  high  temperature,  in  a  plumbago  crucible,  for  five  hours,  8  parts  of  alumi- 
num in  large  pieces,  with  10  parts  of  anhydrous  boracic  acid.  Boron  and 
vitrified  borate  of  alumina  are  produced.  The  metallic  portion  of  the  mass 
is  treated  with  a  boiling  concentrated  solution  of  soda,  w^hich  removes  the 
undecomposed  aluminum;  hydrochloric  acid  is  subsequently  added  to  re- 
move the  iron,  and,  lastly,  nitrohydrofluoric  acid  to  remove  any  silicon.  In 
this  process,  aluminum  passes  to  the  state  of  alumina  at  the  expense  of  the 
oxygen  of  the  boracic  acid  (BOg-f  2Al=Al,03-j-B).  The  boron  thus  ob- 
tained may,  by  repeated  fusions  with  aluminum  in  exctss,  be  obtained  in 
hard  crystals.  These,  however,  retain  both  carbon  and  aluminum.  By  this 
process,  Wohler  and  Deville  procured  three  varieties  of  crystallized  boron  : 
1,  black  and  opaque  brittle  laminae,  which  have  the  lustre  and  nearly  the 


BORON.       CHEMICAL    PROPERTIES.  293 

hardness  of  the  diamond;  these  crystals  consist  of  97*60  of  boron,  and  2*40 
of  carbon ;  2,  long  prismatic  crystals,  perfectly  transparent  and  as  brilliant 
as  diamond,  but  not  so  hard  as  the  first  variety;  these  crystals  contain  89-10 
boron,  6*T0  aluminum,  and  4*20  of  carbon  ;  3,  minute  crystals  of  a  chocolate- 
red  or  pale  yellowish  color,  of  a  sp.  gr.  of  2*68.  These  are  boron  diamonds. 
They  are  as  hard  as  the  diamond,  and  will  scratch  its  surface. 

Properties. — Amorphous  boron  is  a  deep  olive-colored  substance,  infusible, 
inodorous,  insipid,  and  a  non-conductor  of  electricity.  Its  specific  gravity 
exceeds  2.  It  is  not  acted  upon  by  air,  water,  either  hot  or  cold  (at  least 
after  it  has  been  heated  to  redness),  alcohol,  ether,  or  the  oils.  In  the  state 
of  hydrate,  it  long  remains  diffused  through  pure  water,  especially  if  free 
alkali  is  present,  and  it  even  passes  through  filters  ;  but  its  precipitation  is 
accelerated  by  saline  solutions  (sal  ammoniac).  It  undergoes  no  change 
when  heated  in  close  vessels ;  but  when  nearly  red-hot  in  the  air  (600°),  it 
takes  fire  and  burns  with  difficulty  into  boracic  acid,  chiefly  on  the  surface. 
According  to  Despretz,  it  becomes  denser  and  more  closely  aggregated  at  a 
full  red  heat ;  and  under  a  powerful  galvanic  battery,  it  has  been  fused  into  a 
black  bead.  It  is  more  easily  oxidized  by  the  action  of  nitric  acid  ;  the  pure 
hydracids  at  common  temperatures  have  no  Action  upon  it,  but  nitrohydro- 
chloric  acid  converts  it  into  boracic  acid,  and  nitrohydrofluoric  acid  into 
fluoride  of  boron.  At  a  high  temperature,  it  rapidly  decomposes  nitre  with 
explosive  violence ;  under  the  same  circumstances,  it  also  decomposes  and 
deflagrates  with  the  hydrate  and  carbonate  of  potassa :  in  the  former  case 
water  is  decomposed,  and  hydrogen  evolved  ;  in  the  latter,  carbonic  oxide  is 
evolved  in  consequence  of  the  decomposition  of  carbonic  acid  ;  in  both  cases 
borate  of  potassa  is  the  result. 

A  boiling  solution  of  potassa  or  soda  has  no  action  on  boron.  At  a  high 
temperature,  boron  deoxidizes  most  oxides  and  metallic  salts.  It  inflames 
and  burns  in  deutoxide  of  nitrogen,  forming  boracic  acid  and  nitrate  of  boron. 
It  burns  in  chlorine,  when  slightly  heated,  and  also  in  vapor  of  bromine,  pro- 
ducing a  chloride  and  bromide  of  boron.  With  hydrochloric  acid  it  also 
produces  a  chloride,  with  the  evolution  of  light  and  heat.  At  a  full  red  heat 
it  decomposes  aqueous  vapor,  forming  boracic  add  and  setting  hydrogen 
free  ;  a  portion  of  the  boracic  acid  is  at  the  same  time  vaporized  with  water. 
Boron  forms  no  compound  with  hydrogen,  but  it  readily  combines  with  nitro- 
gen to  form  a  nitride.  This  may  be  produced  by  heating  the  metalloid  in  a 
current  of  ammoniacal  gas  ;  hydrogen  rs  liberated.  When  boron  is  heated 
in  the  vapor  of  sulphur,  the  two  bodies  combine  to  form  sulphide  of  boron. 
The  production  of  boracic  acid  in  some  of  the  hot  springs  of  Tuscany,  has 
been  ascribed  to  the  decomposition  of  sulphide  of  boron  issuing  with  aqueous 
vapor  from  the  volcanic  soil.  Boracic  acid  and  sulphuretted  hydrogen  are 
among  the  products  (BS3-}-3HO=B03-f  3HS).  When  boron  is  strongly 
heated  with  boracic  acid  or  borax,  it  fuses  with  the  substance,  producing  a 
vitreous  compound  of  a  black  or  brown  color,  resembling  smoky  quartz. 
When  very  strongly  heated  in  a  close  vessel,  it  acquires  a  chocolate-brown 
color,  and  closely  resembles,  in  appearance,  amorphous  silicon.  (Wohler 
and  Devillb.)  Crystallized  or  adamantine  boron  has  been  heated  to  the 
temperature  at  which  iridium  melts,  without  undergoing  any  change.  Its 
sp.  gr.  is  2-68.  It  resists  the  action  of  oxygen  at  very  high  temperatures ; 
but  at  the  degree  of  heat  at  which  diamond  will  enter  into  combustion,  the 
boron  diamond  will  burn  in  oxygen.  Owing  to  the  surface  becoming  rapidly 
covered  with  a  layer  of  melted  boracic  acid,  the  combustion  soon  ceases. 
Chlorine  combines  with  it  at  red  heat ;  and  when  a  crystal  of  boron  is  heated 
between  layers  of  platinum-foil,  it  combines  with  and  causes  the  fusion  of 
the  metal. 


294  BORACIC    ACID.      CHEMICAL    PROPERTIES. 

Boron  and  Oyygen.  Boracic  Acid  (BO,). — This  acid,  which  is  a  crys- 
talline solid,  is  the  only  known  compound  of  boron  and  oxyp^en.  It  was 
first  obtained  by  Homberg,  in  1702,  and  was  used  in  medicine  under  the 
name  oi  sedative  salt.  Its  composition  was  demonstrated  by  Davy  in  1807. 
It  is  usually  obtained  by  dissolving  one  part  of  borax  in  four  parts  of  hot 
water,  and  subsequently  adding  half  its  weight  of  sulphuric  acid.  As  the 
solution  cools,  white  scaly  crystals  appear,  which,  when  washed  with  cold 
water,  are  nearly  tasteless  ;  they  consist  of  boracic  acid  combined  with  about 
40  per  cent,  of  water  :  they  retain  a  portion  of  the  acid  employed,  which  may 
be  driven  off  at  a  red  heat.  A  hot  saturated  solution  of  borax  may  also  be 
decomposed  by  hydrochloric  acid  (NaO,2B03  +  HCl=XaCl4-HO  +  2B03) : 
the  hydrated  boracic  acid,  which  falls  as  the  liquid  cools,  should  be  washed 
in  very  cold  water  and  dried.  When  it  is  heated  in  a  platinum  crucible,  it 
fuses  into  a  hard  transparent  glass,  and  by  being  thus  heated,  it  loses  any 
traces  of  hydrochloric  acid  which  may  be  mixed  with  it.  The  following 
proportions  will  be  found  convenient  for  the  production  of  the  acid  :  4  parts 
of  borax  dissolved  in  ten  parts  of  boiling  water  may  be  decomposed  by  2| 
parts  of  concentrated  hydrochloric  acid. 

The  specific  gravity  of  the  'acid  before  fusion  is  1  -48,  and  after  fusion 
1-837.  At  a  white  heat,  this  acid  slowly  sublimes  when  exposed  to  air.  It 
sometimes  happens,  that  flashes  of  light  are  observed  during  the  spontaneous 
cracking  of  a  mass  of  fused  boracic  acid. 

The  crystallized  hydrate  of  boracic  acid  (BO^.SHO)  is  soluble  in  about  25 
parts  of  cold,  and  3  of  boiling  water.  The  latter  solution,  as  it  cools,  de- 
posits the  acid  in  pearly  scales  ;  it  is  also  soluble  in  pure  alcohol,  to  the 
flame  of  which  it  communicates  a  beautiful  green  color.  It  is  dissolved  by 
several  of  the  strong  acids,  especially  the  sulphuric.  It  has  little  taste,  and 
feebly  reddens  vegetable  blues  ;  it  renders  turmeric  brown  like  an  alkali. 
The  anhydrous  acid  (BOg)  becomes  opaque  when  exposed  to  air;  it  is  very 
fusible,  and  forms  with  many  of  the  metallic  oxides  a  glassy-looking  sub- 
stance variously  colored  ;  it  is  often  used  as  a  flux,  and  in  the  soldering  of 
metals.  Ebelmen  has  in  this  way  employed  it  as  a  solvent  of  certain  metallic 
oxides,  which  have  afterwards  been  obtained  from  it  in  the  form  of  crystals, 
so  as  to  imitate  native  mineral  products  (Ann.  Ch.  and  Ph.,  3eme  ser.  xxii. 
211),  such  as  the  ruby  and  emerald.  When  boracic  acid  is  perfectly  pure, 
and  is  slowly  depoisted  from  its  aqueous  solution,  it  forms  small  prismatic 
crystals  ;  it  is  more  commonly  seen  in  scaly  crystals. 

Composition. — Boron,  when  burned,  or  acidified  by  nitric  acid,  combines 
with  about  68  per  cent,  of  oxygen  ;  and  with  this  proportion  the  theoretical 
estimate  of  Berzelius  coincides.  There  is,  however,  a  difference  of  opinion 
as  to  the  atomic  constitution  of  boracic  acid,  and  the  equivalent  of  boron. 

Boracic  acid  is  generally  represented  as  BO,,  and  the  equivalent  of  boron 
will  thus  be  10-8.  Adopting  11  as  the  equivalent,  anhydrous  boracic  acid 
will  be  constituted  of 

Boron 

Oxygen       .        . 


Atoms. 

Weights. 

Per  cent. 

,      1      . 

..      11      .. 

.     31-43 

3     . 

..     24     .. 

.     68-57 

Boracic  acid 1  35  100-00 

The  crystallized  hydrate  will  consist  of  56  4  anhydrous  acid  and  43  6  per 
cent  of  water.  The  crystals  of  the  acid,  when  dried  at  212°,  lose  half  their 
water. 

Boracic  acid  is  a  feeble  acid.  It  produces  a  wine  red  color  with  infusion 
of  litmus,  becoming  rather  sombre  red  on  boiling.  This  arises  from  its  slight 
solubility.     It  readily  decomposes  the  solutions  of  the  alkaline  carbonates 


TESTS    FOR    BORACIC    ACID    AND    BORATES.  295 

when  moderately  heated,  and  expels  carbonic  acid  ;  but  concentrated 
solutions  of  borates  are  decomposed  by  nearly  all  other  acids,  even  the 
acetic.  Owing  to  the  fixed  nature  of  the  boracic  acid,  it  expels  at  a  full  red 
heat,  the  sulphuric  and  phosphoric  acids  from  the  sulphates  and  phosphates. 
It  has  no  action  on  the  alkaline  chlorides,  unless  water  is  present,  in  which 
case  a  borate  of  the  alkali  is  formed,  and  hydrochloric  acid  is  set  free.  Ily- 
dro<2jen  and  carbon  have  no  action  upon  the  acid  at  the  highest  temperatures, 
unless  chlorine  is  present.  Under  these  circumstances  the  acid  is  decom- 
posed and  carbonic  oxide  and  chloride  of  boron  are  produced  (BOg-f  3C-f- 
3Cl=BCl3H-3CO).  It  is  deoxidized  at  a  Tiigh  temperature  by  potassium, 
sodium,  and  aluminum.  The  chief  supply  of  boracic  acid  is  from  the  district 
of  Monte  Cerboli  and  Sasso,  in  Tuscany.  It  is  much  employed  as  a  flux  for 
colors  in  the  manufacture  of  porcelain. 

I'ests. — Boracic  acid  may  be  identified  :  1.  By  its  fusibility  and  fixedness 
at  high  temperatures  ;  2.  J3y  its  sparing  solubility  in  water  and  its  entire 
solubility  in  boiling  solutiohs  of  alkalies  and  alkaline  carbonates,  in  the  latter 
with  effervescence;  and  3.  By  its  rich  green  color  which  it  communicates  to 
the  flame  of  strong  alcohol.  Oxide  of  copper  gives  a  similar  tint,  but  this 
may  be  easily  excluded. 

Borates. — 1.  The  alkaline  borates  are  soluble  in  water,  and  have  an  alka- 
line reaction.  2.  When  the  solution  is  concentrated  by  evaporation  if  neces- 
sary, hydrochloric  acid  will  throw  down  scaly  crystals  of,  boracic  acid.  3.  A 
salt  of  baryta  throws  down  a  white  precipitate,  soluble  in  nitric  acid  and 
even  in  an  excess  of  water.  4.  Nitrate  of  silver  gives,  with  a  soluble  borate, 
if  concentrated,  a  white  precipitate,  soluble  in  nitric  acid;  if  diluted,  a  brown 
precipitate  (oxide  of  silver).  Arsenio-nitrate  of  silver  gives  a  yellow  pre- 
cipitate with  a  borate,  whether  the  solution  is  concentrated  or  diluted. 
These  precipitates  are  soluble  in  nitric  acid.  5.  Sulphate  of  magnesia  does 
not  precipitate  a  concentrated  solution  of  a  borate  in  the  cold  ;  but  white 
borate  of  magnesia  is  thrown  down  on  boiling  the  mixture.  6.  Add  sul- 
phuric acid  to  the  borate,  and  then  a  small  quantity  of  alcohol,  ignite  the 
mixture,  and  the  appearance  of  a  green  flame  will  show  the  presence  of 
boracic  acid.  This  acid  may  be  expelled  from  all  minerals,  by  heating  the 
powdered  solid  with  a  mixture  of  sulphuric  and  hydrofluoric  acids.  It 
escapes  as  fluoboric  acid  gas.  A  borate  melts  and  forms  a  glassy-looking 
substance  at  a  high  temperature. 

Nitride  op  Boron  (BN)  has  been  already  referred  to.  It  is  an  amor- 
phous white  light  powder.  It  was  discovered  in  1842  by  Mr.  Balmain, 
who  gave  it  the  name  of  Ethogen.  It  is  most  readily  obtained  by  heating 
to  bright  redness,  in  a  platinum  crucible,  a  mixture  of  two  parts  of  dried 
sal  ammoniac  and  one  part  of  anhydrous  borax,  or  an  equivalent  proportion 
of  boracic  acid.  A  white  porous  substance  remains,  from  which  the 
chloride  of  sodium  may  be  removed  by  washing  It  may  also  be  procured 
by  calcining  a  mixture  of  borax  and  ferrocyanide  of  potassium  in  a  covered 
crucible. 

The  nitride  of  boron  is  an  amorphous  powder,  insoluble,  infusible,  and 
fixed.  It  has  neither  taste  nor  smell.  It  burns  under  the  blowpipe  with 
a  brilliant  flame  of  a  greenish-white  color.  When  heated  in  a  current  of 
aqueous  vapor,  it  produces  ammonia  and  boracic  acid  (borate  of  ammonia). 
Heated  with  hydrate  of  potassa  it  yields  ammonia.  It  is  a  powerful  deox- 
idizer  at  a  high  temperature.  Its  most  remarkable  property  is,  that  when 
calcined  with  dry  carbonate  of  potassa,  it  yields  borate  and  cyanate  of  potassa, 
so  that  it  decomposes  carbonic  acid,  the  carbon  of  which  unites  with  the 
nitrogen  to  form  cyanogen  (BN  +  2(KO,COJ=KO,B03-f  KO,NC,0)  ;  if 


296  CHLORIDE  AND  FLUORIDE  OF  BORON. 

excess  of  the  nitride  is  used,  cyanide  of  potassium  will  also  be  formed.  This 
appears  to  be  the  compound  from  which  native  boracic  acid  is  sometimes 
formed  in  volcanic  districts.  Mr.  Warinp:ton  examined  a  substance  brouf^ht 
from  Ynlcano,  one  of  the  Lipari  Islands,  and  found  it  to  possess  all  the  pro- 
perties of  the  artificial  nitride  of  boron.  Boracic  acid  was  found'condensed 
like  drifted  snow,  within  the  crater  of  this  volcano,  and  at  a  few  inches 
below  the  surface,  there  was  a  mass  of  sal  ammoniac.  As  ammonia  is  com- 
monly found  associated  with  native  boracic  acid,  it  is  not  improbable  that 
these  are  products  of  the  decomposition  of  nitride  of  boron  by  aqueous  vapor 
(BN+SHO^BOg+NH^). 

Chloride  of  Boron  (BCl,). — This  is  a  volatile  liquid  compound  of  the 
two  elements.  It  may  be  procured  by  passing  dry  chlorine  over  heated 
boron,  or  over  a  mixture  of  dry  boracic  acid  and  charcoal  heated  to  redness. 
The  vapor  is  here  mixed  with  carbonic  oxide  (BOg-f  3C  +  3Cl=BCl3  +  3CO). 
The  chloride  is  a  highly  refracting  liquid  of  sp.  gr.  1-35,  boiling  at  a  tem- 
perature of  59°.  Its  vapor  has  a  density  of  4  07.  It  is  resolved  by  water 
into  boracic  and  hydrochloric  acids  (BCl3  +  3HO=3HCH-B03).  There  is 
a  liquid  bromide  (BjBi^)  resembling  the  chloride. 

Fluoride  of  Boron.  Fluoboric  Acid  (BF.J. — This  is  a  gaseous  com- 
pound, which  may  be  obtained  by  heating  a  mixture  of  vitrified  boracic  acid 
and  fluor-spar  (fluoride  of  calcium)  to  w^hiteness ;  fluoboric  acid  passes  over 
as  a  gas,  and  biborate  of  lime  remains  in  the  tube  (TBOg-f  3CaF  =  3[CaO, 
2B03]  +  BF3).  The  gas  may  also  be  procured  by  heating  in  a  glass  retort, 
over  a  lamp,  a  mixture  of  1  part  of  vitrified  boracic  acid,  2  parts  of  finely 
powdered  fluor-spar,  and  12  parts  of  sulphuric  acid  ;  but  in  this  case,  it  is 
generally  contaminated  by  fluosilicic  acid  gas,  derived  from  the  glass.  It 
must  be  collected  over  dry  mercury  (BOg-fSCaF-f  3(S03,HO)  =  3(CaO,S03) 
+  3HO-fBF3). 

Fluoboric  acid  gas  has  a  specific  gravity  of  2  31  ;  it  is  colorless,  of  a 
pungent,  suffocating  odor,  highly  deleterious  when  breathed,  and  it  ex- 
tiuguishes  flame.  The  gas  strongly  reddens  litmus  ;  and  when  bubbles  of  it 
are  allowed  to  escape  into  the  air,  they  produce  remarkably  dense  white 
fumes,  in  consequence  of  their  eager  attraction  for,  and  combination  with 
aqueous  vapor.  It  is  thus  a  good  test  of  humidity.  Water  takes  up  700 
times  its  volume  of  the  gas,  increasing  in  volume  and  density,  and  forming 
a  caustic  and  fuming  solution,  in  which  Berzelius  found  boracic  and  hydro- 
fluoric acids  in  combination  {horohydrofltioric  acid)  :  it  would  seem,  there- 
fore, that  fluoboric  acid  gas  decomposes  water,  and  that  the  hydrogen  of  the 
water  unites  to  the  fluorine  to  form  hydrofluoric  acid,  and  the  oxygen  to  the 
boron,  to  form  boracic  acid  (BFg-f  3HO=3HF-j-B03).  When  the  solution 
is  concentrated,  the  hydrofluoric  and  boracic  acids  again  decompose  each 
other,  and  the  original  compound  is  reproduced.  Neither  the  gas  nor  the 
liquid  acid  act  upon  glass,  but  they  speedily  decompose  almost  all  organic 
substances :  a  piece  of  paper  introduced  into  the  gas  standing  in  a  tall  jar 
over  mercury,  causes  its  rapid  absorption,  and  becomes  charred  as  if  burned, 
in  consequence  of  the  abstraction  of  the  elements  of  water.  When  potas- 
sium is  heated  in  fluoboric  acid  gas,  it  burns,  and  a  brown  compound  results, 
consisting  of  boron  and  fluoride  of  potassium  :  the  latter  may  be  dissolved 
in  water,  and  pure  boron  remains.  .The  gas  gives  a  green  color  to  the 
flame  of  alcohol.  It  forms  in  equal  volumes  a  solid  white  volatile  compound 
with  ammonia,  both  gases  being  in  the  anhydrous  state.  This  compound 
is  decomposed  by  water,  and  is  converted  into  hydrofluate  and  borate  of 
ammonia. 


PREPARATION    OP    SILICON.  297 

As  the  vapor  densities  of  fluorine  and  boron  are  unknown,  it  is  impossible 
to  assi^ni  the  volumetric  constitution  of  the  fluoride.  The  gas  contains  in  100 
parts,  by  weisj:ht,  16- 17  of  boron  and  83'83  of  fluorine,  or  one  atom  of  boron 
and  three  atoms  of  fluorine. 

SILICON  (Si=22). 

Silicon,  like  boron,  may  be  obtained  in  the  amorphous  or  crystalline  state. 
It  so  closely  resembles  boron  in  one  of  its  crystalline  modifications  (the 
graphitic),  that  the  two  metalloids  cannot  be  distinguished  by  their  appear- 
ance. In  1824,  Berzelius  first  procured  pure  amorphous  silicon,  by  decom- 
posing, at  a  high  temperature,  the  silico-fluorideof  potassium  with  an  excess 
of  the  metal.  Wohler  and  Deville  have  since  improved  upon  his  process ; 
and  they  have  first  brought  to  the  knowledge  of  cliemists,  that  silicon  might 
be  procured  in  two,  or,  according  to  them,  in  three  allotropic  conditions — 
namely,  the  amorphous,  graphitic,  and  the  regular  crystalline  forms. 

Freparation. — Amorphous  or  pulverulent  silicon  may  be  obtained  by 
heating  in  an  iron  tube,  a  mixture  of  one  part  of  the  double  fluoride  of 
silicon  and  potassium  (3KF,2SiF3)  (or  the  hydrofluosilicate  of  potassa), 
with  nine  parts  of  potassium.  (The  double  fluoride  is  itself  obtained  by 
saturating  hydrofluosilicic  acid  with  a  strong  solution  of  potassa,  washing 
the  precipitate,  and  drying  it  thoroughly  below  a  red  heat  )  In  heating  the 
mixture,  the  mass  becomes  suddenly  incandescent,  and  the  following  changes 
take  place:  (3KF,2SiF3+6K=9KF  +  2Si).     The  residue,  when  cooled,' is 

treated  with  cold  water,  some  hydrogen  escapes  from  the  decomposition  of 
a  portion  of  silicide  of  potassium,  formed  in  the  process,  and  silicon  is  pre- 
cipitated in  an  insoluble  form.  After  the  liquid,  used  in  washing  the  pre- 
cipitate, ceases  to  be  alkaline,  hot  water  is  employed  in  order  to  remove  any 
undecomposed  double  fluoride;  and  the  silicon  remains  as  a  dark  brown 
powder.  The  decomposition  of  the  vapors  of  the  fluoride  and  chloride  of 
silicon,  in  passing  them  through  a  heated  tube  containing  potassium  or  so- 
dium, furnishes  other  methods  of  procuring  this  metalloid. 

The  most  economical  process  for  obtaining  crystallized  silicon,  according 
to  Caron,  is  to  project  quickly  into  a  red-hot  crucible  (provided  with  a 
cover,  also  kept  red-hot)  a  mixture  of  30  parts  of  dried  silico-fluoride  of 
potassium,  with  40  parts  of  pure  granulated  zinc,  and  8  parts  of  sodium,  in 
small  pieces.  The  mass  is  removed  from  the  crucible  when  cooled ;  and 
while  the  lower  part  contains  the  ingot  of  zinc,  the  crystallized  silicon  will 
be  found  adhering  to  the  upper  portion  of  this  metal.  The  greater  part  of 
the  zinc  is  run  out  by  raising  the  mass  to  its  melting-point;  and  the  small 
quantity  which  adheres  to  the  silicon,  and  any  iron  that  may  be  present,  are 
removed  by  digesting  the  mass  in  concentrated  hydrochloric  acid.  If  lead 
is  present,  this  should  be  removed  by  nitric  acid ;  the  pure  silicon  which 
remains,  may  be  washed  and  dried.  The  silicon  thus  obtained  may  be 
melted  by  mixing  it  with  the  double  fluoride  and  coarsely-powdered  glass, 
and  heating  the  mixture  in  a  double'  crucible  to  the  melting-point  of  iron. 
A  globule  of  silicon  is  formed  in  the  midst  of  the  glass  and  slag.  These 
substances  may  be  removed  mechanically,  and  any  adhering  traces,  by  im- 
mersing the  silicon  in  concentrated  hydrofluoric  acid,  which  has  no  action  on 
this  substance. 

The  scaly  crystals,  or  graphitic  silicon,  were  obtained  by  Deville  in  de- 
composing the  dry  double  fluoride  by  aluminum,  at  the  melting-point  of 
silver:  silicide  of  aluminum  was  produced.  This  compound,  treated  first 
with  boiling  hydrochloric  acid,  and  afterwards  with  hydrofluoric  acid,  left 
pure  silicon  in  scales  resembling  graphite:  the  aluminum  and  the  silica  pro- 


298  SILICON.      CFIEMTCAL    PROPERTIES. 

duced  beinof  completely  removed  by  the  two  acids.  100  parts  of  alnminara 
gave  by  this  process  from  30  to  80  parts  of  silicide,  containing  from  65  to 
75  per  cent,  of  its  weight  of  silicon.  The  aluminum  appears  to  determine 
the  crystalline  form  of  the  silicon,  under  these  circumstances,  just  as  cast-iron 
affects  carbon,  in  producing  artificial  graphite.  In  decomposing  the  vapor 
of  chloride  of  silicon  by  aluminum  in  a  vessel  containing  hydrogen,  Wohler 
and  Deville  obtained  silicon  in  hard  hexahedral  prisms  of  an  iron-gray  color, 
and  of  a  reddish  tint,  by  reflection.  These  crystals,  like  diamond,  had  the 
property  of  scratching  glass,  and  even  cutting  it. 

Properties. — Amorphous  silicon  is  a  dark  brown  powder,  less  fusible  than 
boron,  but  still  capable  of  being  melted  between  the  poles  of  a  powerful 
voltaic  battery,  or  by  fusion,  as  in  the  process  above  described.  It  is  inso- 
luble in  water,  hot  or  cold.  It  is  a  non-conductor  of  electricity.  Nitric, 
hydrochloric,  and  sulphuric  acids,  whether  separately  or  mixed,  have  no 
action  upon  it,  even  when  boiled.  It  may  be  exposed  to  a  very  high  tem- 
perature in  close  vessels,  without  any  other  change  than  an  increase  of  hard- 
ness and  density ;  but  if  heated  in  air  or  oxygen  before  it  has  been  thus  cal- 
cined in  close  vessels,  it  will  take  fire,  and  burn  superficially,  the  silicic  acid 
formed  melting  and  protecting  the  residuary  silicon  from  continued  combus- 
tion. A  full  red  heat  in  a  covered  platinum  crucible,  appears  to  produce  an 
allotropic  change  isj  this  substance.  Pulverulent  silicon,  in  the  amorphous 
state,  decomposes  cold  hydrofluoric  acid,  as  well  as  a  concentrated  hot  solu- 
tion of  potassa,  hydrogen  being  liberated  in  both  cases,  and  silicon  dissolved. 
A  fluoride  is  formed  with  the  acid,  and  a  soluble  silicate  with  the  alkali. 
Silicon,  heated  to  full  redness,  acquires  so  great  a  density  that  it  sinks  in 
sulphuric  acid ;  and  it  loses  the  property  of  burning  in  oxygen  or  air,  even 
when  heated  in  the  flame  of  the  blowpipe.  Hydrofluoric  acid  and  a  boiling 
solution  of  potassa  are  not  decomposed  by  it;  but  nitro-hydrofluoric  acid 
alone  dissolves  it,  with  the  evolution  of  deutoxide  of  nitrogen.     (Fremy.) 

When  heated  with  an  alkaline  carbonate  at  the  temperature  of  fusion,  a 
silicate  of  the  alkali  is  formed,  carbonic  acid  is  decomposed,  and  carbonic 
oxide  escapes.  If  the  silicon  is  in  large  proportion,  this  gas  is  even  deoxi- 
dized, and  carbon  is  set  free.  This  shows  that  silicon  has  a  stronger  aSinity 
for  oxygen  than  carbon,  and  that  its  deoxidizing  powers  are  equal  to  those 
of  the  alkaline  metals.  It  does  not  decompose  nitrate  of  potassa  at  a  dull 
red  heat,  unless  this  salt  is  mixed  with  a  portion  of  carbonate,  when  deoxi- 
dation  takes  place  with  explosive  violence.  At  full  redness  decomposition 
is  produced  without  the  addition  of  the  carbonate.  It  is  oxidized  by  the 
hydrated  alkalies  in  the  melted  state,  but  it  has  no  action  on  boracic  acid  or 
borax,  at  the  temperature  of  fusion.  When  heated  in  a  current  of  chlorine, 
it  undergoes  combustion  and  forms  a  volatile  chloride.  It  fuses  with  plati- 
num, when  melted  in  this  metal,  or  as  it  is  evolved  in  the  nascent  state.  It 
combines  with  hydrogen,  to  form  a  gaseous  silicide  of  hydrogen.  This  gas 
is  spontaneously  inflammable  in  air,  like  phosphide  of  hydrogen,  burning 
with  a  bright  white  flame,  and  producing  wreaths  of  vapor  of  white  silicic 
acid.  The  gas  is  decomposed  at  a  red  heat,  silicon  being  deposited,  and  it 
detonates  violently  when  mixed  with  chlorine.  Its  constitution  has  not  been 
determined. 

Crystallized  silicon  in  the  graphitic  state,  possesses  most  of  the  chemical 
properties  assigned  to  amorphous  silicon  which  has  been  intensely  heated. 
It  has  the  color  and  lustre  of  iodine,  is  very  hard,  and  has  a  specific  gravity 
of  2  49.  It  IS  a  good  conductor  of  electricity.  It  is  insoluble  in  all  acids 
excepting  the  nitro-hydrofluoric.  It  decomposes  fused  carbonate  of  potassa 
at  a  red  heat;  and,  at  the  same  temperature,  burns  in  chlorine,  forming  a 
chloride.  '  o 


VARIETIES    OF    QUARTZ    AND    ROCK    CRYSTAL,  299 

Silicon  and  Oxygen.  Silicic  Acid  (SiOg).  Silica. — This  is  an  abun- 
dant natural  product.  It  is  a  constituent  of  every  soil,  and  is  found  more 
or  less  in  all  spring,  river,  and  sea-waters.  Under  the  form  of  sand  and 
sandstone,  it  covers  a  large  portion  of  the  surface  of  the  earth,  and  it  is  found 
in  all  rocks,  from  the  most  ancient  to  the  most  recent.  Granite,  felspar,  and 
all  the  varieties  of  natural  clays,  contain  a  large  proportion  of  silicic  acid  in 
combination  with  alumina,  oxide  of  iron,  lime,  magnesia,  and  other  bases. 
While  carbon,  the  first  member  of  this  group  of  metalloids,  is  the  main  con- 
stituent of  the  organic,  silicon,  in  the  form  of  silicic  acid,  is  the  chief  con- 
stituent of  the  inorganic  kingdom.  It  is,  however,  not  an  unimportant 
constituent  of  organic  matter.  The  cuticle  or  epidermis  of  the  grasses,  and 
of  the  husks  of  grains,  is  constituted  of  silicic  acid.  The  cuticle  and  scaly 
hairs  of  DeiUzia  contain  a  large  quantity  of  this  substance.  In  the  Equi- 
setacece,  the  whole  structure  of  the  vegetable  is  so  penetrated  by  it,  that  a 
complete  skeleton  of  the  vegetable  structure  in  silicic  acid,  maybe  obtained. 
Silica  is  found,  more  or  less,  in  the  ashes  of  all  vegetables,  especially  of 
those  which  grow  on  sandy  soils.  In  some  species  of  plants  it  forms  13  per 
cent.,  and  in  others  50  per  cent,  of  the  ash.  According  to  Johnston,  it 
forms  65  per  cent,  of  the  ash  of  wheat-straw,  and  74  per  cent,  of  that  of 
rice-straw.  In  the  bamboo  {Bamhusa  arundinacea)  silica  is  often  collected 
at  the  joints  in  masses ;  and  to  these  the  name  of  tahasheer  is  given.  The 
long,  slender,  and  hollow  stems  of  the  grasses,  derive  their  strength  from 
their  silicious  covering.  The  silica  is  generally  deposited  in  plates,  grains 
or  needles:  on  the  leaves  of  deiitzia  scahra,  it  is  deposited  in  a  stellated 
form. 

It  is  but  sparingly  diffused  in  the  bodies  of  man,  and  the  higher  orders  of 
animals ;  but  it  constitutes  the  skeleton  of  whole  tribes  of  infusoria.  The 
substance  called  mineral  flour,  or  mountain-meal  {Bergmehl),  is  almost  en- 
tirely constituted  of  the  silicious  skeletons  of  infusoria.  A  specimen  of  this 
substance,  obtained  by  Dr.  Traill  from  Swedish  Lapland,  and  analyzed  by 
him,  was  found,  in  the  dry  state,  to  consist  of  7 1 '13  parts  of  silicic  acid,  22 
of  organic  matter,  5'31  of  alumina,  and  015  of  oxide  of  iron.  The  cells  of 
the  Diatomacce  have  silicious  coverings,  which  enable  them  to  retain  their 
form,  even  after  digestion  in  strong  acids. 

The  following  are  the  principal  minerals  which  contain  silicic  acid  (silica), 
pure,  or  nearly  so. 

Rock-crystal,  or  quartz,  which  may  be  considered  as  pure  anhydrous  silicic 
acid  (silica).  It  crystallizes  in  the  form  of  a  six-sided  prism,  terminated  by 
six-sided  pyramids.  Some  varieties  are  perfectly  transparent  and  colorless  ; 
others  white  (milk-quartz)  and  more  or  less  opaque.  Its  specific  gravity  is 
2-6.  It  is  so  hard  as  to  give  sparks  when  struck  with  steel,  and  is  nearly 
infusible.  The  primitive  Crystal,  which  is  rare,  is  an  obtuse  rhomb,  the 
angles  of  which  are  94°  24',  and  85°  36'.  The  finest  and  largest  specimens 
of  quartz  are  brought  from  Madagascar,  the  Brazils,  and  the  Alps.  The 
small  and  perfectly  transparent  crystals  found  near  Bristol  and  in  Cornwall, 
are  sometimes  called  Bristol  and  Cornish  diamonds.  The  finest  crystals  are 
cut  into  ornaments,  and  are  used  as  a  substitute  for  glass  in  spectacles  ;  they 
are  then  termed  pebbles  ;  they  are  harder  and  do  not  so  readily  become 
scratched  as  glass.  iThe  refractive  power  of  rock-crystal  is  the  same  as  that 
of  glass,  being  about  1*6.  Water  is  1-3,  and  the  diamond  2-47.  Owing  to 
this  difference,  the  lustre  and  brilliancy  of  rock-crystal  is  far  inferior  to 
that  of  diamond.  Quartz  is  also  of  lower  specific  gravity,  and  although  hard 
enough  to  scratch  glass,  its  surface  is  easily  scratched  by  the  diamond,  as 
well  as  by  the  topaz  and  ruby.  Brown  and  yellow  crystals  of  quarts  are . 
found  in  great  beauty  in  the  mountain  of  Cairn  Gorm,  iu  Scotland.     This 


300  SILICIC    ACID.      OPAL.      JASPER.      AGATES. 

variety  of  quartz  is  sometimes  called  Scotch  topaz  ;  it  varies  in  color  from  a 
pale  yellow  to  a  deep  amber  tint.  The  color  may  be  due  to  the  presence  of 
traces  of  carbon  or  silicon.  The  hrown  quartz  varies  much  in  shade  from  a 
smoky  to  a  very  deep  tint :  the  color  is  probably  due  to  a  similar  cause. 
Fine  samples  of  smoky  quartz  are  found  in  Switzerland.  Purple  quartz,  or 
amethyst,  is  found  in  India,  Ceylon,  and  Persia:  it  owes  its  color  to  traces 
of  iron  and  manganese.  Rose-quartz  derives  its  color  from  manganese. 
Prase,  or  green  quartz,  is  colored  with  oxide  of  iron  ;  and  chrysoprase  is 
tinged  of  a  delicate  apple-green  by  oxide  of  nickel.  Aveniurine  is  a  beauti- 
ful variety  of  quartz,  of  a  rich  brown  color,  which  is  filled  with  bright  span- 
gles of  golden  mica ;  the  finest  specimens  are  from  Cape  de  Gatte  in  Spain. 
The  artificial  aventurine  is  a  variety  of  glass,  containing  tetrahedral  crystals 
of  metallic  copper  produced  by  fusion.  Small  crystals  of  quartz,  tinged 
with  iron,  are  found  in  Spain,  and  have  been  termed  hyacinths  of  Corapo-^ 
Stella. 

Chalcedony,  Carnelian,  Onyx,  Sardonyx,  and  Blood-stone,  or  Heliotrope, 
and  the  numerous  varieties  of  Agates,  are  principally  composed  of  quartz, 
with  various  tinging  materials,  chiefly  oxide  of  iron.  Flint  owes  its  black 
color  apparently  to  organic  matter.  When  heated  in  a  current  of  air  to  a 
very  high  temperature,  it  yields  white  amorphous  silicic  acid,  nearly  pure, 
with  a  trace  of  oxide  of  iron. 

Opalh  among  the  most  beautiful  productions  of  the  mineral  world  ;  it  is 
a  compound  of  about  90  silicic  acid  and  10  water,  and  is  distinguished  by  its 
very  brilliant  play  of  iridescent  colors.  The  finest  specimens  come  exclu- 
sively from  Hungary.  There  is  a  variety  of  opal  called  hydrophane,  which 
is  white  and  opaque  until  immersed  in  water  ;  it  then  resembles  the  former. 
The  proportion  of  water  with  which  silica  is  combined  in  the  different  varie- 
ties of  opal,  is  liable  to  so  much  variation,  that  they  can  scarcely  be  re- 
garded as  definite  hydrates. 

Common  opal  is  usually  of  a  dirty  white  color,  and  does  not  exhibit  the 
colors  of  the  noble  opal;  it  contains  silicic  acid  and  water,  with  a  little  oxide 
of  iron,  and  is  not  of  unfrequent  occurrence.  Wood-opal  is  opaque,  of  a 
brown  color,  and  of  a  ligneous  appearance.  Jasper  is  a  perfectly  opaque 
variety  of  silica,  containing  oxide  of  iron,  and  of  a  red,  brown,  or  green  color  ; 
these  colors  often  alternating  and  giving  a  striped  appearance  to  the  sub- 
stance.    Black  jasper,  or  Lydian  quartz,  forms  the  touchstone  of  jewellers. 

The  term  chalcedony,  from  Chalcedon  in  Bithynia,  near  to  which  it  is 
found  in  large  quantity,  is  applied  to  a  variety  of  bluish  and  translucent 
stalactitic  quartz,  sometimes  of  a  milk-white  or  a  gray  color.  The  milk- 
white  variety  forms  white  carnelian,  and  the  red  variety  forms  red  carnelian. 
When  brown  and  opaque-white  chalcedony  occurs  in  alternate  layers,  it  con- 
stitutes the  07iyx.  If  the  color  is  of  a  deep  bro\fnish-red,  or  by  transmitted 
light,  blood-red,  the  stone  is  termed  sard.  Alternate  layers  of  sard  and 
milk-white  chalcedony,  constitute  Sardonyx.  Heliotrope  has  a  deep  green 
color  :  it  derives  its  name  of  blood-stone  from  the  bright  red  spots  of  per- 
oxide of  iron  scattered  through  it.  It  is  found  in  Siberia  and  Iceland. 
(Thomson.)  Mocha-stone  is  chalcedony  containing  dendrites,  usually  of  a 
black  or  brown  color ;  but  sometimes  green,  and  resembling  certain  mosses. 
Hence  the  term  moss-agates.  The  filaments  which  ha^e  the  appearance  of 
vegetable  fibres  appear  to  be  owing  to  the  infiltration  of  iron,  manganese, 
or  their  compounds.  Mocha-stone  is  chiefly  brought  from  Arabia.  Agate 
has  a  basis  of  chalcedony,  with  sometimes  crystals  of  quartz  or  amethvst  in 
the  centre.  It  consists  of  alternate  layers  of  chalcedony,  quartz,  jasper,"'helio- 
trope,  or  opal,  the  layers  being  occasionally  disposed  in  an  angular  form 
(fortification  agates)  and  variously  colored.     It  is  found  in  Saxony,  Bohemia, 


PREPARATION    OF    SILICIC    ACID.  301 

Siberia,  Iceland,  and  the  Isle  of  Skye.  This  substance  is  useful  to  the  chemist, 
as  it  is  turned  into  mortars  for  grinding  hard  substances.  The  order  of 
hardness  usually  adopted  by  mineralogists  is  as  follows;  1.  talc;  2.  gypsum; 
3.  calcareous  spar ;  4.  fluor-spar ;  5.  phosphate  of  lime ;  6.  felspar  ;  t. 
quartz  ;  8.  topaz  ;  9.  sapphire  and  ruby  ;  10.  diamond.  The  diamond  can 
only  be  powdered  in  hard  steel  mortars.  When  once  reduced  to  fragments 
by  cleavage,  its  own  powder  serves  for  its  further  trituration. 

Obsidian  is  a  glassy-looking  substance,  of  a  greenish  or  brownish-black 
color.  It  is  found  in  the  Lipari  Islands  and  Iceland.  It  is  volcanic-glass. 
It  contains  from  12  to  78  per  cent,  of  silicic  acid  combined  with  alumina, 
potassa,  and  soda.  It  owes  its  color  to  oxide  of  iron.  Pumice  is  a  porous 
fibrous  substance  of  a  gray  color.  It  contains  'Zt'S  per  cent,  of  silicic  acid. 
It  is  found  chiefly  interstratified  with  obsidian  in  the  islands  of  Lipari  and 
Ponza.  In  Lipari,  there  is  a  hill  {Capo  Bianco)  1000  feet  high,  constituted 
entirely  of  pumice. 

Tripoli  contains  90  silicic  acid,  T  alumina,  and  3  of  oxide  of  iron.  It  was 
formerly  brought  from  Tripoli  in  Africa,  whence  its  name.  It  is  found  in 
Bohemia  and  Tuscany.  When  finely  levigated  by  trituration  with  water,  it 
is  much  used  for  polishing  metals,  marble,  glass,  and  other  hard  bodies. 

Preparation. — Silicic  acid  may  be  obtained  for  chemical  purposes*  by  the 
following  process.  Heat  colorless  rock-crystal  to  redness,  quench  it  in 
water,  and  reduce  it  to  a  fine  powder  ;  in  this  state  it  is  silicic  acid,  almost 
perfectly  pure.  Fuse  1  part  of  this  powder  with  3  parts  of  a  mixture  con- 
sisting of  equal  parts  of  carbonate  of  soda  and  carbonate  of  potassa,  in  a 
silver  or  platinum  crucible.  Dissolve  the  resulting  mass  in  vrater,  add  a 
slight  excess  of  hydrochloric  acid,  and  evaporate  to  dryness.  Wash  the  dry 
mass  in  boiling  distilled  water  upon  a  filter,  and  the  white  substance  which 
remains  is  silica.  This  is  the  usual  process.  The  silica  obtained  by  simply 
reducing  the  colorless  rock-crystal  to  powder  is  nearly  pure ;  it  sometimes 
contains  traces  of  oxide  of  iron  and  manganese,  as  well  as  of  alumina.  Pure 
silica  may  also  be  obtained,  by  the  fusion  of  fine  white  sand,  or  powdered 
rock-crystal,  with  carbonate  of  lime;  the  resulting  compound  of  lime  and 
silica  may  be  decomposed  by  dilute  hydrochloric  acid,  and  the  product,  after 
having  been  duly  washed,  is  silica  in  the  form  of  a  light  powder.  When 
gaseous  fluoride  of  silicon  (fluosilicic  acid)  is  passed  into  water,  the  silicic 
acid  which  is  precipitated,  after  having  been  washed  and  dried,  is  also  pure, 
and  in  a  state  of  extreme  mechanical  division. 

At  a  high  temperature,  steam  carries  off  silica  in  the  state  of  vapor,  thus 
establishing  an  analogy  between  the  silicic  and  boracic  acids.  While 
boracic  acid  is  fusible  at  a  red,  and  volatile  at  a  white  heat,  silicic  acid, 
according  to  Deville,  is  less  fusible  than  platinum,  but  is  volatile  at  this 
temperature  in  a  current  of  gas  or  vapor. 

Properties. — Silicic  acid  exists  in  two  states,  the  amorphous  and  crystalline. 
The  acid  obtained  by  precipitation  in  the  processes  above  described,  is  the 
amorphous  variety  ;  while  the  native  rock-crystal  represents  the  crystalline 
form.  They  are  difl'erently  affected  by  reagents.  Amorphous  silicic  acid, 
as  it  is  precipitated  from  its  solutions,  is  supposed  to  be  a  hydrate,  repre- 
sented by  the  formula,  Si03,H0. — When  dried  at  21 2°,  it  is  said  to  lose 
half  its  water,  and  to  become  2(Si03)HO.  According  to  Mitscherlich, 
there  is  no  definite  hydrate  of  silicic  acid.  It  loses  a  variable  quantity  of 
water  in  drying,  and  absorbs  water  in  a  damp  atmosphere.  When  the  pre- 
cipitate is  heated  to  370°,  it  loses  the  whole  of  its  water,  and  forms  the 
insoluble  variety  of  amorphous  silicic  acid  (SiOg).  In  this  state,  it  is  a 
white,  tasteless  powder,  insoluble  in  water,  and  not  forming  with  it  a  cohesive, 
plastic  mass,  like  alumina.     It  has  no  action  on  vegetable  colors,  and  is 


302  SILICIC    ACID.      CHEMICAL    PROPERTIES. 

infusible  except  under  the  intense  heat  of  the  oxyhydrogen  blowpipe,  in  the 
flame  of  which  it  melts,  forming  a  transparent  colorless  globule.  Its  sp.  gr. 
is,  like  that  of  the  crystalline  variety,  2  66.  It  is  not  dissolved  by  any  of 
the  oxacids,  either  separately  or  in  mixture,  even  at  a  boiling  temperature. 
When  a  very  diluted  solution  of  a  silicate  is  treated  with  sulphuric,  hydro- 
chloric, or  nitric  acid,  the  silicic  acid  is  not  precipitated,  but  appears  to  be 
dissolved  by  the  water  as  a  hydrate.  When  the  acid  solution  is,  however, 
concentrated  by  evaporation,  or  the  acid  is  at  once  added  to  a  concentrated 
solution  of  a  silicate,  the  hydrate  is  precipitated  in  a  gelatinous  form,  and 
when  dried  and  strongly  heated  it  forms  the  insoluble  variety. 

Solubility  of  Silicic  Acid. — The  solubility  of  silicic  acid  in  water  has  been 
hitherto  doubted  or  denied  by  chemists.  Some  have  admitted  that  pure 
water  would  dissolve  only  a  thousandth  part  of  its  weight  of  recently  pre- 
cipitated or  gelatinous  silica.  Mr.  Graham  has,  however,  by  the  process  of 
dialysis,  succeeded  in  procuring  a  solution  of  silica  varying  from  5  to  14  per 
cent,  of  the  weight  of  the  water.  He  added  hydrochloric  acid  to  a  solution 
of  silicate  of  soda,  and  placed  the  mixture  in  a  dialyser  (p.  146).  In  a  few 
days  the  chloride  of  sodium  and  hydrochloric  acid  were  entirely  removed, 
while  silica  and  water  alone  remained  in  the  dialyser.  He  calls  this  colloid 
silicic  acid.  The  liquid,  when  left  to  itself,  slowly  deposited  silica  in  a  gela- 
tinous and  insoluble  form  :  hence  it  cannot  be  regarded  as  a  solution  in  its 
proper  chemical  signification  (pp.  47 — 51).  Lime-water,  or  a  solution  of 
carbonate  of  potassa,  added  to  it,  rapidly  caused  the  separation  of  silicic 
acid  in  a  gelatinous  form.  These  facts  may  account  for  the  temporary  solu- 
bility and  deposit  of  silica,  under  circumstances  which  have  hitherto  appeared 
difficult  of  explanation. 

Amorphous  silicic  acid,  either  in  the  state  of  gelatinous  hydrate,  or  in 
powder  dried  but  not  heated,  is  readily  dissolved  in  the  cold  by  concentrated 
hydrochloric,  nitric,  or  sulphuric  acid.  A  strong  solution  of  potassa  or  soda 
will  dissolve  it,  but  with  more  difficulty.  In  evaporating  alkaline  solutions 
in  glazed  porcelain  dishes,  a  portion  of  the  silica  of  the  glaze  is  frequently 
dissolved.     The  alkalift?  also  dissolve  silica  from  flint  glass. 

Silicic  acid  which  has  been  strongly  calcined,  is  as  insoluble  in  alkalies 
and  oxacids  as  the  anhydrous  native  silicic  acid — rock-crystal.  Among 
hydracids,  the  hydrofluoric  is  the  only  one  which  dissolves  silicic  acid, 
forming  water  and  fluoride  of  silicon  (Si03H-3HF=3HO  +  SiF3).  The 
rapidity  of  this  action  is  in  proportion  to  the  concentration  of  the  acid.  If 
the  silicic  acid  is  in  fine  powder,  if  it  has  not  been  calcined,  and  if  a  sufficient 
quantity  of  hydrofluoric  acid  is  employed,  it  is  readily  dissolved.  Insoluble 
silicates,  such  as  the  varieties  of  glass,  are  similarly  attacked  and  dissolved 
by  this  acid  ;  but  crystalline  silicic  acid,  or  native  rock-crystal,  resists  its 
action. 

In  the  precipitation  of  silicic  acid  from  its  alkaline  solutions  by  acids, 
alumina  may  be  associated  with  it.  If  the  residue  is  brought  to  dryness, 
moistened  with  strong  hydrochloric  acid  for  half-an-hour,  and  then  boiled  in 
water,  alumina,  as  well  as  oxide  of  iron,  magnesia,  and  other  bases  present, 
will  be  entirely  dissolved,  while  the  silic  acid  alone  will  remain  utidissolved. 
Its  quantity  may  thus  be  determined. 

Silicic  acid  is  precipitated  from  its  concentrated  solutions  by  nearly  all 
acids,  even  the  carbonic  and  hydrocyanic.  When  its  solutions  are  long 
kept,  or  are  exposed  to  air,  the  silicic  acid  is  deposited  as  an  opaque  white 
mass.  The  silica  thus  precipitated  is  readily  dissolved  by  strong  acids,  but 
n-ot  readily  by  alkaline  solutions,  even  at  a  boiling  temperature.  When  dry 
silicic  acid  is  fused  with  the  hydrates  of  potassa,  soda,  or  baryta,  it  readily 
enters  into  combination,  forming  silicates.      In  the  anhydrous  state,  at  a 


SILICIC    ACID.      CHEMICAL    PROPERTIES.  303 

high  temperature,  it  expels  carbonic  acid  from  alkaline  carbonates  (KO,COa 
-f-Si03=KO,Si03+ COJ.  It  is  worthy  of.  remark,  that  in  this  decompo- 
sition, there  is  no  substitution  of  a  metallic  oxide  for  water,  but  a  displace- 
ment of  one  anhydrous  acid  by  another.  It  is  impossible  to  regard  silicic 
acid  as  a  salt  of  hydrogen.  It  is  an  anhydrous  oxacid,  capable  of  displacing 
other  oxacids  at  a  high  temperature,  without  the  intervention  of  the  elements 
of  water. 

Silicic  acid  is  unaffected  at  the  highest  temperatures  by  hydrogen,  carbon, 
phosphorus,  or  chlorine.  When,  however,  it  is  heated  and  exposed  to  the 
combined  action  of  chlorine  and  carbon,  oxide  of  carbon  and  a  volatile  chlo- 
ride of  silicon  are  produced.  When  heated  with  carbon  in  contact  with 
iron  or  platinum,  it  undergoes  decomposition  :  carbonic  oxide  escapes,  and 
silicides  of  the  metals  result.  Platinum  vessels  may  be  thus  destroyed  by 
nascent  silicon. 

Although  silicic  acid,  as  it  is  commonly  met  with,  is  not  soluble  in  water, 
yet  there  is  scarcely  a  river  or  spring-water  in  which  traces  of  it  may  not 
be  found.  It  appears  to  be  held  in  solution  either  by  alkalies  or  their  car- 
bonates. The  Geyser  springs  of  Iceland  contain  a  large  quantity  of  silicic 
acid.  We  have  found  as  much  as  48  grains  in  a  gallon  of  the  water  of  the 
Great  Geyser  (1856)  :  the  solvent  here  appears  to  be  carbonate  of  soda,  the 
efi'ect  of  which  is  probably  aided  by  the  high  temperature  as  well  as  the 
pressure  to  which  the  heated  column  of  water  is  subjected.  The  silicic  acid 
is  precipitated  from  the  water  in  a  hard  crystalline  form  on  all  the  sur- 
rounding rocks.  It  has  been  already  stated  that  hydrated  silicic  acid  may 
be  volatilized  with  aqueous  vapor  at  a  high  temperature,  like  hydrated 
boracic  acid  (p.  301). 

Composition. — The  amount  of  oxygen  contained  in  100  parts  of  silicic 
acid,  has  been  variously  estimated  at  from  51*98  (Mitscherlich)  to  52  93. 
Assuming  the  former  proportion  to  be  correct,  and  silicic  acid  to  contain  3 
atoms  of  oxygen  united  to  1  atom  of  silicon  (SiOg),  then  (51  "98  :  24  :  : 
4802  :  22-1)  the  equivalent  of  silicon  would  be  22.  This  is  in  accordance 
with  the  views  of  Berzelius  and  the  majority  of  British  and  foreign  chemists, 
including  the  most  recent  writers  on  the  subject,  Pelouze  and  Fr^my.  It 
is  also  consistent  with  the  atomic  constitution  of  boracic  acid,  to  which 
such  acid  bears  a  much  stronger  analogy  in  chemical  and  physical  proper- 
ties, than  it  does  to  the  oxygen  compound  of  carbon  (COj.  It  has,  how- 
ever, been  proposed  to  alter  the  equivalent  of  silicon,  by  making  the  formula 
of  silicic  acid  SiOg ;  but  there  are  no  valid  reasons  for  making  this  change. 
Col.  York,  in  experimenting  with  silicic  acid  on  different  alkaline  salts  and 
bases,  obtained  such  widely  different  results,  that  he  could  draw  no  satis- 
factory conclusion.  Thus,  in  calculating  by  the  amount  of  carbonic  acid 
expelled  by  silicic  acid  from  fused  carbonate  of  potassa,  the  mean  result  of 
four  experiments  gave  as  the  equivalent  of  silicic  acid  30*7,  corresponding 
to  the  formula  SiOg.  Seven  experiments  with  the  carbonate  of  soda,  how- 
ever, gave  an  equivalent  of  21-3,  represented  by  SiOg.  Carbonate  of  lithia 
gave  the  number  1499,  nearly  agreeing  with  the  formula  SiO.  The  fusion 
of  silicic  acid  with  hydrate  of  potassa  gave  a  result  corresponding  to  that 
derived  from  the  carbonate,  30*8  ;  but  hydrate  of  soda  gave  172,  a  result 
approaching  to  that  obtained  by  carbonate  of  lithia.  Such  results  furnish 
no  grounds  for  changing  the  equivalent  of  silicic  acid.  On  the  other  hand, 
in  experimenting  with  other  substances,  this  gentleman  found  that  boracic 
acid  only  gave  results  similar  to  those  obtained  with  silicic  acid.  Proc, 
JR.  S.,  Vol.  8,  JS'o.  25,  p.  441.)  As  this  acid  is  admitted  to  have  the  formula 
of  BO3,  this  simple  fact  justiQes  the  retention  of  the  generally  accepted 
formula,  SiOg.     Apart  from  other  strong   analogies    between    boron   and 


304  ANALYSIS    OF    SOLUBLE    AND    INSOLUBLE    SILICATES. 

silicon,  a  change  in  the  formula  of  silicon  would  be,  therefore,  inexpedient 
and  inconsistent. 

The  experiments  of  Scheerer  {Chem.  Neius,  March  30,  1861,  205)  show 
that,  in  fusing  silicic  acid  with  carbouate  of  soda,  various  silicates  may  be 
produced,  and  variable  amounts  of  carbonic  acid  expelled.  The  result 
depends  on  the  temperature  of  fusion,  the  duration  of  the  fusion,  the  relative 
proportions  of  silicic  acid  and  base,  and  the  chemical  relations  of  carbonic 
acid  to  the  base  at  a  high  temperature.  From  his  results,  Scheerer  con- 
siders the  formula  SiOg  to  be  correct. 

Silicates. — These  salts  form  a  numerous  class  of  substances,  in  some  of 
which  the  acid,  and  in  others  the  base,  predominates.  All  are  insoluble  in 
water,  excepting  those  of  potassa  and  soda.  The  polysilicates  of  these 
alkalies  constitute  varieties  of  glass.  The  aqueous  solution  of  a  soluble 
•silicate  is  alkaline.  It  gives  a  white  precipitate  with  ammonia,  or  carbonate 
of  ammonia,  which  is  not  dissolved  by  a  cold  solution  of  potassa,  or  by 
chloride  of  ammonium  (A  precipitate  given  by  carbonate  of  ammonia  in  a 
salt  of  alumina  is  dissolved  by  a  cold  solution  of  potassa.)  A  silicate  is 
distinguished  from  the  alkaline-earthy  and  all  other  salts,  by  the  fact  that  an 
acid  (even  the  acetic)  will  precipitate  the  silicic  acid  from  a  concentrated 
solution,  as  a  gelatinous  hydrate.  The  white  powder  obtained  on  drying  and 
heating  this  precipitate,  may  be  identified  as  silicic  acid,  by  its  insolubility 
in  all  menstrua  excepting  hydrofluoric  acid.  It  is  dissolved  by  this  acid, 
and  if  the  silicic  acid  contains  no  impurity,  the  whole  of  it  may  be  vola- 
tilized as  fluoride  of  silicon,  by  heating  the  solution  in  a  platinum  capsule. 

Among  other  chemical  characters  of  a  soluble  silicate,  may  be  mentioned 
.the  following:  Nitrate  of  silver  gives  with  the  solution  a  brown,  and  the 
arsenio-nitrate  a  yellow  precipitate.  It  is  precipitated  in  a  gelatinous  form 
by  all  the  salts  of  ammonia,  and  by  all  acids,  including  even  the  hydrocyanic 
and  carbonic.  Nitrate  of  baryta  also  produces  in  it  a  gelatinous  precipitate 
which  is  not  dissolved  by  nitric  acid  ;  but  this  could  not  be  mistaken  for  a 
sulphate,  inasmuch  as  nitric  acid  alone  produces  a  dense  gelatinous  precipi- 
tate in  a  solution  of  a  silicate. 

The  analysis  of  the  insoluble  silicates  is  attended  with  some  difficulties. 
Some  of  these  in  which  the  base  predominates,  as  in  certain  slags,  may  be 
entirely  decomposed,  and  the  silicic  acid  set  free  in  a  gelatinous  form,  by 
digesting  the  finely-powdered  silicate  in  a  strong  acid,  such  as  the  sulphuric, 
hydrochloric,  nitric,  or  even  the  acetic.  The  bases  are  found  in  soluble 
combination  with  the  acid,  which  should  be  selected  accordingly.  The 
greater  number  of  native  silicates  admit,  however,  of  being  correctly  analyzed 
only  by  fusion.  The  silicate,  very  finely  powdered,  may  be  mixed  with  four 
times  its  weight  of  a  mixture  consisting  of  equal  parts  of  the  carbonates  of 
potassa  and  soda,  and  fused  in  a  platinum  crucible  for  half  an  hour.  When 
cold,  the  residuary  mass  may  be  digested  in  an  excess  of  hydrochloric  acid, 
and  geutly  heated.  If  the  decomposition  of  the  silicate  has  been  complete, 
no  insoluble  gritty  matter  will  remain.  When  the  whole  is  dissolved,  the 
acid  liquid  is  evaporated  to  dryness,  the  residue  moistened  with  concentrated 
hydrochloric  acid,  and  after  a  time  boiled  in  water.  The  solution  is  filtered; 
the  silicic  acid,  collected  on  the  filter,  is  well  washed  and  dried.  The  bases 
associated  with  the  silicic  acid  will  be  found  in  the  filtered  liquid.  The 
hydrates  of  potassa  or  soda  act  more  readily  by  fusion,  but  the  process 
cannot  be  carried  on  in  platinum.  If  the  silicic  acid  is  combined  with 
potassa  or  soda,  the  powdered  silicate  may  be  fused  either  with  pure  baryta, 
or  the  carbonate  or  nitrate  of  this  alkaline  earth.  All  the  insoluble  silicates 
fuse  at  a  high  temperature,  and  more  readily  when  mixed  than  when 
separate. 


CHLORIDE    AND    FLUORIDE    OF    SILICON.  305 

Silicic  acid  is  often  associated  with  titanic  acid.  In  order  to  separate 
this,  the  silicate  may  be  fused  in  a  platinum  crucible,  with  bisulphate  of 
potassa.  The  titanic  acid  may  be  dissolved  out  of  the  residue  by  water, 
while  the  silicic  acid  will  remain  undissolved.   (Will.) 

Wohler  and  Buff  have  described  a  hydrated  sesquioxide  of  silicon  (Si^Og, 
2H0)  as  a  light,  white,  amorphous  substance,  oljtained  by  the  action  of 
water  on  the  hydrochlorate  of  the  chloride  of  silicon. 

Chloride  of  Silicon  (SiClg). — Silicon  burns  when  heated  in  a  current  of 
dry  chlorine,  producing  this  gaseous  compound.  It  may  be  produced  by 
passing  dry  chlorine  over  silicon  heated  to  redness,  or  by  passing  the  dry 
gas  over  a  mixture  of  silicic  acid  and  charcoal  similarly  heated  (SiOg+SC 
-f  3Cl  =  SiC]3+3CO).  The  chloride  is  a  yellowish  fuming  liquid  of  a  sp. 
gr.  of  1-52,  boiling  at  122°,  and  converted  by  water  into  hydrochloric  and 
silicic  acids  (SiCl3-f-3riO  =  Si03  +  3HCl).  Its  vapor  has  a  density  of  5-939. 
Each  volume  contains  two  volumes  of  chlorine.  There  is  also  a  Bromide  of 
Silicon  (SiBrg). 

Fluoride  op  Silicon  (SiFg).  Fluosilicic  Acid, — The  only  body  which 
acts  energetically  upon  silicic  acid  is  the  hydrofluoric  acid  :  the  result  of 
this  action  is  a  gaseous  compound.  To  obtain  the  gaseous  fluoride  of  sili- 
con, four  parts  of  pulverized  fluor-spar  and  three  of  powdered  glass,  or  two 
of  silica  finely  powdered,  are  well  mixed  in  a  retort  with  about  five  parts  of 
oil  of  vitriol ;  the  gas  evolved  is  to  be  collected  over  mercury,  and  when  its 
production  slackens,  it  may  be  accelerated  by  a  gentle  heat.  The  mercury 
and  the  glass  vessels  employed  must  be  quite  dry,  for  if  in.  the  least  damp, 
they  acquire  an  adhering  film  of  silica.  This  decomposition  depends  upon 
the  evolution  of  hydrofluoric  acid  and  its  action  upon  the  silica,  water  and 
•fluoride  of  silicon  being  the  ultimate  results  (SiO.^-f  3HF  =  SiF3-f  3H0). 
The  hydrofluoric  acid  is  derived  from  the  action  of  the  aqueous  sulphuric 
acid  on  the  fluoride  of  calcium;  CaF-f  S03,HO  =  HF  +  CaO,S03. 

Fluoride  of  silicon  is  a  colorless  gas ;  its  odor  is  acrid,  somewhat  resem- 
bling that  of  hydrochloric  acid ;  its  taste  very  sour ;  its  specific  gravity  is 
3*6  compared  with  air;  100  cubic  inches  we;gh  nearly  112  grains.  It 
extinguishes  the  flame  of  a  taper,  and  all  combustible  bodies ;  it  has  no 
action  on  glass ;  it  may  be  liquefied  and  solidified  by  cold.  It  produces 
white  fumes  when  in  contact  with  damp  air;  ,and  when  exposed  to  water  it 
is  absorbed,  and  a  soluble  compound  of  silicic  with  hydrofluoric  acid  is 
formed.  The  changes  may  be  thus  represented  :  3SiF3-J-3HO=3HF,2SiF3 
H-SiOg.  The  hydrofluosilicic  acid,  3HF,2SiF3,  is  dissolved  in  the  water^ 
while  the  silicic  acid,  SiOg^  is  precipitated  in  a  gelatinous  state.  If  the  beak 
of  a  retort  from  which  the  gas  is  issuing  is  plunged  into  a  basin  of  water,  it 
will  be  soon  choked  by  a  copious  deposit  of  hydrated  sifica,  which  sometimes 
forms  tubes  through  the  water,  by  which  the  gas  escapes  directly  into  the 
air.  Water  will  dissolve  350  volumes  of  this  gas,  and  when  it  is  intended 
to  make  a  solution,  or  to  produce  gelatinous  hydrate  of  silica,  the  conducting 
tube  or  beak  of  the  retort  should  be  so  fixed  as  to  plunge  just  below  the 
level  of  a  small  quantity  of  mercury  in  a  conical  glass.  Water  may  be  care- 
fully poured  on  the  mercury,  until  the  glass  is  filled,  and  the  distillation  then 
safely  carried  on.  As  each  bubble  of  the  fluoride  of  silicon  escapes  through 
the  mercury  and  rises  into  the  water,  it  becomes  invested  with  an  envelope 
of  the  hydrate  of  silica,  owing  to  the  decomposition  above  described. 

This  gas  is  dissolved  by  alcohol,  but  if  the  alcohol  is  hydrated  there,  is  a 
separation  of  silicic  acid.     The  decomposition  of  this  gas  by  water,  enables 
a  chemist  to  detect  the  slightest  trace  of  silicic  acid  in  any  mineral.     The 
20 


8(H5  HYDROFLUOSILICIC    ACID. 

mineral  should  be  powdered  and  mixed  with  powdered  fluor-spar  (free  from 
silica)  and  sulphuric  acid.  The  mixture  should  be  heated  in  a  platinum 
vessel,  and  the  vapors  carried  by  a  platinum  tube  into  water.  If  siHca  is 
present  in  the  mineral,  there  will  be  a  separation  of  the  gelatinous  hydrate, 
on  contact  with  the  water.  The  whole  of  the  silicic  acid  may  be  thus 
expelled. 

When  a  streak  is  made  on  paper  with  a  solution  of  fluosilicic  acid,  the 
paper  is  not  carbonized  when  heated.  If  sulphuric  acid  is  present  as  an 
impurity,  the  paper  will  be  carbonized. 

Hydrofiuosilicic  Acid  (3HF,2SiF3). — This  is  a  product  of  the  decom- 
position of  the  fluoride  above  mentioned,  in  contact  with  water.  The  acid 
may  be  procured  by  separating  the  gelatinous  silica,  by  means  of  a  linen 
filter,  and  filtering  the  liquid  through  paper.  It  is  also  produced  when 
diluted  hydrofluoric  acid  is  saturated  with  silica. 

The  liquid  has  a  strongly  acid  reaction.  It  may  be  evaporated  in  a  pla- 
tinum vessel  without  change,  but  it  corrodes  glass ;  and,  when  highly  con- 
centrated, it  is  converted  into  hydrofluoric  acid,  and  silica,  which  is  deposited. 
Although  its  solution  has  no  direct  action  on  glass,  it  slowly  acts  upon  the 
alkaline  bases,  potassa,  soda,  lime,  and  oxide  of  iron  existing  in  glass,  and 
forms  a  white  deposit  of  a  hydrofluosilicate  of  the  base.  Its  action  on 
alkalies  and  their  salts  is  remarkable.  It  precipitates  in  an  insoluble  form 
as  hydrojiuosilicates  or  double  silicofluorides  (3MF,2SiF3),  potassa,  soda, 
and  baryta.  Pure  lime  and  strontia  are  not  precipitated  from  their  solutions 
in  water.  Ammonia  in  excess  and  carbonate  of  ammonia  decompose  the 
acid  and  throw  down  gelatinous  silica.  Concentrated  solutions  of  the  salts 
of  potassa,  soda,,  lithia,  baryta,  and  alumina  are  also  precipitated;  those  of 
potassa  so  completely,  that  the  alkali  may  be  thus  separated  from  the  acid. 
In  this  manner  chloric  acid  may  be  obtained  by  adding  hydrofluosilicic  acid 
to  a  strong  solution  of  chlorate  of  potassa  (p.  194).  In  these  cases  the 
hydrogen  of  the  acid  is  simply  replaced  by  the  metal.  A  solution  of  the 
acid  precipitates  a  salt  of  strontia,  but  much  more  slowly  than  a  salt  of 
baryta.  These  precipitates,  like  those  given  by  sulphuric  acid  in  the  solu- 
tions of  the  alkaline-earthy  salts,  are  insoluble  in  nitric  acid,  and  might  be 
mistaken  for  sulphates.  When  calcined,  they  leave  a  fluoride,  which  may  be 
identified  by  its  action  on  glass.  A  sulphate  is  only  decomposed  when 
heated  with  charcoal,  or  cyanide  of  potassium,  and  a  sulphide  then  results. 

Silicon  forms  compounds  with  nitrogen  and  sulphur,  SiXaC?),  and  8183. 


PHYSICAL  PROTERTIES  OF  THE  METALS 


30t 


METALS. 


CHAPTER    XXII. 

PHYSICAL    PROPERTIES   OP   THE    METALS.      RELATIONS    TO 
HEAT,   LIGHT,    ELECTRICITY,    AND   MAGNETISM. 


The  metals  constitute  a  numerous  and  important  class  of  elementary 
bodies  ;  they  are  characterized  by  a  peculiar  and  distinctive  lustre,  by  their 
opacity,  and  by  their  high  conducting  powers  in  regard  to  heat  and  electricity. 
They  are  also  marked  by  a  high  specific  gravity.  Their  oxides  form  bases 
as  well  as  acids.  They  combine  with  each  other  to  form  alloys,  and  some  of 
them  combine  with  mercury  to  form  amalgams.  In  the  following  table 
they  are  enumerated  in  the  order  in  which  they  will  be  described.  A  table 
of  their  symbols  and  equivalents  will  be  found  at  page  67. 

POTASSIUM 

SODIUM 

LITHIUM 

CESIUM 

RUBIDIUM 

THALLIUM 

BARIUM 
STRONTIUM 
CALCIUM 
MAGNESIUM 

ALUMINUM 

GLUCINUM 

ZIRCONIUM 

THORIUM    • 

YTTRIUM 

ERBIUM 

TERBIUM 

Two  which  are  but  imperfectly  known — namely,  Norium,  and  Pelopium — 
are  excluded  from  this  list.  Altogether,  the  number  of  metals  known  is  54. 
Of  these  metals  only  19  are  commonly  met  with,  and  among  these  about  12 
comprise  the  greater  number  employed  in  medicine  and  in  the  arts  and  manu- 
factures. 

The  first  six  ofjhe  metals  in  the  above  list  are  distinguished  as  the  metals 
of  the  alkalies  ;  fneir  oxides  are  powerfully  alkaline;  they  have  an  intense 
aflanity  for  oxygen,  and  decompose  water  at  all  temperatures.  The  four 
metals  in  the  following  group  are  the  bases  of  the  alkaline  earths  ;  with  the 
exception  of  magnesium,  they  also  decompose  water  at  all  temperatures. 
The  ten  succeeding  metals,  with  the  exception  of  aluminum,  have  been  but 


CERIUM 

NIOBIUM 

LANTHANUM 

ILMENIUM 

DIDYMIUM 

MOLYBDENUM 

URANIUM 

IRON 

TELLURIUM 

MANGANESE 

TITANIUM 

ZINC 

ANTIMONY 

INDIUM 

ARSENIC 

TIN 

CADMIUM 

MERCURY 

COPPER 

SILVER 

LEAD 

GOLD 

BISMUTH 

PLATINUM 

COBALT 

PALLADIUM 

NICKEL 

RHODIUM 

CHROMIUM 

RUTHENIUM 

VANADIUM 

OSMIUM 

TUNGSTEN 

IRIDIUM 

COLUMBIUM 

308        HARDNESS.      MALLEABILITY.      DUCTILITY.      TENACITI. 

im#>erfect]y  examined  ;  they  are  generally  designated  as  the  bases  of  the 
earths.  The  following  twenty-three  metals  have  been  sometimes  divided 
into  those  which  form  basic  oxides,  and  those  which  form  acids ;  and  they 
have  been  separated  into  other  distinctive  groups,  having  reference  to  the 
action  of  acids  upon  them,  to  their  action  upon  water  at  high  temperatures, 
and  to  the  isomorphism  of  their  salts ;  these  characters,  however,  are  not 
sufficiently  definite;  and  as  regards  the  basic  or  the  acid  character  of  their 
compounds  with  oxygen,  several  of  them  form  compounds  belonging  to  both 
classes.  The  last  nine  metals  have  been  particularly  designated  as  noble 
metals  ;  they  are  not  changed  by  air  or  by  water,  and  their  affinity  for  oxygen 
is  comparatively  feeble :  to  some  of  these  properties,  however,  osmium  forms 
an  exception. 

Physical  Properties. — A  high  degree  of  lustre  is  one  of  the  leading 
physical  characters  of  the  metals,  the  color  of  the  light  which  they  reflect 
varying  with  the  nature  of  the  metal  and  the  number  of  reflections  to  which 
it  has  been  subjected.  In  most  cases  it  is  nearly  w^hite,  gray,  or  bluish  ; 
•from  gold  it  is  yellow,  and  from  copper,  red  ;  but  the  intensities  of  these 
colors  may  be  greatly  increased  by  repeated  reflections. 

The  opacity  of  metals  is  such,  that  when  in  very  thin  leaves  they  transmit 
no  light.  Gold  is  so  far  an  exception,  that  when  beaten  into  leaves  of  one 
two-hundred-thousandth  of  an  inch  in  thickness  it  transmits  green  light,  and 
if  alloyed  with  silver,  blue  light.  There  are  also  other  means  by  which  ex- 
tremely thin  metallic  films  may  be  obtained,  and  which  often  exhibit  a  cer- 
tain amount  of  transparency. 

Hardness;  Brittleness. — Few  of  the  metals,  when  pure,  are  very  hard; 
they  are  generally  softer  than  steel.  Lead  may  be  scratched  by  the  nail  ; 
and  potassium  at  60°  is  softer  than  wax.  Some,  such  as  antimony,  arsenic, 
and  bismuth,  may  be  easily  pulverized  ;  others  are  brittle  at  one  temperature, 
but  malleable  and  ductile  at  another.  Zinc,  for  instance,  which  at  common 
temperatures  is  comparatively  brittle,  may  be  rolled  and  drawn  into  wire 
when  heated  up  to  300°. 

MaUeahility,  or  the  capacity  of  being  extended  by  hammering  or  rolling, 
belongs  to  some  of  the  metals  in  a  very  remarkable  degree.  Common  gold- 
leaf,  for  instance,  is  not  more  than  a  200,000th  of  an  inch  in  thickness;  and 
3  grains  of  the  metal  are  sufficient  to  cover  a  square  foot.  Silver,  copper, 
and  tin,  also  admit  of  great  extension  under,  the  hammer.  In  hammering 
and  rolling,  some  of  the  metals  become  so  hard  and  brittle  as  to  require 
occasional  annealing;  in  these  cashes  they  give  out  much  heat.  The  follow- 
ing is  the  order  of  malleability — gold,  silver,  copper,  aluminum,  tin,  cadmium, 
platinum,  lead,  zinc,  and  iron. 

Ductility. — The  malleable  metals  are  also  ductile ;  that  is,  they  admit  of 
drawing  out  into  wire.  In  this  respect,  gold,  silver,  platinum,  and  iron, 
stand  at  the  head  of  the  list.  A  grain  of  gold  may  be  drawn  into  500  feet 
of  wire.  A  wire  of  platinum,  not  exceeding  a  30,000th  of  an  inch  diameter, 
fcas  been  obtained  by  placing  it  in  the  axis  of  a  small  cylinder  of  silver,  and 
then  drawing  the  compound  wire  in  the  usual  way,  and  afterwards  dissolving 
off  the  silver  by  nitric  acid.  The  order  of  ductility  is  as  follows  :  gold, 
silver,  platinum,  iron,  copper,  aluminu-m,  zinc,  tin,  and  lead. 

Tenacity,  or  the  power  of  supporting  a  weight  without  breaking,  is  an 
important  property  of  the  metals.  Iron  is  at  the  head  of  the  list,  and  lead 
at  the  bottom  ;  but  the  respective  tenacities  are  much*influenced  by  the 
temperature  at  which  the  comparisons  are  made,  the  manner  in  which  they 
are  tested,  and  more  especially  by  the  process  of  annealing.  A  wire  of 
unannealed  iron,  which  sustained  a  weight  of  26  lbs.  only  bore  12  lbs.  after 
having  been  annealed ;  and  a  wire  of  copper  which  sustained  22  lbs.  before 


SPECIFIC    GRAVITY    OP    THE    METALS. 


309 


annealing:,  was  broken  by  9  lbs.  after  annealing.  The  following  metals  are 
arranged  in  the  order  of  their  tenacities :  iron,  copper,  palladium,  platinum, 
silver,  gold,  zinc,  tin,  lead.  The  tenacity  of  iron  compared  with  lead  is  as 
25  to  1. 

In  the  following  table  the  figures  represent  the  number  of  pounds  required 
to  break  wires  one. tenth  of  an  inch  in  diameter  : — 

Lead,     27-7  Zinc,     100-8  Silver,  187-1  Copper,     302-2 

Tin,       34-7  Gold,    159-7  Platinum,    274-3  Iron,         549-5 

AssnnfUg  the  tenacity  of  lead  to  be  represanted  by  unity,  then,  according  to 
Wertherius'  results,  the  tenacity  will  be  represented  by  the  following  numbers : — 

Lead  .         .         .         .1*  Silver    .  .  .  .8-9 

Cadmium  .         .         .1-2  Platinum  .  ,  .  13* 

Tin 1-3  Palladium  .  .  .15- 

Gold         .        .         .         .5-6  Copper.  .  .  .17* 

Zinc  .         .         .         .8-  Iron       .  .  .  •26- 

The  tenacity  of  a  metal,  with  few  exceptions,  decreases  in  proportion  as 
its  temperature  increases ;  but  iron,  though  less  tenacious  at  212°  than  at 
32°,  is  more  so  at  890°  than  at  212°. 

Crystallization Metals  are  susceptible  of  assuming  the  crystalline  form. 

With  many,  this  may  be  effected  by  fusion  and  slow  cooling,  and  especially 
by  suffering  the  melted  metal  to  concrete  externally,  and  then  perforating 
the  solid  crust,  and  pouring  out  the  liquid  interior.  The  cavity  so  formed 
will  be  then  lined  with  crystals  :  this  mode  of  proceeding  answers  extremely 
well  with  bismuth,  which  furnishes  a  singular  congeries  of  cubic  crystals 
(page  26).  When  the  metals  are  precipitated  by  each  other,  they  often 
crystallize  during  their  deposition,  as  in  the  precipitation  of  silver  by  mer- 
cury, and  in  that  of  lead  by  zinc.  A  stick  of  phosphorus  immersed  in  a 
solution  of  silver  becomes  incrusted  with  metallic  crystals  (p.  236).  Gold 
is  occasionally  deposited  in  a  crystalline  form,  from  its  ethereal  solution. 
During  the  electrolysis  of  metallic  solutions,  especially  when  low  powers  are 
employed,  beautiful  crystals  are  also  occasionally  obtained. 

The  crystalline  structure  of  a  metal  materially  affects  some  of  its  other 
physical  properties.  Copper,  silver,  and  even  gold,  become  comparatively 
hard  and  brittle  when  in  a  crystalline  condition  ;  and  the  most  brittle  metals 
are  those  which  most  readily  assume  the  crystalline  form,  such  as  bismuth 
and  antimony.  Even  iron,  which  in  one  condition  is  fibrous,  tough,  and 
tenacious,  becomes  relatively  brittle,  when  it  assumes  even  an  approach  to 
a  crystalline  structure ;  and  this  change  in  its  condition  is  sometimes  the 
result  of  changes  of  temperature,  and  shows  itself  in  bars  and  axles  which 
have  been  subjected  to  protracted  friction  and  vibration. 

Specific  Gravity. — The  specific  gravities  of  the  metals,  or  their  relativp 
densities,  as  compared  with  distilled  water  at  the  temperature  of  60°,  are 
shown  in  the  following  table ;  they  include  the  lightest  and  the  heaviest 


solids. 


The  metal  lithium  is  lighter  than  all  known  solids  and  1 


Osmium    .     . 

.     21-40 

Platinum 

.     .     21-15 

Iridium     .     . 

.     21-15 

Gold     .     .     . 

.     19-3 

Tungsten  .     . 

.     .     17-6 

Mercury    .     . 

.     .     13-5 

Rhodium  .     . 

.     .     12-0 

Thallium  .     . 

.     .     11-9 

Palladium      . 

.     .     11-8 

Ruthenium    . 

.     .     11-3 

Lead     .     ,     . 

.     .     11-4 

Silver  .     .     . 

.     .     10-5 

Bismuth  .     . 

.     .       9-8 

Cobalt 8-9 

Copper 8*9 

Nickel 8-8 

Molybdenum    .     .     .  8-6 

Cadmium    ....  8-6 

Manganese  ....  8*0 

Iron 7-8 

Iridium 7-2 

Tin 7-2 

Zinc 7-1 

Columbium      ...  6-9 

Antimony   ....  6-7 


Tellurium 

Arsenic  . 

Chromium 

Titanium 

Aluminum 

Strontium 

Glucinum 

Magnesium 

Calcium 

Sodium  . 

Potassium 

Lithium 


quids  :- 


5-9 

5-9 

5-3 

2-6 

2-5 

21 

1-7 

1-5 

0-97 

0-86 

0-59 


310  RELATION    OF    METALS    TO    HEAT 

[The  reader  is  referred  to  the  Appendix  for  the  rules  to  be  observed  in 
taking  the  specific  gravity  of  metals  and  other  solids.] 

'  Relation  OF  Metals  TO  Heat.  Expansion;  Conduction. — The  changes 
of  bulk  which  metals  undergo  vi^ith  changes  of  temperature  are  relatively- 
greater  than  those  of  other  bodies,  but  each  metal  has  its  peculiar  rate  of 
expansion,  as  shown  in  the  following  table,  in  which  1,000,000  parts  of  each 
metal  are  supposed  to  be  heated  from  32°  to  212°  : — 

Increase  Increase  1  Increase      ^      Increase 

in  length.  fn  bulk.  in  length.     ^       in  bulk. 

Platinum  .  .  .  1  in  1131  ...  1  in  377  !  Copper  .     .     .     .  1  in  5^2  ...  1  in  194 

Palladium  .  .  1  in  1000  ...  1  in  333  |  Silver    .     .     .     .  1  in  524  ...  1  in  175 

Antimony  .  .  1  in    923  ...     1  in  307    Tin 1  in  516  ...  1  in  172 

Iron      .     .  .  .  1  in    846  ...  1  in  282    Lead      .     .     .     .  1  in  351  ...  1  in  117 

Bismuth   .  .  .  1  in    718  ...     1  in  239    Zinc 1  in  340  ...  1  in  113 

Gold     .     .  .  .  1  in    682  ...  1  in  227  I 

The  expansion  of  glass  is  nearly  the  same  as  that  of  platinum,  hence  wires 
of  this  metal  may  be  welded  into  fused  glass  without  inconveuience,  but  if 
we  substitute  a  wire  of  another  metal,  its  different  rate  of  contraction  tends 
to  break  the  glass  as  it  cools.  So  also  a  compound  bar  of  iron  and  copper, 
or  of  platinum  and  silver,  formed  by  riveting  strips  of  the  metals  to  each 
Other,  though  it  remains  straight  at  the  temperature  at  which  they  were 
riveted,  becomes  warped  or  curved  when  heated  or  cooled.  The  metallic 
thermometer,  d;nd  the  compensation  pendulum  or  balance-wheel  as  applied 
to  clocks  and  watches,  are  illustrations  of  the  same  principle.  The  force 
exerted  in  this  act  of  metallic  expansion  is  so  considerable  as  often  to  pro- 
duce injurious  effects  when  not  adequately  provided  for,  as  in  railways, 
bridges,  water  and  gas-pipes,  and  in  the  beams,  columns,  and  roofs  of 
buildings. 

That  the  metals  are  excellent  condnctors  of  heat  is  proved  by  the  rapidity 
with  which  heat  passes  from  one  end  to  the  other  of  a  metallic  bar ;  and  that 
the  different  metals  thus  transmit  heat  with  different  degrees  of  facility,  is 
shown  by  comparative  experiments.  If,  for  instance,  two  similar  bars  of 
silver  and  of  platinum  be  heated  at  one  end,  the  silver  will  be  more  rapidly 
heated  throughout  than  the  platinum.  Gold,  silver,  and  copper  are  among 
the  best  conductors ;  then  come  iron,  zinc,  and  tin  ;  and  lastly,  lead.  A 
consequence  of  this  property  of  the  metals  is,  that  they  communicate  and 
abstract  heat  more  readily  than  other  bodies  ;  that  they  feel  hotter  and  colder 
than  wood,  or  other  bad  conductors,  though  of  the  same  temperature.  If 
the  thermo-conducting  power  of  gold  be  assumed  as  =  100,  that  of  silver 
will  be  about  98,  of  copper  90,  of  iron  38,  of  zinc  36,  of  tin  30,  and  of  lead 
Qnly  18. 

The  polished  metals  are  remarkable  for  their  low  power  of  emitting  and  of 
receiving  radiant  heat.  A  polished  metallic  vessel  filled  with  hot  water,  is  a 
long  time  in  cooling ;  and  such  a  vessel  containing  cold  water,  and  placed 
before  the  fire,  is  a  long  time  in  acquiring  heat.  When  the  polish  is  taken 
off,  the  radiating  and  receptive  powers  of  such  vessels  are  increased  ;  but 
under  all  circumstances  the  metals  are  bad  radiators.  If  we  compare  the 
radiating  power  of  a  surface  coated  with  lamp-black,  with  that  of  polished 
gold,  silver,  copper,  or  tin,  it  is  nearly  as  100  to  12  ;  and  all  tarnished  metals 
radiate  better  than  those  which  are  bright  and  clean. 

Fusibility.— "ThQ  metals  are  all  susceptible  of  fusion  by  heat,  but  the  tem- 
peratures at  which  they  liquefy  are  extremely  various.  At  higher  temperatures 
than  those  required  for  their  fusion,  the  metals  are  volatih,  and  many  of  them 
may  be  distilled  in  close  vessels.     Mercury  is  volatile  at  temperatures  above 


RELATIOX    OP    METALS    TO    ELECTRICITY    AND    MAGNETISM.       311 

40^.  A  piece  of  gold  leaf  suspended  over  it  in  a  stopped  b(^tle  becomes 
slowly  whitened  by  amalgamation.  Cadmium,  potassium,  sodium,  tellurium, 
and  zinc,  are  volatile  at  a  red  heat,  and  arsenic  below  a  red  heat.  Gold  and 
silver  are  converted  into  vapor  when  exposed  to  intense  heat;  and  most  of 
the  other  metals  evaporate  under  similar  circumstances. 

Although  the  melting-points  will  be  described  under  the  heads  of  the 
respective  metals,  it  will  be  convenient  to  give  in  this  place  a  table  showing 
how  some  of  the  more  important  metals  differ  from  each  other,  in  regard  to 
the  temperature  at  which  they  pass  from  the  solid  to  the  liquid  state.  The 
metals  are  here  arranged  in  two  groups  :  1,  those  which  are  fusible  helow 
a  red  heat  (1000°)  ;  and  2,  those  which  are  fusible  above  this  temperature. 
The  metals  not  included  in  this  list  can  be  readily  fused  only  under  the  oxy- 
hydrogen  blowpipe — one  only  is  described  as  infusible,  namely  osmium  : — 

FUSIBLE  BELOW  A  RED  HEAT. 

Mercury       ....  — 40O  Lead 620O 

Potassium   .         .         .         .150 


Sodium 

Lithium 

Tin      . 

Cadmium 

Bismuth 

Thallium 


200 
356 
442 
442 

497 
550 


Zinc     .... 

.     773 

Red  heat  in  the  dark  . 

.     980 

Calcium 

.  1000 

Magnesium 

.  1000 

Antimony    . 

.  1160 

Red  heat  in  the  daylight 

.  1160 

lED  HEAT. 

Gold    .... 

.  2016O 

Cast-iron     . 

.  2786 

FUSIBLE  ABOVE  A 

Aluminum  ....  1750O 

Silver 1873 

Copper         ....  1996 

Specific  Heat  of  the  Metals. — By  the  term  specific  heat  is  meant  the 
quantity  of  heat  required  to  raise  similar  quantities  of  different  substances  to 
the  same  temperature.  If  we  thus  compare  oil  and  water,  it  will  be  found 
that  the  quantity  of  heat  required  to  raise  the  temperature  of  a  pound  of  oil 
from  32°  to  212°  is  only  half  that  which  is  required  to  produce  the  same 
'change  of  temperature  in  water  ;  hence  the  specific  heat  of  water  being  =  1, 
that  of  oil  is  0-5  (p.  132).  If  we  thus  compare  water  with  mercury  we  find 
that  the  specific  heat  of  water  being  =  I'OOO,  that  of  an  equal  weight  of 
mercury  is  only  0-033.  The  specific  heat  of  water,  therefore,  or,  in  other 
words,  its  capacity  for  heat,  is  very  great  compared  with  that  of  the  metals, 
as  shown  in  the  following  table;  from  which  it  will  also  be  seen  that  the 
specific  heat  of  bodies  increases  with  their  temperatures,  so  that  it  requires 
more  heat  to  raise  them  a  given  number  of  degrees  when  they  are  at  a  high 
than  when  at  a  low  temperature.  The  specific  heats  are  in  all  cases  com- 
pared with  water,  as  =  1 : — 


Between 

Between 

Between 

Between 

320  and  212=^. 

32^  and  572°. 

323  and  212^. 

32^  and  572°. 

Iron    . 

.     0-1098     . 

..     0-1218 

Antimony 

.     0-0507     . 

.     0-0547 

Zinc    . 

.     0-0927     . 

..     0-1015 

Platinum 

.     0-0335     . 

.     0-0355 

Copper 

.     0-0949     . 

..     0-1913 

Mercury 

.     0-0330     . 

.     0  0350 

Silver 

.     0-0557     . 

..     0-0611 

When  the  specific  heat  of  the  elementary  bodies  is  multiplied  into  their 
atomic  weights,  the  product  is  (with  some  exceptions)  nearly  the  same  (p.  69). 

RELATION   OP   THE   METALS   TO   ELECTRICITY   AND   MAGNETISM. 

In  respect  to  electrical  conduction,  silver  is  the  best,  and  mercury  the  worst 
conductor.  Assuming  the  electro-conduction  of  silver  as  =  100,  that  of  cop- 
per is  about  92,  gold  65,  zinc  24,  tin  14,  iron  12,  lead  and  platinum  about 
8,  and  mercury  2.     Professor  McGauley  gives  the  relative  conducting  power 


312 


POTASSITTM. 


of  the  differ^t  metals  in  reference  to  their  actual  efficiency  in  the  battery  in 
the  following  order  : — 


Silver       . 

.  100- 

Magnesium 

.     25-47 

Coppef 

.     74-74 

Iron 

.     14-44 

Gold 

.     55-15 

Tin  . 

.     11-45 

Sodium     . 

.     37-43 

Platinum 

.     10-53 

Aluminum 

.     33-76 

Lead 

.      7-77 

Potassium 

.     28-85 

Mercury   . 

.       1-63 

Zinc 

.     27-39 

These  conducting  powers  are  remarkably  influenced,  in  some  cases,  by 
temperature.  Thus,  in  reference  to  tin,  if  its  conducting  power  at  32^  be  = 
16,  at  212°  it  will  only  be  =  10  ;  so  that,  in  general,  the  lower  the  tempera- 
ture of  the  metal,  the  higher  its  elertro-conducting  power.  Metals  which 
are  bad  conductors  of  electricity  become  most  heated  by  an  electric  current, 
as  is  well  shown  by  transmitting  a  current  of  electricity  through  a  wire  com- 
posed of  alternate  lengths  of  platinum  and  silver  ;  the  platinum  only  becomes 
red-hot.  The  presence  of  the  metalloids  interferes  with  the  conducting 
power.  Thus  the  conductivity  of  copper  is  greatly  reduced  by  the  presence 
of  arsenic  as  an  impurity. 

Magnetism. — The  peculiarities  of  iron  in  respect  to  magnetism  have  been 
long  known,  as  also  its  permanent  retention  by  steel.  When  a  bar  of  iron 
is  suspended  between  the  poles  of  a  magnet,  it  is  equally  attracted  by  each, 
and  places  itself  parallel  to  the  magnetic  axis.  .Some  metals  are  similarly 
affected,  though  in  an  inferior  degree ;  bnt  there  are  others  which  appear  to 
be  repelled  by  the  magnetic  poles,  and  which,  when  properly  suspended  be- 
tween them,  assume  a  direction  at  right  angles  to  the  magnetic  axis,  placing 
themselves  eqiiatorially.  Faraday,  who  first  observed  these  phenomena, 
terms  such  substances  diamagnetics.  He  has  shown  that  various  solids, 
liquids,  and  gases,  include  magnetic  and  diamagnetic  substances  (p.  85)  ; 
and  that,  as  far  as  the  metals  are  concerned,  they  may  be  arranged  in  the 
following  order : — 


Magnetic. 

Diamagnet 

ic. 

Iron 

Cerium 

Bismuth 

Silver 

Nickel 
Cobalt 

Titanium 
Palladium 

Antimony 
Zinc 

Copper 
Gold 

Manganese 

Platinum 

Tin 

Arsenic 

Chromium 

Osmium 

Cadmium 

Uranium 

Sodium 

Iridium 

Mercury 
Lead 

Tungsten 

CHAPTEE    XXIII 


POTASSIUM  (K  =  39). 

Potassium  (Kalinra)  was  discovered  by  Davy  in  1807.  He  obtained  it 
by  submitting  caustic  potassa  to  the  decomposing  action  of  voltaic  electri- 
city :  the  metal  was  slowly  evolved,  together  with  hydrogen,  at  the  negative 
pole.  By  this  process,  however,  it  could  only  be  procured  in  small  quanti- 
ties, and  -other  methods  have  since  been  devised  :  that  which  is  now  usually 
adopted  consists  in  subjecting  a  mixture  of  carbonate  of  potassa  and  charcoal 
to  a  high  temperature,  in  a  wrought-iron  distillatory  apparatus,  to  which  a 


OXIDES    OF    POTASSIUM.  313 

proper  receiver  is  adapted.  The  potassium  which  first  passes  over  requires 
to  be  purified  by  a  second  distillation,  to  free  it  from  a  quantity  of  bkick 
matter  which  is  of  an  explosive  nature,  and  consists  of  a  compound  of  potas- 
sium with  carbon  and  carbonic  oxide.  In  these  distillations,  the  contact  of 
the  metal  with  air  must  be  carefully  guarded  against :  for  this  purpose  it  is 
usually  received  into,  and  preserved  under,  naphtha,  or  some  liquid  hydro- 
carbon, upon  which  it  has  no  action.  In  this  process  the  carbon  deprives 
the  carbonate  of  potassa  of  its  oxygen,  forming  carbonic  oxide,  which  abun- 
dantly escapes  during  the  distillation  ;  and  if  such  decomposition  were  entire, 
69  parts  of  the  carbonate  should  yield  39  parts  of  potassium.  It  would  be 
as  follows  :  KO,C02+C2=K  +  3CO.  T3ut  the  actual  product  of  potassium 
falls  far  short  of  this  result ;  and  in  consequence  of  some  of  the  potassa 
escaping  decomposition,  and  of  the  formation  of  carbide  and  oxicarbide  of 
potassium,  not  more  than  one-fourth  of  the  potassium  contained  in  the  mix- 
ture subjected  to  distillation,  is  usually  obtained. 

Potassium  is  a  silvery-white  metal  of  great  lustre.  It  instantly  tarnishes 
and  acquires  a  bluish-white  film  by  exposure  to  air,  and  is  gradually  con- 
verted into  an  oxide.  At  60°  it  is  of  the  consistency  of  soft  wax.  Its  sp. 
gr.  is  0*86.  It  is  most  conveniently  preserved  in  naphtha,  in  a  well-stopped 
phial.  It  fuses  at  150° ;  and  at  a  bright  red  heat,  in  close  vessels,  it  boils, 
and  rises  in  green  vapor.  At  32°  it  is  brittle,  and  of  a  crystallized  structure. 
If  heated  in  air,  it  burns  with  a  brilliant  flame.  It  is  a  good  conductor  of 
electricity  and  heat,  and  its  lustre  is  well  shown  by  fusing  it  under  naphtha, 
through  which  it  is  seen  as  brilliant  as  mercury ;  or  by  flatting  a  clean  slice 
of  it  by  pressure  between  two  plates  of  glass.  A  drop  of  water  placed  upon 
it  causes  it  instantly  to  take  fire  and  burn  with  a  violet  flame. 

Potassium,  when  placed  on  alcohol  or  ether,  is  rapidly  oxidized  without 
combustion.  In  reference  to  alcohol,  hydrogen  .is  evolved,  and  ethylate 
of  potash  is  dissolved.  The  metal  simply  displaces  part  of  the  hydrogen. 
If  we  place  potassium  on  a  layer  of  ether  (in  a  test-tube)  floating  on  water 
colored  blue  with  the  infusion  of  cabbage,  the  potassium  will  rapidly  disap- 
pear, hydrogen  being  ^evolved  ;  but  the  oxide  of  potassium  formed  is  not  solu- 
ble in  ether.  On  inverting  the  tube,  and  agitating  the  liquid  after  the 
oxidation  of  the  metal,  the  alkali  will  be  dissolved  by  the  water  producing  a 
green  color  in  the  infusion,  while  the  ether  will  float  to  the  surface  in  a  clear 
and  transparent  stratum.  In  this  experiment,  although  the  metal  is  heavier 
than  ether,  it  is  buoyed  up  by  the  hydrogen,  and  floats  upon  the  surface. 
Potassium  has  no  action  on  chloroform  or  sulphide  of  carbon.  Mr.  Gore 
found,  on  bringing  it  into  contact  with  anhydrous  hydrochloric  acid  gas, 
liquefied  under  pressure,  that  no  gas  was  evolved,  and  it  did  not  dissolve. 
{Proc.  R.  S.,  May,  1865,  p.  208.) 

Potassium  and  Oxygen. — There  are  three  oxides  of  potassium,  namely,  a 
suboxide  =Kfi,  a  protoxide  =K0,  which  in  the  state  of  hydrate  constitutes 
caustic  potassa  =KO,HO,  and  superoxide  =K03. 

.Suboxide  op  Potassium  (K^O)  is  formed  by  heating  potassium  in  a 
limited  portion  of  air,  or  by  heating  i  part  of  potassium  with  \\  of  iiydrate 
of  potassa;  while  hot  it  is  reddish,  but  gray  when  cold:  it  is  fusible  and 
inflammable,  taking  fire  when  gently  heated.  Water  converts  it,  without 
combustion,  into  potassa,  hydrogen  being  evolved. 

Protoxide  op  Potassium. — Anhydrous  Potassa  (KO)  is  most  readily 
obtained  by  heating  1  atom  of  potassium  =39  with  one  of  hydrate  of  potassa 
=56:  hydrogen  is  evolved,  and  2  atoms  of  protoxide  are  formed  (K+KO, 


81^  CAUSTIC    POTASSA. 

H0=2K0  +  H).  When  1  atom  of  potassium  acts  upon  1  atom  of  water 
oiiUof  the  contact  of  air,  it  is  also  produced  (K4-H0=K0  +  H).  When 
peroxide  of  potassium  is  intensely  heated,  it  loses  oxygen  and  leaves  prot- 
oxide. It  is  a  hard,  gray,  brittle  substance,  fusible  at  a  bright  red  heat,  sp. 
gr.  about  2  65 ;  extremely  caustic  and  alkaline. 

The  composition  of  this  oxide  is  learned  by  the  action  of  potassium  upon 
water;  when  the  metal  is  placed  upon  water,  or  even  upon  ice,  it  inflames, 
with  the  evolution  of  hydrogen,  and  burns  with  a  violet-colored  flame,  pro- 
ducing a  small  globule  of  fused  potassa,  which,  in  combining  with  water, 
produces  so  much  heat  as  to  cause  a  slight  explosion.  If  the  potassium  is 
plunged  under  water  the  decomposition  ensues  with  explosive  violence.  By 
carefully  employing  a  small  quantity  of  the  metal,  wrapped  in  blotting  paper, 
and  introducing  it  under  a  tube  inverted  in  water,  the  evolved  hydrogen  may 
be  collected.  It  thus  becomes  the  indicator  of  the  quantity  of  Oxygen  taken 
by  the  potassium,  100  parts  of  which  are  thus  found  to  combine  with  20*51 
of  oxygen:  and  20*51  :  100  ::  8  :  39;  so  that  the  equivalent  of  potassium 
thus  deduced  is  39.  When  a  portion  of  the  metal  is  laid  upon  a  solution  of 
red  litmus  it  burns,  and  the  oxide,  as  it  dissolves,  turns  the  red  litmus  blue. 
In  an  atmosphere  of  nitrogen,  hydrogen  is  simply  liberated  without  combus- 
tion. 

Hydrated  Protoxide  of  Potassium;  Caustic  Potassa  (K0,H0)  is 
procured  in  decomposing  carbonate  of  potassa  by  lime.  The  process  con- 
sists in  boiling  in  a  clean  iron  vessel  pure  carbonate  of  potassa,  with  half  its 
weight  of  pure  quicklime,  in  not  less  than  7  or  8  parts  of  water.  The  lime, 
previously  slaked,  is  gradually  adiled  to  the  boiling  alkaline  solution,  which 
is  kept  constantly  stirred,  and  towards  the  end  of  the  operation  it  is  tested 
by  filtering  a  small  portion,  and  pouring  it  into  two  or  three  times  its  bulk 
of  strong  nitric  acid;  if  there  be  no  effervescence,  sufificient  lime  has  been 
used;  but  if  carbonic  acid  escapes,  the  ebullition  with  lime  must  be  con- 
tinued, taking  care  to  keep  up  the  original  quantity  of  water,  until  the  tested 
portion  shows  no  signs  of  carbonic  acid.  The  whole  is  then  allowed  to 
remain  quiet,  that  the  carbonate  of  lime  and  excess  of  the  hydrate  of  lime 
may  subside  ;  the  clear  liquor,  or  lye,  may  then  be  siphoned  or  poured  off, 
concentrated  by  evaporation,  strained  through  a  clean  calico  filter,  and  set 
by  in  a  well-stopped  bottle  till  it  admits  of  being  decanted  from  any  sedi- 
ment. When  the  lye  is  evaporated  in  a  polished  iron  or  pure  silver  vessel, 
it  assumes  the  appearance  of  an  oily  liquid,  and  concretes  on  cooling.  When 
cast  into  sticks  it  is  employed  in  surgery  as  a  powerful  and  rapidly-acting 
caustic:  in  this  state  it  generally  contains  some  peroxide  and  other  impuri- 
ties, and  evolves  oxygen  and  deposits  a  sediment  when  dissolved  in  water. 
It  is  sometimes  further  purified  by  boiling  it  in  a  silver  basin  with  highly- 
rectified  alcohol  for  a  few  minutes,  and  then  setting  it  by  in  a  stopped  phial ; 
when  the  impurities  are  deposited,  the  alcoholic  solution  may  be  poured  off 
and  rapidly  evaporated  to  dryness  in  a  silver  vessel ;  or  if  the  quantity  of 
alcohol  be  considerable,  it  may  be  distilled  off  in  a  silver  alembic  with  a  glass 
head:  the  heat  may  then  be  raised  so  as  to  fuse  the  potassa,  which  on  cool- 
ing shoAild  be  broken  up  and  preserved  in  well-closed  phials ;  if,  however, 
pure  materials  and  due  care  are  employed,  the  alcoholic  purification  may  be 
dispensed  with,  for  even  when  so  prepared  the  product  contains  traces  of 
carbonate,  and  sometimes  of  acetate  of  potassa. 

The  pure  hydrated  oxide  is  white  and  somewhat  crystalline  in  texture  :  its 
sp.  gr.  2*1.  It  is  fusible  at  a  heat  below  redness,  and  evaporates  from  an 
open  vessel  at  a  bright-red  heat,  in  the  form  of  acrid  fumes.  A  platinum 
wire,  dipped  into  potassa  and  heated,  communicates  a  characteristic  violet 


CAUSTIC    POTASSA.  315 

tint  to  a  colorless  flame.  At  a  white  heat  it  is  decomposed  by  charcoal, 
and  carburetted  hydrofren,  carbonic  oxide,  and  potassium  are  the  pro- 
ducts. It  quickly  absorbs  moisture  and  carbonic  acid  from  the  air,  and  is 
solul)le  in  half  its  weio;ht  of  cold  water.  When  reduced  to  a  powder  and 
slijz^htly  moistened  it  forms  a  crystallized  combination  which  is  a  terhydrate 
(K0,3H0).  By  keeping  a  stronj]^  aqueous  solution  of  potassa  at  a  low  tem- 
perature in  a  stopped  phial,  crystals  may  be  obtained  which  are  a  penta- 
hydrate  (K0,5H0). 

Caustic  potassa  is  highly  alkaline,  reddening  turmeric,  and  changing 
several  vegetable  blues  to  green.  It  acts  energetically  upon  the  greater 
number  of  organic  products,  and  saponifies  the  fat  oils.  When  touched 
with  moist  fingers  it  has  a  soapy  feel,  in  consequence  of  its  action  upon  the 
cu.ticle,  and  it  then  exhales  a  peculiar  odor:  this  is  also  perceptible  in  the 
solution  of  potassa,  and  is  probably  referable  to  the  formation  of  ammonia, 
arising  from  traces  of  organic  matter  accidentally  present.  In  the  fused 
state,  it  produces  heat  when  dissolved  in  water ;  but  in  its  crystallized  state 
it  excites  considerable  cold,  especially  when  mixed  with  snow.  It  dissolves 
sulphur  and  several  sulphides,  and  silica  and  alumina.  The  oxides  of  several 
of  the  other  metals  are  also  soluble  in  an  aqueous  solution  of  potassa. 
*  When  a  solution  of  caustic  potassa  is  required  to  be  filtered,  it  is  apt  to 
act  upon  the  filter  and  to  absorb  carbonic  acid,  so  that  filtration  should  as 
far  as  possible  be  avoided,  and  the  liquor  obtained  clear  by  subsidence.  Oa 
the  large  scale,  linen  strainers  are  generally  used  ;  upon  the  small  scale,  the 
absorption  of  carbonic  acid  may  be  prevented,  by  covering  the  funnel  with 
a  plate  of  glass,  and  receiving  it  into  a  bottle  as  nearly  air-tight  as  possible. 

A  solution  of  potassa  acts  gradually  upon  flint  glass,  which  contains  oxide 
of  lead  ;  hence  green  glass  vessels  are  preferable ;  but  when  the  alkaline 
solution  is  to  be  exposed  to  heat,  or  evaporated  to  dryness,  even  these  com- 
municate impurity,  and  in  such  cases  vessels  of  pure  silver  must  be  used,  for 
almost  all  other  metals,  platinum  not  excepted,  are  more  or  less  acted  upon. 

The  solution  of  caustic  potassa  is  frequently  impure  from  the  presence  of 
carbonic  acid,  silica,  alumina,  lime,  oxide  of  lead,  and  sulphuric  or  hydro- 
chloric acid.  If  an  effervescence  is  produced  when  the  solution  is  dropped 
into  nitric  acid,  it  indicates  the  presence  of  carbonic  acid  ;  if  a  gelatinous 
precipitate  is  formed,  not  soluble  in  a  slight  excess  of  acid,  it  is  silica ;  if 
soluble,  it  is  alumina.  The  presence  of  lime  is  shown  by  adding  oxalate  of 
ammonia  to  the  solution  previously  neutralized  by  nitric  acid  ;  in  the  same 
solution  nitrate  of  silver  will  indicate  hydrochloric  acid,  or  chlorine  ;  and 
nitrate  of  baryta,  sulphuric  acid,  or  sulphates.  Freedom  from  metallic 
impurities  is  shown  by  sulphide  of  ammonium.,  which  should  occasion  no 
precipitate  or  change  of  color. 

The  following  table  shows  the  quantity  of  anhydrods  potassa  contained  in 
aqueous  solutions  of  different  specific  gravities.  The  boiling  point  of  a 
saturated  solution,  sp.  gr.  1-68,  is  329°;  of  the  officinal  solution,  sp.  gr. 
1-OG,  2130 

Specific      Potassa  Specific    Potassa  Specific    Potassa  Specific    Potassa 

gravity,     per  ceat.  gravity,   per  cent.  gravity,   per  cent.  gravity,   per  cent. 


1-68  51-2 

1-60  46-7 

1-52  42-9 

1-47  39-6 


1-44  36-8 

1-42  34-4 

1-39  32-4 

1-36  29-4 


1-33  26-3 

1-28  23-4 

1-23  19-5 

1-19  16-2 


1-15       13- 
1-11         9-5 
1-06        4-7 


Alkalimetry. — One  of  the  most  simple  methods  of  determining  the  strength 
of  a  solution  of  potash  is  to  find,  by  the  use  of  a  graduated  burette,  the 
number  of  measures  of  a  standard  sulphuric  acid  required  to  neutralize  a 
given  weight  of  hydrate  of  potash.     A  convenient  strength  of  acid  for  this 


316  HYPOCHLORITE  OF  POTASSA. 

purpose  may  be  made  by  mixing  about  one  part  of  the  monohydrated  sul- 
phuric acid  by  weight  with  six  parts  of  water.  The  sp.  gr.  of  an  acid  thus 
used  was  1-1268,  and  three  measures  of  it  from  the  burette  were  found  to 
neutralize  ten  grains  of  pure  hydrate  of  potash. 

As  an  illustration,  a  flnidounce  of  a  solution  of  potash,  weighing  500 
grains,  was  colored  of  a  faint  blue  with  litmus  infusio.n.  The  standard  acid 
was  poured  from  the  burette,  and  the  liquid  kept  well  stirred  until  the 
faintest  reddening  of  the  liquid  begins  to  show  itself.  It  was  found  that 
eleven  measures  of  the  acid  had  been  required  to  completely  neutralize  this 
quantityof  the  alkaline  liquid.  Hence,  3  :  10  : :  11  :  36'6  ;  and  36  6^  5= 
T'32  per  cent,  of  hydrate  of  potash  in  the  alkaline  solution.  This  corre- 
sponds to  6' It  per  cent,  of  anhydrous  potash. 

• 

Peroxide  op  Potassium  (KO3)  is  formed  when  potassium  is  burned  with 
free  access  of  air,  or  in  oxygen  gas ;  it  is  a  yellow  fusible  substance,  which, 
on  cooling,  acquires  a  crystalline  apj:Jearance.  It  has  some  singular  pro- 
perties;  it  supports  the  combustion  of  most  of  the  inflammables,  .and,  when 
heated  in  hydrogen,  diminishes  the  bulk  of  the. gas,  and  forms  water;  it 
decomposes  ammonia  under  the  same  circumstances.  When  put  into  water, 
oxygen  is  evolved,  and  a  solution  of  potassa  obtained.  When  hydrated' 
potassa  is  fused  in  an  open  crucible,  a  portion  of  its  water  is  disengaged,  and 
oxygen  is  absorbed,  so  as  to  form  this  peroxide  ;  hence  it  is  that  common 
caustic  potassa  almost  always  gives  out  oxygen  when  put  in  water. 

Potassium  and  Chlorine;  Chloride  of  Potassium  (KCl). — Potassium 
burns  brilliantly  in  chlorine,  especially  if  introduced  into  the  gas  in  the  state 
of  fusion,  as,  otherwise,  a  crust  of  chloride  is  apt  to  form  and  protect  the 
interior  from  further  action.  When  potassium  is  heated  in  gaseous  hydro- 
chloric acid,  chloride  of  potassium  is  formed,  and  hydrogen  evolved : 
K4-HC1=KC1  +  H.  It  is  also  formed  by  dissolving  potassa  or  its  carbonate 
in  hydrochloric  acid,  and  evaporating  to  dryness.  The  affinity  of  potassium 
for  chlorine  exceeds  that  for  oxygen ;  so  that  potassa  heated  in  chlorine, 
loses  oxygen,  and  yields  chloride  of  potassium  :  hence,  also,  potassium  heated 
with  other  chlorides,  evolves  their  bases  and  forms  chloride  of  potassium. 
When  chlorine  is  passed  over  iodide  of  potassium  at  a  red  heat,  iodine  is 
expelled,  and  chloride  of  potassium  formed. 

Chloride  of  potassium  dissolves  in  three  parts  of  water  at  60°.  One  part 
of  the  powdered  salt  stirred  into  four  parts  of  cold  water,  produces  a  de- 
pression of  temperature  of  between  20°  and  25°,  whereas  chloride  of  sodium 
under  the  same  circumstances  only  depresses  the  thermometer  between  2°  and 
3°  :  hence  it  has  been  proposed  to  estimate  the  relative  proportions  of  these 
chlorides  when  mixed,  by  the  depression  of  temperature  resulting  from  their 
solution.  Chloride  of  potassium  crystallizes  in  cubes  ;  its  taste  is  saline  and 
bitter.  Its  sp.  gr.  is  1-9.  In  old  pharmacy  it  was  called  digestive  salt  of 
Sylvius.  It  is  insoluble  in  alcohol.  When  intensely  heated  in  open  vessels, 
it  evaporates  in  the  form  of  white  fumes.  This  salt  is  a  residue  of  several 
chemical  and  pharmaceutical  processes,  and  is  sometimes  found  in  rough 
saltpetre  ;  it  is  also  contained  in  kelp,  and  in  the  juices  of  many  plants. 
The  crystals,  which  occur  in  old  pharmaceutical  extracts,  are  usually  of  this 
salt.  The  manufacturers  of  alum  occasionally  employ  it  as  the  source  of 
potassa  in  that  salt. 

Hypochlorite  of  Potassa  (K0,C10),  called  also  chloride  of  potassa,  and 
chlorinated  potassa  has  only  been  obtained  in  solution  by  adding  aqueous 
hypochlorous  acid  to  a  solution  of  potassa.     When  chlorine  is  passed  into  a 


CHLORATE    OF    POTASSA.  31Y 

solution  of  carbonate  of  potassa  so  as  not  quite  to  saturate  the  alkali,  car- 
bonic acid  is  evolved,  and  a  solution  of  hypochlorite  of  potassa  is  obtained, 
provided  the  liquor  be  kept  cold.  If  heated,  or  if  more  than  one  atom  of 
chlorine  to  one  of  potassa  be  used,  the  hypochlorite  is  decomposed,  and  part 
of  the  bleaching  power  of  the  solution  destroyed.  A  solution  of  hypochlo- 
rite of  potassa  is  also  obtained  by  double  decomposition,  when  solution  of 
hypochlorite  of  lime  is  mixed  with  carbonate  of  potassa.  It  is  colorless, 
powerfully  bleachinj?,  and  antiseptic.  When  chlorine  is  passed  over  slightly 
moistened  carbonate  of  potassa,  a  bleaching  salt  mixed  with  bicarbonate  is 
the  result. 

Chlorate  of  Potassa  (KOjClOj  is  formed- by  passing  excess  of  chlorine 
through  a  strong  solution  of  potassa:  chloride  of  potassium  is  one  of  the 
results,  the  other  is  chlorate  of  potassa,  a  salt  in  brilliant  rhomboidal  tables 
(formerly  called  oxymuriate  of  potassa).  By  concentrating  the  liquid,  the 
chlorate  of  potassa,  which  is  much  less  soluble  in  cold  water  than  the  chloride 
of  potassium,  is  deposited  on  cooling.  The  action  of  chlorine  upon  a  solution 
of  carbonate  of  potassa  at  first  produces  bicarbonate  of  potassa,  which,  by 
the  continued  action  of  chlorine,  is  decomposed,  the  whole  of  the  carbonic 
acid  expelled,  and  hypochlorite  of  potassa  and  chloride^of  potassium  are  then 
formed;  6K0  +  6C1  =  3KC1  +  3[K0,C10]  :  the  hypochlorite  is  itself  after- 
wards resolved  into  chlorate  and  chloride:  3[KO,C10]=KO,C105+2KCl: 
so  that  the  ultimate  result  may  be  thus  represented:  6K0-f  GCl=5KCl-^- 
KO,C105. 

The  following  is  the  most  economical  process  for  the  preparation  of  this 
chlorate  :  One  equivalent  of  carbonate  of  potassa  and  one  of  hydrate  of 
lime  are  mixed  and  exposed  to  a  current  of  chlorine ;  the  mass  becomes  hot, 
and  evolves  water  during  the  absorption  of  the  gas :  when  saturated,  it  is 
gently  heated  to  complete  the  decomposition.  No  oxygen  is  evolved,  the 
action  being  such  that  6[K0,C0J,  and  6[CaO,HO],  acted  on  by  6C1,  yield 
5KCl4-6[CaO,COJ  +  KO,C103;  whilst  6H0  are  evolved.  By  the  action 
of  water,  the  soluble  salts  are  separated  from  the  carbonate  of  lime,  and 
the  chloride  and  chlorate  by  crystallization. 

Chlorate  of  potassa  is  an  anhydrous  salt  of  a  cooling  taste.  It  forms  tabu- 
lar crystals  of  a  pearly  lustre.  Its  specific  gravity  is  19.  When  pure,  its 
aqueous  solution  is  not  rendered  turbid  by  nitrate  of  silver.  When  tritu- 
rated, it  appears  phosphorescent.  It  decrepitates  and  fuses  at  a  temperature 
between  400^  and  500°:  at  a  higher  heat  it  effervesces,  and  gives  out  nearly 
40  per  cent,  of  oxygen,  and  chloride  of  potassium  remains  {see  p.  90).  It  is 
soluble  in  18  parts  of  cold,  and  in  25  of  boiling  water;  and  in  about  120 
parts  of  alcohol.  ,  It  acts  energetically  upon  many  inflammables,  and  when 
triturated  with  sulphur,  phosphorus,  and  charcoal,  produces  inflammation 
and  explosion.  A  mixture  of  three  parts  of  this  chlorate  with  one  of  sulphur, 
detonates  loudly  when  struck  with  a  hammer,  and  even  sometimes  explodes 
spontaneously.  When  sulphuric  acid  is  dropped  upon  mixtures  of  this  salt 
and  combustibles,  ignition  ensues,  in  consequence  of  the  evolution  of  peroxide 
of  chlorine.  A  mixture  of  sugar  and  the  chlorate  thus  treated,  is  immedi- 
ately kindled;  and  a  mixture  of  sulphide  of  antimony  and  the  salt,  suddenly 
deflagrates  with  a  bright  puff  of  flame  and  smoke  ;  the  latter  mixture  requires 
to  be  cautiously  made,  as  it  often  takes  fire  by  gentle  trituration.  When 
mixed  with  finely-powdered  metallic  antimony  or  zinc,  and  a  little  starch  or 
sugar,  it  causes,  on  the  application  of  heat  or  of  sulphuric  acid,  a  violent 
combustion  of  those  metals  with  oxidation.  Two  parts  of  finely-powdered 
magnesium  with  one  of  chlorate,  ignited  by  he||,  produce  the  instantaneous 
light  employed  in  photography.     This  light  has  great  actinic  power.     The 


318  IODIDE    OF    POTASSIUM. 

fulminating  compound  used  in  the  Prussian  needle-gun  consists  of  five  parts 
of  chlorate  of  potash,  three  parts  of  sulphide  of  antimony,  and  two  parts  of 
sulphur — the  ingredients  being  finely  powdered,  and  mixed  together  by 
sifting.    . 

Perchlorate  of  Potassa;  Oxychlorate  of  Potassa  (K0,CI07). — This 
salt  is  formed  when  chlorate  of  potassa  is  heated  in  a  porcelain  crucible  till 
it  fuses,  and  by  giving  out  a  portion  of  oxygen,  becomes  thick  and  pasty ; 
the  cooled  mass,  dissolved  in  hot  water,  deposits  perchlorate  of  potassa  on 
cooling,  which  may  be  purified  by  recrystallization.  The  chloride  of  potas- 
sium and  undecomposed  chlorate  remain  in  solution.  The  action  of  heat  on 
2  equivalents  of  the  chlorate  forms  one  of  chloride  of  potassium,  and  1  of 
perchlorate  ;  while  4  of  oxygen  are  evolved;  2(KO,C105)=KCl  +  KO,CI07 
-fO^.  This  salt  forms  anhydrous  rhombic  crystals,  soluble  in  65  parts  of 
water  at  60  ;  at  a  high  temperature  it  is  resolved  into  oxygen  and  chloride 
of  potassium. 

Iodide  of  Potassium  (KI). — Iodine  and  potassium  act  upon  each  other 
very  energetically,  and  often  with  explosion,  and  a  white,  fusible  crystalline 
compound  is  obtained.  When  hydriodic  acid  is  saturated  with  potassa, 
and  the  solution  carefully  evaporated,  anhydrous  crystals  of  the  iodide  are 
obtained.  The  usual  mode  of  procuring  this  compound  consists  in  dissolving 
iodine  in  solution  of  potassa  till  it  begins  to  assume  a  brown  color ;  on  evapo- 
rating to  dryness,  and  fusing  the  residuary  salt  at  a  red  heat,  iodide  of  potas- 
sium remains,  generally  mixed,  however,  with  a  little  iodate ;  if  a  little 
charcoal  is  added  previous  to  fusion,  the  decomposition  is  complete.  If, 
instead  of  fusing  the  products,  the  solution  be  evaporated  nearly  to  dryness, 
and  alcohol  poured  upon  it,  the  iodide  is  dissolved,  and  iodate  of  potassa 
remains,  which,  at  a  red  heat,  evolves  oxygen,  and  becomes  iodide  of  potas- 
sium. The  action  of  iodine  upon  the  alkali  corresponds  with  that  of  chlorine  ; 
that  is  6K0,  and  61,  produce  5KI,  and  KO,IO, ;  and  then,  by  the  application 
of  heat,  K0,I05  becomes  KI,  and  60  are  given  off.  Iodide  of  potassium 
is  also  prepared  by  decomposing  a  solution  of  iodide  of  iron  or  of  zinc,  by 
carbonate  of  potassa,  and  filtering  and  evaporating  the  resulting  solution; 
Fel  +  KCCOg  become  KI,  and  FeO,CO,. 

Iodide  of  potassium  forms  cubic  crystals,  of  an  acrid  saline  taste ;  they 
are  anhydrous,  and  slightly  deliquescent  in  damp  air.  100  parts  of  water  at 
65°  dissolve  143  of  this  salt,  and  a  considerable  depression  of  temperature 
is  produced  during  the  solution.  It  should  be  purchased  in  crystals,  which 
ought  not  to  be  very  deliquescent,  and  should  dissolve  in  six  or  eight  parts 
of  alcohol,  sp.  gr.  -836.  They  generally  redden  turmeric,  from  the  presence 
of  a  little  carbonate  of  potassa.  The  usual  impurities  in  the  iodide,  are 
chloride  of  potassium  and  sodium,  iodate  of  potassa,  and  water.  To  detect 
chlorine,  the  iodide  may  be  decomposed  by  nitrate  of  silver,  and  the  washed 
precipitate  digested  in  a  strong  solution  of  ammonia;  if  the  filtered  solution, 
acidified  by  nitric  acid,  gives  a  white  precipitate,  it  is  chloride  of  silver.  To 
detect  iodate  of  potassa,  add  to  the  solution  of  iodide  a  solution  of  tartaric 
acid.  If  a  yellow  or  brown  color  is  produced,  this  indicates  the  presence  of 
iodate.  When  starch  is  added,  the  liquid  acquires  a  deep  blue  color.  The 
aqueous  solution  of  iodide  of  potassium  dissolves  a  considerable  portion  of 
iodine  ;  this  solution,  under  the  name  of  ioduretted  iodide  of  potassium,  is 
used  in  medicine.  Iodide  of  potassium  is  decomposed  by  chlorine,  and  even 
When  largely  diluted,  a  minute  quantity  of  chlorine  discolors  the  solution  ; 
sulphuric  or  nitric  acid  (coiltaining  nitrous  acid)  also  decomposes  it.  Chlo- 
ride of  palladium  reddens  a  solution  containing  only  a  12,000th  of  the  iodide ; 


nitrIte  of  potassa.  319 

and  protonitrate  of  mercury  produces  a  yellow  cloud,  where  only  a  CO, 000th 
is  present.  Paper  which  has  been  bleached  by  chlorine  is  generally  dis- 
colored by  iodide  of  potassium;  and  if  characters  are  written  or  figures  drawn 
with  a  solution  of  iodide  of  potassium,  they  are  rendered  visible,  in  the  manner 
of  sympathetic  ink,  by  the  slightest  breath  of  chlorine.  When  paper  imbued 
with  a  mixed  solution  of  starch  and  iodide  of  potassium  is  exposed  to  the  air 
in  certain  situations,  it  sometimes  becon)es  more  or  less  discolored  in  conse- 
quence of  the  presence  of  ozone  (p.  114);  there  are  other  causes,  however, 
which  may  occasionally  produce  this  change.  Ozonized  ether  and  oil  of  tur- 
pentine decompose  it  and  set  free  iodine. 

loDATE  OF  Potassa  (KO.TOJ  is  one  of  the  products  of  the  action  of 
iodine  on  a  solution  of  potassa  ;  after  evaporation  the  iodide  of  potassium 
maybe  separated  from  the  iodate  by  digestion  in  alcohol  sp.  gr.  -810,  which 
leaves  the  latter  salt  undissolved.  Iodate  of  potassa  requires  about  14  parts 
of  water  at  60°  for  its  solution  ;  it  is  insoluble  in  absolute  alcohol.  Its 
crystals  are  small  cubes,  permanent  in  the  air ;  at  a  red  heat  it  gives  out. 
between  22  and  23  per  cent,  of  oxygen,  and  is  converted  into  iodide  of  potas- 
sium, no  periodate  being  intermediately  formed.  Its  aqueous  solution  is 
decomposed  by  sulphuretted  hydrogen,  and  by  sulphurous  and  arsenious 
acids. 

Bromide  of  Potassium  (KBr). — Potassium  and  bromine  act  intensely 
upon  each  other,  evolving  heat  and  light,  and  producing  explosion.  When 
bromine  is  dropped  into  a  solution  of  potassa,  the  mixture  evaporated,  and 
the  residue  heated  to  redness,  bromide  of  potassium  is  also  obtained.  Its 
sp.  gr.  is  2*4  ;  it  is  white,  fusible,  and  crystallizes  in  cubes,  easily  soluble  in 
water,  and  slightly  so  in  alcohol.  It  is  sometimes  prepared  for  medicinal 
use  by  decomposing  bromide  of  zinc  or  bromide  of  iron,  by  carbonate  of 
potassa ;  it  should  be  purchased  in  crystals,  as  it  is  otherwise  apt  to  be 
impure. 

Nitrate  of  Potassa  ;  Nitre ;  Saltpetre  (K0,N05). — This  salt  is  prin- 
cipally brought  to  this  country  from  the  East  Indies,  where  it  is  produced 
by  lixiviation  from  certain  soils  ;  but  the  mode  or  cause  of  its  formation  is 
not  well  understood  ;  it  is  probably  connected  with  the  oxidation  of  ammonia. 
The  greater  part  of  the  rough  nitre  imported  from  the  East  Indies  is  in 
brqJven-down  crystals,  wliich  are  more  or  less  deliquescent ;  exclusive  of  other 
implrities,  it  often  contains  a  considerable  portion  of  common  salt,  which, 
reacting  upon  the  nitre,  sometimes  induces  the  production  of  nitrate  of  soda 
and  chloride  of  potassium  ;  it  also  usually  contains  sulphate  of  lime  and 
traces  of  organic  matter.  In  Germany  and  P'rance,  it  is  artificially  produced 
in  what  are  termed  nitre-beds.  The  process  consists  in  lixiviating  old  plaster 
rubbish,  which,  when  rich  in  nitre,  affords  about  five  per  cent.  Refuse  animal 
and  vegetable  matter,  which  has  putrefiefl  in  contact  with  calcareous  soils, 
produces  nitrate  of  lime,  which  affords  nitre  by  mixture  with  carbonate  of 
potassa. 

Nitre  crystallizes  in  anhydrous,  six-sided  prisms,  usually  terminated  by 
dihedral  summits.  Its  sp.  gr.  is  about  2.  The  solubility  of  nitre  varies 
extremely  with  temperature  :  at  32°,  100  parts  of  water  dissolve  13  2  of  the 
salt;  at  77°,  38  parts;  at  132°,  97  parts  ;  at  176°,  169  parts;  and  at  212°, 
246  parts.  During  the  solution  of  1  part  of  powdered  nitre  in  5  of  water, 
the  temperature  sinks  from  50°  to  35°.  It  is  insoluble  in  pure  alcohol.  The 
crystals  of  nitre,  though  the  salt  is  anhydrous,  generally  contain  interstitial 
water  ;  so  that  they  appear  moist  when  powdered,  and  lose  weight  on  drying. 


3$0  gunpowder! 

The  taste  of  nitre  is  cooling  and  peculiar.  At  a  temperature  of  about  600°, 
nitre  fuses  without  undergoing  change  of  composition,  and  congeals  on  cool- 
ing. Sometimes  it  is  cast  into  small  balls  or  cakes,  called  sal  prunella .  At 
a  red  heat,  nitre  is  slowly  decomposed  ;  and  highly  heated  in  an  earthen  re- 
tort, or  gun-barrel,  it  affords  oxygen  gas,  mixed  with  a  portion  of  nitrogen. 
In  this  decomposition,  the  nitre  is  first  converted  into  byponitrite  of  potassa, 
which  is  somewhat  deliquescent;  potassa  is  the  final  result. 

Nitre  is  rapidly  decomposed  by  charcoal  at  a  red  heat,  and  the  results  are 
carbonic  oxide  and  acid,  nitrogen,  and  carbonate  of  potassa,  sometimes 
called  wJiite  flux.  These  mixtures  of  nitre  and  charcoal  form  the  basis  of  a 
variety  of  compositions  used  for  fireworks,  the  rapidity  of  the  combustion 
being  modified  by  the  relative  proportion  of  the  charcoal.  When  phosphorus 
is  thrown  upon  nitre,  and  inflamed,  a  vivid  combustion  ensues,  and  a  phos- 
phate of  potassa  is  formed.  Sulphur  sprinkled  upon  hot  nitre  burns,  and 
produces  a  mixture  of  sulphate  and  sulphite  of  potassa.  Many  of  the  metals, 
when  in  filings  or  powder,  deflagrate  and  burn  when  thrown  on  red-hot  nitre. 
A  mixture  of  3  parts  of  nitre,  2  of  dry  carbonate  of  potassa,  and  1  of  sul- 
phur, fovm^  fulminating  powder.  If  a  little  of  this  is  heated  to  about  330°, 
it  blackens,  fuses,  and  explodes  with  violence,  in  consequence  of  the  rapid 
action  of  the  sulphur  upon  the  nitre,  and  the  sudden  evolution  of  nitrogen 
and  carbonic  acid,  the  residue  being  chiefly  sulphate  of  potassa,  3[K0,N0J 
-f2[KO,COJ  +  5S=5[KO,S03]  +  3N4-2CO,.  The  action  of  sulphuric 
acid  on  nitre  has  been  already  described  (p.  175).  When  nitre  and  hydro- 
chloric acid  are  heated  together,  chlorine  and  nitrous  acid  are  evolved,  and 
on  evaporation  to  dryness,  chloride  of  potassium  remains. 

Gunpowder  consists  of  a  mixture  of  nitre,  sulphur,  and  charcoal,  the  pro- 
portions varying  according  to  the  uses  made  of  it,  as  follows  : — 


Common 

Shooting 

Shooting 

Miners' 

gunpowder. 

powder. 

powder. 

powder. 

Saltpetre  . 

.     75-0 

78 

76 

65 

Charcoal   . 

.     12-5 

12 

15 

15 

Sulphur    . 

.     12-5 

10 

9 

20 

Per  cent. 

101 

75-0 

16 

11-8 

18 

13-2 

The  explosive  force  of  gunpowder  depends  upon  the  sudden  formation  of 
nitrogen  and  carbonic  acid  gases,  which,  at  the  high  temperature  at  which 
they  are  evolved,  may  be  considered  as  amounting  to  about  1500  times  the 
volume  of  the  powder  employed.  Supposing  the  combustion  perfect,  and 
the  powder  to  consist  of : — 

Per  cent.  ^ 

1  equivalent  of  nitre         .... 
1  "  sulphur   .... 

3  "  carbon     .... 

135  100-0 

the  resulting  products  may  be  thus* represented  :  K0,N03-f  S-f  C3=3CO.,-f 
N-fKS,  the  only  residue  being  sulphide  of  potassium,  which  gives  the  fetid 
odor  to  the  washings  of  a  gun-barrel.  The  temperature  required  for  the 
explosion  of  gunpowder,  is  a  black  heat  between  500°  and  600°.  Below 
600°  the  sulphur  is  volatilized  from  the  other  ingredients.  The  presence  of 
nitrate  of  soda  is  as  a  rule  injurious,  owing  to  its  tendency  to  absorb  moist- 
ure from  the  air,  but  as  it  is  cheaper  than  nitre  it  is  sometimes  added  to  gun- 
powder for  blasting  purposes.  A  powder  of  this  kind  had  the  composition 
of  sulphur  10  parts,  charcoal  15  parts,  nitrate  of  potash  56  parts,  and 
nitrate  of  soda  18  parts. 

In  the  manufacture  of  gunpowder,  the  nitre  and  sulphur  should  be  pure, 


NITRITE    or    POTASSA.  321 

the  charcoal  carefully  selected  and  prepared,  and  the  whole  perfectly  mixed 
in  fine  powder.  This  mixture  is  moistened,  ground  and  pressed  into  a  cake  ; 
it  is  then  granulated,  dried,  and  polished  by  attrition  in  revolving  barrels. 
The  granular  form  of  the  powder  increases  the  rapidity  of  its  combustion,  by 
enabling  the  flame  so  to  penetrate  it  as  to  kindle  every  grain  nearly  at  the 
same  time ;  but  this  combustion,  though  very  rapid,  is  by  no  means  instanta- 
neous, for  in  that  case  scarcely  anything  would  resist  its  power,  and  its 
explosion  would  more  resemble  that  of  fulminating  mercury  or  silver,  and 
would  burst  the  gun  instead  of  propelling  the  ball.  A  cubic  foot  of  good 
gunpowder  should  weigh  about  58  pounds ;  and  2  ounces  of  it  when  ex- 
ploded in  a  mortar  8  inches  in  diameter,  and  placed  at  an  angle  of  45°, 
should  throw  a  68  lb.  shot  about  270  feet.  Gunpowder  is  sometimes  tried 
by  placing  two  heaps  of  about  sixty  grains  each  upon  clean  writing-paper, 
three  or  four  inches  asunder,  and  firing  one  of  them  by  a  red-hot  wire  ;  if 
the  flame  ascends  quickly  with  a  good  report,  sending  up  a  ring  of  white 
smoke,  leaving  the  paper  free  from  specks  and  not  burnt  into  holes,  and  if 
no  sparks  fly  from  it  so  as  to  set  fire  to  the  contiguous  heap,  the  powder  is 
good.  Mr.  Gale  has  lately  patented  a  process  for  rendering  gunpowder  un- 
explosive.  It  consists  in  mixing  4  parts  of  finely-powdered  glass  with  1 
part  of  powder.  When  thoroughly  mixed,  the  gunpowder  does  not  explode 
on  applying  a  red  heat,  but  it  burns  with  deflagration.  The  glass  is  incom- 
bustible and  non-conducting  :  and  it  acts  by  preventing  the  communication 
of  the  flame  from  one  particle  to  another.  The  difiBculty  arises,  however,  in 
rapidly  separating  the  glass  completely,  unless  the  gunpowder  is  made  very 
coarse — the  large  proportion  of  glass  used  would  increase  the  bulk  for  storage 
enormously,  and  in  transport  by  sea  or  rail  the  gunpowder  would  have  a  ten- 
dency to  separate  from  the  glass.  On  the  whole,  the  process  is  not  practi- 
cably available  for  insuring  safety  without  rendering  the  gunpowder  useless. 
Analysis. — Weigh  off  100  grains  of  the  powder,  and  dry  it  at  212°  to 
estimate  the  moisture ;  then  wash  it  upon  a  filter  with  boiling  water,  which 
dissolves  out  the  whole  of  the  nitre  ;  dry  the  washed  residue,  and  digest  it 
in  bisulphide  of  carbon,  which  abstracts  the  sulphur  and  leaves  the  charcoal. 
The  aqueous  solution,  if  the  nitre  be  pure,  should  not  be  affected  by  nitrate 
of  silver  or  nitrate  of  baryta. 

Action  op  Potassium  on  Ammonia  ;  Potassiamide. — When  potassium  is 
heated  in  gaseous  ammonia,  hydrogen  is  evolved,  and  an  olive-colored  sub- 
stance is  obtained,  of  a  crystalline  fracture.  It  burns  in  oxygen,  producing 
hydrated  potassa,  and  nitrogen  ;  exposed  to  air,  it  deliquesces,  and  evolves 
ammonia;  water  acts  upon  it,  producing  potassa  and  ammonia.  The  volume 
of  hydrogen  evolved  by  this  action  of  potassium  on  ammonia,  is  the  same  as 
that  which  it  would  have  evolved  from  water ;  so  that  when  1  atom  of  potas- 
sium acts  upon  1  of  ammonia,  1  of  hydrogen  is  evolved,  and  the  remaining 
elements  of  the  ammonia  (namely,  1  atom  of  nitrogen  and  2  of  hydrogen) 
combine  with  the  potassium.  As  1  of  nitrogen  and  2  of  hydrogen  constitute 
amidogen,  the  resulting  compound  has  been  termed />o«as5^«m^G?e,  its  formula 
being  KjNHg-,  an  atom  of  the  hydrogen  of  the  ammonia  being  replaced  by 
an  atom  of  potassium.  Heated  in  hydrogen,  potassium  absorbs  a  portion  of 
that  gas,  and  forms  a  gray  hydride,  which  is  very  inflammable:  it  is  decom- 
posed by  the  contact  of  mercury  ;  it  is  said  to  consist  of  1  atom  of  hydrogen 
combined  with  4  of  potassium. 

Nitrite  op  Potassa.     Hyponitrite  of  Potassa:  Potassium  Nitride  (KO, 
NOg). — This  salt  is  obtained  by  heating  nitrate  of  potassa  so  as  to  expel  two 
atoms  of  oxygen.     It  is  thus  procured  as  a  white  neutral  deliquescent  solid, 
21 


322  SULPHIDES    OF    POTASSIUM. 

very  soluble  in  water.  It  is  also  soluble  in  alcohol,  and  it  may  thus  be  dis- 
tinguished and  separated  from  the  nitrate.  It  may  be  obtained  crystallized 
from  the  hot  aqueous  solution.  Its  solution  is  precipitated  white  by  nitrate 
of  silver,  and  the  hyponitrite  of  silver  thus  obtained  may  be  decomposed  by 
any  alkaline  chloride  and  other  hyponitrites  produced.  The  silver  salt  is 
soluble  in  a  large  quantity  of  water  and  in  nitric  acid.  Stahlschmidt  has 
found  that  when  finely-divided  zinc  is  boiled  with  a  solution  of  nitrate  of 
potassa,  the  salt  is  reduced  to  hyponitrite.  A  saturated  solution  of  nitrate  is 
gently  heated  with  one-tenth  of  its  volume  of  ammonia,  and  zinc  in  powder 
is  added.  At  from  80°  to  100°  there  is  a  rapid  action  which  may  be  reduced 
if  necessary  by  cooling  the  liquid.  In  half  an  hour  the  reduction  is  so  far 
complete,  that  on  adding  to  the  liquid  twice  its  volume  of  alcohol  there  is  no 
precipitation  of  nitrate.  The  free  potassa  in  the  solution  may  be  neutralized 
by  nitric  acid  and  separated  by  crystallization.  Any  oxide  of  zinc  formed 
may  also  be  removed. 

The  hyponitrite  of  potassa  has  many  useful  reactions.  Sulphuric  acid  added 
to  the  dry  salt  sets  free  deutoxide  of  nitrogen,  producing  in  the  air  the  usual 
ruddy  fumes  of  nitrous  acid.  In  this  respect  the  hyponitrite  is  strongly  dis- 
tinguished from  the  nitrate.  In  the  following  experiments  with  the  solution  of 
hyponitrite,  a  small  quantity  of  diluted  sulphuric  acid  should  be  added.  When 
a  solution  of  hyponitrite  is  added  to  a  diluted  solution  of  chloride  of  gold  and 
the  liquid  is  warmed,  metallic  gold  is  precipitated ;  when  added  to  a  solution  of 
permanganate  of  potash  the  pink  color  is  discharged — to  iodide  of  potassium, 
iodine  is  set  free — to  freshly-precipitated  resin  of  guaiacum,  a  beautiful  blue 
color  is  produced — to  a  solution  of  sulphate  of  indigo  the  color  is  discharged; 
and  lastly,  when  added  to  a  solution  of  green  sulphate  of  iron,  the  liquid 
becomes  of  a  dark  brown  color,  owing  to  the  deutoxide  of  nitrogen  producd 
being  dissolved  by  a  portion  of  the  undecomposed  sulphate.  In  some  of 
these  reactions  the  hyponitrite  acts  by  removing,  and  in  others  by  imparting 
oxygen.     Hence  the  acid  of  this  salt  is  an  oxidizer  and  deoxidizer. 

Sulphides  of  Potassium. — When  sulphur  and  potassium  are  heated  in 
an  exhausted  tube,  vivid  combustion  ensues,  and  if  atomic  proportions  are 
observed,  a  protosulphide  of  potassium  is  formed =KS.  So  also  when  a 
stream  of  hydrogen  is  passed  over  heated  sulphate  of  potassa,  water  and  the 
protosulphide  are  the  results:  (KO.SO^-f  4H=KS-f  4H0).  If  a  mixture 
of  2  parts  of  sulphate  of  potassa  and  1  of  lamp-black  is  heated  out  of  the 
contact  of  air,  a  pyrophorus  is  formed,  which  is  a  mixture  of  the  protosul- 
phide and  charcoal.  A  solution  of  this  protosulphide  is  obtained  by  dividing 
a  solution  of  caustic  potassa  into  two  equal  parts,  and  saturating  one  of 
them  with  sulphuretted  hydrogen,  by  which  the  compound  KS,HS  is  formed, 
and  which,  when  mixed  with  the  other  half  of  the  solution,  is  converted  into 
protosulphide:  KS,HS,+K0=2KS-f  HO.  When  this  solution  is  evapo- 
rated, it  yields  a  nearly  colorless  crystalline  product,  acrid  and  alkaline,  and 
evolving  sulphuretted  hydrogen  when  an  acid  is  added  :  thus  (with  sulphuric 
acid)  KS4-S03HO=KO,S03-f  HS.  It  absorbs  oxygen  when  exposed  to 
air,  and  becomes  yellow. 
^  Bisulphide  of  Potassium  (KS,)  is  formed  by  heating  four  parts  of  potas- 
sium with  three  of  sulphur ;  or  by  exposing  an  alcoholic  solution  of  KS,HS 
to  the  air,  till  it  begins  to  deposit  sulphur,  and  then  evaporating  in  vacuo ; 
it  is  an  orange-colored  fusible  substance.  Tersulphide  of  Potassium  (KS3)  is 
formed  by  passing  the  vapor  of  bisulphide  of  carbon  over  carbonate  of  potassa 
at  a  red  heat ;  carbonic  oxide  and  carbonic  acid  are  evolved  ;  2(K0,C0J  -f 
3CS.=C02-|-4CO,-f  2KS3.  The  substance  formerly  known  under  the  name 
of  Liver  of  Sulphur,  is  a  mixture  of  this  tersulphide  with  sulphate  of  potassa ; 


CARBONATE  OF  POTASSA.  323 

it  is  obtained  by  heatinp:  70  parts  of  carbonate  of  potassa  with  40  of  sulphur  ; 
carbonic  acid  is  evolved  and  3KS3+KO,S03  is  produced.  Tetrasulphide  of 
Potassium  (KSJ  is  formed  by  passing  the  vapor  of  sulphide  of  carbon  over 
heated  sulphate  of  potassa.  Pentasulphide  of  Potassium  (KS^)  is  formed 
when  solutions  of  the  preceding  sulphides  are  boiled  with  excess  of  sulphur  ; 
or  when  a  solution  of  caustic  potassa  and  excess  of  sulphur  are  boiled 
together.  In  this  case,  3  equivalents  of  potassa  and  12  of  sulphur,  yield  2 
equivalents  of  the  pentasulphide  and  1  of  hyposulphite  of  potassa;  3K04- 
12S=2KS,+KO,SA. 

Sulphate  of  Potassa  (KOjSOg). — This  salt  is  the  result  of  several 
chemical  operations  carried  on  upon  a  large  scale  in  the  processes  of  the 
arts.  It  is  the  sal  de  duohus  of  the  old  chemists.  Its  taste  is  bitter  and 
saline.  It  crystallizes  in  short  six-sided  prisms,  terminated  by  six-sided 
pyramids.  They  are  anhydrous,  and  soluble  in  about  12  parts  of  water  at 
60^,  and  insoluble  in  alcohol.  This  salt  is  thrown  down  when  sulphuric 
acid  is  added  to  a  moderately  strong  solution  of  potassa.  When  about  2 
parts  of  sulphate  of  potassa  and  1  of  lamp-black,  intimately  mixed  in  jBne 
powder,  are  heated  to  redness  in  a  coated  phial,  and  great  care  taken  to 
exclude  the  air  during  cooling,  the  product  takes  fire  on  exposure  to  air. 
It  appears  to  contain  a  compound  of  potassium,  which  powerfully  attracts 
oxygen,  and  thus  evolves  heat  enough  to  inflame  the  charcoal  and  sulphur. 

BisuLPHATE  OF  PoTASSA  (KO,HO,2S03)  is  formed  by  heating  in  a  pla- 
tinum crucible  87  parts  of  sulphate  of  potassa  with  49  of  sulphuric  acid. 
When  one  atom  of  sulphate  is  dissolved  in  from  3  to  5  atoms  of  the  acid, 
and  evaporated  to  crystallization,  an  anhydrous  bisulphate  first  forms  in 
acicular  crystals,  but  in  a  few  days  it  liquefies  and  is  converted  into  rhora- 
boidal  hydrated  crystals.  This  salt  is  not  decomposed  below  redness ;  at  a 
red  heat  it  gives  out  sulphuric  acid,  sulphurous  acid,  and  oxygen,  and  is 
converted  into  the  neutral  salt.  It  is  soluble  without  decomposition  in 
about  half  its  weight  of  boiling  water,  but  by  large  quantities  of  water  it  is 
resolved  into  neutral  sulphate  and  acid.  Bisulphate  of  potassa  is  also  formed 
by  the  distillation  of  1  atom  of  nitre  and  2  of  sulphuric  acid,  as  in  the  pro- 
cess for  obtaining  Nitric  Acid.  Under  the  old  name  of  sal  enixum,  it  is 
used  for  cleansing  metals. 

Carbonate  of  Potassa  (KO.COJ  is  a  salt  of  much  importance,  and 
known  in  different  states  of  purity  under  the  names  of  wood-ash,  pot-ash, 
pearl-ash,  subcarbonate  of  potassa :  it  was  formerly  known  as  salt  of  tartar. 
It  may  be  obtained  directly,  by  passing  carbonic  acid  into  a  solution  of 
potassa,  till  saturated,  evapol^ting  to  dryness,  and  exposing  the  dry  mass  to 
a  red  heat ;  or  indirectly,  by  burning  purified  tartar  (bitartrate  of  potassa), 
lixiviating  the  residue,  and  evaporating  to  dryness.  A  mixture  of  purified 
tartar  and  nitre  projected  into  a  crucible  heated  to  dull  redness,  also  affords 
carbonate  of  potassa,  which  may  be  obtained  by  lixiviation  as  the  preceding. 
When  succulent  vegetables  are  dried  and  burned,  their  potassa-salts  are  for 
the  most  part  converted  into  carbonate,  hence  the  term  vegetable  alkali  ; 
and  particular  plants  a'fford  it  in  larger  quantities  than  others.  The  younger 
branches  of  trees  afford  more  than  the  old  wood,  hence  their  selection  as  a 
source  of  wood-ash. 

Carbonate  of  potassa  is  generally  derived  from  two  sources,  namely,  from 
the  carbonate  of  commerce,  or  from  the  bicarbonate.  The  carbonate  of 
potassa  of  commerce  is  purified  by  lixiviating  it  with  its  weight  of  cold 
water  ;  being  more  soluble  than  the  salts  which  usually  accompany  it,  these 


324  CARBONATE    OF    POTASSA. 

remain  undissolved,  and  the  solution,  poured  off,  strained  or  filtered  if  ne- 
cessary, and  evaporated,  leaves  the  carbonate  of  potassa.  Or  the  crude 
carbonate  may  be  dissolved  in  water,  filtered,  evaporated  till  the  solution 
acquires  the  sp.  gr.  1-52,  and  set  aside  in  a  cold  place,  when  the  greater 
part  of  the  foreign  salts  are  deposited,  and  the  solution  of  the  carbonate 
may  be  poured  off;  with  every  precaution,  however,  when  thus  obtained,  it 
is  still  impure.  When  required  pure,  it  is  obtained  by  heating  the  crys- 
tallized bicarbonate  to  a  temperature  below  redness,  but  sufficient  to  expel 
its  water  and  half  of  its  carbonic  acid.  When  equal  parts  of  bitartrate  and 
nitrate  of  potassa  are  burned  in  successive  portions  in  an  iron  crucible,  the 
residuary  carbonate  was  formerly  called  white  flux:  when  2  parts  of  tartar 
are  used  to  1  of  nitre,  the  whole  of  the  charcoal  is  not  consumed,  and  the 
product  was  called  black  flux ;  these  compounds  being  used  in  fusing  or 
fluxing  metallic  ores. 

Carbonate  of  potassa  is  fusible  without  decomposition,  at  a  red-heat;  its 
sp.  gr.  is  2  24  :  it  is  very  soluble  in  water,  which  at  55°  takes  up  nearly  its 
own  weight.  It  deliquesces  by  exposure  to  air,  forming  a  dense  solution, 
formerly  called  oil  of  tartar.  Its  taste  is  alkaline,  and  it  has  a  strong  alka- 
line action  upon  test-papers.  It  is  insoluble  in  absolute  alcohol.  A  satu- 
rated solution  of  carbonate  of  potassa  in  water  contains  about  48  per  cent, 
of  the  salt,  and  has  a  sp.  gr.  of  \h.  When  this  solution  is  evaporated  till 
its  sp.  gr.  becomes  1*62,  it  yields  deliquescent  crystals  which  include  2  atoms 
of  water.  The  solution  will  commonly  be  found  to  contain  traces  of  sulphate 
and  chloride,  as  well  as  oxide  of  lead  dissolved  from  the  glass.  These  im- 
purities may  be  detected  by  their  appropriate  tests.  As  carbonate  of  potassa 
is  usually  derived  from  the  ashes  of  vegetables,  its  production  is  limited  to 
countries  which  require  clearing  of  timber,  or  where  there  are  vast  natural 
forests.  If  vegetables  growing  in  a  soil  not  impregnated  with  sea-salt  are 
burned,  the  residue,  which  is  in  the  form  of  a  brown  saline  mass,  contains  a 
large  relative  proportion  of  this  carbonate,  and  is  commonly  called  rough,  or 
crude  potassa.  If  it  be  again  calcined  so  as  to  burn  away  the  carbonaceous 
matter,  it  becomes  a  white  mass,  generally  termed  poarlash. 

The  pearlash  of  commerce  contains  a  variety  of  impurities,  which  render 
it  of  variable  value.  In  general,  its  purity  may  be  judged  of  by  its  easy 
solubility  in  cold  water,  2  parts  of  which  should  entirely  dissolve  1  part  of 
the  salt;  the  residue  consists  of  impurities.  The  quantity  of  acid  of  a  given 
strength,  requisite  to  saturate  a  given  weight,  may  also  be  resorted  to  as  a 
criterion  of  its  purity.  Now  355  grains  of  diluted  sulphuric  acid  of  the 
specific  gravity  of  1-141  neutralize  100  grains  of  pure  carbonate  of  potassa. 
Hence,  if  we  dissolve  100  grains  of  the  alkali  to  be  examined,  in  six  or 
eight  parts  of  .water,  and  gradually  add  the  test  sulphuric  acid  till  we  find, 
by  the  application  of  proper  test-papers,  that  the  alkali  is  exactly  neu- 
tralized, we  may  deduce,  from  the  weight  of  the  acid  consumed,  the  propor- 
tion of  real  carbonate  present:  for  as  355  is  to  100,  so  is  the  weight  of  the 
test-acid  employed,  to  that  of  the  pure  carbonated  alkali  present.  To  save 
trouble,  the  acid  properly  diluted  may  be  put  into  a  glass  tube  so  graduated 
as  to  show  directly  the  value  of  the  alkali  by  the  quantity  consumed  in  its 
saturation.  Thus  we  find,  by  reference  to  the  scale  of  equivalents,  that  100 
parts  of  carbonate  of  potassa  are  saturated  by  70  of  sulphuric  acid,  specific 
gravity  1-84.  If,  therefore,  we  put  70  grains  of  such  acid  into  a  tube  divided 
into  100  parts,  and  fill  it  up  with  water,  it  follows  that  the  quantity  of  car- 
bonate of  potassa  existing  in  any  sample  of  pearlash  under  examination,  will 
be  directly  shown  by  the  measure  of  such  diluted  acid  required  for  saturation ; 
100  grains  of  the  sample,  if  pure  carbonate,  would  require  the  whole  100 
measures  of  acid  ;  but  if  only  containing  50  ^er  cent,  of  pure  carbonate,  the 


CYANIDE    OP    POTASSIUM.      CYANATE    OP    POTASSA.  325 

100  grains  would  be  saturated  by  50  measures  of  the  test-acid,  and  sq  on. 
Such  graduated  tubes  are  called  alkalimeters,  and  are  to  be  obtained  from 
the  makers  of  chemical  apparatus,  together  with  practical  directions  for 
using  them. 

Bicarbonate  op  Potash  (K0,H0,2C02)  is  formed  by  passing  carbonic 
acid  into  a  solution  of  the  carbonate,  or  by  subjecting  the  moist  carbonate 
to  excess  of  gaseous  carbonic  acid.  It  may  also  be  obtained  by  the  action 
of  sesquicarbonate  of  ammonia  on  carbonate  of  potassa,  in  which  case  pure 
ammonia  is  evolved.  Bicarbonate  of  potassa  forms  hydrated  prismatic  crys- 
tals, which  are  not  deliquescent,  and  taste  slightly  alkaline.  Thej  require 
for  solution  about  four  parts  of  water  at  60°.  Boiling  water  dissolves 
nearly  its  own  weight,  but  during  the  solution  a  portion  of  carbonic  acid  is 
evolved,  and  by  long  boiling,  the  salt  is  said  to  become  a  sesquicarbonate, 
or  even  carbonate.  The  solution  has  an  alkaline  reaction,  and  possesses 
most  of  the  chemical  properties  of  the  carbonate.  It  is  distinguished  from 
the  carbonate — 1,  in  giving  no  precipitate  in  the  cold,  with  a  solution  of 
sulphate  of  magnesia:  and  2,  in  producing  a  pale  yellowish  precipitate 
with  a  few  drops  of  a  solution  of  corrosive  sublimate.  A  solution  of  the 
carbonate  gives  immediately  a  brick-red  precipitate  of  oxychloride  of  mer- 
cury. Bicarbonate  of  potassa  is  nearly  insoluble  in  absolute  alcohol.  Exposed 
to  a  red  heat,  it  evolves  carbonic  acid  and  water,  and  carbonate  of  potassa 
remains.  This  salt  is  generally  pure,  or  very  nearly  so,  and  may  be  con- 
veniently resorted  to  for  the  preparation  of  the  carbonate  and  other  salts, 
when  purity  is  required. 

Cyanide  op  Potassium  (KNCg  or  KCy)  is  obtained  by  heating  to  red- 
ness, in  a  covered  crucible,  a  mixture  of  8  parts  of  dry  ferrocyanide  of 
potassium,  and  3  of  dry  carbonate  of  potassa,  till  it  no  longer  gives  off  gas ; 
the  iron  subsides,  and  the  fused  product,  when  poured  off,  concretes  into  a 
white  mass,  which  is  a  mixture  of  the  cyanide  and  of  cyanate  of  potassa,  the 
reaction  being  as  follows  :  2(K,FeCy3)-f  2(KO,CO,)=5(KGy)  +  KO,CyO  + 
Fe2+2C02.  The  formation  of  the  cyanate  maybe  prevented  by  adding  to 
the  mixture  before  fusion  an  eighth  of  its  weight  of  powdered  charcoal ;  the 
fused  mass  may  then  be  digested  in  boiling  alcohol,  from  which  the  cyanide 
of  potassium  crystallizes  on  cooling. 

Cyanide  of  potassium  should  be  carefully  preserved  out  of  the  contact  of 
air  and  water:  it  may  be  fused  without  decomposition,  provided  air  be 
excluded,  and  is  not  changed  by  a  red  heat ;  but  with  the  access  of  oxygen 
it  becomes  cyanate  of  potassa:  KCy  +  20=KO,CyO.  Its  taste  is  pungent 
and  alkaline,  accompanied  with  the  flavor  of  hydrocyanic  acid,  and  it  is  very 
poisonous.  It  is  very  soluble  in  water,  and  may  be  obtained  from  its  solu- 
tion, in  anhydrous  cubic  crystals  :  it  is  but  little  soluble  in  cold  alcohol, 
which  throws  it  down  from  its  recent  and  cold  aqueous  solution  :  exposed  to 
air,  it  becomes  moist  and  smells  of  hydrocyanic  acid.  It  is  a  powerful 
reducing  agent,  as  respects  oxides  and  sulphides,  and  as  such,  is  used  in 
mineral  analysis :  the  oxides  of  copper,  and  those  of  tin,  iron,  and  lead,  are 
immediately  reduced  when  sprinkled  into  the  fused  cyanide.  When  cyanide 
of  potassium  effervesces  with  acids,  it  contains  either  cyanate  or  carbonate 
ef  potassa  ;  a  yellow  tint  indicates  the  presence  of  iron  :  if  it  blackens  when 
calcined,  it  is  contaminated  by  formate  of  potassa. 

Cyanate  op  Potass  (KO,CyO). — The  \)reparation  of  this  salt  has  been 
described  under  Cyanic  Acid  (p.  280).  It  is  decomposed  both  by  water 
and  acids,  which  convert  the  cyanic  acid  into  carbonic  acid  and  ammonia ; 


326  FERROCYANIDE    OF    POTASSIUM. 

in  fact,  by  exposure  to  air,  it  exhales  ammonia,  and  becomes  bicarbonate  of 
potassa.  It  crystallizes  in  small  plates  ;  tastes  like  saltpetre  ;  is  anhydrous  ; 
and  in  close  vessels  excluded  from  air  and  moisture  may  be  fused  without 
decomposition. 

SuLPHOCYANiDE  OF  POTASSIUM  (K.NCaS^)  may  be  formed  by  boiling  2 
equivalents  of  finely-powdered  sulphur  in  a  solution  of  1  equivalent  of  cya- 
nide of  potassium  :  it  yields  prismatic  crystals  which  are  of  a  cooling  bitter 
taste,  deliquescent,  and  anhydrous.  In  close  vessels  this  salt  fuses  and  con- 
cretes on  cooling  into  an  opaque  crystalline  mass :  heated  in  the  air,  it  is 
decomposed,  and  if  moisture  be  present,  carbonate  of  ammonia  and  sulphide 
of  potassium  are  formed.  For  the  chemical  characters  of  this  and  other 
sulphocyanides,  see  page  288. 

Ferrooyanide  OF  Potassium.  Prussiate  of  Potassa  (K3,Fe,Cy3).— 
When  iron  filings  are  digested  in  a  solution  of  cyanide  of  potassium,  and 
the  mixture  is  exposed  to  air,  oxygen  is  absorbed  and  this  compound  is 
produced.  If  air  is  excluded,  the  water  is  decomposed,  and  hydrogen  is 
liberated.  On  evaporation  a  salt  is  obtained  which  has  the  formula  (Kg 
FeCy3,3HO).  A  mixture  of  sulphide  of  iron  and  cyanide  of  potassium  also 
forms  the  ferrocyanide,  and  sulphide  of  potassium.  When  Prussian  blue  is 
boiled  with  potassa  it  is  decomposed,  oxide  of  iron  is  separated,  and  on 
filtering  and  evaporating  the  solution,  crystals  of  the  ferrocyanide  are  obtained. 
This  salt  is  largely  prepared  as  an  article  of  commerce,  chiefly  for  the  use  of 
calico-printers,  by  calcining  at  a  red  heat,  in  a  globular  iron  vessel,  a  mix- 
ture of  carbonate  of  potassa  with  animal  matters,  such  as  horns  and  hoofs, 
woollen  rags,  or  parings  of  leather.  The  fused  mass  takes  a  portion  of 
iron  from  the  iron  vessel,  and  this  forms  prussiate  cake.  When  cold  it  is 
lixiviated,  and  the  evaporated  solution  yields  an  impure  product,  which,  when 
redissolved  and  slowly  crystallized,  furnishes  the  purified  salt.  In  this 
operation  the  cyanogen  derived  from  the  nitrogen  and  carbon  of  the  organic 
matter  combines  with  the  potassium  and  iron  to  produce  the  ferrocyanide. 

Ferrocyanide  of  potassium  forms  permanent  yellow,  tabular,  and  octahe- 
dral crystals  (=K2Fe,Cy3,3HO),  of  the  specific  gravity  of  1'83:  they  are 
insoluble  in  alcohol.  Water  at  60^  takes  up  about  one-third,  and  at  212^, 
its  own  weight  of  this  salt.  It  has  a  bitter,  saline,  and  sweetish  taste,  and 
is  not  poisonous.  When  moderately  heated  it  loses  color,  and  crumbles 
into  powder,  parting  with  about  13  per  cent,  of  water.  By  a  red  heat  it  is 
converted  with  the  escape  of  nitrogen,  into  carbide  of  iron  and  cyanide  of 
potassium  :  and  in  the  presence  of  air  the  latter  salt  becomes  cyanate  of 
potassa,  and  the  iron  is  oxidized.  Boiled  with  dilute  sulphuric  or  hydro- 
chloric acid,  hydrocyanic  acid  is  given  out,  and  a  white  precipitate  is  formed 
similar  to  that  which  the  salt  produces  in  a  solution  of  protosulphate  of  iron. 
By  nitric  acid  or  by  chlorine  it  is  converted  into  ferricyanide  of  potassium. 
The  action  of  concentrated  sulphuric  acid  upon  this  salt  is  attended  by  the 
evolution  of  carbonic  oxide.  Neither  sulphuretted  hydrogen,  the  hydrosul- 
phates,  the  alkalies,  nor  tincture  of  galls,  produce  any  precipitate  in  solu- 
tions of  this  salt.  Red  oxide  of  mercury  decomposes  it  at  a  moderate  heat, 
peroxide  of  iron  and  metallic  mercury  are  precipitated,  and  qyanide  of  mer- 
cury is  formed ;  so  that  the  iron  is  peroxidized  at  the  expense  of  the  oxide 
of  mercury.  When  a  solution  of  this  salt  forms  insoluble  precipitates  in 
metallic  solutions,  the  nature  of  the  metal  present  may  often  be  judged  of 
by  the  character  and  color  of  th^  precipitate.  This  is  white  or  nearly  so, 
with  the  salts  of  manganese,  zinc,  tin,  cadmium,  lead,  bismuth,  antimony, 
protosalts  of  iron,  mercury  and  silver  ;  yellowish-green  with  those  of  cobalt  j 


TESTS    FOR    POTASSA.  321 

reddish-hrown,  with  tliose  of  copper  and  uranium  ;  blue,  with  the  persalts  of 
iron,  and  pea-green,  with  the  salts  of  nickel.  It,  therefore,  forms  a  good 
eliminating  or  general  test  for  many  metals.  It  is  also  employed  as  a  re- 
ducing agent  for  arsenic  and  its  sulphides.  When  a  mixture  of  ferrocyanide 
of  potassium  with  dilute  sulphuric  acid  is  subjected  to  distillation,  hydro- 
cyanic acid  is  evolved,  and  a  ferrocyanide,  represented  by  the  formula  K, 
FCyCyg,  and  known  as  Everitt's  yellow  salt,  is  among  the  products  (page 
283). 

Ferricyanide  of  Potassium  (Kg.Feg.Cyg). — When  chlorine  is  passed 
through  a  solution  of  ferrocyanide  of  potassium  till  the  liquor  ceases  to  pre- 
cipitate Prussian  blue  from  the  persalts  of  iron,  and  then  filtered  and  slowly 
evaporated,  it  furnishes  right  rhombic  prismatic  crystals,  which,  purified  by 
a  second  solution,  assume  a  ruby-red  color  ;  they  are  anhydrous,  and  require 
3'8  parts  of  cold  water  for  solution,  and  are  nearly  insoluble  in  alcohol. 
They  burn  with  brilliant  scintillations,  and  when  heated  in  close  vessels,  give 
off  cyanogen  and  nitrogen,  and  leave  ferrocyanide  of  potassium  and  carbide 
of  iron.  When  dissolved  in  water,  this  salt  is  decomposed  by  sulphuretted 
hydrogen,  sulphur  and  cyanide  of  iron  are  precipitated,  and  hydrocyanic  acid 
and  ferrocyanide  of  potassium  formed.  This  salt  occasions  no  precipitate  in 
solutions  of  iron  containing  the  peroxide  only,  but  it  is  a  most  delicate  test 
of  the  protoxide,  with  which  it  forms  a  blue  precipitate.  In  its  formation 
the  chlorine  abstracts  one-fourth  of  the  potassium  of  the  ferrocyanide,  pro- 
ducing chloride  of  potassium  and  ferricyanide,  2(K2,Fe,Cy3)  +  Cl,=KCl-f 
K3,Fe.3,Cyg).  There  is  a  remarkable  difference  between  the  ferri  and  ferro- 
cyanide of  potassium  which  it  may  here  be  proper  to  point  out.  The  ferri- 
cyanide acts  like  an  ozonide  on  strychnia,  and  has  been  proposed  by  Dr. 
Davy  as  a  test  for  that  alkaloid.  When  a  crystal  of  ferricyanide  of  potassium 
is  brought  in  contact  with  strychnia  previously  mixed  with  strong  sulphuric 
acid,  a  series  of  colors  are  produced,  commencing  with  a  sapphire  blue  and 
passing  through  various  shades  of  purple  to  a  light  red.  They  are  similar  to 
those  given  under  the  same  circumstances  by  the  peroxides  of  manganese 
and  lead  and  by  bichromate  of  potash.  If  the  ferrocyanide  of  potassium  is 
employed,  these  colors  are  not  produced. 
• 

Silicates  of  Potassa. — When  silica  and  potassa  are  fused  together  they 
combine  in  various  proportions  and  produce  a  series  of  silicates,  differing  in 
solubility  and  fusibility,  according  to  the  preponderance  of  the  base  or  of 
the  acid.  When  the  alkali  is  in  excess,  the  product  is  soluble  in  water ;  but 
with  excess  of  silica  it  is  insoluble,  and  constitutes  a  species  of  glass  {see 
Silicate  of  Soda).  When  finely-divided  silica  is  added  to  fused  carbonate 
of  potassa,  carbonic  acid  is  evolved,  and  by  using  atomic  proportions,  a 
compound  may  be  obtained  represented  by  KO.SiO,,  in  which  47  parts  of 
potassa  are  united  to  46  of  silica.  When  1  part  of  silica  and  4  of  caustic 
potassa  are  fused  together  and  slowly  cooled,  a  part  of  the  compound  may  be 
poured  out  of  the  crucible  before  the  whole  has  solidified,  and  pearly  crystals 
are  formed  in  the  residuary  portion. 

Tests  for  Potassa  and  its  Salts. — A  solution  of  pure  potassa  is  charac- 
terized— 1.  By  a  strong  alkaline  reaction  on  test-paper ;  2.  By  its  giving  a 
brown  precipitate  with  a  solution  of  nitrate  of  silver  (oxide  of  silver).  This 
distinguishes  it  from  solutions  of  carbonate  and  bicarbonate  of  potassa,  both 
of  which  give  a  yellowish-white  precipitate  (carbonate  of  silver).  3.  The 
solution  give.s  a  crystalline  precipitate  of  acid  tartrate  of  potassa,  when  a 
large  excess  of  a  concentrated  solution  of  tartaric  acid  is  added  to  it.     The 


328  SODIUM. 

solution  must  not  be  too  dilute.  The  precipitate  is  soluble  in  180  parts  of 
water,  and  is  readily  dissolved  by  mineral  acids  and  by  alkaline  solutions. 
The  addition  of  a  small  quantity  of  alcohol  promotes  this  reaction.  The 
production  of  the  alkaline  oxide  from  the  metal  is  at  once  indicated  by  plae- 
inp:  a  globule  of  potassium  on  a  solution  of  tartaric  acid  in  a  glass :  4, 
Chloride  of  platinum  gives  with  the  solution  a  yellowish  precipitate  of  plati- 
nochloride  of  potassium  (KCl.PtCla)  (100  parts  of  this  precipitate,  when 
dried,  correspond  to  16'03  of  potassium,  19-33  of  potassa,  and  40*39  of 
platinum);  5.  A  clean  platinum  wire  dipped  into  the  solution,  and  introduced 
into  a  smokeless  flame,  gives  a  pale  violet  color  to  it.  This  color  traverses 
a  solution  of  indigo  or  a  layer  of  blue  glass.  A  small  quantity  of  the  liquid, 
burnt  with  alcohol  in  a  platinum  capsule,  will  give  a  similar  color.  This 
color  is  produced  in  flame  by  all  the  salts  of  potash.  The  spectral  analysis 
of  the  flame  shows  the  presence  of  two  bright  lines,  one  in  the  red  and  an- 
other in  the  violet  portion  of  the  spectrum.     Most  of  the  other  colors  occur. 

The  solution  of  potassa  is  precipitated  by  solutions  of  the  picric,  per- 
chloric, and  fluosilicic  acids.  The  last  is  frequently  employed  for  separating 
the  acid  from  its  salts  (page  306). 

The  solutions  of  the  salts  of  potassa,  when  sufficiently  concentrated,  give 
precipitates  with  tartaric  acid  and  chloride  of  platinum,  similar  to  those 
obtained  with  the  solution  of  the  pure  alkali.  In  the  smallest  quantity  on 
platinum  wire,  they  tinge  flame  of  a  pale  violet  color.  This  color  is  per- 
ceptible through  blue  glass,  or  a  diluted  solution  of  sulphate  of  indigo.  In 
using  chloride  of  platinum  to  detect  potassa-salts,  the  absence  of  ammoniacal 
salts  must  be  previously  ascertained,  as  they  produce  analogous  effects  upon 
this  reagent;  or  the  platinum-test  may  be  applied  after  the  salt  has  been 
subjected  to  a  red  heat,  by  which  the  salts  of  ammonia  will  have  been  decora- 
posed  or  evaporated.  When  chloride  of  platinum  is  used  in  quantitative 
analysis,  it  should  be  added  in  excess  to  the  potassa-solution,  together  with  a 
drop  or  two  of  hydrochloric  acid,  and  the  mixture  evaporated  at  212°.  The 
residue  should  then  be  washed  with  a  mixture  of  equal  parts  of  proof  spirit  and 
water,  which  removes  everything  except  the  platino-chloride  of  potassium. 


CHAPTER    XXIV. 

SODIUM  (Na=23). 

This  metal,  called  also  Natrium,  was  discovered  by  Davy  in  1808.  He 
procured  it  by  the  decomposition  of  the  oxide  under  a  powerful  voltaic  cur- 
rent. It  is  most  abundantly  diffused  as  chloride  in  the  earth,  air,  and  sea. 
Four  gallons  of  sea  water  contain  about  a  pound  of  the  chloride,  and  this  is 
equivalent  to  about  half  a  pound  of  sodium.  As  potassium  is  the  terrestrial, 
sodium  may  be  regarded  as  the  marine  metallic  element.  The  metal  is  now 
obtained  from  carbonate  of  soda  by  a  process  similar  to. that  for  potassium. 
A  mixture  of  carbon  and  carbonate  of  soda,  derived  from  the  calcination  of 
the  acetate  of  soda  in  close  vessels,  is  employed.  To  this,  charcoal  is  added, 
and  the  mixture  is  distilled.  As  this  metal  does  not  combine  with  carbonic 
oxide,  it  is  obtained  more  readily  than  potassium.  One  pound  of  the  cal- 
cined acetate  will  yield  from  five  to  seven  ounces  of  sodium.  Sodium  is  now 
made  in  large  quantity  for  the  manufacture  of  aluminum  and  magnesium  and 
for  preparing  sodium  amalgam.     It  may  be  obtained  at  the  low  price  of  six 


HYDRATE    OP    SODA.  329 

shillino^s  per  pound.  It  is  soft,  malleable,  and  easily  sectile  :  it  does  not, 
like  potassium,  become  brittle  at  32°,  but  even  at  this  low  temperature 
several  globules  may  be  welded  toj]^ether  by  pressure.  In  color  it  somewhat 
resembles  silver,  but  rapidly  tarnishes  on  exposure  to  air.  Its  sp.  gr.  is  0  97. 
It  softens  at  about  122° ;  it  fuses  at  about  200°,  and  is  volatile  at  a  white 
heat,  its  vapor  being  colorless.  It  burns  with  a  yellow  flame  when  heated 
in  contact  with  air,  and  requires  the  same  cautions  to  preserve  it  from  oxida- 
tion as  potassium.  Sodium,  when  placed  on  a  large  surface  of  cold  water, 
does  not  take  fire  and  burn  like  potassium.  It  decomposes  cold  water  with- 
out combustion.  If,  however,  one  or  two  drops  of  water  are  placed  on  a 
fresh-cut  slice  of  sodium,  the  heat  is  so  intense  that  it  immediately  takes  fire 
and  burns  with  a  yellow  flame.  If  wrapped  in  a  small  muslin  bag,  and 
placed  on  water,  or  even  on  ice,  the  metal  will  also  take  fire  and  burn  with 
a  yellow  flame.  It  also  takes  fire  and  burns  on  hot  water.  If  a  globule  of 
sodium  is  wrapped  tightly  in  copper  gauze  and  dropped  into  ajar  of  water, 
a  copious  stream  of  hydrogen  issues  from  it,  rising  in  bubbles  through  the 
water.  By  inverting  a  jar  of  water  and  holding  the  sodium  in  the  gauze 
beneath,  the  hydrogen  may  be  collected.  If  the  jar  is  filled  with  a  solution 
of  litmus,  the  production  and  solution  of  an  alkali  is  indicated  by  the  red 
litmus  being  turned  blue. 

Sodium  and  Oxygen;  Protoxide  op  Sodium;  Soda;  (NaO). — The 
affinity  of  sodium  for  oxygen  appears  to  be  somewhat  less  than  that  of  potas- 
sium. It  is  more  slowly  oxidized  on  exposure  to  air ;  but  the  protoxide  is 
the  result  of  the  action  of  air  or  water.  Anhydrous  soda  is  obtained  in  the 
same  way  as  anhydrous  potassa,  and  resembles  it  in  appearance,  but  is  less 
fusible  and  less  volatile. 

Peroxide  op  Sodium  (Na^Og). — By  heating  sodium  in  oxygen,  it  burns 
vividly,  and  a  yellowish-green  peroxide  is  formed,  which,  by  the  action  of 
water,  evolves  oxygen,  and  produces  a  solution  of  the  protoxide. 

Hydrate  of  Soda  ;  Caustic  Soda  (NaO, HO)  is  obtained  from  the  car- 
honate,  by  the  action  of  lime,  as  described  under  the  head  of  Potassa.  It  is 
now  obtained  as  a  product  in  the  manufacture  of  magnesium.  Pure  hydrate 
of  soda  is  white,  opaque,  brittle,  and  deliquescent ;  its  sp.  gr.  is  2*0  ;  it  re- 
quires a  red  heat  for  fusion  ;  and  when  intensely  heated  evaporates  and 
tinges  the  flame  yellow.  It  has  the  same  general  characters  as  hydrated 
potassa ;  like  it,  it  retains  water  at  a  red  heat,  and  is  deprived  of  it  by  the 
same  means. 

The  following  table  shows  the  proportion  of  anhydrous  soda  in  solutions 
of  ditferent  specific  gravities  : — 


pecific  gravity 

Dry  soda  per  cent 

Specific  gravity 

Dry  soda  per  cent. 

of  solution. 

by  weight. 

of  solution. 

by  weight. 

1-85 

63-6 

1-36 

26-0 

1-72 

53-8 

1-32 

23-0 

1-63 

46-6 

1-29 

19-0 

1-56 

41-2 

1-23 

16-0 

1-50 

36-8 

1-18 

13-0 

1-47 

34-0 

1-12 

9-0 

1-44 

31-0 

1-06 

4-7 

1-49 

29-0 

Hydrated  soda  is  distinguished  from  hydrated  potassa  by  forming  an  efflo- 
rescent paste  when  long  exposed  to  the  atmosphere:  potassa  under  the  same 
circumstances  remains  deliquescent.     The  chemical  properties  of  the  solution 


330  CHLORIDE    OF    SODIUM. 

of  soda  as  an  alkali,  are  similar  to  those  of  potassa,  bat  from  the  trouble  of 
procuring  it,  it  has  been  much  less  used  than  potassa.  Hydrate  of  soda  is 
now,  however,  abundantly  produced  in  the  manufacture  of  magnesium  ;  and 
its  solution  is  likely  to  take  the  place  of  the  solution  of  potassa  for  many 
chemical  purposes.  The  impurities  liable  to  be  found  in  the  solution  of  soda 
are  similar  to  those  described  under  potassa;  thus  oxide  of  lead  is  frequently 
present  in  it,  as  the  result  of  a  chemical  action  on  the  glass.  This  impurity 
is  detected  by  the  addition  of  sulphuretted  hydrogen  or  sulphide  of  ammo- 
nium, either  of  which  will  give  a  brown  color  to  the  liquid,  if  lead  should  be 
present. 

Chloride  OF  Sodium;  Sea  Salt;  Muriate  of  Soda;  (NaCl). — Sodium, 
when  heated  in  chlorine,  burns  vividly,  and  produces  this  compound.  It 
exists  abundantly  in  nature  both  as  a  solid  fossil  (sal  gemme),  and  in  the 
ocean,  and  in  brine  springs.  Extensive  beds  of  it  occur  in  Cheshire,  where 
it  is  known  under  the  name  of  rock-salt.  From  these  sources  the  immense 
demands  are  supplied  ;  that  is,  either  by  evaporating  brine-springs,  or  sea- 
water,  or  quarrying  it  from  the  mine.  In  sea-water  it  amounts  to  about  2*7 
per  cent.,  or  to  about  4  ounces  in  the  gallon.  When  heated,  chloride  of 
sodium  decrepitates.  At  a  red  heat  it  fuses  without  undergoing  decomposi- 
tion, and  on  cooling  concretes  into  a  white  mass ;  at  a  bright-red  heat  it 
sublimes,  and  tinges  flame  of  a  blue  color.  It  is  insoluble  in  absolute  alcohol, 
but  dissolves  in  proof  spirit.  It  is  taken  up  nearly  in  the  same  proportion 
by  cold  and  by  hot  water;  100  of  water  dissolving  37  of  salt;  or  1  of  salt 
to  3*7  of  water.  Concentrated  hydrochloric  acid  precipitates  chloride  of 
sodium  from  its  concentrated  aqueous  solution.  When  pure,  chloride  of 
sodium  does  not  alter  by  exposure  to  air,  though  it  is  generally  more  or  less 
deliquescent,  from  containing  chlorides  of  magnesium  and  calcium.  Obtained 
by  slow  or  spontaneous  evaporation,  it  crystallizes  in  solid  cubes  ;  but  when 
procured  at  a  boiling  heat,  by  removing  its  crystals  from  the  surface  of  its 
solution,  it  forms  hollow  quadrilateral  pyramids.  The  crystals  are  anhy- 
drous, though  they  often  include  interstitial  water.  Their  specific  gravity 
is  2-557. 

Chloride  of  sodium  is  decomposed  by  moist  carbonate  of  ammonia ;  bi- 
carbonate of  soda,  sal-ammoniac  and  free  ammonia  are  formed  ;  with  moist 
carbonate  of  potassa,  it  yields  chloride  of  potassium  and  carbonate  of  soda. 
In  the  process  for  obtaining  hydrochloric  acid  it  is  decomposed  by  sulphuric 
acid.  In  this  decomposition,  the  oxygen  of  the  water  of  the  sulphuric  acid 
is  transferred  to  the  sodium  of  the  salt,  the  chlorine  of  which  combines  with 
the  hydrogen  of  the  water  to  produce  hydrochloric  acid,  and  the  oxide  of 
sodium  unites  with  the  dry  sulphuric  acid  to  produce  sulphate  of  soda 
(NaCl  +  S03,HO=NaO,S03+HCl).  Chloride  of  sodium  is  also  decom- 
posed by  nitric  acid :  effervescence  ensues,  chlorine  tinged  with  nitrous  acid 
is  evolved,  and,  provided  a  sufficiency  of  nitric  acid  has  been  used,  nitrate  of 
soda  remains  on  evaporation  to  dryness.  When  chloride  of  sodium  is  tritu- 
rated with  oxalic  acid  and  heated,  hydrochloric  acid  is  evolved,  and  oxalate 
of  soda  formed,  so  that  when  the  residue  is  heated  to  redness,  carbonate  of 
soda  remains.  When  chloride  of  sodium  and  ferruginous  clay  are  heated 
together,  the  silica  and  alumina  of  the  clay  are  vitrified  by  the  soda  of  the 
salt,  and  its  chlorine  combines  with  the  iron ;  it  is  upon  this  principle  that 
salt  is  used  as  a  glaze  for  stoneware ;  when  thrown  into  the  furnaces  in 
which  the  articles  are  baked,  it  is  volatilized,  and  decomposed  upon  their 
surfaces,  producing  silicate  of  soda,  which  forms  the  glaze  to  the  stoneware. 
This  principle  has  been  applied  by  Mr.  Gossage,  of  Warrington,  in  a  new 
process  for  procuring  hydrate  and  carbonate  of  soda  from  salt.     A  lofty 


NITRATE    OP    SODA.  331 

tower  of  fire-brick  is  filled  with  layers  of  flint  or  balls  of  sand,  so  arranpred  as 
to  receive  the  heat  of  several  gas-furnaces  placed  at  the  lower  part  of  the 
tower.  Two  other  furnaces,  constructed  in  a  similar  manner,  supply  steam 
and  common  salt  in  a  state  of  vapor  to  the  heated  flints.  Hydrochloric  acid 
and  silicate  of  soda  are  the  products.  The  latter,  dissolved  by  the  water, 
flows  down  through  the  flints,  leaving  a  fresh  surface  for  chemical  action. 
The  silicate  of  soda  is  afterwards  decomposed  by  lime  to  produce  the  hydrate 
of  soda,  or  by  a  current  of  carbonic  acid  to  form  the  carbonate  of  soda. 
{Laboratory,  No.  3,  1867,  p.  42.)  It  is  of  most  extensive  use  as  a  preserva- 
tive of  food  ;  as  a  condiment ;  as  a  source  of  soda,  of  hydrochloric  acid,  and 
chlorine ;  and  for  various  agricultural  and  horticultural  purposes. 

Hypochlorite  of  Soda.  Chloride  of  Soda. — These  names  have  been 
applied  to  a  compound  formed  by  passing  chlorine  into  a  cold  and  dilute 
solution  of  caustic  soda,  or  by  decomposing  chloride  of  lime  by  a  solution  of 
carbonate  of  soda.  It  is  powerfully  bleaching,  and  smells  of  chlorine  :  ex- 
posed to  air,  it  absorbs  carbonic  acid  and  evolves  chlorine.  When  heated 
it  undergoes  changes  similar  to  those  produced  by  passing  chlorine  into  a 
solution  of  soda,  that  is,  chlorate  of  soda  and  chloride  of  sodium  are  formed. 

Laharraque's  disinfecting  liquid,  which  is  essentially  a  hypochlorite,  is 
made  by  passing  chlorine  into  a  solution  of  carbonate  of  soda  {see  page  335). 

Bromide  of  Sodium  (NaBr). — Sodium  and  bromine  act  upon  each  other 
with  much  intensity;  the  result  is  a  fusible  compound,  soluble  in  water  and 
in  alcohol,  und  crystallizing  at  86°  in  anhydrous  cubes,  but  at  lower  tem- 
peratures in  hexagonal  tables,  containing  26  37  per  cent,  of  water. 

Iodide  of  Sodium  (Nal). — Iodine  and  sodium  act  upon  each  other  with 
the  same  phenomena  as  in  the  case  of  potassium.  Iodide  of  sodium  may 
also  be  formed  by  adding  iodine  to  a  solution  of  caustic  soda,  evaporating  to 
dryness,  and  fusing  the  residue.  It  is  contained  in  the  mother-liquor  of 
kelp,  in  the  ashes  of  burned  sponge,  and  in  the  oyster.    {See  Iodine,  p.  205.) 

Nitrate  op  Soda  (NaO.NOj).     Chili,  or  South  American  Nitre This 

salt,  which  was  formerly  called  cubic  nitre,  may  be  obtained  by  neutralizing 
carbonate  of  soda  by  dilute  nitric  acid.  It  crystallizes  in  rhomboids,  solu- 
ble in  3  parts  of  water  at  60°.  It  has  a  cool  sharp  flavor,  and  is  somewhat 
deliquescent  in  damp  air,  and  therefore  unfit  for  the  manufacture  of  gun- 
powder. A  mixture  of  5  parts  of  nitrate  of  soda,  1  of  charcoal,  and  1  of 
sulphur,  burns  more  slowly  than  a  similar  mixture  with  nitrate  of  potassa: 
its  flame  is  yellow.  Large  quantities  of  native  nitrate  of  soda  occur  in  Peru, 
formi-ng  a  stratum  covered  with  clay  and  alluvium,  of  many  miles  in  extent, 
and  it  is  now  a  considerable  article  of  trade.  It  may  be  employed  in  fire- 
works, and  used  as  a  substitute  for  nitre  (it  being  cheaper)  in  the  manufac- 
ture of  nitric  acid,  of  sulphuric  acid,  and  in  other  cases  in  which  nitre  is 
consumed.  It  has  been  hitherto  found  too  expensive  as  a  source  of  soda. 
It  is  frequently  employed  as  a  manure.  At  a  red  heat  it  is  decomposed  with 
results  similar  to  those  of  nitrate  of  potassa,  and  is  ultimately  resolved  into 
soda,  nitrogen,  and  oxygen.  As  nitrate  of  soda  is  comparatively  a  cheap 
article.  Dr.  Wagner  has  proposed  to  procure  nitric  acid  from  it  without  sul- 
phuric acid,  and  to  utilize  the  products.  He  found  that  when  the  salt 
was  heated  with  hydrate  of  alumina,  nitric  acid  was  evolved  with  some 
hyponitric  acid,  and  the  residue,  which  consisted  of  aluminate  of  soda, 
when  treated  with  carbonic  acid,  formed  the  useful  compound  carbonate  of 


332  SULPHATE    OF    SODA. 

soda,  and  left  the  alumina  in  the  state  of  hydrate  for  further  use.     This 
ingenious  process  has  not  yet  been  carried  out  on  a  large  scale. 

Sodium  and  Sulphur. — The  account  of  the  action  of  sulphur  on  potas- 
sium and  potassa,  and  of  sulphuretted  hydrogen  upon  solution  of  potassa, 
applies  generally  to  sodium  and  soda,  and  their  corresponding  compounds. 

Hyposulphite  of  Soda  (NaO.SgOg). — This  salt  may  be  procured  by  the 
various  processes  which  have  been  described  at  page  301.  It  is  now  manu- 
factured on  a  large  scale  for  the  purpose  of  photography,  and  is  usually 
seen  in  prismatic  crystals.  It  is  very  soluble  in  water.  Its  solution  has  a 
bitter,  nauseous  taste.  It  is  decomposed  by  heat.  Its  chemical  properties 
have  been  elsewhere  fully  described  (p.  224).  Owing  to  its  being  a  ready  source 
of  sulphurous  acid,  the  hyposulphite  of  soda  admits  of  being  employed  as  a 
bleaching  agent.  M.  Artus  has  used  it  for  the  bleaching  of  sponges.  The 
sponge  is  well  washed  in  a  weak  solution  of  soda ;  the  all^ali  is  entirely 
removed  by  washing  in  water,  and  the  sponge  is  then  transferred  to  a  weak 
solution  of  hyposulphite  of  soda  and  diluted  hydrochloric  acid.  In  a  short 
time  it  is  bleached.  The  hyposulphite  may  be  thus  used  for  bleaching  all 
articles  of  which  the  color  is  removed  by  sulphurous  acid. 

Sulphite  op  Soda  (NaO.SOg)  is  obtained  in  the  same  way  as  sulphite  of 
potassa :  it  is  crystallizable  in  prisms,  soluble  in  four  parts  of  water  at  60°. 
The  crystals  contain  8  atoms  of  water.  There  is  also  a  crystallizable  bisul- 
phite of  soda,  obtained  by  passing  a  current  of  sulphurous  acid  gas  through 
a  solution  of  carbonate  of  soda  till  fully  saturated ;  it  yields,  on  evaporation, 
four-sided  rectangular  prisms,  having  a  sulphurous  taste  and  smell,  and  red- 
dening vegetable  blues. 

Sulphate  of  Soda;  Glauber^ s  Salt;  Sal  Mirahile  (NaO,S03) ;  is  abun- 
dantly produced  in  various  processes  of  the  arts,  by  the  action  of  oil  of 
vitriol  upon  chloride  of  sodium  :  S03,HO,  +  NaCl  =  NaO,S03  +  HCl.  An- 
hydrous sulphate  of  soda  may  be  obtained  by  drying  the  common  hydrated 
crystals  upon  a  sand-heat;  they  fall  into  a  white  powder,  which  reabsorbs 
water  with  the  evolution  of  heat.  When  a  hot  concentrated  solution  of 
sulphate  of  soda  is  suffered  to  deposit  crystals  (at  a  temperature  between 
90°  and  100°)  they  are  anhydrous  rhombic  octahedra.  100  of  water  at  57° 
dissolve  10*58  of  this  anhydrous  salt,  and  the  solution,  set  aside  to  cool  and 
crystallize,  gives  the  common  decahydrated  crystals.  The  ordinary  crystals 
(decahydrated  sulphate  of  soda)  are  deposited  from  solutions  cooled  to  com- 
mon temperatures;  they  are  large  transparent  striated  prisms.  They  are 
efflorescent,  and  by  due  exposure  to  dry  air,  lose  their  water,  crumbling 
into  powder,  which,  however,  in  damp  air,  reabsorbs  water,  with  increase  of 
bulk.  When  gently  heated,  the  crystals  fuse,  and  at  the  same  time  deposit 
anhydrous  sulphate  ;  their  taste  is  saline  and  slightly  bitter ;  they  are  inso- 
luble in  alcohol.  The  solubility  of  sulphate  of  soda  in  water  follows  a  sin- 
gular law.  After  having  increased  rapidly  to  about  the  temperature  of  92°, 
where  it  is  at  its  maximum,  it  diminishes  to  215°,  and  at  that  temperature 
the  salt  is  nearly  of  the  same  solubility  as  at  87°.  This  salt  mixed  with 
starchy  matters  has  been  largely  employed  for  giving  weight  to  cotton 
fabrics. 

BisuLPHATE  OF  SoDA  (NaO,2S03)  ^s  obtained  by  adding  sulphuric  acid  to 
a  hot  solution  of  sulphate  of  soda.  It  crystallizes  in  rhombic  prisms,  soluble 
in  twice  their  weight  of  water  at  60°,  and  containing  water  of  crystallization. 


PHOSPHATES    OP    SODA.  333 

By  adding  half  an  equivalent  of  oil  of  vitriol  to  sulphate  of  soda,  and  evapo- 
rating the  solution,  crystals  of  a  sesquisulphate,  2NaO,3S03,  are  deposited. 

Phosphates  of  Soda.  1.  Trihasic  Phosphates. — There  are  three  phos- 
phates of  soda  belonging  to  the  tribasic  class :  they  have  been  usually  dis- 
tinguished as  common  or  rhombic  phosphate,  subphosphate  and  biphosphate. 
The  ammoniophosphate  also  belongs  to  this  class. 

Common  or  Rhombic  Phosphate,  2(NaO),HO,P05+24HO.— This  salt  (the 
sal  perlatum  of  old  writers)  is  obtained  by  saturating  the  phosphoric  acid 
prepared  from  calcined  bones  by  sulphuric  acid,  with  carbonate  of  soda :  the 
liquor  is  filtered,  evaporated,  and  set  aside  to  crystallize.  The  crystals  are 
alkaline  to  test-paper,  superficially  efflorescent,  and  soluble  in  about  4  parts 
of  cold  water.  This  salt  has  a  slightly  saline  and  alkaline  flavor,  and  has 
been  used  in  medicine  as  an  aperient.  The  crystals,  when  moderately  heated, 
fuse  in  their  water  of  crystallization  ;  at  a  dull  red-heat,  the  salt  runs  into  a 
clear  glass,  which  becomes  opaque  on  cooling  {pyrophosphate).  When  a 
solution  of  this  phosphate  is  dropped  into  nitrate  of  silver,  it  forms  a  yellow 
precipitate  (p.  242). 

Subphosphate  of  Soda,  3[NaO]P05+24HO. — When  excess  of  caustic 
soda  is  added  to  a  solution  of  the  preceding  salt,  it  yields  on  evaporation 
slender  six-sided  prisms,  which  are  permanent  in  the  air,  soluble  in  5  parts 
of  water  at  60°,  and  undergo  watery  fusion  at  1*10°.  The  solution  of  this 
salt  absorbs  carbonic  acid,  and  is  deprived  of  one-third  of  its  alkali  by  the 
weakest  acid.     This  salt  continues  tribasic  after  exposure  to  a  red  heat. 

Biphosphate  of  Soda,  NaO,2(HO),P05-f  2H0,  is  obtained  by  adding  ter- 
hydrated  phosphoric  acid  (p.  291)  to  a  solution  of  the  common  phosphate, 
till  it  ceases  to  precipitate  chloride  of  barium.  The  solution  in  cold  weather 
affords  crystals,  which  are  very  soluble,  and  have  a  distinctly  acid  reaction. 
It  precipitates  nitrate  of  silver  of  a  yellow  color. 

Ammoniophosphate  of  Soda  (NaO,NH40,HO,P05-f  8H0).— This  salt  ex- 
ists in  urine,  whence  it  was  procured  by  the  early  chemists  under  the  names 
of  microcosmic  and  fusible  salt.  It  may  be  formed  by  dissolving  in  water  5 
parts  of  crystallized  rhombic  phosphate  of  soda  with  2  of  crystallized  phos- 
phate of  ammonia,  and  evaporating.  It  forms  transparent  prisms  of  a 
saline  and  cooling  taste,  very  soluble,  and  which  effloresce  and  lose  ammonia 
in  a  dry  atmosphere. 

2.  Bibasic  Phosphates.  Pyrophosphates. — There  are  two  phosphates  of 
soda  belonging  to  this  class,  commonly  called  i\\Q  pyrophosphate  and  bipyro- 
phosphate.  Pyrophosphate  of  Soda  [2(NaO,)  POj-f  lOHO]  is  obtained  by 
heating  the  common  phosphate  to  redness,  when  it  loses  its  basic  water  and 
water  of  crystallization,  and  becomes  anhydrous  pyrophosphate,  =2[NaO,] 
POj.  Dissolved  in  hot  water,  this  anhydrous  salt  yields  permanent  prismatic 
crystals  on  cooling,  containing  10  atoms  of  water;  these  crystals  are  less 
soluble  than  those  of  the  common  phosphate,  and  their  solution  precipitates 
nitrate  of  silver  white,  and  has  an  alkaline  reaction.  The  insoluble  pyro- 
phosphates, with  the  exception  of  that  of  silver,  are  soluble  to  a  certain 
extent  in  the  solution  of  pyrophosphate  of  soda.  The  pyrophosphates  of 
ammonia  and  of  potassa  exist  in  solution,  but  when  they  crystallize  they  pass 
into  tribasic  salts  (p.  242). 

Bipyrophosphate  of  Soda  (NaO,HO,P05). — This  salt  is  formed  by  the 
application  of  a  graduated  heat  to  the  biphosphate  of  soda ;  its  solution  has 
an  acid  reaction,  and  does  not  crystallize.  It  throws  down  white  pyrophos- 
phate of  silver  from  nitrate  of  silver. 

3.  Monobasic  Phosphates;  Metaphosphate  of  Soda  (NaO,POs). — When 
any  of  the  preceding  phosphates  which  contain  only  1  equivalent  of  fixed 


334  PHOSPHATES    OF    SODA.       CARBONATE    OF    SODA. 

base  (soda)  are  heated  to  redness,  they  afford  metaphosphate :  when  bipyro- 
phosphate  is  used,  the  properties  of  the  resulting  salt  vary  with  the  tempera- 
ture to  which  it  has  been  subjected  ;  thus  if  heated  to  500°,  it  becomes  neu- 
tral, but  still  retains  the  characters  of  a  pyrophosphate.  At  a  temperature 
somewhat  higher,  but  below  redness,  it  becomes  very  difficultly  soluble,  and 
only  feebly  acid  ;  when  evaporated,  its  solution  does  not  give  crystals,  but 
dries  into  a  transparent  pellicle  like  gum,  which  retains  at  the  temperature 
of  the  air  somewhat  more  than  a  single  equivalent  of  water.  Added  to 
neutral  and  not  very  dilute  solutions  of  earthy  and  metallic  salts,  metaphos- 
phate of  soda  throws  down  insoluble  hydrated  metaphosphates,  of  which 
the  physical  condition  is  remarkable ;  they  are  all  soft  solid  or  semifluid 
bodies,  the  metaphosphate  of  lime  having  the  degree  of  fluidity  of  Venice 
turpentine  (p.  241). 

Carbonate  of  Soda  (NaO,C02). — This  important  salt  was  formerly  ob- 
tained by  the  combustion  of  marine  plants,  the  ashes  of  which  afforded  by 
lixiviation  the  impure  alkali  called  soda.  Two  kinds  of  rough  soda  were 
known  in  the  market,  barilla  and  kelp ;  besides  which,  some  native  carbonate 
of  soda  was  also  imported  from  Egypt.  Barilla  is  the  semifused  ash  of  the 
salsola  soda.  Kelp  is  the  ash  of  sea- weeds,  collected  upon  many  of  the 
rocky  coasts  of  Britain.  It  seldom  contains  more  than  5  per  cent,  of  car- 
bonated alkali,  and  about  24  tons  of  sea-weed  are  required  to  produce  1  ton 
of  kelp.  The  best  produce  is  from  the  hardest  deep-sea /i<cz,  such  as  the 
serratus,  digitalis  nodosus  and  vesiculosus. 

Kelp  is  now  chiefly  important  as  a  source  of  iodine,  the  large  commercial 
demands  for  carbonate  of  soda  being  supplied  by  the  decomposition  of  sul- 
phate of  soda.  The  process  consists,  1.  In  the  conversion  of  chloride  of 
sodium  into  sulphate  of  soda  or  salt  cake.  2.  In  the  production  of  black  ash, 
by  heating  sulphate  of  soda  with  chalk  and  coal.  3.  In  the  extraction  of 
carbonate  of  soda  from  the  black  ash.  The  furnace  in  which  the  chloride  of 
sodium  is  decomposed  consists  of  an  iron  vessel  of  the  shape  of  a  flattened 
sphere,  having  two  openings,  one  in  front,  for  the  introduction  of  the  charge, 
and  the  other  opposite  to  it,  through  which  the  charge  is  thrust  out  into  the 
roaster.  From  the  upper  part  of  the  decomposing  pan  a  pipe  issues  for  the 
conveyance  of  the  hydrochloric  vapors  into  the  condenser^  which  consists  of 
two  or  more  lofty  turrets  communicating  with  each  other  and  filled  with 
large  pebbles,  or  with  fragments  of  coke,  and  through  each  of  which  a  stream 
of  water  is  allowed  slowly  to  flow  (from  a  reservoir  at  the  summit),  which 
having  absorbed  the  hydrochloric  gas,  runs  off  at  the  bottom  into  a  receiver. 
The  gases  or  vapors  enter  the  first  tower  at  its  base,  and  passing  upwards, 
are  conveyed  by  a  pipe  of  communication,  into  the  upper  part  of  the  second 
tower,  through  which  they  pass  downwards.  The  hydrochloric  acid  is  thus, 
removed,  and  the  uncondensable  gases  pass  off  into  a  lofty  chimney  with 
which  the  base  of  the  second  tower  is  connected  by  a  flue  ;  in  this  way  a 
current  of  air  is  constantly  drawn  from  the  decomposing  pans,  and  from  the 
part  of  the  furnace  called  the  roaster^  which  is  also  supplied  with  a  separate 
pipe  communicating  with  the  condensing  towers.  In  the  decomposing  pans, 
the  original  charge  of  sulphuric  acid  and  salt  is  converted  into  a  mixture  of 
bisulphate  of  soda  and  undecomposed  chloride  ;  but  when  the  charge  is 
pushed  on  into  the  second  division  of  the  furnace,  or  roaster,  the  decomposi- 
tion is  completed  by  the  higher  heat,  and  the  bisulphate  of  soda,  acting  on 
the  undecomposed  chloride,  converts  the  whole  into  neutral  sulphate,  or  salt 
cake.  In  the  next  step  of  the  process,  this  rough  sulphate  of  soda  is  mixed 
with  its  weight  of  bruised  chalk  or  limestone,  and  somewhat  less  than  its 
weight  of  small  coal.     This  mixture  is  heated  and  ultimately  fused  in  a  proper 


CHLORINATED    CARBONATE    OP    SODA.  335 

furnace,  during  which  it  gives  out  jets  of  inflammable  gas;  and  when  these 
cease,  the  charge  is  raked  out  into  iron  barrows,  and  in  this  state  it  is  called 
hall  soda  or  black  ash.  This  is  then  broken  up  and  lixiviated  with  warm 
water,  so  as  to  extract  all  that  is  soluble ;  the  solution  is  allowed  to  settle, 
and  then  evaporated  in  shallow  pans,  and  the  product  so  obtained  is  mixed 
with  sawdust  and  roasted  in  a  reverberatory  furnace ;  it  thus  yields  the  crude 
carbonate  of  soda  known  under  the  name  of  soda  ash,  and  from  this  the  puri- 
fied crystallized  carbonate  is  obtained.  The  chemical  changes  concerned  in 
the  above  operations  are  chiefly  these  ;  when,  as  in  the  preparation  of  black 
ash,  sulphate  of  soda  is  fused  with  carbon  and  carbonate  of  lime,  carbonic 
oxide  is  evolved  and  sulphide  of  sodium  formed  ;  this  and  the  carbonate  of 
lime  then  react  on  each  other  so  as  to  form  carbonate  of  soda  and  sulphide 
of  calcium,  the  latter  being  combined  with  excess  of  lime  so  as  to  be  insolu- 
ble in  water.  1  equivalent  of  sulphate  of  soda,  1  of  carbonate  of  lime,  and 
4  of  carbon,  would  thus  produce  1  of  carbonate  of  soda,  1  of  sulphide  of  cal- 
cium, and  4  of  carbonic  oxide,  NaCSOg-f  CaOjCOg-f  4C=NaO,C03+ 
Ca^  +  4C0.  The  changes  are,  however,  more  complex  than  these  formula 
would  imply.  According  to  Dr.  Roscoe,  about  200,000  tons  of  common  salt 
are  annually  consumed  in  the  alkali-works  of  Great  Britain  for  the  prepara- 
tion of  nearly  the  same  weight  of  soda  ash,  of  which  the  value  is  about  two 
millions  sterling.  Some  other  processes  for  the  production  of  carbonate  of 
soda  from  common  salt  have  been  proposed,  but  none  have  hitherto  super- 
seded the  above. 

The  usual  form  of  the  common  crystallized  carbonate  of  soda  is  a  rhombic 
octahedron.  It  is  soluble  in  twice  its  weight  of  water  at  60^,  and  in  less 
than  its  own  weight  at  212°.  Its  taste  and  reaction  are  alkaline.  It  fuses 
readily  in  its  water  of  crystallization,  and  on  pouring  oif  the  fused  salt,  a 
portion  of  monohydrated  carbonate  remains.  Exposed  to  a  dry  atmosphere, 
the  crystals  effloresce,  and  at  a  red  heat  lose  the  whole  of  their  water. 
When  the  vapor  of  a  boiling  solution  of  carbonate  of  soda  is  introduced  into 
a  flame,  it  gives  it  a  yellow  color,  in  consequence  of  traces  of  the  salt  passing 
ofi"  with  the  aqueous  vapor.  Crystals  containing  smaller  proportions  of 
water  may  be  obtained,  but  these  rarely  occur,  and  the  usual  crystals  are, 
NaO,CO2,10HO.  The  principal  impurities  contained  in  carbonate  of  soda 
are  detected  as  follows :  1.  Sulphate  of  soda.  A  precipitate  by  chloride  of 
barium  when  the  solution  is  supersaturated  with  hydrochloric  acid.  2.  Chlo- 
ride of  sodium.  By  a  precipitate  with  nitrate  of  silver  in  the  solution  super- 
saturated by  nitric  acid.  3.  Salts  of  potassa,  by  chloride  of  platinum,  or 
tartaric  acid.  4.  Lime,  by  oxalic  acid.  Carbonate  of  lime  is  rendered 
soluble  to  a  certain  extent  by  carbonate  of  soda,  and  such  a  solution  cooled 
to  32°  deposits  a  white  crystalline  powder  composed  of  the  two  carbonates. 
Oxide  of  lead  from  flint  glass  is  detected  by  the  solution  giving  a  brown 
precipitate  with  sulphide  of  ammonium. 

Chlorinated  Carbonate  of  Soda. — By  proper  management,  chlorine 
may  be  combined  with  a  solution  of  carbonate  of  soda  ;  the  resulting  combi- 
nation has  been  termed  Labarraque^s  disinfecting  liquid.  It  is  obtained  as 
follows  :  2800  grains  of  crystallized  carbonate  of  soda  are  dissolved  in  r28 
pints  of  water,  and  the  chlorine  slowly  evolved  from  a  mixture  of  967  grains 
of  salt  with  750  grains  of  black  oxide  of  manganese,  and  967  grains  of  sul- 
phuric acid,  previously  diluted  with  750  grains  of  water,  is  carefully  passed 
into  it.  No  carbonic  acid  escapes,  and  a  pale  yellow  liquid  is  the  result ; 
its  taste  is  sharp,  saline,  and  astringent,  and  it  at  first  reddens,  and  then 
bleaches  turmeric  paper.  It  is  but  little  changed  by  a  boiling  heat,  and 
gives  out  no  chlorine.     By  careful  evaporation,  it  furnishes  crystals  which 


336  BORATE    OF    SODA. 

produce  the  original  liquid  when  redissolved ;  but  exposed  to  the  air,  and 
suffered  to  evaporate  spontaneously,  the  chlorine  escapes,  and  crystals  of 
carbonate  of  soda  are  obtained. 

Bicarbonate  of  Soda  (NaO,HO,2C03)  is  formed  by  passing  carbonic 
acid  through  a  strong  solution  of  the  carbonate  :  a  granular  or  crystalline 
powder  is  deposited,  which,  when  carefully  dried  at  common  temperatures, 
is  composed  as  above.  This  salt  may  also  be  obtained  by  condensing  car- 
bonic acid  upon  crystals  of  the  carbonate ;  a  portion  of  the  water  of  the  latter 
salt  separates,  and  when  the  gas  ceases  to  be  absorbed,  it  is  found  converted 
into  a  porous  and  friable  bicarbonate,  which  must  be  carefully  dried  at  a  low 
temperature,  otherwise  it  loses  a  portion  of  its  carbonic  acid.  Bicarbonate 
of  soda  has  a  slight  alkaline  taste  and  reaction.  It  is  much  less  soluble  than 
the  carbonate,  requiring  10  of  water  at  60°.  The  crystals  of  this  bicarbonate 
are  rectangular  prisms.  It  loses  carbonic  acid  if  moistened  and  left  in  the 
vacuum  of  an  air-pump  ;  the  gas  is  also  evolved  when  1  part  of  the  salt  is 
boiled  with  4  of  water.  In  these  cases  it  is  converted  into  a  sesquicarbonate. 
When  long  exposed  to  damp  air,  it  is  converted,  after  some  months,  into 
pentahydrated  monocarbonate  (NaO,C03,5HO).  Its  solution  gives  no  pre- 
cipitate with  sulphate  of  magnesia,  while  a  solution  of  the  carbonate  is  im- 
mediately precipitated. 

Sesquicarbonate  of  Soda  (2NaO,.3C02). — This  carbonate  of  soda  occurs 
native  in  the  Soda  Lakes  of  Hungary;  also  in  Africa,  near  Fezzan,  where 
the  natives  call  it  Trona  ;  it  is  in  hard  striated  crystalline  masses,  not  altered 
by  exposure  to  air  ;  a  productive  soda  lake  also  exists  in  South  America,  at 
Maracaibo. 

Carbonate  op  Soda  and  Potassa  (NaO,C03+KO,C02)  is  obtained  by 
fusing  the  salts  in  single  atomic  equivalents :  the  double  salt  is  much  more 
fusible  than  its  components,  and  is  therefore  conveniently  used  in  many  cases 
of  mineral  analysis  by  fusion,  as  in  the  analysis  of  insoluble  silicates  (page 
304).     When  dissolved  in  water  the  component  carbonates  separate. 

Borate  of  Soda  ;  Borax  ;  Biborate  of  Soda  ;  (NaO,2B03). — This  salt, 
formerly  imported  from  India,  under  the  name  of  Tincal,  is  now  manufac- 
tured by  combining  soda  with  the  native  boracic  acid  procured  from  Tuscany. 
Common  borax  crystallizes  in  transparent  prisms,  slightly  efflorescent.  Its 
taste  is  cooling  and  alkaline  ;  it  has  an  alkaline  reaction  upon  turmeric.  It 
is  soluble  in  12  parts  of  cold,  and  2  of  boiling  water.  When  heated  it  loses 
water  of  crystallization,  and  becomes  a  porous  friable  mass,  called  calcined 
borax.  At  a  red  heat  it  runs  into  a  transparent  glass,  which,  by  exposure 
to  air,  becomes  opaque  and  pulverulent  upon  the  surface.  The  common 
crystallized  borax  is  a  decahydrate  =NaO,2BO3,10HO.  This  salt  is  decom- 
posed by  the  greater  number  of  the  acids.  (See  Boracic  Acid,  page  294.) 
It  is  often  used  as  a  blowpipe  flux  for  vitrifying  metallic  oxides,  and  forming 
beads  of  different  colors  :  violet  with  manganese  ;  green  with  iron,  chromium 
and  copper ;  blue  with  cobalt ;  and  slightly  yellow  with  some  of  the  colorless 
oxides.  In  the  reduction  of  the  metals  by  charcoal,  borax  is  often  useful  as 
forming  a  medium  through  which  the  globules  fall  and  collect  into  a  button, 
being  at  the  same  time  protected  from  the  air.  At  the  potteries  it  is  used 
in  the  glazes  applied  to  the  better  kinds  of  earthenware,  and  to  porcelain. 
Alone,  or  mixed  with  phosphate  of  ammonia  or  soda,  borax  *nay  be  employed 
to  render  muslin,  paper,  wood,  and  other  materials,  to  a  certain  extent  in- 
combustible ;  this  it  does  by  covering  them  with  a  vitrifiable  glaze  by  which 


SILICATES    OF    SODA.  33T 

the  access  of  air  is  prevented.  Borax  is  also  used  in  the  process  of  solder- 
ing ;  when,  for  instance,  two  surfaces  of  cojiper  are  to  be  soldered  together, 
they  are  scraped  or  rubbed  clean,  sprinkled  with  a  mixture  of  powdered 
borax  and  solder-filings,  and  heated  till  the  solder  fuses  so  as  to  alloy  with 
the  copper  and  make  a  perfect  joint :  the  borax  not  only  prevents  the  contact 
of  air,  and  consequent  oxidation  of  the  metals,  but  dissolves  any  oxide  acci- 
dentally formed,  and  so  retains  the  surfaces  in  that  perfectly  clean  state  which 
is  requisite  for  their  union.  An  aqueous  solution  of  borax  dissolves  several 
of  the  resins,  and  some  of  these  solutions,  especially  that  of  lac,  form  good 
vehicles  for  coloring  materials. 

Octahedral  Borax  (NaO,2B03,5HO). — This  salt  contains  5  instead  of 
10  atoms  of  water,  and  is  obtained  by  dissolving  common  borax  in  boiling 
water,  till  the  solution  has  a  specific  gravity  of  1*26  ;  it  is  then  allowed  to 
cool  slowly,  and  between  the  temperatures  of  174°  and  145°  it  deposits 
octahedral  crystals  ;  below  that  temperature,  the  ordinary  prismatic  crystals 
are  formed.  Octahedral  borax  is  harder  than  the  prismatic,  and  is  preferred 
for  brazing  and  soldering. 

• 

Silicates  of  Soda. — The  atomic  constitution  of  these  silicates  is  as  inde- 
finite as  those  of  potassa.  By  the  fusion  of  one  equivalent  of  anhydrous  car- 
bonate of  soda  with  1  of  silica,  53-f  46,  a  silicate  is  formed,  which  when  dis- 
solved in  a  small  quantity  of  water  yields  crystals  of  a  silicate  containing  6 
and  9  atoms  of  water.  When  100  parts  of  silica  are  fused  with  40  of  caustic 
soda,  the  resulting  glass  is  transparent;  but  if  slowly  cooled  exhibits  crystal- 
line points.  When  8  parts  of  dry  carbonate  of  soda,  15  of  fine  white  sand 
or  powdered  flint,  and  1  part  of  powdered  charcoal  are  well  mijfed  and  fused, 
a  glass  is  obtained  which  is  soluble  in  about  6  parts  of  boiling  water  :  this 
solution  has  been  used  to  diminish  the  combustibility  of  wood,  canvas,  and 
similar  materials,  and  more  especially  of  theatrical  scenery  :  it  prevents  its 
burning  with  flame,  by  forming  a  glaze  upon  the  surface.  Silicate  of  soda 
may  also  be  procured  by  decomposing  nitrate  of  soda  at  a  high  temperature 
with  fine  sand.  Wagner  has  suggested  this  as  a  cheap  source  for  procuring 
nitric  acid,  the  silicate  produced  being  a  valuable  commercial  article.  Silicates 
of  soda  always  have  a  greenish  or  bluish  tint,  however  pure  the  materials 
used  in  their  production,  and  this  is  an  obstacle  to  the  substitution  of  soda 
for  potassa  in  certain  kinds  of  glass. 

Manufacture  of  Glass. — Glass  is  a  compound  of  silica  with  potassa  or 
soda,  other  substances,  or  silicates,  more  especially  those  of  lead,  lime,  or 
iron,  being  occasionally  added;  transparency  and  insolubility  in  water  being 
among  its  most  essential  qualities.  It  should  also  resist  the  action  of  other 
solvents,  such  as  acids  and  alkalies,  and  for  many  purposes,  it  should  not 
fuse  or  even  soften  at  a  red  heat.  The  insolubility  of  glass  depends  much 
upon  its  aggregation,  for  if  reduced  to  fine  j)6wder,  it  reddens  turmeric 
paper  when  moistened,  restores  the  blue  color  to  red  litmus,  and  gives  a 
yellow  precipitate  with  arsenio-nitrate  of  silver.  A  portion  of  the  alkali  is 
frequently  abstracted  from  glass  which  has  been  long  exposed  to  the  action 
of  air  and  water.  The  varieties  of  glass  which  contain  oxide  of  lead  are 
readily  discolored  by  sulphuretted  hydrogen,  when  in  powder  and  difl"used  in 
water,  although  they  long  resist  its  action  in  their  ordinary  state.  The  more 
fusible  glasses,  containing  excess  of  alkali,  of  oxide  of  lead,  or  of  lime,  are 
also  apt  to  be  acted  on  by  acids  and  alkalies,  and  are  unfit  for  the  retention 
of  such  solutions.  All  glass  is  more  or  less  disintegrated  by  the  action  of 
water  at  very  high  temperatures. 

As  the  varieties  of  glass  are  mixtures  rather  than  definite  compounds  of 


338  MANUFACTURE    OF    GLASS. 

their  component  silicates,  they  scarcely  admit  of  being  represented  by  for- 
mulae, though  in  some  cases  the  proportion  which  the  oxygen  of  the  bases 
bears  to  that  contained  in  the  silica  may  be  usefully  stated.  The  large  pro- 
portion of  oxide  of  lead  in  flint-glass  gives  it  a  high  refractive  power  and 
brilliancy  when  cut,  but  renders  it  soft,  easily  fusible,  and  liable  to  be  acted 
on  by  many  chemical  agents.  In  plate-glass  the  predominance  of  silicate  of 
soda  gives  a  more  liquid  combination  than  potassa,  and  enables-  it  to  be 
poured  out  of  the  crucible  in  which  it  is  melted,  upon  a  cast-iron  table,  and 
rolled  into  sheets,  which,  after  careful  annealing,  are  ground  to  a  level  sur- 
face with  emery,  and  ultimately  polished  with  colcothar.  Large  quantities 
of  the  waste  and  broken  glass  of  former  operations  are  frequently  melted 
up  (under  the  name  of  cullet)  with  the  materials  in  the  crucible.  The 
remarkable  tenacious  viscidity  of  glass,  when  in  a  fit  state  for  the  operations 
of  the  glass-house,  and  the  facility  with  which  it  is  shaped,  by  blowing, 
moulding,  and  other  manipulations,  into  its  infinitely  various  forms,  can  only 
be  understood  by  personal  inspection. 

The  following  table  will  give  a  notion  of  the  relative  proportions  of  the 
components  of  several  kinds  of  glass  in  common  use,  but  these  vary  to  such 
an  extent  as  not  to  admit  of  being  r^resented  by  any  satisfactory  formulae. 
A  glass  composed  of  borate  and  silicate  of  lead  has  been  used  by  Faraday 
for  some  optical  purposes,  and  the  borosilicate  of  zinc  has  been  similarly 
applied  by  Maez  and  Clemandot. 

Plate.         Crown.        Flint.         Bottle.         Tube.        Optical. 


Silica  . 

.     78 

63 

52 

59 

73 

43 

Potassa 

.       2 

22 

14 

2 

12 

12 

Soda  . 

.     13 

... 

10 

3 

Lime  .  * 

.       5 

a 

... 

20 

11 

"i 

Alumina     . 

.       2 

3 

i 

2 

1 

Oxide  of  lead 

. 

33 

44 

Oxide  of  iron 



"i 

... 

■» '" 

100  100  100  100  100  100 

All  glass  requires  to  be  carefully  annealed — that  is,  suffered  to  cool  very 
slowly — otherwise  it  becomes  liable  to  fly  to  pieces  upon  the  slightest  touch 
of  any  substance  hard  enough  to  scratch  its  surface.  Small  unannealed 
flasks,  blown  from  samples  taken  from  the  pot,  for  the  purpose  of  ascertain- 
ing the  quality  of  the  glass,  and  known  in  the  glass-house  under  the  name 
of  proofs,  will  show  this.  When  a  fragment  of  flint  is  dropped  into  them 
they  immediately  crack  ;  and  if  melted  bottle-glass  be  dropped  into  water, 
so  as  to  form  what  are  called  RuperVs  drops,  the  instant  that  their  thin  end 
is  broken  off  they  crumble  into  powder  with  a  kind  of  explosion.  This 
probably  arises  from  the  unequal  tension  of  the  layers  of  glass  in  consequence 
of  the  sudden  cooling  of  the  exterior,  whilst  the  interior  remains  dilated,  or 
even  red-hot.  When  large  masses  of  glass  are  slowly  cooled,  crystallized 
nodules  are  sometimes  formell,  more  or  less  opaque,  and  imbedded  in  the 
transparent  glass.  These  appear  to  arise  from  the  formation  of  definite 
silicates. 

When  glass,  imbedded  in  sand,  is  heated  up  to  a  point  a  little  below  that 
of  fusion,  and  allowed  to  cool  slowly,  it  is  converted  into  Reaumer's  porce- 
lain :  It  has  become  hard,  white,  opaque,  and  somewhat  less  fusible  ;  changes 
which  have  been  referred  to  the  formation  of  certain  definite  crystallizable 
silicates,  more  especially  those  of  lime  and  alumina.  These  phenomena  of 
devitrification  are  best  shown  with  common  green  bottle  glass.  A  peculiar 
glass  IS  used  for  the  manufacture  of  artificial  gems,  called  strass  or  paste, 
containing  a  large  quantity  of  oxide  of  lead,  and  frequently  borate  of  lead  : 
It  IS  easily  fusible,  highly  refractive,  and  very  soft 


MANUFACTURE    OF    GLASS.  339 

The  art  of  coloring  glass  depends  upon  its  power  of  dissolving  certain 
metals,  metalloids,  or  metallic  oxides.     The  principal  metals  thus  employed 
are,  1.    Gold;  it  imparts  various  shades  of  red  or  pink,  inclining  to  purple, 
but  here  there  is  reason  to  believe  that  the  gold  is  in  the  metallic  state.  2. 
8^7^'er /oxide,  chloride,  or  phosphate  of  silver,  give  a  yellow  color.  3.  Iron, 
The  oxides  of  iron  produce  blue, 'green,  yellow,  or  brown,  dependent  upon 
the  state  of  oxidation  and  quantity.     The  protoxide  gives  various  shades  of 
green  ;  the  peroxide  of  brownish  yellow.     4.  Manganese.     The  protoxide 
leaves  the  glass  colorless,  but  the  peroxide  gives  it  various  tints  of  violet, 
and,  if  added  in  excess,  renders  it  black.     This  oxide  was  formerly  called 
glass  soap,  from  its  property  of  destroying  the  green  tint  communicated  by 
protoxide  of  iron,  derived  from  the  use  of  impure  materials  ;  this  it  effects  by 
converting  the  protoxide  of  iron  into  peroxide,  which,  in  small  proportions, 
does  not  materially  affect  the  color  of  the  glass  ;  whilst  the  peroxide  of  man- 
ganese, losing  oxygen,  becomes  protoxide,  and  in  this  state  is  also  not  inju- 
rious.    A  little  nitre  is  sometimes  used  for  the  same  purpose.     5.    Copper. 
The  protoxide  gives  a  rich  green,  and  the  dioxide  a  ruby  red.     The  glitter- 
ing appearance  of  aventurin  glass  is  due  to  the  dissemination  of  minute  tetra- 
hedral  crystals  of  metallic  copper,  produced  by  the  fusion  of  a  mixture  of 
iron  and  copper  scales  in  the  glass.     This  glass  has  been  hitherto  manufac- 
tured at  Venice,  and  cut  into  ornaments.  It  is  so  called  from  its  resemblance 
to  aventurine  quartz,  which  is  a  variety  of  rock  crystal,  being,  interspersed 
through   it — minute  scaly  crystals  of  golden   mica  which  reflect  light  in 
various  directions.    6.    Cobalt,  in  the  state  of  oxide,  gives  beautiful  blues  of  all 
shades ;  in  large  quantity  black,     t.   Chromium  produces  greens  and  red, 
depending  upon  its  state  of  oxidation.     According  to  Pelouze,  a  beautiful 
aventurine  glass  may  be  made  by  fusing  together  250  parts  of  sand,  100 
parts  of  carbonate  of  soda,  50  parts  of  carbonate  of  lime,  and  40  parts  of 
bichromate  of  potash.    The  resulting  glass,  which  is  very  hard,  contains  from 
6  to  7  per  cent,  of  chromium,  partly  combined  with  the  glass,  giving  to  it  a 
greenish-yellow  color,  and  partly  distributed  through  it  in  brillfant  crystalline 
scales.     8.    Uranium  is  the  source  of  the  peculiar  opalescent  yellowish-green 
glass.    9.   Tin,  in  the  state  of  bioxide  gives  the  varieties  of  opalescent  glass, 
terminating  in  opaque  white  enamel,  in  which  there  is  also  a  little  oxide  of 
of  lead.     An  alloy  of  1  part  of  tin  and  2  of  lead  is  calcined  for  the  produc- 
tion of  the  oxides,  and  these  are  mixed  with  powdered  glass.     When  sur- 
faces are  to  be  enamelled,  this  mixture  is  applied  with  a  brush,  and  then 
fused  by  exposure  to  heat  in  a  muffle.     The  colors  used  in  enamel  painting 
are  derived  from  the   metals  above  enumerated.     A  species  of  enamel  is 
sometimes  applied  to  iron  saucepans  and  other  vessels ;  it  is  a  vitrifiable 
mixture  of  powdered  flint  with  carbonate  of  soda,  borax,  and  Cornish  clay, 
with  a  little  oxide  of  tin  ;  this  is  brushed  over  the  surface,  then  carefully 
dried,  and  heated  in  a  muffle  to  bright  redness;  10.  Arsenic.     Arsenious 
acid  is  much  employed  for  giving  an  opal  tint  to  glass.     This  glass  is  trans- 
lucent, of  a  pale  bluish-white  color,  with  a  reddish  hue  when  viewed  in  cer- 
tain lights.     On  powdering  this   glass,   and  applying   the  usual  tests  for 
arsenic,  the  presence  of  this  substance  may  be  readily  detected.     Arsenious 
acid,  in  small  quantity,  by  peroxidizing  iron,  which  usually  gives  a  green 
tint,  tends  to  render  glass  colorless.     The  metal  arsenic  is  volatilized  in 
this  process  ;  hence  arsenic  is   not  found   in   glass-tubing,  or  in  ordinary 
chemical  glass.   11.  The  Metalloids.  Some  of  these  have  the  property  of  giving 
a  color  to  glass.     Carbon  imparts  various  shades  of  yellow  or  straw  yellow. 
Sulphur  gives  a  yellow  color,  and   Selenium,  in  the  proportion  of  one  per 
cent.,  communicates  to  glass  a  beautiful  orange  tint,  resembling  that  of  some 
varieties  of  topaz  and  zircon-hyacinth.     (Pelouze.) 


340  TESTS    FOR    SODA. 

Sodium  and  Potassium  form  an  alloy  whicli,  if  composed  of  1  part  of 
potassium,  and  3  of  sodium,  remains  fluid  at  32^.  Equal  parts  of  the  metals 
form  a  brittle  crjstallizable  alloy.  When  added  to  a  small  quantity  of  mer- 
cury they  form  a  solid  amalgam,  with  the  production  of  great  heat  and  a 
partial  combustion  of  the  alkaline  metals.^ 

Tests  for  Soda  and  its  Salts — Pure  soda  and  its  carbonates,  like  pure 
potash  and  its  carbonates,  have,  in  solution,  an  alkaline  reaction,  and  pro- 
duce with  a  solution,  of  nitrate  of  silver  similar  precipitates.  The  differ- 
ences between  these  alkalies  are  chiefly  of  a  negative  kind.  Thus  a  solution 
of  soda  gives  no  precipitate  with  a  solution  of  chloride  of  platinum  :  but  the 
platino-chloride  of  sodiurii  possesses  a  property  not  observed  in  the  platino- 
chloride  of  potassium.  Dr.  Andrews  has  found  that  the  sodium  salt  in  the 
minutest  traces  produces  a  brilliant  display  of  prismatic  colors  when  under 
the  action  of  polarized  light,  and  he  has  thus  been  enabled  to  detect  the 
100,000th  of  a  grain  of  soda.  The  potassium  salt  has  no  action  on  polarized 
light.  Soda  and  its  salts  are  not  precipitated  by  picric  or  perchloric  acid. 
When  nelitralized  by  nitric  acid  and  crystallized,  soda  yields  rhombic  plates, 
while,  under  the  same  circumstances,  potassa  yields  long  prisms.  The  essen- 
tial character  of  soda  is  that  in  the  smallest  quantity  it  will  give  a  well- 
marked  yellow  color  to  the  flame  of  alcohol,  either  when  burnt  with  a  small 
portion  of  that  liquid,  or  when  a  minute  film  of  the  alkali,  on  a  fine  platinum 
wire,  is  introduced  into  the  flame  of  a  spirit-lamp.  This  color  is  very  pow- 
erful, and  tends  to  conceal  the  pale  violet  tint  given  by  potassa.  Unless 
the  soda  flame  is  very  intense,  it  will,  however,  be  intercepted  by  blue  glass, 
or  a  diluted  solution  of  indigo  ;  so  that  if  potassa  is  mixed  with  soda,  the 
pale  violet  color  of  the  potassa  flame  only  will  be  seen  through  this  colored 
medium.  It  is  thus  easy  to  determine  the  fact  of  the  admixture  of  their  alka- 
lies when  no  other  chemical  means  are  available  for  this  purpose.  In  a 
colorless  flame  an  intense  yellow  color  is  at  once  produced  by  imponderable 
quantities  of 'sodium.  When  this  colored  flame  is  submitted  to  spectral 
analysis,  the  spectrum  of  sodium  is  characterized  by  a  fine  bright  double  line 
which  is  identical  in  position  with  the  dark  solar  line  called  D.  This  alka- 
line metal  gives  a  monochromatic  light :  all  the  other  colors  are  absorbed, 
and  tUe  spectral  space  is  black.  A  portion  of  sodium-salt  less  than  the 
1-180,000, 000th  of  a  grain  can  be  detected  in  the  atmosphere  by  the  produc- 
tion of  this  line.  Dr.  Roscoe  observes  that  every  substance  which  has  been 
exposed  to  the  air  for  a  moment,  gives  the  soda  line  in  a  colorless  flame. 
The  cleanest  platinum  wire  touched  by  the  finger  removes  sufficient  chloride 
of  sodium  from  the  skin  to  give  the  yellow  color  and  the  yellow  spectral 
line.  Thus  sodium  may  be  detected  in  the  atmosphere  and  in  all  kinds  of 
impalpable  dust.  The  salts  of  soda  are  very  soluble  in  water  ;  they  give  the 
same  negative  results  with  tests  as  the  pure  alkali.  They  are  readily  distin- 
guished by  the  strong  yellow  light  imparted  to  flame. 


LITHIUM.      LITHIA.  341 


CHAPTER    XXV. 

LITHIUM.      CESIUM.      RUBIDIUM.     THALLIUM. 

LITHIUM  (Li  =  t). 

LiTHiA,  which  is  the  oxide  of  this  metal,  was  discovered  by  Arfwedson,  in 
ISIT.  To  obtain  lithium,  its  chloride  may  be  decomposed  by  an  electric 
current.  The  metal  is  reddish-white,  softer  than  lead,  and  admits  of  welding 
and  of  being  pressed  into  wire  :  it  is  the  lightest  known  solid,  its  specific 
gravity  being  0*594,  so  that  it  floats  on  naphtha  ;  it  fuses  at  356°,  but  is  not 
volatile  at  a  red  heat.  Lithium  is  ductile  :  it  may  be  formed  into  wire  by 
strong  compre'ssion  when  in  a  heated  state  through  an  aperture  in  a  close 
metallic  box.  It  decomposes  water  without  combustion,  setting  free  hydro- 
gen. It  burns  when  placed  on  strong  nitric  acid.  It  forms  only  one  oxide. 
When  heated  in  air  it  burns  with  an  intensely  white  light,  forming  lithia. 

LiTHiA  (LiO)  has  only  been  found  in  a  few  minerals ;  and,  by  spectral 
analysis,  in  minute  quantities  in  the  sea  and  many  mineral  waters.  By  this 
delicate  method  of  research,  traces  of  it  have  been  detected  in  the  Thames 
water,  fireclay,  and  a  variety  of  other  substances — Lepidolite,  triphane,  and 
petalite,  are  the  principal  minerals  from  which  it  has  been  obtained,  in  pro- 
portions varying  from  3  to  6  per  cent.  The  mineral,  in  very  fine  powder,  is 
intensely  heated  in  a  covered  platinum  crucible,  with  about  twice  its  weight 
of  lime  for  half  an  hour.  The  resulting  mass  is  then  digested  in  diluted 
hydrochloric  acid,  and  the  whole  evaporated  to  dryness  ;  when  this  residue 
is  dissolved  in  dilute  sulphuric  acid,  and  the  solution  is  treated  with  oxalate 
of  ammonia  to  separate  lime,  and  with  baryta  water  to  separate  sulphuric 
acid,  it  yields,  on  filtration  and  evaporation,  hydrate  of  lithia.. — Hydrate  of 
Lithia  (LiO, HO)  is  less  soluble  in  water  than  potassa  or  soda;  its  solution 
has  an  acrid  taste,  and  a  powerful  alkaline  reaction.  It  is  sparingly  soluble 
in  alcohol.  It  does  not  deliquesce  by  exposure,  but  absorbs  carbonic  acid 
and  becomes  opaque.  At  a  high  temperature  it  attacks  platinum  in  its  pure 
and  carbonated  state,  and  hence  must  be  fused  in  a  silver  crucible. — Chloride 
of  Lithium  (LiCl)  differs  from  the  chlorides  of  potassium  and  sodium,  in 
being  very  deliquescent  and  soluble  in  absolute  alcohol  ;  it  being  decomposed 
when  strongly  heated  in  the  open  air  ;  when  it  loses  chlorine,  absorbs  oxygen, 
and  becomes  alkaline ;  it  being  with  difficulty  crystallizable,  and  in  tinging 
the  flame  of  alcohol  of  a  crimson-red  color. — Nitrate  of  Lithia  (LiO,N05) 
is  a  very  soluble  and  deliquescent  salt :  it  crystallizes  in  rhombic  and  acicular 
prisms,  and  is  dissolved  by  alcohol. — Sulphate  of  Lithia  (LiO,S03).  The 
anhydrous  salt  is  white  and  with  difficulty  fusible,  unless  sulphate  of  lime  is 
present,  when  it  fuses  below  redness  ;  its  taste  is  saline,  but  not  bitter  ;  it 
crystallizes  in  rhombic  prisms,  which  are  slightly  efflorescent  and  soluble  in 
alcohol. — Phosphate  of  Lithia  may  be  obtained  by  adding  phosphoric  acid  to 
sulphate  of  lithia  ;  no  precipitate  is  at  first  formed,  but  upon  adding  excess 
of  ammonia  and  warming  the  liquid  a  white  insoluble  phosphate  of  lithia 
falls.  This  property  enables  us  to  separate  lithia  from  potassa  and  soda. 
The  phosphate  of  lithia  may  be  decomposed  by  dissolving  it  in  acetic  acid, 
and  adding  acetate  of  lead:  acetate  of  lithia  remains  in  solution.  By  heat- 
ing this,  carbonate  of  lithia  may  be  procured. — Carbonate  of  Lithia  (LiO, 


342  CESIUM. 

CO^).  When  a  strong  solution  of  carbonate  of  ammonia  is  added  to  a  con- 
centrated solution  of  sulphate  of  lithia  and  the  mixture  is  heated,  a  white 
precipitate  of  carbonate  is  formed.  It  requires  at  least  100  parts  of  water 
at  60°  for  its  solution,  and  is  insoluble  in  alcohol.  It  is  fusible  at  a  full  red 
heat,  but  does  not  lose  carbonic  acid.  The  aqueous  solution  has  a  strong 
alkaline  reaction.  Carbonate  of  lithia  is  rendered  more  soluble  in  water  by 
carbonic  acid.  Some  Bohemian  mineral  springs  contain  lithia  in  this  state. 
An  artificial  water  of  this  description  has  lately  been  employed  in  medicine 
under  the  name  of  Aerated  lithia  water. 

Tests  for  Lithia  and  its  Salts. — Lithia  is  characterized  by  the  splendid 
crimson-red  color  which  it  imparts  to  flame,  as  well  as  by  the  peculiar  spectrum 
which  the  colored  flame  produces  (p.  62).  The  carbonate  of  lithia  is  less 
soluble  in  water  than  the  carbonates  of  potassa  and  soda  ;  but  much  more 
soluble  than  the  carbonates  of  the  four  alkaline  earths.  1.  A  solution  of  the 
carbonate  is  strongly  alkaline,  and  gives  a  yellowish- white  precipitate  with 
nitrate  of  silver.  2.  It  gives  a  dense  white  precipitate  with  the  salts  of 
baryta,  strontia,  and  lime,  as  well  as  with  the  aqueous  solutions  of  these 
three  alkaline  earths.  3.  It  gives  no  precipitate  with  sulphate  of  magnesia 
until  boiled  ;  and  only  slowly  precipitates  a  solution  of  corrosive  sublimate. 
(In  these  respects  it  resembles  the  bicarbonates  of  potassa  and  soda.)  A 
small  portion  of  the  carbonate  on  platinum  wire  imparts  a  crimson-red  color 
to  the  flame  of  alcohol.  A  concentrated  solution  of  lithia  is  precipitated 
by  solution  of  ammonia ;  but  the  precipitate,  which  is  hydrate  of  lithia,  is 
redissolved  when  heated. 

The  other  salts  of  lithia  possess  these  general  characters.  1.  Carbonate 
of  potassa  will  slowly  give,  with  their  solutions  if  concentrated,  a  precipitate 
of  carbonate  of  lithia.  The  precipitation  is  accelerated  by  heat.  2.  Phos- 
phate of  soda  slowly  precipitates  them  in  the  cold,  but  immediately  when 
heated.  3.  Chloride  of  platinum,  and  diluted  sul|>tiuric  as  well  as  oxalic 
acid,  produce  no  change  in  the  solution.  4.  Ammonia  gives  no  precipitate 
in  a  solution  of  a  salt  of  lithia,  and,  when  diluted,  the  addition  of  phosphate 
of  soda  causes  only  a  slow  precipitation.  If  the  mixture  is  boiled,  a  pre- 
cipitate is  formed  immediately.  5.  The  solubility  of  the  chloride  in  abso- 
lute alcohol,  enables  a  chemist  to  separate  this  base  from  potassa  and  soda. 
6.  The  crimson-red  color  given  to  flame  by  all  the  salts,  is  characteristic  of 
lithia.  This  color  traverses  blue  glass  or  blue  solution  of  indigo.  The  red 
is  sometimes  concealed  by  the  presence  of  soda,  but  the  yellow  of  soda  is 
absorbed  by  the  blue  medium.  The  spectrum  of  lithium  is  characterized  by 
one  bright  red  line  whereby  the  smallest  traces  of  its  salts  may  be  easily 
detected.  Dr.  Roscoe  states  the  six  millionth  part  of  a  grain  of  lithium  may 
thus  be  detected.  Although  lithium  is  a  rare  metal  in  reference  to  quantity, 
and  has  been  hitherto  found  in  only  four  or  five  minerals,  it  is  proved  by 
spectrum  analysis  that  it  is  very  widely  diffused  but  in  minute  quantities. 
Thus  it  has  been  detected  in  almost  all  spring  waters,  in  Artesian  waters 
issuing  from  a  great  depth  in  chalk ;  in  tea,  tobacco,  milk,  and  blood. 

CESIUM  (C8e=133). 

This  alkaline  metal  was  discovered  hy  Bunsen  and  Kirchoff  in  1860,  by  a 
spectral  analysis  of  the  residue  of  the  mineral  water  of  Durckheim  (p.  62). 
A  ton  of  the  water  was  estimated  to  yield  not  more  than  three  grains  of 
chloride  of  caesium.  The  metal  derives  its  name  from  the  Latin  ccssius, 
signifying  grayish  blue,  this  being  the  color  of  the  two  lines  produced  in  its 
spectrum.  It  exists  in  small  quantity  in  the  mineral  water  of  Kreuznaeh, 
forming  not  more  than  l-3,000,000th  part  of  the  solid  contents.  Bunsen 
obtained  about  250  grains  of  the  platinum  salt  of  cassium  from  the  residue 


RUBIDIUM.  343 

of  twenty  tons  of  this  water.  The  residue  of  9000  gallons  of  the  Durckheini 
water  yielded  about  an  ounce  of  the  pure  chloride.  Coesium  was  procured 
in  tlie  state  of  amalgam  with  mercury  by  the  electrolysis  of  the  fused  chlo- 
ride. The  first  step  in  the  process  was  to  separate  from  the  residue  of  the 
water,  the  salts  of  all  other  ali^alies,  excepting  those  of  potassa  and  soda. 
Chloride  of  platinum  was  then  added.  Compounds  of  potassa  and  cassia 
(KCl,PtCla,C8eCl,.PtCla)  were  thrown  down.  The  platino-chloride  of  potas- 
sium was  separated  from  that  of  caesium  by  boiling  distilled  water,  in  which 
the  latter  is  biJt  little  soluble. 

The  metal  coesium  decomposes  water,  setting  free  hydrogen,  and  forming 
a  strongly  alkaline  solution  of  protoxide  of  caesium  (CaeO),  or  cassia.  The 
hydratQ  of  caesia  (CaeO, HO)  is  soluble  in  alcohol,  corrodes  platinum  like 
lithia,  and  is  volatile  at  a  high  temperature.  The  carbonate  is  soluble  in 
water  and  alcohol,  is  highly  alkaline,  deliquescent  in  air,  absorbs  carbonic 
acid,  and  forms  a  bicarbonate  which  crystallizes  in  prisms.  The  nitrate 
and  sulphate  are  anhydrous  crystalline  salts,  soluble  in  water  :  the  latter  forms 
an  alum  with  sulphate  of  alumina.  The  chloride  (CieCl)  crystallizes  in  cubes, 
which  are  deliquescent,  in  which  respect  it  resembles  chloride  of  lithium, 
and  differs  from  the  chlorides  of  potassium,  sodium,  and  rubidium.  It  is 
fusible  and  volatile. 

Caesium  is  always  found  associated  with  rubidium.  It  appears  to  be 
extensively  diffused,  but  exists  only  in  traces  ;  and  probably  but  for  spectral 
analysis,  it  would  have  remained  undetected.  This  is  at  present  the  only 
available  method  of  determining  its  presence  in  the  residues  of  water.  The 
1-70, 000th  part  of  a  grain  of  caesia  may  be  thus  detected. 

RUBIDIUM  (Rb  =  85). 

This  metal  derives  its  names  from  two  intensely  red  lines  which  its  spec- 
trum produces  near  the  extreme  end  of  the  less  refrangible  rays.  It  requires 
about  the  30,000th  of  a  grain  of  the  chloride  to  render  the  lines  visible 
(see  p.  62.)  Rubidium  is  commonly  found  associated  with  caesium,  but 
it  appears  to  be  more  abundant.  Thus,  a  ton  of  the  Durckheim  water 
gave  about  four  grains  of  chloride  of  rubidium.  Bunsen  estimates  the  pro- 
portion of  rubidia  in  the  Durckheim  spring,  at  1-2,000,000  part  of  the 
weight  of  the  water.  Sea-water  contains  1-400,000,  and  the  lepidolite  of 
Moravia  l-2,000th  of  its  weight  of  the  oxide  of  this  metal. 

For  the  separation  of  the  mptal,  about  300  pounds  of  lepidolite  are  em- 
ployed in  one  operation.  The  lithia  is  separated  by  the  usual  process  (p. 
341),  and  the  residue,  concentrated  by  evaporation,  is  precipitated  by  chloride 
of  platinum.  The  platino-chloride  of  potassium  (KCl,PtCl2)  is  separated 
by  successive  quantities  of  hot  water,  by  which  the  rubidium  salt,  like  the 
caesium  salt,  is  not  readily  dissolved.  It  requires  158  times  its  weight  of 
boiling  water  for  solution,  while  the  potassium  salt  requires  only  19  times 
its  weight.  (According  to  Bunsen,  100  parts  of  boiling  water  will  dissolve 
5-18  of  the  potassium  salt,  0*634  of  the  rubidium  salt,  and  0'37V  of  the 
caesium  salt.)  The  platino-chloride  of  rubidium  (RbCl,PtC1.2)  is  decomposed 
by  hydrogen,  and  chloride  of  rubidium  is  obtained.  When  the  chloride  is 
fused  and  submitted  to  electrolysis,  the  metal  is  obtained  at  the  negative  pole. 

Rubidium  is  a  volatile  metal,  and  may  be  obtained  by  distilling  a  mixture 
of  carbonate  of  rubidia  and  carbon.  Calcined  bitartrate  of  rubfdia  yields 
it ;  75  parts  of  this  salt  give  5  of  rubidia.  Rubidium  is  a  white  metal 
having  a  specific  gravity  of  152.  Its  melting  point  is  stated  to  be  as  low 
as  101°.  Like  potassium,  it  decomposes  water  with  great  violence,  and 
burns  when  placed  in  contact  with  it.  Under  these  circumstances,  hydrogen 
is  liberated,  and  an  oxide  is  formed  having  a  powerful  alkaline  reaction 


344  THALLIUM. 

(RbO).  It  is,  according  to  Btinsen,  a  powerful  base,  and  is  more  electro- 
positive than  potassium,  llubidia  forms  a  hydrate  soluble  in  water  and 
alcohol.  Like  hydrate  of  potassa,  it  is  fusible,  and  when  exposed  to  air 
absorbs  water  and  carbonic  acid.  The  carbonate  of  rubidia  (RbO,CO,^,nO) 
is  fusible,  deliquescent,  and  soluble  in  water,  producing  a  strongly  alkaline 
liquid.  It  is  not  soluble  in  absolute  alcohol  ;  and  as  the  carbonate  of  cJBsia 
is  soluble  in  this  liquid,  alcohol  furnishes  a  method  of  separating  the  two 
alkalies.  The  sulphate  and  bisulphate  are  similar  to  those  of  potassa.  The 
chloride  (Rb,Cl),  like  that  of  potassium,  is  colorless  and  crystaflizes  in  cubes: 
it  is  not  deliquescent,  but  it  is  fusible  and  volatile. 

Rubidia  and  csesia  resemble  potassa  in  giving  precipitates  with  chloride 
of  platinum,  which  are  less  soluble  than  the  platino-chloride  of  potassium. 
They  also  give  crystalline  precipitates  with  tartaric  acid,  and  uncrystalline 
precipitates  with  fluosilicic  acid.  These  new  alkalies  are  therefore  liable  to 
be  mistaken  for  potassa.  Irrespective  of  the  ditference  in  the  solubility  of 
the  chlorides,  the  only  certain  method  of  distinguishing  them  is  that  by 
which  they  were  discovered,  namely,  spectral  analysis. 

Rubidium  and  caesium  have  been  found  in  nearly  all  mineral  waters  abound- 
ing in  salts  of  potassa,  soda,  and  lime,  and  only  in  infinitesimal  quantities. 

THALLIUM  (Tl  =  204). 

This  metal,  which  in  some  of  its  properties  resembles  lead,  and  in  others 
silver,  is  here  placed  with  the  alkaline  group,  for  the  following  reasons.  It 
is  rapidly  oxidized  by  exposure  to  air,  forming  a  soluble  oxide  having  strongly 
alkaline  properties.  This  oxide  resembles  potassa  in  taking  carbonic  acid 
from  the  air  and  forming  a  soluble  carbonate,  in  producing  with  chloride  of 
platinum  an  insoluble  platino-chloride,  and  in  forming  an  octahedral  alum 
with  sulphate  of  alumina.  Like  lead,  thallium  gives  a  white  precipitate  with 
hydrochloric  acid  and  alkaline  chlorides,  and  a  brown  or  black  precipitate 
with  sulphuretted  hydrogen  and  alkaline  sulphides.  Like  silver,  it  forms  a 
soluble  and  crystallizable  sulphate  and  an  insoluble  chloride. 

Thallium  was  discovered  by  Mr.  Crookes  in  1861,  and  its  discovery  was 
one  of  the  results  of  spectral  analysis.  Thallium  and  its  salts  have  the 
property  of  producing  a  splendid  bright  monochromatic  green  line  in  the 
spectrum,  from  which  the  metal  has  received  its  name  (6>a>.xta,  a  bud  or  germ), 
the  green  color  being  similar  to  that  of  the  buds  of  leaves  in  spring.  The 
position  of  this  line  corresponds  to  Ba  8  of  Kirchoff.  It  exists  in  small 
proportion,  associated  with  sulphur  in  place  of  arsenic,  in  certain  kinds  of 
pyrites.  Spanish  pyrites  are  a  favorable  source  of  it,  but  even  in  these  it 
forms  no  more  than  one  or  two  grains  in  a  pound. 

The  flue-dust  from  the  combustion  of  pyrites  consists  of  sulphur  containing 
thallium :  the  sulphur  is  burnt  away,  oxide  of  thallium  is  left,  and  the  metal 
is  obtained  from  this  by  the  ordinary  process  of  reduction  by  flux.  Various 
other  sources  of  thallium  have  been  recently  announced.  Mr.  Scott  states 
that  he  has  found  it  in  the  violet  and  red  sands  of  Alum  Bay  to  the  extent 
of  0-3  to  0*4  per  cent.  An  alloy  of  copper,  silver,  and  thallium,  containing 
as  much  as  lY  per  cent,  of  the  latter  metal,  is  stated  to  have  been  found  in 
Norway.  Mr.  Crookes  did  not  find  it  in  any  ore  in  larger  proportion  than 
ten  ounces  to  the  ton. 

Properties. — Thallium  is  a  white  metal  with  the  lustre  of  tin.  It  is  very 
heavy,  having  a  specific  gravity  of  11-9.  It  melts  at  550°  is  volatile  at  a 
full  red  heat,  and  when  strongly  heated  in  oxygen  it  takes  fire  and  burns 
with  a  bright  green  flame.  It  is  one  of  the  most  diamagnetic  bodies  known, 
and  in  electric  conductivity  is  but  little  inferior  to  lead.  It  is  soft,  and  can 
be  easily  drawn  into  wire.     It  produces  a  mark  on  paper  like  lead,  but  it  is 


THALLIUM.  345 

SO  rapidly  oxidized  in  air  that  if  the  mark  is  made  on  paper  stained  with 
turmeric  or  red  litmus,  and  the  part  is  wetted,  it  will  show  a  strong  alkaline 
reaction.  The  metal^does  not  decompose  water,  but  it  is  rapidly  oxidized 
and  tarnished  in  acids,  acquiring  a  dark  incrustation  of  oxide  (TIO).  This 
may  be  dissolved  off  by  water,  especially  if  boiling,  and  the  bright  white 
surface  of  the  metal  will  then  appear.  When  the  solution  takes  place  slowly, 
it  brings  out  a  crystalline  structure.  It  is  ductile  and  can  be  drawn  into 
wire,  but  it  has  no  great  tenacity. 

Thallium  forms  two  oxides,  TIO  and  TIO3.  The  protoxide  Thallia  is 
obtained  by  simple  exposure  of  the  metal  to  the  air,  or  by  the  decomposition 
of  its  salts.  It  resembles  potassa  in  many  of  its  properties.  It  is  soluble  in 
alcohol  and  water.  Its  aqueous  solution  has  an  alkaline  reaction,  and,  like 
potassa,  gives  a  brown  precipitate  with  nitrate  of  silver,  and  a  yellow  precipi- 
tate with  the  arsenio-nitrate.  The  solution  is  not  precipitated  by  carbonate 
of  potassa.  On  exposure  to  air,  it  combines  with  carbonic  acid  and  forms  a 
soluble  carbonate.  This  requires,  however,  25  parts  of  water  for  its  solution. 
The  metal  or  its  oxide  rapidly  deoxidizes  permanganic  acid,  and  destroys 
the  color  of  a  solution  of  permanganate  of  potassa. 

The  sulphate  and  nitrate  of  thallium  are  white  crystal lizable  salts  soluble 
in  water.  Nitric  acid  is  the  best  solvent  of  the  metal,  but  it  decomposes 
and  is  dissolved  by  concentrated  boiling  sulphuric  acid.  The  sulphate  of 
thallium  thus  formed  may  be  obtained  crystallized  in  six-sided  prisms.  It 
combines  with  sulphate  of  alumina  to  form  an  octahedral  alum,  thus  replacing 
potash,  soda,  and  ammonia.  The  chloride  is  not  very  soluble  in  water.  The 
metal  is  precipitated  from  its  solutions  by  magnesium  and  zinc. 

Tests  for  Thallium  and  its  Salts. — A  wire  of  platinum  warmed  and 
drawn  over  the  surface  of  the  metal,  or  dipped  in  a  solution  of  the  oxide  or 
any  of  the  salts,  and  introduced  into  a  colorless  flame,  imparts  to  it  a  brilliant 
bright  green  color.  This  traverses  a  solution  of  indigo  or  blue  glass  of  a 
pale  green  color,  thus  revealing  the  metal  when  mixed  with  potash  or  soda. 
The  green  color  given  to  flame  is  unlike  that  imparted  by  oxide  of  copper, 
boracic  acid  or  a  salt  of  baryta.  The  green  color  given  to  flame  by  thallium 
has  been  hitherto  considered  to  be  monochromatic  in  its  character.  Dr.  Mil- 
ler found,  on  exposing  thallium  to  the  flames  of  burning  hydrogen  and  of  the 
oxyhydrogen  jet,  that  as  the  temperature  increased  in  intensity,  the  brilliancy 
of  the  thallium  green  line  increased  also,  but  no  new  lines  made  their  appear- 
ance. When  the  induction  coil  was  employed,  and  the  sparks  were  examined 
by  the  spectroscope,  besides  the  intense  line  in  the  green,  five  others  were 
observed  :  1,  a  very  faint  one  in  the  orange ;  2,  two  of  nearly  equal  intensity 
in  the  green,  more  refrangible  than  TIO,  with  a  third  much  fainter,  the  three 
lines  in  the  green  being  nearly  equidistant;  there  was  also  a  well-defined  line 
in  the  blue.  When  examined  photographically,  the  spectrum  resembled  those 
of  cadmium  and  zinc  more  than  that  of  lead. 

A  solution  of  any  of  the  salts  has  the  following  reactions :  1.  Chloride  of 
platinum  gives  a  yellowish-colored  precipitate  in  the  most  diluted  solution. 
It  requires  15,585  parts  of  water  to  dissolve  it.  2.  Iodide  of  potassium 
gives  a  yellow  precipitate  which  is  not  dissolved  by  a  solution  of  potassa. 
3.  Chromate  of  potassa  also  gives  a  yellow  precipitate  not  soluble  in  a  solution 
of  potassa,  4.  Sulphuric  acid  does  not  give  a  precipitate,  except  in  a  strong 
solution.  5.  Hydrochloric  acid,  or  an  alkaline  chloride,  throws  down  an 
insoluble  white  chloride  even  in  a  very  diluted  solution.  6.  The  solution  is 
not  precipitated  by  potassa  or  its  carbonate.  T.  Sidphuretted.  hydrogen,  or  an 
alkaline  stdphide,  gives  a  brown  or  black  precipitate  (TIS).  Thallium  is 
slowly  thrown  down  from  its  solutions  in  a  crystalline  state  or  as  a  black 
powder  by  zinc  and  magnesium.     The  platino-chloride,  acidulated  with  sul- 


346  BARIUM,    STRONTIUM,    CALCIUM,    MAGNESIUM. 

phuric  acid  and  treated  with  zinc,  yields  thallium  in  the  form  of  a  black 
powder. 

This  metal  and  its  salts  have  not  yet  been  put  to  any  use.  They  are  at 
present  too  costly.  Experiment  has  shown  that  the  salts  have  a  poisonous 
action  on  animals.  They  produce  griping  pains,  with  trembling  of  the  limbs 
and  a  state  of  paralysis.  Less  than  two  grains  has  sufficed  to  kill  a  dog. 
A  curious  application  has  been  made  of  spectrum  analysis  in  reference  to 
this  substance.  The  presence  of  absorbed  thallium  in  the  body  of  an  animal 
has  been  proved  by  drying  and  burning  a  portion  of  the  liver.  The  mono- 
chromatic green  band  in  the  spectrum  showed  the  presence  of  thallium. 


CHAPTER    XXVI. 

BARIUM,   STRONTIUxM,  CALCIUM,   MAGNESIUM. 

BARIUM  (Ba=69). 

This  metal  was  discovered  in  1808  by  Davy,  who  obtained  it  by  the  voltaic 
decomposition  of  its  oxide.  It  may  also  be  procured  by  passing  potassium 
in  vapor  over  baryta  heated  to  redness  in  an  iron  tube,  or  in  decomposing 
the  fused  chloride  by  an  electric  current.  Barium  is  of  a  gray  color,  and 
rapidly  absorbs  oxygen ;  when  gently  heated,  it  burns  with  a  red  light.  It 
is  not  fusible  at  the  melting  point  of  glass.  Its  sp.  gr.  is  4  5  (Pelouze). 
It  decomposes  water  without  combustion,  evolving  hydrogen,  and  forming 
a  solution  of  baryta ;  its  properties,  however,  have  not  been  accurately 
ascertained. 

Oxide  of  Barium  ;  Baryta  (BaO)  is  obtained  by  exposing  pure  nitrate 
of  baryta  to  a  bright  red  heat  in  a  porcelain  crucible;  some  iron  filings 
facilitate  the  decomposition.  It  acts  upon  platinum,  and  if  a  silver  crucible 
be  employed,  the  heat  required  is  such  as  to  endanger  its  fusion.  Baryta 
may  also  be  obtained  by  subjecting  artificial  carbonate  of  baryta  to  an 
intense  white  heat,  thoroughly  mixed  with  about  10  per  cent,  of  finely- 
powdered  charcoal.  Baryta  is  generally  in  the  form  of  a  porous  mass,  or 
gray  powder,  and,  when  pure,  is  very  difficult  of  fusion.  Its  specific  gravity 
is  about  4,  hence  the  name  Baryta,  as  being  the  heaviest  of  the  substances 
usually  called  earths  (from  jSipvj,  heavy).  It  is  very  poisonous.  It  has  a 
strong  alkaline  taste,  and  reaction  on  vegetable  colors.  It  is  insoluble  in 
alcohol.  It  eagerly  absorbs  water,  heat  is  evolved,  and  a  white  hydrate  is 
formed.  After  long  exposure  to  air  it  becomes  white,  and  is  a  mixture  of 
the  hydrate  and  carbonate. 

Hydrate  op  Baryta  (BaO.HO).— When  pure  baryta  is  sprinkled  with 
water  it  becomes  intensely  hot,  and  crumbles  into  a  bulky  white  powder, 
which  fuses,  but  does  not  give  out  water  at  a  red  heat.  It  dissolves  in  20 
parts  of  cold  and  in  3  of  boiling  water,  forming  a  solution  which  is  a  very 
delicate  test  of  the  presence  of  carbonic  acid,  and  which  speedily  becomes 
covered  with  a  film  of  carbonate  of  baryta  when  exposed  to  air.  A  saturated 
solution  of  baryta  in  hot  water  deposits  hexagonal  prisms  as  it  cools,  con- 
taining 10  equivalents  of  water. 


CHLORIDE    OF    BARIUM.  347 

PERO^tiDE  OF  Barium  (BaOg)  is  obtained  when  dry  oxygen  gas  is  passed 
over  baryta  heated  to  dull  redness  in  a  glass  or  porcelain  tube  :  it  may  also 
be  formed  by  adding  1  part  of  chlorate  of  potassa  to  4  of  baryta,  previously 
heated  to  redness  in  a  platinum  crucible ;  the  oxygen  of  the  chlorate  com- 
bines with  the  baryta,  and,  by  the  action  of  cold  water,  the  remaining 
chloride  of  potassium  may  be  washed  out,  and  a  hydrated  peroxide  of  barium 
remains.  When  the  anhydrous  peroxide,  which  is  of  a  gray  color,  is  put 
into  cold  water,  it  does  not  evolve  heat,  but  becomes  a  white,  pulverulent, 
and  insoluble  hydrate  (BaO^jOHO) ;  but  if  this  is  boiled  in  water,  it  will  give 
out  an  equivalent  of  oxygen,  and  revert  to  the  state  of  protoxide,  which  is 
soluble.  When  peroxide  of  barium  is  heated  in  hydrogen  it  becomes  incan- 
descent, emitting  a  greenish  flame,  and  absorbing  the  gas ;  protohydrate  of 
baryta  is  the  product.  Peroxide  of  barium  is  also  formed  when  dry  air  is 
passed  over  heated  baryta:  the  temperature  required  for  this  absorption  of 
oxygen  is  a  dull  red  heat:  at  a  bright  red  heat  not  only  is  no  oxygen 
absorbed,  but  the  peroxide  is  itself  decomposed,  and  giving  off  1  atom  of 
oxygen,  reverts  to  the  state  of  protoxide,  which  may  thus  be  used  to  absorb 
and  evolve  oxygen  by  turns:  this  has  been  proposed  as  an  economical  source 
of  oxygen,  but  independently  of  the  diEBculty  in  the  due  adjustment  of  the 
heat,  the  capacity  of  baryta  for  absorbing  oxygen  gradually  decreases  by 
repeated  use  (p.  92).  Peroxide  of  barium,  when  treated  with  hydrochloric 
acid,  does  not  evolve  chlorine,  like  peroxide  of  manganese,  but  it  produces 
peroxide  of  hydrogen,  the  barium  combining  with  the  chlorine,  and  being 
replaced  by  hydrogen.  Any  acid  added  to  this  compound,  diffused  in  water, 
produces  peroxide  of  hydrogen.  When  a  current  of  carbonic  acid  is  used, 
the  baryta  is  precipitated  as  carbonate,  and  peroxide  of  hydrogen  is  con- 
tained in  the  liquid. 

Nitrate  of  Baryta  (BaO,N05)  may  be  produced  by  dissolving  the  native 
carbonate  in  dilute  nitric  acid,  evaporating  to  dryness,  redissolving  and 
crystallizing;  or  by  decomposing  a  solution  of  sulphide  of  barium  by  dilate 
nitric  acid.  It  forms  permanent  octahedral  crystals,  which  are  anhydrous, 
and  taste  acrid  and  astringent.  It  is  soluble  in  12  parts  of  cold  and  4  of 
boiling  water.  It  is  insoluble  in  alcohol.  If  a  moderately  strong  iolution 
of  nitrate  of  baryta  is  added  to  nitric  acid,  a  precipitation  of  the  nitrate  of 
baryta  takes  place,  in  consequence  of  the  difficult  solubility  of  the  nitrate  in 
the  dilute  acid ;  in  the  concentrated  acid  the  nitrate  is  insoluble  ;  hence,  in 
using  nitrate  of  baryta  as  a  test  of  the  presence  of  sulphuric  acid  in  nitric 
acid,  the  latter  should  be  considerably  diluted,  lest  the  precipitated  nitrate 
of  baryta  be  mistaken  for  sulphate. 

Chloride  of  Barium  (BaCl). — This  compound  may  be  obtained  by  heat- 
ing baryta  in  chlorine  (in  which  case  oxygen  is  evolved,  to  the  amount  of 
half  a  volume  for  every  volume  of  chlorine  absorbed) ;  or  in  hydrochloric 
acid  gas,  when  it  becomes  red  hot,  and  chloride  of  barium  and  water  are  the 
results.  It  is  generally  formed  by  dissolving  carbonate  of  baryta  in  diluted 
hydrochloric  acid,  evaporating  to  dryness,  and  fusing  the  residue  in  a  covered 
platinum  crucible.  Chloride  of  barium,  after  it  has  been  thus  fused,  is 
translucent  and  of  a  grayish  color  ;  sp.  gr.  3*8  ;  its  taste  is  acrid  ;  it  is  not 
deliquescent,  but  absorbs  moisture  and  becomes  opaque,  increasing  in  weight 
after  a  few  days  to  the  amount  of  13  to  14  per  cent.  ;  when  moistened  it 
evolves  heat :  100  parts  of  water  at  32^  dissolve  between  32  and  33  parts  of 
this  anhydrous  chloride :  it  is  insoluble  in  absolute  alcohol,  but  imparts  a 
pale  greenish-yellow  color  to  its  flame  during  combustion.  Its  aqueous 
solution  yields,  when  evaporated,  flat  four-sided  crystals  =BaCl,2H0,  which 


348  TESTS    FOR    BARYTA    AND    ITS    SALTS. 

effloresce  in  dry  air.     At  212°  the  water  is  expelled,  and  anhydrous  chloride 
remains.     100  parts  of  water  at  60°  dissolve  about  43  parts  of  these  crystals. 

Sulphide  of  Barium  (BaS)  is  formed,  1.  By  passing  sulphuretted  hydro- 
gen over  red-hot  baryta  in  a  coated  glass  or  porcelain  tube,  as  long  as  water 
is  formed;  it  yields  a  gray  granular  compound:  BaO  +  HS=BaS  +  HO. 
2.  By  passing  hydrogen  over  finely- powdered  sulphate  of  baryta  at  a  bright 
red  heat :  BaO,S03  +  4B[=BaS  +  4HO.  3.  By  the  action  of  charcoal  upon 
ignited  sulphate  of  baryta  ;  BaO,S03  +  4C=BaS  +  4CO.  Mix  sulphate  of 
baryta,  in  fine  powder,  into  a  paste,  with  an  equal  volume  of  flour,  place  it 
in  a  covered  crucible,  and  expose  it  to  a  white  heat  for  an  hour  or  two.  On 
pouring  hot  water  on  the  product,  the  sulphide  of  barium  is  dissolved,  and 
may  be  separated  from  undecomposed  sulphate  and  excess  of  charcoal,  by 
filtration.  Sulphide  of  barium  is  readily  soluble  in  hot  water,  and  the  solu- 
tion on  cooling  out  of  the  contact  of  air,  deposits  hydrated  crystals.  By 
exposure  to  air,  it  absorbs  carbonic  acid  and  oxygen,  yielding  carbonate  and 
hyposulphite  of  baryta.  It  dissolves  sulphur,  forming  a  pentasulphide. 
When  its  solution  is  boiled  with  oxide  of  copper  till  it  ceases  to  blacken 
acetate  of  lead,  and  filtered  whilst  hot,  it  yields  on  evaporation,  pure  baryta. 

Sulphate  of  Baryta  (BaOjSOg)  is  an  abundant  natural  product  known 
under  the  name  of  heavy  spar ;  it  is  insoluble  in  water,  hence  the  solutions 
of  baryta  are  accurate  tests  of  the  presence  of  sulphuric  acid  and  the  soluble 
sulphates.  Recently  precipitated  sulphate  of  baryta  is  sometimes  very 
obstinate  in  subsiding  from  water,  and  not  only  long  remains  suspended,  but 
adheres  to  the  glass,  and  even  passes  through  filtering-paper :  heat,  and  a 
little  excess  of  acid,  greatly  facilitate  its  deposition.  It  may  be  heated  to 
redness  without  change,  and  hence  the  filter  containing  it,  in  some  cases  of 
quantitative  analysis,  may  be  conveniently  burned  away ;  but  the  carbon  of 
the  paper  converts  a  minute  portion  of  the  sulphate  into  sulphide.  100 
grains  of  the  incinerated  sulphate  correspond  to  65  63  grains  of  baryta. 

Carbonate  of  Baryta  (BaO,C03). — This  salt  falls  in  the  form  of  a  white 
powder,,  when  the  soluble  salts  of  baryta  are  precipitated  by  carbonate  of 
ammonia.  It  is  so  nearly  insoluble,  that  water  at  60°  only  takes  up  about 
l-4300th  part.  Water  saturated  with  carbonic  acid  dissolves  l-820th.  It 
has  no  alkaline  reaction  on  vegetable  colors.  Native  carbonate  of  Baryta, 
or  Witherite,  is  found  crystalline  and  massive.  Its  density  is  4-33.  It  is 
useful  as  a  source  of  pure  baryta  and  its  salts.  Though  scarcely  soluble  in 
water,  it  is  poisonous,  probably  in  consequence  of  its  solubility  in  the  acids 
of  the  stomach.  It  dissolves  more  sparingly  in  solution  of  carbonic  acid 
than  the  precipitated  carbonate,  and  is  not  so  easily  decomposed.  Sulphate 
and  carbonate  of  baryta  are  largely  employed  for  mixing  with  white  lead, 
although  they  are  far  inferior  to  the  latter  for  the  purposes  of  a  pigment. 
This  practice  of  adulterating  white  lead  appears  to  be  carried  on  to  a  great 
extent,  and  thus  we  find  that  the  minerals  of  baryta  raised  in  1865,  in  the 
United  Kingdom  amounted  to  6768  tons. 

Tests  for  Baryta  and  its  Salts— A  solution  of  baryta  has  an  alkaline 
reaction:  and  it  gives  a  brown  precipitate  with  nitrate  of  silver.  It  differs 
from  the  solutions  of  potassa  and  soda  in  acquiring  a  white  incrustation  (car- 
bonate of  baryta)  on  exposure  to  air.  It  is  immediately  precipitated  as  a 
white  carbonate,  by  a  current  of  carbonic  acid,  or  by  the  addition  of  a  few 
drops  of  a  solution  of  carbonate  or  bicarbonate  of  potassa,  soda,  or  ammonia. 

There  are  two  soluble  barytic  salts,  the  nitrate  and  the  chloride.     They 


NITRATE    OF    STRONTIA.  349 

are  characterized  by  the  following  properties:  1.  The  solution  is  neutral;  2. 
It  gives  a  white  precipitate  with  alkaline  carbonates  and  bicarbonates  ;  3. 
It  is  precipitated  white  by  sulphuric  acid  and  all  soluble  sulphates,  even  by 
the  sulphates  of  lime  and  strontia.  This  precipitate,  sulphate  of  baryta,  is 
insoluble  in  diluted  acids  and  alkalies;  4.  It  gives  a  white  precipitate  with 
fluosilicic  acid  ;  and  5.  A  white  precipitate  with  an  alkaline  hyposulphite; 
6.  It  gives  a  yellowish-white  precipitate  with  a  solution  of  chromate  of  pot- 
assa;  7.  Oxalic  acid  does  not  precipitate  the  solution  of  either  of  these  salts 
unless  they  are  highly  concentrated,  and  then  after  a  time  a  crystalline  pre- 
cipitate of  binoxalate  of  baryta  may  be  formed  ;  8.  When  a  small  portion  of 
the  salt  is  introduced  into  the  flame  of  alcohol,  it  produces  a  pale  greenish- 
yellow  color,  which  when  viewed  through  a  solution  of  indigo,  appears  bluish- 
green.  The  spectrum  produced  by  this  flame  presents  a  variety  of  well- 
marked  colors  (p.  62),  and  is  distinguished  from  all,  excepting  that  of  calcium, 
by  numerous  green  bands. 

In  reference  to  the  insoluble  salts,  the  carbonate  may  be  dissolved  by  nitric 
acid,  and  the  sulphate  converted  into  sulphide  (p.  348),  and  this  compound 
into  chloride  by  hydrochloric  acid.    They  may  then  be  tested. 

Strontium  (Sr=44). 

Strontia  was  first  discovered  in  the  state  of  carbonate  at  Strontian  in  Ar- 
gyleshire,  and  was  supposed  to  be  a  carbonate  of  baryta :  it  was  first  shown 
to  contain  a  peculiar  earth  by  Dr.  Hope,  in  1*792.  It  is  a  substance  of  rare 
occurrence.  The  existence  of  strontium,  as  the  metallic  base  of  the  earth, 
was  first  demonstrated  by  Davy  in  1808.  It  is  a  fixed  metal  of  a  gray  color 
with  a  reddish  reflection.  It  has  been  recently  obtained,  but  in  small  quan- 
tities, by  Bunsen  and  Matthiessen.  The  fused  chloride  was  decomposed  by 
electrolysis,  iron  being  employed  for  the  poles  of  the  battery.  The  strontium 
which  adhered  to  this  metal  was  removed,  and  preserved  in  naphtha,  in  which 
it  could  be  moulded.  It  was  rapidly  oxidized  on  exposure  to  air  ;  it  decom- 
posed water  without  combustion,  setting  free  hydrogen,  and  forming  a  solu- 
ble protoxide.     The  metal  has  a  sp.  gr.  of  2*5,  it  therefore  sinks  in  water. 

Protoxide  of  Strontium. — Strontia  (SrO)  may  be  obtained  from  the 
nitrate,  the  carbonate,  and  the  sulphate  of  strontia,  by  processes  similar  to 
those  directed  in  regard  to  baryta.  It  is  a  grayish-white  porous  substance  : 
its  specific  gravity  is  3  9;  it  is  extremely  infusible,  not  volatile,  has  an  acrid 
taste,  and  an  alkaline  reaction. 

Hydrate  of  Strontia  (SrO, HO). — When  strontia  is  sprinkled  with 
water  it  becomes  heated  and  falls  to  powder,  forming  a  white  hydrate,  which, 
when  subjected  for  a  long  time  to  a  high  temperature,  gradually  becomes 
anhydrous.  It  is  insoluble  in  alcohol.  It  dissolves  in  about  60  parts  of 
water  at  60°.  Boiling  water  dissolves  it  more  abundantly,  and  on  cooling 
deposits  crystals  containing  lOHO. 

Nitrate  of  Strontia  (SrO,N05)  is  obtained  by  processes  similar  to  those 
for  obtaining  nitrate  of  baryta:  it  crystallizes  in  octahedra,  soluble  in  5  parts 
of  water  at  60°,  and  in  half  its  weight  of  boiling  water.  It  is  insoluble  in 
anhydrous  alcohol.  Its  taste  is  pungent  and  cooling.  At  a  red  heat  the 
acid  is  evolved  and  decomposed,  and  strontia  remains.  It  is  used  in  the  red 
fire  employed  at  the  theatres,  which  consists  of  40  parts  of  fused  nitrate  of 
strontia,  13  of  powdered  sulphur,  5  of  chlorate  of  potassa,  and  4  of  sulphide 
of  antimony.    The  chlorate  and  sulphide  should  be  separately  powdered  and 


350  TESTS    FOR    STRONTIA    AND    ITS    SALTS. 

cautiously  mixed  with  the  other  ingredients.  This  mixture,  if  kept  in  quan- 
tity in  a  dry  place,  is  liable  to  spontaneous  combustion.  When  nitrate  of 
strontia  is  linely  powdered  and  mixed  with  alcohol,  it  communicates  a  beau- 
tiful red  tint  to  the  flame. 

Chloride  of  Strontium  (SrCl)  is  obtained  by  dissolving  carbonate  of 
strontia  in  hydrochloric  acid,  evaporating  to  dryness,  and  fusing  the  residue. 
It  is  of  a  gray  color  and  an  acrid  taste;  its  sp.  gr.  is  2-8.  The  aqueous 
solution  of  the  chloride  when  concentrated  furnishes  white  prismatic  crystals, 
which  are  deliquescent.  The  chloride  is  soluble  in  alcohol.  These  proper- 
ties enable  a  chemist  to  distinguish  baryta  from  strontia,  and  to  separate 
the  two  bases  when  in  the  state  of  chloride.  Chloride  of  barium  crystallizes 
in  quadrangular  plates,  which  are  not  deliquescent,  and  are  insoluble  in 
alcohol. 

Sulphate  of  Strontia  (SrO,S03)  is  of  very  sparing  solubility,  1  part 
requiring  3600  of  water.  It  is  distinguished  from  sulphate  of  baryta  by 
being  slowly  soluble  in  solution  of  chloride  of  sodium.  It  is  insoluble  in 
solution  of  sal-ammoniac.  It  is  soluble  in  boiling  sulphuric  acid,  but  falls 
upon  dilution.  When  heated  with  charcoal,  its  acid  is  decomposed,  and 
sulphide  of  strontium  formed.  Native  sulphate  of  strontia  is  sometimes  of  a 
blue  tint,  and  has  hence  been  called  ccelestine.  The  finest  crystallized  speci- 
mens are  accompanied  with  native  sulphur,  from  Sicily. 

Carbonate  of  Strontia  (SrO,C03),  when  artificially  formed,  is  a  white 
powder,  soluble  in  1586  parts  of  hot  water.  Native  Carbonate  of  Strontia^ 
or  Strontianite^  is  a  rare  mineral.  It  has  a  greenish  tint,  and  occurs  in 
radiated  masses,  and  sometimes  in  acicular  and  hexahedral  crystals. 

Tests  for  Strontia  and  its  Salts. — A  solution  of  strontia  resembles 
that  of  baryta  in  alkaline  reaction — in  giving  a  brown  precipitate  with 
nitrate  of  silver,  and  producing  a  white  incrustation  of  carbonate  by  expo- 
sure to  air,  or  on  the  addition  of  a  solution  of  an  alkaline  carbonate.  The 
solutions  of  baryta  and  strontia  may  be  thus  distinguished:  1.  Sulphuric 
acid  gives  a  white  precipitate,  immediately  with  baryta,  slowly  with  strontia. 
2.  Sulphate  of  lime  precipitates  baryta,  but  not  strontia.  3.  Fluosilicic 
acid  precipitates  baryta,  but  not  strontia.  4.  Oxalic  acid  precipitates  both ; 
a  slight  excess  of  the  acid  will  redissolve  oxalate  of  baryta,  but  oxalate  of 
strontia  is  insoluble  in  the  acid. 

The  principal  sohible  salts  are  the  nitrate  and  chloride.  They  are 
neutral.  Like  those  of  baryta,  they  are  precipitated  white  by  alkaline  car- 
bonates and  bicarbonates.  The  difl"erences  are:  1.  Sulphuric  acid  and 
alkaline  sulphates  precipitate  strontia  slowly,  but  baryta  immediately. 
2.  Sulphate  of 'strontia  produces  no  precipitate  in  them.  3.  Fluosilicic 
acid  precipitates  a  concentrated  solution  of  a  salt  of  strontia  very  slowly. 
4.  They  are  not  precipitated  by  an  alkaline  hyposulphite,  or  by  chromate 
of  potassa.  5.  Oxalic  acid  produces  slowly  a  white  granular  precipitate. 
6.  A  salt  of  strontia  gives  to  the  flame  of  alcohol  a  rich  red  color,  which 
traverses  a  stratum  of  solution  of  indigo,  and  appears  of  a  deep  crimson 
tint.  By  spectral  analysis  this  color  is  resolved  into  eight  lines  or  bands- 
red,  orange,  and  blue,  but  there  are  no  green  lines  (p.  61). 

Calcium  (Ca=20). 

The  existence  of  calcium,  as  the  metallic  base  of  lime,  was  first  demon- 
strated by  Davy  in  1808.  Like  strontium,  calcium  has  been  obtained  by 
the  electrolysis  of  its  chloride,  iron  poles  being  employed  with  the  battery. 


OXIDE    OF    CALCIUM.      LIME.  351 

« 

(BuNSEN.)  This  metal  has  a  yellowish  color,  is  harder  than  lead,  malleable, 
fusible  at  a  red  heat,  but  not  volatile,  and  is  only  slowly  oxidized  when 
exposed  to  humid  air.  It  burns  with  scintillations,  producing  a  bright  white 
light  when  heated  in  the  air,  and  it  undergoes  vivid  combustion  in  chlorine, 
and  in  the  vapor  of  bromine,  iodine,  and  sulphur.  Its  specific  gravity  is 
1  '57  ;  it  sinks  in  water,  and  rapidly  decomposes  it  without  combustion, 
hydrogen  being  liberated,  and  lime  (protoxide  of  calcium)  being  dissolved 
by  the  water. 

Oxide  of  Calcium  ;  Lime  ;  QuicUime  (CaO). — Lime  may  be  obtained  in 
a  state  of  considerable  purity  by  exposing  humid  carbonate,  or  nitrate  of 
lime,  to  a  white  heat  for  an  hour,  in  an  open  crucible  (p.  142).  Pure  lime 
is  white,  acrid,  caustic,  and  alkaline  ;  its  specific  gravity  is  3  08.  It  is  infu- 
sible, but  remarkably  promotes  the  fusion  of  some  other  oxides,  and  is, 
therefore,  used  in  several  metallurgic  processes,  as  a  flux.  When  intensely 
heated — as,  for  instance,  by  the  oxyhydrogen  blowpipe — it  is  remarkable  for 
its  luminosity,  and  at  this  very  high  temperature  a  minute  quantity  is  vola- 
tilized (p.  124).  It  is  an  essential  ingredient  in  mortar  and  other  cements. 
Exposed  to  air,  it  absorbs  water  and  then  carbonic  acid,  and,  losing  its 
causticity,  becomes  partially  converted  into  carbonate  of  lime ;  so  that  when 
used  for  agricultural  purposes,  it  should,  generally  speaking,  be  speedily 
ploughed  in,  and  not  left  in  heaps  upon  the  surface  so  as  to  acquire  carbonic 
acid.  In  its  caustic  state,  it  is  most  active  in  the  destruction  of  vermin,  and 
in  effecting  chemical  changes  upon  the  organic  and  inorganic  constituents  of 
the  soil.  Its  powerful  affinity  for  water  renders  it  useful  in  various  cases  of 
dehydration,  as  in  drying  certain  gases,  and  abstracting  water  from  alcohol 
and  some  other  liquids ;  in  the  state  of  hydrate,  or  diffused  through  water 
(cream  and  milk  of  lime),  it  is  also  used  as  an  absorbent  of  carbonic  acid; 
when  perfectly  dry  or  anhydrous  it  does  not  absorb  that  gas. 

Lime-burning. — Although  all  carbonates  of  lime  may,  by  burning,  be 
brought  to  the  state  of  quicklime,  chalk  and  compact  limestone  are  alone 
used  for  this  purpose  in  the  large  way.  The  limekiln  at  present  almost  uni- 
versally employed  in  this  country,  is  a  cup-shaped  concavity,  in  a  solid  mass 
of  masonry,  open  at  top  and  terminated  at  bottom  by  a  grate,  immediately 
above  which  is  an  iron  door.  This  simple  furnace  is  first  charged  with  fuel 
(either  wood,  or  coal  and  cinders),  upon  which  is  afterwards  laid  a  stratum 
about  a  foot  thick,  of  chalk  or  limestone,  broken  into  pieces  not  larger  than 
the  fist ;  to  this  succeeds  a  charge  of  fuel,  and  so  on  alternately,  keeping  the 
kiln  always  full.  The  pieces  of  limestone  descend  towards  the  bottom  of  the 
kiln  in  proportion  as  the  fuel  is  consumed,  being  in  the  meantime  kept  at  a 
pretty  full  red  heat.  At  this  temperature  the  water  and  carbonic  acid  are 
driven  off;  and  by  the  time  the  limestone  arrives  at  the  bottom  of  the  kiln, 
which  happens  in  about  forty-eight  hours,  it  is  rendered  perfectly  caustic. 
The  door  above  the  grate  is  then  opened,  and  the  lime  below  the  next 
descending  stratum  of  fuel  is  raked  out;  the  remaining  contents  of  the  fur- 
nace sink  down,  and  a  fresh  charge  is  laid  on  the  top.  The  compact  lime- 
stone, after  having  undergone  this  process,  though  lighter  and  more  porous 
than  before,  still  retains  its  figure  unaltered;  hence  it  is  readily  separable 
from  the  ashes  of  the  fuel,  and  is  sufficiently  hard  to  be  carried  from  place 
to  place  without  falling  to  pieces. 

Hydrate  of  Lime;  Slaked  Lime;  (CaO, HO). —When  a  small  quantity 
of  water  is  poured  upon  lime,  a  rise  of  temperature  ensues  from  the  solidifi- 
cation and  combination  of  a  portion  of  the  water,  and  a  bulky  white  powder 
is  obtained,  which  is  a  hydrate.     The  rise  of  temperature  is  so  great,  when 


352  CHLORIDE    OF    LIME. 

large  heaps  of  good  lime  are  suddenly  slaked,  as  to  scorch  wood  (p.  145). 
Hydrate  of  lime  may  be  obtained  in  a  crystalline  form,  by  placing  lime-water 
under  the  receiver  of  an  air-pump,  containing  another  vessel  of  sulphuric 
acid.  The  water  is  thus  slowly  evaporated,  and  six-sided  crystals  (CaO,HO) 
are  formed. 

Lime-water. — At  a  temperature  of  60°,  150  parts  of  water  are  required  for 
the  solution  of  one  part  of  lime.  Boiling  water,  however,  does  not  dissolve 
so  large  a  quantity  ;  1  part  of  lime  requiring  1280  parts  of  water  at  212^^  for 
its  solution  ;  at  32°,  1  part  of  lime  is  soluble  in  656  of  water.  When  lime- 
water  is  boiled,  a  portion  of  the  lime  is  therefore  precipitated  in  small  crys- 
talline grains.  Lime-water  is  limpid  and  colorless  ;  its  taste  is  nauseous  and 
alkah'ne,  and  it  has  an  alkaline  reaction  ;  and  although  the  quantity  of  lime 
which  it  contains  is  relatively  small,  its  alkaline  reaction  is  very  marked.  It 
is  usually  prepared  by  pouring  warm  water  upon  powdered  lime,  and  allowing 
the  mixture  to  cool  in  a  close  vessel  ;  the  clear  part  is  then  decanted  from 
the  remaining  undissolved  portion.  When  lime-water  is  exposed  to  the  air, 
a  pellicle  of  carbonate  of  lime  forms  upon  its  surface,  which,  if  broken,  is 
succeeded  by  others,  until  the  whole  of  the  lime  is  thus  separated. 

Chloride  of  Calcium;  Muriate  of  Lime;  (CaCl). — This  compound 
occurs  in  sea-water  and  in  some  saline  springs,  where  it  is  sometimes  accom- 
panied by  traces  of  bromine  and  of  iodine.  It  is  formed  by  dissolving  car- 
bonate of  lime  in  hydrochloric  acid,  evaporating  to  dryness,  and  exposing 
the  residue  to  a  red  heat  in  close  vessels.  It  soon  deliquesces  when  exposed 
to  air,  and  is  frequently  employed,  after  it  has  been  fused,  to  deprive  gases 
of  aqueous  vapor  ;  but  when  thus  used,  its  absorptive  powers  in  regard  to 
some  gases  must  not  be  overlooked.  It  is  also  used  as  a  means  of  depriving 
alcohol,  ether,  and  other  liquids,  of  water,  for  which  purpose  they  are  gene- 
rally distilled  off  dry  chloride  of  calcium.  Its  taste  is  bitter  and  acrid.  One 
part  of  water  at  66°  dissolves  four  parts  of  this  chloride  ;  its  solubility,  how- 
ever, is  greatly  influenced  by  temperature,  for  at  82°  one  part  of  water  will 
not  dissolve  more  than  two  of  the  salt,  and  at  212°  it  takes  up  nearly  any 
quantity.  It  is  copiously  soluble  in  alcohol,  and  heat  is  evolved  during  the 
solution,  which  in  cold  weather  affords  crystals  containing  about  60  per  cent, 
of  alcohol,  instead  of  water  of  crystallization.  By  the  solubility  of  this  chlo- 
ride in  alcohol,  lime  may  be  separated  from  potassa,  soda,  and  baryta. 
While  hydrated  hydrochloric  acid  and  lime  react  upon  each  other  powerfully, 
it  appears  from  the  experiments  of  M.  Gore  that  hydrochloric  acid  gas  lique- 
fied under  great  pressure,  may  be  brought  in  contact  with  caustic  lime 
without  any  chemical  change  taking  place  between  the  hydrogen  acid  and 
the  oxygen  base.  The  solid  porous  lime  was  everywhere  penetrated  by  the 
liquefied  acid,  but  there  was  no  chemical  action  between  them;  thus  affording 
another  proof  that  for  the  neutralization  of  bases  by  acids,  and  the  produc- 
tion of  salts,  water  is  necessary.     {Proc.  JR.  S.,  May,  1865,  p.  213.) 

Chloride  of  Lime;  Hypochlorite  of  Lime. — This  important  bleaching 
material  is  made  by  passing  chlorine  into  chambers  containing  hydrate  of 
lime  in  fine  powder,  by  which  the  gas  is  copiously  absorbed.  It  is  a  dry 
white  powder,  smelling  feebly  of  chlorine,  and  having  an  acrid  taste  ;  it  is 
partially  soluble  in  water,  and  the  solution  is  used  under  the  name  of  bleach- 
ing-liquor.  Exposed  to  air,  it  slowly  evolves  chlorine  and  absorbs  carbonic 
acid  ;  ultimately  some  chloride  of  calcium  is  formed,  and  it  deliquesces. 
When  heated,  it  gives  off  oxygen,  and  chloride  of  calcium  results,  an  expe- 
riment which  shows  the  superior  attraction  of  calcium  for  chlorine  as  com- 
pared with  oxygen,  the  latter  being  expelled  from  the  lime. 


CHLORIDE    OF    LIME.  353 

The  solution  obtained  by  digesting  bleaching-powder  in  distilled  water 
has  a  strong  alkaline  reaction  upon  most  of  the  usual  tests,  and  its  bleaching 
power  is  only  slowly  developed  unless  some  acid  is  added,  when  it  is  power- 
ful and  immediate ;  thus  it  is  that  calico-printers  produce  white  figures  upon 
colored  ground,  by  printing  the  pattern  intended  to  be  brought  out  upon 
the  colored  calico,  in  citric  or  tartaric  acid  thickened  with  starch  or  gum  ; 
the  goods  are  then  rapidly  wound  through  a  properly-adjusted  solution  of 
chloride  of  lime,  and  the  bleaching  power  only  shows  itself  where  the  acid 
pattern  had  been  previously  applied.  In  the  same  way  a  solution  of  the 
chloride  may  be  colored  blue  by  litmns,  or  green  by  red  cabbage,  or  brown 
by  turmeric,  and  on  the  addition  of  a  few  drops  of  acid  the  color  disappears. 
By  exposure  to  air,  the  absorption  of  carbonic  acid  effects  the  same  change  ; 
and  the  evolution  of  that  acid  in  respiration  is  well  shown,  by  tinging  a 
weak  solution  of  chloride  of  lime  blue  by  litmus,  and  then  breathing  through 
it  by  means  of  a  tube,  when  the  blue  color  gradually  disappears. 

The  best  samples  of  commercial  chloride  of  lime  contain  on  an  average 
about  30  per  cent,  of  chlorine  ;  and  when  chlorine  is  passed  over  hydrate  of 
lime  in  an  experiment  upon  the  small  scale,  it  cannot  be  made  to  absorb 
more  than  about  40  per  cent. ;  but  if  hydrate  of  lime  is  diffused  through 
water,  it  will  absorb  its  own  weight  of  chlorine,  and  a  solution  containing  1 
equivalent  of  lime  (or  of  hydrate  of  lime)  and  1  of  chlorine  (which  is  the  true 
atomic  compound)  is  obtained.  In  its  ordinary  state,  bleaching-powder  may 
be  regarded  as  containing  : — 

Chlorine  ...     1         36         32-72 

Hydrate  of  lime      .         .     2        74        67-28 


Bleaching-powder   .         .     1  110  100-00 

When  put  into  water,  1  atom  of  hydrate  of  lime  remains  undissolved,  and 
the  solution  contains  1  atom  of  lime  and  1  of  chlorine  (p.  192).  Some  have 
considered  bleaching-powder  as  containing  a  hypochlorite  of  lime,  and  repre- 
sent its  formation  as  follows:  2CaO-f 2Cl=CaCl  +  CaO,C10.  But  when 
properly  prepared,  it  yields  no  chloride  of  calcium  when  digested  in  alcohol, 
and  it  is  not  deliquescent.  When  used  as  a  bleaching  agent  for  calico,  the 
goods  are  in  the  first  instance  washed,  and  then  boiled  in  a  weak  solution  of 
soda  to  cleanse  them  of  greasy  and  other  impurities  ;  they  are  then  put  into 
a  weak  solution  of  the  chloride  of  lime,  and  afterwards  into  water  slightly 
acidulated  by  sulphuric  acid.  These  operations  are  repeated  if  necessary, 
and  the  process  is  completed  by  thoroughly  washing  the  goods  in  running 
water.  When  employed  as  a  disinfectant,  cloths  soaked  in  a  solution  of  the 
chloride  are  suspended  in  the  apartments,  where  they  slowly  evolve  chlorine 
in  consequence  of  the  action  of  the  carbonic  acid  of  the  air.  Or,  if  a  larger 
and  more  sudden  evolution  of  chlorine  is  required,  dilute  sulphuric  acid  is 
added  to  the  powder  or  its  solution. 

The  quality  of  chloride  of  lime  may  be  determined  either  by  testing  its 
bleaching  power  by  means  of  a  standard  solution  of  indigo,  or  by  determin- 
ing the  quantity  of  protoxide  of  iron  in  acid  solution,  which  is  convertible 
into  peroxide  by  a  given  weight  of  the  powder;  in  this  case,  supposing-  pro- 
tosulphate  of  iron  to  be  used,  07ie  equivalent  of  chlorine  will  convert  two 
equivalents  of  that  salt  into  one  of  persulphate  of  iron.     (Graham.) 

Fluoride  of  Calcium.    Fluor-Spar  (CaF). — This  compound  may  be  pro- 
duced by  saturating  dilute  hydrofluoric  acid  with  carbonate  of  lime,  or  by 
precipitating  a  neutral  salt  of  lime  with  a  soluble  fluoride  :  in  this  case  it, 
forms  a  gelatinous  mass,  the  precipitation  of  which  is  accelerated  by  the 
23 


354  SULPHIDES    OF    CALCIUM. 

addition  of  caustic  ammonia.  Native  fluoride  of  calcium,  or  fluor-spar,  is  a 
mineral  found  in  many  parts  of  the  world,  but  in  great  beauty  and  abundance 
in  England,  and  especially  in  Derbyshire,  where  it  is  commonly  called  blue 
John.  It  occurs  in  cubic  crystals,  which  may  be  cleaved  into  octahedra  and 
tetraheda.  Its  colors  are  various.  Its  specific  gravity  =  3.  It  phospho- 
resces when  exposed  to  heat,  and  at  a  high  red  heat  it  fuses,  and  is  some- 
times used  as  a  flux  for  promoting  the  fusion  of  other  minerals.  It  generally 
occurs  in  veins  :  in  the  Odin  mine  at  Castleton,  it  is  found  in  detached  masses, 
from  an  inch  to  more  than  a  foot  in  diameter  ;  their  structure  is  divergent, 
and  the  colors,  which  are  various,  disposed  in  concentric  bands.  It  is  the 
only  variety  which  admits  of  being  turned  in  the  lathe  into  vases  and 
other  ornamental  articles.  Compact  fluor  is  a  scarce  variety ;  the  finest 
specimens  come  from  the  Hartz.  A  third  variety  is  cldoro2)hane,  so  called 
from  the  beautiful  pale-green  light  which  it  exhibits  when  heated.  The 
nature  of  the  coloring-matter  of  blue  and  green  fluor-spar  is  not  understood: 
it  is  liable  to  fade,  and  the  blue  varieties  become  red  and  brown  by  heat. 
Fluoride  of  calcium  exists  in  small  quantity  in  bone  :  it  has  been  found  in 
coprolites,  and  in  some  fossil  bones,  to  the  extent  of  10  per  cent.  Pure 
fluoride  of  calcium  is  slowly  decomposed  by  cold  sulphuric  acid,  forming 
with  it  a  viscid  mixture.  At  a  temperature  of  abo^t  100°  its  decomposition 
is  rapid,  sulphate  of  lime  is  formed,  and  hydrofluoric  acid  is  evolved.  If  the 
fluor-spar  contain  silica,  sulphuric  acid  immediately  acts  upon  it,  evolving 
white  fumes  of  fluosilicic  acid.  Fused  with  carbonate  of  potassa,  carbonate 
of  lime  and  fluoride  of  potassium  are  produced. 

Nitrate  of  Lime  (CaO,N05). — This  is  a  deliquescent  salt  soluble  in 
one-fourth  its  weight  of  water  at  60°.  It  is  found  in  old  plaster  and  mortar, 
from  the  washing  of  which  nitre  is  procured  by  the  addition  of  carbonate  of 
potassa.  It  sometimes  occurs  in  spring  and  river  water.  It  may  be  crys- 
tallized by  very  low  evaporation.  It  is  soluble  in  alcohol.  When  exposed 
to  heat  it  fuses,  and  on  cooling  concretes  into  a  phosphorescent  substance 
called  Balduin's  phosphorus.  At  high  temperatures  the  acid  is  driven  off, 
and  pure  lime  remains. 

Sulphide  of  Calcium  (CaS)  is  formed  by  passing  sulphuretted  hydrogen 
over  red-hot  lime,  when  water  is  evolved:  CaO  +  HS=CaS-f  HO.  It  is 
also  formed  by  the  action  of  charcoal,  or  of  hydrogen,  upon  sulphate  of  lime 
at  a  red  heat.  It  is  slowly  acted  upon  by  water,  forming  a  colorless  solu- 
tion.    When  freshly  prepared  it  is  phosphorescent  {Canton'' s phosphorus). 

Bisulphide  of  Calcium  (CaS^).— When  sulphur  and  hydrate  of  lime,  in 
about  equal  weights,  are  boiled  together  in  water,  and  the  solution  cooled, 
yellow  prismatic  crystals  form,  which,  after  having  been  dried  in  vacuo,  are 
permanent :  their  taste  is  alkaline  and  sulphurous ;  they  contain  1  atom  of 
calcium,  2  of  sulphur,  and  3  of  water :  when  gently  heated  in  vacuo  they 
become  anhydrous,  and  the  bisulphide  remains.  The  yellow  liquor,  from 
which  the  crystals  are  deposited,  retains  hyposulphite  of  lime  in  solution  : 
6S  +  3CaO=CaO,S302-l-2CaS2.  By  exposure  to  air  it  becomes  colorless,  in 
consequence  of  its  conversion  into  hyposulphite. 

Pentasulphide  of  Calcium  (CaS,).~When  excess  of  sulphur  is  boiled 
in  water  with  quicklime,  a  compound  of  5  atoms  of  sulphur  with  1  of  calcium 
is  formed,  which  is  not  crystallizable :  it  is  soluble  in  alcohol ;  and  when 
its  aqueous  solution  is  evaporated  in  vacuo,  it  leaves  a  yellow  mass  contain- 


SULPHATE    OF    LIME.  355 

ing  about  80  per  cent,  of  sulphur.  By  heat  it  loses  sulphur,  and  becomes 
protosulphide. 

•  Hyposulphite  op  Lime  (CaO.SgOJ. — When  crystals  of  hydrated  bisul- 
phide of  calcium  are  ground  in  a  mortar  with  sulphurous  acid,  it  loses  its  o^or, 
and  when  filtered  it  is  found  to  be  a  solution  of  hyposulphite  of  lime.  By 
passing  sulphurous  acid  through  the  yellow  liquor  obtained  by  boiling  lime 
and  sulphur  in  water,  the  same  product  is  obtained  ;  and  if  the  solution  be 
filtered  and  evaporated,  at  a  temperature  not  exceeding  140°,  it  furnishes 
hexagonal  crystals  (CaO,S302,  +  6HO),  which  at  the  temperature  of  ebul- 
lition are  decomposed  into  sulphite  of  lime  and  sulphur.  The  crystals  are 
little  altered  by  air,  very  soluble  in  water,  and  insoluble  in  alcohol.  This 
salt  is  occasionally  employed  in  photography  as  a  means  of  removing  the 
salts  of  silver  from  drawings,  so  as  to  render  them  permanent  when  exposed 
to  light. 

Sulphite  of  Lime  (CaO,SO„)  is  formed  by  passing  sulphurous  acid  into 
a  mixture  of  lime  and  warm  water.  It  is  a  white  powder  of  a  slightly  sul- 
phurous taste  ;  it  requires  about  800  parts  of  water  at  60°  for  solution  :  it 
is  rendered  soluble  by  excess  of  sulphurous  acid,  and  then  separates  in  hex- 
angular  prisms,  of  difficult  solubility,  efflorescent,  and  passing  into  sulphate 
of  lime  by  exposure  to  air. 

Sulphate  of  Lime  (CaO.SOg)  occurs  native  in  selenite,  gypsum,  and 
plaster-stone.  It  is  formed  artificially  by  decomposing  a  solution  of  a  soluble 
salt  of  lime,  by  sulphuric  acid  or  by  a  soluble  sulphate.  When  slowly 
deposited,  it  forms  silky  crystals  soluble  in  350  parts  of  water.  When  these, 
or  the  native  crystallized  sulphate  (CaO.SOgSHO),  are  exposed  to  a  heat  of 
about  300,  they  lose  20  per  cent,  of  water,  and  fall  into  a  white  powder 
{plaster  of  Paris),  which,  made  into  a  paste  with  water,  soon  solidifies,  and, 
when  in  large  quantity,  with  very  sensible  increase  of  temperature  :  hence 
its  use  in  taking  casts  for  busts,  figures,  and  ornaments  :  it  is  also  the  basis 
of  stucco,  and  scagliola  or  artificial  marble,  which  is  made  by  mixing  plaster 
of  Paris,  colored  in  various  ways,  with  size  and  water;  when  it  has  indurated, 
its  surface  is  polished.  It  is  a  useful  cement  for  joining  substances  which  are 
liable  to  be  exposed  to  heat.  Mixed  with  alum  its  cementing  properties  are 
said  to  be  improved  for  joining  metals  to  glass  and  similar  purposes.  When 
sulphate  of  lime  is  exposed  to  a  red  heat,  but  short  of  its  fusing-point,  it 
loses  this  property  of  recombining  with  water.  The  sp.  gr.  of  anhydrous 
sulphate  of  lime  (artificial)  is  2-927.  It  requires  about  500  parts  of  water 
at  60°,  and  450  parts  at  212°,  for  its  solution.  Like  other  sulphuric  salts, 
it  is  slowly  decomposed  when  its  solution  is  subjected  to  the  action  of  decay- 
ing vegetable  matter,  in  which  case  the  odor  of  sulphuretted  hydrogen 
becomes  apparent.  As  sulphate  of  lime  is  more  soluble  in  water  than  pure 
lime,  sulphuric  acid  affords  no  precipitate  when  added  to  lime-water.  Nearly 
all  spring  and  river  waters  contain  traces  of  this  salt,  and  in  those  waters 
which  are  called  hard  it  is  often  abundant;  it  renders  them  unfit  for  washing 
and  for  culinary  purposes.  At  a  very  high  temperature  sulphate  of  lime  is 
fusible,  but  suffers  no  decomposition ;  heated  with  charcoal  it  is  converted 
into  sulphide  of  calcium.  It  dissolves  in  dilute  nitric  and  hydrochloric  acids, 
and  separates  from  these  solutions  in  silky  crystals.  It  is  decomposed  by  the 
alkaline  carbonates.  Sulphate  of  lime  is  sometimes  employed  as  a  manure, 
and,  when  sprinkled  over  the  land  in  small  quantity,  is  said  to  improve 
certain  soils,  especially  for  the  growth  of  clover :  is  used  for  many  purposes 
in  the  arts. 


356  PHOSPHATE    OF    LIME. 

Native  sulphate  of  lime  occurs  in  various  forms.  The  crystallized  or 
hydrous  variety,  CaO,S03,2HO,  is  called  selenite ;  the  fibrous  and  earthy, 
gypsum;  and  the  granular  or  massive,  alabaster.  The  primitive  form  of 
selenite  is  a  rhomboidal  prism.  The  crystals  are  commonly  transparent,  of 
a  s^cific  gravity  of  2  32,  and  may  be  scratched  by  the  nail.  A  beautiful 
fibrous  variety,  called  satin  gypsum,  is  found  in  Derbyshire,  applicable  to 
ornamental  purposes.  Massive  and  granular  gypsum  is  found  in  the  sand- 
stone accompanying  the  salt-deposits  in  Cheshire.  It  abounds  in  the  strata 
of  Montmartre,  near  Paris.  In  the  Tyrolese,  Swiss,  and  Italian  Alps,  it  is 
found  upon  the  primitive  rocks.  It  is  turned  in  the  lathe,  and  sculptured 
into  a  variety  of  beautiful  forms.  There  is  a  variety  of  sulphate  of  lime 
which  has  been  called  anhydrous  gypsum  or  anhydrite,  in  reference  to  its 
containing  no  water.  It  is  harder  and  denser  than  selenite,  its  specific 
gravity  being  2*96  :  it  sometimes  contains  common  salt,  and  is  then  called 
muriacite.  It  is  rarely  crystallized.  It  has  been  found  in  Derbyshire  and 
Nottinghamshire,  of  a  pale-blue  tint ;  sometimes  it  is  pijik  or  reddish,  and 
often  white.  A  compound  of  sulphate  of  lime  and  sulphate  of  soda  is  found 
in  the  salt  mines  of  New  Castile,  which  mineralogists  have  described  under 
the  name  of  Glauherite,  and  which  may  be  formed  artificially  by  fusing  the 
two  salts. 

Phosphide  of  Calcium  (CaP). — By  passing  the  vapor  of  phosphorus 
over  lime  heated  to  dull  redness,  a  brown  compound  is  produced,  which  de- 
composes water  with  the  evolution  of  phosphuretted  hydrogen,  and  consists 
of  the  phosphide  of  calcium  and  phosphate  of  lime ;  the  oxygen  of  the  lime 
at  this  temperature  converts  a  portion  of  the  phosphorus  into  phosphoric 
acid,  and  the  evolved  calcium  combines  with  another  portion  of  phosphorus 
to  form  phosphide.  In  a  damp  atmosphere  this  substance  crumbles  into  a 
brown  powder,  and  in  this  state  does  not  produce  a  spontaneously  inflamma- 
ble gas  when  put  into  water.  It  is  rapidly  decomposed  by  the  dilute  acids. 
{See  Phosphides  of  Hydrogen,  p.  244.) 

Hypophosphite  of  Lime  (CaO,PO,2HO)  may  be  obtained  by  carefully 
boiling  phosphorus  in  a  thin  cream  of  lime,  filtering  the  solution,  and  pass- 
ing carbonic  acid  through  it,  to  separate  excess  of  lime.  It  is  also  formed 
by  the  action  of  boiling  water  on  phosphide  of  calcium,  and  treating  the 
clear  liquor  in  the  same  way.  The  solution  evaporated  in  vacuo,  furnishes 
rectangular  prismatic  crystals  of  the  hypophosphite,  which  are  nearly 
equally  soluble  in  hot  and  cold  water,  and  quite  insoluble  in  alcohol  :  they 
contain  from  18  to  22  per  cent,  of  water  of  crystallization.  This  salt  is  used 
in  medicine. 

Phosphates  of  Lime. — There  appears  to  be  several  definite  combinations 
of  lime  with  phosphoric  acid,  but  the  following  is  the  most  important. 

Common  Phosphate  of  Lime  ;  Tribasic  Phosphate  of  Lime  ;  Bone 
Phosphate  ;  (3(CaO),POs).— This  salt  occurs  abundantly  in  bone-ash,  and 
is  found  as  a  mineral  product.  On  adding  chloride  of  calcium  to  the  tribasic 
phosphate  of  soda,  a  corresponding  phosphate  of  lime  precipitates.  When 
a  solution  of  bone-earth  in  hydrochloric  or  nitric  acid  is  boiled  to  expel  all 
carbonic  acid,  and  decomposed  by  caustic  ammonia,  the  bone-phosphate 
separates  in  the  form  of  a  bulky  precipitate,  which,  when  perfectly  dried,  is 
white  and  amorphous.  When  bone-phosphate  is  digested  in  dilute  sulphuric 
acid,  it  is  resolved  into  sulphate  of  lime  and  (if  a  sufficiency  of  sulphuric 
acid  be  used)  phosphoric   acid:  3(CaO),P05-f 3S03=3[CaO,SOJ  +  P05. 


CARBONATE    OF    LIME.  351 

If  less  sulpliiiric  acid  be  used,  an  acid  phosphate  of  lime  is  formed.  Hydro- 
chloric and  nitric  acids  readily  dissolve  bone-phosphate.  Acetic  acid,  and 
water  saturated  with  carbonic  acid,  also  dissolve  it.  Caustic  ammonia 
added  to  these  acid  solutions  throws  down  the  original  phosphate.  It  is 
also  slightly  soluble  in  solutions  of  ammoniacal  salts,  and  of  chloride  of 
sodium  ;  and  when  recently  precipitated,  it  is  slightly  soluble  in  water. 
Water  containing  starch  or  gelatine  in  solution,  dissolves  it  somewhat  more 
freely. 

Native  phosphate  of  lime  (bone  phosphate)  occurs  in  apatite,  associated 
with  fluor-spar  its  primitive  form  is  a  six-sided  prism:  it  also  occurs  in  some 
volcanic  products.  Crystallized  apatite  is  found  of  great  beauty  in  Cornwall 
and  Devon,  and  the  massive  varieties  in  Bohemia  and  in  Spain.  This  is  one 
of  the  most  beautiful  of  the  phosphorescent  minerals.  When  fragments  of  it 
are  placed  upon  iron  heated  just  below  redness,  they  emit  a  brilliant  pale 
green  light.  In  these  minerals  the  phosphate  is  generally  associated  with 
fluoride  of  calcium,  the  formula  of  apatite  being  3[3CaO,P05]-fCaP.  The 
substances  known  under  the  name  of  coprolites,  and  which  appear  to  be  the 
excrements  of  fossil  reptiles,  also  abound  in  phosphate  of  lime.  On  the  shore 
at  Lyme  Regis,  and  in  the  lias  of  the  estuary  of  the  Severn,  they  are  singu- 
larly abundant.  They  occur  throughout  the  lias  of  England,  and  in  strata 
of  all  ages  that  contain  the  remains  of  carnivorous  reptiles ;  in  external  form 
they  resemble  oblong  pebbles,  varying  in  size  with  the  cells  of  the  intestines 
which  have  produced  them.  They  contain  fluoride  of  calcium.  Phosphate 
of  lime  occurs  in  small  quantities  in  some  varieties  of  chalk,  and  in  certain 
schists  and  other  rocks.  It  is  present  in  all  fertile  soils,  and  in  the  vegeta- 
bles they  produce,  through  which  it  is  conveyed  to  the  animals  that  feed 
upon  them.  These  facts  bear  importantly  upon  agriculture,  and  give  great 
interest  to  the  economy  of  bone-manure,  and  other  sources  of  the  phosphates. 
Minute  quantities  of  phosphate  of  lime  and  phosphate  of  iron  have  been 
detected  in  the  water  of  the  deep  wells  of  London. 

Carbonate  of  Lime  (CaOjCOJ  is  the  most  abundant  compound  of  this 
alkaline  earth  ;  it  exists  in  river  and  spring  water,  and  consequently  in  the 
ocean,  and  is  an  essential  ingredient  in  fertile  soils.  When  lime-water  is 
exposed  to  air,  it  becomes  gradually  covered  with  an  insoluble  film  of  car- 
bonate of  lime  ;  hence  its  use  as  a  test  of  the  presence  of  carbonic  acid  ;  but 
excess  of  carbonic  acid  redissolves  it,  producing  a  supercarbonate.  It  follows, 
therefore,  that  if  lime-water  be  added,  in  equivalent  proportion,  to  water 
holding  carbonate  of  lime  in  solution  by  excess  of  carbonic  acid,  the  whole 
of  the  lime  may  be  thrown  down  in  the  form  of  an  insoluble  carbonate,  and 
the  water  will  remain  pure.  Carbonate  of  lime  is  also  precipitated  by  the 
carbonated  alkalies,  from  solutions  of  calcareous  salts.  It  is  a  tasteless  white 
powder,  insoluble  in  pure  water,  and  having  no  alkaline  reaction.  Exposed 
for  a  sufficient  time,  in  a  humid  state,  to  the  joint  action  of  a  red  heat  and 
current  of  air,  the  whole  of  the  carbonic  acid  escapes,  to  the  amount  of  44 
per  cent,  and  quick-lime  is  obtained.  Cream  of  lime  gradually  absorbs 
carbonic  acid  to  the  amount  of  half  an  equivalent  when  exposed  to  the  air,  and 
forms  a  definite  compound  of  hydrate  and  carbonate.  It  also  appears,  that 
in  burning  lime,  one-half  of  the  carbonic  acid  escapes  more  easily  than  the 
other,  indicating  the  existence  of  a  dicarbonate=2(CaO),C03. 

Native  carbonate  of  lime  occurs  in  great  abundance  and  in  various  forms. 
The  primitive  form  of  the  crystallized  carbonate  or  calcareous  spar,  is  an  ob- 
tuse rhomboid.  Its  specific  gravity  is  2*72.  It  occurs  in  every  kind  of  rock, 
and  its  secondary  forms  are  more  numerous  than  those  of  any  other  substance. 
What  is  termed  Iceland  spar  is  this  substance  in  its  primitive  form,  and  of 


358  MORTARS  AND  CEMENTS. 

extreme  purity ;  it  is  highly  doubly  refractive  when 'transparent.  Some  of 
the  varieties  are  opaque  or  translucent,  snow-white,  or  tinned  of  different 
hues.  It  is  recognized  by  its  rhomboidal  fracture  and  moderate  hardness, 
being  scratched  by  fluor-spar  ;  before  the  blowpipe  it  loses  carbonic  acid, 
and  becoming  lime,  is  intensely  luminous.  Carbonate  of  lime  sometimes 
forms  stalactites  and  stalagmites,  of  which  some  of  the  caverns  of  Derbyshire 
furnish  magnificent  specimens;  it  is  there  deposited  from  its  solution  in  water 
containing  carbonic  acid,  and  substances  immersed  in  this  water  become 
incrusted  by  carbonate  of  lime  when  the  excess  of  acid  flies  off.  A  fibrous 
carbonate  of  lime,  called  satin-spar,  is  found  in  Cumberland. 

A  peculiar  variety  of  carbonate  of  lime,  originally  found  in  Arragon,  ia 
Spain,  has  been  termed  Arragonite ;  it  often  occurs  in  six-sided  crystals  of  a 
reddish  color,  and  is  harder  than  the  common  carbonate.  There  is  also  an 
acicular  or  fibrous  variety,  found  in  France  and  Germany. 

All  the  varieties  of  marble  and  limestone  consist  essentially  of  carbonate  of 
lime  :  of  these,  white  granular  limestone,  or  primative  marble,  is  most 
esteemed  ;  there  are,  also,  many  colored  varieties  of  extreme  beauty.  The 
most  celebrated  statuary  marble  is  that  of  Paros,  and  of  Mons  Pentelicus, 
near  Athens ;  and  of  Carrara,  or  Luni,  on  the  eastern  coast  of  the  Gulf  of 
Genoa ;  it  is  milk  white  and  less  crystalline  than  the  Parian.  Many  beautiful 
secondary  marbles  for  ornamental  purposes  are  quarried  in  Derbyshire,  and 
especially  the  black  marble.  Westmoreland  and  Devonshire  also  afford 
varieties  of  ornamental  marble ;  and  in  Anglesea,  a  marble  intermixed  with 
green  serpentine  is  found,  little  inferior  in  beauty  to  the  verd  antique.  Among 
the  inferior  limestones,  we  enumerate  many  varieties,  such  as  common  marble  ; 
bituminous  limestone,  abundant  upon  the  Avon,  near  Bristol,  and  known 
under  the  name  of  swinestone,  or  stink-stone,  from  the  peculiar  smell  which 
it  affords  when  rubbed ;  Oolite,  or  Roestone,  of  which  the  houses  of  Bath 
are  built ;  Portland-stone  ;  Pisolite,  or  pea-stone,  consisting  of  small  rounded 
masses  composed  of  concentric  layers,  with  a  grain  of  sand  in  the  centre  ; 
an  lastly,  chalk  and  marl. 

All  these  substances  are  more  or  less  employed  for  ornamental  or  useful 
purposes ;  they  afford  quicklime  when  burned,  and  in  that  state  are  of  great 
importance  in  agriculture,  and  as  ingredients  in  the  cements  used  for 
building. 

Silicates  of  Lime. — There  are  several  native  silicates  of  lime  ;  apophylite 
is  a  hydrated  potassio-silicate,  and  datolite  and  botryolite  are  hydrated  boro- 
silicates  of  lime.  Silicate  of  lime  is  also  an  ingredient  in  many  varieties  of 
glass,  and  in  the  slags  of  iron-furnaces.  Silica  and  lime  have  been  combined 
by  fusion,  but  this  requires  a  very  high  temperature,  and  the  results  "have  not 
been  minutely  examined  ;  the  most  common  silicate  of  lime  is  that  in  which 
the  oxygen  in  the  base  is  to  that  in  the  acid  as  1  :  3  (CaO,Si03). 

Mortars. — Lime  and  silica  are  the  principal  components  of  mortars  and 
cements,  but  common  mortar  is  a  mixture  rather  than  a  compound.  When 
lime,  made  into  a  paste  with  water,  is  applied  to  the  surface  of  porous  stones, 
or  bricks,  the  greater  part  of  the  water  is  absorbed,  and  a  layer  of  hydrated 
lime  adheres  to  the  surface  :  but  this  adhesion  is  much  greater  if  the  lime  be 
previously  mixed  with  two  or  three  parts  of  silicious  sand,  and  more  espe- 
cially if  the  too  rapid  absorption  of  the  water  be  prevented  by  previously 
wetting  the  surface  of  the  brick  or  stone  to  which  the  mixture  is  applied. 
Much  of  the  excellence  of  the  mortar  depends  upon  the  selection  of  the  sand, 
which  should  be  clean,  sharp,  and  rather  coarse-grained,  and  upon  the  quality 
of  the  lime,  and  the  care  with  which  they  are  blended ;  and  it  should  be 
spread  thinly,  and  not  allowed  to  dry  too  rapidly.  Under  these  circum- 
stances it  adheres  firmly  to  the  surfaces  to  which  it  is  applied ;  and  as  it 


TESTS    FOR    LIME    AND    ITS    SALTS.  359 

dries,  it  absorbs  carbonic  acid  when  exposed  to  the  air,  and  a  strong  adhe- 
sion ensues  between  the  lime  and  sand,  in  consequence,  probably,  of  the 
formation  of  a  thin  layer  of  silicate  of  lime  upon  each  grain  of  the  latter. 
But  although  good  mortar  is  excellent  for  all  common  purposes,  it  is  soon 
disintegrated  under  water ;  and  where  buildings  are  to  resist  such  action, 
peculiar  kinds  of  limstones  are  required,  so  as  to  constitute  what  are  called 
hydraulic  cements.  There  are  several  substances  more  or  less  effective  in 
imparting  to  mortar  the  valuable  property  of  hardening  under  water.  Lime- 
stone containing  alumina,  silicate  of  alumina,  carbonate  of  magnesia,  or 
oxide  of  iron,  are  of  this  class  ;  and  consequently,  meagre  limes  as  they  are 
called,  or  limestones  containing  c^a^^,  afford,  when  burned,  an  hydraulic  lime  ; 
and  artificial  mixtures  of  particular  kinds  of  clay,  with  chalk  or  other  lime- 
stones, and  a  proportion  of  sand,  when  duly  calcined  in  properly  constructed 
kilns,  are  employed  for  this  important  manufacture.  Portland  cement  and 
Roman  cement,  are  hydraulic  mortars  or  cements  of  this  description  ;  the 
former,  when  dry,  resembling  Portland  stone  ;  and  the  latter,  being  a  substi- 
tute for  the  cements  containing  puzzuolana,  a  volcanic  product  found  at 
Puzzuoli,  near  Naples,  and  long  celebrated  as  conferring  hydraulic  proper- 
ties on  common  lime  :  it  contains  the  silicates  of  alumina,  lime,  and  soda. 
The  rapidity  with  which  these  cements  harden  in  damp  places,  or  when 
exposed  to  water,  varies  with  their  composition  :  10  or  12  per  cent,  of  clay 
confers  hydraulic  properties,  but  the  cement  requires  about  twenty  days  to 
harden.  With  20  to  30  per  cent,  of  clay,  it  sets  in  two  or  three  days ;  and 
with  25  to  35  per  cent,  it  is  hard  in  a  few  hours.  The  last  mixtures  are 
those  in  common  use  for  facing  buildings,  and  when  the  cement  is  of  good 
quality  and  very  carefully  prepared,  it  is  extremely  durable  and  weather-proof, 
and  admits  of  elaborate  moulding.  A  mixture  of  hydraulic  mortar  with 
coarse  gravel,  or  broken  flints,  is  largely  used  under  the  name  of  concrete, 
for  the  foundations  of  buildings  ;  it  soon  hardens  and  becomes  impermeable 
to  moisture. 

Tests  for  Lime  and  its  Salts. — A  solution  of  litne  (lime-water)  is 
alkaline,  and  has  the  general  properties  of  solutions  of  baryta  and  strontia, 
in  reference  to  the  action  of  nitrate  of  silver,  and  precipitation  by  carbonic 
acid,  or  any  alkaline  carbonate.  It  is  distinguished  from  a  solution  of  baryta, 
it  not  being  precipitated  by  diluted  sulphuric  or  fluosilicic  acids ;  also  by  the 
fact  that  the  precipitate  given  by  oxalic  acid  in  the  solution  is  not  dissolved 
by  an  excess  of  the  acid.  In  the  last-mentioned  character,  lime  resembles 
strontia;  but  the  non-precipitation  of  lime  by  sulphuric  acid  furnishes  a 
sufficient  distinction.  Of  the  three  alkaline-earthy  solutions,  lime-water  is  the 
only  one  which  yields  a  deposit  when  boiled. 

The  soluble  salts  of  lime  are  neutral.  They  are  precipitated — 1.  By 
alkaline  carbonates  and  bicarbonates.  ^  2.  When  the  solutions  are  diluted, 
they  are  not  precipitated  by  sulphuric  acid  or  alkaline  sulphates  ;  3.  They 
are  not  precipitated  by  a  solution  of  sulphate  of  lime,  or  chromate  of  potassa. 
4.  They  are  precipitated  by  oxalic  acid,  and  oxalate  of  ammonia.  The 
oxalate  of  lime  is  insoluble  in  oxalic  and  acetic  acids,  but  is  dissolved  by 
mineral  acids.  The  oxalate  of  ammonia  will  detect  one  part  of  lime  in 
50,000  of  water  ;  it  is  generally  resorted  to  for  the  quantitative  determination 
of  lime.  73  parts  of  oxalate  of  lime  carefully  dried  at  212°,  indicate  28  of 
lime  ;  or  the  oxalate  may  be  converted,  by  a  very  low  red  heat,  into  carbonate 
of  lime,  or  by  a  higher  heat  into  quicklime.  They  are  mostly  soluble  in 
nitric  and  hydrochloric  acids.  5.  When  chloride  of  calcium  is  burnt  in  the 
flame  of  alcohol,  it  imparts  to  it  an  orange-red  color.  This  is  resolved  by 
spectral  analysis  into  green  and  orange  bands  (p.  62),  no  other  alkaline 
metal  giving  a  green  color,  excepting  barium.  There  are  no  blue  rays  in  the 


360  MAGNESIUM. 

calcium  spectrnm.  Those  salts  of  lime  which  are  insohihle  in  water  are 
nearly  decomposed  when  boiled  in  solution  of  carbonate  of  soda  or  potassa, 
and  so  afford  carbonate  of  lime. 

Magnesium  (Mg=12). 

Magnesium  was  first  obtained  by  Davy  in  1808,  by  passing  the  vapor  of 
potassium  over  white-hot  magnesia,  but  was  not  accurately  examined  till 
1830,  when  Bussy  prepared  it  by  heating  anhydrous  chloride  of  magnesium 
•with  sodium.  Bunsen  and  Matthiesen  have  recently  procured  this  metal,  by 
electrolyzing  the  fused  chloride  of  magnesium.  It  is  a  white  ductile  mallea- 
ble metal  resembling  silver  in  appearance,  sometimes  tough  and  at  others 
brittle.  It  is  hard,  but  is  readily  softened  by  heat,  and  in  this  state  it  may 
be  forced  by  hydraulic  pressure  through  a  small  orifice.  It  issues  like  a 
solid  stream  of  silver  into  wire.  It  is  fusible  at  about  1000°  and  volatile  at 
a  still  higher  temperature.  When  strongly  heated  in  air,  it  burns  with  great 
brilliancy,  evolving  an  intensely  white  light,  and  produces  anhydrous  oxide 
of  magnesium,  a  solid  innocent  product.  Its  light  is  almost  insupportable 
when  the  metal  is  burnt  in  oxygen.  The  intensity  of  its  light  is  calculated 
to  be  about  l-225th  of  that  of  the  sun,  but  its  active  power  is  much  greater 
in  proportion,  amounting  according  to  some  experiments  to  l-36th  of  that 
of  the  sun.  Magnesium  burns  when  once  ignited  in  carbonic  acid.  It  also 
burns  when  heated  in  chlorine  and  bromine.  Its  specific  gravity  is  1*74.  It 
is  not  readily  changed  by  dry  air,  but  in  damp  air  it  loses  its  lustre,  being 
slowly  oxidized.  It  may  be  boiled  in  a  solution  of  potash  without  under- 
going any  change,  and  in  this  respect  it  differs  strikingly  from  zinc  and 
aluminum,  both  of  which  decompose  water  in  alkaline  solutions  and  set  free 
hydrogen. 

Magnesium  is  now  manufactured  on  a  large  scale  by  the  reaction  of  sodium 
on  chloride  of  magnesium  and  the  magnesium,  is  afterwards  purified  by  dis- 
tillation. It  may  be  obtained  in  plates  or  wire  at  the  rate  of  about  eight 
shillings  an  ounce.  The  pure  or  distilled  metal  is  now  substituted  for  zinc 
in  toxicological  researches,  and  it  has  the  advantage  over  zinc  that  it  is  never 
likely  to  contain  arsenic  or  antimony.  The  weakest  acid  causes  the  libera- 
tion of  hydrogen  when  added  to  water  in  which  a  bar  of  pure  magne- 
sium has  been  placed  :  hence  dilated  acids  which  are  entirely  free  from  arsenic 
may  be  employed  with  the  magnesium.  Pure  zinc  is  with  difficulty  acted  on 
by  hydrochloric  acid,  while  in  reference  to  magnesium  hydrogen  is  liberated 
from  the  most  diluted  solution  :  M.  Roussin  has  investigated  the  properties 
of  this  metal  and  his  researches  show  that  it  is  an  important  agent  in  the  hands 
of  the  chemist.  If  solutions  of  the  proto  and  persalts  of  iron,  of  zinc,  of  prot- 
oxide of  cobalt,  or  of  nickel  slightly  accidulated  are  brought  in  contact  with 
pure  magnesium,  there  is  an  escape  o/  hydrogen  and  the  different  metals  are 
precipitated  in  a  metallic  state.  These  metals  w^hen  washed  and  dried 
acquire  by  compression  great  metallic  brilliancy,  and  they  entirely  dissolve 
in  acids.  Iron,  cobalt,  and  nickel  so  obtained  are  highly  magnetic  :  zinc 
takes  the  form  of  a  large  spongy  mass  which  the  least  compression  renders 
brilliant.  Magnesium  equally  precipitates  solutions  of  platinum,  gold,  mer- 
cury, lead,  copper,  tin,  cadmium,  bismuth,  and  thallium.  It  does  not  readily 
combine  with  mercury  to  form  an  amalgam,  and  it  does  not  precipitate  alumi- 
num in  a  metallic  state  from  its  acid  solutions.  Arsenic  and  antimony  pass 
off  chiefly  with  the  hydrogen  in  the  form  of  gas.  We  have,  however,  obtained 
deposits  of  metallic  arsenic  on  this  metal  and  subsequently  procured  crystals 
of  arsenious  acid  by  sublimation.  Powdered  magnesium  at  a  high  tempera- 
ture readily  reduces  arsenious  acid  and  gives  a  sublimate  of  metallic  arsenic. 


OXIDE    OF    MAGNESIUM.  361 

The  absence  of  any  ordinary  metal  from  a  solution  may  now  be  inferred  if 
there  is  no  deposit  or  precipitate  on  the  addition  of  magnesium,  or  no  escape 
of  a  metal  in  the  form  of  gas.  As  it  adds  only  a  salt  of  magnesia  to  the 
liquid,  it  does  not  interfere  with  any  further  analysis  that  may  be  required. 

Although  magnesium  does  not  decompose  water  like  the  other  metals  of 
the  allialine  earths,  very  slight  causes  bring  about  its  oxidation  by  the  decora- 
position  of  water.  Thus  a  band  of  platinum-foil  wound  round  a  bar  of 
magnesium  produces  a  slight  electric  current  when  the  metals  are  immersed 
in  pure  water,  but  sufficient  to  cause  the  slow  decomposition  of  the  liquid. 
The  most  diluted  acids  added  to  water  in  which  magnesium  is  placed  causes 
its  decompositionandaliberationofthehydrogen.  A  weak  solution  of  common 
salt,  of  chloride  of  ammonium,  or  of  chloride  of  platinum,  has  the  same  effect. 
As  distilled  magnesium  contains  no  silicon  or  carbon,  the  hydrogen  liberated 
from  water  is  quite  pure.  Magnesium,  unlike  silver,  is  not  tarnished  by  sul- 
phur-vapors, and  its  bright  silvery  lustre  may  be  preserved  by  covering  its 
surface  when  polished,  with  a  thin  layer  of  shell-lac,  in  spirit.  It  is  perhaps 
the  only  metal  which  occurs  in  commerce  in  a  state  of  absolute  purity.  It 
forms  alloys  with  other  metals,  but  they  are  for  the  most  part  very  brittle  and 
have  a  great  tendency  to  tarnish.  The  most  permanent  is  that  which  it 
forms  with  zinc,  but  this  has  not  yet  been  found  applicable  to  any  useful 
purpose.  Mr.  Parkinson  states  that  when  these  two  metals  are  heated 
together  in  air  or  under  a  flux,  the  reaction  is  violent  and  explosive.  He 
found  it  necessary  to  combine  them  under  a  current  of  hydrogen.  The  alloy 
with  bismuth  containing  10  per  cent,  of  magnesium,  was  found  to  have  re- 
markable properties.  Thus  it  deliquesced  when  exposed  to  air,  and  the 
action  of  moist  air  was  so  great  that  the  alloy  hissed  when  held  in  the  hand. 
{Proc.Chern.  Soc.)  Magnesium  does  not  readily  amalgamate  with  mercury, 
but  if,  as  in  the  case  of  zinc,  the  metal  is  shaken  in  a  bottle  with  a  mixture 
of  mercury  and  diluted  sulphuric  acid  an  amalgam  is  formed.  This  amalgam 
decomposes  water  violently  and  nascent  hydrogen  is  copiously  evolved.  It 
is  more  powerful  in  this  respect  than  sodium  amalgam. 

Oxide  of  Magnesium.  Magnesia  (MgO). — This,  which  is  the  only 
compound  of  magnesium  and  oxygen,  is  procured  by  exposing  carbonate  of 
magnesia  to  a  red  heat.  It  forms  a  bulky  white  insipid  powder,  sp.  gr. 
about  3*4,  nearly  insoluble  in  water,  and  having  an  alkaline  reaction  upon 
vegetable  colors.  Notwithstanding  its  great  insolubility,  the  alkalinity  of 
the  oxide  may  be  clearly  proved  by  mixing  a  portion  of  it  with  blue  infusion 
of  cabbage  or  red  litmus.  The  former  is  turned  green,  and  the  blue  of  the 
latter  is  restored.  If  the  oxide  is  diffused  in  water,  and  a  solution  of  sul- 
phuretted hydrogen  added,  followed  by  a  few  drops  of  a  solution  of  nitro- 
prusside  of  sodium,  a  rich  rose-pink  color  is  brought  out.  Its  basic  character 
and  power  of  displacing  metallic  oxides  are  also  proved  by  mixing  it  with  a 
solution  of  nitrate  of  silver  ;  brown  oxide  of  silver  is  separated.  If  arsenio- 
nitrate  of  silver  is  used,  a  yellow  precipitate  of  arsenite  of  silver  is  produced. 
Magnesia  is  almost  infusible,  and  a  mixture  of  lime  and  magnesia  is  scarcely 
more  fusible  than  the  separate  earths.  It  does  not  absorb  carbonic  acid,  or 
moisture,  when  exposed  to  air,  nearly  so  rapidly  as  the  other  alkaline  earths; 
and  scarcely  any  heat  is  produced  by  pouring  water  upon  it,  but  it  is  con- 
verted into  a  hydrate  (MgO, HO).  When  thrown  down  from  its  solutions 
by  potassa,  collected  upon  a  filter,  and  dried  at  212°,  it  still  retains  water; 
but  at  a  temperature  below  redness,  it  becomes  anhydrous.  It  is  insoluble 
in  solutions  of  potassa  and  soda,  but  it  should  be  entirely  dissolved  on  boil- 
ing it  with  diluted  sulphuric  acid.  It  forms  bitter  saline  compounds  with 
the  acids ;  and  is  readily  distinguished  by  the  solubility  and  bitter  taste  of 


362  CHLORIDE    OP    MAGNESIUM. 

its  sulphate.  The  attractions  of  magnesia  for  the  acids  correspond,  in  most 
instances,  closely  with  those  of  ammonia,  which  is  in  some  cases  displaced 
by,  and  in  others  displaces,  magnesia.  Native  hydrate  of  magnesia  is  found 
in  the  serpentine  rocks  of  Hoboken,  in  New  Jersey  ;  and  in  Unst,  one  of  the 
Shetland  Isles.  It  has  a  pale  greenish  hue,  and  a  soft  lamellar  texture ;  sp. 
gr.  2*3.     Sometimes  it  forms  prismatic  crystals. 

Nitrate  of  Magnesia  (MgO,N05). — This  salt  may  be  procured  by 
digesting  carbonate  of  magnesia  in  diluted  nitric  acid,  and  evaporating  to 
produce  crystallization.  It  is  very  deliquescent,  and  is  obtained  crystallized 
with  difficulty,  in  rhomboidal  prisms.  It  is  soluble  in  half  its  weight  of 
water,  and  in  nine  parts  of  alcohol.  It  has  a  cooling  and  bitter  taste.  It  is 
decomposed  at  a  red  heat,  leaving  anhydrous  oxide  of  magnesium.  St.  Clair 
Deville  found  that  when  this  was  mixed  with  water  it  was  converted  into  a 
compact  crystallized  hydrate.  When  made  into  a  paste  with  chalk  or  pow- 
dered marble,  it  soon  became  extremely  hard,  making  a  kind  of  artificial 
marble.  Magnesia  in  this  form  appears  to  have  good  hydraulic  properties. 
Nitrate  of  magnesia  is  occasionally  found  in  the  saline  residue  of  river  or 
spring  water.  Its  presence  causes  a  fallacy  in  determining  the  amount  of 
organic  matter  by  heating  the  residue,  the  nitrate  beginning  to  undergo 
decomposition  and  evolving  nitrous  acid  fumes  below  redness. 

Chloride  of  Magnesium  (MgCl). — Hydrochloric  acid,  when  combined 
with  water,  has  a  powerful  action  on  this  metal.  It  is  rapidly  dissolved  as 
chloride  of  magnesium,  and  hydrogen  is  evolved.  M.  Gore  found,  however, 
that  bright  magnesium,  when  placed  in  liquefied  hydrochloric  acid  gas,  be- 
came dull  without  any  visible  evolution  of  gas.  Magnesium  cannot  separate 
chlorine  from  hydrogen  except  in  the  presence  of  water.  If  magnesia  or  its 
carbonate  is  treated  with  hydrated  hydrochloric  acid,  chloride  of  magnesium 
is  formed  ;  but  on  attempting  to  procure  it  in  the  solid  state,  the  whole  of 
the  hydrochloric  acid  is  expelled  and  magnesia  remains.  The  chloride  may, 
however,  be  obtained  by  dissolving  1  part  of  magnesia  in  hydrochloric  acid, 
and  then  adding  3  parts  of  sal-ammoniac,  and  evaporating  the  mixed  solution 
to  dryness.  The  resulting  double  salt  (NH4,Cb2MgCl)  is  then  decomposed 
by  a  red  heat  in  a  covered  platinum  crucible.  When  the  sal-ammoniac  is 
expelled,  chloride  of  magnesium  remains,  and  concretes  on  cooling ;  it  forms 
a  crystalline  mass,  which  evolves  heat  when  acted  on  by  water.  It  cannot 
be  obtained  by  simply  evaporating  its  aqueous  solution  to  dryness,  for  in 
that  ease  hydrochloric  acid  escapes,  and  magnesia  remains.  This  magnesia 
has  the  same  properties  as  that  obtained  from  the  decomposition  of  the 
nitrate.  When  a  concentrated  solution  of  chloride  of  magnesium  is  exposed 
to  a  cold  atmosphere,  it  yields  prismatic  hydrated  crystals  (MgCl,6H0), 
deliquescent,  very  soluble  in  water  and  alcohol,  and  of  a  bitter  and  biting 
taste.  This  salt  is  found  in  a  few  saline  springs,  and  in  the  water  of  the 
ocean,  forming  a  principal  ingredient  in  the  liquid  which  remains  after  the 
separation  of  sea  salt,  and  which  is  usually  called  bittern  (p.  147).  Chloride 
of  magnesium  is  now  largely  manufactured  from  it  as  a  source  for  procuring 
magnesium.      Bromide  of  magnesium  is  also  a  constituent  of  sea- water. 

Chloride  of  Magnesia.  Hypochlorite  of  Magnesia.— Hhh  compound  may  be 
produced  by  a  process  similar  to  that  employed  for  the  hypochlorite  of  lime. 
It  appears  to  be  a  weaker  base  than  lime,  and  much  more  readily  parts  with 
its  chlorine,  hence  it  has  been  recently  recommended  as  a  more  rapidly 
bleaching  agent  than  the  lime  compound.  Bolley  states  that  it  is  a  good 
bleacher  for  straw. 


SULPHATE    OF    MAGNESIA.  363 

Sulphate  OF  Magnesia  (MgO,SOJ. — The  commercial  demands  for  sul- 
phate of  mag:nesia  are  chiefly  supplied  from  sea-water,  and  from  magnesian 
limestone.  When  sea-water  is  resorted  to,  the  greater  part  of  the  common 
salt  is  first  removed  by  evaporation,  and  the  remaining  bittern,  consisting 
chiefly  of  a  solution  of  chloride  of  magnesium  and  sulphate  of  magnesia,  is 
boiled  down  with  the  addition  of  sulphuric  acid,  or  with  sulphate  of  soda,  by 
either  of  which  the  chloride  is  ultimately  decomposed  and  converted  into 
sulphate.  The  bittern  may  be  also  decomposed  by  hydrate  of  lime,  and  the 
resulting  precipitate  afterwards  treated  by  sulphuric  acid,  by  which  sulphate 
of  magnesia  and  sulphate  of  lime  are  obtained.  When  magnesian  limestone 
is  used  as  a  source  of  sulphate  of  magnesia,  it  is  calcined,  and  reduced  to 
powder  by  sprinkling  it  with  water ;  it  is  then  diffused  through  water,  and 
sulphuric  acid  is  added,  and  as  sulphate  of  magnesia  is  so  much  ftiord  soluble 
than  sulphate  of  lime,  it  is  easily  separated.  According  to  Mr.  Swindells, 
the  manufacture  is  carried  on  on  a  large  scale,  as  the  salt  is  in  great  demand 
for  the  use  of  warp-sizers,  to  add  weight  to  the  cloth  and  thereby  give  a 
false  impression  of  its  value.  The  qy^ntity  thus  disposed  of  in  Manchester 
alone  amounts,  according  to  him,  to  150  tons  per  week,  and  he  sets  down- 
the  annual  production  in  this  country  at  12,000  tons.  The  salt  is  of  course 
removed  in  the  first  washing  of  the  cloth.  It  gives  a  greater  stiffening- pro- 
perty to  starch.     (Chem.  Hews,  April,  186t.) 

A  solution  of  sulphate  of  lime  may  be  also  decomposed  by  carbonate  of 
magnesia,  as  is  sometimes  seen,  where  water  holding  sulphate  of  lime  in  solu- 
tion, filters  through  strata  of  magnesian  limestone.  The  sulphate  of  magnesia 
from  bittern  is  sometimes  preferred  as  a  source  of  magnesia,  or  of  carbonate 
of  magnesia,  in  consequence  of  the  absence  of  iron,  traces  of  which  are  always 
discoverable  in  the  sulphate  obtained  from  magnesian  limestone  ;  but  as  the 
latter  is  free  from  chloride  of  magnesium,  and  consequently  not  deliquescent, 
and  may  be  obtained  nearly  pure,  it  is  generally  preferred  for  medicinal  use. 

There  are  some  saline  springs,  or  mineral  waters,  in  which  sulphate  of 
magnesia  is  the  leading  ingredient,  as  those  of  Seidlitz,  Seydschutz,  Egra, 
and  formerly  those  of  Epsom  in  Surrey,  whence  the  name  of  Epsom  salt ;  it 
is  also  largely  obtained  in  some  alum  works.  It  not  unfrequently  occurs  as 
a  fine  capillary  incrustation  upon  the  damp  walls  of  cellars  and  new  buildings. 
It  has  been  found  native,  constituting  the  hair  salt  of  mineralogists.  It 
appears  to  be  produced,  in  some  springs,  by  a  reaction  of  sulphate  of  lime 
in  the  water,  on  carbonate  of  magnesia  in  the  soil. 

Crystallized  sulphate  of  magnesia  (MgOjSOg.THO)  forms,  at  ordinary 
temperatures,  four-sided  prisms  with  reversed  dihedral  summits ;  or  four- 
sided  pyramids.  When  the  crystals  are  produced  at  about  70°  to  80°,  they 
contain  6H0  :  at  32°  they  are  large  and  contain  12 HO.  Their  density  is 
1*7.  Exposed  to  air,  the  salt  has,  when  pure,  a  slight  tendency  to  efflores- 
cence, but  the  salt  of  commerce  is  often  deliquescent  from  the  presence  of 
chloride  of  magnesium.  Its  taste  is  saline  and  bitter.  The  crystals  are 
soluble  in  about  their  own  weight  of  water  at  60°,  and  in  three-fourths  their 
weight  of  boiling  water.  When  exposed  to  heat,  they  readily  lose  six  equiva- 
lents of  water,  but  retain  one  equivalent,  up  to  500.  At  a  red  heat  this 
salt  becomes  anhydrous,  and  at  a  higher  temperature  it  runs  into  a  white 
enamel.  The  anhydrous  salt  regains  water  from  the  atmosphere,  and  when 
sprinkled  with  water  evolves  much  heat.  The  aqueous  solution  of  sulphate 
of  magnesia  furnishes  a  precipitate  of  hydrated  carbonate,  upon  the  additioQ 
of  carbonate  of  potassa,  or  of  soda  ;  but  carbonate  of  ammonia  does  not 
even  render  it  turbid,  unless  heat  be  applied,  in  which  case  a  precipitate  of 
hydrated  carbonate  is  also  thrown  down.  The  alkaline  bicarbonates  occa- 
sion no  precipitate  when  added  to  a  cold  solution  of  sulphate  of  magnesia, 


364  CARBONATE    OP    MAGNESIA. 

but  after  some  hours  crystals  of  hydrated  carbonate  of  magnesia  are  de- 
posited. 

Sulphate  of  magnesia  forms  compound  sulphates  with  the  sulphates  of 
potash,  soda,  and  ammonia. 

Phosphates  of  Magnesia.  Trihasic  phosphate  of  magnesia  and  water 
(2(MgO)HO,P05-f  14:H0). — This  phosphate  is  formed  by  mixing  a  solu- 
tion of  two  parts  of  crystallized  sulphate  of  magnesia  in  32  of  water,  with 
a  solution  of  three  parts  of  common  crystallized  phosphate  of  soda  in  32  of 
water  :  after  twenty-four  hours,  acicular  crystals  are  deposited,  having  the 
above  formula.  They  effloresce  in  the  air,  and  are  sparingly  soluble  in 
water,  but  readily  soluble  in  dilute  acids.  At  a  red  heat  this  salt  becomes 
a  'pyrophospiiate=^{M.gQ)VOr. 

Phosphate  of  Ammonia  and  Magnesia  (2(MgO)NHp,P05+12HO). — 
This  salt,  formerly  designated  triple  phosphate,  is  produced  when  ammonia, 
or  an  ammoniacal  salt,  is  added  to  a  mixture  of  common  phosphate  of  soda 
with  any  magnesian  salt.  Thus  on  adding  ammonia  or  carbonate  of  ammonia 
to  a  mixed  solution  of  phosphate  of  soda,  and  sulphate  of  magnesia,  the 
ammonia-magnesian  phosphate  falls  in  the  form  of  a  white  granular  precipi- 
tate, insoluble  in  the  liquid  from  which  it  is  thrown  down,  but  sparingly 
soluble  in  pure  water,  so  that  it  cannot  be  washed  upon  the  filter  without 
loss.  It  is  readily  soluble  in  the  greater  number  of  diluted  acids.  If  bicar- 
bonate of  ammonia  is  used  in  its  formation,  it  falls  slowly,  but  its  appearance 
is  accelerated  by  drawing  lines  with  a  glass  rod  upon  the  surface  of  the  glass 
or  basin  containing  the  mixed  solutions,  when  the  double  phosphate  pre- 
sently appears  upon  those  lines.  When  this  phosphate  is  heated,  it  loses 
water  and  ammonia,  and  at  a  red  heat  glows  like  tinder,  and  leaves  a  phos- 
phate of  magnesia  =2MgO,PO-,  containing  therefore  35't  per  cent,  of  mag- 
nesia. It  is  often  resorted  to  for  the  determination  or  the  presence,  and  of 
the  quantity  of  magnesia. 

This  salt  is  frequently  deposited  from  urine,  in  the  form  of  white  sand,  or 
as  a  superficial  crystalline  film,  especially  in  cases  where  the  natural  acidity 
of  the  urine  is  diminished  by  diet,  medicine,  or  morbid  action,  constituting 
what  has  been  termed  the  phosphatic  diathesis ;  it  frequently  forms  urinary 
calculi  ;  and  it  occurs  in  intestinal  concretions.  The  presence  of  phosphate 
of  magnesia  in  the  husk  of  grain,  in  the  potato,  and  other  plants,  is  im- 
portant to  the  agriculturist,  and  shows  why  phosphoric  acid  and  magnesia 
are  contained  in  fertile  soils :  its  existence  in  urine,  and  almost  all  animal 
manures,  contributes  therefore  to  their  efiBcacy  :  it  has  been  said  especially  to 
promote  the  growth  of  potatoes.  It  may  be  detected,  in  considerable  quan- 
tity, in  good  malt  liquor. 

Carbonate  op  Magnesia.— This  term  is  applied  to  the  precipitate 
obtained  by  adding  carbonate  of  soda  to  a  solution  of  sulphate  of  magnesia, 
and  edulcorating  and  drying  it :  it  is  generally  obtained  from  boiling  solu- 
tions, and  great  attention  should  be  paid  to  the  purity  of  the  water  employed 
m  washing  the  precipitate,  and  to  the  method  of  drying  it.  It  usually  con- 
tains from  40  to  43  per  cent,  of  magnesia,  36  to  37  of  carbonic  acid,  and 
from  20  to  22  of  water  ;  so  that  it  may  be  regarded  as  =5MgO,4C02,6HO  : 
or  4  atoms  of  monohydrated  carbonate,  in  combination  with  1  atom  of  bin- 
hydrate  of  magnesia.  A  light  and  a  heavy  carbonate  of  magnesia  are  pre- 
pared for  pharmaceutical  use,  dependent  upon  the  strength  and  temperature 
of  the  solutions  from  which  they  are  precipitated  :  if  these  be  dilute,  it  is 
light  and  bulky ;  if  more  concentrated,  the  product  is  more  dense.     When 


BORATES    OF    MAGNESIA.      SILICATES    OF    MAGNESIA.  365 

a  current  of  carbonic  acid  is  passed  through  a  mixture  of  water  and  car- 
bonate of  magnesia,  under  pressure,  a  clear  solution  is  obtained,  which  has  a 
bitter  taste,  and  which,  when  surcharged  with  carbonic  acid,  affords  a  useful 
medicinal  preparation  ;  but  a  crystallized  hicarhonate  of  magnesia  cannot  be 
obtained.  When  magnesia  is  precipitated  by  carbonate  of  soda,  a  portion  of 
a  double  soda  salt  is  formed,  unless  the  liquid  is  boiled.  An  excess  of  sul- 
phate of  magnesia  easily  dissolves  the  precipitated  carbonate. 

There  is  a  carjbonate  of  lime  and  magnesia  in  the  mineral  known  under  the 
name  of  hitter  spar;  it  consists  of  one  atom  of  each  of  its  component  car- 
bonates. The  mineral  called  Dolomite  or  magnesian  limestone  is  similarly 
constituted,  being  MgO,C03+CaOC02.  There  is  a  band  of  this  mineral 
extending  from  Sunderland  to  Nottingham,  a  distance  of  about  ninety  miles. 
It  is  of  various  shades  of  ochre  or  light  brown  color,  owing  to  the  presence 
of  oxide  of  iron,  and  in  some  districts  it  is  hard,  in  others  soft.  The  hard 
variety  forms  a  good  building  stone.  This  mineral  is  the  principal  source 
of  magnesia  and  magnesian  compounds.  When  calcined  at  a  low  red  heat, 
and  made  into  a  paste,  it  is  said  to  form  under  water  a  stone  of  extraordinary 
hardness.  It  has  long  been  known  to  produce  a  good  hydraulic  cement.  If 
calcined  at  too  high  a  temperature,  its  hydraulicity  is  destroyed.  The  cal- 
cined mineral  should  be  very  finely  ground  to  act  as  a  cement.  Dr.  Calvert 
states  from  his  experiments  that  the  strength  of  the  cement  is  in  proportion 
to  the  amount  of  magnesia  present. 

Native  Carbonate  of  Magnesia  has  been  found  in  Piedmont  and  Moravia, 
and  at  Hoboken,  in  North  America,  in  veins  in  a  serpentine  rock,  accom- 
panying the  native  hydrate.  A  variety  of  native  carbonate  of  magnesia  has 
also  been  brought  from  India. 

Some  of  the  magnesian  limestones  are  well  adapted  for  rough  sculpture, 
and  building  materials ;  but  when  porous,  or  granular,  they  are  subject  to 
decay,  especially  in  a  London  atmosphere,  where  the  rain  always  brings  down 
some  sulphate  of  ammonia,  a  salt  which  acts  on  the  magnesian  limestone, 
forming  carbonate  of  ammonia,  and  sulphate  of  magnesia  and  lime  :  these 
sulphates,  by  crystallizing  in  the  pores  of  the  stone,  tend  to  its  gradual  dis- 
integration. It  has  been  attempted  to  check  this  crumbling,  by  washing  the 
surface  first  with  a  solution  of  silicate  of  soda,  and  then  with  chloride  of 
calcium,  so  as  to  form  an  insoluble  silicate  of  lime  in  the  pores  of  the  stone, 
which  tends  to  cement  and  indurate  it,  and  trials  of  this  kind  are  now  being 
made  at  the  Palace  of  Westminster  :  how  far  it  may  be  possible  to  arrest 
the  decay  unfortunately  going  on  in  many  parts  of  that  building  remains  to 
be  proved. 

Borates  op  Magnesia. — Several  of  these  salts  have  been  described,  but 
the  only  one  of  interest  is  Boracite.  It  is  found  in  Holstein.  It  sometimes 
contains  lime.  Its  sp.  gr.  is  2-95:  it  is  with  difficulty  fusible  before  the 
blowpipe,  insoluble  in  water,  and  slowly  soluble  in  acids.  It  consists  of  3 
atoms  of  magnesia  combined  with  4  of  boracic  acid.  Sulphate  of  magnesia 
does  not  give  a  precipitate  with  borax  until  the  mixture  is  boiled. 

Silicates  of  Magnesia. — These  compounds  are  difficult  of  fusion,  but 
become  less  so  by  the  addition  of  silicate  of  lime  :  the  neutral  silicate,  MgO, 
SiOg,  may  be  melted  in  a  blast-furnace.  Native  silicates  of  magnesia  are 
abundant :  the  varieties  of  serpentine  are  silicates  combined  with  hydrates  of 
magnesia.  7a/c,  steatite,  soap-stone,  French-chalk,  and  meerschaum,  are  also 
magnesian  silicates.  Viennese  meerschaum  is  an  artificial  compound  pre- 
pared by  mixing  100  parts  of  silic.ate  of  soda  with  60  parts  of  carbonate  of 
magnesia  and  80  parts  of  native  meerschaum   or  of  pure  alumina.     The 


366  TESTS    FOR    MAGNESIA    AND    ITS    SALTS. 

mixture  is  finely  powdered  and  sifted,  mixed  with  water,  boiled  for  ten 
minutes,  and  then  poured  into  moulds  from  which  the  water  can  easily  drain 
away.  Jade,  so  extensively  used  for  ornamental  purposes  by  the  Chinese,  is 
a  silicate  of  magnesia  and  lime.  Olivine,  or  chrysolite,  and  peridot,  found  in 
igneous  rocks,  and  occasionally  accompanying  meteoric  iron,  is  a  silicate  of 
magnesia  and  iron.  Many  other  double  magnesian  silicates  are  common 
mineral  products. 

Tests  for  Magnesia  and  its  Salts. — The  oxide  of  magnesium,  or  mag- 
nesia, is  distinguished  from  the  other  alkalies  and  alkaline  earths,  by  its 
insolubility  in  water.  With  this  exception,  it  has  the  usual  properties  of  an 
alkali  in  its  action  on  vegetable  colors,  and  on  a  solution  of  nitrate  of  silver. 
It  is  dissolved  by  acids,  forming  the  salts  of  magnesia,  which  are  neutral  and 
characterized  by  a  bitter  taste. 

The  aqueous  solutions  are  precipitated  :  1.  By  potassa  or  soda,  the  pre- 
cipitate being  soluble  in  hydrochloric,  nitric,  and  sulphuric  acids,  and  in 
hydrochlorate,  nitrate,  and  sulphate  of  ammonia,  but  not  in  potassa  or  soda. 
2.  Ammonia  throws  down  only  part  of  the  magnesia  from  a  diluted  solution, 
and  forms  a  double  salt.  The  precipitated  hydrate  of  magnesia  is  soluble  in 
hydrochlorate  of  ammonia.  Ammonia  does  not  precipitate  the  solutions  of 
any  other  alkali  or  alkaline  earth.  3.  Carbonate  of  potassa  or  soda  throws 
down  only  a  part  of  the  magnesia,  unless  the  solution  is  heated,  when  nearly 
the  whole  is  precipitated.  Sal-ammoniac  redissolves  this  precipitate,  and 
when  previously  added  to  the  magnesian  solution,  no  precipitate  ensues  on 
adding  the  alkaline  carbonates,  unless  the  liquor  is  heated.  4.  The  carbo- 
nate of  ammonia  and  bicarbonates  of  potassa  and  soda  give  no  precipitate 
in  magnesian  solutions,  unless  boiled.  These  tests  distinguish  a  magnesian 
salt  from  the  salts  of  baryta,  strontia,  and  lime,  which  are  precipitated  in  the 
cold.  5.  Common  phosphate  of  soda  only  precipitates  concentrated  magne- 
sian solutions,  but  if  ammonia  or  carbonate  of  ammonia  is  added,  the  mag- 
nesia is  precipitated  in  the  form  of  ammonio-magnesian  phosphate,  insoluble 
in  hydrochlorate  of  ammonia,  and  diluted  ammonia.  Moistened  with  acetate 
of  cobalt,  and  heated  before  the  blowpipe,  the  magnesian  salts  give  pale 
rose-colored  compounds  :  the  tint  is  only  distinct  on  cooling,  and  never 
very  intense.  6.  Sulphuric  acids  and  the  alkaline  sulphates,  oxalic  acid  and 
the  oxalates,  give  no  precipitate  in  a  solution  of  a  salt  of  magnesia.  7.  A 
magnesian  salt,  if  pure,  gives  no  color  to  the  flame  of  alcohol.  The  light  of 
magnesium,  burning  in  oxygen  or  air,  produces  a  spectrum  similar  to  that 
of  solar  light.  The  colors  are  perfect,  and  of  the  most  intense  description. 
It  thus  shows  the  colors  of  all  objects. 

^  In  quantitative  analysis,  magnesia  is  almost  always  precipitated  by  a  solu- 
tion of  phosphate  of  soda,  to  which  ammonia  or  its  carbonate  has  been  pre- 
viously added ;  it  is  collected  and  washed  with  the  precautions  above  men- 
tioned, and  ignited  so  as  to  be  weighed  in  the  state  of  pyrophosphate. 
Every  100  parts  of  ammonio-magnesiura  phosphate,  dried  at  60°,  indicate 
16-26  of  magnesia:  every  100  parts  of  its  residue,  after  ignition,  indicate 
35  T  parts  of  magnesia,  and  64-3  of  phosphoric  acid. 


OXIDE    OF    ALUMINUM.  36t 


CHAPTEE    XXVII. 

ALUMINUM  — G  LUC  INUM  — ZIRCONIUM  — THORIUM  — YTTRIUM 
— E  R  B  I  U  M— T  E  R  B I  U  M— C  ERIUM— LANTHANU  M— D  I D  Y  M I U  M . 

Aluminum  (AI  =  14). 

Aluminum  is  obtained  on  decomposing  the  chloride  of  aluminum  by 
sodium  at  a  high  temperature  :  intense  ignition  ensues,  and  the  jeduced 
aluminum  forms  metallic  globules  in  the  midst  of  the  chloride  of  sodium, 
which  is  removed  by  water.  (Al3Cl3+3Na=2Al+3NaCl).  The  mineral 
called  cryolite  (a  double  fluoride  of  aluminum  and  sodium)  has  also  been  used 
as  a  source  of  the  metal,  and  is  decomposed  when  heated  with  sodium, 
yielding  globules  of  aluminum,  imbedded  in  fused  fluoride  of  sodium,  which 
is  easily  dissolved  by  water.  The  changes  which  take  place  may  be  thus 
represented :  Al,F3,3NaF+3Na  =  2Al  +  6NaF. 

Aluminum  is  a  bluish  white  malleable  and  ductile  metal,  of  about  the 
hardness  of  silver  ;  its  specific  gravity,  when  rolled,  is  about  2-67,  and  when 
cast  2-56.  Its  point  of  fusion  is,  according  to  Deville,  1750^.  It  is  not 
acted  upon  by  air  or  water  at  common  temperatures,  but  damp  air  slowly 
tarnishes  it.  When  intensely  heated  in  a  current  of  air,  it  suffers  only  slight 
oxidation :  heated  to  redness  in  an  atmosphere  of  steam,  it  is  slowly  oxid- 
ized. It  is  readily  acted  upon  by  hydrochloric  acid,  which  evolves  hydro- 
gen and  forms  chloride  of  aluminum  :  neither  sulphuric  nor  nitric  acid 
affects  it  at  common  temperatures,  but  when  boiled  in  the  latter,  it  is  oxidized 
only  so  long  as  the  heat  is  maintained.  These  acids,  when  diluted,  do  not 
affect  it,  and  it  may  be  boiled  in  acetic  acid  without  undergoing  any  chemi- 
cal change.  Hydrofluoric  acid  is  decomposed  by  it,  hydrogen  is  set  free, 
and  fluoride  of  aluminum,  a  constituent  of  the  topaz  and  of  cryolite,  is  pro- 
duced. Weak  alkaline  solutions  of  potash  and  soda  slowly  act  upon  and 
dissolve  it,  giving  to  the  surface  a  frosted  appearance ;  but  when  the  solu- 
tions are  concentrated,  it  is  oxidized,  and  hydrogen  is  liberated.  This  action 
is  increased  when  the  alkaline  solution  is  heated.  It  forms  alloys  with  many 
of  the  other  metals,  but  does  not  combine  with  mercury.  It  is  not  affected 
by  sulphur  or  sulphuretted  hydrogen,  or  by  solutions  of  the  alkaline  sul- 
phides. The  metal  is  now  largely  manufactured  in  England  and  France, 
and  is  much  used  for  ornamental  and  other  purposes.  Its  lightness  is  a 
great  recommendation.  Under  the  same  bulk  it  has  only  about  one-fifth  of 
the  weight  of  silver.  It  forms  a  golden-colored  alloy  with  copper  in  the 
proportion  of  90  parts  of  very  pure  copper  to  10  of  aluminum — called 
aluminum  bronze — the  specific  gravity  of  which  is  7  "689.  It  has,  when  fresh 
polished,  a  deep  golden  lustre,  but  is  rapidly  tarnished.  There  is  a  white 
alloy  with  silver,  but  this  has  not  been  much  used. 

Oxide  op  Aluminum.  Alumina  (Al^OJ. — To  obtain  alumina  we  de- 
compose a  solution  of  alum  by  excess  of  carbonate  of  ammonia,  wash  the 
precipitate  with  repeated  portions  of  hot  distilled  water  until  all  soluble 
matters  are  removed.  In  this  state  alumina  is  obtained  as  a  white  gelati- 
nous hydrate.  When  dried  and  heated  to  redness,  it  forms  anhydrous 
alumina.     This  may  be  at  once  obtained  by  igniting  pure  ammonia-alum, 


368  HYDRATES  OF  ALUMINA. 

sulphate  of  ammonia  evaporates,  and  alumina  remains,  perfectly  white,  and 
soft  to  the  touch,  but  almost  insoluble  in  acids. 

Alumina  is  a  colorless,  insipid,  and  insoluble  powder,  without  any  action 
upon  vegetable  colors ;  in  other  words,  a  perfectly  neutral  compound.  It 
does  not  set  free  oxide  of  silver  from  a  solution  of  nitrate ;  and  when  dif- 
fused in  water,  it  produces  no  change  of  color  with  sulphuretted  hydrogen 
and  a  solution  of  nitro-prusside  of  sodium.  Its  specific  gravity  is  2,  but 
after  exposure  to  an  intense  heat,  about  4.  By  the  oxy hydrogen  blowpipe 
it  may  be  fused  into  a  colorless  globule.  It  has  a  strong  attraction  for 
moisture,  which  it  rapidly  absorbs  from  humid  air,  to  the  amount  of  one- 
third  of  its  weight.  When  mixed  with  water,  alumina  is  characterized  by 
the  plasticity  of  the  mixture ;  and  if  the  paste  be  dried  in  the  air,  and  then 
heated,  it  shrinks  considerably  in  consequence  of  the  loss  of  water,  but  it 
retains  its  form.  Alumina  has  a  strong  affinity  for  various  organic  com- 
pounds, and  its  use  in  the  arts  of  dyeing  and  calico-printing  depends  upon 
its  attraction  for  different  coloring- principles,  and  for  woody  fibre.  If  am- 
monia is  added  to  a  solution  of  alum  in  infusion  of  cochineal,  or  of  madder, 
the  alumina  falls  in  combination  with  the  coloring-matter,  and  the  super- 
natant liquor  remains  colorless.  Colors  thus  prepared  are  called  Zcd-es. 
A  small  quantity  of  hydrate  of  alumina  added  to  hard  and  impure  water, 
tends  to  purify  it.  The  alumina  is  slowly  deposited  with  the  organic  impu- 
rities. A  few  drops  of  a  solution  of  alum,  added  to  water  containing  calca- 
reous or  soda  salts,  operates  in  a  similar  manner,  alumina  being  precipitated 
and  acting  as  a  clarifier  to  the  water.  Moist  hydrate  of  alumina  is  readily 
soluble  in  most  of  the  concentrated  acids;  but  after  the  expulsion  of  its 
water  by  heat,  it  is  dissolved  with  more  difficulty,  and  may  be  con^dered 
insoluble.  It  is  sparingly  soluble  (when  moist)  in  caustic  ammonia ;  but 
potassa  and  soda  readily  dissolve  it ;  it  is  also  soluble,  to  a  small  extent,  in 
the  aqueous  solutions  of  baryta  and  strontia.  It  forms  no  combination  with 
carbonic  acid.  The  fixed  alkaline  solutions  of  alumina  are  decomposed  by 
the  acids,  and  by  ammoniacal  salts. 

Alumina,  like  other  sesquioxides,  is  a  comparatively  feeble  base ;  none  of 
its  salts  are,  in  fact,  neutral,  but  have  an  acid  reaction ;  and  in  respect  to 
the  more  powerful  basic  oxides,  it  has  been  represented  as  performing  the 
part  of  an  acid,  so  that  such  compounds  have  been  termed  Aliuninates. 
Many  of  these  combinations  exist  native.  Alumina  in  the  state  of  hydrate 
is  recognized  by  its  solubility  in  caustic  potassa;  by  the  formation  of  octa- 
hedral crystals  of  alum  on  evaporating  its  sulphuric  acid  solution»with  the 
addition  of  sulphate  of  potassa ;  by  the  astringent  sweetness  of  this  sul- 
phate ;  by  the  octahedral  crystals  of  alum  deposited  on  evaporation ;  and  by 
the  blue  color  which  it  affords  when  moistened  with  nitrate  of  cobalt  and 
strongly  heated. 

Native  alumina  constitutes  the  sapphire,  which  occurs  either  colorless  or 
pale-bkie,  is  extremely  hard,  and  occasionally  crystallized;  its  specific 
gravity  is  about  3-5.  The  oriental  ruby  and  the  oriental  topaz  are  red  and 
yellow  varieties  of  sapphire.  Corundum  adamantine  spar,  and  emery,  also 
consist  chiefly  of  alumina,  with  less  than  2  per  cent,  of  oxide  of  iron,  and  a 
trace  of  silica  :  the  specific  gravity  of  corundum  is  about  4.  All  these  sub- 
stances are  extremely  hard,  being,  in  that  respect,  second  only  to  diamond. 
They  are  aluminous  minerals,  and  consist  chiefly  of  anhydrous  alumina 
slightly  colored. 

Hydrates  of  Alumina.— Alumina,  precipitated  from  its  solutions,  and 
dried  at  between  70^  and  80°,  retains  about  60  per  cent,  of  water;  but  its 
physical  characters  vary,  dependent  upon  the  strength  of  the  solution  from 


SULPHATE    OF    ALUMINA    AND    POTASSA.  369 

which  it  is  precipitated.  When  thrown  down  from  a  saturated  solution  of 
alum,  it  is  pulverulent ;  but  from  a  dilute  solution,  gelatinous  :  the  pulveru- 
lent hydrate  loses  its  water  at  a  red  heat.  Diaspore  and  Gihbsite  are  native 
hydrates  of  alumina. 

Chloride  of  Aluminum  (Al^Clg). — This  compound  may  be  obtained  as 
follows  :  Alumina  is  mixed  into  a  paste  with  powdered  charcoal,  oil,  and 
sugar,  and  this  is  heated  in  a  covered  crucible  till  the  organic  matter  is 
decomposed :  an  intimate  mixture  of  the  alumina  with  charcoal  is  thus 
obtained,  which  is  introduced,  whilst  hot,  into  a  porcelain  tube,  placed  in  a 
convenient  furnace  ;  dried  chlorine  is  then  passed  through  it  into  a  receiver 
attached  to  the  other  end  of  the  tube,  and  the  air  being  thus  expelled,  the 
tube  is  heated  red-hot,  and  chlorine  gradually  passed  into  it ;  carbonic  oxide 
is  disengaged,  and  chloride  of  aluminum  formed,  which  chiefly  collects 
within  the  tube,  and  ultimately  plugs  it  up.  This  was  chiefly  made  for  the 
extraction  of  aluminum.  Alumina  is  mixed  with  charcoal,  and  chlorine  is 
passed  over  the  mixture  when  heated  to  a  high  temperature.  The  volatile 
chloride  of  aluminum  distils  over.  It  is  a  volatile  yellow-colored  solid; 
it  fumes  and  deliquesces  when  exposed  to  air;  it  is  energetically  acted  upon 
by  water,  and  is  very  soluble  in  alcohol ;  it  may  be  preserved  in  naphtha. 
When  a  solution  of  alumina  in  hydrochloric  acid  is  evaporated,  a  deliques- 
cent hydrated  chloride  remains,  which  at  a  higher  temperature  evolves  hy- 
drochloric acid  and  leaves  alumina. 

Sulphate  of  Alumina  (Al.^Og.SSOg)  is  formed  by  digesting  hydrate  of 
alumina  in  sulphuric  acid  diluted  with  an  equal  bulk  of  water;  the  solution 
is  evaporated  and  alcohol  added,  which  throws  down  the  tersnlphate.  It 
dissolves  in  2  parts  of  water,  and  forms  small  lamellar  crystals,  of  a  sweet 
and  astringent  taste,  which  include  18  atoms  of  water.  When  excess  of  hy- 
drated alumina  is  boiled  in  the  diluted  acid,  and  the  solution  filtered,  and 
evaporated  in  vacuo  over  sulphuric  acid,  it  congeals  into  a  soft,  white,  semi- 
transparent  mass,  which  may  be  dried  on  blotting  paper,  and  is  not  altered 
by  the  air.  When  ammonia  is  added  to  a  solution  of  sulphate  of  alumina, 
a  white  powder  falls,  which  is  not  decomposed  by  excess  of  ammonia,  and 
which,  when  well  washed  and  carefully  dried,  has  the  formula  of  a  basic 
sulphate  (AlgOajSOajOHO).  It  exists  native,  forming  the  mineral  called 
aluminite. 

Sulphate  of  Alumina  and  Potassa  ;    Common  Alum;  Potassa  Alum 

(K0,S03;  Al3,03,3S03 ;  24HO) This  useful  salt  is  manufactured  upon  an 

extensive  scale.  Aluminous  slate,  or  shale,  which  is  an  argillaceous  slaty 
rock  containing  sulphide  of  iron,  is  roasted  so  as  to  oxidize  the  iron  and 
acidify  the  sulphur ;  on  lixiviating  the  roasted  ore,  a  sulphate  of  alumina  is 
obtained,  which,  with  the  addition  oi  sulphate  of  potassa,  yields  alum.  The 
shales  or  wastes  of  old  coal  mines,  which  fall  down  in  a  decomposing  state, 
yield,  on  lixiviation,  especially  after  prolonged  exposure  to  air  and  moisture, 
considerable  quantities  of  sulphate  of  alumina  and  sulphate  of  iron  ;  the 
solution  of  these  salts  is  evaporated,  and,  when  sufficiently  concentrated,  is 
run  out  into  coolers,  where  the  sulphate  of  iron  crystallizes,  and  the  sulphate 
of  alumina,  being  more  soluble,  remains  in  the  mother-liquors.  TJo  these, 
when  heated,  sulphate,  or  chloride  of  potassium  is  added,  and  they  then  yield 
crystals  of  alum,  not  at  first  pure,  but  rendered  so,  and  obtained  in  beauti- 
fully-perfect octahedra,  by  recrystallization.  When  chloride  of  potassium  is 
used,  it  decomposes  the  sulphate  of  iron  of  the  alum-liquors,  forming  chloride 
of  iron  and  sulphate  of  potassa;  the  latter  salt  goes  to  the  formation  of  alum, 
24 


370  SULPHATE    OF    ALUMINA    AND    AMMONIA 

leaving  the  chloride  of  iron  in  solution.  There  are  other  methods  of  manu- 
ifacturing  alum,  such  as  by  the  decomposition  of  clay  by  sulphuric  acid,  and 
by  the  lixiviation  of  certain  alum  stones,  as  they  are  called,  which  are  pro- 
ducts of  the  joint  action  of  sulphurous  acid  and  oxygen  upon  volcanic  rocks 
containing  alumina  and  potassa. 

Ordinary  alum  has  a  sweet  and  astringent  taste,  accompanied  by  some 
degree  of  acidity  ;  its  sp.  gr.  is  ri2  :  it  reddens  vegetable  blues  :  it  dissolves 
in  about  16  parts  of  cold  water,  and  in  less  than  its  weight  of  boiling  water. 
The  crystals  are  permanent  in  the  air,  or  only  very  slightly  efflorescent  in  a 
dry  atmosphere  ;  when  heated,  they  fuse  in  their  water  of  crystallization,  and 
when  this  is  expelled  the  dry  (anhydrous)  alum  becomes  opaque  and  spongy, 
and  in  this  state  is  termed  roche  alum,  or  burnt  alum.  At  a  temperature  of 
140°,  alum  gradually  loses  18  atoms  of  its  water  of  crystallization.  When 
long  retained  in  fusion  it  loses  18'95  percent,  of  water,  and  ultimately  forms 
a  vitreous  mass,  which  retains  14  atoms  of  water:  if  in  this  state  it  be  kept 
at  a  temperature  of  248°  for  12  hours,  the  loss  of  water  amounts  to  about 
38  per  cent.,  and  it  forms  a  porous  mass  retaining  5  atoms  of  water ;  it  then 
remains  unchanged  up  to  320°  ;  but  at  856  it  sustains  a  farther  loss  of  water, 
amounting  on  the  whole  to  43  5  per  cent.,  so  that  the  residue  only  retains 
one  atom  of  water,  which  is  not  expelled  under  a  temperature  approaching 
to  redness.  Anhydrous  alum  gradually  absorbs  water  from  the  atmosphere. 
When  freshly  prepared,  and  put  into  water,  it  appears  almost  insoluble,  and 
remains  for  a  long  time  nearly  unchanged  ;  but  if  previously  exposed  to  the 
atmosphere,  it  dissolves  more  readily.  At  a  red-heat,  alum  first  loses  that 
portion  of  its  acid  belonging  to  the  alumina,  and  ultimately  the  sulphate  of 
potassa  is  itself  decomposed  under  the  influence  of  the  alumina,  which  com- 
bines with  the  potassa  forming  an  aluminate  and  displaces  the  sulphuric  acid. 

If  the  quantity  of  carbonate  of  soda  necessary  to  neutralize  a  portion  of 
alum  be  divided  into  three  equal  portions,  and  added  in  a  gradual  manner 
to  the  aluminous  solution,  it  will  be  found  that  the  alumina  first  precipitated 
is  redissolved  upon  stirring,  and  that  no  permanent  precipitate  is  produced  till 
nearly  2  parts  of  alkaline  carbonate  are  added.  It  is  in  the  condition  of  this 
partially-neutralized  solution  that  alum  is  generally  applied  as  a  mordant. 
When  this  solution  is  concentrated,  alum  crystallizes  from  it,  generally  in  the 
cubic  form,  hence  the  name  cubic  alum,  and  the  excess  of  alumina  is  precipi- 
tated. Alum  is  a  salt  of  extensive  use  in  the  arts,  especially  for  the  prepara- 
tion of  mordants  employed  by  the  dyer  and  calico-printer  ;  it  is  also  employed 
in  preparing  and  preserving  skins  ;  in  pharmacy  it  is  used  as  an  astringent 
and  a  styptic.  When  potassa-alum  is  ignited  with  charcoal,  a  spontaneously- 
inflammable  compound  results,  which  has  long  been  known  under  the  name 
of  Homberg^s  pyrophorus.  The  potassa  is  decomposed  in  this  process,  as 
well  as  the  acid  of  the  alum  ;  the  pyrophorus  is  probably  a  compound  of 
sulphur,  charcoal,  potassium,  and  aluminum.  Potassa  is  not  readily  disco- 
vered in  potassa-alum  until  the  alumina  has  been  removed.  Thus  neither 
fluosilicic  acid  nor  tartaric  acid  will  precipitate  potassa  from  a  concentrated 
solution  ;  and  chloride  of  platinum  produces  after  a  time  only  a  slight  tur- 
bidness.  Potassa-alum  may,  however,  be  easily  identified  by  the  lilac  color 
given  to  flame  when  a  small  portion  of  the  powder  is  heated  beyond  fusion 
on  fine  platinum  wire  ;  soda-alum  gives  under  the  same  circumstances  a  yel- 
low color;  and  ammonia-alum,  if  free  from  these  two  bases,  imparts  no  color 
to  flame. 

Sulphate  of  Alumina  and  Ammonia.  Ammonia' Alum  (XH^0,S03 ; 
AlaOg.SSOg ;  24FIO). — This  salt  is  obtained  exactly  as  the  preceding,  only 
sulphate  of  ammonia  is  substituted  for  sulphate  of  potassa  :  its  atomic  con- 


SILICATES    OF    ALUMINA.  371 

stitution  also  resembles  that  of  potassa-aliira  ;  and  it  is  so  similar  in  other 
respects,  that,  as  far  as  mere  appearance  and  more  obvious  properties  are 
concerned,  the  two  salts  are  not  readily  distinguished.  It  is  recognized  by 
evolving  ammonia,  when  triturated  with  lime  or  potassa.  This  variety  of 
alum  is  manufactured  on  a  large  scale  with  the  sulphate  of  ammonia  derived 
from  gas-works.  It  has  no  ammoniacal  odor.  When  heated  it  loses  water, 
then  ammonia,  and  at  a  very  high  heat,  its  acid,  the  residue  being  pure 
alumina. 

Sulphate  of  Alumina  and  Soda.  Soda-Alum  (NaO.SOg ;  Al^Oa.SSOa; 
24HO). — This  salt  is  formed  when  the  sulphate  of  potassa  of  common  alum 
is  replaced  by  sulphate  of  soda  ;  it  crystallizes  in  octahedra,  which  are  less 
hard,  smooth,  and  regular,  than  those  of  potassa-alum  ;  they  efiSoresce  in  dry 
air,  and  at  110^  to  120°  become  opaque  and  gradually  lose  their  water  of 
crystallization,  the  whole  of  which  is  expelled  at  a  red  heat.  They  dissolve 
in  214  of  water  at  55°,  and  in  their  own  weight  at  212°. 

The  three  alums  are  isomorphous,  and  the  bases  may  replace  each  other 
without  altering  the  crystalline  form.  So  the  alumina  may  be  replaced  by 
isomorphous  oxides — e.  g.,  the  sesquioxides  of  iron,  chromium,  and  manga- 
nese ;  hence  the  following  may  be  taken  as  a  general  formula  for  the  alums  ; 
KO(NH,0,NaO,C£eO,RbO)S03,Al,03(FeA»CrAMnA)3S03,24HO.    (p. 

Sulphate  of  Alumina  and  Lithia.  Lithia  Alum  (LiO,S03 ;  AI2O3, 
3SO3;  24HO). — When  an  aqueous  solution  of  sulphate  of  lithia  and  sulphate 
of  alumina  is  subjected  to  spontaneous  evaporation  at  a  temperature  not 
exceeding  52°,  it  yields  octahedral  and  rhombic  dodecahedral  crystals  solu- 
ble in  24  parts  of  cold,  and  0*87  of  boiling  water. 

The  new  alkalies,  caesia  and  ruhidia  also  form  alums  with  sulphate  of  alu- 
mina, similar  in  constitution  and  form  to  potassa-alum. 

Phosphates  of  Alumina. — Common  phosphate  of  soda  gives  a  gelatinous 
precipitate  with  solution  of  alum,  which  dries  into  a  white  insipid  powder, 
insoluble  in  water,  and  in  solution  of  sal-ammoniac,  but  soluble  in  acids  and 
in  solution  of  potassa.  The  mineral  known  under  the  name  of  Wavellite  is  a 
hydrated phosphate  of  Alumina,  SAlgOg",  2P03,12HO.  Turquois  or  Galaite 
is  a  phosphate  of  alumina  =2(Al303)P05-f-5HO,  colored  by  oxide  of  copper. 
Amhligonite  is  a  phosphate  of  alumina  and  lithia,  and  Lazulite  contains  phos- 
phate of  alumina  with  phosphate  of  iron. 

Alumina  does  not  combine  with  carbonic  acid. 

Silicates  of  Alumina. — All  the  varieties  of  clay  are  silicates  or  hydrated 
silicates  of  alumina;  they  are  frequently  largely  mixed  with  other  substances, 
but  their  important  uses  in  agriculture  and  the  arts  are  referable  to  the  above 
silicate.  Several  minerals  are  definite  crystalline  silicates,  which  by  disin- 
tegration or  decomposition,  contribute  to  the  formation  of  clay;  common 
felspar  is  a  silicate  of  alumina  and  potassa  ;  Al^Og;  3Si03+KO,Si0.j:  it  is 
one  of  the  constituents  of  granite,  and  some  of  its  varieties  crumble,  when 
exposed  to  the  joint  action  of  air  and  water,  int(5  a  white  clay  :  Cornish  clay, 
and  the  Kaolin  of  China,  are  clays  so  formed,  and  may  be  represented  as 
Al2,03;  SSiOg-f  2H0.  Other  clays  are  less  pure,  from  the  admixture  of 
sand,  oxide  of  iron,  or  carbonate  of  lime,  substances  which  importantly 
modify  their  properties.  The  varieties  of  marl  are  calcareous  clays  ;  and 
the  colored  clays  generally  derive  their  various  tints  from  the  oxides  of 
iron.     The  presence  of  these  and  some  other  extraneous  matters,  renders 


312  POTTERY  AND  PORCELAIN. 

some  clays  very  fusible  :  the  pure  aluminous  silicates  are  nearly  infusible, 
but  when  lime,  maprnesia,  or  oxide  of  iron,  is  present,  they  become  more  or 
less  fusible  or  vitrifiable,  in  proportion  to  tlie  quantity  of  these  bases  present 
in  the  cla!f.  The  varieties  oti  fire- day  used  for  lining  furnaces,  and  other 
similar  purposes,  are  nearly  pure  silicates  =Al2, 03,88103,  with  mere  traces  of 
alkaline  bases  and  oxide  of  iron.  The  different  red  and  yellow  ochres,  and 
boles,  are  mixtures  of  clay  and  hydrated  peroxide  of  iron  ;  some  of  them  con- 
tain oxide  of  manganese.  FuUer^s  earth,  used  for  the  capillary  absorption  of 
greasy  matters,  is  also  a  porous  silicate  of  alumina.  Clay  has  some  remark- 
able distinctive  properties  ;  it  exhales  a  peculiar  odor  when  wetted  or  breathed 
upon,  and  when  dry  and  applied  to  the  tongue,  it  adheres  to  it,  in  consequence 
of  the  rapidity  with  which  it  absorbs  moisture;  it  readily  absorbs  ammonia, 
and  many  other  gases  and  vapors  generated  in  fertile  and  manured  soils  ; 
hence  its  agricultural  value.  The  important  quality  o{  plasticity,  upon  which 
the  manufacture  of  porcelain  and  pottery  depends,  belongs  exclusively  to 
aluminous  combinations  in  their  humid  state,  so  that  they  admit  of  being 
turned  in  the  lathe  or  upon  the  potter's  wheel,  or  of  being  moulded  into  the 
infinite  variety  of  useful  and  ornamental  products  of  the  ceramic  art.  These 
forms  are  rendered  permanent  by  careful  drying,  and  subsequent  exposure  to 
high  temperatures. 

Tests  for  the  Salts  of  Alumina. — These  salts  have  an  astringent, 
sweet,  and  subacid  taste,  and  redden  litmus.  1.  They  are  precipitated  by 
potassa  or  soda,  the  precipitate  being  redissolved  when  the  alkalies  are  added 
in  excess,  but  the  alumina  is  ag«in  precipitated  by  hydrochlorate  of  ammonia. 

2.  The  precipitate  produced  by  ammonia  is  not  soluble  to  any  extent  in 
excess  of  that  alkali,  and  it  is  not  dissolved  by  hydrochlorate  of  ammonia. 

3.  The  carbonates  and  bicarbonates  of  potassa,  soda,  and  ammonia,  throw 
down  hydrated  alumina,  with  the  escape  of  carbonic  acid,  and  the  precipitate 
is  nearly  insoluble  in  an  excess  of  the  precipitants.  4.  Sulphate  of  potassa, 
with  a  little  sulphuric  acid,  added  to  an  acid  solution  of  alumina,  deposits, 
by  concentration,  a  crystalline  compound,  which  is  alum.  5.  Phosphate  of 
soda  produces  a  flocculent  precipitate  of  phosphate  of  alumina.  6.  When 
aluminous  substances  are  heated  by  the  blowpipe  with  nitrate  of  cobalt,  they 
acquire  a  blue  color,  which  is  only  distinctly  seen  by  daylight  after  the  mix- 
ture has  cooled.  T.  Hydrosulphate  of  ammonia  gives  a  precipitate  which  is 
gelatinous  hydrate  of  alumina — sulphuretted  hydrogen  being  set  free.  This 
result  is  owing  to  the  action  of  ammonia — as  sulphuretted  hydrogen  produces 
no  precipitate  (of  sulphide)  in  the  solutions.  The  gelatinous  hydrate  is 
readily  dissolved  by  a  solution  of  potassa.  This  test  serves  to  distinguish 
a  solution  of  alum  from  one  of  magnesia,  since  unless  the  hydrosulphate 
contain  free  ammonia,  it  will  give  no  precipitate  with  a  salt  of  magnesia.  If 
a  precipitate  is  formed  (by  reason  of  the  presence  of  ammonia)  it  is  recog- 
nized as  hydrate  of  magnesia  by  its  being  dissolved  by  hydrochlorate  of 
ammonia.  Hydrate  of  alumina  is  insoluble  in  this  liquid.  Ferrocyunide  of 
potassium  has  no  action  upon  a  salt  of  alumina. 

Pottery  and  Porcelain  —The  better  kind  0^ pottery,  called  in  this  country 
Staffordshire  ware,  is  made  'of  a  mixture  of  alumina  and  silica ;  the  former 
obtained  in  the  form  of  a  fine  clay,  from  Devonshire  chiefly,  and  the  latter, 
consisting  of  chert  or  flint,  heated  red-hot,  quenched  in  water,  and  then  re- 
<3uced  to  powder.  Each  material,  carefully  powdered  and  sifted,  is  diffused 
through  water,  mixed  by  measure,  and  brought  to  a  due  consistency  by 
evaporation :  it  is  then  highly  plastic,  and  may  be  formed  upon  the 
potter's  wheel  and  lathe  in  circular  vessels,  or  moulded  into  other  forms, 


POTTERY  AND  PORCELAIN.  3T3 

which,  after  having  been  dried  in  a  warm  room,  are  inclosed  in  baked  clay 
cases,  called  seggars ;  these  are  ranp^ed  in  a  kiln  so  as  nearly  to  fill  it,  leaving 
only  space  enou«?h  for  the  fuel  ;  here  the  ware  is  kept  red  hot  for  a  consider- 
able time,  and  thus  brought  to  the  state  of  biscuit.  This  is  afterwards  glazed^ 
which  is  done  by  dipping  the  biscuit-ware  into  a  tub  containing  a  mixture  of 
about  60  parts  of  litharge,  10  of  clay,  and  20  of  ground  flint,  diffused  in 
water  to  a  creamy  consistence,  so  that  when  taken  out,  enough  adheres  to  the 
piece  to  give  an  uniform  glazing  when  heated.  The  pieces  are  then  again 
packed  up  in  the  seggars,  with  small  bits  of  pottery  interposed  between 
each,  and  fired  in  a  kiln  as  before.  The  glazing-mixture  fuses  at  a  moderate 
heat,  and  gives  an  uniform  glossy  coating,  which  finishes  the  process  when 
it  is  intended  for  common  white  ware.  The  presence  of  lead  in  glazes  is  often 
objectionable,  and  may  be  dispensed  with  by  using  borax,  which,  however, 
is  too  expensive  for  common  use.  100  parts  of  silica,  80  pearlash,  10  nitre, 
and  20  lime,  fused,  and  then  finely  powdered,  form  a  good  glaze. 

Glazed  cast-iron  vessels  for  culinary  and  other  purposes  are  manufactured, 
in  which  the  absence  of  lead  in  tlie  glaze  is  important :  those  manufactured 
at  Wolverhampton  are  glazed  with  a  mixture  of  borax,  potter's  clay,  and 
pulverized  flints,  to  which  powdered  plate,  or  crown  glass  (free  from  lead), 
and  a  little  carbonate  of  soda,  are  added.  These  ingredients  are  fused 
together;  and  the  mass,  reduced  to  a  fine  powder,  is  mixed  with  water  and 
applied  to  the  clean  surface  of  the  iron,  upon  which  it  is  dried,  and  vitrified 
by  exposure  to  heat  in  a  muffle. 

The  patterns  upon  ordinary  earthenware,  which  are  chiefly  in  blue,  in  con- 
sequence of  the  facility  of  applying  cobalt,  are  generally  first  printed  off 
upon  paper,  which  is  applied  to  the  plate,  or  other  article,  while  in  the  state 
of  biscuit ;  the  color  adheres  permanently  to  the  surface  when  heat  is  properly 
applied.  In  the  manufacture  of  porcelain,  the  materials  are  so  selected  that 
the  compound  shall  remain  perfectly  white  after  exposure  to  heat,  endure  a 
high  temperature  without  fusing,  and  at  the  same  time  acquire  a  semivitreous 
texture,  and  a  peculiar  translucency  and  toughness.  These  qualities  are 
united  in  some  of  the  Oriental  porcelain,  or  China,  and  of  the  French,  Eng- 
lish, and  German  porcelain.  The  Berlin  porcelain,  so  justly  esteemed  in 
the  laboratory,  consists  of  about  71  silica,  24  alumina,  2  potassa,  1*5  pro- 
toxide of  iron,  and  1*5  lime  and  magnesia.  The  colors  employed  in  painting 
porcelain,  are  the  metallic  oxides  which  are  used  for  coloring  glass  ;  and  in 
all  the  more  delicate  patterns  they  are  laid  on  with  a  camel-hair  pencil,  and 
generally  previously  mixed  with  a  little  oil  of  spike-lavender  or  of  turpen- 
tine. When  several  colors  are  used,  they  often  require  various  tempera- 
tures for  their  perfection ;  in  which  case  those  that  bear  the  highest  heat 
are  first  applied,  and  subsequently  those  which  are  brought  out  at  lower 
temperatures.  This  art  of  painting  on  porcelain,  or  in  enamel,  is  of  the 
most  delicate  description :  much  experience  and  skill  are  required  in  it,  and 
with  every  care  there  are  frequent  failures.  The  gilding  of  porcelain  is 
generally  performed  by  applying  finely-divided  gold  mixed  up  with  gum- 
water  and  borax;  upon  the  application  of  heat  the  gum  burns  off,  and  the 
borax  vitrifying  upon  the  surface,  causes  the  gold  firmly  to  adhere ;  it  is 
afterwards  burnished. 

Crucibles  composed  of  one  part  of  good  clay  mixed  with  three  of  coarse 
sand,  slowly  dried  and  annealed,  resist  a  very  high  temperature  without  fusion, 
and  generally  retain  metallic  substances  ;  but  when  the  metals  oxidize,  there 
are  few  which  do  not  act  upon  earthen  vessels ;  and  when  saline  fluxes  are 
used,  the  best  of  them  suffer.  Whenever  silica  and  alumina  are  blended, 
the  compound  softens,  and  the  vessel  loses  its  shape  if  exposed  to  a  white 
heat ;  this  is  even  the  case  with  Hessian  crucibles.     The  most  refractory  of 


374  GLUCINUM.      ZIRCONIUM. 

all  vessels  are  those  made  entirely  of  clay,  coarsely-powdered  burned  clay 
being  used  as  a  substitute  for  sand  :  these  resist  saline  fluxes  longer  than 
others,  and  are  therefore  used  for  the  pots  in  glass-furnaces.  Plumbago  is  a 
good  material  for  crucibles,  and  applicable  to  many  purposes  ;  when  mixed 
with  clay,  it  forms  a  very  difficultly  fusible  compound,  and  is  protected  from 
the  action  of  the  air  at  high  temperatures. 

Liites. Under  this  term,  a  variety  of  compounds  are  used  for  securing  the 

junctures  of  vessels,  or  protecting  them  from  the  action  of  heat.  Slips  of 
wetted-bladder ;  linseed  meal  made  into  a  paste  with  gum- water ;  white  of 
e^g  and  quicklime ;  glazier's  putty,  which  consists  of  chalk  and  linseed  oil ; 
2knd  fat  lute,  composed  of  pipeclay  and  drying-oil,  are  useful  for  retaining 
vapors  ;  but  to  withstand  the  action  of  a  high  temperature  earthy  compounds 
are  required.  Loam,  or  a  mixture  of  clay  and  sand  well  beaten  into  a  paste 
and  then  thinned  with  water,  and  applied  by  a  brush  in  successive  layers,  to 
retorts,  tubes,  &c.,  enables  them  to  bear  a  high  temperature  ;  if  a  thick  coating 
is  required,  care  should  be  taken  that  the  cracks  are  filled  up  as  the  lute 
dries ;  a  little  tow  mixed  with  it  renders  it  more  permanent.  If  the  lute  is 
intended  to  vitrify,  as,  for  instance,  to  prevent  the  porosity  of  earthenware  at 
high  temperatures,  a  portion  of  borax,  or  of  red-lead,  may  be  mixed  with  it. 

Glucinum  (G='7). 

Glucinum  is  obtained  in  decomposing  its  chloride  by  means  of  sodium. 
•It  is  a  gray  malleable  metal,  sp.  gr.  2-1.     Its  fusing  point  is  a  little  below 
that  of  silver:  it  is  not  altered  by  exposure  to  air,  and  is  difiQcult  of  oxida- 
tion, even  in  the  flame  of  the  blowpipe. 

Oxide  op  Glucinum  or  Glucina  (GaOg),  was  first  discovered  in  the  beryl: 
it  also  exists  in  the  emerald,  in  euclase,  in  the  chrysoberyl,  in  phenakite,  and 
in  a  few  other  rare  minerals.  It  is  white,  insipid,  and  insoluble  in  water; 
it  has  no  action  on  vegetable  colors ;  its  specific  gravity  is  2-97.  It  dis- 
solves, especially  in  the  state  of  hydrate,  in  solution  of  caustic  potassa  and 
soda,  but  not  in  ammonia.  It  differs  from  alumina  in  being  soluble,  when 
freshly  precipitated,  in  carbonate  of  ammonia.  With  the  acids  it  forms 
saline  compounds  of  a  sweetish  astringent  taste.  From  these  solutions  the 
carbonates  of  potassa  and  soda  throw  it  down  in  the  form  of  a  bulky  hydrated 
carbonate. 

Characters  of  the  Salts  of  Glucina. — These  salts  are  astringent  and  sweet ; 
they  are  precipitated  by  the  caustic  fixed  alkalies,  and  the  precipitate  is  re- 
dissolved  by  their  excess,  and  sparingly  by  their  carbonates :  it  is  not  solu- 
ble in  caustic  ammonia,  but  readily  so  in  carbonate  of  ammonia,  and  the 
oxide  is  again  precipitated  on  boiling  the  liquid.  A  characteristic  property 
of  glucina  is,  that  when  a  warm  solution  of  it  is  mixed  with  a  warm  solution 
of  fluoride  of  potassium,  till  a  precipitate  begins  to  appear,  and  the  mixture 
is  then  suffered  to  cool,  a  difiBcultly  soluble  double  salt  separates  in  the  form 
of  lamellar  crystals.  Sulphate  of  glucina  does  not  form  a  erystallizable 
double  salt  (like  alum)  when  mixed  with  sulphate  of  potassa. 

Zirconium  (Zr=34). 

Zirconium  is  obtained  by  acting  upon  the  potassio-fluoride  of  zirconium 
by  potassium  at  a  red  heat.  When  cold  the  product  is  thrown  into  water, 
and  the  zirconium  separates  in  the  form  of  a  black  powder,  having  the  appear* 
ance  of  plumbago.  Troost  obtained  it  in  a  crystallized  state,  by  heating 
the  double  fluoride,  of  zirconium  and  potassium  with  aluminum.  After 
heating  the  mixture  to  a  temperature  equal  to  that  of  melted  iron,  crystal- 


TIIORINUM,    OR    THORIUM.  375 

line  plates  of  zirconium,  lyin^^  close  tof^ether,  like  the  leaves  of  a  book,  were 
found  upon  the  surface  of  the  alurainura.  Some  zirconium  combines  with 
the  aluminum  and  at  the  temperature  of  melted  silver  only  an  alloy  of  the 
two  is  obtained.  Troost  considers  zirconium  to  belong  to  the  carbon  group 
and  places  it  between  silicon  and  aluminum.  {Quart.  Journ.  of  Science, 
1865.)  It  is  not  easily  soluble  in  acids,  with  the  exception  of  the  hydro- 
fluoric, which  readily  dissolves  it,  evolving  hydrogen.  Heated  in  the  atmos- 
phere it  burns  into  zirconia. 

Oxide  of  Zirconium  ;  Zirconia  {7i\\0^)  is  of  rare  occurrence,  having 
only  been  found  in  tlie  Zircon  or  Jargon,  and  a  few  other  scarce  minerals. 
Zircon,  when  colorless  and  transparent,  ranks  among  the  gems :  when 
colored  brown  or  red,  it  is  termed  hyacinth.  This  mineral  contains  between 
60  and  70  per  cent,  of  zirconia,  combined  with  silica  and  a  little  oxide  of  iron. 
Zirconia  is  obtained  by  fusing  finely  powdered  zircon  with  soda,  saturating 
the  product  with  hydrochloric  acid,  evaporating  the  solution  to  dryness,  re- 
dissolving  in  water,  and  precipitating  by  excess  of  ammonia:  the  precipitate 
is  then  washed,  dried,  and  ignited.  Zirconia  is  a  white  infusible  substance, 
insoluble  in  water;  specific  gravity  4*3:  it  gives  intense  luminosity  to  the 
blowpipe  flame.  After  having  been  heated  to  redness  it  resists  the  action 
of  the  acids,  with  the  exception  of  the  sulphuric.  It  is  insoluble  in  caustic 
alkalies.  Chloride  of  Zirconium  forms  efflorescent  acicular  crystals,  soluble 
in  water  and  in  alcohol. 

The  Salts  of  Zirconia  have  an  astringent  taste.  They  are  precipitated  by 
caustic  potassa,  and  the  precipitate  is  nofr  soluble  in  excess  of  the  alkali. 
When  boiled  with  sulphate  of  potassa,  a  sparingly  soluble  subsulphate  of 
zirconia  subsides.  Infusion  of  galls  produces  in  them  a  yellow  precipitate  ; 
and  phosphate  of  soda  throws  down  a  white  phosphate  of  zirconia.  The 
recently  precipitated  carbonate  of  zirconia  is  soluble  in  excess  of  bicarbonate 
of  ammonia  or  of  potassa. 

Thorinum,  or  Thorium  (Th=60). 

By  passing  a  current  of  dry  chlorine  over  a  mixture  of  thorina  and  char- 
coal-powder, a  crystalline  chloride  of  thorinum  is  obtained,  which  is  easily 
decomposed  by  potassium,  and  the  product  is  thorinum.  It  is  of  a  gray 
color,  metallic  lustre,  and  apparently  malleable.  It  is  not  oxidized  by  water, 
but  when  heated  in  the  air  it  burns  into  thorina.  It  is  feebly  acted  on  by 
sulphuric  acid,  and  scarcely  by  nitric  acid ;  it  is  not  attacked  by  the  caustic 
alkalies  at  a  boiling  heat.  Hydrochloric  acid  dissolves  it,  with  the  evolu- 
tion of  hydrogen. 

Oxide  of  Thorinum  :  Thorina  (ThO). — This  oxide,  hitherto  only  found 
in  a  rare  Norwegian  mineral,  Thorite,  is  white,  and  insoluble  in  the  acids, 
with  the  exception  of  the  sulphuric.  When  thrown  down  in  the  state  of 
hydrate  it  dissolves  more  readily,  and  exposed  to  the  air  absorbs  carbonic 
acid. 

Thorina  is  distinguished  from  the  other  oxides  by  the  following  proper- 
ties :  from  alumina  and  glucina,  by  its  insolubility  in  pure  potassa ;  from 
yttria,  by  forming  with  sulphate  of  potassa  a  double  salt,  which  is  insoluble 
in  a  cold  saturated  solution  of  sulphate  of  potassa;  from  zirconia,  by  the 
circumstance  that  after  being  precipitated  from  a  hot  solution  of  sulphate 
of  potassa,  it  is  almost  insoluble  in  water  and  the  acids.  Thorina  is  precipi- 
tated also  by  ferrocyanide  of  potassium,  which  does  not  separate  zirconia 
from  its  solutions.     Sulphate  of  thorina  is  more  soluble  in  cold  than  in  hot 


376      YTTRIUM.      ERBIUM.      CERIUM.      LANTHANUM.      DTDYMIUM. 

water,  so  that  a  cold  saturated  solution  becomes  turbid  when  heated,  and,  on 
cooling,  recovers  its  transparency. 

Yttrium  (Y=32). 

Yttrium  is  obtained  by  decomposing  its  chloride  by  potassium  :  it  is  gray, 
brittle,  and  resists  the  action  of  air  and  water. 

Oxide  of  Yttrium,  or  Yttria  (YO),  was  first  discovered  in  Gadolinite,  a 
mineral  found  at  Ytterby,  in  Sweden ;  it  also  occurs  in  a  very  few  other  rare 
minerals. 

Erbium.     Terbium. 

According  to  Mosander,  Yttria  is  always  accompanied  hy  Erhia  and  Terhia, 
the  oxides  of  two  distinct  metallic  bases.  Erbia  Is  pale  yellow,  and  Terbia 
pale  red  ;  but  none  of  these  substances  have  been  adequately  examined  or 
identified. 

Cerium  (Ce=46). 

By  heating  chloride  of  cerinm  with  potassium,  an  alloy  is  obtained  which 
evolves  hydrogen  when  put  into  water,  and  leaves  cerium  in  the  form  of  a 
gray  metallic  powder.  Heated  in  the  air  it  burns  into  an  oxide,  and  it  is 
soluble  in  the  weakest  acids  with  the  evolution  of  hydrogen. 

Cerium  forms  two  oxides  :  the  protoxide  (CeO),  which  forms  colorless 
salts;  and  the  sesquioxide  (Ce203),  which  forms  red  salts.  Cerium  has 
hitherto  been  found  in  a  few  minerals  only,  and  it  seems  doubtful  how  far  the 
properties  ascribed  to  its  oxides  and  salts,  are  not  more  or  less  dependent 
upon  the  presence  of  other  bodies.  Its  most  characteristic  salt  is  the  double 
sulphate  of  cerium  and  potassa.  The  oxalate  of  cerium  has  been  lately 
employed  in  medicine. 

Lanthanum  (La=44). 

This  metal  is  associated  with  Cerium.  All  its  salts  are  said  to  be  color- 
less. When  the  oxalate  is  heated,  it  leaves  a  white  carbonate,  which  at  a 
higher  temperature,  is  converted  into  a  light  brown  anhydrous  oxide  :  the 
white  hydrated  oxide  attracts  carbonic  acid  so  rapidly,  that  it  cannot  be 
completely  washed  upon  a  filter  without  conversion  into  carbonate. 

Didymium  (Di=48). 

Didymium  accompanies  lanthanum  and  cerium  in  the  minerals  containing 
the  latter  metal.  It  appears  to  form  one  oxide  only,  of  a  brown  color  ;  and 
all  its  sorts  are  colored,  some  being  pink,  others  violet.  The  sulphate  and 
nitrate  are  rose-colored ;  the  hydrated  oxide,  carbonate,  and  oxalate  are 
violet,  and  when  ignited  leave  a  dark-brown  anhydrous  oxide,  readily  soluble 
in  dilute  acids,  and  absorbing  carbonic  acid  from  the  air. 

The  atomic  weights  attached  to  these  metals  are  of  doubtful  accuracy. 
(Watts's  Jour.  Ghera.  Soc,  ii.  131.) 


CHAPTER    XXVIII. 

QUALITATIVE    ANALYSIS    OF    THE   OXIDES    AND    SALTS    OF 
THE    PRECEDING    METALS. 

The  oxides  of  the  metals  described  in  the  preceding  chapters  form  three 
well-marked   groups.      1.  The   Alkalies,  comprising   potassa,  soda,  lithia, 


CHEMICAL  CHARACTERS  OF  ALKALIES  AND  EARTHS     3TT 

coesia,  rubidia,  and  thallia  (Tlo),  to  which  may  be  added  ammonia,  the 
chemical  characters  of  which  have  been  considered  at  paj^e  181.  2.  AlknUne 
earths,  baryta,  strontia,  lime,  and  magnesia ;  and  3.  The  Earths,  of  which 
only  one  is  selected  as  a  type  of  the  others,  namely,  alumina. 

The  bases  comprised  in  these  three  groups,  whether  in  acid  or  neutral 
solutions,  are  not  precipitated  by  a  current  of  sulphuretted  gas.  One  of 
them,  alumina,  is  precipitated  from  its  solution  as  hydrated  oxide  by  a  solu- 
tion of  sulphide  of  ammonium. 

1.  The  Alkalies. — This  name  is  applied  to  the  oxides  of  those  metals 
which  are  soluble  in  water  and  alcohol ;  they  are  marked  by  the  following 
characters  :  1.  They  have  an  acrid  caustic  taste.  2.  Tiiey  are  corrosive  to 
organic  matter.  3.  They  neutralize  acids,  and  form  salts.  4.  They  com- 
bine with  the  oily  acids  to  form  soaps.  5.  They  exert  a  peculiar  action  on 
vegetable  colors.  As  it  is  by  the  last-mentioned  character  that  their  pre- 
sence is  commonly  recognized  in  analysis,  it  may  be  stated  that  an  alkali 
restores  the  blue  color  to  red  litmus  ;  that  it  renders  blue  infusion  of  cabbage 
green,  and  yellow  tincture  of  turmeric  red-brown.  Blue  litmus-paper,  red- 
dened by  a  weak  acid,  turmeric-paper,  or  rose-paper  (paper  impregnated 
with  a  strong  infusion  of  red  roses),  may  be  employed  in  the  preliminary 
testing  for  alkalies.  Well-made  rose-paper  is  nearly  colorless,  and  it 
acquires  a  bright  green  color  as  the  result  of  the  action  of  a  diluted  alkali. 
If  the  alkaline  solution  is  concentrated,  the  coloring  matter  is  destroyed,  and 
the  rose-paper  acquires  a  brownish-yellow  tint.  Blue  infusion  of  cabbage, 
the  method  of  preparing  which  has  been  elsewhere  described  (p.  t6),  is 
admirably  adapted  for  a  test-liquid.  It  acquires  a  red  color  from  an  acid 
solution,  a  green  color  from  an  alkaline  solution,  and  it  remains  blue  if  the 
solution  is  neutral.  The  nitro-prusside  of  sodium  is  also  a  delicate  test  of 
alkalinity  in  a  liquid.  In  order  to  employ  it,  a  small  quantity  of  sulphu- 
retted hydrogen  is  passed  into  the  suspected  solution,  and  a  few  drops  of 
nitro-prusside  of  sodium  are  added.  A  magnificent  rose,  purple,  blue,  or 
crimson  color  speedily  manifests  itself,  according  to  the  strength  of  the  alka- 
line solution.  The  color  soon  disappears.  This  test  thus  indicates  alka- 
linity in  weak  solutions  of  the  phosphates,  borates,  carbonates,  and  even 
among  the  least  soluble  oxides,  such  as  lime  and  magnesia  (p.  361). 

2.  The  Alkaline  Earths. — These  oxides  have  the  general  properties  of 
alkalies,  but  they  are  specially  marked  by  the  following  characters:  1.  They 
are  insoluble  in  alcohol,  and  much  less  soluble  in  water  than  the  alkalies: 
one  of  them  (magnesia)  is  nearly  insoluble  in  water.  2.  They  form  insolu- 
ble compounds  with  carbonic  and  phosphoric  acids. 

3.  The  Earths. — These  oxides  differ  from  the  two  preceding  groups,  in 
the  following  points :  They  are  white  tasteless  powders.  2.  They  have  no 
alkaline  reaction.  3.  They  are  insoluble  in  water  and  alcohol.  4.  As 
hydrates,  they  combine  with  acids  and  alkalies  to  form  salts ;  and  5.  Their 
oxides  are  not  reducible  at  a  red  heat  by  hydrogen  or  carbon. 

Acids,  as  contrasted  with  alkalies,  have  the  property  of  rendering  vege- 
table blues  (litmus  and  cabbage)  red.  They  neutralize  alkalies  and  form 
salts.  They  exist  in  the  gaseous,  liquid,  and  solid  state,  sometimes  soluble 
in  water,  at  other  times  only  sparingly  so,  as  the  boracic  and  arsenious 
acids;  and  in  some  instances  quite  insoluble,  as  calcined  silicic  acid.  Those 
which  are  soluble  are  characterized  by  a  sour  taste,  and  sometimes  by  a 
strongly  corrosive  action  on  organic  matter.  Those  only  which  are  dis- 
solved by  water  redden  blue  litmus-paper  ;  this  is  the  indication  of  acidity 
on  which  a  chemist  chiefly  relies.  The  special  tests  for  the  principal  acids 
have  been  already  described  in  the  first  part  of  the  work. 

Under  each  of  the  metals  in  the  preceding  chapters,  the  tests  for  its  saline 


378  QUALITATIVE    ANALYSIS    OP    BASES. 

combinations  have  been  given  in  detail.  It  will  now,  therefore,  only  be 
necessary  to  select  a  few  of  the  more  important  of  these  tests,  in  order  to 
show  how  the  presence  of  a  base  belonging  to  one  of  the  three  groups  of 
oxides  may  be  determined. 

In  this  summary,  we  include  among  the  alkalies,  ammonia.  Although 
not  an  oxide  (page  182),  it  bears  in  its  chemical  properties  the  strongest 
analogies  to  potassa  and  soda,  which  are  oxides  of  metals.  Among  the 
earthy  bases,  we  select  alumina  as  the  only  one  which  will  probably  present 
itself  in  the  ordinary  course  of  analysis.  The  bases  selected  will  be  there- 
fore the  following:  potassa  (KO),  soda  (NaO),  ammonia  (NH.,),  lithia 
(LiO),  baryta  (BaO),  strontia  (SrO),  lime  (CaO),  magnesia  (MgO),  and 
alumina  (AlgOg),  It  will  be  necessary  to  consider  them  (I)  in  the  uncom- 
hined  or  free  state,  as  bases ;  and  (2)  in  the  combined  or  saline  state,  as  salts. 
The  elements,  radicals,  and  acids  with  which  the  metals  or  their  oxides  are 
supposed  to  be  combined,  have  been  already  described  in  the  chapters  on 
the  Metalloids  ;  and  to  these  the  reader  is  referred  for  a  description  of  the 
characters  of  each  class  of  salts,  in  so  far  as  they  depend  on  the  acid. 

Bases. — Out  of  the  nine  bases  selected,  three  may  be  at  once  recognized; 
ammonia  by  its  odor  and  volatile  reaction  ;  and  magnesia  and  alumina  by 
their  insolubility  in  water.  The  two  latter  may  be  dissolved  in  hydrochloric 
or  sulphuric  acid  with  certain  precautions,  converted  into  salts,  and  tested 
as  such,  in  the  combined  state ;  but  when  uncombined,  they  are  easily  dis- 
tinguished by  a  solution  of  nitrate  of  silver.  Magnesia  separates  the  brown 
oxide  of  silver,  while  alumina  has  no  effect  upon  the  solution  of  nitrate.  If 
the  bases  are  diffused  in  water,  and  to  each  of  them  a  small  quantity  of  sul- 
phuretted hydrogen  and  nitro-prusside  of  sodium  are  added,  the  magnesia 
imparts  a  pale  rose-color  to  the  liquid,  and  the  alumina  produces  no  change 
whatever. 

In  the  following  table,  P  signifies  precipitated,  and  D  dissolved. 

If  the  oxides  are  presented  in  a  solid  form,  their  physical  properties  will 
serve  in  a  great  measure  to  identify  them.  It  may  be  assumed,  however, 
that  they  are  dissolved  in  water.  In  this  case  the  solution  will  have  a  strong 
alkaline  reaction,  and  nitrate  of  silver  will  give  with  all  of  them  a  precipitate 
of  hrown  oxide  of  silver. 

Not  P.  by  Carbonate  of  Potassa.  P.  by  Carbonate  of  Potassa. 


KO  NaO  LiO         BaO  SrO  CaO 


P.  by  chloride  of       Not  P.  by  chloride  of  P.  by  sulphuric  Not  P.  by  sul- 

platinum.  platinum.  acid.  phuric  acid. 


Rapidly.     Slowly. 


5  g  o  'i  Lilac.  Yellow.       Crimson.  ^     ,.        ., 

°  S  o  Oxalic  acid. 


BaO  SrO  CaO 


P.  soluble.  P.  insoluble. 

*  i  r 

o  I   (  Greenish-  Red.  Orange- 

3  ?a  I    yellow.  red. 


Salts. — The  following  table  refers  to  the  qualitative  analysis  of  the  solu- 
ble salts  of  the  following  bases :  KO,  NaO,  NH3,  LiO,  BaO,  SrO,  CaO,  MgO, 
AI2O3.  Many  of  these  are  neutral :  some  have  an  acid  and  others  an  alkaline 
reaction.     All  are  fixed  at  a  high  temperature,  excepting  those  of  ammonia; 


QUALITATIVE    ANALYSIS    OF    SALTS. 


S79 


hence  an  amraoniacal  salt  is  excluded,  after  the  dry  residue  of  evaporation 
has  been  strong^ly  heated.  For  the  purposes  of  this  analysis,  it  is  assumed 
that  the  salt  is  dissolved  in  water. 


Not  P.  by  Carbonate  of  Potassa. 


P.  by  Carbonate  of  Potassa. 


KO,  NaO,  NH3,                   LiO 

BaO,  SrO,  CaO        MgO             Al^Og 

P.  on  boiling  if 
concentrated. 

P.  by  Chloride  of  Platinum. 

D.byNH.CL  D.  by  KO. 
Not  D.  by     Not  D.  by 
KO.            NH^Cl. 

Sulphate  of  Lime. 

KO                              NH3 

BaO                       SrO               CaO 

1.  Salts  fixed  by       1.  Salts  volatile. 

heat. 

2.  Lilac  flame  to      2.  Boiled  with  KO, 

alcohol.              ammonia  evolved. 

Precipitated                    Not  P. 
Chromate  of  Potassa. 

Not  P.  by  Chloride  of  Platinum. 

BaO                SrO               CaO 

NaO                              LiO 

P.             P.  only  if         Not  P. 
concentrated. 

Oxalic  Acid. 

Not  P.  by  alkaline       P.  by  alkaline 
phosphate  and           phosphate  and 
ammonia.                 ammonia  on 
boiling. 

BaO               SrO                    CaO 

S  S  -S  i  Yellow.                  Crimson. 

Not  P.                 Precipitated. 
Hyposulphite  of  Lime. 

BaO               SrO                   CaO 

P.                  Not  precipitated. 

Solution  of  Ammonia. 


BaO 


SrO 


CaO 


MgO 


ALO. 


2  07^  r 

}    yellow. 


Not  precipitated.- 


Oqa  OS  [ 


Red. 


Orange- 
red. 


Precipitated. 
P.  soluble  in  P.  insoluble  in 

chlor.  chlor. 

ammonium.  ammonium. 

NotD.byKO.,  D.  byKO. 


The  salts  of  magnesia  and  alumina  impart  no  color  to  the  flame  of  alcohol. 
When  strongly  heated  in  the  blowpipe  flame  with  a  solution  of  nitrate  of 
cobalt,  magnesia  acquires  a  pale-red  color,  and  alumina  a  bright-blue  color. 
In  the  compound  sulphates  of  magnesia  and  alumina  with  potassa  and  soda, 
the  peculiar  colors  given  by  these  alkalies  to  flame  announce  their  presence. 

It  will  be  observed,  in  considering  these  groups,  that  the  alkalies  are  linked 
to  the  alkaline  earths  by  lithia,  and  the  alkaline  earths  to  the  earths  by  mag- 
nesia. Thus  carbonate  of  lithia  may  be  precipitated  from  the  concentrated 
solutions  of  that  alkali  by  carbonate  of  potassa  or  soda  ;  but  the  carbonate 
of  lithia  is  at  the  same  time  sufficiently  soluble  in  water  to  throw  down  car-, 
bonates  of  baryta,  strontia,  and  lime  from  the  salts  of  these  bases.  The 
phosphate  of  lithia  occupies  also  this  intermediate  position,  in  respect  to 
solubility.  Magnesium  and  its  oxide  (magnesia)  approach  closely  to  alumi- 
num and  alumina  in  properties.  Magnesium  is  not  readily  oxidized  by  ex- 
posure to  air ;  it  does  not  decompose  water.     It  forms  one  oxide,  which  is  nearly 


380  IRON. 

insoluble  in  water.  Its  salts  are  precipitated  by  ammonia  and  lime-water. 
No  sulphide  of  the  metal  can  be  obtained  by  boilinj?  its  oxide  with  sulphur,  and 
DO  chloride  by  digesting  its  oxide  in  hydrochloric  acid,  and  evaporating  to 
dryness.  In  these  respects  the  resemblances  to  alumina,  and  the  differences 
from  the  bases  with  which  magnesia  is  usually  associated,  are  very  remark- 
able. 

In  dealing  with  a  mixture  of  the  salts  of  the  first  and  second  groups,  car- 
bonate of  ammonia  may  be  selected  as  the  precipitant.  If  this  reagent, 
mixed  with  a  small  quantity  of  ammonia  and  chloride  of  ammonium,  is  added 
to  the  liquid,  and  the  liquid  is  warmed,  baryta,  strontia,  and  lime  only  will 
be  precipitated.  The  filtrate  will  contain  potassa,  soda,  and  magnesia. 
The  latter  may  be  precipitated  by  adding  phosphate  of  ammonia.  When 
this  is  separated  by  filtration,  potassa,  and  soda  will  remain  in  the  filtrate. 
This  is  evaporated  to  dryness,  and  sharply  heated  :  all  the  surplus  ammoniacal 
salts  are  driven  off,  and  salts  of  potassa  and  soda  only  remain  for  subsequent 
testing.  The  base  of  the  third  group  (alumina)  is  precipitated  with  the 
alkaline  earths  by  carbonate  of  ammonia.  Alumina  may  be  removed  from 
the  alkaline  earthy  carbonates  by  a  solution  of  potassa. 


CHAPTER    XXIX. 

Iron  (Fe=28). 

Iron  is  found  largely  diffused  in  the  state  of  oxides  and  carbonate  ;  it  is 
also  found  combined  with  sulphur,  and  with  several  acids,  and  is  a  constitu- 
ent in  greater  or  lesr?  proportion  of  a  large  number  of  minerals.  It  occurs 
in  small  quantity  in  some  animal  and  vegetable  bodies,  and  mineral  waters, 
and  it  enters  largely  into  the  composition  of  many  meteoric  stones.  It  is 
one  of  the  most  abundant  metals  on  the  earth,  but  is  never  found  in  a  pure 
state.  It  is  chiefly  seen  under  the  forms  of  cast-iron,  wrought-iron  and  steel. 
{See  Nickel.) 

Manufacture  of  Iron. — The  argillaceous  iron  ore  of  the  coal-measures  is 
the  principal  source  of  British  iron.  It  occurs  in  nodules  and  seams,  alter- 
nating with  coal,  shale,  and  limestone,  and  contains  from  70  to  80  per  cent. 
of  carbonate  of  iron,  the  remainder  being  chiefly  clay  and  carbonate  of  lime. 
It  is  first  roasted,  either  in  kilns  or  heaps,  and,  mixed  with  coke  and  lime- 
stone, is  subjected  to  the  intense  heat  of  the  blast-furnace ;  these  materials 
being  successively  thrown  in  from  the  top,  and  gradually  descending  till  they 
reach  the  lower  or  hottest  part.  In  their  descent  the  iron  is  reduced,  and  in 
combination  with  a  portion  of  carbon,  falls  through  the  fused  slags  to  the 
bottom  of  the  furnace,  whence  it  is  withdrawn  at  intervals,  by  opening  the 
tap-hole,  while  the  slags  are  allowed  to  run  off  by  an  aperture  left  for  the 
purpose:  they  consist  chiefly  of  the  silicates  of  lime  and  alumina,  with 
smaller  proportions  of  the  silicates  of  magnesia,  manganese,  and  iron.  The 
smelting  or  blast  furnaces  are  usually  about  50  feet  high,  and  15  feet  in  the 
.widest  part  of  their  internal  diameter;  they  are  constructed  of  strong 
masonry  and  brickwork,  and  lined  with  the  most  refractory  fire-stone.  They 
are  worked  day  and  night  for  several  successive  years,  air  being  supplied  to 
them  by  powerful  blowing  machines,  generally  so  constructed  as  to  throw  it 
in  m  a  heated  state,  or  as  a  hot  blast,  and  to  the  amount  of  about  six  tons' 
weight  per  hour.     It  is  estimated  that  by  the  use  of  hot  instead  of  cold  air, 


CAST    AND    WROUGHT    IRON.  381 

a  very  large  saving  of  fuel  is  effected.  With  the  cold  blast,  about  eight  tons 
of  coal  are  consumed  in  the  production  of  a  ton  of  iron  ;  whereas  with  the 
hot  blast,  less  than  three  tons  are  sufficient,  and  with  it,  coal  may  be  substi- 
tuted for  coke.  These  furnaces  are  usually  tapped  night  and  morning, 
furnishing  from  eight  to  ten  tons  of  metal  daily,  and  requiring  an  hourly 
supply  of  about  a  ton  and  a  half  of  the  mixture  of  roasted  ore,  limestone, 
and  coal  or  coke.  The  melted  metal  is  suffered  to  run  into  rough  moulds  of 
sand,  and  in  this  state  constitutes  the  cast  or  pig  iron  of  commerce. 

Cast  Iro7i. — There  are  several  varieties  of  cast  iron,  but  they  are  commer- 
cially distinguished  as  1.  gray,  2.  mottled,  and  3.  white.  They  are  all  carbides^ 
and  the  gray  and  mottled  varieties  include  a  portion  of  graphite  diffused 
through  them,  which  remains  undissolved  and  unchanged  after  the  action  of 
dilute  sulphuric  acid,  and,  whilst  the  greater  part  of  the  combined  carbon 
unites  to  the  hydrogen,  forming  hydrocarbons.  Cast  iron  also  contains 
silicon,  phosphorus,  manganese,  and  traces  of  calcium,  aluminum,  and  sul- 
phur. Gray  cast  iron  is  soft  and  somewhat  tough  ;  it  admits  of  being  bored, 
and  turned  in  the  lathe.  When  immersed  in  dilute  hydrochloric  acid  it 
leaves  a  black  insoluble  residue  ;  its  texture  resembles  bundles  of  small 
needles.  Mottled  iron  is  coarser  grained,  and  small  particles  of  graphitic 
carbon  may  be  discerned  in  its  fracture.  White  cast  iron  is  very  hard  and 
brittle  ;  acids  act  but  slowly  upon  it,  and  develop  a  lamellar  rather  than  a 
radiated  texture  :  it  sometimes  contains  as  much  as  5  per  cent,  of  carbon,  so 
that  it  is  nearly  represented  by  Fe^C,  and  may  be  regarded  as  iron  saturated 
with  carbon.  When  small  articles  of  cast  iron  are  imbedded  in  oxide  of 
iron,  such  as  powdered  haematite,  and  kept  for  some  hours  at  a  red  heat, 
they  are  to  a  great  extent  decarbonized,  and  so  far  softened  as  to  resemble 
wrought  iron,  especially  when  they  are  slowly  cooled.  In  this  operation 
the  carbon  of  the  bar  of  cast  iron  appears  to  be  gradually  removed,  in  the 
form  of  carbonic  oxide,  at  the  expense  of  a  part  of  the  oxygen  of  the  oxide 
in  which  they  are  imbedded. 

Wrought,  or  malleable  iron  is  the  metal  in  a  comparatively  pure  state, 
though  it  retains  traces  of  carbon  and  of  some  of  the  other  impurities  of 
cast  iron.  To  effect  the  conversion  of  cast  into  wrought  iron,  the  cast  metal 
is  in  the  first  instance  refined,  by  subjecting  it  to  the  action  of  air  at  a  very 
high  temperature,  in  a  kind  of  forge  furnace  ;  much  of  the  carbon  is  thus 
burned  off ;  and  the  silicon,  converted  into  silica,  forms  a  fusible  slag  with 
the  oxide  of  iron,  which  tends  to  the  further  purification  of  the  mass.  The 
fused  metal  is  then  ruH  off,  and  formed  into  cakes,  which  are  rapidly  cooled 
by  the  affusion  of  water.  The  silicate  of  iron  formed  in  this  process  is 
partly  derived  from  the  rough  cast  iron,  and  partly  from  added  sand ;  it 
approaches  the  composition  3(FeO)Si03,  and  itself  performs  a  part,  in 
cleansing  the  metal,  by  acting  as  an  oxidizing  agent.  The  further,  and  final 
purification  of  the  metal,  is  effected  by  a  process  called  puddling,  carried  on 
in  a  reverberatory  furnace,  which  admits  of  the  fusion  of  the  refined  iron  by 
a  current  of  intensely  heated  air  and  flame,  without  direct  contact  with  the 
fuel ;  here  the  metal  is  well  stirred,  so  that  the  superficial  oxide  may  be 
mixed  in  the  mass,  which  soon  begins  to  heave  and  emit  jets  of  carbonic 
oxide,  and  gradually  growing  tough  and  less  fusible,  becomes  at  length  pul- 
verulent ;  the  fire  is  then  urged  so  that  the  particles  again  agglutinate  at  a 
welding-heat,  and  admit  of  being  made  up  into  globular  masses,  or  blooms, 
and  in  that  state  of  intense  heat  are  subjected  to  the  shingling -press,  or  to 
rollers  by  which  extraneous  matters  are  squeezed  out  in  the  form  of  slag,  and 
the  density  of  the  metal  increased  ;  it  now  admits  of  being  rolled  into  bars, 
which  are  cut  into  convenient  lengths,  placed  in  parcels  in  a  very  hot  rever- 
beratory furnace,  and  again  rolled.     The  metal  is  now  tough,  flexible,  and 


382  PROPERTIES    OF    IRON. 

malleable,  but  less  fusible,  and  is,  in  fact,  nearly  pure,  retaining  not  more 
than  one  two-hundredth  part  of  carbon,  and  mere  traces  of  other  matters. 
A  new  process  for  saving  the  time  wasted  in  puddling  and  refining  has  been 
brought  out  by  Mr.  Bessemer.  The  carbon  and  silicon  of  cast  iron  are 
burnt  off  by  passing  a  blast  of  atmospheric  air  at  a  great  pressure  through 
the  molten  metal,  and  such  a  quantity  of  pure  cast  iron  is  then  added  to  the 
wrought  iron,  produced  by  this  process,  as  at  once  to  convert  the  whole 
mass  into  steel,  which  is  then  cast  in  the  usual  way.  This  process  has 
answered  with  some  kinds  of  iron,  e.  g.,  that  reduced  by  charcoal,  but  not 
with  other  varieties.  In  these  it  is  said  to  have  led  to  a  great  w^aste  of 
metal.  Dr.  Roscoe  states  that  by  the  Bessemer  process,  six  tons  of  cast  iron 
can  at  one  operation  be  converted  into  steel  in  twenty  minutes.  Iron  is  now 
largely  manufactured  by  this  process  into  railway  axles  and  rails. 

The  slags  formed  in  the  ordinary  operations  of  refining  and  puddling, 
containing  about  60  per  cent,  of  iron,  are  reduced  in  the  blast  furnace,  in 
the  same  way  as  the  original  ore,  but  the  iron  so  produced  is  cold  short;  it 
admits  of  working  at  a  red  heat,  but  is  brittle  when  cold,  a  quality  supposed 
to  depend  upon  the  presence  of  phosphide  of  iron,  derived  from  phosphate  of 
iron  existing  in  the  slag.  Iron  is  also  occasionally  red  short,  that  is,  brittle 
at  a  red  heat,  though  malleable  when  cold  ;  this  quality  has  been  ascribed  to 
traces  of  arsenic  and  copper.  Various  processes  have  been  suggested  for 
hardening  iron.  M.  Goudin  found  that  a  small  quantity  of  boron  gave 
hardness  to  the  metal,  and  that  cast  iron  fused  with  phosphate  of  iron  and 
peroxide  of  manganese  acquired  great  hardness.  The  mixture  could  not  be 
forged,  but  admitted  of  being  cast.  A  still  harder  material  for  making 
cutting  tools  hgis  been  produced  by  the  addition  of  tungsten. 

Properties. — Pure  iron  has  a  bright  white  color,  and  when  polished  a  great 
lustre.  It  is  fusible  at  a  white  heat,  but  with  great  difficulty  when  perfectly 
pure.  It  requires  the  highest  heat  of  a  wind-furnace  to  run  down  soft  iron 
nails  into  a  button,  and  therefore  a  temperature  equal  to  about  3300^.  Its 
sp.  gr.  is  7 "8.  Its  texture  varies  with  the  method  of  working;  in  bars  or 
wires  it  appears  longitudinally  fibrous,  but  when  long  kept  at  a  red  heat  it 
acquires  a  crystalline  texture,  and  a  tendency  to  cuboidal  fracture.  It  is 
the  hardest  and  toughest  of  the  ductile  metals  :  it  may  be  drawn  into  very 
fine  wire,  but  its  malleability  is  not  so  great  as  its  ductility.  Sheets  have 
been  obtained  equal  to  42  square  inches  of  surface,  and  have  weighed  only 
69  grains.  It  is  stated  that  the  thinnest  sheets  yet  produced  had  a  surface 
of  69  square  inches  and  weighed  only  49  grains.  They  were  of  about  the 
two  thousandth  of  an  inch  thick  and  only  about  half  the  thickness  of  the 
thinnest  tissue  paper.  {Scientific  Review,  June,  1866,  p.  54.)  Iron  is  very 
tenacious,  even  in  the  thinnest  wire.  At  a  bright  red  or  orange  heat  it 
admits  of  being  welded  or  joined  by  hammering  to  another  piece  of  red  hot 
metal.  In  the  state  of  wrought  iron  the  metal  has  a  fibrous  structure,  and 
its  value  depends  greatly  upon  this.  When  uniformly  hammered  or  sub- 
mitted to  vibration,  it  acquires  a  granular  crystalline  structure.  It  has  now 
lost  its  toughness  and  become  brittle.  Accidents  have  occurred  from  the 
breaking  of  railway  axles,  owing  to  the  wrought  iron  originally  used  having 
(as  the  result  of  vibrating  motion)  assumed  thi^  crystalline  and  brittle  state. 
Iron  slowly  decomposes  water  at  common  temperatures  when  acid  and  car- 
bonic acid  are  present.  Water  simply  filtered  through  iron  filings  acquires 
a  chalybeate  (inky)  taste,  and  a  dissolved  salt  of  iron  (carbonate)  may  be 
proved  to  be  present  in  it  by  the  usual  tests.  When  the  vapor  of  water  is 
passed  over  iron  heated  to  redness,  the  iron  takes  the  oxygen  and  hydrogen 
is  evolved.^  At  this  high  temperature  the  iron  appears  to  pass  to  the  state 
of  magnetic  oxide.     In  iron  pipes  heated  to  redness  through  which  super- 


OXIDES    OF    IRON.  383 

heated  steam  is  passed,  the  first  effect  is  to  set  free  hydrogen,  but  when  a 
layer  of  magnetic  oxide  has  been  once  formed,  there  is  no  further  decom- 
position of  water.  The  gas  associated  with  superheated  steam  is  chiefly 
nitrogen  derived  from  the  air  in  water. 

One  of  the  special  characters  of  iron  is  that  it  is  attracted  to  the  magnet, 
but  it  does  not  retain  magnetism  when  pure.  Iron  is  thus  readily  detected, 
although  it  may  be  completely  covered  by  zinc,  tin,  and  other  metals.  At  a 
bright  red  heat,  iron  loses  all  its  magnetic  power,  but  this  returns  when  it  is 
cooled  to  a  black  heat. 

According  to  the  Mineral  Statistics  of  the  United  Kingdom,  published  by 
M.  Hunt,  it  appears  that  in  1865  the  iron  ore  raised  amounted  to  9,910,045 
tons.  This  yielded  4,819,254  tons  of  pig  iron.  Of  this  quantity  543,018 
tons  were  exported,  and  the  remainder  was  converted  into  finished  iron. 

To  obtain  pure  iron,  fine  iron  wire  or  filings  of  the  best  bar-iron  are  mixed 
with  about  one-fifth  their  weight  of  pure  peroxide  of  iron,  and  exposed 
(covered  with  pounded  glass  quite  free  from  lead)  in  a  well-closed  crucible, 
for  about  an  hour,  to  the  strongest  heat  of  a  forge.  Another  method  con- 
sists in  exposing  the  peroxide  of  iron  heated  in  a  tube  to  a  high  temperature 
to  a  current  of  pure  hydrogen.  The  oxide  is  reduced  and  water  is  formed. 
The  iron  is  left  in  a  state  of  fine  powder  {ferrum  redactum),  and  unless  re- 
tained in  an  atmosphere  of  hydrogen  until  quite  cold,  it  is  liable  to  take  fire 
on  exposure  to  air  and  become  oxidized.  Iron  in  this  state  readily  dissolves 
in  an  acid  with  the  evolution  of  hydrogen.  If  it  is  in  the  state  of  oxide,  it 
dissolves  without  any  escape  of  hydrogen. 

Exposed  to  heat  and  air,  iron  becomes  superficially  converted  into  a  fusible 
oxide;  when  exposed  to  a  damp  atmosphere,  it  becomes  incrusted  by  a  brown 
rust.  When  in  a  state  of  extreme  division  its  aflBnity  for  oxygen  is  such, 
that  it  becomes  heated,  and  may  even  be  ignited,  on  exposure  to  air  ;  this  is 
the  case  with  the  metal  as  obtained  by  the  action  of  hydrogen  upou  red-hot 
oxide  of  iron,  and  when  thus  reduced,  at  a  temperature  not  sufficient  to  cause 
the  adhesion  of  the  particles  of  the  metal,  and  suffered  to  cool  in  an  atmos- 
phere of  hydrogen,  it  requires  the  same  precautions  for  its  preservation  as 
potassium.  A  spontaneously  combustible  form  of  iron  is  also  obtained  by 
the  ignition  of  Prussian  blue.  In  a  dense  mass,  iron  is  not  afi*ected  by  dry 
air,  and  it  even  retains  its  polish  when  immersed  in  pure  water  which  has 
been  deprived  of  air ;  but  in  common  water,  or  in  water  exposed  to  air,  it 
soon  rusts.  This  oxidation  by  water  is  prevented  by  the  alkalies ;  and  in 
lime-water,  or  in  a  weak  solution  of  ammonia,  potassa,  or  soda,  the  metal 
keeps  its  lustre,  probably  owing  to  the  entire  exclusion  of  free  carbonic  acid. 

Oxides  of  Iron. — Iron  is  susceptible  of  four  definite  degrees  of  oxidation 
forming  a  protoxide  (FeO),  which  has  not  been  isolated,  but  which  is  the 
bases  of  a  seriqs  of  well-defined  salts ;  a  sesquioxide  (FegOg),  generally  termed 
red  oxide  or  peroxide;  a  Mack  intermediate  oxide,  known  also  under  the 
name  of  magnetic  oxide  (FegOJ  ;  and  a  hyperoxide,  called /erne  acid  (FeOg), 
but  which,  like  the  protoxide,  has  not  been  isolated. 

Protoxide  of  Iron  ;  Ferrous  Oxide  (FeO). — When  a  solution  of  potassa 
is  added  to  a  solution  of  a  pure  protosalt  of  iron,  every  precaution  being 
taken  to  exclude  oxygen,  a  white  precipitate  falls,  which  is  a  hydrated  prot- 
oxide ;  it  is  difficult  to  wash  and  dry  it  under  entire  exclusion  of  air ;  but 
when  this  is  done,  it  is  pale  green,  not  magnetic,  and  absorbs  oxygen  when 
exposed  to  air,  and  is  converted  into  peroxide  ;  it  rapidly  absorbs  carbonic 
acid,  and  dissolves  in  the  dilute  acids.  The  pure  protosulphite  of  iron  for 
this  purpose  may  be  obtained  by  shaking  in  a  stoppered  bottle,  for  a  few 


884  OXIDES    OF    IRON. 

minutes,  a  mixture  of  clean  iron  filings  with  a  fresh  and  strong  solution 
of  sulphurous  acid.  On  filtering  and  adding  potash,  a  white  hydrated 
oxide  of  the  metal  is  procured,  which,  however,  rapidly  absorbs  oxygen  from 
the  air  and  passes  to  the  state  of  peroxide.  The  salts  of  this  oxide,  when 
crystallized  or  hydrated,  are  mostly  greenish-blue.  The  green  tint  is  owing 
to  the  admixture  of  some  yellow  persalt  with  the  blue  protosalt.  The  crys- 
tals become  white  or  nearly  so  when  anhydrous.  Thus  crystals  of  the  green 
protosulphate  are  whitened  by  immersion  in  strong  sulphuric  acid.  In 
aqueous  solution  they  have  an  inky  taste,  and  are  very  prone  to  pass  into  salts 
of  peroxide.  The  fixed  alkalies  throw  down  this  oxide  as  hydrate.  With 
ammonia,  only  half  the  oxide  is  precipitated,  and  a  green  solution  is  formed, 
which,  on  exposure,  becomes  covered  with  a  brown  film.  Carbonates  of 
potassa  and  of  soda,  and  sesquicarbonate  of  ammonia,  throw  down  a  white 
protocarbonate  of  iron,  which  soon  becomes  brown,  and  which,  if  solution 
of  sal-ammoniac  be  added,  is  re-dissolved.  Bicarbonates  of  potassa  and  soda 
produce  the  same  preci[)itate,  unless  the  solution  be  very  dilute,  in  which 
case  the  mixture  is  clear,  but  deposits  protocarbonate  of  iron  if  boiled,  and 
when  exposed  to  air  it  gradually  lets  fall  hydrated  oxide.  The  protosalts  of 
iron  act  as  powerful  deoxidizers.  Nitric  acid  is  decomposed  by  them,  and 
deutoxide  of  nitrogen  is  set  free,  which  is  dissolved  by  a  portion  of  protosalt, 
and  forms  a  dark  olive-green  solution  (p.  110).  The  protosalt  is  at  the  same 
time  converted  into  persalt.  When  added  to  solutions  of  chloride  of  gold  or 
nitrate  of  silver,  gold  and  silver  are  separated  in  the  metallic  state.  It 
deoxidizes  a  solution  of  permanganate  of  potassa;  hence,  a  standard  solution 
of  permanganate  is  used  volumetrically  to  determine  the  quantity  of  prot- 
oxide in  a  liquid. 

Sesquioxide  of  Iron  ;  Peroxide  of  Iron  ;  Ferric  Oxide  (FegOg). — 
When  a  protosalt  of  iron  is  boiled  with  nitric  or  nitro-hydrochloric  acid,  it 
becomes  peroxidized,  and  on  adding  ammonia  a  brown  hydrated  precipitate 
falls,  which,  when  washed  and  ignited,  is  the  sesquioxide.  When  protosul- 
phate of  iron  is  decomposed  by  a  very  high  temperature  a  red  powder  re- 
mains, which  is  also  the  peroxide,  and  which  was  formerly  called  colcothar, 
and  is  used  as  a  red  paint,  and  for  polishing  glass  and  metals.  The  color  of 
peroxide  of  iron  varies  according  to  the  mode  of  its  formation  and  the  tem- 
perature to  which  it  has  been  subjected  :  it  is  generally  a  reddish  or  yellow- 
brown  powder,  which  acquires  a  darkened  hue  by  a  moderate  heat,  and  is  not 
magnetic  except  when  it  has  been  overheated:  in  this  case  it  appears  to  under- 
go partial  reduction.  This  oxide  is  a  weak  base,  or  what  has  sometimes  been 
called  'dn  indifferent  oxide  :  its  salts  generally  have  a  brown  color  and  an  acid 
reaction  ;  and,  when  very  dilute,  their  solutions  are  decomposed  by  boiling, 
in  which  case  the  acid  of  the  salt  combines  with  the  water,  and  the  peroxide 
or  a  basic  salt  is  precipitated.  In  some  cases  this  oxide  acts  as  an  acid.  It 
is  thrown  down  from  its  solutions  by  ammonia,  potassa,  and  soda,  in  the  form 
of  a  bulky  brown  hydrate,  and  in  this  state  is  easily  redissolved  by  acids  ; 
but  when  it  has  been  dried,  and  exposed  to  a  full  red  heat  for  some  time,  it 
is  difficultly  soluble.  It  is  also  partly  converted  into  magnetic  oxide  by 
losing  oxygen,  3Fe,03=2Fe30,  +  0.  The  best  solvent  for  this  oxide  is  the 
hydrochloric  acid.  When  dried  at  212°,  it  is  2Fe^03  +  3HO;  at  400°  it 
becomes  Fe.Oa-j-HO.  A  temperature  exceeding  500^  is  required  to  drive 
ofl'  the  whole  of  the  water.  When  produced  under  exposure  to  air,  it  almost 
always  contains  traces  of  ammonia.  When  precipitated  by  excess  of  the 
fixed  alkalies,  or  their  carbonates,  it  carries  down  a  portion  of  the  alkali, 
which  cannot  be  entirely  removed  by  washing  ;  and  if  the  alkali  be  not  in 
excess,  the  precipitated  oxide  is  not  free  from  the  acid,  or  from  a  subsalt : 


OXIDES    OF*  IRON.  385 

hence  the  necessity  of  precipitating  by  excess  of  ammonia,  when  the  result- 
ing hydrated  oxide  may  be  deprived,  by  heat,  both  of  water  and  of  excess  of 
the  precipitant.  When  certain  organic  substances  are  present  in  solutions 
of  this  oxide  they  prevent  its  precipitation  by  the  alkalies.  This  is  the  case 
with  hot  solutions  of  gelatine,  starch,  gum,  and  sugar.  Tartaric,  citric,  and 
some  other  acids,  produce  the  same  effect.  This  oxide  of  iron  is  reduced  by 
hydrogen  at  a  temperature  even  below  redness.  When  gently  heated  with 
charcoal  it  is  converted  into  magnetic  oxide,  and  at  a  high  temperature  is 
reduced. 

The  salts  of  this  oxide  are  changed  into  those  of  the  protoxide  by  adding 
sulphurous  acid  or  bisulphite  of  soda,  and  warming  the  liquid  ;  or  by  adding 
to  the  warm  liquid  pure  zinc,  in  which  case  hydrogen  is  generated,  and  the 
persalt  is  converted  into  a  protosalt.  A  standard  solution  of  permanganate 
of  potassa,  which  is  not  affected  by  a  persalt,  may  be  employed  voluraetri- 
cally,  to  determine  by  the  discharge  of  color  the  amount  of  protoxide,  and 
by  calculation  of  the  peroxide  present.  Care  should  be  taken  that  all  the 
sulphurous  acid  is  expelled  from  the  liquid  before  adding  the  solution  of  per- 
manganate. A  current  of  sulphuretted  hydrogen  will  also  reduce  the  per- 
salts  to  the  protosalts,  but  in  this  case  there  is  a  separation  of  sulphur. 

Black  Oxide  of  Iron  ;  Magnetic  Oxide  of  Iron;  Ferrosoferrio  Oxide 
(FcaOj ;  or  FeO,Fe203) This  oxide  is  formed  by  passing  steam  over  red- 
hot  iron.  The  scales  of  iron  obtained  from  the  smith's  forge,  the  oxide 
formed  when  iron  is  burned  in  oxygen  gas,  and  the  black  powder  formed  by 
the  action  of  air  on  moistened  iron  filings,  and  formerly  called  Martial 
Ethiops,  are  also  allied  to  this  oxide;  but  in  these  the  protoxide  or  peroxide 
may  occasionally  predominate.  A  solution  of  this  oxide  in  hydrochloric  acid 
has  the  properties  of  the  proto  and  persalts  of  the  metal. 

A  hydrate  of  this  oxide  may  be  obtained  by  dissolving  equal  weights  of 
protosulphate  of  iron  in  two  separate  portions  of  water,  boiling  one  of  them 
with  a  sufficiency  of  nitric  acid  to  peroxidize  it,  and  then  mixing  it  with  the 
other,  and  pouring  the  mixture  into  a  solution  of  potassa  or  soda,  sufficient 
in  quantity  and  strength  to  decompose  the  whole  :  the  precipitate  at  first 
consists  of  a  mixture  of  protoxide  and  peroxide  of  iron,  but  when  boiled  for 
a  few  minutes  they  combine,  and  the  black  oxide  fails  in  the  form  of  a  dense 
crystalline  powder,  very  obedient  to  the  magnet,  and  readily  soluble  in  hy- 
drochloric and  in  nitric  acid.  The  salts  of  this  oxide  are  mixtures  of  those 
of  the  two  oxides.     Magnetic  iron  ore  is  a  native  black  oxide. 

Ferric  Acid  (FeOg). — Ferric  acid  is  only  known  in  combination  with 
bases :  it  is  one  of  those  acids  which  cannot  be  separated  without  undergoing 
decomposition.  When  sesquioxide  of  iron  is  mixed  with  four  parts  of  nitre, 
and  exposed  for  an  hour  to  a  full  red-heat  in  a  covered  crucible,  it  forms  a 
deliquescent  reddish-brow^n  mass,  which  should  be  powdered  while  warm, 
and  put  into  a  stopped  phial;  this  {^ferrate  of  potassa:  its  solution  in  water 
has  an  amethystine  tinge  so  deep  as  to  be  nearly  opaque,  and  gradually 
evolves  oxygen,  and  deposits  sesquioxide  of  iron  ;  this  decomposition  is  im- 
mediate and  perfect  at  212^^.  A  solution  of  ferrate  of  potassa  yields  red  in- 
soluble precipitates  in  solutions  of  baryta,  strontia,  and  lime,  which  are 
easily  decomposed  by  acids. 

Native  Oxides  of  Iron. — These  constitute  an  extensive  and  important  class 
of-  ores.  They  vary  in  color,  depending  upon  mere  texture  in  some  cases ; 
in  others,  upon  the  degree  of  oxidizement.  Some  are  magnetic,  and  those 
which  contain  least  oxygen  are  attracted  by  the  magnet.  The  following  are 
some  of  their  principal  mineralogical  varieties  :  1.  Magnetic  iron  ore,  which 
25 


386  CHLORIDES    OF    IRON. 

is  generally  black,  with  a  slight  lustre.  It  occnrs  massive  and  octahedral, 
and  is  often  powerfully  magnetic  ;  its  specific  gravity  is  4-5.  It  is  abundant 
in  Sweden,  where  it  is  manufactured  into  a  bar-iron  much  esteemed  for 
making  steel.  2.  The  specular  and  micaceoiis  iron  ore.  It  is  found  crystal- 
lized, of  singular  beauty,  in  Elba,  and  occasionally  among  volcanic  products. 
Its  specific  gravity  is  5-0  to  5*2  ;  it  yields  a  reddish  powder.  3.  Hcematite, 
or  red  ironstone,  occnrs  in  globular  and  stalactitic  masses,  having  a  fibrous 
and  diverging  structure.  It  is  sometimes  cut  into  instruments  used  for  bur- 
nishing;  its  density  is  4*8  to  5.  It  abounds  in  Lancashire.  Sometimes  it 
is  of  a  brown,  black,  or  ochraceous  color.  This,  as  well  as  the  iron-glance, 
is  a  sesquioxide,  and  does  not  affect  the  magnet.  There  are  also  several 
varieties  of  hydrated  peroxide  of  iron,  such  as  the  fibrous  haematite,  the 
granular  and  pisiform  iron  ore,  and  certain  varieties  of  ochre  and  umber. 
4.  A  fourth  variety  of  oxide  of  iron  is  known  under  the  name  of  Bog  ore, 
found  in  low  marshy  places,  and  generally  of  recent  origin. 

Iron  and  Chlorine. — There  are  two  chlorides  of  iron,  corresponding  in 
composition  to  the  protoxide  and  sesquioxide.  Protochloride  of  iron  (FeCl) 
may  be  obtained  by  passing  dry  hydrochloric  acid  gas  over  red-hot  iron  wire; 
or  by  digesting  iron  filings  in  hydrochloric  acid,  in  which  case,  as  in  the 
former,  hydrogen  is  set  free  ;  or  by  employing  protosulphide  of  iron  instead 
of  metallic  iron,  when  sulphuretted  hydrogen  is  evolved ;  in  both  cases  a 
green  solution  is  obtained,  which,  evaporated  out  of  the  contact  of  air,  leaves 
a  residue  which  is  to  be  exposed  to  a  red  heat.  Protochloride  of  iron  is  of 
a  gray  color,  and  after  fusion  acquires  a  foliated  crystalline  texture ;  it  is 
volatile  at  a  high  red  heat,  and  may  be  condensed  in  pale  gray  crystals. 
When  heated  with  access  of  air,  sesquichloride  of  iron  sublimes,  and  peroxide 
of  iron  remains  (6FeCl  +  30  =  2[Fe2Cl3]-f  Fe^Og).  When  the  vapor  of  water 
is  passed  over  it  at  a  dull  red  heat,  hydrochloric  acid  and  hydrogcFi  are 
evolved,  and  black  magnetic  oxide  remains  :  (3FeCl-f  4HO=Fe304  4-3HCi 
H-H).  Hydrated  Protochloride  of  Iron. — Dissolved  in  water  free  from  air, 
and  evaporated  in  vacuo,  this  chloride  furnishes  a  crystallizable  hydrate. 
When  a  saturated  solution  of  iron  in  hydrochloric  acid  is  evaporated,  air 
being  excluded,  it  yields  blue  rhombic  crystals,  which  become  green  and 
effloresce  in  dry  air,  into  a  white  powder.  Their  formula  is  FeGl,4H0. 
They  are  soluble  in  alcohol,  and  when  heated  in  the  air,  leave  peroxide. 

Perchloride  of  Iron  ;  Sesquichloride  of  Iron  (FegClg). — When  fine 
iron  wire,  heated  to  redness,  is  introduced  into  a  bell-jar  of  chlorine,  it  burns 
with  a  lurid  red  light  and  much  red-brown  smoke,  and  this  compound  is 
formed.  A  mixture  of  equal  weights  of  chloride  of  calcium  and  calcined 
sulphate  of  iron,  heated  to  redness,  also  afi'ords  a  sublimate  of  sesquichloride. 
Sesquichloride  of  iron  forms  brilliant  and  iridescent  brown  crystals,  volatile 
at  a  temperature  below  redness. 

Hydrated  Sesquichloride  of  Iron. — Sesquichloride  of  iron  is  deliquescent 
and  very  soluble  in  water  ;  when  the  solution  is  evaporated  in  the  air,  hydro- 
chloric acid  passes  off,  and  peroxide  of  iron  remains.  A  solution  of  this 
chloride  is  obtained  by  dissolving  peroxide  of  iron  in  hydrochloric  acid  ;  it 
forms  a  deep  brown  liquid,  which,  when  concentrated  and  exposed  to  cold, 
yields  crystals,  the  form  of  which  varies  with  their  respective  quantities  of 
water :  when  they  form  acicular  and  radiating  tufts,  they  include  about  40 
per  cent,  of  water,  being  Fe2Cl3,12HO  ;  but  when  they  form  larger  tabular 
crystals,  they  contain  about  22  per  cent,  and  are  Fea,Cl3,5IIO  ;  these  latter 
are  best  obtained  by  placing  the  former  over  a  surface  of  oil  of  vitriol  under 
-a  bell-glass ;  they  deliquesce  into  a  thick  fluid,  which  gradually  passes  into 


NITRATES    OP    IRON.  38t 

a  mass  of  the  crystals  containing  5  atom^  of  water.  When  a  current  of  chlo- 
rine is  passed  through  a  solution  of  protochloride  of  iron,  or  when  nitric  acid 
is  gradually  added  to  it  when  heated,  it  is  converted  into  sesquichloride.  If 
a  dilute  solution  of  the  protochloride  be  exposed  for  some  days  to  the  atmo- 
sphere in  a  tall  jar,  and  a  few  drops  of  ammonia  be  then  introduced  at  dif- 
ferent depths,  by  means  of  a  glass  tube,  the  precipitate  near  the  surface  will 
be  green  ;  a  little  lower,  blue  ;  still  lower,  gray  ;  then  of  a  dirty  white  ;  and 
at  the  bottom,  quite  white,  provided  the  solution  has  not  been  so  long  ex- 
posed as  to  have  become  oxidized  throughout.  The  sesquichloride  is  soluble 
in  alcohol  and  ether. 

Ammonio- chlorides  of  Iron. — Protochloride  of  iron  absorbs  ammonia  and 
forms  a  bulky  white  powder,  which  is  resolved  by  water  into  hydrochlorate 
of  ammonia  and  hydrated  oxide  of  iron.  If  iron-filings  are  boiled  in  a  satu- 
rated solution  of  sal-ammoniac,  hydrogen  and  ammonia  are  evolved,  and  the 
liquor  deposits  green  crystals  of  hydrated  protochloride  of  iron  and  ammonia. 
When  sesquichloride  of  iron  is  exposed  to  ammonia  it  is  slowly  absorbed, 
and  the  compound  furnishes  a  clear  red  solution  with  water  ;  it  contains 
about  9  per  cent,  of  ammonia,  being  (NHajFe^Clg).  A  mixed  solution  of 
sal-ammoniac  and  sesquichloride  of  iron  evaporated  in  vacuo  over  oil  of 
vitriol,  furnishes  brown  crystals  which  are  =(2NH4Cl,Fe2Cl3,2HO).  When 
hydrochlorate  of  ammonia  and  sesquioxide  of  iron  are  mixed  and  heated, 
a  yellow  sublimate  is  obtained,  which  is  the  Ferri  ammonio- chloridum  of  ipheiv- 
macy. 

Protiodide  of  Iron  (Fel)  is  formed  by  digesting  iron-turnings,  or  wire, 
with  iodine  in  water,  taking  care  to  have  excess  of  metal  present ;  a  green 
solution  is  obtained,  which,  by  evaporation  out  of  contact  of  air,  leaves  a 
gray  fusible  protiodide  of  iron.  It  is  soluble  in  water  and  alcohol,  but  the 
solution  absorbs  oxygen  and  deposits  peroxide,  unless  metallic  iron  is  present ; 
so  that  to  preserve  it  unchanged,  some  pieces  of  clean  iron  wire  should  be 
immersed  in  it.  By  careful  evaporation  i7i  vacuo  crystals  of  a  hydrated 
protiodide  of  iron,  including  5  atoms  of  water,  may  be  obtained.  This  salt 
is  used  medicinally,  and  its  oxidation  is  prevented  by  mixing  it  with  syrup. 
It  is  employed  in  the  production  of  iodide  of  potassium.  There  is  also  a 
Bromide  of  iron  (FeBr). 

Nitrates  of  Iron.  Protonitrate. — This  compound  is  formed  by  digesting 
iron  filings  on  very  dilute  nitric  acid  (specific  gravity  1'16).  But  little  gas 
is  evolved,  and  the  liquid  assumes  an  olive-brown  color  from  the  nitric  oxide 
which  it  contains,  but  when  exposed  to  the  air  it  becomes  pale-green  incon- 
sequence of  the  escape  of  this  gas.  Alkalies  produce  a  green  precipitate 
in  this  solution  ;  the  salt  cannot  be  obtained  in  crystals  by  the  usual  process, 
and  passes  into  pernitrate  by  exposure  to  air.  It  may,  however,  be  crystal- 
lized by  evaporation  in  an  exhausted  receiver  over  sulphuric  acid  ;  it  then 
forms  crystals  of  a  light  green  color  =FeO,NO,,7HO.  When  protosulphide 
of  iron  is  dissolved  in  dilute  nitric  acid  sulphuretted  hydrogen  escapes,  and 
a  green  solution  of  protonitrate  is  obtained,  which,  when  gently  heated, 
speedily  becomes  brown,  in  consequence  of  the  formation  of  peroxide.  Pro- 
tonitrate of  iron  is  also  formed  when  solutions  of  protosulphate  of  iron  and 
nitrate  of  baryta  are  mixed  in  atomic  prpportions.  The  solution  of  the  neu- 
tral protonitrate  is  decomposed  near  the  boiling  temperature,  with  the  evo- 
lution of  nitric  oxide,  and  the  abundant  precipitation  of  a  subnitrate  of  the 
peroxide.  Iron  turnings  may  be  dissolved  in  cold  and  highly  concentrated 
nitric  acid,  so  as  to  produce  ammonia  and  protonitrate  of  iron,  without  the 
extrication  of  gas  (8Fe,-fl0NO5-t-4HO=8[FeO,NOjH-NH,O,NO5).  Per- 
nitrate of  Iron;  ISesquinitrate  of  Iron. — Nitric  acid,  diluted  with  a  little 
water,  acts  violently  on  iron  and  peroxidizes  it ;  a  large  quantity  of  gas  is 


388  SULPHIDES    OF    IRON. 

generated,  consisting  of  nitrous  and  nitric  oxides,  and  a  solution  is  formed 
of  a  reddish-brown  color,  containing  pernitrate  of  iron,  and  affording  a  brown 
precipitate  with  the  alkalies.  \Yhen  this  solution  is  evaporated,  a  brown 
deliquescent  mass  remains,  soluble  in  water  and  alcohol ;  it  is  decomposed 
at  a  red  heat,  and  peroxide  of  iron  remains.  If  this  solution  be  mixed  with 
excess  of  carbonate  of  potassa,  the  precipitate  at  first  thrown  down  is  redis- 
solved  by  the  alkali,  and  a  deep-brown  liquid  obtained  {Liquor  ferri  alka- 
lini.) 

Passive  condition  of  Iron,  in  respect  to  the  action  of  Nitric  Acid. — In  ordi- 
nary cases  nitric  acid  of  the  specific  gravity  1-35  acts  powerfully  upon  iron, 
but  under  certain  circumstances  the  metal  becomes  inert.  This  state  is 
brought  about:  1.  By  slightly  oxidizing  the  extremity  of  an  iron  wire  by 
holding  it  in  the  flame  of  a  spirit  lamp,  and  when  cold  dipping  it  gradually 
into  the  acid,  taking  care  to  introduce  the  oxidized  end  first.  2.  By  dipping 
the  end  of  the  wire  into  strong  nitric  acid,  and  washing  it  in  water.  3.  By 
first  introducing  a  platinum  wire  into  the  acid,  and  then  the  iron  wire  in 
contact  with  it,  which  contact  may,  however,  afterwards  be  broken.  4.  An 
iron  wire  already  rendered  passive  acts  as  the  platinum  wire,  and  renders 
other  wires  passive  in  the  same  way. 

Protosulphide  of  Iron  (FeS). — When  sulphur  is  dropped  upon  red-hot 
iron  wire,  or  fused  with  iron  filings,  a  compound  is  obtained,  which,  after 
having  been  heated  to  expel  excess  of  sulphur,  is  soluble  in  dilute  sulphuric 
acid,  with  the  evolution  of  sulphuretted  hydrogen,  and  is  a  protosulphide  of 
iron.  So  also,  when  a  bar  of  wrought  iron  is  heated  nearly  to  whiteness, 
and  the  surface  is  rubbed  with  a  roll  of  sulphur,  the  protosulphide  melts 
from  the  surface  of  the  metal,  and  may  be  collected  in  a  vessel  of  cold  water. 
It  should  be  perfectly  dried.  Protosulphide  of  iron  is  of  a  dark-bronze 
color,  and  influences  the  magnet.  It  is  much  more  fusible  than  iron  ;  it 
loses  no  sulphur,  even  at  a  white  heat,  out  of  contact  of  air ;  when  pure,  it 
is  soluble  without  residue  in  dilute  acids,  with  the  evolution  of  sulphuretted 
hydrogen  and  the  formation  of  a  protosalt  of  iron.  It  is  much  employed, 
with  diluted  sulphuric  acid,  for  the  purpose  of  obtaining  sulphuretted  hydro- 
gen gas.  When  heated  in  air  or  oxygen,  sulphurous  acid  and  oxide  of  iron 
are  formed.  When  the  moist  hydrated  protosulphide  is  exposed  to  air,  the 
iron  becomes  oxidized,  and  sulphur  separates,  and  more  or  less  sulphurous 
and  sulphuric  acids  are  often  formed  with  heat  enough  to  produce  inflamma- 
tion. The  formation  of  this  sulphide,  by  the  action  of  sulphuretted  hpdrogen 
upon  hydrated  peroxide  of  iron,  has  already  been  mentioned  (p.  228). 

Bisulphide  of  Iron  (FeSg)  is  formed  when  the  protosulphide  is  well 
mixed  with  half  its  weight  of  sulphur,  and  subjected  to  a  high  temperature, 
which,  however,  should  be  below  redness  ;  a  bulky,  dark-yellow  metallic 
powder  is  the  result,  not  attracted  by  the  magnet,  and  insoluble  in  dilute 
sulphuric  and  hydrochloric  acids.  Bisulphide  of  iron  is  the  occasional  result 
of  the  slow  decomposition  of  a  solution  of  sulphate  of  iron  by  organic  matter. 
Thus,  the  bones  of  some  mice,  which  had  accidentally  fallen  into  a  solution 
of  the  sulphate,  were  found  incrusted  with  bisulphide.  Its  presence  in 
masses  of  wood  found  in  clay,  or  in  coal,  may  be  explained  upon  similar 
principles. 

Native  Sidphides  of  Iron. — Magnetic  pyrites  is  a  protosulphide  of  iron, 
and  common  or  yellow  pyrites  a  bisulphide.  Common  pyrites  is  found  mas- 
sive, and  crystallized  in  a  variety  of  forms;  it  often  occurs  in  radiated  nodules, 
which,  when  rolled  amongst  the  shingles  upon  the  sea-beach,  are  sometimes 
called  thunder-holts;  it  is  of  different  shades  of  brass  yellow.  It  is  used  in 
the  formation  of  sulphate  of  iron,  or  green  vitriol,  for  which  purpose  it  is 
gently  roasted  and  exposed  to  air  and  moisture.     The  cubical  bisulphide  is 


PROTOSULPHATE    OF    IRON.  389 

very  permanent,  but  some  of  the  prismatic  varieties  spontaneously  pass  into 
sulphate,  and  when  in  large  masses  generate  heat  enough  to  produce  igni- 
tion ;  in  this  way  beds  of  coal  have  been  set  oh  fire  in  consequence  of  the 
absorption  of  oxygen  by  their  contained  pyrites.  Pyrites  has  also  been  used 
as  a  source  of  sulphur,  and  as  a  substitute  for  sulphur  in  the  production  of 
sulphuric  acid.  This  article  is  now  an  important  article  in  British  manufac- 
tures. In  1865,  according  to  Mr.  Hunt,  the  quantity  of  iron-pyrites  raised 
in  the  United  Kingdom  amounted  to  114,195  tons,  and  of  this  quantity  the 
county  of  Wicklow  in  Ireland  yielded  81,993  tons. 

Sesquisulphide  OF  Iron  (Fe^S.^). — This  compound  is  formed  either  by 
passing  sulphuretted  hydrogen  over  sesquioxide  of  iron  at  a  temperature  not 
exceeding  212^,  or  by  the  action  of  the  same  gas  upon  the  hydrated  sesqui- 
oxide, at  common  temperatures.  It  is  formed  in  the  humid  way  by  adding 
neutral  persulphate  of  iron  drop  by  drop,  to  a  solution  of  an  alkaline  hydro- 
sulphate  ;  it  then  falls  as  a  black  powder,  which  cannot  be  dried  in  the  air 
without  change. 

Hyposulphite  of  Protoxide  op  Iron  (FeOjS^Og)  is  obtained  together 
with  sulphite,  by  digesting  finely-divided  metallic  iron  in  sulphurous  acid 
(2Fe  +  3S02=FeO,SA-f  FeO,SOJ.  When  sulphuric  or  hydrochloric  acid 
is  added  to  its  solution,  sulphurous  acid  is  evolved,  and  sulphur  precipitated. 
This  solution  furnishes  a  perfect  protosalt  of  iron  ;  and  by  keeping  a  few 
filings  of  iron  in  it,  it  may  be  retained  in  this  state.  It  gives  a  white  pre- 
cipitate with  ferrocyanide  of  potassium,  becoming  blue  by  exposure  to  oxygen 
or  air.     Infusion  of  galls  does  not  immediately  discolor  its  solution. 

Protosulphate  of  Iron  (FeO,S03)  \s  the  copperas  and  green  vitriol  o^ 
commerce,  and  is  often  prepared  by  exposing  roasted  pyrites  to  air  and 
moisture,  in  which  case  the  salt  is  impure.  It  is  usually  formed  by  dissolving 
iron  in  dilute  sulphuric  acid,  filtering  and  evaporating  the  solution,  and 
setting  it  aside  to  crystallize.  It  is  also  obtained,  free  from  persulphate,  by 
acting  upon  protosidphide  of  iron  by  dilute  sulphuric  acid.  This  salt  forms, 
when  pure,  bluish-green  crystals  in  the  form  of  oblique  rhombic  prisms, 
soluble  in  about  2  parts  of  water  at  60°;  of  a  styptic  taste,  reddening  vege- 
table blues,  and  including  T  atoms  of  water  (FeO,SO,^,*7HO).  When  chlorine 
is  passed  through  an  aqueous  solution  of  protosulphate  of  iron,  hydrochloric 
acid  is  formed,  and  the  iron  becomes  peroxidized,  so  that  water  is  decom- 
posed. Protosulphate  of  iron  is  insoluble  in  alcohol,  and  in  sulphuric  acid, 
both  of  which  deprive  the  crystals  of  water,  and  precipitate  the  salt  in  the 
form  of  a  white  powder.  The  green  vitriol  of  commerce  usually  contains 
persulphate,  and  has  a  grass-green  color.  Exposed  to  dry  air,  this  salt 
effloresces,  and  in  moist  air  absorbs  oxygen,  becoming  of  a  rusty  or  reddish 
color,  whence  the  French  term  couperose,  applied  to  it,  corrupted  into  cop- 
peras. When  heated  in  close  vessels,  it  fuses,  and  at  238°  loses  6  equiva- 
lents of  water,  but  retains  1  equivalent  till  heated  above  535° :  this  may  be 
driven  off  at  a  higher  temperature,  arfd  the  salt  is  then  white,  pulverulent, 
and  anhydrous.  At  a  higher  temperature  the  anhydrous  protosulphate  is 
converted  into  an  anhydrous  persulphate,  and  sulphurous  acid  is  at  the  same 
time  evolved:  2[FeO,S03]  =  Fe303,S034-S02 ;  and  at  a  full  red-heat  the 
persulphate  is  itself  decomposed,  and  leaves  peroxide,  while  the  sulphuric 
acid  partly  passes  off  in  an  anhydrous  state,  and  is  partly  resolved  into  sul- 
phurous acid  and  oxygen  (Saxgn  acid).  The  residuary  oxide  is  of  a  deep- 
red  color,  and  was  formerly  known  under  the  name  of  colcothar,  or  caput 
mortuum  vitrioli.  It  is  in  consequence  of  this  decomposition  that  sulphate 
of  iron  is  often  used  as  a  substitute  for  sulphuric  acid,  to  separate  w^eaker 
acids  from  their  bases,  at  high  temperatures.  Native  green  vitriol  is  fre- 
quently found  associated  with  pyrites,  and  produced  by  its  decomposition. 


390  PHOSPHATES    OF    IRON. 

Persulphate  op  Iron  (FeaOg.oSOp  is  made  by  adding  1  equivalent  of 
sulphuric  acid  to  a  solution  of  2  equivalents  of  protosulphate,  boiling,  and 
then  dropping  in  nitric  acid  as  long  as  red  fumes  are  evolved  ;  a  buff  colored 
deliquescent  mass  is  obtained  on  evaporation,  slowly  soluble  in  water,  and 
which,  when  carefully  heated,  leaves  an  anhydrous  salt :  it  is  decomposed  at 
a  red  heat.  In  this  compound  the  number  of  atoms  of  acid  are  equal  to  the 
number  of  atoms  of  oxygen  combined  with  the  metal.  Persulphate  of  iron  forms 
double  salts  with  the  sulphates  of  ammonia  and  of  potassa,  which,  in  form 
and  composition,  resemble  alum.  The  formula  of  the  ammonia-salt  is  NH^O, 
SO.^+FegO^.SSO^-f  24HO,  and  that  of  the  potassa-salt  KO.SOg+Fe^Og, 
3803+24110.  It  is  sometimes  found  associated  with  sulphate  of  alumina  in 
chalybeate  waters. 

Phosphide  of  Iron  (Fe^P)  is  formed  by  dropping  phosphorus  into  a 
crucible  containing  red-hot  iron  wire :  it  is  a  brittle  gray  compound,  and 
acts  upon  the  magnet.  It  may  also  be  procured  by  the  ignition  of  a  mixture 
of  iron  filings,  phosphoric  acid,  and  charcoal  powder ;  or  of  a  phosphate  of 
iron  and  charcoal.  It  is  not  readily  dissolved  by  acids.  A  small  portion  of 
this  compound  is  said  to  be  present  in  cold-short  iron  ;  it  is  injurious  to  the 
quality  of  the  metal  when  contained  in  it  to  the  amount  of  1  percent.  Phos- 
phorus increases  the  fusibility  of  iron.  The  fine  thread-like  Berlin  castings 
are  said  to  be  produced  from  iron  containing  the  phosphide. 

Protophosphate  of  Iron  (2(FeO)HO,P03)  is  insoluble  in  water.  It 
may  be  formed  by  adding  a  solution  of  common  phosphate  of  soda  to  proto- 
sulphate of  iron.  It  is  at  first  white,  but  becomes  blue  by  exposure  :  it  fuses 
and  forms  a  crystalline  bead  before  the  blowpipe ;  it  is  soluble  in  most  of 
the  acids,  from  which  it  may  be  again  precipitated  by  ammonia,  but  it  is 
soluble  in  excess  of  ammonia.  When  it  has  acquired  a  full  blue  tint,  it  is 
probably  analogous  to  the  7iative  phosphate,  and  is  a  hydrated  compound  of 
the  phosphate  of  the  protoxide  with  phosphate  of  the  peroxide.  This  blue 
phosphate  may  be  produced  by  adding  phosphate  of  soda  to  the  solution  of 
the  mixed  sulphates  of  iron  ;  it  is  not  changed  by  exposure  to  air  ;  its 
formula  is  HO,2(FeO)P03+2(Fe,03)r'03.  The  analyses  of  the  crystal- 
lized and  amorphous  native  phosphates  agree  with  the  formula  3(FeO)P05 
+  8H0. 

Perphosphate  of  Iron  is  a  white  insoluble  compound  which  is  precipi- 
tated on  adding  common  phosphate  of  soda  to  persulphate  or  perchloride  of 
iron  ; -or  by  adding  phosphoric  acid  to  a  mixture  of  acetate  of  soda  and  a 
persalt  of  iron.  The  precipitate  is  rendered  brown  by  solution  of  ammonia, 
but  is  not  soluble  in  ammonia  unless  excess  of  the  phosphate  of  soda  is 
present,  when  it  forms  a  brown  solution,  which  remains  clear  with  ferro- 
cyanide  of  potassium  till  an  acid  is  added,  when  Prussian  blue  is  thrown 
down.  It  is  also  dissolved  by  a  large  excess  of  peracetate  of  iron.  Owing 
to  the  insolubility  of  the  perphosphate  in  acetic  acid,  an  aliialine  phosphate 
forms  a  valuable  test  for  this  metal  (page  397),  and  enables  a  chemist  to 
separate  iron  from  the  alkaline  earths,  as  well  as  the  peroxide  from  the  prot- 
oxide of  the  metal. 

Iron  and  Carbon.  Carbide  of  Iron. — It  is  doubtful  how  far  any  defi- 
nite carbide  of  iron  can  be  separately  obtained,  but  these  compounds  have 
important  bearings  upon  the  properties  of  cast  iron  and  steel.  The  deter- 
mination of  the  quantity  of  carbon  in  them  ie  usually  effected  by  mixing 
from  50  to  100  grains  of  the  sample  in  very  fine  filings,  with  about  tea 
times  its  weight  of  chromate  of  lead,  heating  the  mixture  in  a  combustion- 
tube,  such  as  is  used  in  organic  analyses,  to  a  red-heat,  and  passing  over  it 
a  stream  of  pure  and  dry  oxygen  :  in  this  way  the  iron  and  carbon  are  both 
burned,  and  the  carbonic  acid  formed  by  the  latter,  when  absorbed  by  a 


MANUFACTURE    AND    PROPERTIES    OF    STEEL.  391 

solution  of  potassa,  becomes  the  indicator  of  the  quantity  of  carbon  present. 
But  cast  iron  contains  carbon  mechanically  mixed,  as  well  as  chemically 
combined ;  and  to  ascertain  their  relative  proportions,  the  iron  may  be  dis- 
solved in  hydrochloric  acid,  when  the  chemically  combined  carbon  goes  off 
in  the  form  of  hydrocarhons,  while  the  graphite  or  other  forms  of  carbon, 
which  were  mechanically  mixed,  remain,  together  with  silica,  and  may  be 
separated  by  filtration,  washed,  and  dried.  This  residue,  wiien  properly 
burned,  so  as  to  consume  the  carbon,  leaves  the  silica,  and  the  loss  of  weight 
gives  the  quantity  of  carbon. 

MoMufacture  of  Steel. — Steel  is  generally  regarded  as  a  compound  of  iron 
with  a  quantity  of  carbon,  varying  from  one  to  two  per  cent.  ;  but  the  exact 
nature  of  this  valuable  substance  is  perhaps  scarcely  understood.  In  some 
samples  the  proportion  of  carbon  has  been  found  below  0  2  per  cent.  ;  in 
others,  nitrogen  has  been  detected  ;  and  under  the  supposition  that  these 
small  quantities  of  foreign  matters  cannot  confer  upon  steel  the  remarkable 
properties  upon  which  its  value  depends,  it  has  been  assumed  that  it  may 
be  an  allotropic  condition  of  iron.  Traces  of  silicon,  manganese,  phos- 
phorus, arsenic,  and  aluminum,  have  also  been  discovered  in  steel  of  good 
quality. 

Steel  combines  the  fusibility  of  cast,  with  the  malleability  and  ductility  of 
bar  or  wrought  iron  ;  its  texture  varies,  some  of  the  varieties  being  granular 
or  lamellar,  and  others  exhibiting  a  silky  fracture  ;  but  it  is  never  fibrous, 
like  the  iron  from  which  it  is  obtained.  After  it  has  been  highly  heated, 
and  then  suddenly  cooled,  it  acquires  extreme  hardness,  and  becomes  more 
or  less  brittle,  and  very  elastic  ;  but  if,  after  having  been  heated  to  redness, 
it  be  allowed  to  cool  very  slowly,  it  becomes  nearly  as  tough  and  soft  as 
pure  iron.  But  the  most  characteristic  quality  of  steel  is,  that  it  may  be 
brought  to  any  intermediate  degree  of  hardness  between  these  extremes,  by 
the  process  called  tempering,  to  which  we  shall  presently  advert.  Steel  is 
also  distinguished  from  iron  by-its  permanent  retention  of  magnetism.  Steel 
may  be  obtained  from  the  purer  varieties  of  cast  iron,  or  from  some  of  the 
native  oxides  of  iron,  by  so  modifying  the  process  of  reduction  as  to  leave 
the  iron  in  combination  with  no  more  carbon  than  is  requisite ;  and,  in  that 
case,  it  has  been  termed  natural  steel.  Iron  may  also  be  converted  into 
steel  by  passing  carburetted  hydrogen  over  the  bars  at  a  full  red  heat ;  but 
it  is  generally  made  by  a  process  called  cementation,  which  consists  in  heating 
to  full  redness  bars  of  the  purest  iron,  in  contact  with  charcoal,  to  which  a 
little  common  salt  and  wood-ash  is  usually  added.  This  process  requires 
from  6  to  10  days,  according  to  the  thickness  of  the  iron  bars,  which,  when 
removed  from  the  furnace,  exhibit  a  blistered  surface,  arising,  as  has  been 
supposed,  from  the  production  of  carbonic  oxide.  When  blistered  steel  is 
drawn  down  into  smaller  bars,  and  forged  by  the  tilt  hammer,  it  forms  tilted 
steel;  and  this,  when  broken  up,  and  again  welded  and  drawn  into  bars,  forms 
shear  steel.  Cast  steel  is  prepared  by  fusing  blistered  steel  with  a  carbonaceous 
and  vitrifiable  flux,  and  casting  it  into  ingots,  which  are  afterwards  hammered 
or  rolled  into  bars.  It  has  a  more  uniform  texture  and  composition  than  the 
other  varieties,  and  is  used  in  the  manufacture  of  superior  cutlery,  and  for 
the  matrices,  punches,  and  dies  of  the  medal  engraver  and  coiner.  The  best 
cast  steel  seldom  contains  less  than  99  per  cent,  of  iron,  the  remaining  1  per 
cent,  being  made  up  of  carbon,  silicon,  phosphorus,  manganese,  and  occa- 
sional traces  of  the  other  substances  found  in  cast  iron. 

Case-hardening  is  an  operation  performed  upon  cast  or  wrought-iron,  by 
which  it  is  superficially  converted  into  steel :  the  article  is  for  this  purpose 
either  heated  to  redness  in  contact  with  charcoal  powder  ;  or  sometimes,  if 
small  and  delicate,  is  wrapped  round  with  leather,  and  then  gradually  heated 


392  MANUFACTURE    AND    PROPERTIES    OF    STEEL. 

to  redness,  and  kept  iu  that  state  till  its  surface  is  duly  carbonized.  Ferro- 
cyanide  of  potassium  is  also  a  valuable  material  as  a  case-hardener,  and  in 
various  operations  connected  with  the  management  of  steel. 

Hardening  and  Tempering  Steel — When  steel  is  heated  to  a  cherry-red 
color,  and  then  plunged  into  cold  water,  it  becomes  so  extremely  hard  and 
brittle,  as  to  be  unfit  for  almost  any  practical  purpose.  To  reduce  it  from 
this  extreme  hardness  it  is  subjected  to  the  process  of  tempering,  which  is 
effected  by  again  heating  the  steel  up  to  a  certain  fixed  point.  The  surface 
being  a  little  brightened,  exhibits,  when  thus  heated,  various  colors  depend- 
ing upon  the  formation  of  thin  films  of  oxide,  which  constantly  change  as 
the  temperature  is  increased,  and  by  these  colors  it  is  customary  to  judge  of 
the  temper  of  the  steel.  But  a  more  accurate  method  is  to  use  a  bath  and 
thermometer;  the  bath  may  be  of  oil,  mercury,  or  fusible  metal.  Into  this 
the  articles  to  be  tempered  are  put,  together  with  the  bulb  of  a  thermometer 
graduated  to  the  boiling  point  of  mercury.  The  corresponding  degrees  at 
which  the  various  colors  appear  are  from  430°  to  600°.  The  first  change 
is  about  430°,  but  this  is  very  faint.  At  460°  the  color  is  straw,  at  500°, 
brown  ;  this  is  followed  by  a  red  tinge,  then  purple,  and  at  nearly  600°,  it  is 
hlue.  Lancets,  certain  surgical  instruments,  and  razors,  are  tempered  between 
430°  and  460°  ;  penknives,  and  fine  cutlery,  at  460°  to  500  ;  table  and  carv- 
ing-knives at  500°  to  530° ;  and  sword-blades,  saws,  and  articles  requiring 
great  elasticity,  at  530°  to  600°. 

When  a  mass  of  steel,  a  die,  for  instance,  has  been  heated  red-hot,  and 
suddenly  quenched  in  cold  water,  it  retains  when  cold,  the  bulk  that  it  had 
when  heated ;  the  consequence  is,  that  its  particles  are  thrown  into  a  state 
of  very  unequal  tension,  so  that  it  frequently  cracks  off  or  flies  to  pieces.  Its 
specific  gravity  is  also  diminished.  The  specific  gravity  of  a  plug  die  of  the 
best  cast-steel,  weighing  about  2600  grains,  after  having  been  well  annealed, 
was  7  "8398  ;  after  having  been  indented  by  a  punch  in  a  fly-press,  its  specific 
gravity  was  T*8605;  it  was  then  hardened  by  heating  it  to  bright  redness 
and  plunging  it  into  water  at  55°.  By  this  process  its  sp.  gr.  was  reduced 
to  7-1525. 

The  quality  of  steel  is  sometimes  tested  by  washing  its  clean  surface  with 
dilute  nitric  acid,  which  ought  to  produce  a  uniform  gray  color ;  if  the  steel 
is  imperfect,  and  contains  veins  or  pins  of  iron,  they  become  evident  by  their 
difference  of  color.  When  some  particular  kinds  of  iron  or  steel  are  thus 
tested;  a  mottled  appearance  is  produced,  as  if  it  were  composed  of  layers 
or  wires  of  iron  and  steel  welded  together  ;  hence  is  supposed  to  arise  the 
peculiar  character  of  the  celebrated  Damascus  sword-blades.  According  to 
Rinman  {Chem.  News,  April,  1867),  tempered  steel  dissolves  in  hot  or  cold 
hydrochloric  or  sulphuric  acid  without  leaving  any  carbonaceous  residue  : 
untempered  steel  dissolves  in  hot  acid,  without,  and  in  cold  acid  with,  a  car- 
bonaceous residue.  Iron  dissolved  in  acid  sets  free  carbon  in  three  states — 
as  graphite  in  pig-iron,  as  ferrocarbon  in  untempered  steel,  and  as  hydro- 
carbon in  tempered  steel. 

Alloys  of  Steel — Attempts  have  been  made  to  improve  the  quality  of  steel 
by  alloying  it  with  manganese,  silver,  and  some  other  metals,  but  none  of 
these  combinations  have  been  found,  after  due  experience,  to  be  superior  to 
the  best  ordinary  steel. 

Protocarbonate  of  Iron  (FeO,C03).— When  a  solution  of  a  pure  proto- 
salt  of  iron  is  precipitated  by  carbonate  of  potassa  or  soda,  a  white  hydrated 
protocarbonate  of  iron  falls,  which,  if  washed  and  dried,  with  all  the  requisite 
precautions  for  excluding  oxygen,  forms  a  greenish  tasteless  powder,  contain- 
ing from  24  to  30  per  cent,  of  carbonic  acid ;  it  may  therefore  be  considered 
as  FeO,C02,IIO.     When  air  is  not  excluded,  the  white  precipitate  presently 


CYANIDES    OF    IRON.  393 

passes  through  various  shades  of  green,  and  if  exposed  to  air  becomes  brown, 
losing  carbonic  acid,  and  passing  into  hydrated  peroxide.  When  carbonic 
acid  in  aqueous  solution  is  digested  with  iron  filings,  a  colorless  solution  of 
the  protocarbonate  is  obtained.  It  is  not  an  uncommon  ingredient  in  mineral 
waters,  where  it  is  held  in  solution  by  excess  of  carbonic  acid.  The  most 
celebrated  springs  of  this  kind  in  England  are  those  of  Tunbridge  Wells. 
These  waters  have  an  inky  flavor,  are  blackened  by  vegetable  astringents ; 
and  wlien  boiled,  or  when  exposed  to  air,  deposit  hydrated  peroxide  of  iron. 
Chalybeate  waters  seldom  contain  as  much  as  a  grain  of  carbonate  of  iron 
in  a  pint ;  the  chalybeate  springs  in  and  about  Tunbridge  Wells  contain 
from  2  to  3  grains  in  the  gallon  (p.  150). 

Native  Protocarbonate  of  Iron,  or  Spaihose  Iron  Ore  {VeO,CO,^)  occurs  in 
rhombic  crystals.  Its  color  is  yellowish,  or  brownish-gray.  It  generally 
contains  manganese,  lime,  and  a  trace  of  magnesia;  it  slowly  dissolves  in 
hydrochloric  acid,  evolving  carbonic  acid.  The  clai/  iron  ore  of  our  coal 
districts,  from  which  British  iron  is  chiefly  obtained,  is  an  impure  protocar- 
bonate of  iron,  usually  containing  from  30  to  40  per  cent,  of  oxide  (p.  380). 
Carbonic  acid  does  not  form  a  definite  or  permanent  compound  with  per- 
oxide of  iron. 

Iron  and  Cyanogen. — These  substances  give  rise  to  several  important 
compounds,  in  which  they  exist  either  combined  in  various  proportions  or  as 
a  compound  radical  or  base,  in  union  with  other  bodies.  Protocyanide  of 
Iron  (FeCy)  is  obtained,  in  the  form  of  a  gray  powder,  by  gently  heating 
ammonio-cyanide  of  iron  (ferrocyanide  of  ammonium)  out  of  the  contact  of 
air.  It  is  also  formed  by  digesting  recently- prepared  Prussian  blue  in  a 
well-stopped  phial  with  a  saturated  solution  of  sulphuretted  hydrogen  ;  it 
becomes  white,  and  the  solution  contains  hydrocyanic  acid.  When  solutions 
of  cyanide  of  potassium  and  protosulphate  of  iron  are  mixed,  an  abundant 
reddish  precipitate  falls,  which  is  redissolved  by  excess  of  the  cyanide,  and 
then  forms  ferrocyanide  of  potassium.  But  it  is  doubtful  whether  a  jyure 
protocyanide  of  iron  has  been  isolated.  According  to  Pelouze,  a  combina- 
tion of  cyanogen  and  iron  (FcgCyJ,  corresponding  to  the  magnetic  oxide,  is 
obtained  by  passing  a  current  of  chlorine  into  a  boiling  solution  of  ferrocy- 
anide of  potassium  ;  a  green  powder  precipitates,  which  is  to  be  boiled  in  8 
or  10  parts  of  concentrated  hydrochloric  acid,  by  which  peroxide  and  cyan- 
ide of  iron  are  dissolved,  and  a  green  powder  remains,  which,  when  washed 
and  dried  in  vacuo,  constitutes  this  intermediate  combination  =FeCy+ 
FcgCyg  +  ^HO.  Heated  to  355°,  it  loses  water,  cyanogen,  and  a  little  hydro- 
cyanic acid,  and  acquires  a  deep  purple  color.  By  a  solution  of  caustic 
potassa,  it  is  converted  into  peroxide  of  iron,  and  a  mixture  of  the  ferro  and 
ferricyanides  of  potassium. 

Percyanide  of  Iron  ;  Sesquicyanide  of  Iron  (FCgCyg). — This  compound 
has  not  been  isolated.  It  is  obtained  in  solution  when  ferricyanide  of  potas- 
sium is  decomposed  by  silico-fluoride  of  iron,  forming  a  brown  astringent 
liquid,  but  on  evaporation  it  deposits  Prussian  blue.  The  varieties  of  Prus- 
sian blue  are  compound  cyanides  of  iron. 

Ferrocyanides  and  Ferricyanides. — The  cyanides  of  iron  combine  with 
other  cyanides  and  produce  two  classes  of  salts,  which  have  been  termed 
ferrocyanides  ^w^  ferricyanides ,  the  former  Q,oxii^\mx\^ferrocyanogen  =FeCy3, 
and  the  latter  ferricyanogen  =Fe2Cyg.  Neither  ferrocyanogen  nor  ferricya- 
nogen  has  been  isolated,  but  the  hypothesis  of  their  existence  as  distinct 
radicals  is  so  convenient,  as  to  have  led  to  its  general  adoption.  Ferrocya- 
nogen, Fey,  containing  1  atom  of  iron  and  3  of  cyanogen,  is  dibasic.  Fer- 
ricyanogen, Fdcy,  containing  2  atoms  of  iron  and  6  of  cyanogen,  is  tribasic. 
The  ferrocyanide  of  potassium,  for  instance,  is  K^jFcy,  and  the  ferricyanide, 


394  MANUFACTURE    OF    PRUSSIAN    BLUE. 

Kg.Fdcy  ;  the  ultimate  elements  of  the  former  being  KaFeNgCg ;  and  those 
of  the  latter,  KgFegNeC.a.     They  are  isomeric  (p.  19). 

Ferrocyanide  of  Hydrogen  ;  Ferrocyanic  Acid;  Hydroferrocyanio 
Acid  (H3,Fcy=H3Fe,Cy3). — {Ferrochyazic  acid  o^  Porret,  by  whom  it  was 
discovered  in  1818.) — This  acid  maybe  obtained  by  the  following  processes: 

1.  Dissolve  58  grains  of  crystallized  tartaric  acid  in  alcohol,  and  pour  the 
solution  into  a  phial  containing  50  grains  of  ferrocyanide  of  potassium  dis- 
solved in  3  drachms  of  warm  water  ;  the  potassa  is  precipitated  in  the  state 
of  bitartrate,  and  the  hydroferrocyanic  acid  remains  dissolved  in  the  alcohol, 
from  which  it  may  be  obtained,  by  careful  evaporation,  in  small  crystals.  2. 
Mix  a  cold  saturated  solution  of  ferrocyanide  of  potassium  with  one-fourth 
of  its  volume  of  strong  hydrochloric  acid,  and  agitate  it  with  half  its  volume 
of  ether  ;  a  white  crystalline  substance  separates,  which,  when  washed  with 
ether  and  dried,  or,  if  necessary,  dissolved  in  alcohol,  and  again  precipitated 
by  ether,  is  hydroferrocyanic  acid.  In  this  decomposition,  1  atom  of  ferro- 
cyanide of  potassium  and  2  of  hydrochloric  acid  yield  1  of  hydroferrocyanic 
acid  and  2  of  chloride  of  potassium.  Hydroferrocyanic  acid  thus  obtained, 
is  soluble  in  water  and  alcohol,  and  powerfully  acid :  it  decomposes  the  alka- 
line carbonates  with  effervescence,  forming  ferrocyanides  of  their  bases.  It 
is  inodorous,  and  not  poisonous  :  it  is  permanent  in  the  dry  state,  but  when 
moistened  and  exposed  to  air  it  forms  Prussian  blue. 

Ferrocyanogen,  regarded  as  a  bibasic  radical,  forms  two  sets  of  salts,  com- 
bining, namely,  with  2  atoms  of  the  same  metal,  as  in  the  ferrocyanide  of 
potassium,  F^Fcy ;  or  with  2  atoms  of  different  metals,  as  in  the  ferrocyanide 
of  potassium  and  calcium,  K,Ca,Fcy  ;  and  when  these  salts  are  formed  by 
the  hydroferrocyanic  acid,  the  2  atoms  of  its  constituent  hydrogen  are 
replaced  by  2  atoms  of  the  same  or  of  different  metals.  The  ferrocyanides 
are  decomposed  by  heat  with  various  phenomena.  1.  The  ferrocyanogen 
evolves  nitrogen  and  becomes  converted  into  carbide  of  iron,  which  remains 
mixed  with  the  basic  cyanide  ;  this  is  the  case  with  ferrocyanide  of  potassium. 

2.  The  cyanogen  of  both  the  cyanides  is  decomposed,  nitrogen  evolved,  and 
metallic  carbides  of  iron  and  of  the  basic  metal  are  formed  ;  as  with  ferro- 
cyanide of  lead.  3.  The  basic  cyanide  evolves  cyanogen,  and  is  reduced ; 
as  in  the  case  of  ferrocyanide  of  silver. 

Ferrocyanide  of  Iron. — When  ferrocyanide  of  potassium  is  added  to  a 
pure  protosalt  of  iron,  a  whitish  precipitate  falls,  which  becomes  blue  by 
exposure,  and  is  =K,Fe3,Cy3.  The  same  salt  is  thrown  down  on  adding 
hydrochloric  acid  to  a  solution  of  ferrocyanide  of  potassium.  Representing 
this  salt  by  the  formula  KFe,Fcy,  it  comes  under  the  class  of  ferrocyanides 
with  two  basic  metals. 

Prussian  Blue. — This  pigment  was  accidentally  discovered  by  Diesbach, 
a  color-maker  at  Berlin,  in  the  year  ITIO.  It  is  largely  consumed  in  the 
decorative  arts,  in  dyeing,  and  calico-printing  :  it  is  used  in  making  some 
of  the  varieties  of  what  is  called  stone-blue,  and  is  sometimes  added  to  starch, 
though  for  this  purpose,  as  well  as  for  covering  the  yellow  tint  of  paper, 
smalt  or  cobalt  blue  is  preferable.  Prussian  blue  is  prepared  of  different 
degrees  of  purity,  by  precipitating  solutions  of  peroxide  of  iron  by  ferrocy- 
anide of  potassium,  various  additions  being  made  according  to  the  purposes 
for  which  it  is  required. 

Pure  Prussian  blue  is  obtained  by  adding  a  solution  of  ferrocyanide  of 
potassium  to  persulphate  of  iron,  thoroughly  washing  the  precipitate,  first 
with  water  slightly  acidulated  by  sulphuric  acid,  and  then  with  pure  water, 
and  ultimately  drying  it  in  a  warm  place.  Prussian  blue  is  of  a  peculiarly 
rich  and  intense  blue,  with  a  copper  tint  upon  its  surface  ;  it  is  insipid,  in- 
odorous, insoluble  in  water,  in  alcohol,  and  in  dilute  acids,  and  is  not  poison- 


PERRICYANOGEN.      FERRICYANTDES.  395 

ous.  Concentrated  snlphnrio  acid  forms  with  it  a  white  pasty  mass  by  dehy- 
drating it,  from  which  water  again  separates  it  as  Prussian  blue ;  nitric  acid 
decomposes  it ;  concentrated  hydrochloric  acid  ultimately  abstracts  part  of 
its  iron.  Sulphuretted  hydrogen,  and  nascent  hydrogen,  gradually  destroy 
its  color.  The  alkalies  decompose  it  into  soluble  ferrocyanides  and  oxide 
of  iron,  hence,  as  a  dyeing  material,  it  does  not  resist  the  action  of  soap. 
Boiled  in  water  with  peroxide  of  mercury,  it  forms  cyanide  of  mercury,  and 
an  insoluble  compound  of  cyanide  and  oxide  of  iron.  A^ccording  to  Chevreul, 
Prussian  blue  becomes  white  in  the  direct  rays  of  the  sun,  but  regains  its 
blue  color  in  the  dark.  It  is  occasionally  used  in  the  composition  of  writing 
fluids.  It  is  hygrometric,  and  after  having  been  well  dried,  speedily  attracts 
moisture.  When  subjected  to  destructive  distillation,  it  yields  a  little  water 
with  hydrocyanate  of  ammonia,  and  then  carbonate  of  ammonia  ;  a  black 
pyrophoric  carbide  of  iron  remains. 

Prussian  blue  is  regarded  as  a  compound  of  cyanogen  and  iron,  but  various 
views  have  been  taken  of  its  atomic  constitution,  according  as  it  has  beea 
considered  to  contain,  or  not  to  contain,  the  elements  of  water.  When  an- 
hydrous, it  contains  7  atoms  of  iron  and  9  of  cyanogen  ;  or  4  atoms  of  iron 
and  3  of  ferrocyanogen  ;  but  it  is  generally  admitted  that  it  cannot  practi- 
cally be  obtained  in  this  state,  and  that  it  always  contains  water,  or  the  ele- 
ments of  water,  which  cannot  be  expelled  without  the  decomposition  of  the 
compound ;  if  so,  it  is  probably  a  hydroferrocyanate  of  the  sesquioxide  of 
iron. 

Ferrocyanide  of  Potassium  and  Iron. — It  has  already  been  observed  that 
the  white  precipitate  resulting  from  the  action  of  ferrocyanide  of  potassium 
upon  a  protosalt  of  iron,  contains  1  atom  of  potassium,  2  of  iron,  and  3  of 
cyanogen,  and  is  identical  with  the  salt  produced  by  the  action  of  sulphuric 
acid  upon  ferrocyanide  of  potassium  ;  it  is  therefore  a  ferrocyanide,  in  which 
1  atom  of  potassium  is  replaced  by  an  atom  of  iron  =K,Fe2Cy3 ;  or*it  may 
be  regarded  as  a  compound  of  1  atom  of  ferrocyanide  of  potassium  with  3  of 
cyanide  of  iron  =(K2,Fe,Cy3)H-3FeCy=2(K,Fe^,Cy3).  When  this  white  com- 
pound is  exposed  to  air,  it  absorbs  oxygen  and  becomes  blue,  forming  what 
has  been  termed  soluble  or  basic  Prussian  blue,  a  compound  of  Prussian 
blue  with  peroxide  of  iron  =(Fe7,Cyg+Fe303).  When  washed  with  water, 
the  ferrocyanide  is  first  washed  away,  but  if  the  washing  be  continued,  the 
whole  of  the  precipitate  is  gradually  dissolved,  furnishing  a  dark-blue  liquor, 
which  maybe  evaporated  to  dryness  without  decomposition.  The  blue  liquor 
is  not  precipitated  by  alcohol,  but  when  solution  of  sulphate  of  potassa  (and 
certain  other  salts)  is  added,  a  blue  precipitate  falls,  which  is  again  perfectly 
soluble  in  pure  water. 

Ferricyanogen  (Fe3Cy8=Fdcy). — This  assumed  tribasic  salt  radical  is 
isomeric  with  ferrocyanogen,  being  formed  by  the  coalescence  of  2  atoms  of 
that  compound. 

Ferricyanide  of  Hydrogen.  Hydroferricyanic  Acid  (Il3,Fe^Cye  or  Hg, 
Fdcy). — This  acid  is  prepared  by  decomposing  recently  precipitated  ferricy- 
anide of  lead  by  dilute  sulphuric  acid,  or  by  sulphuretted  hydrogen  :  on  fil- 
tration a  yellow  liquor  is  obtained,  which  by  very  slow  spontaneous  evapora- 
tion deposits  crystals  ;  if  heat  be  used,  a  brown  powder  remains  :  the  aqueous 
solution  gradually  decomposes,  especially  if  heated,  and  deposits  a  blue  crys- 
talline powder.  This  acid,  in  combining  with  metallic  oxides,  produces  water 
and  metallic  ferricyanide,  its  hydrogen  being  replaced  by  the  metal ;  its  com- 
pounds with  the  metals  of  the  alkalies  and  alkaline  earths  are  soluble  in 
water;  the  others  are  insoluble,  and  are  formed  by  the  reaction  of  a  soluble 
ferricyanide  upon  solutions  of  the  metallic  salts  (p.  289). 

Ferricyanide  of  Iron  (FesCyg=Fe3,Fdcy).  —  This  is  the  precipitate 


396  TESTS    FOR    THE    SALTS    OF    IRON. 

formed  by  adding  solution  of  ferricjanide  of  potassium  to  a  protosalt  of  iron; 
it  is  produced  by  the  substitution  of  3  atoms  of  iron  for  3  of  potassium  ;  it  is 
known  in  commerce  as  TiirnhulVs  blue  (K3,Fdcy)  +  3(FeO,S03)  =  (Fe3,Fdcy  + 
3KO,S03).  It  may  also  be  prepared  by  adding  to  a  protosalt  of  iron  a  mix- 
ture of  ferrocyanide  of  potassium  and  chloride  of  soda,  to  which  hydrochloric 
acid  has  been  previously  added.  It  is  distinguished  from  common  Prussian 
blue  by  its  action  on  ferrocyanide  of  potassium,  for  when  boiled  in  a  solution 
of  the  latter  salt  it  decomposes  it  into  ferricyanide,  which  is  dissolved,  and 
into  an  insoluble  gray  residue  of  ferrocyanide  of  iron  and  ferrocyanide  of 
potassium. 

Hydronitroprussic  Acid  and  Nitroprussides. — When  binoxide  of  nitrogen 
is  passed  through  an  aqueous  solution  of  hydroferricyanic  acid,  one  of  the 
products  is  hydronitroprussic  acid,  the  formula  of  which  is  H2,Fe.3Cy5,N03 : 
it  forms  a  well-defined  series  of  salts,  discovered  by  Dr.  Playfair  {Phil. 
Trans.  1848).  One  of  the  most  characteristic  of  these  is  the  nitroprusside 
of  sodium:  Na2,Fe3Cy5,N03-|-4Aq.  It  is  obtained  by  the  action  of  5  parts 
of  nitric  acid  (diluted  with  its  bulk  of  water)  upon  2  parts  of  pulverized  fer- 
rocyanide of  potassium  ;  cyanogen  and  hydrocyanic  acid  are  evolved,  and, 
when  the  effervescence  has  ceased,  the  solution  is  heated  in  a  water-bath  till 
it  produces  a  gray  (instead  of  a  blue)  precipitate  with  a  protosalt  of  iron  : 
it  is  then  set  aside,  and  crystals  of  nitre,  with  some  oxamide,  are  deposited ; 
these  being  removed,  the  solution  is  neutralized  by  carbonate  of  soda,  which 
throws  down  a  greenish-brown  precipitate,  and,  on  filtering  and  evaporating 
the  liquid,  crystals  of  the  nitroprusside  and  of  the  nitrates  of  potassa  and 
soda  are  obtained :  the  former  are  picked  out  and  purified  by  another  crys- 
tallization. Nitroprusside  of  sodium  forms  red  prismatic  crystals,  soluble  in 
about  2|-  parts  of  water.  The  solution,  when  exposed  to  light,  deposits 
Prussian  blue,  and  evolves  nitric  oxide;  when  an  alkaline  sulphide  is  added 
to  it,  ev?n  in  a  most  diluted  state,  it  assumes  a  deep  and  characteristic  purple 
color,  which,  however^  soon  disappears  (p.  288).  Nitroprusside  of  Barium 
(Ba.-5,FeeCy5,N03-f-6Aq)  forms  red  octahedral  crystals. 

Alloys  of  Iron. — These  compounds  are  not  of  much  importance,  except 
perhaps  those  of  zinc  and  tin,  as  far  as  they  are  concerned  in  the  production 
of  zinced  and  tinned  iron,  which  are  mentioned  under  those  metals. 

Tests  for  the  Salts  of  Iron.  Protosalts. — The  solutions  of  these  salts 
have  a. greenish  color,  and  a  peculiar  metallic  inky  taste.  1.  Sulphuretted 
hydrogen  gives  no  precipitate  in  a  solution  of  a  protosalt,  provided  it  is 
acid.  2.  Hydrosulphate  of  ammonia  gives  a  precipitate  of  greenish  black 
sulphide,  part  of  which  is  dissolved,  and  imparts  a  green  tint  to  the  alkaline 
liquid.  When  exposed  to  the  air,  this  precipitate  is  converted  into  a  red- 
dish-brown basic  salt  of  the  peroxide.  3.  Potassa  and  soda  throw  down  a 
white  hydrated  oxide,  insoluble  in  the  alkali.  This,  by  exposure  to  air, 
rapidly  becomes  green,  and  ultimately  brown  (hydrated  peroxide).  When 
precipitated  under  similar  circumstances,  the  oxide  of  manganese  becomes 
brown,  but  without  passing  through  any  shade  of  green.  4.  Ammonia  gives 
a  similar  precipitate,  which  is  partly  dissolved  by  an  excess,  forming  a  green- 
ish colored  liquid ;  but  on  exposure,  the  solution  or  precipitate  undergoes 
similar  changes.  5.  Alkaline  phosphates  and  arsenates  throw  down  white 
precipitates  (phosphate  and  arsenate)  which  pass  through  similar  changes. 
The  precipitated  phosphate  of  the  protoxide  is  soluble  in  acetic  acid.  6. 
Ferrocyanide  of  potassium  gives  a  white  precipitate  (p.  394),  which,  by  the 
rapid  absorption  of  oxygen,  acquires  a  dark  blue  color  (Prussian  blue). 
Hence  this  white  precipitate  forms  a  useful  test  for  free  oxygen  (p.  99).  T. 
The  ferricyanide  of  potassium  gives  a  rich  blue  precipitate  (p.  289).  The 
precipitates  given  by  this  and  the  preceding  test  are  insoluble  in  strong 


SEPARATION    AND    ESTIMATION    OP    THE    OXIDES    OF    IRON.       39T 

hydrochloric  acid.  If  the  solution  is  alkaline,  they  are  not  produced,  since 
alkalies  decompose  them.  8.  Tincture  of  galls  (tannic  acid)  produces  no 
change  of  color  in  the  solutions  of  pure  protosalts,  but  by  the  absorption  of 
oxygen,  and  the  oxidation  of  the  protoxide,  the  liquid  soon  acquires,  on  the 
surface,  a  pink,  purple,  blue,  or  even  black  tint,  according  to  the  quantity 
of  peroxide  of  iron  produced.  Sulphocyanide  of  potassium  and  succinate 
and  benzoate  of  ammonia  produce  no  precipitate  or  change  of  color. 

Persalts  of  Iron. — The  solutions  are  generally  brownish-yellow  and  very 
acid.  The  more  neutral  they  are,  the  deeper  the  color.  1.  Sulphuretted 
hydrogen  gives  with  the  solution  a  milky-white  precipitate  of  sulphur — the 
persalt  being  converted  to  a  protosalt  (Fe,033S034-HS=2(FeOS03)  +  HO, 
SOg-j-S).  2.  Hydrosidphate  of  ammonia  gives  a  black  precipitate  of  sul- 
phide of  iron  (FeS)  with  a  separation  of  sulphur.  This  precipitate  is  soluble 
in  hydrochloric  acid.  It  becomes  brown  by  exposure  to  air.  3.  Foiassa, 
soda,  and  ammonia,  as  well  as  their  carbonates  and  hicarhonates,  throw  down 
brown  hydrated  peroxide,  insoluble  in  an  excess  of  the  alkalies  or  their  salts, 
as  well  as  in  chloride  of  ammonium.  Some  organic  substances,  if  present, 
will  interfere  with  this  action  of  the  alkalies  (p.  385).  In  this  case  hydro- 
sulphate  of  ammonia  should  be  employed.  4.  Phosphate  or  arsenate  of  soda 
gives,  in  a  diluted  and  nearly  neutral  solution  of  a  persalt,  a  whitish  or  pale 
brown  precipitate  of  phosphate  or  arsenate  of  iron,  insoluble  in  acetic  acid, 
but  dissolved  by  mineral  acids ;  this  precipitation  is  promoted  by  boiling. 
Peroxide  of  iron  may  thus  be  separated  from  the  alkalies  and  alkaline  earths, 
as  well  as  from  any  protoxide  of  iron  which  may  be  present:  these  bases  are 
held  in  solution.  5.  Ferrocyanide  of  potassium  produces,  even  in  a  very 
diluted  solution,  a  blue  precipitate  (Prussian  blue,  p.  394)  which  is  insoluble 
in  hydrochloric  acid.  6.  Ferricyanide  of  potassium  gives  a  deep  emerald 
green  color  to  the  liquid,  but  no  precipitate  of  Prussian  blue  is  formed,  t. 
Sidpliocyanide  of  potassium  gives  a  blood-red  tint  even  when  the  persalt  is 
largely  diluted.  This  color  is  destroyed  by  heat  and  by  solutions  of  chloride 
of  gold  and  corrosive  sublimate.  8.  Tincture  of  galls  (tannic  acid)  gives 
immediately  a  blue-black  color,  which  is  destroyed  by  strong  mineral  and 
some  vegetable  acids.  9.  Succinate  and  benzoate  of  ammonia  (if  the  solution 
is  not  too  acid)  throw  down  pale  reddish-brown  precipitates  (persuccinate 
and  perbenzoate  of  iron).  The  protosalts  of  iron  and  the  salts  of  manganese 
are  not  precipitated  by  these  two  reagents. 

The  protoxide  may  be  separated  from  the  peroxide  of  iron  by  various 
processes.  1.  The  solution  of  the  two  salts,  nearly  neutralized,  may  be 
treated  with  acetate  of  soda,  and  a  small  quantity  of  phosphoric  acid  then 
added.  The  perphosphate  of  iron  alone  is  precipitated,  especially  when  the 
liquid  is  boiled,  the  protophosphate  remaining  dissolved  in  the  acetic  acid. 

2.  The  mixed  oxides  should  be  dissolved  in  hydrochloric  acid,  and  the 
liquid  warmed.  If  carbonate  of  baryta  is  then  added  to  this  liquid  in  a 
covered  vessel,  the  hydrated  peroxide  of  iron  only  is  precipitated.  On 
warming  the  acid  liquid,  the  protosalt  is  obtained  in  solution  in  the  filtrate. 

3.  A  solution  of  permanganate  of  potassa  loses  its  red  color  by  admixture 
with  the  proto,  but  not  with  the  persalts,  hence  the  proportions  of  the  mixed 
oxides  may  be  determined  volumetrically.  Dissolve  the  oxides  in  hydro- 
chloric acid  and  dilute  the  liquid  until  it  is  colorless.  A  standard  solution 
of  permanganate  of  potassa,  of  which  a  certain  number  of  measures  corre- 
spond to  a  grain  of  protoxide,  is  now  added.  When  the  color  is  ho  longer 
discharged,  the  operation  is  stopped,  and  the  number  of  measures,  repre- 
senting grains  of  protoxide,  read  off.  It  has  been  hitherto  the  custom  to 
estimate  iron  by  precipitating  it  by  ammonia  as  peroxide  from  a  persalt. 
The   precipitate   is  simply  washed  with  warm  water,  dried,  calcined,  and 


398  MANGANESE. 

weighed.  The  volumetric  method,  however,  is  preferable.  If  a  few  zinc 
filings  are  placed  in  the  acid  liquid,  warmed,  or  a  little  sulphite  or  bisulphite 
of  soda  is  added  to  it,  the  persalt  is  rapidly  converted  into  protosalt,  and  in 
this  state  the  proportion  present  admits  of  speedy  determination  by  the  use 
of  permanganate  of  potassa.  The  zinc  should  contain  no  iron,  and  the  whole 
of  the  sulphurous  acid  should  be  removed  by  boiling.  36  parts  of  anhydrous 
protoxide  are  equal  to  40  parts  of  anhydrous  peroxide.  Iron  may  be  readily 
separated,  as  peroxide,  from  all  the  alkalies,  as  well  as  from  baryta,  strontia, 
and  lime,  by  adding  to  the  acid  solution,  ammonia  and  hydrochlorate  of 
ammonia.  It  may  be  separated  from  magnesia,  the  protoxide  of  manganese, 
nickel,  and  cobalt,  by  diluting  the  liquid  containing  the  persalt  of  iron,  and 
adding  a  solution  of  carbonate  of  soda,  until  it  has  acquired  a  brownish-red 
color.  If  acetate  of  soda  is  then  added  and  the  liquid  boiled,  the  hydrated 
peroxide  of  iron  is  precipitated  (Will).  A  very  delicate  test  for  the 
presence  of  a  protosalt  in  a  persalt,  is  to  boil  the  diluted  liquid  with  chloride 
of  gold.  If  a  trace  of  protosalt  is  present,  metallic  gold  is  deposited,  other- 
wise not. 

The  only  metals  which  precipitate  iron  in  a  metallic  state  are  magnesium, 
zinc,  and  cadmium  :  they  effect  an  imperfect  precipitation  from  some  of  its 
protosalts,  in  vessels  excluded  from  the  access  of  air.  Before  the  blowpipe, 
peroxide  of  iron  produces  with  microcosmic  salt,  or  borax,  in  the  exterior 
flame,  a  glass  which  is  blood-red  while  hot,  but  yellow  when  cold.  The 
protoxide  forms  a  green  glass,  which,  by  increasing  the  proportion  of  the 
oxide,  passes  through  bottle-green  to  black,  and  is  opaque.  The  glass  from 
the  peroxide  which  is  reddish-colored  in  the  exterior,  becomes  green  in  the 
interior  flame  :  it  is  there  reduced  to  protoxide,  and  becomes  attractable  by 
the  magnet. 

The  native  compounds  of  iron  may  be  dissolved  by  hydrochloric  or  nitro- 
hydrochloric  acid.  The  silicates  containing  iron  should  be  fused  with  four 
times  their  weight  of- the  mixed  carbonates  of  potassa  and  soda.  The  iron 
then  becomes  entirely  soluble  in  hydrochloric  acid. 


CHAPTER    XXX. 

MANGANESE    (Mn  =  28). 

The  common  ore  of  manganese  is  the  black,  or  peroxide  ;  it  is  found  in 
considerable  abundance,  and  is  of  great  importance  as  a  source  of  oxygen, 
and  for  the  production  of  chlorine  from  seasalt,  and  as  a  chemical  agent  in 
various  arts  and  manufactures.  Manganese  also  occurs  in  several  mineral 
compounds,  and  traces  of  it  are  found  in  the  ashes  of  some  plants,  in  a  few 
animal  products,  and  in  some  spring  waters.  To  obtain  metallic  manganese, 
carbonate  of  manganese,  mixed  into  a  paste  with  oil,  is  subjected  to  a  heat 
gradually  raised  to  redness,  in  a  close  vessel.  The  carbonaceous  mixture 
thus  obtained  is  then  rammed  into  a  good  crucible,  filled  up  with  charcoal- 
powder,  and  submitted  for  two  hours  to  a  white  heat :  a  metallic  button  is 
thus  obtained,  which  is  manganese,  containing  a  little  carbon  and  silicon, 
from  which  it  may  be  freed,  by  fusion  with  borax  in  a  crucible  coated  with 
charcoal ;  it  is  doubtful,  however,  whether  in  this  case  it  does  not  retain 
boron  or  sodium. 


OXIDES    OF    MANGANESE.  399 

Properties. — Manganese  is  a  hard  gray  metal  of  a  reddish  white  color, 
with  a  granular  or  slightly  crystalline  fracture.  Sp.  gr.  8-013.  It  is  best 
preserved  in  naphtha,  for  in  the  air  it  tarnishes  by  oxidation  and  crumbles 
into  powder ;  it  undergoes  the  same  change  in  water,  with  the  evolution  of 
hydrogen.  When  handled  with  moist  fingers,  it  exhales  a  disagreeable  odor, 
and  when  acted  on  by  acids,  the  purest  specimens  afford  traces  of  carbon. 

Manganese  and  Oxygen. — There  are  five  compounds  of  manganese  and 
oxygen,  three  of  which  are  oxides,  and  two  acids;  together  with  two  inter- 
mediate oxides,  namely,  the  red  oxide,  and  the  mineral  called  Yarvicite. 
Their  formulae  are  as  follows  : — 

Protoxide     .........  Mn  0 

Sesquioxide Mn^Oj 

Binoxide  (Peroxide)    .......  Mu  O2 

Red  oxide  (Hausmannite) MiigO^^ 

Varvicite      .........  Mn^O^ 

Manganic  acid      ........  Mn  O3 

Permanganic  acid MngO^ 

Protoxide  op  Manganese  ;  Manganous  Oxide,  (MnO),  is  obtained  by 
passing  a  current  of  dry  hydrogen  over  carbonate  of  manganese,  in  a  porce- 
lain tube,  exposed  to  a  red  heat.  It  should  be  allowed  to  cool  before  re- 
moval from  the  tube,  otherwise  it  is  apt  to  absorb  oxygen.  It  is  of  a  dingy 
green  color ;  when  heated  in  the  air  it  is  converted  into  sesquioxide ;  and  at 
a  temperature  of  about  600°  burns  sometimes  like  tinder.  It  is  soluble  in 
the  dilute  acids,  and  is  the  basis  of  the  ordinary  manganesian  salts,  which 
are  soluble  in  water,  and  are  nearly  colorless  when  pure,  but  often  have  a 
slightly  pink  hue.  When  ammonia  is  added  to  solutions  of  this  oxide,  the 
whole  is  not  precipitated,  but  a  double  salt  is  formed,  as  with  magnesia : 
thus  2[MnO,S03]  +  NH3=[MnO,NH32S03]  +  MnO.  When  the  salts  of 
this  oxide  are  decomposed  by  potassa  or  soda,  a  bulky  white  precipitate  falls, 
which  is  hydrated  protoxide  of  manganese ;  it  speedily  becomes  brown  by 
exposure  to  air,  absorbing  oxygen  and  a  little  carbonic  acid ;  and,  when  col- 
lected and  washed  upon  a  filter,  it  gradually  becomes  a  hydrate  of  the  sesqui- 
oxide. A  similar  change  is  immediately  produced  by  solution  of  chlorine  or 
chloride  of  lime,  by  which  a  hydrate  of  the  sesquioxide,  or  of  the  binoxide 
is  formed.  The  recently  precipitated  and  moist  hydrate  of  the  protoxide  is 
soluble  in  ammonia,  but  not  in  potassa  or  soda. 

Sesquioxide  of  Manganese;  Manganic  Oxide;  (MuaOg). — When 
protoxide  or  carbonate  of  manganese  is  exposed  for  some  time  to  a  red  heat 
in  an  open  vessel,  it  absorbs  oxygen,  and  is  converted  into  a  deep-brown 
powder.  An  oxide  similarly  constituted  is  also  obtained  by  heating  the  pure 
peroxide  in  a  platinum  crucible  till  it  ceases  to  give  out  oxygen  at  dull  red- 
ness. By  exposing  protonitrate  of  manganese  to  a  red  heat,  the  sesquioxide 
remains  as  a  black  powder ;  and  this  is  the  most  certain  way  of  obtaining  it. 
The  characters  of  this  oxide,  in  respect  to  solvents,  differ  with  its  state  of 
aggregation;  its  acid  solutions,  which  are  at  first  red,  become  colorless  when 
heated,  when  exposed  to  air  and  light,  or  in  contact  with  organic  matter, 
and  deposit  peroxide,  while  a  portion  of  protoxide  remains  in  solution. 
They  are  rendered  colorless  by  sulphuretted  hydrogen,  by  sulphurous  acid, 
and  some  other  deoxidizers.  Heated  with  hydrochloric  acid,  it  evolves 
chlorine  ;  and  with  sulphuric  acid,  oxygen  ;  and  a  protochloride  and  proto- 
sulphate  of  manganese  result.  Digested  with  nitric  acid,  protonitrate  and 
peroxide  are  formed.  As  a  base,  this  oxide  is  isomorphous  with  sesquioxide 
of  iron  (FCaOg),  and  with  alumina  {A\fi^).     It  may  replace  either  of  these 


400  OXIDES    OP    MANGANESE. 

oxides  by  formino^  a  manganese  alum.  It  gives  a  violet,  or,  in  small  quan- 
tity, a  pink  tinge,  to  glass,  and  appears  to  be  the  coloring  principle  of 
amethyst.  It  constitutes  the  mineral  called  hraunite,  which  occurs  in  octa- 
hedral crystals. 

Hydrated  Sesquioxide  of  Manganese  (Mn203+HO).is  obtained  by  exposing 
the  hydrated  and  moist  protoxide  to  the  action  of  air;  or  by  passing  chlorine 
through  water  holding  protocarbonate  of  manganese  in  suspension,  and 
leaving  excess  of  the  latter ;  for  if  the  chlprine  be  in  excess,  hydrated 
binoxide  is  formed.  It  is  a  common  natural  product  (the  manganite  of 
mineralogists),  occurring  crystallized  and  massive,  sp.  gr.  4-3,  and  so  closely 
resembling  the  peroxide,  that  it  is  often  difficult  to  distinguish  them  ;  the 
powder  of  the  hydrated  sesquioxide  is,  however,  generally  brown,  that  of  the 
peroxide  hlach;  the  former,  heated  in  a  tube,  gives  off  water  and  little 
oxygen  ;  the  latter  little  moisture  and  much  oxygen. 

Binoxide  OF  Manganese  ;  Peroxide  of  Manganese  (MnOg). — This  is 
the  oxide  which  most  frequently  occurs  native.  It  is  common  in  Devonshire, 
Somersetshire,  and  Aberdeenshire.  It  is  found  in  a  variety  of  forms  :  com- 
pact and  massive,  pulverulent  and  crystallized.  Many  of  the  latter  varieties 
have  a  gray  metallic  lustre,  and  are  found  acicularly  radiated,  and  in  rhom- 
boidal  prisms.  Its  specific  gravity  varies  between  4*8  and  49.  It  is  the 
pyrolusite  of  some  mineralogists.  Under  the  name  of  manganese  it  is  met 
with  in  commerce,  and  is  largely  consumed  in  the  manufacture  of  bleaching 
compounds.  In  the  laboratory,  it  is  resorted  to  as  a  source  of  oxygen  gas 
(2Mn02=Mn203  +  0),  for  which  purpose  it  should  be  well  dried  before  it  is 
heated.  Carbonate  of  lime,  silica,  oxide  of  iron,  and  some  other  substances, 
are  not  unfrequently  associated  with  it.  In  the  arts  it  is  used  to  give  a 
black  color  to  earthenware,  and  to  remove  the  green  color  which  glass 
derives  from  protoxide  of  iron  ;  in  this  case  MnO^,  acting  on  2FeO,  produces 
MnO  and  FcgOg,  neither  of  which  in  small  quantity  gives  color  to  glass.  A 
little  excess  of  the  oxide  of  manganese  is  apt  to  give  the  pink  tint  which  is 
sometimes  seen  in  plate-glass  windows.  This  oxide  is  a  good  conductor  of 
electricity.  It  forms  no  combinations  with  the  acids  ;  but  such  of  them  as 
appear  to  dissolve  it,  reduce  it  to  the  state  of  protoxide.  Gently  heated 
with  hydrochloric  acid,  chlorine  is  liberated,  in  consequence  of  the  decompo- 
sition of  the  acid  by  the  oxygen  of  the  oxide  (Mn03+2HCl  =  MnCl  +  2HO 
-f  CL)  The  chloride  in  solution  has  all  the  properties  of  the  protosalts  of 
manganese.  Boiled  with  sulphuric  acid,  oxygen  is  evolved,  and  a  soluble 
sulphate  of  the  protoxide  is  formed,  [MnO„4-S03=:MnO,S03  +  0].  This 
is  one  of  the  methods  of  procuring  oxygen,  but  it  is  an  objectionable  pro- 
cess, on  account  of  the  hard  cake  of  sulphate  of  manganese  produced.  This 
is  liable  to  break  the  retort.  Winkerlius  suggested  the  use  of  bisulphate  of 
soda,  the  residue  left  on  distilling  common  salt  with  hydrochloric  acid,  as  a 
substitute  for  sulphuric  acid.  He  finds  that  a  mixture  of  three  parts  of 
bisulphate  and  one  of  manganese  answers  well.  The  mixture  fuses  under 
the  heat  of  a  spirit-lamp,  and  remains  liquid  to  the  end,  oxygen  being  gently 
given  off.  The  acid  sulphate  of  potash,  a  waste  residue  left  on  distilling 
nitre  with  sulphuric  acid,  would  also  answer  the  purpose.  Nitric  acid  has 
no  action  on  peroxide  of  manganese  unless  it  contains  sesquioxide,  or  some 
deoxidizing  agent  is  at  the  same  time  present.  Many  vegetable  acids 
decompose  it  by  the  aid  of  heat. 

The  commercial  value  of  this  oxide  may  be  said  to  depend  upon  the  pro- 
portion of  chlorine  which  a  given  weight  of  it  will  evolve  when  heated  with 
hydrochloric  acid  ;  or,  in  other  words,  the  quantity  of  oxygen  which  it  con- 


MANGANIC    ACID.      MANGANATES.  401 

tains  beyond  that  contained  in  the  protoxide.  The  usual  mode  of  deter- 
mining this  excess  of  oxygen,  is  founded  upon  the  mutual  action  of  the  oxide 
and  oxalic  acid  in  the  presence  of  free  sulphuric  acid,  when  protosulphate  of 
manganese  and  carbonic  acid  are  formed. 

A  hydrated  peroxide,  =Mn02,  +  H0,  is  formed  by  precipitating  proto- 
chloride  of  manganese  by  chloride  of  lime.  In  this  state  it  is  brown,  while 
the  anhydrous  oxide  is  black.  The  soft  black  mineral  known  under  the  name 
of  IVad,  is  also  a  hydrate  of  this  peroxide. 

Jied  Oxide  of  Manffanese  {Mn.fi^). — This  oxide  exists  native,  constituting 
the  mineral  termed  Hausmannite .  It  is  said  to  be  formed  when  the  hydrated 
protocarbonate  of  manganese,  after  having  been  dried,  is  exposed  in  the  air 
to  a  red  heat.  Varvicite  (Mn^Oy). — This  name  has  been  given  to  a  peculiar 
oxide  of  manganese  from  Warwickshire.  It  is  harder  and  has  more  lustre 
than  the  native  peroxide. 

Manganic  Acid  (MnOg). — This  acid  is  met  with  only  in  a  state  of  com- 
bination with  alkaline  bases.  It  may  be  obtained  as  manganate  of  potassa 
by  fusing  equal  parts  of  peroxide  of  manganese  in  fine  powder,  and  hydrate 
of  potassa,  with  a  small  quantity  of  nitrate,  in  a  covered  crucible;  a  greenish 
black  mass  results,  which  with  water  affords  a  deep  green  solution  of  manga- 
nate of  potassa.  This  is  permanent  with  excess  of  alkali,  but  otherwise  it 
becomes  blue,  purple,  and  ultimately  red  on  exposure  to  air,  in  consequence 
of  the  formation  of  permanganate  of  potassa  by  the  absorption  of  oxygen 
{chameleon  mineral).  At  the  same  time  it  deposits  a  brown  powder,  which 
is  hydrated  peroxide  of  manganese,  and  free  alkali  is  separated :  (3[K0, 
Mn03]=KO,MnaOy4-Mn03+2KO.)  Nitric  acid  or  chlorine  added  to  the 
liquid,  changes  the  green  into  the  red  compound.  When  set  free  from  the 
base,  manganic  acid  is  resolved  into  hydrated  peroxide  and  oxygen. 

Manganate  of  Potassa  (KOjMnOg),  may  be  obtained  in  a  purer  state  as 
follows  :  Mix  4  parts  of  finely-powdered  peroxide  of  manganese  with  3|  of 
chlorate  of  potassa,  and  add  them  to  5  parts  of  hydrate  of  potassa  dissolved 
in  a  small  quantity  of  water.  The  mixture  is  evaporated  to  dryness,  pow- 
dered, and  then  ignited  in  a  platinum  crucible,  but  not  fused,  at  a  low  red 
heat.  Digested  in  a  small  quantity  of  cold  water,  and  filtered  through  as- 
bestos, this  affords  a  deep  emerald  green  solution  of  the  alkaline  manganate, 
which  may  be  obtained  in  crystals  of  the  same  color  by  evaporating  the  solu- 
tion over  sulphuric  acid  in  the  air-pump.  The  crystals  are  isomorphous  with 
the  sulphate  and  chromate  of  potassa.  They  are  anhydrous.  They  are 
soluble  in  a  moderately  concentrated  solution  of  potassa,  forming  an  intensely 
green  solution,  and  are  again  deposited  without  change  when  evaporated  in 
vacuo.  The  changes  of  color  which  the  compound  undergoes  may  be  well 
illustrated  by  placing  a  quantity  of  the  manganate  in  powder  in  a  capacious 
jar,  and  very  gradually  adding  to  it  a  large  quantity  of  water  which  is  aerated. 
As  the  oxygen  is  absorbed  by  the  manganic  action,  it  changes  in  color  from 
emerald  green  to  blue,  violet,  purple,  and  at  length  remains  of  a  ruby  or 
amethyst  red.  It  is  now  permanganate  of  potassa.  This  conversion  is  im- 
mediately brought  about  by  the  addition  of  an  acid,  even  by  acetic  acid. 
Acids  operate  by  removing  the  base.  The  change  is  also  rapidly  effected  by 
boiling,  showing  that  the  manganic  is  a  very  unstable  acid.  It  is  reduced  to 
the  state  of  hydrated  peroxide  by  many  kinds  of  organic  matter,  especially 
if  in  a  decomposing  state.  It  is  instantly  decomposed  and  rendered  colorless 
by  sulphurous,  phosphorous,  and  nitrous  acids.  Arsenious  acid  also  reduces 
it.  The  tendency  of  this  acid  therefore  is  to  pass  either  to  a  lower  or  higher 
state  of  oxidation.. 
26 


402  PERMANGANIC    ACID. 

Permanganic  Acid  (Mn^Oy). — When  the  green  solution  of  manganate  of 
potassa  in  water,  moderately  diluted,  is  boiled,  it  rapidly  becomes  purple  by 
conversion  into  the  permanganate  of  potassa  (KOjMn^Oy).  As  the  solution 
is  decomposed  by  contact  with  organic  matter,  it  must  be  filtered  through 
asbestos,  and  concentrated  by  evaporation.  Deep  ruby-colored  crystals  are 
thus  obtained,  which  are  soluble  in  16  parts  of  water  at  60°,  and  possess  an 
intense  coloring  power ;  one  or  two  grains  will  give  a  deep  amethyst  red 
tint  to  a  large  quantity  of  water. 

The  solution  of  this  salt  is  now  much  employed  in  volumetric  analysis.  It 
readily  parts  with  its  oxygen  to  organic  matter  and  deoxidizing  bodies 
generally  ;  it  loses  its  color,  and  brown  hydrated  peroxide  of  manganese  is 
deposited.  Thus  the  color  of  the  permanganate  is  discharged  by  sulphurous, 
phosphorous,  nitrous,  and  arsenious  acids,  as  well  as  by  their  salts  when  an 
acid  is  added.  Sulphuretted  hydrogen,  a  protosalt  of  iron,  thallium  and 
its  oxide,  grape-sugar,  aiid  nicotina  immediately  deoxidize  it.  Iodide  of 
potassium  converts  a  concentrated  solution  to  green  manganate,  but  deoxi- 
dizes entirely  a  weak  solution.  Ammonia  is  slowly  oxidized  by  the  solution: 
when  the  decolorized  permanganate,  to  which  ammonia  has  been  added,  is 
filtered  and  evaporated,  it  has  been  observed  that  on  the  addition  of  an  acid  to 
the  dry  residue,  red  fumes  have  been  evolved  showing  the  presence  of  some 
nitrite  or  hyponitrite  of  potash.  A  diluted  solution  of  permanganate  is  not 
affected  in  the  cold  by  magnesium,  zinc  or  aluminum  ;  but  mercury  agitated 
with  it  is  converted  into  suboxide,  and  the  solution  loses  its  color.  The 
action  takes  place  more  strongly  if  the  metal  is  boiled  in  the  solution,  but  in 
this  case  some  oxide  of  mercury  is  formed.  A  standard  solution  of  the 
permanganate  has  been  employed  for  determining  the  presence  of  organic 
matter  in  air  and  water,  (pp.  131,  163).  It  has  been  erroneously  supposed 
that  it  would  determine  the  precise  amount  of  organic  matter  present  in  a 
given  volume  of  water,  but  experiment  shows  that  different  kinds  of  organic 
matter  require  different  quantities  of  the  permanganate,  and  therefore  no 
reliance  can  be  placed  upon  quantitative  results,  unless  we  are  aware  of  the 
nature  of  the  organic  matter  which  is  present  in  the  water.  Dr.  Frankland 
found  on  dissolving  three  grains  of  each  of  the  following  organic  substances 
in  distilled  water,  and  testing  by  a  standard  solution  of  permanganate,  that 
the  following  quantities  were  indicated  : — 


Of  Gum  acacia    . 

.     -082 

Creatine 

, 

.     -064 

Cane  sugar     . 

.     -051 

Alcohol 

, 

.     -074 

Starch    . 

.     -114 

Urea    . 

^ 

.     -074 

Gelatine 

.     -634 

Oxalic  acid 

. 

.  2-998 

The  only  result  approaching  to  correctness  was  given  by  oxalic  acid,  the 
standard  deoxidizer  used.  The  determination  of  the  weight  of  oxidizable 
organic  matter  by  means  of  this  test  is  therefore  based  on  a  pure  fallacy. 
At  the  same  time  it  is  a  safe  guide  in  forming  an  opinion  of  the  freedom  of 
water  from  decomposing  organic  matter.  If  six  or  eight  ounces  of  water 
retain  a  pink  color  for  several  hours  from  the  addition  of  a  few  drops  of  a 
weak  solution  of  permanganate,  it  may  be  inferred  that  the  water  is  com- 
paratively pure  and  free  from  any  undue  amount  of  decomposing  organic 
matter  and  gaseous  impurities.  Foul  water  may  be  thus  purified,  and  after 
filtration  rendered  fit  for  drinking  purposes.  For  the  preparation  of  the 
purest  water.  Star  recommends  that  permanganate  of  potash  should  be  added 
and  the  mixture  distilled.     Rain  water  may  be  thus  purified. 

Under  the  name  of  Condifs  Disinfecting  Liquid,  a  solution  is  generally 
sold  in  a  concentrated  form  in  the  state  of  green  manganate,  but  it  becomes 
converted  into  purple  or  red  permanganate  by  the  necessary  dilution  with 


CHLORIDES    OP    MANGANESE.  403 

water.  As  it  is  a  fixed  compound,  it  can  operate  only  as  a  deodorizer  by 
direct  contact  with  the  liquid  or  solid,  emitting  offensive  effluvia.  Linen 
wetted  with  it,  and  suspended  in  a  foul  atmosphere,  removes  the  effluvia 
from  that  portion  of  air  which  comes  in  contact  with  it,  but  it  does  not,  like 
chlorine,  diffuse  itself  through  the  apartment  so  as  to  destroy  the  noxious 
matter  in  all  parts.  For  this  purpose  ozonized  ether  is  preferable  to  the 
permanganate.  The  acid  loses  three  atoms  of  oxygen  during  this  process, 
and  is  reduced  to  hydrated  peroxide  which  causes  stains  on  linen.  Per- 
manganate also  operates  as  a  bleacher  by  oxidation.  Thus  a  few  drops  of 
the  solution  added  to  a  solution  of  indigo  discharges  the  color.  This  salt 
has  become  a  most  useful  substance  in  the  laboratory.  A  solution  of  it  is 
sold  under  the  name  of  Ozonized  water.  When  used  as  a  lotion,  it  removes 
the  smell  of  fetid  breath,  of  offensive  ulcers,  and  also  of  effluvia  from  the 
hands. 

If  a  solution  of  nitrate  of  silver  is  added  to  a  hot  concentrated  solution 
of  permanganate  of  potassa,  red  crystals  of  permanganate  of  silver  are 
deposited  on  cooling.  By  double  decomposition  with  the  chlorides,  per- 
manganates of  the  alkaline  earths  may  be  obtained.  If  a  concentrated  solu- 
tion of  potassa  is  poured  into  a  diluted  solution  of  permanganate,  the  liquid 
becomes  first  violet  and  by  very  gradual  additions  of  the  alkali,  passes  through 
various  shades  of  purple  to  emerald  green.  Manganate  of  potassa  is  formed, 
and  a  double  quantity  of  base  enters  into  combination  (KO,Mn207+KO  = 
2(KO,Mn03)-fO)  :  the  oxygen  being  retained  in  the  liquid.  A  perman- 
ganate is  more  stable  in  water  than  a  manganate,  since  it  may  be  boiled 
without  being  decomposed.  The  acid  is,  however,  slowly  changed  by  ex- 
posure to  air,  into  peroxide  of  manganese.  Permanganic  acid  may  be 
obtained  in  combination  with  water,  by  decomposing  permanganate  of  baryta 
with  diluted  sulphuric  acid.  Its  formula  is  MO,^i\fi^.  The  solution  is  of 
a  red  color.  It  is  rapidly  decomposed  even  at  common  temperatures.  A 
portion  of  the  oxygen  in  this  acid  is  supposed  by  Sch'onbein  to  be  in  an 
allotropic  state,  as  ozone  (p.  113). 

PROTOCHLORIDE  OF  MANGANESE  (MnCl). — When  peroxide  of  manganese 
is  heated  with  hydrochlorate  of  ammonia,  a  solution  of  chloride  of  manganese 
may  be  obtained  from  the  residue,  which  furnishes  transparent  pinkish  crys- 
tals of  hydrated  chloride.  The  same  salt  is  obtained  by  dissolving  carbonate 
of  manganese  in  diluted  hydrochloric  acid,  and  evaporating  the  solution. 
The  higher  oxides  of  this  metal,  when  treated  with  hydrochloric  acid,  give  off 
chlorine,  and  are  converted  into  protochloride  of  manganese.  Thus  a  man- 
ganate, treated  with  an  excess  of  hydrochloric  acid,  acquires  the  usual  chemi- 
cal properties  of  the  protosalts. 

Exposed,  out  of  the  contact  of  air,  to  a  red  heat,  the  hydrated  crystals 
of  the  protochloride  lose  water  to  the  amount  of  about  40  per  cent.,  and 
leave  a  lamellar  anhydrous  chloride  of  manganese  ;  heated  in  the  contact  of 
air,  the  chloride  is  decomposed  and  converted  into  an  oxide,  like  the  cor- 
responding chloride  of  magnesium.  100  parts  of  water  at  60°  dissolve 
about  40  parts  of  the  anhydrous  salt :  alcohol  dissolves  half  its  weight,  and 
the  solution,  when  evaporated  in  vacuo,  affords  a  crystalline  alcoate,  contain- 
ing two  equivalents  of  alcohol.  When  ammonia  is  added  to  a  solution  of 
the  chloride,  half  of  the  manganese  is  thrown  down  in  the  state  of  hydrated 
protoxide,  and  the  remainder  forms  a  double  salt.  When  a  recently  precipi- 
tated hydrated  protoxide  of  manganese  is  digested  in  a  solution  of  sal- 
ammoniac,  the  double  chloride  is  formed.  A  large  quantity  of  this  chloride, 
in  an  impure  state,  is  obtained  as  a  waste  product  in  the  manufacture  of 
chloride  of  lime. 


1$ 

404  SULPHATES    OF    MANGANESE. 

Sesquichloride  or  Manganese  (Mn^Clg)  is  formed  when  the  sesquioxide 
is  dissolved  at  a  low  temperature  in  hydrochloric  acid;  a  dark  brown 
solution  is  obtained  which,  with  a  slight  elevation  of  temperature,  evolves 
chlorine. 

Perchloride  of  Manganese  (MngCly)  is  produced  by  adding  fused  chlo- 
ride of  sodium  to  a  solution  of  permanganate  of  potassa  in  sulphuric  acid ; 
the  compound  passes  off  in  the  form  of  a  green  vapor,  condensible  at  0° 
into  an  olive-colored  liquid.  If  the  vapor  be  conveyed  into  a  moistened 
flask,  it  acquires  a  red  tint,  and  hydrochloric  and  permanganic  acids  are 
generated. 

Nitrate  of  Manganese  (MnOjNOg). — Dilute  nitric  acid  dissolves  moist 
protoxide  or  protocarbonate  of  manganese,  and  forms  a  protonitrate,  which 
may  be  obtained  by  evaporation  in  vacuo,  in  hydrated  prismatic  crystals,  de- 
liquescent, very  soluble  in  water  and  in  alcohol,  and  of  a  bitter  taste ;  their 
alcoholic  solution  burns  with  a  green  flame. 

Sulphide  of  Manganese  (MnS). — When  dried  protosulphate  of  manga- 
nese is  ignited  with  one-sixth  its  weight  of  finely-powdered  charcoal,  or  when 
a  current  of  sulphuretted  hydrogen  is  passed  over  the  protocarbonate  or 
protosulphate  heated  to  redness,  a  sulphide  of  manganese  is  obtained.  It 
has  a  gray  metallic  lustre,  and  is  soluble  in  dilute  sulphuric  and  hydro- 
chloric acid,  with  the  evolution  of  sulphuretted  hydrogen.  It  is  identical 
with  the  native  sulphide  of  manganese,  a  rare  ore,  found  in  Cornwall  and 
Transylvania. 

Sulphate  of  Manganese  (MnO,S03)  's  formed  by  dissolving  the  prot- 
oxide or  protocarbonate  in  dilute  sulphuric  acid,  or  by  mixing  peroxide  of 
manganese  into  a  paste  with  sulphuric  acid,  and  heating  the  mixture  to  dull 
redness ;  in  the  latter  case  oxygen  is  evolved.  The  dry  residue  washed  with 
water  affords  a  solution  of  the  sulphate  of  the  protoxide,  which  may  be 
crystallized  by  evaporation.  This  salt  is  used  in  dyeing  and  calico-printing. 
When  cloth  is  passed  through  its  solution,  and  afterwards  through  a  caustic 
alkali,  protoxide  of  manganese  is  precipitated  upon  it  and  rapidly  becomes 
brown  in  the  air;  or  it  is  at  once  peroxidized  by  passing  the  cloth  through 
a  solution  of  chloride  of  lime.  This  color  is  called  manganese  hrown. 
Sulphate  of  manganese,  as  it  is  obtained  by  gentle  evaporation  from  the 
neutral  solution,  forms  rhombic  prisms  which  contain  4  atoms  of  water. 
When  the  crystals  are  formed  between  45°  and  68°  they  contain  5  atoms  of 
water ;  when  formed  under  42°  they  include  7  atoms  of  water ;  and  when  a 
concentrated  solution  of  sulphate  of  manganese  is  mixed  with  sulphuric 
acid,  it  yields  on  evaporation  small  granular  crystals  containing  only  1  atom 
of  water.  The  solubility  of  sulphate  of  manganese  varies  with  its  water  of 
crystallization  ;  the  anhydrous  salt  is  soluble  in  2  parts  of  water  at  60°,  and 
in  its  own  weight  at  212°.  It  is  insoluble  in  alcohol.  The  taste  of  sul- 
phate of  manganese  is  styptic  and  bitterish,  and  the  crystals  have  generally 
a  slight  tinge  of  rose-pink.  At  240°,  they  lose  3  atoms  of  water,  but  retain 
1  until  heated  above  400° ;  at  a  red  heat  the  salt  becomes  anhydrous.  This 
compound  forms  double  salts  with  potassa  and  ammonia. 

Sesquisulphate  of  Manganese  (Mn^Og-f  SSOg)  is  formed  by  dissolving 
the  sesquioxide  in  sulphuric  acid  :  the  solution  is  of  a  crimson  color.  When 
heated  it  gives  off  oxygen  and  becomes  colorless  :  it  is  instantly  bleached  by 
sulphurous  acid  or  any  deoxidizing  agent.  Its  most  important  property  is 
that  of  forming,  with  sulphate  of  potassa  or  of  ammonia,  double  salts  crys- 
tallizing in  octahedra,  which  are  manganese  alums,  similar  in  constitution  to 
ordinary  alum,  but  with  AI3O3,  replaced  by  Mn^Og  (p.  369).  1  part  of  per- 
oxide of  manganese  mixed  with  13  of  oil  of  vitriol,  and  gently  heated  till 


r 
TESTS    FOR    THE    SALTS    OP    MANGANESE.  405 

half  the  quantity  of  oxygen  thus  separable  has  escaped,  yields  a  mass  from 
which  water  extracts  the  sesquisulphate ;  1  part  gives  a  red  color  to  1280 
parts  of  water. 

Carbide  of  Manganese  is  probably  always  contained  in  the  metal  reduced 
by  charcoal.  The  quality  of  steel  is  said  to  be  improved  by  the  presence  in 
it  of  carbide  of  manganese.  The  plumbago-like  substance  called  kish,  occa- 
sionally produced  in  iron  furnaces,  contains  this  carbide. 

Carbonate  of  Manganese  (MnOjCOJ  is  white,  insipid,  and  insoluble  in 
water.  It  is  precipitated  as  a  hydrate,  by  alkaline  carbonates,  from  the  pro- 
tochloride  or  protosulphate  :  it  becomes  brown  by  drying  in  the  air.  Car- 
bonate of  manganese  constitutes  the  spathose  manganese  of  mineralogy,  and 
often  accompanies  spathose  iron. 

Tests  for  the  Salts  of  Manganese. — The  proto-saltsare  soluble  in  water. 
The  solution  is  either  colorless  or  slightly  pink,  and  has  an  acid  reaction. 
It  has  a  bitter  astringent  taste,  and  becomes  brown  and  turbid  when  long 
exposed.  1.  Sulphuretted  hydrogen  produces  no  precipitate,  but  hydrosul- 
phate  of  ammonia  throws  down  a  flesh-colored  sulphide,  which  is  easily  dis- 
solved by  acetic  acid.  The  precipitates  become  brown  by  exposure  to  air. 
2.  Potassa  or  soda  throws  down  a  white  hydrated  oxide,  which  rapidly 
becomes  brown  on  exposure,  owing  to  its  conversion  into  sesquioxide.  Before 
undergoing  this  change  the  precipitate  is  soluble  in  hydrochlorate  of  ammonia : 
it  is  insoluble  in  potassa  or  soda.  3.  Ammonia  also  precipitates  partially  a 
white  hydrated  oxide,  which  becomes  brown  when  exposed.  4.  Carbonates 
and  hicarhonates  of  potassa,  soda,  or  ammonia,  throw  down  a  white  carbo- 
nate, which  is  dissolved  by  hydrochlorate  of  ammonia,  and  becomes  slowly 
brown  by  exposure.  5.  Ferrocyanide  of  potassium  produces  a  white  precipitate, 
with  a  shade  of  blue  if  iron  is  present,  and  red  if  copper  is  present.  6.  Fer- 
ricyanide  of  potassium  gives  a  brownish-red  precipitate.  T.  Chlorine  produces 
no  effect  on  the  solution,  but  when  any  alkali  is  added,  brown  hydrated  per- 
oxide of  manganese  is  precipitated.  Chloride  of  lime  immediately  gives  a 
brown  precipitate.  8.  Heat  a  few  grains  of  minium  in  a  few  drops  of  strong 
nitric  acid;  and  add  to  the  liquid  a  small  quantity  of  the  peroxide  of  manga- 
nese. Permanganic  acid  is  produced,  which  may  be  recognized  by  the  pink 
color  of  the  solution,  as  soon  as  the  oxide  of  lead  has  subsided.  9.  On  a  loop 
of  platinum  wire  melt  some  carbonate  of  soda  with  a  little  nitre.  If  a  mere 
trace  of  oxide  of  manganese  be  fused  with  the  mixed  salts  in  the  inner  flame 
of  the  blowpipe,  or  of  a  Bunsen's  jet,  manganate  of  soda  is  produced, 
known  by  its  greenish  color  (if  the  manganese  is  not  in  excess).  If  the 
wire  is  placed  in  a  few  drops  of  water  in  a  tube,  an  emerald  green  solution 
is  obtained,  which,  when  diluted  and  warmed,  or  an  acid  is  added,  is  converted 
into  a  pink  solution  of  permanganate  of  potassa.  This  is  probably  the  most 
delicate  test  for  manganese,  whether  in  a  soluble  or  in  an  insoluble  form. 

The  peroxide  of  manganese  as  well  as  the  manganic  and  permanganic  acids 
belong  to  this  class  of  ozonides.  They  readily  part  with  a  portion  of  their 
oxygen  which  is  supposed  to  be  evolved  in  the  form  of  ozone.  Thus,  when 
placed  in  contact  with  strychnia  moistened  with  sulphuric  acid,  they  produce 
blue,  violet,  purple,  and  red  colors,  and  serve  as  tests  for  that  alkaloid. 
When  added  to  freshly-precipitated  tincture  of  guaiacum,  they  impart  to  it  a 
beautiful  blue  color,  a  result  of  the  oxidation  of  the  precipitated  resin. 


406  ZINC    AND    OXYGEN. 


CHAPTER    XXXI. 

ZINC  — INDIUM  — TIN  — CADMIUM. 

Zinc  (Zn=32). 

The  Zinc  of  commerce  is  produced  from  the  native  sulphide  {blende)  or 
carbonate  {calamine).  The  ore  is  picked,  broken  into  small  pieces,  submitted 
to  a  dull  red  heat  in  a  reverberatory  furnace,  by  which  carbonic  acid  is  driven 
off  from  the  calamine,  and  sulphur  from  the  sulphide.  It  is  then  washed, 
ground,  and  thoroughly  mixed  with  about  one-eighth  of  its  weight  of  powdered 
charcoal.  This  mixture  is  put  into  large  earthen  pots,  not  unlike  oil-jars, 
six  of  which  are  usually  placed  in  a  circular  furnace.  Each  pot  has  an  iron 
tube  passing  from  its  lower  part,  through  the  floor  of  the  furnace,  and 
dipping  into  water;  they  are  everywhere  else  firmly  luted.  Upon  the  ap- 
plication of  a  full  red  heat,  the  metal  distils  through  the  tube  into  the  water 
beneath,  whence  it  is  collected,  melted,  and  cast  into  cakes.  This  process  is 
called  distillatio  per  descensum.  Commercial  zinc  generally  contains  traces 
of  sulphur,  iron,  and  arsenic.  In  1865  the  products  of  the  mines  of  the 
United  Kingdom  in  blende  and  calamine  amounted  to  1*1,842  tons,  yielding 
4,460  tons  of  metallic  zinc. 

Properties. — Zinc  is  a  bluish  white  metal,  with  considerable  lustre,  rather 
hard,  of  a  specific  gravity  of  about  6-8  in  its  usual  state,  but  when  drawn 
into  wire,  or  rolled  into  plates,  its  density  is  augmented  to  7*  or  7  1.  It  has 
a  peculiar  odor  when  breathed  upon,  or  handled  with  moist  fingers.  In  its 
ordinary  state  and  at  common  temperatures  it  is  tough,  but  becomes  brittle 
when  its  temperature  approaches  that  of  fusion,  which  is  about  773°.  At  a 
temperature  a  little  above  212°,  and  between  that  and  300°,  it  is  ductile  and 
malleable,  and  may  be  rolled  into  thin  leaves  or  drawn  into  wire.  If  slowly 
cooled  after  fusion,  its  fracture  is  very  crystalline.  It  is  volatile  at  a  bright 
red  heat,  and  admits  of  distillation,  but  if  its  vapor  be  exposed  to  air,  it 
burns  with  intense  brilliancy. 

When  a  surface  of  clean  and  polished  zinc  is  exposed  to  dry  air,  it  remains 
bright;  in  damp  air  it  tarnishes,  and  then  remains  unchanged.  Under 
water  it  becomes  enfilmed  with  hydrated  oxide,  or  with  a  hydrated  basic 
carbonate  if  carbonic  acid  be  present.  At  common  temperatures  it  does  not 
decompose  water,  but  does  so  at  a  red  heat,  or  in  the  presence  of  acids.  In 
pure  water,  from  which  air  has  been  carefully  excluded,  it  remains  bright. 
The  energy  with  which  zinc  is  acted  on  by  dilute  sulphuric  acid  is  greatly 
dependent  upon  the  purity  of  the  metal ;  when  perfectly  pure  the  action  is 
feeble,  but  when  it  contains  minute  portions  of  other  metals,  it  becomes 
rapid:  this  is  apparently  owing  to  a  galvanic  action  ;  and  when  a  piece  of 
pure  zinc  is  wound  round  with  platinum  wire  an  equivalent  effect  is  produced. 
Zinc  and  all  its  compounds,  excepting  blende,  are  soluble  in  hydrochloric 
acid ;  hydrogen  is  evolved,  when  the  metal  is  employed.  A  strong  solution 
of  potassa,  or  soda,  when  heated,  also  dissolves  the  metal  with  the  evolution 
of  hydrogen.  If  the  zinc  contains  arsenic,  the  hydrogen  evolved,  whether 
as  the  result  of  the  action  of  an  acid  or  an  alkali,  are  mixed  with  arsenuretted 
hydrogen.  This  may  be  inferred  when  the  gas  blackens  paper  impregnated 
with  a  solution  of  nitrate  of  silver.     Phosphorus  combined  with  hydrogen 


OXIDE    OF    ZINC.      SULPHIDE    OF    ZINC.  40T 

will  produoe  a  similar  action  op  nitrate  of  silver.  If  the  hydrogen  contains 
sulphur,  this  will  be  indicated  by  tlie  discoloration  of  paper  impregnated  with 
a  salt  of  lead.  Zinc,  in  consequence  of  its  lightness  and  cheapness,  is  much 
used  for  roofing,  gutters,  and  chimney-tops;  but  it  should  not,  as  is  some- 
times the  case,  be  riveted  with  copper  or  iron  nails,  the  contact  of  which 
with  the  zinc  accelerates  the  destruction  of  the  latter  by  electric  action; 
indeed,  any  of  the  common  metals  in  metallic  contact  with  zinc,  tend  to  pro- 
duce its  oxidation. 

Zinc  and  Oxygen. — The  high  attraction  between  zinc  and  oxygen  is 
shown  by  the  facility  with  which  many  of  the  other  metallic  oxides,  in  solu- 
tion, are  reduced  to  the  metallic  state  by  its  means.  Its  important  electro- 
generative  power  in  Voltaic  arrangements,  is  also  referable  to  this  cause. 
As  the  zinc  compounds  are  now  easily  reduced  by  magnesium,  this  metal  is 
likely  to  take  the  place  of  zinc  for  electrical  and  other  purposes  so  soon  as 
it  can  be  cheaply  manufactured.  By  exposing  zinc  to  the  joint  action  of 
heat  and  air,  at  a  temperature  just  sufficient  to  fuse  it,  it  is  converted  into  a 
gray  powder,  which  is  probably  a  mere  mixture  of  metallic  zinc  and  oxide  of 
zinc,  although  by  some  it  is  regarded  as  a  true  suboxide,  Zn^O. 

Oxide  of  Zinc  (ZnO). — This  is  the  only  salifiable  oxide  of  zinc  ;  it  is 
obtained  by  intensely  heating  the  metal  exposed  to  air,  when  its  vapor  takes 
fire,  burns  with  a  very  bright  flame,  and  forms  a  white  flocculent  substance, 
formerly  called  7iihtl  album,  philosopher^  wool,  and  flowers  of  zinc.  When 
this  combustion  goes  on  with  violence,  the  oxide,  though  in  itself  not  volatile, 
is  carried  up  in  flocculi  by  the  current  of  air,  which  are  so  light  as  to  remain 
for  a  long  time  floating  about  the  atmosphere.  A  piece  of  zinc-leaf  may 
also  be  inflamed  by  a  spirit-lamp,  and  will  continue  to  burn  brilliantly  even 
when  removed  from  the  flame ;  if  inflamed  and  plunged  into  oxygen,  the 
combustion  is  as  vivid  as  that  of  phosphorus — indeed,  the  splendor  of  the 
flame  probably  arises  in  both  instances  from  the  same  cause,  namely,  the 
ignition  of  finely-divided  solid  incombustible  matter  (p.  102).  The  oxide  of 
zinc,  as  prepared  by  combustion,  generally  contains  small  particles  of  the 
metal,  which  render  it  gritty  :  it  may  also  contain  other  impurities,  so  that 
for  pharmaceutical  use  it  should  be  procured  by  decomposing  a  solution  of 
pure  sulphate  of  zinc  at  a  boiling  heat  by  its  equivalent  of  carbonate  of  soda. 
The  precipitate  well  washed,  dried,  and  exposed  to  a  dull-red  heat,  is  a  pure 
oxide  ;  or  the  cold  solution  of  the  sulphate  may  be  decomposed  by  carbonate 
of  ammonia,  and  the  precipitate  washed  and  dried  as  before.  Traces  of  sul- 
phuric acid,  or  of  soda,  may  be  detected  in  the  oxide  from  cold  solutions 
when  carbonate  of  soda  has  been  used,  and  if  a  hot  solution  be  precipitated 
by  carbonate  of  ammonia,  the  oxide  will  retain  sulphuric  acid. 

Oxide  of  zinc  obtained  by  the  combustion  of  the  metal,  or  by  passing  steam 
oyer  red-hot  zinc,  is  sometimes  crystalline;  its  specific  gravity  is  between 
5*6  and  5-7.  It  is  commonly  met  with  in  the  form  of  a  white  powder, which 
at  a  high  temperature  acquires  a  yellow  tint,  but  again  whitens  as  it  cools. 
It  has  been  used  as  a  pigment,  both  with  oil  and  water ;  and  is  employed  in 
medicine  as  a  tonic,  and  as  an  external  application.  Oxide  of  zinc  is  readily 
soluble  in  acids ;  it  also  dissolves,  especially  in  the  state  of  hydrate,  in  the 
caustic  fixed  alkalies,  and  in  pure  and  carbonated  ammonia.  The  strong 
ammoniacal  solution  becomes  turbid  when  dilute,  and  deposits  the  oxide 
when  boiled.  When  a  solution  of  alumina  in  caustic  potassa  is  mixed  with 
an  ammoniacal  solution  of  oxide  of  zinc,  a  definite  combination  of  the  two 
oxides  is  thrown  down,  containing  6  atoms  of  alumina  and  1  of  oxide  of  zinc, 
being  identical  in  composition  with  the  mineral  called  Gahnite. 

Nitrate  op  Zinc  (ZnO,N05,6HO)  is  a  deliquescent  salt,  which  crystal- 


408  CARBONATE    OF    ZINC. 

lizes  with  difiBculty  in  four-sided  prisms:  it, is  very  soluble  in  water  and  in 
alcohol. 

Chloride  of  Zinc  (ZnCl)  is  formed  by  heatinp:  leaf-zinc  in  chlorine  ;  or 
by  evaporating  a  solution  of  zinc  in  hydrochloric  acid  to  dryness,  and  heating 
the  residue  to  dull  redness.  It  is  a  white  translucent  substance,  extremely 
deliquescent,  fusible  at  300°,  and  volatile  at  a  bright-red  heat:  its  vapor 
condenses  in  acicular  crystals.  It  has  a  nauseous  styptic  taste,  and  is  power- 
fully emetic.  It  was  formerly  called  hitter  of  zinc.  It  is  readily  soluble  ia 
water,  and  the  solution  gives  on  evaporation  a  crystallizable  but  deliquescent 
hydrate  (ZnCl, HO),  which,  when  heated  in  the  open  air,  partly  sublimes  ia 
the  form  of  chloride,  and  is  partly  resolved  into  hydrochloric  acid  and  oxide 
of  zinc.  Sir  William  Burnett's  disinfectant  liquid,  and  preservative  against 
dry-rot,  is  a  strong  solution  of  chloride  of  zinc  ;  its  sp.  gr.  is  1'019.  Chlo- 
ride of  zinc  forms  several  double  salts,  with  the  chlorides  of  the  alkaline 
metals.  Zinc  combines  directly  with  bromine  and  iodine  to  form  a  bromide 
and  an  iodide. 

Sulphide  op  Zinc  (ZnS)  may  be  formed  by  heating  oxide  of  zinc  with 
excess  of  sulphur;  it  is  also  produced  by  heating  a  mixture  of  zinc  filings 
and  sulphide  of  mercury.  When  a  salt  of  zinc  is  precipitated  by  an  alkaline 
sulphide,  a  white  compound  is  obtained,  which  is  probably  a  monohydrated 
sulphide  of  zinc*  Native  sulphide  of  Zinc,  or  Blende,  occurs  in  crystals 
which  are  brittle,  soft,  and  of  different  shades  of  brown  and  black.  Its 
primitive  form  is  the  rhomboidal  dodecahedron.  It  usually  contains  traces 
of  iron  and  lead.  It  is  an  abundant  mineral,  and  important  as  a  source  of 
the  metal,  which  is  obtained  by  roasting  the  ore,  and  afterwards  exposing  it 
to  heat  in  proper  distillatory  vessels,  mixed  with  charcoal.  The  English 
miners  call  the  sulphide  from  its  color  black  jack.  It  is  dissolved  by  nitro- 
hydrochloric  acid. 

Sulphate  of  Zinc  (ZnO,S03). — Zinc  is  readily  oxidized  and  dissolved  by 
dilute  sulphuric  acid,  and  hydrogen  is  given  off;  the  zinc  so  decomposes 
water  that  an  atom  of  zinc  is  substituted  for  an  atom  of  hydrogen  :  HO, 
S03  4-Zn=ZnO,S03  4-H ;  and  a  solution  of  sulphate  of  zinc  results,  which 
by  evaporation  affords  crystals  =ZnO,S03,'7HO,  in  the  form  of  right  rhombic 
prisms.  This  salt  is  soluble  at  2-5  parts  of  water  at  60°.  The  crystals  are 
slightly  efflorescent:  at  212°  they  lose  6  atoms  of  water,  retaining  I  till 
heated  nearly  to  dull  redness.  The  anhydrous  sulphate  is  white  and  friable  ; 
exposed  to  humid  air  it  gradually  resumes  7  atoms  of  water ;  it  heats  when 
sprinkled  with  water  ;  at  a  high  temperature  it  evolves  sulphuric  and  sul- 
phurous acid  and  oxygen,  and  at  a  white  heat  is  decomposed,  leaving  oxide 
of  zinc.  It  is  soluble  in  hydrochloric  acid  without  decomposition.  White 
vitriol,  or  the  sulphate  of  zinc  of  commerce,  is  often  obtained  by  the  oxida- 
tion of  blende,  and  is  impure  ;  it  generally  contains  a  sulphate  of  zinc, 
together  with  the  sulphates  of  iron,  copper,  cadmium,  alumina,  and  some- 
times lead  :  it  usually  occurs  in  amorphous  masses.  The  sulphate,  like  the 
chloride  of  zinc,  forms  double  salts  with  the  sulphates  of  the  alkalies. 

Carbonate  of  Zinc. — The  precipitate  formed  by  adding  carbonate  of 
potassa  to  sulphate  of  zinc  is  a  mixture  of  carbonate  and  hydrated  oxide, 
analogous  to  the  magnesia  alba,  its  formula  being  2(ZnO,C03)  +  3(ZnO,HO,) 
or  when  precipitated  in  the  cold,  ZnO,CO.,+2(ZnO,HO).  Native  Carbonate 
of  Zinc,  or  Calamine,  occurs  both  crystallized  and  massive.  It  is  often  found 
investing  carbonate  of  lime,  which  has  sometimes  been  decomposed,  and  the 
calamine  remains  in  pseudo-crystals.  It  abounds  in  Somersetshire,  Flint- 
shire, and  Derbyshire.  A  beautiful  variety  colored  by  carbonate  of  copper 
is  found  at  Matlock.     The  variety  of  calamine  known  by  the  name  of  electric 


TESTS    FOR    THE    SALTS    OF    ZINC.  409 

calamine,  from  its  property  of  becorain,2^  electrical  when  gently  heated,  con- 
sists of  oxide  of  zinc  in  combination  with  silica. 

Zinced  Iron;  Galvanized  Iron. — If  plates  of  hot  iron  be  dipped  into 
melted  zinc,  they  acquire  the  appearance  of  tin-plate,  for  which  they  are  a 
valuable  substitute,  inasmuch  as  the  zinced  iron  is  prevented  from  oxidation 
and  rusting,  by  the  electrical  relations  of  the  metals ;  the  zinc,  it  is  true,  is 
more  subject  to  oxidation  than  tin,  but  so  long  as  any  of  it  remains,  the  iron 
is  protected,  and  when  covered  by  a  coat  of  paint  is  extremely  durable. 
Hurdles,  fences,  and  all  out  of  door  iron-work,  as  well  as  implements  used  in 
damp  situations,  and  employed  in  contact  with  water,  may  be  thus  defended. 
The  wires  of  electric  telegraphs  are  generally  of  zinced  iron,  and  their  sec- 
tion, when  exposed  to  air  and  water,  sometimes  exhibits  a  fresh  deposition 
of  zinc,  arising  from  the  galvanic  precipitation  of  small  portions  of  dissolved 
zinc  upon  the  electro-negative  iron.  The  zincing  of  iron  is  generally  per- 
formed by  dipping  the  iron,  previously  well  cleaned,  into  melted  zinc,  the 
surface  of  which  is  kept  carefully  covered  with  sal-ammoniac  to  prevent 
oxidation,  and  so  enable  the  iron  to  become  thoroughly  wetted,  as  it  were, 
and  superficially  combined  with  the  zinc.  The  zinc  is  fused  in  large  wrought 
iron  vessels,  placed  over  proper  furnaces,  and  after  the  frequent  dippings  of 
the  iron  articles,  there  is  ultimately  found  at  the  bottom  of  the  melted  metal, 
a  quantity  of  a  granular  alloy  of  zinc  and  iron.  The  process  is  not  appli- 
cable to  the  generality  of  vessels  used  for  culinary  purposes,  in  consequence 
of  the  contaminations  by  oxide  of  zinc  which  would  often  ensue,  especially 
with  acidulous  or  saline  liquids.  In  using  zinced  iron,  care  should  be  taken 
that  where  nails  or  rivets  are  required,  they  should  also  be  coated  with  zinc. 

Tests  for  the  Salts  of  Zinc. — They  are  mostly  soluble  in  water  ;  the 
solutions  are  colorless,  and  have  an  astringent  and  metallic  taste.  1.  Potassa, 
soda,  and  ammonia,  form  white  precipitates,  soluble  in  excess  of  the  alkali, 
and  in  dilute  sulphuric  acid.  In  this  case  the  precipitate  is  distinguished 
from  alumina  by  its  solubility  in  excess  of  ammonia,  as  well  as  in  chloride  of 
ammonium.  2.  The  precipitate  formed  in  solutions  of  zinc  by  the  carbonates 
of  potassa.  and  soda  is  not  soluble  in  excess  of  these  carbonates,  but  when 
carbonate  of  ammonia  is  employed,  the  precipitate  produced  is  again  dis- 
solved. Zinc  is  thus  separated  from  oxide  of  lead,  alumina  and  the  alkaline 
earths.  3.  Sulphuretted  hydrogen  throws  down  a  white  hydrated  sulphide  of 
zinc  in  neutral  solutions,  but  not  in  those  which  are  acid  or  alkaline.  4. 
Hydrosulphate  of  ammonia  produces  a  white,  or  yellowish-white  precipitate. 
5.  Ferrocyanide  of  potassium  gives  a  white  bulky  precipitate,  and  ferricya- 
nide  a  brownish  precipitate.  The  soluble  phosphates,  oxalates,  and  borates, 
produce  white  precipitates  soluble  in  acids  and  alkalies.  The  salts  of  zinc 
which  are  insoluble  in  water,  dissolve  in  dilute  sulphuric  acid,  and  are  pre- 
cipitated by  ammonia,  but  are  redissolved  by  an  excess  of  acid  or  of  precipi- 
tant. Metallic  zinc  is  readily  thrown  down  from  its  solutions  by  magnesium 
and  in  some  exceptional  cases  by  iron. 

The  special  characters  of  a  salt  of  zinc  are,  that  the  oxide  is  soluble  both 
in  potassa  and  ammonia,  and  that  from  the  alkaline  solutions  it  is  precipitated 
as  a  white  sulphide  by  sulphuretted  hydrogen,  but  it  is  not  precipitated  from 
them  by  chloride  of  ammonium.  By  these  characters  it  is  distinguished  from 
alumina  and  other  oxides  which  are  soluble  in  potassa.  Zinc  is  the  only 
metal  which  forms  a  white  sulphide  with  sulphuretted  hydrogen. 

Before  the  blowpipe,  or  on  platinum  foil,  oxide  of  zinc  becomes  yellow 
when  heated,  but  whitens  as  it  cools.  A  small  proportion  forms  with  borax 
a  clear  glass,  which  becomes  opaque  on  increasing  the  quantity  of  oxide.  If 
a  drop  of  nitrate  of  cobalt  is  added  to  the  oxide,  and  this  is  dried  and  ignited, 
it  becomes  green.     With  soda,  in  the  interior  flame,  oxide  of  zinc  is  reduced, 


410  INDIUM.      TIN. 

and  the  metal  burns  with  its  characteristic  flame,  depositing  its  oxide  upon 
the  charcoal.  Mixed  with  oxide  of  copper,  and  reduced,  the  ziuc  will  be 
fixed  and  brass  obtained. 

Indium  (In=35-9). 

This  metal,  the  result  of  investigations  by  spectral  analysis,  was  discovered 
in  1863  by  Richter  and  Reich,  chemists  of  Freiburg.  It  was  discovered  by 
them  in  the  Freiburg  zinc  blende,  which  contains  it  in  small  proportion.  It 
received  the  name  of  Indium  from  the  fact  that  it  imparted  a  beautiful  blue 
color  to  a  colorless  flame,  and  gave  in  its  spectrum  a  well-marked  indigo- 
blue  line.  It  may  be  obtained  from  the  Freiburg  zinc  by  operating  on  the 
dark-colored  residue  which  is  left  undissolved  by  diluted  hydrochloric  acid. 
This  consists  of  lead,  iron,  arsenic,  cadmium,  and  indium,  but  lead  is  the 
principal  ingredient.  The  metals  are  separated  from  indium  by  a  series  of 
chemical  processes,  and  the  metal  indium  is  ultimately  obtained  in  decompos- 
ing its  oxide  by  a  current  of  hydrogen  or  heating  it  with  cyanide  of  potassium. 
It  is  a  white  metal  with  the  lustre  of  cadmium.  It  is  so  soft  that  it  may  be 
cut  with  a  knife  :  it  is  ductile  and  malleable  :  it  melts  at  about  the  same 
temperature  as  lead,  and  is  volatile  at  a  bright  red  heat.  Heated  to  this  tem- 
perature in  air,  it  burns  with  a  blue  flame,  producing  a  powdery  yellow  oxide 
which  is  deposited.  It  is  volatile  at  a  high  temperature  and  has  a  peculiar 
odor.  It  is  not  readily  tarnished  on  exposure  to  air.  Its  specific  gravity  in 
the  hammered  state  is  7*27.  It  is  easily  attacked  by  most  acids.  One  oxide 
is  only  known  (InO)  :  This  by  combining  with  acids  forms  colorless  salts. 
The  precipitated  oxide  is  insoluble  in  ammonia,  and  is  thus  distinguished  and 
separated  from  oxide  of  cadmium.  The  special  character  of  the  salts  of 
indium  is  that  they  readily  impart  a  blue  color  to  a  smokeless  flame,  and  in 
the  spectrum  there  is  a  deep  blue  line. 

The  atomic  weight  has  been  variously  given  at  79,  74,  and  35-9.  The 
two  first  numbers  are  calculated  on  the  scale  of  oxygen  being  16. 

Indium  is  a  rare  and  costly  metal.  Its  present  price  is  about  two  shillings 
per  grain.  In  the  French  Exhibition  for  1867,  two  ingots  were  showing 
weighing  together  7700  grains.     Their  value  was  estimated  at  £370. 

Tin  (^n=50). 

Tin  (Jupiter  2J_  of  the  alchemists)  has  been  known  from  remote  ages,  and 
was  obtained  at  a  very  early  period  from  Spain  and  Britain  by  the  Phoeni- 
cians. It  occurs  most  abundantly  in  Cornwall,  the  mines  of  which  afford 
about  3000  tons  annually  :  it  is  also  found  in  Germany,  Bohemia  and  Hun- 
gary ;  in  Chili  and  Mexico  ;  in  the  Peninsula  of  Malacca  ;  and  in  India,  in 
the  Island  of  Banca.  The  native  peroxide  is  the  principal  ore  of  tin :  the 
metal  is  obtained  by  heating  it  to  redness  with  charcoal  or  culm,  and  a  little 
lime  ;  the  first  product  is  impure,  and  is  returned  into  the  furnace,  and  care- 
fully heated  so  as  to  fuse  the  tin,  which  runs  off  into  an  iron  kettle,  while 
the  principal  impurities  remain  unmelted  ;  in  the  kettle  the  tin  is  kept  in 
fusion,  stirred,  and  agitated  by  plunging  wet  charcoal  into  it,  by  which  a 
quantity  of  impurities  collect  upon  the  surface,  and  are  removed  by  a  skim- 
mer :  thus  refined,  the  metal  is  cast  into  blocks  of  about  three  cwt.  each. 
The  common  ores  are  known  under  the  name  of  mine  tin,  and  furnish  a  less 
pure  metal  than  that  obtained  from  stream  tin.  The  purest  tin  is  known 
under  the  name  of  grain  tin,  a  term  formerly  applied  exclusively  to  the  metal 
obtained  from  the  stream  ore  :  block  tin  is  less  pure,  and  is  the  produce  of 
the  common  ore.  The  peculiar  columnar  fracture  which  pure  tin  exhibits 
when  broken,  is  given  by  heating  the  ingot  till  it  becomes  brittle,  and  then 
letting  it  fall  from  a  height  upon  a  hard  pavement. 


OXIDES    OF    TIN.  411 

Tin  has  a  silver-white  color,  with  a  slight  tint  of  yellow,  and  when  so 
viewed  as  to  exclude  the  white  light  reflected  from  its  surface,  it  is  decidedly 
yellow  :  it  is  softer  than  gold,  but  harder  than  lead  :  it  is  malleable,  though 
imperfectly  ductile.  What  is  termed  tin-foil  is  the  metal  beaten  out  into 
thin  leaves.  The  malleability  of  the  metal  is  such  that  it  may  be  beaten  into 
leaves  of  only  the  1-1 000th  of  an  inch  in  thickness.  It  has  a  slightly  yellow- 
ish reflection.  A  spurious  foil,  under  the  name  of  patent  tin-foil,  is  largely 
sold  and  used  as  a  substitute  for  pure  tin.  It  is  nothing  more  than  lead  with 
a  thin  facing  of  tin.  It  is  more  easily  oxidized  than  pure  tin,  and  produces 
a  poisonous  salt  of  lead.  It  is  much  used  for  wrapping  children's  food, 
articles  of  confectionery,  &c.,  and  we  have  found  food  thus  superficially  con- 
taminated with  carbonate  of  lead,  the  spurious  foil  being  eaten  into  holes  by 
chemical  changes.  The  spurious  foil  has  a  dark  bluish  reflection,  and  when 
treated  with  diluted  nitrohydrochloric  acid,  the  tin  is  removed  and  a  grayish, 
blue  layer  chiefly  consisting  of  lead  is  left.  The  genuine  tin-foil  thus  treated 
presents  a  crystalline  surface  of  a  bright  lustrous  appearance.  Traces  of 
arsenic  are  sometimes  found  in  tin.  The  sp.  gr.  of  the  metal  fluctuates  from 
t*28  to  7  6,  the  lightest  being  the  purest  metal.  When  bent,  it  occasions  a 
peculiar  crackling  noise  ;  and  when  rapidly  bent  backwards  and  forwards 
several  times  successively,  it  becomes  hot.  When  rubbed,  it  exhales  a  pecu- 
liar odor.  It  melts  at  442°,  and  slightly  contracts  on  consolidation.  By 
exposure  to  heat  and  air  it  is  gradually  converted  into  protoxide  ;  but  if  the 
heat  is  continued  till  metallic  tin  no  longer  remains,  the  protoxide  passes 
into  peroxide.  Placed  upon  ignited  charcoal  under  a  current  of  oxygen  gas, 
it  enters  into  rapid  combustion,  forming  the  peroxide ;  and  if  an  intensely- 
heated  globule  of  the  metal  be  thrown  upon  a  slieet  of  dark-colored  paper, 
it  subdivides  into  small  particles,  which  burn  very  brilliantly,  and  leave  lines 
of  white  oxide.  It  volatilizes  at  a  very  high  temperature.  When  a  polished 
surface  of  tin  is  heated  it  becomes  yellow  and  iridescent,  in  consequence  of 
superGcial  oxidation.  A  preparation,  under  the  name  of  powdered  iin,^  is 
sometimes  made  by  shaking  the  melted  metal  in  a  wooden  box  rubbed  with 
chalk  on  the  inside.  When  it  has  become  solid  it  is  in  the  state  of  fine 
powder.  By  diffusion  in  water  the  coarser  particles  are  readily  separated ; 
the  tin  powder  is  then  made  into  a  paste  with  glue,  and  is  applied  in  any 
desired  pattern  to  steel,  iron,  or  other  articles.  When  dry  it  is  burnished 
and  afterwards  varnished.  It  acquires  and  retains  great  brilliancy.  Pure 
tin  is  not  readily  oxidized  by  exposure  to  air.  It  retains  its  lustre  for  a 
considerable  period.  We  have  seen  in  the  Bodleian  Library  at  Oxford,  a 
missal  of  the  ninth  century  of  the  date  of  Alfred,  in  which  the  margin  of  the 
page- had  been  illuminated  with  tin  laid  on  in  fine  powder  or  foil,  and  bur- 
nished. It  retained  the  white  lustre  of  the  metal  but  little  diminished, 
although  a  thousand  years  had  probably  elapsed  since  it  was  first  laid  on  the 
vellum.  Tin  putty  or  putty  powder  used  for  polishing  plate  is  made  by 
levigating  the  crusts  of  oxide  that  form  on  melted  tin.  It  is  often  injuriously 
mixed  with  mercury,  an  adulteration  which  may  be  discovered  by  heating  a 
portion  in  a  reduction  tube,  when  the  mercury  will  sublime  in  globules.  The 
quantity  of  tin  ore  produced  from  our  tin  mines  in  Cornwall  and  Devonshire  in 
1865  amounted  to  15,686  tons,  from  which  10,039  tons  of  metallic  tin  were 
obtained.     {HunVs  Mineral  Statistics  of  the  United  Kingdom,  1866.) 

Protoxide  of  Tin  ;  Stannous  Oxide  (SnO)  is  obtained  by  precipitating 
a  solution  of  protochloride  of  tin  by  ammonia  ;  it  falls  in  the  state  of  hydrate: 
when  dried,  out  of  the  contact  of  air,  it  is  of  a  dark  color.  When  the  pro- 
tochloride is  decomposed  by  a  carbonated  alkali,  the  precipitate  is  also  a 
hydrated  protoxide,  retaining  no  carbonic  acid.  It  is  obtained  anhydrous^ 
by  heating  it  in  a  glass  tube,  passing  a  current  of  dry  carbonic  acid  over  it 


412  CHLORIDES    OF    TIN. 

till  the  water  is  carried  of,  and  suffering  it  to  cool  out  of  the  contact  of  air. 
The  specific  gravity  of  this  oxide  is  6-6.  It  forms  a  dark-gray  or  black 
powder,  which,  on  the  contact  of  a  red-hot  wire,  burns  like  tinder  into  per- 
oxide. In  the  hydrated  state  it  dissolves  readily  in  sulphuric,  hydrochloric, 
and  dilute  nitric  acids,  as  well  as  in  caustic  potassa  and  soda,  but  not  in  am- 
monia, nor  in  the  alkaline  carbonates.  It  is  soluble  in  lime-water,  and  in 
baryta-water.  Its  alkaline  solution,  when  long  kept,  deposits  metallic  tin  in 
arborescent  crystals,  and  becomes  a  solution  of  the  peroxide. 

Sesquioxide  of  Tin  (Sn^Oa). — When  a  solution  of  protochloride  of  tin  is 
mixed  with  moist  hydrated  sesquioxide  of  iron  and  boiled,  an  interchange 
of  elements  takes  place,  by  which  protochloride  of  iron  and  sesquioxide  of 
tin  are  formed:  in  this  case,  2(SnCl)  and  Fefi.^,  become  Sn203  and  2(FeCl). 
The  solubility  of  this  oxide  in  ammonia  distinguishes  it  from  protoxide  ;  and 
its  giving  a  purple  precipitate  with  chloride  of  gold  from  peroxide.  It  is 
soluble  in  concentrated  hydrochloric  acid.  It  may  be  represented  as  a  stan- 
nate  of  the  protoxide  by  the  formula  SnO.SnOg. 

Peroxide  op  Tin  ;  Binoxide  of  Tin  (SnO^). — This  is  the  common  ore  of 
tin  :  in  its  crystalline  form  it  is  insoluble  in  acids,  but  when  heated  with 
potassa  or  soda  it  forms  a  soluble  compound.  There  are  two  remarkable 
varieties  of  the  hydrate  of  this  oxide,  which  have  been  distinguished  as  stan- 
nic and  metastannic  acid.  Stannic  acid  (SnO^HO)  is  obtained  by  precipi- 
tating a  solution  of  bichloride  of  tin  by  ammonia,  and  washing  and  carefully 
drying  the  precipitate  :  it  is  soluble  in  acids,  and  in  solutions  of  potassa  and 
soda,  but  not  in  ammonia.  When  heated  to  about  300°,  it  passes  into 
metastannic  acid.  Stannate  of  Potassa  is  formed  when  peroxide  of  tin  is 
heated  with  potassa  :  the'  product,  when  dissolved  and  evaporated,  yields 
crystals  (KO,Sn03,4HO).  Their  aqueous  solution  is  alkaline,  absorbs  car- 
bonic acid,  and  is  precipitated  by  most  of  the  salts  of  potassa,  soda,  and 
ammonia.  Stannate  of  soda  (NaO,Sn02,4HO)  may  be  similarly  prepared 
and  crystallized :  it  is  largely  used  as  a  mordant  by  dyers  and  calico- 
printers. 

Metastannic  acid  is  the  result  of  the  action  of  nitric  acid  upon  tin  :  in  its 
most  concentrated  form  this  acid  does  not  immediately  act,  but  on  the  addi- 
tion of  a  few  drops  of  water  violent  effervescence  ensues,  much  heat  is 
evolved,  together  with  nitric  oxide  and  nitrous  acid  vapor ;  some  nitrate  of 
ammonia  is  also  formed  (p.  182)  ;  and  the  metastannic  acid  remains  in  the 
form  of  a  white  insoluble  powder :  it  may  be  purified  by  washing,  and  dried 
at  a  dull-red  heat.  When  dried  in  the  air  it  consists  of  Sn50io,10E[0  :  dried 
at  212°  it  loses  5H0,  and  at  a  red  heat  becomes  anhydrous,  and  acquires  a 
pale  buff  color.  Hydrated  metastannic  acid  is  insoluble  in  nitric  acid :  it 
dissolves  in  sulphuric  acid,  forming  a  compound  soluble  in  water,  but  decom- 
posed by  boiling.  It  dissolves  in  solutions  of  potassa  and  soda  and  their 
carbonates,  but  not  in  ammonia.  The  metastannates  are  not  crystallizable. 
When  the  hydrated  acid  is  moistened  with  protochloride  of  tin  it  forms  a 
characteristic  yellow  metastannate  of  tin. 

Native  Peroxide  of  Tin  is  generally  gray,  brown,  or  black,  and  sometimes 
transparent  or  translucent ;  its  specific  gravity  is  T  :  its  primitive  crystal  is 
an  obtuse  octahedron,  of  which  the  modifications  are  extremely  numerous. 
In  some  of  the  valleys  of  Cornwall  it  is  found  in  nodules  mixed  with  pebbles, 
and  is  called  stream  tin.  A  modification  of  stream  tin,  in  small  banded  frag- 
ments or  globular  masses,  is  called  wood  tin. 

Protochloride  of  Tin  (SnCl)  is  obtained  by  subjecting  a  mixture  of 
equal  weights  of  calomel  and  of  an  amalgam  of  tin  and  mercury  to  distilla- 
tion, in  a  retort  gradually  raised  to  a  dull-red  heat;  or  a  mixture  of  1  part 
of  tin  filings  and  2  of  corrosive  sublimate  may  be  treated  in  the  same  way. 


CHLORIDES    AND    SULPHIDES    OF    TIN.  413 

When  hydrochloric  acid  gas  is  passed  over  heated  tin  in  a  glass  tube,  the 
protochloride  is  also  formed  and  hydrogen  given  off.  When  tin  is  dissolved 
in  hydrochloric  acid,  the  solution  evaporated,  and  the  dry  residue  carefully 
heated  to  incipient  redness  in  a  small  tube  retort,  so  as  to  exclude  air,  the 
protochloride  of  tin  remains  nearly  pure.  It  is  in  the  form  of  a  gray  solid, 
fusible  and  volatile'at  a  high  heat  (Butter  of  Tin).  When  its  solution  in  a 
small  quantity  of  water  is  evaporated  it  yields  prismatic  crystals,  which 
include  3  atoms  of  water,  of  which  the  greater  part  may  be  expelled  at  212°. 
When  a  large  quantity  of  water  is  poured  upon  these  crystals  they  are  partly 
decomposed,  hydrochloric  acid  is  separated,  and  a  white  powder  formed, 
which  is  an  oxicJdoride  of  tin  =SnO,SnCl,2HO.  The  protochloride  of  tin, 
or  salt  of  tin  of  commerce,  is  made  by  putting  1  part  of  granulated  tin  into 
a  basin  upon  a  sand-bath,  and  pouring  upon  it  1  part  of  hydrochloric  acid, 
so  that  when  heated  it  may  be  exposed  to  the  joint  action  of  the  acid  and 
air ;  after  some  hours  3  parts  more  of  the  acid  are  added,  and  the  mixture 
stirred  and  digested  till  a  saturated  solution  is  obtained.  During  the  pro- 
cess, fetid  hydrogen  gas  is  given  off,  and  the  greater  part  of  the  tin  is  dis- 
solved ;  when  the  clear  liquor  is  poured  off  it  is  set  aside  to  crystallize  ;  the 
mother-liquors  are  again  evaporated  as  long  as  they  afford  crystals,  and  the 
residue  is  afterwards  employed  for  conversion  into  bichloride. 

In  consequence  of  the  decomposition  above  mentioned,  the  aqueous  solu- 
tion of  protochloride  of  tin  is  turbid,  but  becomes  clear  on  the  addition  of 
hydrochloric  acid.  This  acid  solution  quickly  absorbs  oxygen,  and,  when 
added  to  certain  metallic  solutions,  it  revives  or  deoxidizes  them.  It  preci- 
pitates sulphur  from  sulphurous  acid.  It  reduces  the  persalts  of  iron  to  pro- 
tosalts,  and  converts  arsenic  acid  into  arsenious  acid,  and  chromic  acid  into 
oxide  of  chromium.  With  a  weak  solution  of  corrosive  sublimate  it  forms  a 
gray  precipitate  of  metallic  mercury.  Added  to  a  dilute  solution  of  chloride 
of  platinum  it  changes  its  color  to  a  deep  blood-red.  With  solution  of  gold 
it  produced  a  purple  precipitate  used  in  painting  porcelain,  and  known  under 
the  name  of  Purple  of  Cassius.  With  infusion  of  cochineal  it  produces  a 
purple  precipitate ;  and  it  is  much  used  to  fix  and  alter  colors  in  dyeing  and 
calico-printing. 

Perchloride  of  Tin  (SnClg). — If  tin  is  heated  in  excess  of  chlorine,  or 
if  a  mixture  of  1  part  of  tin  filings  and  4  of  corrosive  sublimate  is  distilled, 
the  perchloride  will  pass  over.  It  is  a  transparent  colorless  fluid,  formerly 
called  Lihavius^s  Fuming  Liquor:  it  exhales  copious  fumes  when  exposed 
to  moist  air ;  and  with  one-third  its  weight  of  water  it  forms  a  crystallized 
hydrate  =(SnCl25HO).  It  does  not  congeal  at  — 20^.  Its  boiling  point 
is  250°;  and  the  density  of  its  vapor  is  919.  It  is  instantly  decomposed 
by  metallic  zinc,  forming  chloride  of  zinc  and  a  precipitate  of  metallic  tin. 
A  solution  of  perchloride  of  tin  much  used  by  dyers,  is  made  by  dissolving 
tin  in  a  mixture  of  2  measures  of  hydrochloric  acid,  1  of  nitric  acid,  and  1 
of  water.  The  perchloride  forms  double  salts  with  the  chlorides  of  ammo- 
nium, potassium,  and  sodium. 

Protosulphide  of  Tin  (SnS)  may  be  formed  by  heating  tin  with  sulphur. 
A  hydrated  protosulphide  of  tin  is  precipitated  from  the  salts  of  the  prot- 
oxide, by  sulphuretted  hydrogen ;  it  is  of  a  brownish-black  color,  and 
loses  water  when  heated.  Sulphide  of  tin  is  a  brittle  black  compound, 
soluble  in  hydrochloric  acid  with  the  evolution  of  sulphuretted  hydrogen. 

Sesquisulphide  op  Tin  (Sn^Sa)  is  obtained  by  heating  the  protosulphide 
with  one-third  its  weight  of  sulphur  :  it  is  of  a  yellowish-gray  color,  metallic 
lustre,  and  when  digested  in  hydrochloric  acid  gives  out  sulphuretted  hydro- 
gen, and  leaves  a  yellow  residue  of  bisulphide. 

Bisulphide  of  Tin  (SnSJ  is  obtained  as  follows ;    Take  12  oz.  of  tin 


414  ALLOYS    OF    TIN. 

and  amalgamate  it  with  6  oz.  of  mercury ;  reduce  it  to  powder,  and  mix  it 
with  7  oz.  of  sublimed  sulphur  and  6  oz.  of  sal-ammoniac,  and  put  the 
■whole  into  a  glass  matrass  placed  on  a  sand-bath.  Apply  a  gentle  heat  till 
the  white  fumes  abate,  then  raise  the  heat  to  redness,  and  keep  it  so  for  a 
due  time.  On  cooling  and  breaking  the  matrass,  the  bisulphide  of  tin  is 
found  at  the  bottom.  The  use  of  the  mercury  is  to  facilitate  the  fusion  of 
the  tin  and  its  combination  with  the  sulphur,  while  the  sal-ammoniac  pre- 
vents such  increase  of  temperature  as  would  reduce  the  tin  to  the  state  of 
protosulphide.  A  hydrated  bisulphide  of  tin  is  formed  by  decomposing  a 
solution  of  perchloride  of  tin  by  sulphuretted  hydrogen.  The  precipitate 
becomes  a  dingy  yellow  when  dried,  and  has  a  vitreous  fracture. 

The  extraordinary  golden  lustre  of  the  bisulphide  of  tin,  and  its  flaky 
texture,  rendered  it  an  object  of  great  interest  to  the  alchemist :  it  was 
termed  aurum  musivum,  and  mosaic  gold.  When  well  made,  it  is  in  soft 
golden  flakes,  friable  and  adhering  to  the  fingers;  sp.  gr.  4-4  to  4*6.  It  is 
insoluble  in  acids,  except  in  nitrohydrochloric  acid ;  it  is  soluble  in  caustic 
potassa,  but  not  without  partial  decomposition.  It  dissolves  in  sulphide  of 
sodium,  and  the  concentrated  solution  yields  crystals  of  a  hydrated  double 
sulphide,  the  formula  of  which  is  2NaS+SnS2H-12HO.  It  is  used  for 
ornamental  work,  under  the  name  of  hronze-powder^  especially  by  the  manu- 
facturers of  paper-hangings:  it  is  chiefly  imported  from  Holland  and  Germany. 

Tin  pyrites  is  a  rare  mineral  composed  of  the  disulphides  of  copper  and 
iron  with  bisulphide  of  tin,  =2(Fe2,S)SnS,+  2(Cu„S)SnS2. 

Sulphates  of  Tin. — When  excess  of  the  tin  is  boiled  in  sulphuric  acid,  a 
solution  is  obtained  which  deposits  white  acicular  crystals  of  protosulphate 
of  tin.  Protosulphate  of  tin  is  also  precipitated  by  pouring  sulphuric  acid 
into  protochloride  of  tin.  When  tin  is  boiled  in  excess  of  sulphuric  acid,  a 
persulphate  is  formed. 

Alloys. — Tin-plate  is  a  most  useful  alloy  of  tin  and  iron,  in  which  iron 
plate  is  superficially  combined  with  tin,  and  to  the  surface  of  which  a  quan- 
tity of  tin  further  adheres,  without  being  in  combination.  It  is  made  by 
dipping  cleansed  iron  plates  into  a  bath  of  melted  tin.  An  objection  to 
such  combinations  is,  that  in  consequence  of  the  electrical  relations  of  the 
metals,  the  iron,  if  anywhere  exposed,  has  an  increased  tendency  to  oxida- 
tion :  for  although  the  surface  of  the  tin  itself  is  sufficiently  durable,  no 
sooner  is  any  portion  so  abraded  as  to  denude  the  iron,  than  a  spot  of  rust 
appears  and  rapidly  extends  :  hence  the  superiority  of  iron  plate  covered 
by  zinc  instead  of  tin,  zinc  being  electro-positive,  whereas  tin  is  electro-nega- 
tive in  regard  to  iron,  under  the  influence  of  common  oxidizing  agents. 

Moire  metallique  is  tin  plate  which  has  been  superficially  acted  on  by  an 
acid,  so  as  to  display,  by  reflected  light,  the  crystalline  texture  of  the  tin  : 
the  tin  plate  being  best  suited  for  the  purpose  is  that  which  has  rather  a 
thick  coating  of  pure  tin.  It  should  first  be  well  cleansed  by  washing  its 
surface  with  a  little  caustic  potassa,  then  in  water,  and  drying  it.  The  acid 
employed  is  always  some  modification  of  the  nitrohydrochloric,  more  or  less 
diluted  ;  a  mixture  of  8  parts  of  water,  2  of  nitric,  and  three  of  hydrochloric 
acid,  generally  answers  well.  The  plate  should  be  slightly  heated,  and  then 
quickly  sponged  over  with  the  acid,  so  as  to  bring  out  the  moire ;  it  should 
then  be  immediately  dipped  into  water  containing  a  little  potassa  dissolved 
in  It,  well  washed,  and  perfectly  dried.  If  the  acid  has  blackened  or  oxidized 
the  surface,  a  weak  solution  of  caustic  potassa  will  generally  clean  it.  The 
crystals  on  the  unprepared  tin  .plate  are  usuallv  large  and  indistinct,  so  that 
It  IS  often  modified  expressly  for  the  purpose,  by  heating  it  up  to  the  point 
of  the  fusion  of  the  tin,  powdering  it  over  with  sal-ammoniac  to  remove  the 
oxide,  and  then  plunging  it  into  cold  water  ;  in  this  way  the  crystals  are 


TESTS  FOR  THE  SALTS  OP  TIN.   CADMIUM.         415 

generally  small.  By  sprinkling  the  surface  of  the  heated  plate  with  water, 
or  by  only  partially  fusing  the  tin  by  holding  the  plate  over  the  flame  of  a 
spirit-lamp,  or  running  a  blowpipe  flame  over  it,  various  modifications  of 
the  crystalline  surface  may  be  obtained,  or  different  devices  sketched  as  it 
were  upon  it.  The  plates  are  generally  finished  by  a  coating  of  transparent 
or  colored  varnish. 

The  tinning  of  pins  is  effected  by  boiling  them  for  a  few  minutes  in  a 
solution  of  1  part  of  bitartrate  of  potassa,  2  of  alum,  and  2  of  common  salt, 
in  10  or  12  of  water,  to  which  some  tin  filings,  or  finely-granulated  tin  are 
added ;  they  soon  become  coated  with  a  film  of  tin,  and  are  then  taken  out, 
cleaned  and  dried.  The  pins  are  made  of  brass  wire,  and  require  to  be  per- 
fectly clean  before  they  are  put  into  the  tinning  liquor.  Tin  medals,  or  casts 
in  tin,  are  bronzed  by  being  first  well  cleaned,  wiped,  and  washed  over  with 
a  solution  of  1  part  of  protosulphate  of  iron,  and  1  of  sulphate  of  copper, 
in  20  of  water :  this  gives  a  gray  tint  to  the  surface ;  they  are  then  brushed 
over  with  a  solution  of  4  parts  of  verdigris  in  11  of  distilled  vinegar;  left 
for  an  hour  to  dry ;  and  polished  with  a  soft  brush-and  colcothar. 

Tests  for  the  Salts  of  Tin. — The  protosalts  are  colorless  and  acid ;  they 
are  generally  represented  by  protochloride  :  1.  Sulphuretted  hydrogen,  2i\\di 
hydrosulphate  of  ammonia,  give  a  deep  brown  precipitate  of  protosulphide 
(SnS).  This  is  dissolved  by  an  excess  of  the  hydrosulphate,  and  is  con- 
verted into  bisulphide  (SnSg).  Acids  throw  it  down  yellow  from  this  solu- 
tion. 2.  Potassa  gives  a  white  precipitate  (hydrated  oxide),  soluble  in  an 
excess  of  the  alkali,  and  in  hydrochlorate  of  ammonia.  3.  Ammonia,  and 
alkaline  carbonates  and  bicarbonates  produce,  in  diluted  solutions,  white  pre- 
cipitates, insoluble  in  an  excess  of  the  reagents  as  well  as  in  hydrochlorate 
of  ammonia.  4.  Corrosive  sublimate  gives  a  white  precipitate,  becoming 
gray  or  black  when  heated,  provided  the  salt  of  tin  is  in  excess.  This  is 
owing  to  the  separation  of  metallic  mercury.  5.  Chloride  of  gold  gives, 
with  a  diluted  solution,  a  red-brown  color,  which  becomes  of  a  deep  purple 
red  when  heated.  6.  When  heated  with  a  salt  of  copper,  the  salt  is  reduced 
to  white  dichloride,  which  is  precipitated  on  the  addition  of  water.  A  piece 
of  granulated  zinc,  placed  in  the  diluted  liquid  acidified,  separates  tin  in  crys- 
tals. The  jyer5a/^5  of  tin  (perchloride)  :  1.  Sulphuretted  hydrogen  2.w.^  hydro- 
sulphate  of  ammonia  give  a  dingy  yellow  precipitate  of  bisulphide  of  tin, 
which  is  soluble  in  an  excess  of  the  hydrosulphate.  2.  Potassa  gives  a  white 
precipitate  soluble  in  an  excess  of  the  alkali,  but  insoluble  in  hydrochlorate 
of  ammonia.  3.  Ammonia,  and  all  alkaline  carbonates  give  a  white  pre- 
cipitate, insoluble  in  an  excess  and  in  the  hydrochlorate  of  ammonia.  4  and 
5.  Corrosive  sublimate  and  chloride  of  gold  produce  no  change  in  the  solution. 
In  a  mixture  of  proto  and  persalts,  chloride  of  gold,  in  small  quantity,  gives 
a  deep  ruby-red  color,  or  precipitate. 

Cadmium  (Cd=56). 

This  metal  was  discovered  in  1811  by  Stromeyer  ;  he  called  it  Cadmium^ 
from  xaSjufto,  a  term  formerly  applied  both  to  calamine  and  to  the  substance 
which  sublimes  from  the  furnace  during  the  manufacture  of  brass.  It  is  con- 
tained in  certain  ores  of  zinc,  and  being  more  volatile  than  zinc,  passes  over 
with  the  first  portions  of  distilled  metal,  from  which  it  may  be  separated  by 
dissolving  it  in  dilute  sulphuric  acid,  and  passing  sulphuretted  hydrogen 
through  the  solution  :  the  sulphide  of  cadmium  thus  precipitated,  is  then 
dissolved  in  hydrochloric  acid,  and  precipitated  by  carbonate  of  ammonia. 
This  precipitate,  after  having  been  washed  and  dried,  is  mixed  with  char- 
coal, and  reduced  in  an  earthen  retort ;  the  cadmium  passes  over  at  a  dull 
red  heat. 


416  CADMIUM. 

Cadmium,  in  its  physical  properties,  much  resembles  tin,  but  it  is  rather 
harder  and  more  tenacious  :  it  crackles  when  bent.  Its  sp.  gr.  is  from  8-60 
to  8-69.  It  fuses  at  about  the  temperature  required  by  tin  (442°),  and  distils 
over  a  heat  somewhat  below  redness,  condensing  into  metallic  globules :  its 
vapor  is  inodorous.  Air  scarcely  acts  upon  it  except  when  heated,  when  it 
forms  an  orange-colored  oxide,  not  volatile,  and  easily  reducible.  Owing  to  the 
production  of  this  fixed  oxide,  the  metal  cannot  be  volatilized  except  in 
close  vessels  or  tubes  of  narrow  bore.  A  portion  is  always  converted  into 
yellow  oxide  during  sublimation. 

Oxide  of  Cadmium  (CdO). — Cadmium  slowly  dissolves  in  diluted  sulphu- 
ric or  hydrochloric  acid,  with  the  evolution  of  hydrogen.  The  oxide  is  best 
obtained  by  dissolving  the  metal  in  dilute  nitric  acid,  and  precipitating  it  in 
the  state  of  carbonate,  which  is  then  washed,  dried  and  ignited.  It  is  of  a 
reddish-brown  or  orange  color,  neither  volatile  nor  fusible ;  but  when  mixed 
with  carbonaceous  matter  it  appears  to  be  volatile,  in  consequence  of  its  easy 
reduction,  and  the  oxidation  of  the  separated  cadmium.  When  thrown  down 
from  its  solutions  by  alkalies,  it  forms  s,^\\\iQ  hydrate,  which  absorbs  carbonic 
acid  from  the  atmosphere,  and  is  soluble  in  excess  of  ammonia,  but  insoluble 
in  potassa  and  soda. 

Nitrate  of  Cadmium  (CdO,N054HO)  forms  radiated  acicular  crystals, 
which  are  deliquescent,  and  soluble  in  alcohol. 

Chloride  of  Cadmium  (CdCl)  is  formed  by  dissolving  the  hydrated  oxide 
in  hydrochloric  acid  :  on  evaporation,  small  prismatic  crystals  are  obtained, 
very  soluble  in  water ;  they  readily  fuse,  and,  losing  water,  concrete  into  a 
lamellar  crystalline  mass  of  anhydrous  chloride,  which,  at  a  very  high  tem- 
perature, is  volatile,  and  condenses  in  the  form  of  a  nacreous  sublimate.  It 
forms  double  salts  with  the  alkaline  chlorides. 

Bromide  of  Cadmium  (CdBr). — This  may  be  procured  by  digesting  in  a 
tubulated  retort  connected  with  a  receiver,  2  parts  of  cadmium  in  fine  shav- 
ings, 1  part  of  bromine,  and  10  of  water.  When  the  reaction  has  ceased, 
and  the  liquid  is  colorless,  it  may  be  filtered,  and  concentrated  in  a  porcelain 
vessel.  White,  silky-looking  prismatic  crystals  are  deposited  ;  they  are 
readily  dissolved  by  water,  alcohol,  and  ether. 

Iodide  of  Cadmium  (Cdl). — The  iodide  may  be  procured  directly  by  a 
process  similar  to  that  above  described  for  the  preparation  of  the  bromide. 
The  proportions  are,  2  parts  of  cadmium  in  fine  shavings,  4  parts  of  iodine, 
and  10  parts  of  water.  The  operation  is  continued  until  the  liquor  is  color- 
less. It  is  then  evaporated,  and  the  iodide  is  deposited  on  cooling,  in  wiiite 
scaly  crystals  of  a  nacreous  appearance.  It  is  soluble  in  water,  alcohol,  and 
ether.  This  salt  is  remarkable  for  its  fixedness,  whether  solid  or  in  solution. 
With  the  bromide,  it  is  largely  used  in  photography.  Collodion,  prepared 
with  iodide  or  bromide  of  cadmium,  retains  its  properties  unchanged  for  a 
long  period. 

Sulphide  of  Cadmium  (CdS)  is  obtained  in  the  form  of  a  bright  yellow 
powder,  insoluble  in  ammonia  and  in  the  fixed  alkalies,  by  precipitating  the 
solutions  of  the  metal  with  sulphuretted  hydrogen,  or  an  alkaline  sulphide. 
It  dissolves,  with  the  evolution  of  sulphuretted  hydrogen,  in  hydrochloric 
acid,  and  is  not  volatile  at  a  white  heat.  It  furnishes  a  yellow  pigment,  which 
mixes  well  with  other  colors,  and  closely  resembles  sulphide  of  arsenic. 

Sulphate  of  Cadmium  (CdO,S03,4HO)  yields  transaprent  prismatic 
colorless  crystals,  very  soluble  in  water,  and  forming  a  double  salt  with  sul- 
phate of  potassa. 

Carbonate  of  Cadmium  (CdOjCOJ  is  a  white  anhydrous  powder,  which 
loses  its  acid  at  a  red  heat. 


MANUFACTURE    OF    COPPER.  41T 

Tests  for  the  Salts  of  Cadmium. — 1.  Sulphuretted  hydrogen  gives  a 
bright  yellow,  passing  to  an  orange-yellow  precipitate,  even  in  acid  solutions. 
This  precipitate  is  insoluble  in  potassa  and  ammonia,  but  is  dissolved  by 
strong  hydrochloric  acid.  By  these  properties,  the  sulphide  of  cadmium  is 
easily  distinguished  from  that  of  arsenic.  2.  Hydrosulphate  of  ammonia 
gives  a  yellow  sulphide,  insoluble  in  an  excess  of  the  reagent.  3.  Potassa 
throws  down  a  white  oxide,  insoluble  in  an  excess  of  the  alkali,  and  in  hydro- 
chlorate  of  ammonia.  4.  Ammonia,  a  white  oxide,  soluble  in  excess,  not 
precipitated  by  hydrochlorate  of  ammonia,  but  thrown  down  as  yellow  sul- 
phide by  sulphuretted  hydrogen.  5.  Carbonate  of  ammonia  and  other 
alkaline  carbonates,  a  white  precipitate,  insoluble  in  excess.  The  carbonate 
of  zinc  is  soluble  in  the  precipitant,  so  that  by  this  test  zinc  and  cadmium 
may  be  distinguished  and  separated  from  each  other.  6.  Ferrocyunide  of 
potassium,  gives  a  white  precipitate,  insoluble  in  hydrochloric  acid  ;  and  the 
ferricyanide  a  brownish-yellow  precipitate,  soluble  in  a  large  excess  of  hydro- 
chloric acid.  Magnesium  and  zinc  precipitate  cadmium  in  a  metallic  state 
from  its  solutions. 


CHAPTER    XXXII. 

COPPER  AND   LEAD. 

Copper  (Co =32). 

Copper,  Cuprum,  or  Venus,  of  the  alchemists  (9),  was  known  in  the  early 
ages  of  the  world,  and  was  the  principal  ingredient  in  the  manufacture  of 
domestic  utensils,  and  instruments  of  war,  previous  to  the  discovery  of  malle- 
able iron.  The  word  copper  is  derived  from  Cyprus,  the  island  where  it  was 
first  wrought  by  the  Greeks.  It  is  found  native,  and  in  various  states  of 
combination.  The  sulphides  are  its  most  abundant  ores,  and  from  them, 
commercial  demands  are  almost  exclusively  supplied. 

Manufacture  of  Copper. — The  ore,  having  been  picked  and  broken,  is 
heated  in  a  reverberatory  furnace,  by  which  arsenic  and  sulphur  are  in  great 
part  driven  off.  It  is  then  transferred  to  a  smaller  reverberatory,  where  it 
is  fused,  a  large  portion  of  the  sulphide  of  iron  having  been  converted  into 
oxide,  which,  by  the  addition  of  silicious  sand,  forms  a  vitreous  slag.  When 
the  iron  is  thus  separated,  the  sulphur  begins  to  burn  out  of  the  sulphide  of 
copper,  and  the  copper  becoming  oxidized,  is  reduced  by  the  carbonaceous 
matter.  The  impure  metal  is  then  granulated  by  letting  it  run  into  water: 
it  is  afterwards  remelted  and  granulated  two  or  three  times  successively,  in 
order  further  to  separate  impurities,  which  are  chiefly  sulphur,  iron,  and 
arsenic ;  and  it  is  ultimately  cast  into  oblong  pieces  called  pigs,  which  are 
broken  up,  roasted,  ai>d  melted  with  a  portion  of  charcoal  in  the  refining- 
furnace.  Malleability  is  here  conferred  upon  the  copper,  and  its  texture 
improved,  by  stirring  the  metal  with  a  pole  of  green  wood :  assays  are  occa- 
sionally taken  out,  and  the  metal,  originally  crystalline  and  granular  when 
cold,  now  becomes  fine  and  close,  so  as  to  assume  a  silky  hue  when  the 
assays  are  half  cut  through  and  broken.  The  metal  is  then  cast  into  cakes. 
The  whole  process  of  refining  copper,  and  toughening  it  bj  poling,  requires 
much  care ;  and  if  it  be  over-poled,  the  metal  is  even  rendered  more  brittle 
than  in  its  original  state.  The  effect  of  poling  has  not  been  satisfactorily 
explained  :  it  may  consist  in  the  separation  of  a  small  portion  of  oxide  of 
2Y 


418  IMPURITIES    IN    COPPER. 

copper ;  and  the  effect  of  over-poling  may  possibly  depend  npon  the  combi- 
nation of  the  copper  with  a  portion  of  carbon.  Copper  for  brass-making  is 
granulated  by  pouring  the  metal  through  a  perforated  ladle  into  water ; 
when  this  is  vvarm,  the  copper  assumes  a  rounded  form,  and  is  called  bean- 
shot ;  but  if  a  constant  supply  of  cold  water  is  kept  up,  it  becomes  ragged, 
and  is  called  feathered  shot.  Another  form  into  which  copper  is  cast,  is  in 
pieces  of  the  length  of  six  inches,  and  weighing  about  eight  ounces  each  : 
the  copper  is  dropped  from  the  moulds,  immediately  on  its  becoming  solid, 
into  a  cistern  of  cold  water,  and  thus,  by  a  slight  oxidation  of  the  metal,  the 
sticks  acquire  a  rich  red  color  on  the  surface.     This  is  called  Japan  copper. 

Copper  may  be  obtained  by  the  voltaic  decomposition  of  a  solution  of  the 
sulphate  ;  or  by  dissolving  the  copper  of  commerce  in  nitric  acid,  with  the 
addition  of  a  little  sulphuric  acid  ;  the  solution  is  diluted,  and  a  plate  of  iron 
is  immersed,  upon  which  the  copper  is  precipitated;  after  having  been  pre- 
vipusly  washed  in  dilute  sulphuric  acid,  to  separate  a  little  adhering  iron,  it 
may  be  fused  into  a  button. 

The  usual  impurities  in  ordinary  copper  are  traces  of  arsenic,  antimony, 
tin,  lead,  iron,  oxide  of  copper,  and  carbon.  From  recent  researches  it 
appears  that  all  English  "  refined"  copper,  whether  in  the  state  of  foil  or  the 
finest  wire,  contains  a  notable  proportion  of  arsenic.  This  impurity  does  not 
affect  the  ductility  or  malleability  of  copper  to  the  extent  alleged  by  some 
chemical  writers ;  but,  according  to  Dr.  Mathiessen's  experiments,  it 
diminishes  to  a  considerable  extent  the  conducting  power  of  the  metal  in 
reference  to  electricity,  so  that  such  interference  might  almost  be  made  a  test 
of  the  presence  of  this  impurity.  Copper  free  from  arsenic  cannot  be 
obtained,  except  with  the  greatest  difficulty.  The  presence  of  arsenic  in 
small  quantity  is  easily  overlooked,  and  thus  samples  which  contain  it  are 
frequently  sold  as  pure.  The  Burra  Burra  copper,  as  well  as  about  forty 
samples  of  copper,  British  and  foreign,  which  we  have  examined,  contained 
arsenic  in  variable  proportion.  The  arsenic  is  associated  in  the  ore  with 
the  sulphides  of  iron  and  copper,  and-  cannot  be  expelled  from  the  metal 
by  heat,  or  in  the  ordinary  process  of  refining.  Some  coppers  from 
America,  obtained  from  native  carbonates,  have  been  found  free  from  arsenic. 
Dr.  Percy  {Metallvrgy,  Yol.  I.,  p.  381)  takes  exception  to  the  statement 
here  made  respecting  the  presence  of  arsenic  in  all  the  copper  used  in  com- 
merce, the  arts,  and  chemistry,  yet  our  experience  since  the  publication  of 
the  former  edition  of  this  work  has  only  tended  to  confirm  its  correctness. 
Having  procured,  by  Dr.  Percy's  recommendation,  some  of  what  he  describes 
as  "  best  selected  copper,"  and  from  sources  recommended  by  him,  we  have 
tried  experiments  on  this,  and  found  as  much  arsenic  in  it  as  in  ordinary 
copper.  Dr.  Percy  does  not  state  that  he  has  ever  found  a  sample  without 
arsenic,  but  an  inference  might  be  drawn  from  his  remarks  which  would  lead 
to  the  use  of  arsenical  copper  for  toxicological  purposes  and  thus  give  rise 
to  serious  mistakes.  Non-arsenical  copper  may  be  procured  of  special  dealers 
at  the  cost  of  about  one  guinea  a  pound.  It  is  deposited  by  a  voltaic  current 
from  a  solution  of  the  pure  sulphate,  and  afterwards  undergoes  certain  re- 
fining processes.  It  is  to  be  obtained  in  the  form  of  a  fine  powder  or  foil. 
Neither  the  refined  nor  the  "best  selected"  can  be  trusted  as  free  from  arsenic. 
We  have,  under  Oxide  op  Copper  (p.  420),  given  a  process  for  obtaining 
this  metal  pure  ;  and  under  Subchloride  of  Copper  (p.  422),  we  have  de- 
scribed a  method  for  the  detection  of  arsenic  in  copper.  Native  copper 
occurs  in  a  variety  of  forms;  massive, dendritic,  granular,  and  crystallized 
in  cubes  or  octahedra.  It  is  found  in  Cornwall,  Siberia,  Saxony,  Hanover, 
Sweden,  America,  Cuba,  and  Australia.    The  copper  mines  of  Great  Britain 


OXIDES    OF    COPPER.  419 

and  Ireland  produced,  in  1865,  198,298  tons  of  copper  ore,  yielding  11,888 
tons  of  metallic  copper. 

Properties. — Copper  is  the  only  metal  which  has  a  red  color :  it  has  much 
lustre,  and  is  very  malleable,  ductile,  and  tenacious:  it  exhales  a  peculiar  smell 
when  warmed  or  rubbed.  It  melts  at  a  temperature  intermediate  between 
the  fusing-points  of  silver  and  gold,  =  1996^  Fahr.,  and  when  in  fusion 
absorbs  small  quantities  of  oxygen,  which  again  escape  when  the  metal 
solidifies,  occasioning  a  spirting  out  of  portions  of  the  liquid  copper.  At  a 
very  high  temperature,  copper  emits  fumes  which  condense  upon  cold  surfaces 
into  minute  globules  of  protoxide  with  a  metallic  nucleus.  Its  specific 
gravity  varies  from  8t88  to  8958;  the  former  being  the  least  density  of 
cast  copper,  the  latter  the  greatest  of  rolled  or  hammered  copper.  The  sp. 
gr.  of  some  samples  of  copper,  containing  a  little  of  the  protoxide,  does  not 
exceed  8-5,  and  such  copper  is  of  inferior  ductility.  When  copper  is  in  a 
state  of  extreme  division,  it  burns  like  tinder  ;  under  a  flame  urged  by  oxygen 
gas,  it  burns  with  a  green  light.  Exposed  to  damp  air,  copper  becomes 
covered  with  a  thin  greenish  crust  of  hydrated  oxide  and  carbonate.  If 
heated  and  plunged  into  water,  a  quantity  of  reddish  scales  separate,  con- 
sisting of  an  imperfect  oxide.  The  same  scales  fly  off,  during  cooling,  from 
a  plate  of  the  metal  which  has  been  heated  red-hot.  Copper  does  not 
decompose  water  at  a  red  heat.  It  deoxidizes  nitric  acid  (sp.  gr.  1*5) 
rapidly  in  the  cold.  It  has  no  action  on  sulphuric  acid,  except  at  a  boiling 
temperature,  when  it  deoxidizes  this  acid,  and  sets  free  sulphurous  acid. 
Hydrochloric  acid  exerts  no  action  on  it  in  the  cold,  unless  the  metal  is  at 
the  same  time  exposed  to  air ;  but  if  heated,  chloride  of  copper  is  formed, 
and  hydrogen  escapes.  Hydrogen,  however,  is  only  slowly  eliminated,  even 
under  these  circumstances,  and  it  is  commonly  combined  with  arsenic  or 
antimony. 

Copper  and  Oxygen. — There  are  two  oxides  of  copper,  a  suboxide  or 
dioxide,  Cu^O,  and  a  protoxide,  CuO  :  the  latter  is  the  basis  of  the  staple 
and  common  salts  of  copper.  The  dioxide  combines  directly  with  only  a  few 
of  the  acids,  and  is  in  most  cases  resolved  by  them  into  metallic  copper  and 
the  oxide:  (CuaO  =  Cu  +  CuO). 

Suboxide  of  Copper;  Dioxide  of  Copper  (Cu^O). — This  oxide  maybe 
formed  by  adding  to  an  aqueous  solution  of  equal  weights  of  sulphate  of 
copper  and  sugar,  a  sufficiency  of  soda  to  redissolve  the  first  precipitate,  and" 
then  boiling  the  resulting  blue  liquor:  the  suboxide  falls  as  a  red  powder, 
which,  when  washed  and  dried,  is  permanent  in  the  air.  By  boiling  a 
solution  of  acetate  of  copper  with  a  sufficiency  of  grape-sugar,  it  is  readily 
obtained  without  the  addition  of  caustic  alkali.  It  is  yellow  or  orange- 
colored  in  the  hydrated  state,  as  it  is  at  first  precipitated  ;  but  it  becomes 
anhydrous  and  of  a  deep  red  color,  by  continued  boiling.  This  oxide 
occurs  native  as  Ruby  copper,  crystallized  in  octahedra.  When  dioxide  of 
copper  is  heated  in  the  air,  it  passes  into  oxide.  The  dilute  acids  mostly 
decompose  it  and  separate  metallic  copper.  It  dissolves  in  concentrated 
hydrochloric  acid ;  it  also  dissolves  in  ammonia,  forming  a  colorless  solution 
when  kept  from  air;  but  it  is  not  soluble  in  solutions  of  potassa  or  of  soda. 
Its  salts  are  frequently  formed  by  the  action  of  deoxidizing  agents  on  the 
protosalts. 

Copper  vessels,  such  as  tea-urns,  and  medals,  are  often  superficially  coated 
with  oxide,  or  bronzed;  it  gives  them  an  agreeable  appearance,  and  prevents 
tarnish.  For  this  purpose  two  processes  are  resorted  to.  1.  The  copper 
surface  is  cleaned,  and  then  brushed  over  with  peroxide  of  iron  (generally 
colcothar)  made  into  a  paste  with  water,  or  with  a  very  dilute  solution  of 
acetate  of  copper ;  heat  is  then  cautiously  applied  in  a  proper  furnace  or 


.480  OXIDES    OF    COPPER. 

muflQe,  till  it  is  found,  on  brushing  ofif  the  oxide,  that  the  surface  beneath  has 
acquired  its  proper  hue.  2.  Two  parts  of  verdigris  and  one  of  sal-ammoniac 
are  dissolved  in  vinegar :  the  solution  is  boiled  in  a  pipkin,  skimmed,  and 
diluted  with  water  until  it  only  tastes  slightly  of  copper  and  ceases  to  dej^osit 
a  white  precipitate  :  it  is  then  poured  into  another  pipkin  or  copper  pan, 
and  rapidly  brought  to  boil,  and  the  medal,  previously  rendered  perfectly 
clean,  is  dipped  into  the  boiling  solution,  which  may  be  most  conveniently 
done  by  placing  it  in  a  small  perforated  copper  ladle.  The  surface  of  the 
medal  becomes  at  first  black  or  dark  blue,  and,  in  about  five  minutes,  acquires 
the  desired  brown  tint ;  it  must  then  be  instantly  withdrawn  and  washed  in 
a  stream  of  water,  and  lastly,  carefully  wiped  and  dried.  The  medal  is 
generally  perfected  by  afterwards  giving  it  one  gentle  pinch  between  the  dies. 
When  there  are  many  medals,  each  must  be  bronzed  separately  ;  they  must 
not  be  allowed  to  touch  each  other,  and  care  should  be  taken  to  rest  them 
upon  as  few  points  of  contact  as  possible.  The  bronzing-liquid  must  not  be 
suffered  to  concentrate  by  evaporation,  but  must  be  diluted  if  necessary,  so  as 
to  keep  it  in  a  proper  state,  and  especially  to  avoid  all  appearance  of  a  white 
precipitation  in  it.  A  weak  solution  of  chloride  of  gold  forms  a  good  bronz- 
ing liquid  for  copper. 

Oxide  of  Copper.  Protoxide  (CuO). — When  sheet  copper  is  exposed  in 
the* air  to  a  red  heat,  black  scales  form  upon  it,  which  are  thrown  off  on 
plunging  it  into  water,  or  which  fly  off  as  it  cools,  in  consequence  of  the 
comparatively  rapid  contraction  of  the  metal.  Wlien  these  scales  are  re- 
duced to  powder,  and  stirred  in  contact  with  air  at  a  red  heat,  they  yield  the 
oxide.  When  nitrate  of  copper  is  exposed  to  heat  gradually  raised  to  red- 
ness, it  fuses  and  is  decomposed,  and  ultimately  this  oxide  remains  as  a 
Telvety  black  powder.  The  oxide  may  be  at  once  prepared  in  large  quantity, 
by  dissolving  copper  in  one  part  of  nitric  acid  and  two  parts  of  water, 
evaporating  to  dryness,  and  heating  the  residue  to  redness  in  a  platinum 
dish.  The  arsenic  contained  in  "refined"  copper  is  converted  into  arsenic 
6cid.  It  may  be  separated  from  the  black  oxide  by  boiling  it  in  distilled 
water,  until  nitrate  of  silver  no  longer  gives  a  red  color  with  the  residue  of 
the  evaporated  water.  When  the  purified  oxide  is  dissolved  in  sulphuric 
acid,  and  the  metal  is  precipitated  by  voltaic  electricity,  it  is  free  from  arsenic, 
and  may  be  regarded  as  pure  copper.  Thus  procured,  it  is  brittle,  and  admits 
of  lamination  with  difficulty.  It  requires  frequent  annealing  to  reduce  it  only 
to  a  moderately  thin  sheet. 

Oxide  of  copper  is  black;  its  specific  gravity  is  6-4.  Before  the  blow- 
pipe, it  fuses  when  intensely  heated  in  the  point  of  the  flame,  upon  charcoal : 
in  the  interior  of  the  flame  it  affords  a  globule  of  metal.  Heated  alone,  it 
is  not  decomposed  at  the  highest  temperature,  but  it  is  easily  and  rapidly 
decomposed  at  a  dull  red  heat,  or  even  below  it,  by  hydrogen  or  carbon.  It 
is  also  decomposed  when  heated  in  contact  with  organic  substances,  con- 
verting their  hydrogen  into  water,  and  their  carbon  into  carbonic  acid  ;  hence 
•  its  use  in  their  analysis  :  it  is  hygrometric,  and  if  weighed  whilst  hot,  aug- 
ments in  weight^  after  cooling,  in  consequence  of  the  absorption  of  aerial 
moisture.  It  is  insoluble  in  water,  but  it  dissolves  in  the  greater  number  of 
the  acids,  and  is  the  basis  of  all  the  common  salts  of  copper.  When  alkalies 
are  dropped  into  its  solutions,  they  throw  it  down  as  a  bulky  blue  hydrate, 
which,  however,  is  not  permanent  at  a  boiling  heat,  but  becomes  black  and 
anhydrous  whe;i  boiled  in  an  excess  of  the  alkaline  liquid.  This  oxide  of 
copper  is  not  soluble  in  the  liquid  fixed  alkalies,  except  in  the  presence  of 
sugar,  tartrate  of  potassa,  albumen,  caseine,  lactose,  glycerine,  and  some 
other  substances.  With  grape-sugar  and  an  excess  of  the  alkaline  liquid, 
the  hydrated  oxide  of  copper  forms  a  rich  sapphire-blue  solution,  which 


CHLORIDES    OF    COPPER.  421 

reduces  the  protoxide  to  suboxide  slowly  in  the  cold  but  rapidly  when 
heated.  This  constitutes  Trommer''s  test  for  sn^rar.  Other  reducing  agents 
operate  in  a  similar  manner.  Thus,  if  arsenious  acid  is  present,  potassa 
forms  with  the  oxide,  a  blue  solution  which,  when  boiled,  yields,  like  su^ar, 
a  hydrated  or  anhydrous  suboxide  of  copper.  When  carbonate  of  potassa 
or  of  soda  is  fused  with  it,  it  expels  carbonic  acid,  and  combines  to  form  a 
blue  or  green  compound.  Its  combination  with  ammonia  will  presently  be 
noticed.  It  communicates  a  green,  and  sometimes  a  blue  tint  to  vitreous 
compounds;  and  is  the  basis  of  certain  colors  used  by  the  aticients,  which 
had  been  supposed  to  contain  cobalt.  The  dioxide  gives  a  beautiful  ruby 
red  color  to  glass. 

Hydrated  Oxide  of  Copper  (CuO,HO),  as  thrown  down  from  a  solution  of 
sulphate  of  copper  by  dilute  potassa  or  soda,  is  at  first  blue,  but  soon  changes 
to  green,  especially  if  it  be  dried  :  it  sustains,  when  dry,  a  temperature  of 
212°  without  decomposition,  but  a  little  above  that  it  becomes  discolored. 
When  boiled  in  the  liquor  from  which  it  has  been  precipitated,  or  when  a 
solution  of  copper  is  added  to  a  boiling  solution  of  soda  or  potassa,  it 
becomes  anhydrous  and  nearly  black. 

Nitrate  op  Copper  (CuO,NOg,3HO). — Nitric  acid  diluted  with  3  parts 
of  water,  rapidly  oxidizes  copper,  evolving  nitric  oxide,  and  ultimately  form- 
ing a  bright-blue  solution,  which  affords  deliquescent  prismatic  crystals,  of 
a  fine  blue  color,  very  soluble  in  water  and  in  alcohol.  They  liquefy  at  a 
temperature  below  212° ;  at  a  higher  temperature  they  lose  water  and  acid, 
becoming  a  subnitrate,  and  are  entirely  decomposed  at  a  red-heat,  leaving 
protoxide  of  copper.  At  low  temperatures  this  salt  crystallizes  in  rhora- 
boidal  plates,  which  contain  6  atoms  of  water,  but  these  effloresce  into  the 
terhydrate  in  vacuo  over  oil  of  vitriol.  Potassa  forms,  in  the  solution  of 
this  nitrate,  a  bulky  blue  precipitate  of  hydrated  oxide  of  copper,  which,  as 
already  observed,  when  boiled  in  potassa  or  soda,  becomes  black  from  the 
loss  of  its  combined  water.  When  nitrate  of  copper  is  coarsely  powdered, 
sprinkled  with  a  little  water,  and  quickly  rolled  up  in  a  sheet  of  pure  tinfoil, 
there  is  great  heat  produced,  nitrous  gas  is  rapidly  evolved,  and  the  metal 
often  takes  fire.  Ammonia  added  to  a  solution  of  nitrate  of  copper,  occa- 
sions a  precipitate  of  the  hydrated  oxide;  but  if  added  in  excess,  the  pre- 
cipitate is  redissolved,  and  an  ammonia-nitrate  is  produced. 

Ammonia  and  Oxide  of  Copper. — When  copper  filings  are  digested  in 
aqueous  ammonia  exposed  to  air,  the  solution  soon  becomes  blue  :  if  air  be 
then  excluded,  it  gradually  loses  color,  but  again  acquires  a  blue  color  on 
the  contact  of  air:  in  the  blue  liquor  the  copper  exists  as  oxide ;  in  the 
colorless  liquor  as  dioxide.  If  a  tall  glass  be  filled  with  liquid  ammonia  and 
a  few  drops  of  solution  of  suboxide  of  copper  (subchloride)  are  added,  the 
surface  becomes  blue,  but  it  remains  colorless  below.  The  solution  of  the 
oxide  of  copper  in  ammonia  is  obtained  by  exposing  copper  filings  in  solu- 
tion of  ammonia  to  air,  or  by  dissolving  the  hydrated  oxide  in  ammonia  :  it 
is  of  a  splendid  deep-blue  color. 

Copper  and  Chlorine. — Gaseous  chlorine  acts  upon  finely-divided  copper 
with  great  energy,  producing  the  phenomena  of  combustion  ;  two  chlorides 
are  the  result  of  this  action  ;  the  one  a  comparatively  fixed  fusible  substance, 
which  is  the  subchloride :  the  other  a  yellow  substance,  which  is  a  chloride. 

Subchloride  of  Copper. — Bichloride  (Cu^CI)  may  be  obtained  by  ex- 
posing copper  filings  to  the  action  of  chlorine,  not  in  excess  :  or  by  evapo- 
rating the  solution  of  dioxide  of  copper  in  hydrochloric  acid,  and  heating 
the  residue  in  a  vessel  with  a  very  small  orifice;  or  by  heating  the  proto- 
chloride  in  the  same  way.  It  is  also  precipitated,  on  adding  protochloride 
of  tin  no  a  strong  solution  of  the  chloride.     It  is  insoluble  in  water,  but 


422  SULPHIDES    OF    COPPER. 

soluble  in  ammonia — a  solution  employed  in  eudiometry.  It  is  also  dissolved 
by  hydrochloric  acid,  from  which  potassa  throws  down  the  hydrated  dioxide  : 
when  water  is  added  to  its  hydrochloric  solution,  it  is  thrown  down  in  the 
form  of  a  white  granular  or  crystalline  hydrate,  the  crystals  having  sometimes 
a  tetrahedral  form  :  its  color  varies,  being  brown  when  fused,  but  if  slowly 
cooled,  it  is  yellow,  translucent,  and  crystalline  ;  when  in  fine  division  it  is 
nearly  white  :  it  must  be  preserved  out  of  contact  of  air.  If  moistened  and 
exposed  to  air,  it  acquires  a  green  color,  and  becomes  converted  into  a 
hydrated  oxy  chloride,  which  has  been  termed  suhmuriate  of  copper,  or  Bruns- 
wick green  ;  the  same  compound  may  be  formed  by  adding  hydrated  oxide  of 
copper  to  a  solution  of  the  chloride  :  or  by  exposing  to  the  atmosphere  slips 
of  copper  partially  immersed  in  hydrochloric  acid.  In  this  case,  the  follow- 
ing changes  first  take  place  :  HCl  +  2Cu-f-0(air)  =  Cu2Cl-j-nO.  A  portion 
of  the  metal  becomes  oxidized,  and  the  oxychloride  results.  A  mixture  of 
this  kind  was  employed  by  Gay-Lussac  in  the  analysis  of  the  atmosphere, 
and  it  serves  as  a  process  for  obtaining  nitrogen  (p.  153).  After  24  hours 
the  acid  liquid  in  which  the  copper  has  been  partially  immersed,  acquires  a 
dark  greenish-brown  color  from  the  production  of  dichloride.  In  this  state, 
if  the  liquid  is  submitted  to  distillation  at  a  moderate  temperature,  any 
arsenic  present  in  the  copper  will  be  distilled  over  with  hydrochloric  acid,  as 
chloride  of  arsenic  {see  Arsenic).  By  evaporating  this  subchloride  to  dry- 
ness, the  whole  of  the  arsenic  may  be  driven  off ;  and  by  further  exposure  in 
contact  with  pure  hydrochloric  acid,  pure  oxychloride  of  copper  may  be 
obtained.  As  these  precautions  are  not  taken  in  practice,  the.  oxychloride, 
as  it  is  generally  prepared,  contains  arsenic. 

Chloride  op  Copper  (CuCl)  may  be  formed  by  heating  copper  filings  in 
excess  of  chlorine,  or  by  dissolving  oxide  of  copper  in  hydrochloric  acid,  and 
evaporating  to  dryness  by  a  heat  below  400°.  Chloride  of  copper  is  brown 
when  anhydrofs,  but  becomes  blue  by  exposure  to  air;  it  is  soluble  in  water 
and  alcohol,  and  very  difficultly  crystallizable.  The  prismatic  crystals  are 
CuCl, 2110.  The  concentrated  aqueous  solution  is  green ;  when  diluted, 
blue;  but  the  solution  again  becomes  green  when  heated  to  212°.  Exposed 
to  a  red  heat  in  a  tube  with  a  small  orifice,  chlorine  is  expelled,  and  it 
becomes  a  subchloride.  When  acted  upon  by  potassa  not  added  in  excess, 
and  only  so  as  partially  to  decompose  it,  a  green  oxychloride  is  thrown 
down. 

Oxychloride  of  Copper,  3(CuO)CuC],4HO,  is  found  native  m  Peru  and 
Chili,  sometimes  in  the  form  of  green  sand,  and  sometimes  massive  and  crys- 
tallized. The  green  sand  was  first  found  in  the  desert  of  Atacama,  sepa- 
rating Pern  from  Chili.  Chloride  of  copper  has  also  been  found  upon  some  of 
the  lavas  of  Vesuvius. 

Subiodide  of  Copper  ;  Diniodide  of  Copper  (CuJ).— When  iodide  of 
potassium  is  added  to  a  solution  of  the  protosulphates  of  copper  and  iron, 
both  in  crystals,  in  the  proportion  of  1  to  2^,  the  protoxide  of  iron  takes  the 
oxygen  of  the  oxide  of  copper,  and  the  iodine  the  metallic  copper,  with 
which  it  forms  a  white  precipitate  of  the  insoluble  subiodide ;  it  may  be 
dried  in  close  vessels.  In  the  manufacture  of  iodine  the  mixed  sulphates  are 
sometimes  employed  for  precipitating  the  iodine  from  the  iodides  in  kelp 
(p.  205).  When  iodide  of  potassium  is  added  to  a  salt  of  oxide  of  copper, 
iodine  is  set  free,  and  a  brown  subiodide  falls. 

Copper  and  Sulphur  ;  Disulphide  of  Copper  (Cu^S)  may  be  formed  by 
heating  a  mixture  of  8  parts  of  copper  fillings  and  3  of  sulphur  :  as  soon  as 
the  latter  melts  the  copper  becomes  red-hot,  undergoes  combustion,  and  a 
black  brittle  compound  is  formed.  It  is  soluble  in  hydrochloric  acid  with 
the  evolution  of  sulphuretted  hydrogen.      Vitreous  copper  is  a  native  ^isul- 


SULPHATES    OF    COPPER.  423 

phide  ;  it  occurs  crystallized  and  massive  in  Cornwall  and  Yorkshire.  It  has 
a  gray  color,  a  metallic  lustre,  and  a  sp.  gr.  of  about  ST.  Sulphide  (CuS) 
occurs  native,  associated  with  the  disulphide.  It  is  thrown  down  from  solu- 
tions of  salts  of  copper  by  sulphuretted  hydrogen,  as  a  dark-brown  hydrate, 
insoluble  in  alkalies  and  diluted  acids.  Ferrosulphides ;  Copper  pyrites,  or 
yellow  copper  ore  is  the  ore  from  which  commercial  copper  is  chiefly  derived. 
It  is  a  compound  of  sulphur,  copper,  and  iron,  the  proportions  of  the  sul- 
phides being  subject  to  variation,  but  commonly  represented  by  CugSjFCaSa, 

Sulphate  OF  Copper;  Roman  Vitriol;  Blue  Vitriol  (CuO,S03). — This 
salt  is  formed  by  boiling  copper  in  sulphuric  acid,  a  process  which  furnishes 
an  abundance  of  sulphurous  acid  (Cu4-2S03=CuO,S03-f  SOg).  It  is  also 
made  by  exposing  roasted  sulphide  of  copper  to  air  and  moisture  ;  thus  ob- 
tained, it  is  impure,  generally  containing  iron  and  arsenic  and  often  zinc, 
and  it  is  obtained  in  large  quantities,  and  nearly  pure,  in  certain  processes, 
afterwards  to  be  described  for  refining  gold  and  silver.  Sulphate  of  copper 
forms  rhomboidal  crystals  containing  5  atoms  of  water,  (CuO.SOgjSHO)  : 
sp.  gr.  2-27.  The  crystals  are  sometimes  very  large,  of  a  beautiful  sapphire- 
blue  color,  and  slightly  efflorescent  in  a  dry  atmosphere  ;  they  are  soluble  in 
4  parts  of  cold  water.  This  salt  has  a  peculiarly  nauseous  metallic  taste. 
When  heated  to  212°,  it  loses  4  atoms  of  water  of  crystallization,  and  crum- 
bles down  into  a  pale  powder;  heated  to  400°  it  becomes  white  and  anhy- 
drous ;  in  this  state  it  slowly  reabsorbs  water  from  the  air,  and  regains  its 
blue  color ;  or  if  sprinkled  with  water  heat  is  evolved,  and  the  salt  crumbles 
down  into  a  blue  hydrate.  By  a  continued  high  red  or  white  heat,  sulphuric 
acid,  and  some  sulphurous  acid  and  oxygen,  are  evolved,  and  black  oxide  of 
copper  remains.  Anhydrous  sulphate  of  copper,  by  reason  of  its  great  affin- 
ity for  water,  removes  it  from  liquids,  such  as  alcohol,  ether,  chloroform,  and 
pyroxylic  spirit.  It  is  occasionally  used  in  dehydrating  these  liquids  by 
distillation.  The  powder  changes  in  color  from  white  to  blue.  When  the 
blue  crystals  of  the  salt  are  digested  in  concentrated  sulphuric  acid,  they  are 
dehydrated  and  become  white.  This  salt  (the  Vitriol,  or  Salt  of  Venus,  of 
the  alchemists)  is  much  used  as  a  source  of  several  blue  and  green  colors. 
It  is  employed  by  dyers  and  calico-printers,  and  is  an  ingredient  in  some 
kinds  of  writing-ink.  It  has  been  used  to  prevent  smut  in  corn,  by  steeping 
the  grain  in  a  dilute  solution  of  the  salt.  It  appears  to  operate  by  coagulat- 
ing the  albumen  of  the  seed.  It  is  also  employed  for  the  same  reason  to 
prevent  dry  rot  by  steeping  timber  or  planks  in  its  solution;  and  it  is  a  power- 
ful preservative  of  animal  substances.  The  commercial  sulphate  sometimes 
contains  sulphate  of  iron  as  impurity.  In  order  to  detect  this,  ammonia  may 
be  added  to  the  diluted  solution  of  sulphate  in  sufficient  quantity  to  redis- 
solve  the  whole  of  the  oxide  of  copper  which  is  at  first  precipitated.  As 
oxide  of  iron  is  not  permanently  dissolved  by  ammonia,  this  after  some  hours 
will  be  deposited  as  hydrated  peroxide  at  the  bottom  of  the  tube.  There  is, 
however,  a  more  serious  impurity — namely,  the  presence  of  arsenic — not  only 
in  the  commercial  but  the  officinal  sulphate.  This  may  be  detected  by  distil- 
ling the  powdered  crystals  with  strong  hydrochloric  acid.  Chloride  of  arsenic 
passes  over  into  the  receiver  {see  Arsenic).  Several  basic  sulphates  of 
copper  have  been  described. 

Sulphates  of  Ammonia  and  Copper. — 1.  Ammonio-sulphate  of  copper. 
Anhydrous  sulphate  of  copper  rapidly  absorbs  gaseous  ammonia,  heats,  and 
forms  a  bulky  blue  powder  soluble  in  water,— 5XH3,-f2(CuOS03).  2.  Gupro- 
sulphate  of  ammonia.  When  a  solution  of  sulphate  of  copper  is  supersatu- 
rated by  ammonia  so  as  to  redissolve  the  precipitate  at  first  formed,  and 
crystallized  by  evaporation,  dark  blue  transparent  crystals  are  obtained, 
soluble  in  1-5  of  cold  water,  but  insoluble  in  alcohol,  =  CuO,S03-f2NHgHO. 


424  ALLOTS    OF    COPPER. 

The  crystals,  when  exposed  to  air,  lose  ammonia,  becoming  at  first  opaque 
and  pale  blue,  and  then  crumble  into  a  green  powder,  which  is  a  mixture  of 
sulphate  of  ammonia  and  basic  sulphate  of  copper.  When  the  aqueous  solu- 
tion of  this  salt  is  largely  diluted,  it  deposits  basip  sulphate  of  copper.  3. 
Sulphate  of  ammonia  and  copper.  (NH,0,SO,  +  CuO,S03  +  6HO).  This 
salt  crystallizes  out  of  the  mixed  solution  of  sulphate  of  ammonia  with  sul- 
phate of  copper ;  it  effloresces  in  dry  air.  The  solution  of  the  ammonio- 
sulphate  of  copper  is  used  as  a  test  for  arsenic. 

Carbonates  OF  Copper. — When  hot  solutions  of  copper  are  precipitated 
by  the  carbonated  fixed  alkalies,  carbonic  acid  is  evolved,  and  a  bulky  green 
hydrated  dicarlonate  of  copper  falls,  =  2(CuO),C02,HO.  Its  tint  is  im- 
proved by  repeated  washing  with  boiling  water.  It  is  prepared  as  a  pigment, 
under  the  name  of  mineral  green,  or  greeii  verditer.  When  a  cold  dilute 
solution  of  sulphate  of  copper  is  decomposed  by  carbonate  of  soda,  a  blue 
precipitate  falls,  which,  by  careful  drying,  retains  its  color,  and  is  known 
under  the  name  Uue  verditer.  It  differs  from  the  green  carbonate  in  contain- 
ing more  water.  There  is  an  inferior  pigment,  also  called  verditer,  which  is 
a  mixture  of  subsulphate  of  copper  and  chalk.  Native  Carbonates  of  Cop- 
per ;  Malachite  (na^dxr;,  7nalloio,  from  its  color),  or  the  green  hydrated  car- 
bonate,=2{CnO),CO^,IIO,  is  found  in  various  forms,  but  never  regularly 
crystallized,  the  octahedral  variety  being  a  pseudo-crystal  derived  from  the 
decomposition  of  the  red  oxide  :  it  occurs  in  great  beauty  in  a  stalactitic 
form  in  Siberia,  and  in  Australia;  it  is  rarely  found  in  Cornwall.  It  is  of 
various  shades  of  green,  and  often  cut  into  small  slabs,  or  used  as  beads  and 
brooch-stones.  The  pulverulent  variety  has  been  termed  chrysocolla,  and 
moimtain-green.  The  blue  hydrated  car6on«;e,  =  3(CuO)C0.2,IIO,  is  found 
in  great  perfection  at  Chessy,  near  Lyons.  It  occurs  crystallized  in  rhom- 
boids and  imperfect  octahedra  ;  it  is  also  found  in  small  globular  masses. 
The  earthy  variety  is  sometimes  called  copper-azure  or  mountain-blue.  The 
dioptase,  or  copper  emerald,  a  rare  mineral,  hitherto  found  only  in  Siberia,  is 
a  hydrated  silicate  of  copper  ;  some  of  the  varieties  of  malachite  also  appear 
to  contain  a  silicate  of  copper. 

Cyanide  of  Copper. — Hydrocyanic  acid,  and  cyanide  of  potassium,  throw 
dowm  a  white  curdy  precipitate  in  a  solution  of  dichloride  of  copper,  =  Cu2, 
Cy.  It  combines  with  other  metallic  cyanides,  forming  a  class  of  cuprocya- 
nides.  When  cyanide  of  potassium  is  added  to  sulphate  of  copper,  a  brown 
precipitate, =CuCy  is  formed,  which  by  giving  otf  cyanogen  passes  into  a 
double  cyanide,=Cu2,Cy4-CuCy.  When  CuCy  is  digested  in  excess  of 
cyanide  of  potassium,  it  forms  two  cuprocyanides,  CuCy,KCy,  and  CuCy, 
3KCy. 

Alloys  of  Copper. — Many  of  these  are  of  great  use  in  the  arts,  especially 
those  with  zinc  and  tin,  and  with  silver  and  gold. 

Brass. — This  important  alloy  of  copper  with  zinc  was  formerly  made  by 
mixing  granulated  copper  with  calamine  and  charcoal,  and  exposing  the 
mixture  to  a  heat  sufficient  to  reduce  the  calamine  and  melt  the  alloy.  It  is 
now  usually  prepared  by  melting  granulated  copper  with  about  half  its  weight 
of  zinc,  but  the  relative  proportions  of  the  two  metals  vary  in  the  different 
kinds  of  brass  ;  and  some  contain  a  little  lead  and  tin.  An  alloy  of  54  parts 
of  zinc  and  46  of  copper  is  white  and  crystalline,  but  it  assumes  the  yellow 
color  of  brass  when  the  zinc  is  increased,  as  well  as  when  it  is  diminished. 
Ordinary  brass  contains  about  64  per  cent,  of  copper.  The  new  Austrian 
gun  metal  is  stated  to  have  the  following  composition  :  Copper  55  04  :  zinc 
42  36  :  iron  1-77  and  tin  0-88  in  100  parts.  Maniz^s  patent  sheathing  metal^ 
which  has  been  found  an  excellent  substitute  for  copper  in  the  sheathing  of 
ships,  is  an  alloy  of  about  60  copper  and  40  zinc :  it  admits  of  being  rolled 


ALLOYS    OP    COPPER.      BRASS.       BRONZE.      BELL-METAL.         425 

hot,  whereas  the  common  varieties  of  brass  generally  split  under  such  circum- 
stances, and  are  therefore  rolled  cold,  which  requires  more  time. 

Brass  is  very  malleable  and  ductile  (when  cold),  and  its  color  recommends 
it  for  many  purposes  of  the  arts  :  it  specific  gravity  varies  from  7  9  to  8-9, 
and  exceeds  the  mean  of  its  components.  Tutenag,  Tombac,  Dutch  gold., 
Similor,  Prince  RuperVs  metal,  Pinchbeck  and  Manheim  gold,  are  alloys 
containing  more  copper  than  exists  in  brass,  and  consequently  made  by  fusing 
various  proportions  of  copper  with  brass.  An  alloy  of  570  parts  of  copper, 
69  of  tin,  and  48  of  brass,  is  equal  to  brass  in  hardness,  and  may  be  worked 
with  the  same  facility ;  it  has  been  used  for  standard  measures,  as  being  less 
liable  than  brass  to  oxidation  when  exposed  to  air.  Brass  containing  25 
per  cent,  of  zinc  melts  at  about  1750^,  and  its  fusibility  is  increased  by  a 
larger  proportion  of  zinc.  The  malleable  alloy  known  as  Dutch  leaf  gold  is 
a  compound  of  15*4  of  zinc  and  84  6  of  copper.  Its  malleability  is  sucli  that 
it  may  be  beaten  into  leaves  of  the  l-50,000th  of  an  inch  in  thickness.  It  is 
frequently  used  as  a  substitute  for  gold  leaf,  but  it  rapidly  tarnishes  when 
exposed  to  damp  air.  Gold  paper  hangings  are  usually  prepared  with  this 
alloy — the  fine  dust  being  laid  on  a  yellow  adhesive  ground.  The  alloy  is 
immediately  dissolved  by  nitric  acid,  forming  blue  nitrate  of  copper.  When 
platinum  is  added  in  a  certain  proportion  to  the  alloy,  it  resists  the  nitric 
acid  test  and  may  be  mistaken  for  gold.  {See  Gold  Alloys.)  Speculum 
metal  is  an  alloy  of  copper  and  tin,  with  a  little  arsenic  ;  about  6  copper,  2 
tin,  1  arsenic.  The  Earl  of  Rosse  employed  copper  and  tin  only  in  the  spec- 
ulum of  his  large  telescope  ;  the  proportions  he  used  were  126*4  of  copper, 
to  58  9  of  tin  (about  4  atoms  of  copper  to  one  of  tin). 

Bronze ;  Bell-metal. — These  are  alloys  of  copper  and  tin  ;  they  are  harder 
and  more  fusible,  but  less  malleable  than  copper.  The  specific  gravity  of 
bronze  exceeds  the  mean  of  its  component  metals,  when  carefully  hammered 
and  free  from  air-blebs  :  but  bronze  castings  are  apt  to  be  porous  unless 
considerable  care  and  skill  have  been  used  in  fusing  and  pouring  the  metal, 
and  in  the  construction  of  the  mould  ;  and  in  large  castings,  owing  to  the 
gradual  cooling  of  the  mass,  there  is  often  a  want  of  uniformity  in  the  com- 
position of  different  parts  of  it ;  that  portion  containing  the  least  tin  being 
the  first  to  solidify,  while  the  more  fusible  portion  to  a  certain  extent  sepa- 
rates, and  is  sometimes  projected  from  the  mould.  In  large  bronze  castings, 
SQch  as  statutes,  porosity  and  bubbles  require  carefully  to  be  avoided  :  where 
they  exist  so  as' to  deface  the  appearance  of  the  work,  they  are  sometimes 
filled  up  with  substances  which  are  only  temporarily  durable,  or  which,  \h 
metallic,  give  rise  to  electrical  effects  which  time  renders  prejudicially  evi- 
dent, For  this  reason,  the  different  pieces  of  a  large  statue  should  be  fused 
together,  or  united  by  bronze,  and  not  by  a  more  fusible  solder  ;  and  iron 
bars,  and  leaden  junctions  for  the  support  or  fixing  of  the  work,  should, 
upon  the  same  principle,  be  avoided,  as  they  are  themselves  liable,  under 
such  circumstances,  to  corrosion,  and  this  may  affect  the  stability  or  safety 
of  the  statue,  independently  of  other  influences.  Of  the  difficulty  of  casting 
a  large  and  perfect  bell  in  bronze,  the  Great  Bell  at  Westminster  has  fur- 
nished a  memorable  instance.  When  bronze  is  frequently  renielted  it  gradu- 
ally loses  tin  by  oxidation,  so  that  in  such  cases  fresh  additions  of  tin  may 
sometimes  be  requisite ;  and  it  is  apparently  this  oxidation  of  the  tin  which 
tends  to  deteriorate  the  texture  of  remelted  bronzes,  and  renders  them  more 
subject  to  bubbles  and  porosity  when  recast,  an  effect  which  may  be  prevented 
by  the  action  of  carbonaceous  fluxes,  or  by  the  operation  of  poling,  as  in  the 
case  of  copper. 

Tempering  produces  upon  bronze  an  effect  directly  opposite  to  that  upon 
steel  J  and  in  order  to  reader  bronze  malleable,  it  must  be  heated  to  redness 


426  TESTS    FOR    TflE    SALTS    OF    COPPER. 

and  quenched  in  water.  The  alloy  which  thus  acquires  the  greatest  tenacity 
is  that  of  8  of  copper  and  1  of  tin,  and  this  is  consequently  preferable  for 
medals  ;  the  advantage  of  bronze  over  copper  for  these  purposes  being  hard- 
ness, and  resistance  to  oxidation  ;  the  former  quality  resists  friction,  and  the 
latter  has  handed  down  to  us  the  works  of  the  ancients  with  little  deteriora- 
tion, though  buried  for  ages  in  damp  soil,  or  immersed  in  water.  The  small 
value  of  bronze,  as  compared  with  gold  and  silver,  is  also  another  important 
consideration,  as  affecting  the  preservation  of  such  works  of  art.  The  alloy 
employed  in  the  recent  bronze  coinage  is  composed  of  95  copper,  4  tin,  1 
zinc.  The  pound  avoirdupois  is  coined  into  48  pence,  each  piece  weighing 
145-83  grains;  into  80  halfpence,  each  weighing  87  50  grains;  into  160 
farthings,  each  weighing  43  75  grains.  Analysis  made  of  ancient  Roman 
coins  by  M.  Commaille  have  shown  that  they  consist  of  copper  nearly  pure, 
with  small  quantities  of  tin,  lead,  and  silver.  Cadmium  and  gold  have  been 
found  in  some  of  them.  In  certain  coins  ten  per  cent,  of  tin  and  as  much  as 
28  per  cent,  of  lead  have  been  detected.  The  coins  of  Vespasian  and  Mar- 
cus Aurelius  consisted  of  copper  with  traces  of  tin — and  those  of  Titus  con- 
tain 2'Tl  per  cent,  of  zinc.  The  Roman  AS  was  found  to  be  composed  of 
copper  69'65  :  of  lead  2437,  and  of  tin  5*98.  We  have  found  arsenic  in 
these  ancient  coins  and  in  the  ancient  alloys  of  copper  and  zinc :  used  for 
sepulchral  brasses. 

The  analysis  of  brass  is  best  effected  by  the  action  of  nitric  acid.  The 
solution  may  be  tested  for  the  presence  of  lead  by  sulphuric  acid  :  if  tin  is 
present  it  is  converted  into  an  insoluble  oxide  :  the  clear  nitric  solution  eva- 
porated to  dryness  leaves  nitrate  of  copper  and  nitrate  of  zinc  :  this  residue, 
redissolved,  may  be  decomposed  by  a  slight  excess  of  caustic  potassa,  and 
boiling,  by  which  the  oxide  of  copper  is  thrown  down.  The  oxide  is  col- 
lected on  a  filter,  washed,  dried,  and  gently  ignited,  the  clear  filtrate  holds 
the  oxide  of  zinc  in  solution  :  it  may  be  neutralized  by  hydrochloric  acid, 
and  precipitated  by  carbonate  of  soda ;  the  precipitate,  after  washing,  dry- 
ing, and  ignition,  is  oxide  of  zinc. 

Tinned  Copper. — Vessels  of  copper  for  culinary  purposes  are  usually 
coated  with  tin,  to  prevent  the  food  being  contaminated  by  copper.  Their 
interior  surface  is  first  cleaned,  then  rubbed  ^ver  with  sal-ammoniac  :  the 
vessel  is  then  heated,  a  little  pitch  spread  over  the  surface,  and  a  bit  of  tin 
rubbed  over  it,  which  instantly  unites  with  and  covers  the  copper.  Much 
care  is  requisite  in  the  manipulations  of  this  process,  and  independently  of 
Jhe  tin  permanently  adhering  to  and  combining  with  the  surface  of  the  cop- 
per, there  is  generally  a  portion  in  excess,  which  fuses  off,  the  first  time  the 
pan  is  used  for  frying.  Lead  is  sometimes  added  to  the  tin  used  in  tinning, 
and  sometimes  a  small  quantity  of  mercury,  but  these  are  very  objectionable 
additions. 

Tests  for  the  Salts  of  Copper.— The  solutions  of  these  salts  have  either 
a  blue  or  green  color,  and  an  acid  reaction.  1.  Sulphuretted  hydrogen  and 
hydrosulphate  of  ammonia  give,  even  in  acid  solutions,  a  brownish-black 
precipitate,  not  soluble  in  the  precipitants,  in  alkalies,  or  diluted  acids.  2. 
Ammonia,  when  added  in  excess,  produces  a  deep  blue  solution.  3.  Ferro- 
cyanide  of  potassium  produces  a  deep  red-brown  precipitate  in  strong  solu- 
tions, but  a  red  color  in  those  which  are  very  dilute.  This  may  be  regarded 
as  a  most  delicate  test  for  copper.  The  blue  ammoniacal  solution  above 
mentioned  under  2,  when  rendered  feebly  acid  by  the  addition  of  dilute  sul- 
phuric acid,  will  give  a  red  precipitate  with  the  ferrocyanide.  Thus  two  of 
the  most  important  tests  may  be  applied  to  the  same  portion  of  liquid.  4. 
A  polished  needle,  or  any  clean  surface  of  iron,  is  coated  with  a  layer  of 
metallic  copper  of  its  usual  red  color,  when  immersed  or  suspended  in  the 


LEAD.      EXTRACTION    OF    LEAD.  4^t 

solution  slightly  acidified  with  diluted  sulphuric  acid.  The  deposit  takes 
place  .slowly  when  the  solution  of  copper  is  very  dilute.  The  needle,  with 
the  red  deposit,  when  washed  and  placed  in  a  reduction  tube  with  a  small 
quantity  of  solution  of  ammonia,  imparts  a  blue  color  to  the  liquid  by  the 
production  and  solution  of  the  oxide.  A  coil  of  fine  steel  wire  may  be  used 
in  place  of  a  needle. 

Before  the  blowpipe,  black  oxide  of  copper  is  not  altered  by  the  exterior 
flame,  but  becomes  red  suboxide  in  the  interior.  With  borax  it  forms  a 
green  glass,  while  hot,  which  becomes  blue-green  as  it  cools.  When  strongly 
heated  on  charcoal  in  the  interior  flame,  the  metal  is  reduced. 

Analysis  in  cases  of  Poisoning. — A  colored  liquid  containing  organic 
matter,  and  suspected  to  contain  copper  in  solution,  may  be  thus  treated  : 
Place  a  portion  of  the  liquid,  acidified  with  dilute  sulphuric  acid,  in  a  plati- 
num capsule;  touch  the  platinum  through  the  liquid  with  a  piece  of  zinc 
foil;  a  bright  layer  of  metallic  copper,*of  a  red  color,  will  be  deposited  on 
every  part  of  the  platinum  touched  by  the  zinc.  Wash  out  the  capsule  with 
distilled  water ;  dissolve  the  film  of  deposited  metal  in  a  few  drops  of  nitric 
acid  and  water ;  expel  any  excess  of  acid,  and  add  ammonia,-  and  subse- 
quently ferrocyanide  of  potassium  (p.  426).  The  blue  and  red  colors  will 
at  once  indicate  the  presence  of  copper.  This  is  the  best  method  of  pro- 
ceeding in  cases  of  poisoning ;  as  the  metal  is  first  obtained  and  converted 
into  a  salt,  when  the  tests  give  the  results  described,  there  can  be  no  doubt 
of  the  presence  of  copper. 

In  order  to  procure  a  solution  of  the  metal,  the  organic  matter  may  be 
dried,  incinerated  in  platinum,  and.  the  ash  digested  in  1  part  of  nitric  acid 
and  2  of  water.  Pickles  or  fruits  suspected  to  contain  copper  may  be 
treated  by  the  'following  process  :  Pass  a  bright  needle  through  the  sub- 
stance ;  if  it  is  impregnated  with  copper,  there  will  be  a  deposit  of  this 
metal  upon  the  iron.  It  will  be  proper  to  state  in  this  place,  that  as  copper 
and,  generally  speaking,  all  its  salts,  may  contain  arsenic,  this  poison  may 
be  found  in  an  organic  liquid,  or  in  a  cupreous  medicine,  as  the  result  of  im- 
purity. 

Lead  (Pb=104). 

Lead  has  been  known  from  the  earliest  ages.  The  alchemists  gave  to  it 
the  symbol  and  name  of  Saturn,  \,  which  is  the  symbol  of  Jupiter  or  Tin 
inverted.  The  native  compounds  of  lead  are  numerous,  but  the  most  import- 
ant is  the  sulphide  known  under  the  name  of  galena,  from  which  the  greater 
proportion  of  commercial  lead  is  obtained. 

Extraction  of  Lead. — The  reduction  of  galena  upon  the  large  scale  is 
eflfected  by  heating  and  raking  the  prepared  ore,  mixed  with  a  little  lime,  in 
a  reverberatory  furnace ;  a  large  proportion  of  the  sulphur  is  in  this  way 
burned  off,  and  a  mixture  of  oxide,  sulphate,  and  sulphide  of  lead  obtained  ; 
the  temperature  is  then  so  raised  as  to  fuse  this  mixture,  when  the  substances 
further  react  upon  each  other,  and  metallic  lead  separates  from  the  mass. 
If  it  contains  tin  or  antimony,  it  is  further  refined  by  fusing  it  in  a  shallow 
vessel,  when  those  metals,  being  more  easily  oxidized  than  lead,  are  removed 
from  the  surface.  If  the  lead  contains  silver  in  such  proportion  as  to  render 
it  worth  separating,  this  is  effected  by  dipping  into  the  fused  metal,  during 
cooling,  a  large  perforated  iron  ladle,  whereby  the  lead,  which  is  the  first  to 
separate  in  crystals,  is  removed.  The  granular  crystals  are  ladled  out,  and 
are  nearly  pure  lead  (p.  26),  the  silver  being  retained  in  the  more  fusible 
portion.  By  a  repetition  of  this  process  of  desilvering  the  melted  lead,  the 
silver  gradually  accumulates  in  the  latter,  from  which  it  is  subsequently 
separated  by  cupellation.     Six  tons  of  lead  thus  treated,  were  desilvered  by 


428  ACTION    OP    AIR    AND    WATER    ON    LEAD. 

this  process  in  about  two  hours,  the  weight  of  the  argentiferous  alloy  left  in 
the  melting-pan  being  seven  hundred  weight.  The  iron  ladle  employed  held 
about  one  hundred  weight  of  liquid  metal.  The  amount  of  silver  in  the  lead 
was  increased  twentyfold,  one  tou  of  the  alloy  containing  as  much  silver  as 
twenty  tons  of  the  original  lead.  In  the  factory  at  Newcastle,  in  which  we 
witnessed  this  operation,  60  tons  of  lead  were  desilvered  weekly,  producing 
about  600  ounces  of  silver.  In  1858,  it  was  calculated  that  the  quantity  of 
silver  thus  extracted  from  lead  in  this  country  was  not  less  than  600,000 
ounces  per  annum.  This  valuable  process  was  discovered  by  the  late  Mr. 
H.  L.  Pattinson,  of  Newcastle.  The  lead,  thus  deprived  of  its  silver,  is 
improved  in  quality,  and  is  cast  into  the  oblong  masses,  or  pigs,  in  which  it 
occurs  in  commerce.  The  total  quantity  of  lead  ore  raised  in  the  United 
Kingdom  in  1865  was  90,452  tons,  from  which  were  obtained  67,181  tons 
of  metallic  lead  and  724,856  ounces  of  silver. 

When  lead  containing  silver  is  exposed  at  a  high  heat  to  a  current  of  air, 
the  lead  is  converted  into  protoxide,  and  may  be  run  off  in  a  fused  state  from 
the  surface;  whilst  the  silver,  which,  under  these  circumstances,  resists  oxida- 
tion, ultimately  remains  upon  the  cupel.  This  operation  closely  resembles 
that  which  is  conducted  upon  a  small  scale  by  the  assayer,  and  will  again  be 
adverted  to  in  the  chapter  on  Silver.  The  proportion  of  silver  contained 
in  argentiferous  galena  varies  very  considerably.  The  average  is  about  ten 
ounces  in  the  ton  :  when  it  amounts  to  120  ounces  to  the  ton,  it  is  considered 
very  rich  ;  but  silver  may  be  profitably  extracted  when  as  low  as  from  3  to 
4  ounces  to  the  ton.  The  English  lead-mines  afford  an  annual  produce  of 
from  60,000  to  70,000  tons  of  metal,  froju  the  greater  part  of  which  the 
silver  is  extracted  by  the  process  above  described. 

Perfectly  pure  lead  may  be  obtained  either  by  reducing  pure  nitrate  of 
lead  by  charcoal,  at  a  red  heat,  or  by  heating  oxalate  of  lead  in  a  covered 
crucible.  Its  color  is  bluish-white  :  it  has  much  brilliancy,  is  remarkably 
flexible  and  soft,  and  leaves  a  dark  streak  on  paper  ;  when  handled  it  exhales 
a  peculiar  odor.  Its  specific  gravity  is  1 1  "4.  It  admits  of  being  rolled  into 
thin  sheets,  and  drawn  into  moderately  fine  wire,  but  its  tenacity  is  so  low 
as  to  render  the  latter  operation  difficult.  It  melts  in  about  620^^,  and  by 
the  united  action  of  heat  and  air  is  readily  oxidized.  In  perfectly  close 
vessels  it  does  not  sublime  at  a  bright  red  heat ;  but  before  the  oxygen  blow- 
pipe it  boils  when  heated  to  whiteness,  and  is  dissipated  in  copious  fumes  of 
oxide.  When  slowly  cooled  it  forms  octahedral  crystals,  and  contracts 
during  solidification;  in  bullets,  therefore,  and  in  castings  of  lead  rapidly 
cooled,  there  is  generally  a  cavity  which  interferes  with  the  rectilinear  pas- 
sage of  the  ball. 

At  common  temperatures,  and  in  its  ordinary  state,  lead  undergoes  little 
change;  but  when  in  a  state  of  very  fine  division,  as  it  is  obtained  by  ex- 
posing tartrate  of  lead  to  a  red  heat  in  close  vessels,  it  takes  fire  when 
brought  into  contact  with  the  air;  so  also  the  finely-divided  lead  obtained 
by  the  reduction  of  the  oxide  by  hydrogen  at  a  temperature  insufficient  for 
its  fusion,  burns  when  gently  heated  in  the  air.  It  is  generally  considered 
that  water  is  not  decomposed  by  lead,  but  Stolba  asserts  that  on  boiling  pure 
water  witli  a  relatively  large  quantity  of  lead  in  foil  or  granulated,  hydrogen 
was  evolved,  and  a  strongly  alkaline  fluid  remained  in  the  flask.  {Quar. 
Jour,  of  Science,  1865,)  In  distilled  water,  free  from  air,  and  in  close  ves- 
sels, a  clean  surface  of  lead  remains  bright ;  but  in  open  vessels  it  tarnishes, 
and  small  crystalline  white  scales  of  hydrated  oxide  of  lead  are  formed,  a 
portion  of  which  dissolves  in  the  water,  and  is  again  slowly  precipitated  in 
the  form  of  oxycarbonate.  This  oxycarbonate  is  itself  very  insoluble,  so 
that  if  water  holding  a  little  oxide  of  lead  in  solution  be  exposed  to  air,  the 


OXIDES    OF    LEAD.      LITHARGE.  429 

more  soluble  oxide  passes  into  the  state  of  the  less  soluble  oxycarbonate ; 
and  after  a  few  hours,  if  the  water  be  Altered,  it  will  be  found  almost  abso- 
lutely free  from  lead  in  solution,  pure  water  not  dissolving  more  than  about 
one  four-millionth  of  its  weight  of  this  oxycarbonate,  or  about  one-sixteenth 
of  a  grain  in  a  gallon.  The  action  of  water  upon  lead  is  much  modified  by 
the  presence  of  saline  substances.  It  is  increased  by  chlorides  and  nitrates, 
and  diminished  by  carbonates,  sulphates,  and  phosphates,  and  especially  by 
carbonate  of  lime,  which,  held  in  solution  by  excess  of  carbonic  acid,  is  a 
frequent  ingredient  of  spring  and  river  water.  But  water  highly  charged 
with  carbonic  acid  may  become  dangerously  impregnated  with  lead,  in  the 
absence  of  any  protecting  salt,  in  consequence  of  its  solvent  power  over  car- 
bonate of  lead.  In  general,  water  which  is  not  discolored  by  a  current  of 
sulphuretted  hydrogen  gas,  may  be  considered  as  free  from  lead  ;  but  there 
are  very  few  waters  which  have  passed  through  leaden  pipes,  or  have  been 
retained  in  leaden  cisterns,  in  which  a  minute  analysis  will  not  detect  a  trace 
of  the  metal ;  and  were  it  not  for  the  great  convenience  of  lead,  iron  pipes 
and  slate  cisterns  would,  in  a  sanitary  point  of  view,  be  in  all  cases  preferable. 
Another  cause  of  contamination  of  lead  may  arise  from  electric  action,  as 
where  iron,  copper,  or  tin  is  in  contact  with,  or  soldered  into  lead  :  and  in 
these  cases,  owing  to  the  action  of  alkaline  bases  as  well  as  of  acids  upon 
the  lead,  danger  may  occur  when  it  is  thrown  into  an  electro-negative  as 
well  as  an  electro-positive  state.  Cisterns  are  sometimes  corroded,  and  their 
bottoms  are  perforated  by  pieces  of  mortar  having  dropped  into  them,  the 
lime  of  which  has  caused  the  oxidation  of  the  metal  and  a  solution  of  the 
oxide. 

Oxides  of  Lead. — There  are  four  definite  combinations  of  lead  and  oxy- 
gen, namely,  suboxide  or  dioxide  (PbgO)  ;  a  protoxide  (PbO)  ;  an  interme- 
diate oxide  generally  known  as  red  oxide  (PbgOJ  ;  and  a  peroxide  (PbOg). 
Of  these,  the  protoxide  only  is  salifiable. 

Suboxide  of  Lead;  Dioxide  of  Lead  (PbgO). — When  oxalate  of  lead  h 
carefully  heated  to  about  570°  in  a  small  retort,  carbonic  oxide  and  car- 
bonic acid  are  evolved,  and  this  oxide  remains  in  the  form  of  a  gray  powder, 
which  is  resolved  by  acids  into  protoxide  and  metallic  lead. 

Protoxide  of  Lead  (PbO)  is  formed,  1.  By  raising  the  temperature  of 
melted  lead  to  a  white  heat,  when  it  burns  with  a  brilliant  flame,  and  forms 
copious  fumes  of  protoxide.  2.  By  exposing  the  gray  powder  which 
gradually  collects  upon  the  surface  of  melted  lead,  to  the  further  action  of 
heat  and  air,  until  it  acquires  an  uniform  yellow  color.  3.  By  exposing 
nitrate  or  carbonate  of  lead  to  a  dull  red  heat  out  of  contact  of  air,  and 
taking  care  to  avoid  fusion;  4.  When  a  solution  of  acetate  of  lead  is 
dropped  into  a  solution  of  ammonia,  the  white  crystalline  powder  which 
falls  is  a  hydrated  oxide.  When  this  oxide  is  heated  it  has  a  red  color,  but 
in  its  ordinary  state  it  is  lemon  or  orange-yellow,  according  to  the  mode  in 
which  it  has  been  prepared,  and  is  known  under  the  name  of  Massicot,  At  a 
high  red  heat,  it  fuses  and  forms,  on  cooling,  a  lamellar  vitreous  mass  of  a 
reddish-brown  color :  this  is  often  obtained  in  scales,  under  the  name  of 
Litharge  {xiOo^  dpyvpov,  silver  stone),  which,  when  red  from  the  presence  of 
minium,  was  called  Litharge  of  Gold,  the  paler  varieties  being  termed  Litharge 
of  Silver.  Protoxide  of  lead  is  a  salifiable  base,  forming  neutral  salts  with 
the  acids;  and,  in  many  instances,  subsalts  which  have  an  alkaline  reaction  ; 
it  absorbs  carbonic  acid  from  the  atmosphere,  and  gradually  acquires  the 
property  of  dissolving  in  acids  with  effervescence.  It  is  soluble  in  potassa 
and  soda,  forming  yellow  liquids,  which  after  a  time  gradually  deposit  crystals 
of  anhydrous  oxide  of  lead  :  it  combines  with  baryta,  strontia,  and  lime, 
forming  compounds  of  sparing  solubility,  and  easily  decomposed  even  by  the 


430         RED  OXIDE  OF  LEAD.   PEROXIDE  OF  LEAD. 

weakest  acids.  A  paste  or  wash  containing  hydrate  of  lime  mixed  with  80 
to  90  per  cent,  of  oxide  of  lead,  is  used  to  blacken  hair,  which  it  does  in 
consequence  of  the  formation  of  a  black  sulphide  arising  out  of  the  combi- 
nation of  the  sulphur  in  the  hair  with  the  metal  of  the  oxide,  while  the  lime, 
by  its  action  on  the  organic  matter,  promotes  the  effect.  The  use  of  this 
compound  is  liable  to  give  rise  to  an  attack  of  lead  palsy. 

When  oxide  of  lead  is  fused  with  the  earths  and  metallic  oxides,  it  forms 
vitreous,  and  in  some  cases  very  fusible  compounds,  hence  its  use  in  the 
manufacture  of  glass  (p.  337)  ;  hence  also  the  readiness  with  which  it  corrodes 
common  crucibles  when  kept  in  fusion  in  them.  Heated  with  charcoal,  this 
and  the  other  oxides  of  lead  are  easily  reduced  to  the  state  of  metal  ;  they 
are  also  reduced  when  heated  in  hydrogen  or  coal  gas.  The  white  or  hydrated 
oxide,  when  dried  at  about  100°,  is  a  soft  crystalline  powder,  =3(PbO)HO  : 
it  is  slightly  soluble  in  pure  water,  and  the  solution  has  an  alkaline  reaction  ; 
it  loses  water  and  gradually  becomes  anhydrous  when  heated  to  about  160°. 
The  influence  of  carbonic  acid  and  minute  portions  of  saline  substances  upon 
the  solubility  of  this  hydrate,  has  been  above  noticed. 

Red  Oxide  of  Lead  ;  Minium  ;  Red  Lead  (?hfi^). — This  substance, 
which  is  well  known  as  a  red  pigment,  is  made  by  exposing  protoxide  of 
lead  to  heat  and  air  so  as  to  oxidize  without  fusing  it,  the  temperature 
required  for  this  purpose  being  between  570°  and  580°  ;  it  gradually  acquires 
a  fine  red  color,  the  splendor  of  which,  however,  goes  off  by  exposure  to 
light.  The  minium  of  commerce  is  of  variable  composition,  and  generally 
contains  excess  of  protoxide,  which  may  be  separated  by  very  dilute  acetic 
acid,  or  by  digestion  in  solution  in  acetate  of  lead.  When  exposed  to  a  tem- 
perature above  that  required  for  its  formation,  minium  gives  off  oxygen,  and 
reverts  to  the  state  of  protoxide.  The  most  brilliant  minium  is  obtained  by 
heating  and  stirring  pure  carbonate  of  lead  in  a  current  of  air  at  a  tempera- 
ture a  little  short  of  600°.  Minium  has  a  sp.  gr.  between  8  6  and  9.  It  is 
decomposed  by  acids  ;  nitric  acid  resolves  it  into  insoluble  peroxide,  while  a 
soluble  nitrate  of  the  protoxide  is  at  the  same  time  formed.  Hydrochloric 
acid,  in  small  quantity  (2  atoms  to  1  of  minium),  produces  with  it  chloride 
and  peroxide  of  lead,  and  water— PbgO^-f  2HCl  =  2(PbCl)  +  PbO,4-2HO  : 
in  larger  quantity,  the  products  are,  chloride  of  lead,  water,  and  free  chlorine  ; 
Pb30^+4HCl=3PbCl  +  4HO  +  Cl.  With  an  aqueous  solution  of  chlorine 
it  affords  chloride  and  peroxide  of  lead  ;  (Pb30,+Cl=PbCl-f  2PbO,). 

Peroxide  of  Lead;  Binoxide  of  Lead-,  Plumhic  Add  (PbOj.— This 
oxide  is  obtained  in  the  form  of  an  insoluble  brown  powder,  by  digesting 
minium  in  cold  nitric  acid  ;  or  by  heating  salts  of  lead  with  chloride  of  soda 
or  lime;  or  by  passing  chlorine  through  minium  diffused  in  water,  or  through 
a  solution  of  acetate  of  lead,  and  thoroughly  washing  the  product  in  hot  water 
to  remove  the  chloride  of  lead.  The  first  is  the  best  process,  if  the  minium 
and  nitric  acid  are  pure  ;  the  resulting  oxide  only  requires  to  be  boiled  in 
very  dilute  nitric  acid,  then  washed,  and  dried  at  212°. 

This  oxide  is  a  conductor  of  electricity.  At  a  red  heat  it  gives  off  oxy- 
gen, and  is  converted  into  protoxide.  By  the  continued  action  of  light,  or 
of  a  gentle  heat,  it  is  resolved  into  oxygen  and  minium.  Digested  in  liquid 
ammonia,  a  mutual  decomposition  takes  place,  and  water  and  nitrate  of  lead 
are  formed.  Triturated  with  a  fifth  of  its  weight  of  sulphur,  it  inflames  spon- 
taneously;  or  with  half  its  weight  of  sulphur  when  touched  with  oil  of  vitriol. 
It  is  also  decomposed,  with  the  evolution  of  heat,  when  rubbed  with  an 
eighth  part  of  its  weight  of  sugar  ;  or  with  its  weight  of  crystallized  oxalic 
acid,  with  which  it  forms  water,  carbonic  acid,  and  carbonate  of  lead.  With 
hydrochloric  acid,  it  furnishes  chlorine  and  chloride  of  lead.  When  boiled 
in  nitric  or  sulphuric  acid,  oxygen  is  evolved  and  salts  of  the  protoxide  are 


NITRATE    AND    CHLORIDE    OF    LEAD.  431 

formed.  It  absorbs  sulphurous  acid  gas  with  the  evolution  of  much  heat, 
or  even  with  ignition,  and  forms  sulphate  of  lead ;  hence  its  occasional  use 
in  the  analysis  of  gaseous  mixtures,  to  separate  sulphurous  from  carbonic 
acid  gas.  It  is  supposed  to  contain  the  second  equivalent  of  oxygen  in  the 
form  of  ozone  (p.  113).  It  decomposes  a  solution  of  iodide  of  potassium 
and  bleaches  sulphate  of  indigo.  It  oxidizes  the  resin  of  guaiacum,  turning 
it  blue,  and  it  gives  blue  and  purple  colors  with  strychnia  when  used  with 
sulphurous  acid. 

Plumhate  of  Potossa. — When  potassa,  moistened  with  a  little  water,  and 
peroxide  of  lead  are  heated  for  a  short  time  in  a  silver  crucible,  a  compound 
is  obtained  which,  dissolved  in  a  small  proportion  of  water  and  slowly  evapo- 
rated, yields  crystals  =KO,PbOa,3HO  :  they  are  deliquescent  rhomboids, 
soluble  without  decomposition  in  solution  of  potassa,  but  resolved  by  water 
into  hydrated  peroxide  of  lead,  and  a  brown  solution  of  hiplumhafe  of  potassa. 
Phimbate  of  Soda  may  be  obtained  in  the  same  way,  but  it  is  little  soluble 
in  water.  The  insoluble  plumbates  are  formed  by  heating  mixtures  of  the 
bases  with  protoxide  of  lead,  in  the  air,  when  oxygen  is  absorbed.  Plumhate 
of  lime  and  of  baryta  are  so  formed.  Under  this  aspect  minium  is  a  plumbate 
of  lead,  =2(PbO),PbO,. 

Metallo- chromes. — When  solutions  of  the  salts  of  lead  are  electrolyzed,  they 
deposit  the  peroxide  on  the  positive  electrode.  When  thin  films  of  peroxide 
of  lead  are  thus  formed  upon  polished  steel  plates,  they  give  rise  to  the 
prismatic  tints  described  under  the  above  name. 

Hyponitrite  of  Lead  {Tetranitrite  of  Lead). — When  1  part  of  neutral 
nitrate  of  lead  and  2  of  metallic  lead  are  boiled  together  for  12  hours  in  a 
large  quantity  of  water,  the  filtered  solution  yields  red  crystals,  alkaline  to 
tests,  soluble  in  about  1200  parts  of  cold  and  34  of  boiling  water  =4(PbO), 
NO„HO. 

Nitrite  of  Lead. — When  166  parts  of  neutral  nitrate  of  lead,  and  156 
of  metallic  lead,  are  boiled  in  a  large  proportion  of  water,  the  yellow  filtrate 
yields  orange-colored  crystals^  soluble  in  1250  of  cold,  and  34  of  boiling 
water  =7(PbO),2N04,2HO.  When  166  parts  of  neutral  nitrate  of  lead 
and  104  of  lead  (I  atom  and  1)  are  digested  together  in  water  at  about  160, 
the  solution  deposits  yellow  crystals,  acid  to  litmus,  soluble  in  80  parts  of 
water  at  77°  =2(PbO),NO„HO. 

Nitrate  of  Lead  (PbO,NOg)  is  obtained  by  dissolving  the  metal  (or 
better,  litharge)  not  in  excess,  in  hot  nitric  acid  diluted  with  two  parts  of 
water,  and  evaporation.  It  crystallizes  in  octahedra,  which  are  white,  anhy- 
drous, translucent,  and  of  a  styptic  taste  ;  they  decrepitate  when  heated,  and 
give  out  nitrous  acid  and  oxygen,  and  protoxide  of  lead  remains:  they  are 
soluble  in  between  7  and  8  parts  of  water  at  60° :  they  are  insoluble  in 
alcohol  and  in  nitric  acid.  Soft  wood,  or  paper,  impregnated  with  this  salt, 
burns  like  a  slow  match,  with  slight  deflagration.  Nitric  acid  forms  with 
oxide  of  lead  a  dinitrate,  trisnitrate,  and  a  sexbasic  nitrate. 

Chloride  of  Lead  (PbCl). — When  laminated  lead  is  heated  in  chlorine, 
the  gas  is  absorbed,  and  a  chloride  of  lead  results.  The  same  substance  is 
obtained  by  adding  hydrochloric  acid,  or  a  solution  of  chloride  of  sodium,  to 
a  concentrated  solution  of  nitrate  of  lead,  washing  the  precipitate  in  cold 
water,  and  drying  at  212°;  it  is  also  formed  when  the  oxides  of  lead  are 
digested  with  heat  in  hydrochloric  acid.  It  is  white  and  fusible,  and,  on 
cooling,  forms  a  yellow  horn-like  substance  {phimhum  corneum).  It  does  not 
absorb  ammonia.  It  volatilizes  at  a  high  temperature,  provided  air  has  access, 
in  which  case  a  portion  of  oxide  of  lead  is  also  formed.  It  dissolves  in  about 
40  parts  of  water  at  212°,  separating,  as  its  solution  cools,  in  small  anhy- 
drous acicular  crystals,  unchanged  by  exposure  to  air,  and  of  a  sweetish 


432  IODIDE,    BROMIDE,    AND    SULPHIDE    OF    LEAD. 

taste.  Its  solubility  in  water  is  greatly  diminished  by  the  presence  of  a  little 
hydrochloric  acid,  yet  it  is  soluble  in  strong  hydrochloric  acid,  and  is 
precipitated  on  dilution.  It  dissolves  rather  copiously  in  solutions  of  potassa 
and  soda,  and  of  the  alkaline  hyposulphites.     It  is  insoluble  in  alcohol. 

Native  chloride  of  lead  occurs  amongst  the  products  of  Vesuvius,  in  small 
acicular  crystals  ;  a  dichloride  of  lead  (PbgCl)  has  been  found  in  the  Mendip- 
hills,  in  Somersetshire  ;  it  forms  fibrous  yellow  crystalline  masses,  upon  a  black 
ore  of  manganese ;  a  native  oxychloride  of  lead  has  also  been  found  in  the 
same  locality. 

Oxychloride  of  Lead. — When  chloride  of  lead  is  heated  in  the  air  till  it 
ceases  to  give  off  fumes,  a  compound  remains  =PbCl  +  PbO;  it  may  also  be 
formed  by  fusing  together  atomic  equivalents  of  chloride  and  oxide,  or 
chloride  and  carbonate  of  lead  :  it  is  a  yellow  crystalline  compound.  A 
hydrated  compound  of  chloride  and  oxide  of  lead  is  obtained  by  acting  upon 
a  solution  of  common  salt  by  litharge  ;  solution  of  soda,  and  oxide  and 
chloride  of  lead  are  formed  ;  this  insoluble  residue,  when  rendered  anhydrous 
by  fusion,  is  known  under  the  name  oi patent  yellow,  Tumer^s  yellow,  or  Cas- 
sel  yellow,  =PbCl  +  7PbO.  A  similar  compound  may  be  obtained  by  fusing 
together  1  part  of  chloride  with  4  or  5  of  oxide  of  lead,  or  by  heating  sal- 
ammoniac  with  oxide  of  lead. 

Iodide  of  Lead  (Pbl)  may  be  formed  by  heating  leaf-lead  with  iodine ; 
but  it  is  most  readily  obtained  by  adding  iodide  of  potassium  to  a  solution  of 
nitrate  of  lead,  in  equivalent  proportions  ;  it  then  falls  in  the  form  of  a  bright 
yellow  powder,  soluble  in  about  1250  of  cold  and  200  parts  of  boiling  water, 
and  separates,  as  this  solution  cools,  in  brilliant  flakes,  which  are  hexahedral, 
or  derivatives  of  the  hexahedron.  In  this  crystalline  state  it  retains  its  color, 
but  the  pulverulent  iodide  becomes  pale  by  exposure  to  light.  When  gently 
heated  it  becomes  deeper  colored,  and  even  brown,  but  again  yellow  on  cool- 
ing :  at  higher  temperatures  it  fuses,  and  volatilizes  at  a  strong  red  heat. 
It  is  soluble  in  aqueous  solutions  of  potassa  and  soda,  forming  colorless  double 
salts:  boiled  with  carbonate  of  potassa,  it  forms  carbonate  of  lead  and  iodide 
of  potassium.  It  becomes  white  when  digested  in  caustic  ammonia,  forming 
the  compound,  =NH3,PbI ;  the  same  compound  is  obtained  by  the  action  of 
gaseous  ammonia  upon  the  iodide.  Iodide  of  lead  is  soluble  in  hydrochloric 
acid,  and  if  concentrated  by  heat,  the  solution  as  it  cools  deposits  radiated 
prismatic  crystals  of  a  yellow  color,  composed  of  iodide  and  chloride  of  lead. 
It  dissolves  in  concentrated  solutions  of  the  alkaline  iodides,  and  in  the  ace- 
tates of  potassa,  soda,  and  ammonia.  An  iodide  of  lead  and  sodium  is  thus 
formed  by  adding  slight  excess  of  iodide  of  sodium  to  a  hot  solution  of  iodide 
of  lead,  and  placing  the  liquid  in  a  warm  place;  it  separates  in  yellow  shin- 
ing laminae  =NaI,2PbI.  It  forms  a  similar  crystallizable  double  salt  with 
iodide  of  potassium. 

Bromide  of  Lead  (PbBr)  is  precipitated  from  a  solution  of  lead  by  hydro- 
bromic  acid  or  bromide  of  potassium  :  it  is  white,  crystalline,  fusible,  and 
concretes  on  cooling  into  a  yellow  mass.  It  is  sparingly  soluble  in  water, 
and  its  boiling  solution  deposits  shining  acicular  crystals. 

Fluoride  of  Lead  (PbF)  is  almost  insoluble,  and  obtained  by  adding 
hydrofluoric  acid  to  a  nitrate  of  lead,  when  it  fivlls  in  the  form  of  a  white 
powder,  soluble  in  nitric  and  hydrochloric  acids. 

Sulphide  of  Lead  (PbS)  may  be  formed  by  fusion;  when  the  lead  melts, 
it  suddenly  combines  with  the  sulphur  with  ignition.  Its  lustre  and  color 
much  resemble  pure  lead,  but  it  is  brittle,  and  requires  a  bright  red  heat  for 
fusion.  Its  specific  gravity  is  7  58.  Boiled  with  hydrochloric  acid,  chloride 
of  lead  and  sulphuretted  hydrogen  are  formed  ;  by  nitric  acid  it  is  converted 
into  sulphate  of  lead.     Sulphide  of  lead  may  be  obtained  in  the  humi'd  way, 


SULPHATE  AND  CARBONATE  OF  LEAD.  433 

by  precipitating  any  salt  of  lead  by  sulphuretted  hydrogen  :  the  precipitate 
is  black,  or  brown  if  the  solution  is  dilute  :  this  is  so  delicate  a  test  of  lead, 
that  a  solution  containing  the  three  hundred-thousandth  part  of  the  metal  is 
discolored  by  it,  provided  no  excess  of  acid  be  present.  Native  sulphide  of 
lead,  or  galena,  is  the  principle  source  of  the  commercial  demands  of  the 
metal.  It  occurs  massive,  and  crystallized  in  cubes  and  their  modifications. 
When  galena  is  finely  powdered  and  heated  with  strong  nitric  acid,  it  is  con- 
verted into  sulphate  of  lead,  the  other  metals  associated  with  it  (copper  and 
silver)  being  dissolved  as  nitrates.  When  the  nitric  acid  is  diluted,  some 
nitrate  of  lead  is  formed  and  dissolved,  and  a  portion  of  sulphur  is  pre- 
cipitated. 

Sulphite  of  Lead  (PbOjSOJ  is  formed  by  digesting  protoxide  of  lead 
in  aqueous  sulphurous  acid  ;  or  by  adding  the  acid  to  nitrate  of  lead.  It  is 
white,  insoluble  in  water,  and  tasteless. 

Sulphate  of  Lead  (PbO.SOa)  — Cold  sulphuric  acid  has  but  little  action 
upon  metallic  lead  ;  when  the  metal  is  boiled  in  the  concentrated  acid,  sul- 
phurous acid  is  evolved,  and  sulphate  of  lead  is  formed.  The  purer  the  lead 
the  more  readily  is  a  chemical  action  set  up  between  it  and  sulphuric  acid. 
It  is  easily  produced  by  adding  dilute  sulphuric  acid,  or  a  soluble  sulphate, 
to  a  solution  of  nitrate  of  lead,  when  it  falls  in  the  form  of  a  dense  white 
powder  :  hence  the  applicalnon  of  the  soluble  salts  of  lead,  especially  the 
nitrate,  as  tests  of  the  presence  of  sulphuric  acid  and  sulphates.  After  hav- 
ing been  dried  at  400°,  it  may  be  heated  to  redness  without  losing  weight. 
Heated  on  charcoal  by  the  blowpipe,  it  is  ultimately  reduced.  Sulphate  of 
lead  is  insoluble  in  water  and  in  alcohol.  It  is  sparingly  soluble  in  excess 
of  sulphuric  acid,  and  separates  from  it  in  small  prismatic  crystals.  It  is 
soluble,  when  recently  precipitated,  in  hydrochloric  acid,  the  fixed  alkalies, 
and  sparingly  so  in  their  carbonates,  and  in  some  of  the  salts  of  ammonia, 
especially  the  acetate.  Its  acid  is  expelled  by  the  action  of  silica  and  of 
alumina  at  a  red  heat,  hence  its  decomposition  when  fused  in  earthen  cru- 
cibles. This  compound  is  found  native,  crystallized  in  rhombs  in  Angle- 
sea,  Scotland,  and  other  localities. 

Phosphate  OF  Lead. — Each  modification  of  phosphoric  acid  gives  a  white 
precipitate  in  the  soluble  salts  of  lead,  which  is  soluble  in  nitric  acid. — 
Native  phosphate  of  lead.  The  mineral  usually  so  called  is  a  compound  of 
phosphate  and  chloride  of  lead,  in  which  3  atoms  of  the  tribasic  phosphate 
are  combined  with  1  of  chloride  (9PbO,3PO,-|-PbCl).  It  has  been  found 
in  the  mines  of  Cumberland,  Durham,  Yorkshire,  and  of  Wanlock  Head  in 
Scotland,  and  in  many  of  the  foreign  mines.  Its  color  is  various  shades  of 
green,  yellow,  and  brown.  It  usually  occurs  in  six-sided  prisms,  semitrans- 
parent  and  brittle. 

Carbonate  OF  Lead.  Ceruse;  White  Lead.  (PbO,COa). — This  impor- 
tant compound  is  extensively  employed  as  an  oil-pigment :  it  is  chiefly  made 
in  London  and  at  Newcastle-on-Tyne,  to  the  annual  quantity  of  about  16,000 
tons.  There  are  many  processes  by  which  it  may  be  obtained,  and  much  in- 
genuity has  been  displayed  in  their  modification  and  improvement,  the  great 
objects  being  to  obtain  it  in  such  a  state  that  it  shall  form  the  most  opaque 
and  densest  body  as  it  is  called,  when  ground  up  with  linseed,  or  other  dry- 
ing oil,  and  shall  at  the  same  time  be  of  a  pure  and  perfect  white. 

The  following  is  an  outline  of  the  several  methods  by  which  this  carbonate 
may  be  formed.  1.  By  the  precipitation  of  soluble  salts  of  lead  by  alkaline 
carbonates.  A  solution  of  nitrate  or  acetate  of  lead  is  thus  decomposed  by 
carbonate  of  soda;  it  yields  a  dense  white  precipitate,  which,  when  washed 
and  dried,  is  of  a  pure  white,  but  when  examined  by  a  magnifier,  is  found  to 
consist  of  minute  crystalline  grains,  a  circumstance  which  interferes  with  its 
28 


434  MANUFACTURE    OF    WHITE    LEAD. 

body  or  opacity  to  such  an  extent  as  to  render  it  unfit  for  oil-paint :  it  is 
also' a  pure  or  neutral  carbonate,  and  it  will  appear  that  the  most  esteemed 
white  lead  generally  contains  more  or  less  oxide  or  hydrated  oxide  of  lead. 
It  varies  in  texture  according  as  the  carbonate  is  added  to  the  nitrate,  or  the 
nitrate  to  the  carbonate  ;  the  latter  mode  of  precipitation,  with  properly 
diluted  solutions,  furnishes  the  most  impalpable  powder.  When  the  carbonate 
has  once  acquired  a  crystalline  texture,  no  grinding  or  mechanical  comminu- 
tion is  capable  of  conferring  upon  it  the  qualities  which  fit  it  for  an  oil  pig- 
ment. 2.  When  carbonic  acid  gas  is  passed  through  a  hot  solution  of  sub- 
nitrate  of  lead,  carbonate  of  lead  is  thrown  down,  and  the  solution  reverts 
to  the  state  of  neutral  nitrate  ;  this  is  reconverted  into  subnitrate  by  boiling 
with  protoxide  of  lead  (powdered  litharge),  and  the  precipitation  continu- 
ously repeated.  3.  Subacetate  of  lead  is  decomposed  by  passing  through  it 
a  current  of  purified  carbonic  acid  gas.  The  celebrated  white  lead  of  Clichy 
is  thus  prepared.  4.  Finely-powdered  litharge  is  moistened,  mixed  with  a 
very  little  acetate  of  lead  (about  a  hundredth  part),  and  submitted  during 
constant  stirring  to  a  current  of  heated  carbonic  acid  :  in  this  process  a  sub- 
acetate  of  lead  is  successively  formed  and  decomposed  ;  a  small  quantity  only 
of  the  original  acetate  therefore  is  required.  5.  In  the  Dutch  process  lead 
is  cast  into  plates  or  bars,  or  into  the  form  of  stars,  or  circular  gratings  of 
six  or  eight  inches  in  diameter,  and  from  a  quarter  to  half  au  inch  in  thick- 
ness :  five  or  six  of  these  are  placed  one  above  another  in  the  upper  part  of 
a  conical  earthen  vessel,  something  like  a  garden-pot,  in  the  bottom  of  which 
there  is  a  little  strong  acetic  acid.  These  pots  are  then  arranged  side  by 
side,  on  the  floor  of  an  oblong  brick  chamber,  and  are  imbedded  in  a  mixture 
of  new  and  spent  tan  (ground  oak-bark  as  used  in  the  tanyard).  The  first 
layer  of  pots  is  then  covered  with  loose  planks,  and  a  second  range  of  pots 
imbedded  in  tan  is  placed  upon  the  former  ;  and  thus  a  stack  is  built  up  so 
as  entirely  to  fill  the  chamber  with  alternate  ranges  of  the  pots  containing 
the  lead  and  acetic  acid,  surrounded  by  and  imbedded  in  the  tan.  Several 
ranges  of  these  stacks  occupy  each  side  of  a  covered  building,  each  stack 
containing  about  12,000  of  the  pots,  and  from  50  to  60  tons  of  lead.  Soon 
after  the  stack  is  built  up  the  tan  gradually  heats  or  ferments,  and  begins  to 
exhale  vapor,  the  temperature  of  the  inner  parts  of  the  stack  rising  to  140^ 
or  150°.  The  acetic  acid  is  slowly  volatilized,  and  its  vapor  passing  readily 
through  the  gratings  or  folds  of  lead,  gradually  corrodes  the  surface  of  the 
metal,  upon  which  a  crust  of  subacetate  is  successively  formed  and  con- 
verted into  carbonate,  there  being  an  abundant  supply  of  carbonic  acid  fur- 
nished by  the  slow  fermentative  decomposition  of  the  tanners'  bark.  In  the 
course  of  from  4  to  6  weeks  the  process  is  completed,  and  now,  on  unpack- 
ing the  stacks,  the  lead  is  found  to  have  undergone  a  remarkable  change : 
the  form  of  the  castings  is  retained,  but  they  are  converted,  with  consid- 
erable increase  of  bulk,  into  carbonate  of  lead  ;  this  conversion  is  sometimes 
entire,  at  others  it  penetrates  only  to  a  certain  depth,  leaving  a  central  skele- 
ton of  metallic  lead,  the  conversion  being  unequal  in  different  parts  of  the 
stack,  and  varying  in  its  perfection  at  different  seasons,  temperatures,  and 
states  of  the  atmosphere.  The  stacks  are  so  managed  that  they  are  succes- 
sively being  built  up  and  unpacked.  The  corroded  and  converted  gratings, 
or  cakes,  are  then  passed  through  rollers,  by  which  the  carbonate  of  lead 
(white  lead)  is  crushed  and  broken  up,  and  the  central  core  of  metallic  lead 
(blue  lead),  if  any  remain,  is  easily  separated  :  the  white  lead  is  then  trans- 
lerred  to  the  mills,  where  it  is  ground  up  into  a  thin  paste  with  water,  and 
is  ultimately  reduced,  by  the  process  of  elutriation,  or  successive  washings 
and  subsidences,  to  the  state  of  an  impalpable  powder;  it  is  then  dried  ia 
wooden  bowls  placed  upon  shelves  in  a  highly-heated  stove,  and  thus  brought 


CARBONATE    OF    LEAD.  435 

to  the  state  of  masses  easily  rubbed  between  the  fingers  into  a  fine  powder, 
in  which  the  microscope  does  not  enable  us  to  discern  the  slightest  traces 
of  crystalline  character.  If  intended  for  the  use  of  the  painter,  it  is  next 
submitted  to  grinding  with  linseed  oil  ;  and  it  is  found  that  a  hundred 
weight  of  this  white  lead  is  formed  into  a  proper  consistence  with  8  pounds 
of  oil,  whereas  precipitated  white  lead  requires  16  pounds  of  oil  for  the 
same  purposes  ;  the  one  covering  the  surface  so  much  more  perfectly,  and 
having  so  much  more  body  than  the  other.  It  is  sometimes  supposed  that 
in  this  process  the  oxygen  and  carbonic  acid  required  to  form  the  carbon- 
ate of  oxide  of  lead  are  derived  from  the  decomposition  of  the  acetic  acid ; 
but  this  is  evidently  not  the  case,  for  not  more  than  100  pounds  of  real 
acetic  acid  exists  in  the  whole  quantity  of  the  dilute  acid  contained  in  the 
several  pots  of  each  stack  ;  and  in  100  pounds  of  acetic  acid  there  are  not  more 
than  4t  to  48  pounds  of  carbon,  whereas  6740  pounds  would  be  required 
to  furnish  the  carbonic  acid  which  should  convert  50  tons  of  lead  (the 
average  weight  of  that  metal  in  each  stack)  into  carbonate  of  lead.  Tiiere 
can  be  no  doubt  then  that  the  carbon  or  carbonic  acid  must  come  from 
the  tan,  and  that  the  oxygen  is  partly  derived  from  the  same  source,  and 
partly  from  the  atmosphere  :  the  principal  action  of  the  acetic  acid,  there- 
fore, is  to  form  successive  portions  of  subacetate  of  lead,  which  are  suc- 
cessively decomposed  by  the  carbonic  acid:  the  action  is,  however,  of  a  very 
remarkable  description,  for  even  masses  of  lead,  such  as  blocks  of  an  inch 
or  more  in  thickness,  are  thus  gradually  converted  through  and  through 
into  carbonate,  so  that  if  due  time  is  allowed,  there  is  no  central  remnant 
of  metallic  lead.  The  original  texture  of  the  lead  is  much  concerned  in 
the  extent  and  rapidity  of  the  conversion.  Rolled  or  sheet  lead  will  not 
answer,  and  the  gratings,  coils,  and  stars  which  are  employed,  are  all  of  cast 
lead.  The  purest  metal  is  also  required;  for  if  it  contain  iron,  the  resulting 
white  lead  acquires  a  tawny  hue ;  and  if  a  trace  of  silver,  it  acquires  a  per- 
ceptible dinginess  when  subjected  to  the  action  of  liglit. 

Sulphate  of  baryta  is  frequently  added  to  commercial  white  lead,  by 
which  its  valuable  properties  are  proportionately  deteriorated  ;  the  adultera- 
tion is  easily  detected  by  digesting  the  sample  in  dilute  nitric  acid,  which 
dissolves  the  carbonate  of  lead,  but  leaves  the  sulphate  of  baryta  ;  the 
articles  known  under  the  name  of  Venice  white,  Hamburgh  white,  and  Butch 
white,  are  avowedly  mixtures  of  sulphate  of  baryta  with  carbonate  of  lead. 
Clichy  white,  Krems  or  Kremnitz  white,  and  Silver  white,  are  pure  white  lead. 
A  minute  addition  of  indigo  or  of  lamp-black  is  sometimes  made  to  white 
lead,  to  give  it  a  slight  bluish  shade. 

Carbonate  of  lead  is  usually  in  the  form  of  a  heavy  white  powder,  insolu- 
ble in  water,  and  very  sparingly  soluble  in  aqueous  carbonic  acid  ;  its  specific 
gravity  varies  from  6*4  to  6  75.  It  entirely  dissolves  with  effervescence  in 
acetic  and  in  dilute  nitric  acid.  It  is  immediately  discolored  and  ultimately 
blackened  by  sulphuretted  hydrogen,  whence  the  necessity  of  the  cautious 
exclusion  of  all  sources  of  that  compound  in  white-lead  works.  When  care- 
fully heated  in  contact  of  air  carbonate  of  lead  loses  carbonic  acid,  and 
furnishes  by  proper  management  a  beautiful  minium.  The  usual  composi- 
tion of  commercial  white  lead,  prepared  by  the  Dutch  process,  is  represented 
by  Phillips  {Journ.  Ghem.  Soc,  iv.  170)  as  2(PbO,COJ-f  PbO,HO.  It 
loses  the  whole  of  its  water  at  300°,  and  at  350°  the  carbonic  acid  begins  to 
be  evoKed. 

Native  Carbonate  of  Lead  is  one  of  the  most  beautiful  of  the  metallic 
ores  ;  it  occurs  crystallized,  and  fibrous,  the  former  transparent,  the  latter 
generally  opaque.  It  is  soft  and  brittle,  and  occasionally  tinged  green  with 
carbonate  of  copper,  or  gray  by  sulphide  of  lead. 


436  TESTS    FOR    THE    SALTS    OF    LEAD. 

Cyanide  of  Lead  (PbCy)  falls  in  the  form  of  an  insolnble  white  powder 
when  cyanide  of  potassium  is  added  to  a  solution  of  nitrate  of  lead,  or  when 
hydrocyanic  acid  is  dropped  into  acetate  of  lead  :  heated  to  redness  in  a 
glass  tube,  it  gives  out  nitrogen,  and  leaves  a  pyrophoric  carbide  of  lead. 

Borate  of  Lead  is  precipitated  in  the  form  of  a  white  powder  when 
borate  of  soda  is  mixed  with  nitrate  or  acetate  of  lead  :  it  fuses  into  a  color- 
less glass,  and  probably  consists  of  2  atoms  of  boracic  acid  and  1  of  protoxide 
of  lead.  Boracic  acid  and  oxide  of  lead  may  be  fused  together  in  all  pro- 
portions ;  112  of  oxide  and  24  of  acid  give  a  soft  yellow  glass,  sp.  gr.  6*4 ; 
with  48  of  acid  the  glass  is  less  yellow  and  harder  ;  and  with  Y2  of  acid  it 
is  colorless,  as  hard  as  flint  glass,  and  highly  refractive. 

Alloys  of  Lead. — With  tin,  lead  forms  several  useful  alloys,  which  are 
somewhat  less  dense  than  the  mean.  Common  pewter  consists  of  about  80 
parts  of  tin  and  20  of  lead.  Equal  parts  of  lead  and  tin  constitute  plumbers^ 
solder.  When  pieces  of  copper  are  thrown  into  red-hot  melted  lead,  they 
soon  disappear,  and  form  a  gray,  brittle,  and  granular  alloy.  In  coating 
iron  with  lead,  the  surface  of  the  metal  is  first  cleaned  with  hydrochlorate  of 
ammonia :  it  is  then  dipped  into  melted  zinc,  and  afterwards  into  a  bath  of 
melted  lead. 

Tests  for  the  Salts  of  Lead. — The  salts  are  for  the  most  part  white, 
and  those  which  are  soluble  form  colorless  solutions.  They  have  a  sweetish 
metallic  taste.  1.  Sulphuretted  hydrogen  gives  a  brownish  discoloration 
even  when  less  than  1-300, 000th  part  of  a  salt  of  lead  is  present.  In  ordi- 
nary solutions,  it  throws  down  a  brown-black  precipitate  (sulphide  of  lead), 
insoluble  in  alkalies  and  in  diluted  mineral  acids,  but  decomposed  by  strong 
nitric  acid.  2.  Hydrosidphate  of  ammonia  gives  a  similar  precipitate,  not 
soluble  in  an  excess  of  the  reagent,  and  having  the  other  properties  of  the 
sulphide.  The  insoluble  salts  of  lead,  such  as  the  sulphate  and  phosphate, 
are  decomposed  by  this  liquid,  and  a  soluble  salt  of  the  acid  is  formed. 
3.  Diluted  mlphuric  acid  throws  down  a  white  precipitate,  slowly  in  acid 
solutions.  This  precipitate  is  soluble  in  potassa  and  strong  hydrochloric 
acid.  4.  Potnssa  and  soda  throw  down  a  white  precipitate,  soluble  in  excess 
of  the  alkaline  liquid.  5.  Ammonia  precipitates  a  white  hydrated  oxide, 
not  soluble  in  an  excess  of  the  alkali.  6.  All  the  alkaline  carbonates  throw 
down  white  precipitates,  insoluble  in  an  excess.  7.  Iodide  of  potassium 
gives  a  yellow  precipitate,  soluble  in  potassa  and  in  hydrochloric  acid. 
8.  Chloride  of  sodium  gives  a  white  precipitate,  partly  dissolved  when 
boiled,  and  readily  dissolved  by  potassa  or  strong  nitric  acid.  The  lead- 
precipitates  dissolved  by  alkalies  are  thrown  down  black  by  sulphuretted 
hydrogen  or  hydrosulphate  of  ammonia.  9.  Ferrocyanide  of  potassium 
gives  a  white  precipitate. 

The  salts  insoluble  in  water  are  dissolved  by  soda  and  potassa,  or  by  nitric 
acid,  when  the  metal  is  rendered  manifest  by  sulphuretted  hydrogen  and 
other  tests.  When  these  salts  are  boiled  with  carbonate  of  soda,  they  afford 
carbonate  of  lead,  which  may  be  dissolved  in  acetic  or  dilute  nitric  acid,  and 
subjected  to  the  usual  tests.  Heated  by  the  blowpipe  upon  charcoal,  with 
carbonate  of  soda  or  cyanide  of  potassium,  they  afford  a  globule  of  metal. 
Lead  is  precipitated  from  its  solutions,  in  the  metallic  state,  by  magnesium 
and  zinc.  All  the  soluble,  as  well  as  the  insoluble,  salts  of  lead  may  be 
decomposed  and  reduced,  by  mixing  them  with  dilute  nitric  acid,  and  im- 
mersing a  plate  of  either  of  these  metals  in  the  liquid. 

When  solutions  of  the  salts  of  lead  are  filtered  through  charcoal,  which 
is  sometimes  done  for  the  purpose  of  decoloration,  part  or  even  the  whole  of 
the  oxide  of  lead,  if  it  only  amount  to  about  one-twentieth  of  the  charcoal 
employed,  will  be  abstracted  by  the  charcoal.     This   renders  charcoal  in 


OXIDES    OF    BISMUTH.  43*7 

coarse  powder  most  useful  in  the  construction  of  the  filters  for  domestic  pur- 
poses. Any  casual  imprei!::nation  of  water  by  lead  may  thus  be  removed, 
and  the  water  rendered  wholesome.  So  small  a  quantity  as  one  grain  of 
lead  in  a  gallon  of  water  has  been  known  to  produce  the  effects  of  lead- 
poisoning. 


CHAPTER     XXXIII. 

BISMUTH  — COBALT  — NICKEL  — CHROMIUM. 

Bismuth  (Bi=213). 

This  metal  was  first  described  by  Agricola,  in  1529.  It  is  sometimes 
called  marcasite.  It  is  neither  of  common  occurrence,  nor  very  abundant. 
Native  bismuth  is  found  in  Cornwall,  and  in  Saxony,  Transylvania,  and 
Bohemia  ;  and  it  has  been  recently  discovered  in  South  Australia.  It  is 
readily  extracted  from  its  ores  by  fusion.  Bismuth  is  a  brittle  white  metal, 
with  a  slight  tint  of  red.  It  fuses  at  497°,  and  expands  and  crystallizes  on 
cooling.  Its  sp.  gr.  is  9  8.  To  obtain  fine  crystals,  it  should  be  purified 
by  fusion  with  nitre,  and  when  thus  refined,  carefully  melted  and  poured  into 
a  heated  mould,  and  suffered  slowly  and  quietly  to  cool.  When  the  surface 
has  solidified,  the  crust  is  pierced,  and  the  liquid  metal  poured  out  from  the 
interior :  the  mould  is  then  suffered  to  cool,  ai\d  the  superior  crust  carefully 
removed,  when  the  cavity  is  found  lined  with  iridescent  cubical  crystals  (pp. 
25  and  309).  Arsenic,  iron,  copper,  nickel,  silver,  and  other  metals,  are 
frequently  found  in  the  bismuth  of  commerce.  To  purify  it,  it  may  be  dis- 
solved in  nitric  acid,  and  the  clear  solution  poured  off  into  water,  which 
occasions  a  precipitation  of  a  subnitrate  of  bismuth,  easily  reducible  by  fusion 
with  charcoal  or  black  flux  in  an  earthen  crucible. 

Bismuth  and  Oxygen There  are  two  well-defined  oxides  of  bismuth,  a 

teroxide  =Bi03,  and  an  acid  oxide  =Bi05.  A  third  oxide  has  been  described 
as  a  compound  of  these  =Bi03,Bi05. 

Oxide  of  Bismuth;  Teroxide  of  Bismuth  (BiOg). — When  bismuth  is 
exposed  at  a  white  heat  to  a  current  of  air,  it  burns,  and  produces  an  abun- 
dant yellow  smoke,  which  condenses  in  the  form  of  a  yellowish-white  subli- 
mate. The  readiest  mode  of  obtaining  this  oxide  consists  in  dissolving 
bismuth  in  nitric  acid,  precipitating  by  dilution  with  water,  edulcorating  the 
precipitate,  and  heating  it,  when  dry,  nearly  to  redness.  Owing  to  imperfect 
washing,  it  frequently  contains  traces  of  arsenic  acid.  At  a  red  heat,  this 
oxide  fuses,  and  when  in  fusion  it  acts  upon  other  oxides  much  in  the  same 
way  as  oxide  of  lead.  It  forms,  on  cooling,  a  yellow  vitreous  mass  of  a  spe- 
cific gravity  of  8*2.  It  is  easily  reduced  by  hydrogen,  charcoal,  and  several 
of  the  metals.  It  combines  with  water,  forming  a  white  hydrate,  which  is 
best  obtained  by  digesting  the  precipitate  formed  by  pouring  the  nitric 
solution  of  bismuth  in  water,  into  caustic  potassa  or  soda,  and  after  washing, 
drying  it  at  80°.  It  is  insoluble  in  excess  of  the  alkalies  (and  their  car- 
bonates) ;  and  when  boiled  with  them  becomes  yellow  and  anhydrous.  It 
is  also  insoluble  in  tartaric  acid,  by  which  it  is  known  from  the  antimonial 
precipitate  in  water.  Native  oxide  of  bismuth  is  a  rare  mineral,  found  in 
Cornwall  and  Saxony  :  it  is  the  bismuth  ochre  of  some  mineralogists. 

Peroxide  of  Bismuth  ;  Bismuthic  Acid  (BiO^). — This  oxide  is  obtained 
by  dropping  nitrate  of  bismuth  into  a  solution  of  caustic  potassa.     The  pre- 


438  SALTS    OF    BISMUTH. 

cipitate  should  be  boiled  in  the  alkaline  liquor,  washed,  and,  while  moist, 
diffused  through  a  solution  of  potassa  into  which  chlorine  is  passed.  A  red 
precipitate  is  thus  formed,  which  consists  of  bismuthic  acid  and  teroxide,  and 
which  is  to  be  digested  in  nitric  acid  of  sufficient  strength  to  dissolve  the 
oxide.  The  remaining  acid,  which  is  a  hydrate,  is  to  be  well  washed,  and 
dried  at  100°;  it  is  a  red  powder,  becoming  brown  and  anhydrous  when 
dried  at  266° ;  at  higher  temperatures  it  begins  to  lose  oxygen.  It  is  de- 
composed by  sulphuric  acid,  and  by  hot  nitric  acid. 

Nitrate  of  Bismuth  (BiOg.SNOjjOHO). — When  nitric  acid  is  poured 
upon  powdered  bismuth,  the  action  is  intensely  violent.  Nitrate  of  bismuth 
is  usually  made  by  dissolving  the  metal  to  saturation  in  2  parts  of  nitric  acid 
and  1  of  water;  nitric  oxide  is  copiously  evolved,  and  the  solution  affords 
prismatic  crystals,  which  may  be  dissolved  in  a  small  quantity  of  water;  but 
if  the  solution,  even  when  acid,  is  poured  into  a  large  quantity  of  water,  it 
is  decomposed,  and  affords  a  white  and  somewhat  crystalline  precipitate, 
commonly  called  sahnitrate  of  bismuth^  and  formerly  known  as  magistery  of 
bismuth,  pearl  white,  and  blanc  cfEspagiie  ;  it  is  insoluble  in  water,  and  when 
dried  in  the  air  is  =Bi03,N05,H0  ;  but  becomes  anhydrous  when  adequately 
dried.  This  compound  is  used  in  medicine  :  it  frequently  contains  arsenic 
in  the  form  of  arsenic  acid,  owing  to  imperfect  washing  of  the  precipitate. 
Out  of  five  druggist's  samples,  we  have  found  arsenic  in  three.  The  presence 
of  this  impurity  may  lead  to  a  serious  error.  It  may  be  detected  by  boiling 
the  subnitrate  in  some  ounces  of  distilled  water,  filtering,  evaporating  the 
liquid  to  dryness,  and  then  adding  to  the  residue  a  few  drops  of  a  solution 
of  nitrate  of  silver.  A  brick-red  stain  or  precipitate  indicates  the  presence 
of  arsenic  acid. 

The  nitrate  is  not  so  completely  decomposed  by  water  as  the  chloride  : 
hence,  in  order  to  procure  the  complete  decomposition  of  the  nitrate,  some 
hydrochloric  acid  should  be  added  to  the  solution,  and  this  should  be  after- 
wards concentrated  by  evaporation.  The  addition  of  a  large  quantity  of 
water  to  the  residue  will  then  produce  a  copious  white  precipitate.  {See 
Chloride.) 

Chloride  of  Bismuth  ;  Terchloride.  (BiClg)  is  procured  by  gently  heat- 
ing the  metal  in  chlorine ;  it  burns,  and  forms  a  gray  compound.  This  ter- 
chloride may  also  be  prepared  by  heating  2  parts  of  corrosive  sublimate  with 
I  of  powdered  bismuth,  and  expelling  the  excess  of  the  former  by  heat ;  or 
by  evaporating  the  solution  of  oxide  of  bismuth  in  hydrochloric  acid  to  dry- 
ness, and  heating  the  residue  in  close  vessels.  It  was  formerly  called  Butter 
of  Bismuth.  It  is  of  a  gray  color,  and  fuses  at  about  480°.  When  exposed 
to  air  it  deliquesces.  It  is  decomposed  by  a  large  quantity  of  water.  A 
solution  of  the  chloride  may  be  obtained  by  dissolving  pure  teroxide  of  bis- 
muth, or  the  pure  sulphide,  in  hydrochloric  acid,  and  evaporating  the  liquid. 
.  When  added  to  a  large  quantity  of  water,  a  white  oxychloride  of  the  metal 
is  precipitated  (3BiCl3+6HO=BiCl3,2Bi03+6HCl).  A  small  quantity  of 
oxide  of  bismuth  is,  however,  retained  by  the  acid  liquid.  This  precipitate 
has  also  received  the  name  of  pearl  lohite. 

Sulphide  of  Bismuth  (BiSg)  is  of  a  bluish  and  metallic  lustre  ;  it  is  less 
fusible  than  bismuth.  It  may  be  formed  by  fusion  ;  and  also  by  precipitating 
the  salts  of  bismuth  by  sulphuretted  hydrogen,  when  it  forms  a  black  or 
dark-brown  precipitate  (hydrated),  which,  when  dried  and  heated,  acquires 
a  metallic  lustre. 

Sulphate  of  Bismuth  (Bi03,3S03)  is  obtained  by  heating  powdered  bis- 
muth in  sulphuric  acid.     It  is  a  white  compound,  insoluble  in,  but  decom- 
posed by  water,  which  converts  it  into  a  subsulphate  and  supersulphate. 
Carbonate  of  Bismuth  is  thrown  down  from  the  nitrate  by  carbonated 


TESTS    FOR    THE    SALTS    OF    BISMUTH.      COBALT.  439 

alkalies;  it  is  a  white  powder,  insoluble  in  water  and  in  carbonic  acid,  and 
soluble  in  nitric  acid  with  effervescence. 

Alloys  of  Bismuth. — Those  with  tin  and  lead  are  remarkable  for  the  low 
temperature  at  which  they  enter  into  fusion,  and  for  the  extraordinary  irre- 
gularities of  expansion  and  contraction  which  they  exhibit  with  changes  of 
temperature.  An  alloy  of  2  parts  of  bismuth,  I  of  lead,  and  1  of  tin,  fuses 
at  200°.  The  alloy  of  8  parts  of  bismuth,  5  of  lead,  and  3  of  tin,  fuses  at 
a  little  below  212°  :  the  addition  of  1  part  of  mercury  or  of  cadmium  renders 
it  still  more  fusible.  It  may  be  employed  for  taking  casts  from  medals,  and 
even  from  the  surface  of  wood  and  embossed  paper :  some  beautiful  casts  of 
the  internal  ear  have  also  been  made  in  this  alloy,  showing  the  complexities 
of  its  bony  cavities.  When  the  alloy  is  poured  upon  a  marble  slab,  and 
broken  as  soon  as  it  is  cool  enough  to  be  handled,  its  surfaces  are  bright  and 
conchoidal,  and  the  whole  extremely  brittle ;  after  this  it  becomes  hot,  and 
loses  its  brittleness,  its  fractured  surface  becoming  granular  and  dull. 

Tests  for  the  Salts  of  Bismuth. — Many  of  them  are  resolved  by  water 
into  a  soluble  acid  salt,  and  a  less  soluble  or  insoluble  and  more  basic  com- 
pound. 1.  In  the  clear  acid  solutions  of  oxide  of  bismuth,  potassa,  soda, 
and  ammonia,  and  their  carbonates,  produce  white  precipitates,  insoluble  in 
excess  of  the  alkali,  or  its  carbonate,  and  insoluble  in  hydrochlorate  of  am- 
monia. 2.  Hydrosulphate  of  ammonia  and  sulphuretted  hydrogen  produce 
brown  or  black  precipitates,  insoluble  in  the  precipitants,  but  soluble  in 
boiling  nitric  acid,  and  easily  reduced  to  metallic  bismuth  when  mixed  with 
soda,  and  fused  in  the  inner  flame  of  the  blowpipe.  3.  Chromate  of  potassa 
gives  a  golden-yellow  precipitate,  soluble  in  nitric  acid,  but  insoluble  in 
potassa.  4.  Iodide  of  potassium  gives  a  purple-brown  precipitate.  5.  Sul- 
phuric acid  does  not  precipitate  the  solution  ;  and  by  this  reagent  lead  may 
be  detected  in,  and  separated  from,  bismuth.  6.  Ferrocyanide  of  potassium 
gives  a  greenish-white  precipitate,  and  ferricyanide  a  similar  precipitate,  but 
of  a  deeper  color.  T.  The  acid  solutions  of  bismuth  are  decomposed  by 
magnesium,  zinc,  lead,  tin,  and  cadmium.  When  a  salt  of  bismuth  is  boiled 
with  polished  copper  in  diluted  hydrochloric  acid,  there  is  a  deposit  of  white 
metal  on  the  copper,  but  this  is  not  volatilized  by  heat.  A  piece  of  zinc  in- 
troduced into  a  solution  of  a  salt  of  bismuth,  the  surface  is  soon  covered  with 
a  black  uncrystalline  deposit  of  reduced  bismuth,  which  protects  it  from  the 
further  action  of  the  acid.  All  the  compounds  of  bismuth  give  a  metallic 
button  on  charcoal  under  the  blowpipe  flame.  The  metal  is  surrounded  with 
a  yellow  border  of  anhydrous  oxide. 

Bismuth  may  be  mistaken  for  antimony  from  the  fact  that  its  salts,  espe- 
cially the  chloride,  produce  v/hite  precipitates  when  added  to  a  large  quan- 
tity of  water,  provided  too  much  of  the  acid  is  not  present.  The  white  preci- 
pitate from  bismuth  is  not  soluble  in  tartaric  acid,  and  is  blackened  by  sul- 
phuretted hydrogen  ;  that  from  antimony  is  easily  dissolved  by  tartaric  acid, 
and  acquires  a  deep  orange-red  color  from  the  gas. 

Cobalt  (Co=30). 

The  native  combinations  of  cobalt  are  the  oxide,  and  compounds  of  the 
metal  with  iron,  nickel,  arsenic,  and  sulphur.  The  ore  called  glance  cobalt 
is  a  sulpho-arsenide.     The  red  ore  is  an  arseniate. 

Cobalt  is  never  employed  in  the  metallic  state,  so  that  the  processes  for 
its  reduction  are  generally  carried  on  upon  a  small  scale,  and  confined  to  the 
experimental  laboratory  ;  but  there  is  much  difficulty  in  obtaining  it  pure. 
It  is  a  metal  of  a  reddish-gray  color,  brittle,  and  difficultly  fusible.  Its  sp.  gr. 
is  89.  It  forms  two  oxides,  a  protoxide  and  a  sesquioxide,  and  these  com- 
bine with  each  other. 


440  COBALT  :    OXIDES,    CHLORIDES,    AND    SULPHIDES. 

Protoxide  of  Cobalt  (CoO),  formed  by  adding  potassa  to  the  nitrate 
and  washing  and  drying  the  precipitate  out  of  contact  of  air,  appears  nearly 
black.  By  exposure  to  heat  and  air  it  absorbs  oxygen,  and  is  converted 
into  peroxide.  The  protoxide,  when  recently  precipitated  and  moist,  is  blue ; 
if  left  in  contact  of  water,  it  becomes  a  red  hydrate ;  it  then  absorbs  oxygen, 
and  acquires  a  green  tint.  It  may  also  be  obtained  by  heating  the  carbon- 
ate of  cobalt  out  of  contact  of  air ;  it  is  then  of  a  greenish-gray  color.  It 
is  recognized  by  the  facility  with  which  it  imparts  a  blue  tint  to  vitrifiable 
compounds,  and  to  white  enamel.  When  hydrogen  is  passed  over  it  at  a  red 
heat,  it  is  decomposed,  and  porous  metallic  cobalt  remains,  which  is  some 
times  pyrophoric. 

Peroxide  of  Cobalt;  Sesquioxide  of  Cobalt  (Co^Og). — When  the  prot- 
oxide is  heated  in  the  air,  it  absorbs  oxygen,  and  acquires  a  dark-brown 
color,  forming  an  oxide  intermediate  between  the  peroxide  and  protoxide, 
=  €'0304.  When  chlorine  is  passed  through  a  mixture  of  the  hydrated  prot- 
oxide and  water,  or  when  a  solution  of  chloride  of  cobalt  is  decomposed  by 
chloride  of  lime,  a  black  precipitate  falls,  which  is  the  hydrated  peroxide 
(Co^Og.SHO),  and  which  may  be  deprived  of  water  by  cautious  drying ;  it  is 
then  black,  and  insoluble  in  dilute  acids  ;  it  does  not  form  salts ;  when  acted 
on  by  hydrochloric  acid  it  evolves  chlorine,  and  yields  a  protochloride. 

Nitrate  of  Cobalt  (CoOjNOJ. — With  nitric  acid  the  oxide  of  cobalt 
furnishes  a  brownish-red  deliquescent  salt,  in  rhombic  crystals,  consisting 
of  CoO,N05,6HO.  Characters  written  with  it  upon  paper  become  pink  in 
dry  air,  and  disappear  in  a  damp  atmosphere.  It  thus  forms  a  red  sympa- 
thetic ink. 

Chloride  of  Cobalt  (CoCl). — When  oxide  of  cobalt  is  dissolved  in  hydro- 
chloric acid,  evaporated  to  dryness,  and  the  residuum  heated  to  redness  out 
of  the  contact  of  air,  a  substance  of  a  blue  color  a?id  micaceous  texture  is 
obtained,  which  is  anhydrous  chloride  of  cobalt.  When  this  chloride  is  dis- 
solved in  water,  it  yields  a  pink  solution,  which,  if  written  with,  becomes 
invisible  when  dry  ;  but  if  gently  heated,  the  writing  appears  in  brilliant  blue 
(auhydrous  chloride),  which  soon  vanishes  as  the  paper  cools,  in  consequence 
of  the  salt  absorbing  aerial  moisture  (hydrochlorate  of  the  oxide,  p.  T6)  ;  if 
overheated,  the  writing  blackens.  This  solution  has  been  termed  sympatlietic 
ink.  When  evaporated,  it  forms  red  crystals,  composed  of  1  atom  of  the 
chloride  and  5  of  water. 

Protosulphide  of  Cobalt  (CoS)  is  yellowish-gray  ;  it  fuses  at  a  red-heat, 
and  is  easily  soluble  in  acids. 

Sesquisulphide  of  Cobalt  (Co^Sg)  is  obtained  by  decomposing  sulphate 
of  cobalt  by  sulphuretted  hydrogen  at  a  red  heat.  It  is  dark  gray,  and  occurs 
native. 

Sulphate  of  Cobalt  (CoO,S03)  forms  oblique  rhombic  prisms,  soluble  in 
24  parts  of  water  at  60°,  and  insoluble  in  alcohol.  It  may  be  made  by  dis- 
solving the  newly-precipitated  protoxide  or  carbonate  of  cobalt  in  sulphuric 
acid  diluted  with  its  bulk  of  water.  When  dried  at  a  temperature  of  500° 
the  crystals  fall  into  a  blue  powder,  which  in  a  red  heat  fuses,  but  does  not 
give  off  acid  except  at  a  very  high  temperature.  When  1  part  of  sulphate 
of  cobalt  and  2  or  3  of  sulphate  of  zinc  are  dissolved  together  and  precipitated 
by  carbonate  of  soda,  a  precipitate  falls  which,  when  washed  and  calcined, 
has  been  used  as  a  pigment,  under  the  name  of  Rinmami's  green. 

Phosphate  of  Cobalt  (3CoO,PO,)  may  be  formed  by  adding  phosphate 
of  soda  to  chloride  of  cobalt;  it  is  insoluble  in  water,  of  a  lilac  color,  and 
soluble  in  excess  of  phosphoric  acid.  When  phosphate  of  cobalt  is  mixed 
with  pure  and  moist  alumina,  and  exposed  to  heat;  it  produces  a  blue  com- 
pound, which  has  beeu  employed  as  a  substitute  for  ultramarine,  under  the 


TESTS  FOR  THE  SALTS  OF  COBALT.  441 

name  of  Thenard^s  Blue.  A  pure  salt  of  cobalt  free  from  nickel,  and  pure 
alumina  free  from  iron,  are  essential  to  the  production  of  a  fine  l)lne. 

Carbonate  of  Cobalt. — When  nitrate,  chloride,  or  sulphate  of  cobalt, 
is  decomposed  by  carbonate  of  soda,  a  purple  powder  is  precipitated,  be- 
coming pink  when  dried,  and  soluble  with  effervescence  in  the  acids.  Heated 
in  close  vessels  it  gives  off  carbonic  acid,  and  a  gray  protoxide  remains  :  it 
is  a  mixture  of  carbonate  and  hydrated  oxide  =5CoO,2C02,4HO. 

Ammonia  Compounds  of  Cobalt. — Several  of  the  salts  of  cobalt  form 
double  salts  with  those  of  ammonia.  When  hydrated  oxide  of  cobalt  is  dis- 
solved in  an  ammoniacal  solution  of  sal-ammoniac,  it  absorbs  oxygen  from 
the  air,  and  acquires  a  purple  color  ;  and  if  excess  of  hydrochloric  acid  be 
then  added,  and  the  mixture  boiled,  a  crimson  precipitate  falls,  leaving  the 
liquor  colorless.  When  this  precipitate  is  dissolved  in  hot  water,  acidulated 
by  hydrochloric  acid,  it  deposits  red  octahedral  crystals,  insoluble  in  hydro- 
chloric acid,  and  which,  at  a  red  heat,  lose  ammonia  and  hydrochlorate  of 
ammonia:  their  composition  is  3(NII^Cl-f  2(CoO)NH3). 

CoBALTOCYANiDES. — When  cyanide  of  potassium  is  added  to  a  solution  of 
cobalt  salt,  a  brown  precipitate  (CoCy)  falls,  which,  dissolved  in  an  excess 
of  cyanide  of  potassium,  yields  a  double  cyanide  =KCy,CoCy.  When  this 
salt  is  exposed  to  the  air,  or  when  a  solution  of  hydrated  oxide  of  cobalt  in 
potassa  is  supersaturated  with  hydrocyanic  acid,  a  salt  is  formed  =K3,Co2, 
Cyg.  It  corresponds  to  the  ferricyanide  of  potassium.  Similar  salts,  with 
sodium  and  other  bases,  have  been  obtained. 

Borate  of  Cobalt. — Solution  of  borax  occasions  a  pink  precipitate  in 
solution  of  chloride  of  cobalt,  which  is  a  borate  of  cobalt,  and  which  produces 
a  beautiful  blue  glass  when  fused. 

Uses  of  Cobalt. — The  chief  use  of  cobalt  is  in  the  state  of  oxide  as  a 
coloring  material  for  porcelain,  earthenware,  and  glass;  it  is  principally  im- 
ported from  Germany  in  the  state  of  zaffre,  and  smalt,  or  azure.  Zaffre  is 
prepared  by  calcining  the  ores  of  cobalt,  by  which  sulphur  and  arsenic  are 
volatilized,  and  an  impure  oxide  of  cobalt  remains,  which  is  mixed  with 
about  twice  its  weight  of  finely-powdered  flint.  Smalt  and  azure  blue  are 
made  by  fusing  zaffre  with  glass,  or  by  calcining  a  mixture  of  equal  parts  of 
roasted  cobalt  ore,  common  potassa,  and  ground  flint.  In  this  way  a  blue 
glass  is  formed,  whicil,  while  hot,  is  dropped  into  water,  and  afterwards  re- 
duced to  impalpable  powder.  Thenard's  blue  is  a  valuable  pigment,  and 
has  been  substituted  for  smalt  in  the  manufacture  of  paper,  though  it  is  said 
not  to  be  so  effectual  in  covering  the  yellow  tint  of  the  paper.  There  was 
formerly  a  large  addition  of  smalt  made  to  bank-note  paper,  and  consequently 
the  ash  obtained  by  the  periodical  combustion  of  notes  at  the  Bank,  often 
assumed  by  fusion  the  appearance  of  a  deep  blue  glass :  so  also  the  blue- 
tinted  writing-papers  leave  a  fine  blue  ash  when  burned,  and  often  exhale  an 
aliaceous  odor  from  the  presence  of  arsenic  in  the  smalt.  Smalt  generally 
contains  traces  of  arsenic,  and  this  substance  may  be  thus  transferred  to 
starch  and  paper.  In  paper-making,  there  is  some  difficulty  in  keeping  the 
smalt  uniformly  suspended  in  the  pulp,  so  that  the  under  side  of  the  sheet  is 
generally  bluer  than  the  upper.  The  manufacturers  of  paper-hangings  also 
use  smalt  and  Thenard's  blue  for  all  brilliant  and  durable  blues. 

Tests  for  the  Salts  of  Cobalt. — The  salts  are  generally  blue  in  the 
anhydrous  state,  as  well  as  in  concentrated  acid  solutions.  If  diluted,  they 
have  a  crimson  or  pink-red  color.  1.  Sulphuretted  hydrogen  does  not  pre- 
cipitate an  acid  solution.  If  acetate  of  soda  is  added  to  the  liquid,  a  dark- 
brown  precipitate  (CoS)  falls.  2.  Hydrosidphate  of  ammonia  produces  a 
dark-brown  or  black  precipitate,  which  is  quite  insoluble  in  an  excess  of  the 
reagent.     3.  Ammonia  gives  a  bluish  precipitate,  soluble  in  an  excess  of  the 


442  NICKEL    AND    ITS    OXIDES. 

alkali  :  the  precipitate,  on  exposure  to  air,  rapidly  acquires  a  green,  and 
finally  a  brown  color.  4.  Potassa  throws  down  a  deep  blue  precipitate, 
which,  when  boiled  without  exposure  to  air,  becomes  rose-red.  The  blue 
precipitate  exposed  to  air  becomes  olive-green,  and  finally  brown.  5.  Alka- 
line carbonates  give  a  light-red  precipitate  of  basic  carbonate.  This  preci- 
pitate is  dissolved  by  carbonate  or  hydrochlorate  of  ammonia,  forming  a  rich 
crimson-red  solution.  6.  Ferrocyanide  of  potassium  produces  a  deep  green, 
and  Ferrocyanide  of  potassium,  a  red-brown  colored  precipitate. 

The  salts  of  cobalt  which  are  insoluble  in  water  are  dissolved  by  hydro- 
chloric and  sulphuric  acids.  The  hydrochloric  solution  on  paper  is  identified 
by  the  red  spot  or  streak  acquiring  a  rich  blue  color  when  dried  by  a  mode- 
rate heat,  and  by  its  resuming  the  ordinary  red  color  when  exposed  to  damp 
air  (p.  76).  Before  the  blowpipe,  borax  and  raicrocosmic  salt  acquire  a 
blue  color  from  cobalt  and  the  compounds  containing  it. 

Nickel  (Ni=30). 

Nickel  was  discovered  by  Cronstedt,  in  1751.  Its  commonest  ore  was 
termed  by  the  German  mm^vs,  kupfernichel,  or  "  false-co|)per  :"  it  is  au 
arsenide  of  nickel.  The  common  commercial  source  of  nickel  is  an  impure 
fused  arsenide,  known  under  the  name  of  Speiss ;  it  generally  contains  be- 
tween 50  and  60  per  cent,  of  nickel.  The  pure  metal  may  be  obtained  from 
this  arsenide  by  roasting  it,  dissolving  the  product  in  a  mixture  of  equal 
parts  of  nitric  and  hydrochloric  acids,  and  evaporating  the  solution  to  dry- 
ness, so  as  to  expel  excess  of  acid ;  then  redissolving  the  residue  in  water, 
passing  a  current  of  sulphuretted  hydrogen  through  the  solution,  and  filter- 
ing. A  little  nitric  acid  is  added  to  the  filtrate,  and  after  boiling  it,  an 
excess  of  caustic  ammonia  is  added  ;  it  is  again  filtered,  and  solution  of  pot- 
assa added  until  the  blue  color  of  the  liquid  nearly  disappears  ;  this  produces 
a  green  precipitate,  which,  when  thoroughly  washed  with  boiling  distilled 
water,  dried,  and  exposed  to  a  red  heat  in  a  current  of  hydrogen  gas,  leaves 
the  nickel  in  a  finely-divided  state.  It  may  be  obtained  in  the  form  of  a 
button  by  fusion  at  a  white  heat. 

Properties. — Nickel  is  a  white,  ductile,  and  malleable  metal,  nearly  as 
difficult  of  fusion  as  iron  :  it  is  magnetic,  but  its  magnetism  is  more  feeble 
than  that  of  iron,  and  vanishes  at  a  heat  somewhat  below  redness.  It  is 
not  oxidized  at  common  temperatures,  but  when  heated  it  acquires  various 
tints,  like  steel,  and  at  a  red  heat  becomes  coated  with  a  gray  oxide.  Its 
sp.  gr.  is  8*8.  It  is  slowly  soluble  in  dilute  sulphuric  and  hydrochloric 
acids,  evolving  hydrogen,  and  producing  protosalts :  nitric  acid  is  its  best 
solvent. 

Protoxide  of  Nickel  (NiO)  is  obtained  by  adding  potassa  to  the  solution 
of  the  nitrate  or  sulphate;  a  green  precipitate  falls,  which  is  a  hydrated 
protoxide  ;  this,  heated  to  redness,  affords  a  gray  protoxide.  The  carbonate, 
oxalate,  and  nitrate  of  nickel,  when  heated  to  redness,  also  afford  the  prot- 
oxide in  the  form  of  a  gray  powder :  when  intensely  heated  out  of  contact 
of  air,  the  oxide  becomes  green.  It  is  not  magnetic.  This  oxide,  in  the 
state  of  hydrate,  dissolves  in  ammonia,  forming  a  sapphire-blue  solution,  a 
property  made  use  of  to  separate  oxides  of  nickel  and  iron,  the  latter  (per- 
oxide) being  insoluble  in  ammonia. 

Peroxide  of  Nickel  Sesquioxide  of  Nickel  (Ni^Og).— When  nitrate 
or  carbonate  of  nickel  is  carefully  heated  nearly  to  redness,  a  black  powder 
remains,  which  is  this  oxide.  It  may  be  obtained  as  a  hydrate  by  passing 
chlorine  through  the  hydrated  protoxide  diffused  in  water,  in  which  case  a 
solution  of  protochloride  is  obtained,  and  peroxide  is  formed  (3NiO-f  Cl= 


SALTS    OF    NICKEL.  443 

NiCl  +  NiaOa).  It  may  also  be  formed  by  the  action  of  a  warm  solution  of 
chloride  of  lime  upon  the  hydrated  protoxide.  When  this  hydrated  oxide 
is  carefully  dried,  it  is  =Ni.jO,^,3IIO.     It  does  not  combine  with  acids. 

CfiLORiDE  OF  Nickel  (NiCl). — When  finely-divided  nickel  is  heated  in 
chlorine,  it  burns,  and  a  golden-colored  chloride  results.  This  compound 
may  also  be  obtained  by  dissolving  the  oxide  in  hydrochloric  acid,  evaporating 
to  dryness,  and  heating  the  residue  to  redness  in  a  glass  tube  :  it  then 
remains  in  the  form  of  a  yellow  lamellar  substance,  volatile  at  a  high  red 
heat,  which  dissolves  in  hot  water,  and  leaves  on  evaporation  a  confusedly 
crystalline  mass  of  an  apple-green  color,  and  sweetish  taste  =NiCl,9B[0. — 
Ammonio- chloride  of  Nickel.  100  parts  of  anhydrous  chloride  of  nickel 
absorb  74  8  of  ammonia,  becoming  a  bulky  white  powder  =3(NH3),NiCl, 
which  yields  a  blue  solution  with  water. 

Nitrate  of  Nickel  (NiO,N05,5IIO). — Nitric  acid  acts  upon  nickel  with 
disengagement  of  nitric  oxide,  and  a  bright  green  solution  of  protoxide  is 
obtained,  which  yields  prismatic  crystals :  exposed  to  heat,  part  of  the  acid 
may  be  driven  off  so  as  to  leave  a  green  insoluble  subnitrate,  and  this  at  a 
higher  temperature  is  decomposed,  peroxide,  or  ultimately  protoxide,  of 
nickel  remaining.  The  crystals  of  nitrate  of  nickel  effloresce  in  dry  air,  but 
deliquesce  in  a  damp  atmosphere  ;  they  are  soluble  in  2  parts  of  water  a  60°, 
and  also  in  alcohol. 

Sulphide  of  Nickel  (NiS)  may  be  formed  by  heating  nickel  filings  with 
sulpliur;  they  combine  with  ignition;  also  by  heating  oxide  of  nickel  with 
sulphur  ;  or  by  passing  sulphuretted  hydrogen  over  the  heated  oxide.  It  is 
yellow,  and  resembles  pyrites. 

SuPHATE  OF  Nickel  (NiO.SOg.THO)  is  formed  by  dissolving  the  oxide 
or  carbonate  of  nickel  in  diluted  sulphuric  acid  :  it  yields  emerald-green 
prismatic  crystals,  soluble  in  about  3  parts  of  water  at  60°,  and  efflorescent 
by  exposure;  its  taste  is  sweet  and  astringent;  it  is  insoluble  in  alcohol  and 
in  ether.  Exposed  to  heat,  the  crystals  crumble  down  into  a  yellow  powder  : 
at  a  white  heat  the  acid  is  expelled,  and  protoxide  remains.  When  the 
ordinary  crystals  (containing  7  atoms  of  water)  are  exposed  to  the  sunshine, 
or  when  long  kept,  they  become  a  congeries  of  small  octahedral  crystals, 
which  are  opaque,  but  retain  the  original  quantity  of  combined  water. 

Sulphate  of  Ammonia  and  Nickel. — (NH^O,NiO,2S03,5HO)  Js  obtained 
by  evaporating  a  mixed  solution  of  sulphate  of  ammonia  and  sulphate  of 
nickel ;  it  forms  four-sided  prismatic  crystals,  of  a  blue-green  color,  soluble 
in  four  parts  of  cold  water.  Anhydrous  sulphate  of  nickel  absorbs  gaseous 
ammonia,  evolving  heat,  and  forming  a  bulky  pale  blue  powder,  which  gives 
a  blue  solution  in  water,  and  deposits  green  hydrated  oxide :  the  amount  of 
ammonia  absorbed  is  about  56  per  cent.,  so  that  the  compound  may  be  re- 
presented as  3(NH3)NiO,S03.  Sulphate  of  Potassa  and  Nickel  (K.O,'N\0, 
2S03,6HO)  is  obtained  by  evaporating  the  mixed  solution  of  sulphate  of 
nickel  and  sulphate  of  potassa.  It  forms  pale  green  rhomboidal  crystals, 
isomorphous  with  the  corresponding  magnesian  salt.  Double  sulphates  of 
nickel  and  iron,  and  of  nickel  and  zinc,  may  also  be  obtained. 

Phosphate  of  Nickel  3(NiO)P05,  being  nearly  insoluble,  is  precipitated 
upon  adding  phosphate  of  soda  to  a  solution  of  nickel.  It  is  of  a  pale-green 
color,  and  sometimes  forms  a  crystalline  powder. 

Carbide  of  Nickel  occasionally  remains  in  the  form  of  a  shining  powder, 
when  a  button  of  the  metal  which  has  been  fused  for  a  long  time  in  contact 
with  carbon  is  dissolved  in  nitric  acid. 

Carbonate  of  Nickel  (NiOjCO^)  falls  as  a  crystalline  powder  when  a 
solution  of  nitrate  of  nickel  is  dropped  into  a  solution  of  bicarbonate  of 
soda.     There  is  also  a  basic  carbonate. 


444  CHR0311UM    AND    ITS    OXIDES. 

Cyanide  of  Nickel  (NiCy)  is  thrown  down  as  a  green  precipitate  when 
a  soluble  cyanide  is  added  to  a  solution  of  nickel,  or  when  hydrocyanic  is 
mixed  with  acetate  of  nickel. 

PoTASSio-CYANiDE  OF  NiCKEL  (KCy,NiCy). — When  freshly-precipitated 
cyanide  of  nickel  is  dissolved  in  a  solution  of  cyanide  of  potassium,  yellow 
rhombic  prisms  are  obtained  on  evaporation,  which  are  this  double  cyanide 
with  1  atom  of  water.  Similarly  constituted  salts  may  be  obtained  with  the 
cyanides  of  ammonium,  calcium,  and  barium. 

Alloys  of  Nickel. — An  alloy  of  nickel  and  iron  forms  a  principal  metallic 
ingredient  in  most  aerolites  or  meteoric  stones,  and  in  the  masses  of  native 
iron  found  in  various  parts  of  the  world,  in  which  the  proportion  of  nickel 
varies  from  TS  to  8 "5  per  cent.  With  copper,  nickel  forms  a  hard  white  alloy. 
The  lohite  copper  of  the  Chinese,  or  Pakfong,  consists  of  40 '4  parts  of  copper, 
3r6  of  nickel,  25*4  of  zinc,  and  26  of  iron.  A  similar  alloy  is  often  used 
as  a  substitute  for  silver,  or  for  plated  articles,  under  the  name  of  German 
silver ;  it  should  consist  of  8  parts  of  copper,  3  to  4  of  nickel,  and  3j  of 
zinc.  A  variety  of  articles  are  now  plated  with  nickel  by  electrolytic  pre- 
cipitation from  a  solution  of  sulphate  of  nickel,  the  process  Being  similar  to 
that  in  which  copper  is  used. 

Tests  for  the  Salts  of  Nickel. — The  salts  of  nickel  are  green  in  the 
hydrated,  and  yellow  in  the  anhydrous  state.  Their  solutions  have  a  green 
color  and  an  acid  reaction.  1.  Sulphuretted  hydrogen  produces  no  precipitate 
in  an  acid  solution  ;  but  if  acetate  of  soda  is  added  to  the  liquid  in  small 
quantity  ;  there  is  a  dark-brown  or  black  precipitate.  2.  Hydrosulphate  of 
ammonia  gives  a  similar  precipitate,  which  is  only  partially  dissolved  by  an 
excess  of  the  reagent.  3.  Ammonia  gives,  in  neutral  solutions,  a  pale 
greenish  precipitate,  which  is  dissolved  by  an  excess  of  the  alkali,  forming  a 
blue  solution.  The  precipitate  is  also  soluble  in  hydrochlorate  of  ammonia. 
4.  Potassa  gives  a  pale  green  precipitate  of  hydrated  protoxide,  insoluble  in 
an  excess  of  the  alkali,  but  dissolved  by  hydrochlorate  of  ammonia.  Potassa 
in  excess  gives  a  pale  green  precipitate  in  the  blue  solution  formed  by 
ammonia  with  a  salt  of  nickel  (3).  The  blue  solution  of  a  salt  of  copper  in 
ammonia  is  not  affected  by  the  addition  of  potassa.  5.  Alkaline  carbonates 
give  a  similar  precipitate  soluble  in  an  excess  of  carbonate  of  ammonia, 
forming  a  blue  solution.  6.  Ferrocyanide  of  potassium  gives  a  pale  greenish 
precipitate  even  in  the  ammoniacal  solution  of  nickel.  This  test  forms  a  clear 
distinction  between  nickel  and  copper.  The  Ferricyanide  gives  a  greenish- 
yellow  precipitate.  Before  the  blowpipe,  these  salts  give  with  borax  a 
reddish-yellow  bead,  which  becomes  paler  as  it  cools,  and  which,  in  the 
reducing  flame,  yields  grayish  particles  of  reduced  nickel. 

Chromium  (Cr=26). 

Chromium  was  discovered  by  Yauquelin  in  179t.  Its  two  native  combi- 
nations are  the  chromate  of  lead,  and  the  chromite  of  iron,  a  compound  of  the 
oxides  of  chromium  and  iron. 

Metallic  chromium  may  be  obtained  by  intensely  igniting  its  oxide  witli 
about  a  tenth  of  its  weight  of  charcoal,  but  the  reduction  is  difficult  and 
imperfect.  Its  color  resembles  that  of  platinum  ;  it  scratches  glass,  and 
takes  a  good  polish.  Its  sp.  gr.  is  5-9.  It  has  also  been  obtained  by  the 
action  of  potassium  on  chloride  of  chromium,  and  is  then  pulverulent,  burns 
when  heated,  into  an  oxide,  and  is  energetically  acted  on  by  most  of  the 
acids;  whereas,  when  obtained  by  the  usual  modes  of  reduction,  it  is  com- 
paratively fndiflferent  to  the  action  of  powerful  reagents. 

Chromium  and  Oxygen. — There  are  four  oxides  of  chromium — namely, 


CHROMIC    AND    PERCHROMIC    ACIDS.  445 

protoxide,  CrO  ;  a  sesquioxide,  Cr^O. ;  an  intermediate  oxide,  OvO,Qv,p.^', 
and  lastly,  chromic  acid,  CrOg.  In  addition  to  these,  a  perchromic  acid  has 
been  announced,  having  the  formula  Crfij. 

Protoxide  of  Chromium  (CrO)  is  obtained  in  the  form  of  a  brown 
hydrate,  by  the  action  of  potassa  on  the  corresponding  protochloride :  it  is 
unstable,  and  passes  by  the  action  of  air  or  water  into  the  intermediate  oxide, 
which  is  isomorplious  with  the  magnetic  oxide  of  iron. 

Sesquioxide  of  Chromium  (CrgOJ  is  obtained  by  heating  chroraate  of 
mercury,  or  chromate  of  ammonia,  to  dull  redness;  it  is  also  formed  by  the 
action  of  a  red  heat  upon  bichromate  of  potassa  :  in  this  case  neutral  chromate 
of  potassa  is  formed,  which  may  be  removed  by  washing  the  product.  This 
oxide  is  of  a  green  color,  and  not  changed  by  heat,  and  is  much  used  in 
enamel  and  porcelain  painting  ;  it  also  forms  an  ingredient  in  the  pink  color 
of  common  earthenware,  which  is  prepared  by  heating  a  mixture  of  1  part 
of  cliromate  of  potassa  with  30  of  peroxide  of  tin,  and  10  of  chalk,  to  a 
red  heat,  and  then  washing  the  finely-powdered  product  with  dilute  hydro- 
chloric acid.  In  its  hydrated  state  this  oxide  is  obtained  by  precipitation 
from  its  acid  solutions  :  for  this  purpose  a  solution  of  bichromate  of  potassa 
may  be  strongly  acidulated  with  sulphuric  or  hydrochloric  acid,  and  boiled 
with  the  addition  of  a  little  alcohol,  by  which  the  red  salt  is  deoxidized,  and 
a  green  solution  obtained,  from  which  ammonia  throws  down  a  bulky  greenish 
precipitate,  which,  when  washed  and  dried  in  the  air,  is  CryOg.lOHO.  When 
this  hydrate  has  been  heated,  it  shrinks,  and  is  difficultly  soluble.  At  a 
temperature  a  little  below  a  red  heat  it  suddenly  becomes  incandescent.  It 
is  a  weak  base,  and  forms  green  and  purple  solutions ;  the  former  do  not 
crystallize,  but  the  latter  readily  yield  crystallizable  salts.  Native  Sesquioxide 
of  Chromium  has  been  found  in  the  form  of  a  green  incrustation.  It  is  the 
coloring  matter  of  the  emerald,  and  exists  in  a  few  other  minerals,  such  as  a 
diallage  and  some  varieties  of  serpentine. 

Chromic  Acid  (CrOJ. — This  acid  is  most  readily  obtained  by  mixing  4 
measures  of  a  cold  saturated  solution  of  bichromate  of  potassa  with  5  of 
sulphuric  acid  :  the  chromic  acid  separates,  as  the  liquid  cools,  in  crimson 
needles,  which  may  be  dried  upon  a  porous  tile,  under  a  bell-glass.  The 
crystals  are  very  soluble  in  water,  but  sparingly  soluble  in  sulphuric  acid  of 
the  specific  gravity  of  1'55  :  they  are  anhydrous,  and  become  of  a  very  dark 
color  when  heated,  but  resume  their  scarlet  tint  on  cooling  ;  they  fuse  at 
about  400°,  and  when  more  highly  heated  become  incandescent,  giving  off 
oxygen,  and  yielding  sesquioxide.  They  taste  sour  and  metallic.  Chromic 
acid  dissolves  in  alcohol,  and  the  solution  gradually  deposits  green  oxide. 
It  is  a  powerful  oxidizing  and  bleaching  agent,  yielding  half  its  oxygen  to 
oxidizable  bodies,  and  being  reduced  to  sesquioxide  ;  (2Cr03=Cr203-f  O3) : 
hence  a  mixture  of  bichromate  of  potassa  and  sulphuric  acid  is  frequently 
resorted  to  as  a  means  of  oxidizing  organic  bodies.  It  oxidizes  and  turns 
blue  the  precipitated  resin  of  guaiacum.  It  decomposes  a  solution  of  iodide 
of  potassium,  and  sets  free  iodine,  producing  the  usual  blue  color  when 
starch  is  added  to  the  mixture.     It  is  considered  to  be  an  ozonide. 

Perchromic  Acid  {Qvjd^). — When  chromic  acid  is  agitated  with  peroxide 
of  hydrogen,  the  liquid  acquires  a  beautiful  blue  color  (pp.  118,  153)  ;  and 
by  means  of  ether,  the  blue-colored  compound  may  be  separated  from  the 
watery  solution.  It  has  not  been  obtained  in  an  isolated  state,  or  in  com- 
bination with  bases,  but  it  is  supposed  to  be  chromic  acid  in  a  higher  stage 
of  oxidation  ;  and  its  formula  is  assumed  to  be  similar  to  that  of  the  per- 
manganic acid. 

Chromate  of  Potassa  (KOjCrOg)  is  prepared  by  exposing  a  mixture  of 
4  parts  of  powdered  native  chromite  of  iron  with  1  of  nitre,  to  a  strong  heat 


446  CHROMATE    AND    BICHROMATE    OP    POTASSA. 

for  some  hours,  and  washing  out  the  resulting  soluble  matter :  The  process 
is  repeated  until  the  ore  is  decomposed.  The  washings  yield  chromate  of 
potassa  by  evaporation.  This  process  is  now  generally  conducted  so  as  to 
yield  a  bichromate,  by  heating  the  pulverized  chrome-iron  ore  with  carbonate 
of  potassa  and  a  little  nitre  in  a  reverberatory  furnace,  and  constantly  stirring 
the  mixture,  to  complete  the  oxidation  :  the  product  is  then  digested  in 
water,  and  the  yellow  solution  is  supersaturated  by  nitric  acid,  which  throws 
down  silica,  and  by  abstracting  a  portion  of  potassa  leaves  bichromate. 
Chromate  of  potassa  forms  yellow  prismatic  crystals  of  a  disagreeable 
metallic  taste,  soluble  in  about  twice  its  weight  of  water,  and  insoluble  in 
alcohol.  When  heated  to  400°  it  acquires  a  crimson  color,  but  becomes 
again  yellow  on  cooling.  When  fused  it  crystallizes  on  cooling,  but  is  not 
decomposed  except  in  contact  of  carbonaceous  matter,  when  carbonate  of 
potassa  and  oxide  of  chromium  are  produced. 

Bichromate  of  Potassa  (KOjSCrOg)  is  obtained  by  adding  a  sufficiency 
of  sulphuric  or  other  acid  to  a  solution  of  the  chromate  to  give  it  a  sour 
taste,  and  setting  it  aside  for  a  day  or  two,  when  deep  orange-colored  or  red 
crystals  are  de})osited  ;  the  acid  abstracts  half  the  potassa,  and  if  sulphuric 
acid  is  used,  there  is  some  difficulty  in  separating  the  sulphate  from  the 
chromate ;  nitric  acid  is  preferable.  The  crystals  are  anhydrous  prisms, 
permanent  in  the  air,  of  a  metallic  taste,  soluble  in  10  parts  of  water  at  60°, 
and  much  more  soluble  in  boiling  water.  At  a  red  heat  they  fuse  into  a 
transparent  liquid,  which  congeals  into  a  crystalline  mass  on  cooling,  and 
then  falls  to  powder.  At  a  white  heat,  half  the  acid  of  the  salt  is  decom- 
posed, forming  a  mixture  of  oxide  of  chromium  and  neutral  chromate  of 
potassa.  When  3  parts  of  bichromate  of  potassa  are  gently  heated  with  4 
of  sulphuric  acid,  potassio-sulphate  of  chromium  is  formed,  and  oxygen 
evolved:  (KO,2Cr03-|-4(S03,HO)  =  [KO,S03-f CrA,3SOJ-(-4HO  +  30). 
Both  the  chromate  and  bichromate  have  a  deleterious  action  on  the  system 
when  their  solutions  are  brought  much  in  contact  with  the  skin,  causing 
sores  which  are  difficult  to  heal.  Paper  impregnated  with  these  salts  has 
photographic  properties.  The  effect  of  light  is  to  reduce  the  soluble  chromic 
acid  to  the  state  of  insoluble  sesquioxide  of  chromium.  The  drawing  is 
fixed  by  simply  removing  the  unchanged  portion  of  salt  by  washing  in  water. 
Paper  impregnated  with  the  bichromate  of  potash  and  dried  burns  like 
tinder,  undergoing  a  species  of  deflagration.  When  the  bichromate  of 
ammonia  is  used,  the  ash  produced  is  of  a  dark-greenish  black  color,  and  it 
assumes  the  form  of  dried  green  tea  leaves.  Chromic  acid  is  an  ozonide, 
possessing  powerful  bleaching  properties.  When  sulphuric  acid  is  added  to 
it,  it  forms  a  mixture  in  which  various  substances  can  be  bleached.  A 
mixture  of  this  kind  is  used  for  bleaching  phosphorus.  They  have  been  era- 
ployed  for  bleaching  phosphorus  and  other  substances. 

Bichromate  of  Chloride  of  Potassium  (KCl,2Cr03).— When  2  atoms 
of  chromic  acid  and  1  of  chloride  of  potassium  are  dissolved  in  hydrochloric 
acid,  crystals  of  this  salt  may  be  obtained  in  the  form  of  flat  prisms,  having 
the  color  of  the  bichromate.  This  salt  is  permanent  in  the  air,  and  may  be 
dissolved  without  decomposition  in  dilute  hydrochloric  acid  ;  but  by  pure 
water  it  is  resolved  into  hydrochloric  acid  and  bichromate.  Similar  bichro- 
mates of  the  chlorides  of  sodium,  calcium,  magnesium,  and  ammonium  have 
been  formed. 

Chromate  OF  Soda  (NaO,Cr03)  crystallizes  in  oblique  rhombic  prisms  of 
a  fine  yellow  color,  very  soluble  in  water,  and  sparingly  so  in  alcohol. 

Bichromate  of  Soda  (NaO,2CrO,)  is  more  soluble  than  the  preceding  : 
it  forms  prismatic  and  tabular  crystals. 

Chromate  op  Lead  (PbO.CrOa).— When  chromate  of  potassa  is  added 


THE    SALTS    OF    CHROMIUM.  447 

to  any  of  the  soluble  salts  of  lead,  a  fine  yellow  powder  falls,  which  is  the 
neutral  chromate  :  it  is  insoluble  in  water,  but  soluble  in  nitric  acid,  and  in 
solution  of  potassa  :  solution  of  carbonate  of  potassa  fornis  with  it  carbonate 
of  lead  and  chromate  of  potassa.  It  is  decomposed  by  sulphuric  acid,  sul- 
phate of  lead  is  formed,  and  chromic  acid  set  free.  Native  Chromate  of 
Lead  is  of  a  deep  orange-red  color  ;  it  occurs  crystallized  in  prisms,  some- 
what translucent  and  brittle.     Specific  gravity,  6. 

DiCHROMATE  OF  Lead  ;  SuBCHROMATE  OF  Lead,  2(PbO),Cr03,  is  formed 
by  digesting  the  neutral  chromate  in  a  dihite  solution  of  caustic  potassa;  it 
is  of  a  scarlet  color.  These  chromates  of  lead  are  valuable  pigments,  and 
used  both  as  oil  and  water  colors,  and  in  calico-printing  and  dyeing.  The 
mineral  called  Vauquelinite  is  a  double  chromate  of  lead  and  copper,  having 
the  formula  2(PbO)CuO,3Cr03.  The  dark-red  mineral,  which  has  been 
termed  melanochroit,  is  a  sesquichromate  of  lead,  =3PbO,2Cr03. 

Protochloride  of  Chromium  (Or CI)  is  formed  by  passing  hydrogen 
over  the  sesquichloride  at  a  dull  red  heat,  when  a  white  crystalline  mass 
remains,  which  at  a  higher  heat  fuses,  and  on  cooling  presents  a  fibrous 
texture. 

Sesquichloride  of  Chromium  (Cr^Clg)  is  formed  along  with  the  proto- 
chloride in  the  process  just  described  :  it  is  also  obtained  by  evaporating  to 
dryness  the  hydrochloric  solution  of  the  sesquioxide,  and  heating  the  residue 
intensely  in  a  retort,  or  in  a  stream  of  chlorine ;  it  forms  a  crystalline  pink 
sublimate,  which  yields  a  green  solution  with  water. 

OxYCHLORiDE  OF  CHROMIUM;  Chromate  of  Terchloride  of  Chromium; 
Chlorochromic  Acid  (CrCl3,2Cr03). — This  compound  is  obtained  by  heating 
a  mixture  of  chromate  of  potassa,  chloride  of  sodium,  and  sulphuric  acid  ; 
sulphate  of  potassa  and  sulphate  of  soda  remain  in  the  retort,  and  the  oxy- 
chlorite  of  chromium  distils  over':  3(KO,Cr03)+3NaCl-f-6S03=3(KO,803) 
-f  3(NaO,S03)  +  (CrCl3,2Cr03).  It  is  a  fuming  liquid  of  a  deep  red  color: 
it  decomposes  water,  forming  chromic  and  hydrochloric  acids.  When  passed 
through  a  red  hot  tube,  it  is  resolved  into  oxygen,  chlorine,  and  sesquioxide 
of  chromium:  2(CrCl3,2Cr03)  =  3(Cr,03)-f03-+-Cl8. 

Terfluoride  OF  Chromium  (CrFg)  is  obtained  by  distilling  4  parts  of 
chromate  of  lead,  3  of  powdered  fluor-spar,  and  8  of  sulphuric  acid,  in  a 
platinum  retort :  the  vapor  which  passes  over  may  be  condensed  by  cold 
into  a  red  liquid,  which  is  converted  by  the  moisture  of  the  air  into  chromic 
and  hydrofluoric  acids  :  CrF3+3UO,  =  Cr03+3HF. 

Sesquisulphide  of  Chromium  (Cr^^Sa)  is  formed  by  passing  the  vapor  of 
sulphide  of  carbon  through  a  red-hot  porcelain  tube  containing  protoxide 
of  chromium  :  it  is  of  a  dark-gray  color,  and  when  heated  in  the  air  it  burns 
into  oxide.     It  is  a  weak  sulphur  base,  and  forms  a  few  sulphur  salts. 

Sulphate  of  Chromium. — When  a  solution  of  8  parts  of  hydrated  oxide 
of  chromium  in  9  of  sulphuric  acid  is  exposed  to  the  air  in  a  covered  basin 
it  concretes  in  a  few  weeks  into  a  blue-green  crystalline  mass;  when  this  is 
dissolved  in  water,  and  alcohol  added,  a  blue  crystalline  compound  falls, 
soluble  in  about  its  weight  of  water  at  60°  :  it  consists  of  Crjj03,3S03,15HO. 
With  sulphate  of  potassa  it  forms  a  beautiful  double  salt,  which  crystallizes, 
in  green  and  purple  octahedra,  and  has  been  termed  chrome  alum,  its  formula 
being  K0,S03,  H-Cr203,3S03,  +  24HO.  It  also  forms  a  similar  aluminoid 
compound  with  sulphate  of  ammonia, =NH40,S03+Cr303,3S03,H-24HO. 
This  blue  sulphate,  when  heated  to  212°,  becomes  green,  losing  10  atoms  of 
water,  and  though  soluble,  is  no  longer  crystallizable.  If  either  of  these 
sulphates  is  heated  to  about  700°,  a  red  insoluble  anhydrous  salt  remains 
=  Cr303,3S03,  which,  however,  by  long  digestion  in  water,  reverts  to  the 
soluble  varieties. 


448  VANADIUM    AND    ITS    COMPOUNDS. 

Tests  for  the  Compounds  of  Chromium. — The  sesquisalts  of  this  metal 
are  of  various  shades  of  green,  blue,  or  purple,  and  their  solutions  are  usually 
red  by  transmitted  light.  1.  With  potassa  and  soda,  and  their  carhonates, 
they  give  green  precipitates,  soluble  in  an  excess  of  the  precipitant,  forming 
green  solutions,  but  again  thrown  down  as  anhydrous  oxide  on  boiling  the 
liquid.  2.  Ammonia  and  the  hydrosulphate  of  ammonia  throw  down  a  bluish- 
green  hydrated  oxide,  partially  soluble  in  excess  of  ammonia,  forming  a  pink 
solution.  Carbonate  of  ammonia  acts  in  a  similar  manner.  The  salts  of  the 
protoxide  soon  absorb  oxygen,  and  are  decomposed,  or  pass  into  sesquisalts. 

The  chromates  are  all  deeply  colored :  they  are  decomposed  when  boiled 
with  deoxidizing  agents  (grape-sugar,  arsenious  acid,  alcohol,  wood-spirits), 
and  the  sesquioxide  is  formed.  A  solution  of  chromate  of  potassa  gives  a 
characteristic  yellow  precipitate  with  the  soluble  salts  of  lead,  orange  with 
those  of  mercury,  and  red  with  those  of  silver.  A  compound  of  chromium 
fused  at  a  high  temperature,  with  a  mixture  of  carbonate  of  soda  and  chlorate 
of  potassa,  forms  a  soluble  chromate  of  the  alkali,  producing  a  yellow  solu- 
tion in  water,  which  may  be  tested  in  the  manner  above  described.  Before 
the  blowpipe,  they  color  borax  green  in  the  interior,  and  yellow  or  red  in 
the  exterior  flame. 


CHAPTER    XXXIV. 

VANADIUM  — TUNGSTEN— CO  LUMBIUM  — NIOBIUM  — I LMENIUM 
—  NORIUM  —  PELOPIUM— MOLYBDENUM  — URANIUM— TELLU- 
RIUM—TITANIUM. 

Vanadium  (Y=68). 

This  metal  was  discovered  in  1830,  and  named  after  Vanadis,  a  Scandi- 
navian deity.  It  occurs  in  certain  iron  and  lead  ores.  Mr.  Riley  states  that 
he  has  found  this  rare  metal  in  the  Wiltshire  oolitic  iron-ore,  and  in  the  pig- 
iron,  smelted  from  it.  This  will  yield  it  readily,  as  it  contains  more  vanadium 
than  that  obtained  from  the  Taberg  ore  of  Sweden.  Vanadium  is  procured 
by  decomposing  chloride  of  vanadium  by  a  current  of  dry  ammonia,  in  a  glass 
tube  heated  over  a  spirit-lamp  ;  sal-ammoniac  sublimes,  and  metallic  vana- 
dium remains.  It  may  also  be  obtained  by  heating  vanadic  acid  with 
potassium. 

Vanadium  has  a  silvery  lustre,  is  brittle,  and  not  acted  upon  by  air  or 
water  at  common  temperatures;  at  a  dull  red  heat  it  burns  into  a  black 
oxide ;  it  is  not  acted  upon  by'sulphuric  or  hydrochloric  acid,  but  nitric  and 
nitrohydrochloric  acids  yield  with  it  dark-blue  solutions. 

Oxides  of  Vanadium. — There  are  three  compounds  of  this  metal  with 
oxygen  ;  two  oxides,  and  an  acid. — Protoxide  of  Vanadium  ( VO).  When 
a  stream  of  dry  hydrogen  gas  is  passed  over  heated  vanadic  acid,  water  is 
formed,  and  a  black  substance  remains,  which  is  infusible,  and  which,  when 
heated  in  the  air,  is  converted  by  slow  combustion  into  the  binoxide.  It  is 
not  salifiable. — Binoxide  of  Vanadium:  Vanadious  Acid  {YO,^).  This  is 
the  only  salifiable  oxide :  it  may  be  obtamed  in  the  state  of  hydrate,  by  pre- 
cipitation from  its  acid  solutions  by  carbonate  of  soda  in  very  slight  excess. 
It  yields  blue  solutions  with  the  acids,  and  dissolves  in  caustic  potassa  and 
in  ammonia,  forming  brown  liquids.—  Vanadic  Acid  (VO3).  When  vanadate 
of  ammonia  is  heated  in  an  open  vessel  it  acquires  a  red  color,  and  leaves 


TUNGSTEN    AND    ITS    COMPOUNDS    WITH    OXYGEN.  449 

vanadlc  acid:  heated  in  a  close  vessel,  the  hydrogen  of  the  anitnonia  deoxi- 
dizes the  acid,  and  the  binoxide  is  the  product.  Vanadic  acid,  when  fused, 
is  red,  but  when  in  powder,  brown  :  it  fuses  at  a  dull  red  heat,  and  in  the 
act  of  cooling  it  contracts  in  bulk,  and  becomes  incandescent.  It  undergoes 
no  change  by  heat,  provided  deoxidizing  agents  are  excluded  ;  but  when  com- 
bustible matter  is  present  it  passes  into  oxide  :  it  is  tasteless,  insoluble  in 
alcohol,  and  nearly*  so  in  water  —  Vanadates,  These  compounds  are  gene- 
rally yellow,  but  sometimes  are  produced  colorless,  without  apparent  change 
of  composition,  and  give  a  blue  solution,  distinctly  opposed  to  the  green  of 
chromium.  The  soluble  vanadates  are  deoxidized  by  alcohol,  sulphuretted 
hydrogen,  and  sulphurous  acid.  Vanadic  acid  dissolves  and  forms  colored 
compounds  with  the  binoxide :  they  are  formed  when  the  binoxide  in  water 
is  exposed  to  air;  it  gradually  forms  vanadic  acid,  and  the  solution  becomes 
blue,  green,  yellow,  and  red,  according  to  the  extent  of  acidification. 

Vanadium  combines  with  chlorine,  bromine,  iodine,  sulphur,  and  cyanogen. 
—  Chloride  of  Vanadium.  When  dry  chlorine  is  passed  over  a  red-heated 
mixture  of  protoxide  of  vanadium  and  charcoal,  in  a  glass  tube,  a  yellow 
liquid  is  obtained,  which  when  acted  upon  by  water  yields  hydrochloric  and 
vanadic  acids :  it  is  therefore  a  terchloride  (VC1.J. — Sulphide  of  Vanadium. 
By  passing  sulphuretted  hydrogen  over  the  binoxide  heated  to  redness,  a 
hisidphide  if  formed.  When  sulphuretted  hydrogen  is  passed  through  vana- 
dic acid  in  water,  a  mixture  of  hydrated  binoxide  and  sulphur  is  precipitated  ; 
but  when  a  solution  of  vanadic  acid  in  hydrosulphate  of  ammonia  is  acidu- 
lated by  hydrochloric  acid,  a  brown  hydrated  tersulphide  subsides. 

Tungsten  (W=92). 

This  metal,  called  also  Wolframium,  was  discovered  in  1781.  It  derives 
its  name  tungsten  from  two  Swedish  words,  signifying  heavy  stone.  Its 
native' sources  are  wolfram,  which  is  a  tungstate  of  iron  and  manganese, =^ 
MnO,W03,  +  3(FeO,W03),  and  tungstate  of  lime,  CaO.WOg.  It  is  obtained 
by  passing  hydrogen  over  ignited  tungstic  acid  mixed  with  charcoal.  It  is 
very  difficult  of  fusion,  hard,  brittle,  and  of  an  iron-gray  color.  Its  specific 
gravity  is  It  6.  It  is  oxidized  by  the  action  of  heat  and  air,  and  by  nitric 
acid.  It  is  also  oxidized  and  gradually  dissolved  by  a  solution  of  potassa, 
with  the  evolution  of  hydrogen,  and  tungstate  o{  potassa  is  produced^ — Oxide 
of  Tungsten  ;  Binoxide  of  Tungsten  (WO^).  This  oxide  may  be  obtained  by 
mixing  finely-powdered  wolfram  with  twice  its  weight  of  carbonate  of  potassa, 
and  fusing  it  in  a  platinum  crucible.  Tungstate  of  potassa  is  thus  formed, 
which  is  dissolved  in  hot  water  with  half  its  weight  of  sal-ammoniac,  evapo- 
rated to  dryness,  and  heated  red  hot  in  a  Hessian  crucible.  The  mass  is 
then  well  washed  in  boiling  water,  and  digested  in  a  weak  solution  of  potassa. 
The  residue  is  oxide  of  tungsten.  Thus  prepared,  the  oxide  is  black,  and 
when  heated  to  redness  it  suddenly  ignites  and  burns  into  tungstic  acid.  It 
does  not  combine  with  acids.  When  a  current  of  hydrogen  is  passed  over 
heated  tungstic  acid,  it  is  partially  deoxidized  and  converted  into  a  chocolate- 
colored  oxide,  which  neither  combines  with  acids  nor  bases,  and  which  is 
identical  in  composition  with  the  above.  If  the  action  of  hydrogen  be  con- 
tinued, the  oxide  itself  is  reduced. 

A  compound  of  this  oxide  with  soda  is  obtained  by  adding  as  much  tung- 
stic acid  to  fused  tungstate  of  soda  as  it  will  dissolve,  and  then  passing  hy- 
drogen over  the  compound  at  a  red  heat ;  on  washing  out  the  undecomposed 
tungstate  with  water,  a  golden-colored  substance  remains,  in  cubes  and  scales- 
of  a  metallic  lustre,  and  insoluble  in  caustic  alkalies  and  in  nitric,  sulphuric, 
and  nitrohydrochloric  acids,  but  soluble  in  hydrofluoric  acid. 
29 


459  COLUMBIUM. 

TuNGSTic  Acid  (WO,)  is  obtained  when  the  oxide  is  heated  red  hot,  and 
stirred  in  an  open  vessel.  When  finely-powdered  native  tnngstate  of  lime  is 
boiled  for  some  hours  in  nitric  acid,  tungstic  acid  is  separated,  in  the  form  of 
a  yellow  powder,  which  may  be  freed  from  adherinf?  nitric  acid  by  dissolving 
it  in  ammonia  and  heating  the  tungstate  of  ammonia  to  redness.  Tungstic 
acid  is  a  yellowish  powder,  insoluble  in  water,  but  soluble  in  the  caustic  alka- 
lies, when  in  its  hydrated  state  ;  after  it  has  been  heated  it  is  difficultly  acted 
upon  by  solvents,  but  most  of  its  compounds  may  be  obtained  by  fusion  at  a 
red  heat.  The  tungstate  of  soda  is  employed  for  the  purpose  of  rendering 
cotton  and  linen  unintiammable.  The  most  delicate  lace  impregnated  with 
a  weak  solution  of  this  salt  dried  and  burnt,  is  converted  into  carbon  without 
inflaming. 

Chloride  of  Tungsten  (WClg). — When  tungsten  is  heated  in  chlorine, 
it  forms  a  red  crystalline  compound,  fusible,  and  volatile,  which  becomes  blue 
in  water. — Perchloride  of  Tungsten  (WCI3).  When  sulphide  of  tungsten  is 
heated  in  chlorine,  it  forms  a  perchloride,  which  condenses  in  red  crystals. 
This  chloride  is  resolved  by  the  moisture  of  the  air  into  tungstic  and  hydro- 
chloric acids. 

Sulphide  op  Tungsten. — When  sulphuretted  hydrogen  is  passsd  over 
tungstic  acid  heated  highly  in  a  porcelain  tube,  a  black  powder  is  obtained, 
which  is  a  bisulphide  =WS2. 

Characters  of  the  Compounds  of  Tungsten. — Before  the  blowpipe, 
tungstic  acid  becomes  upon  charcoal  at  first  a  brownish-yellow,  is  then  reduced 
to  a  brown  oxide,  and  lastly  becomes  black  without  melting  or  smoking. 
With  microcosmicsalt,  in  the  internal  flame,  and  in  small  proportion,  it  forms 
a  blue-colored-glass ;  if  iron  is  present  the  color  is  blood-red. 

The  tungstates  of  the  alkalies  are  colorless,  and  form  colorless  solutions. 
When  a  little  hydrochloric  acid  is  added,  and  a  bar  of  zinc  is  placed  in  the 
solution,  the  liquid  soon  acquires  a  rich  blue  color  from  the  production  of 
oxide  of  tungsten.  The  presence  of  this  metal  in  any  mineral  may  be  thus 
easily  recognized.  The  substance  should  be  powdered,  and  fused  with  four 
times  its  weight  of  carbonate  of  soda  mixed  with  some  nitre.  A  soluble 
tungstate  is  thus  produced,  which  may  be  tested  by  the  process  above  described. 
Mineral  acids,  excepting  the  phosphoric,  precipitate  tungstic  acid  from  solu- 
tion of  tungstates,  in  an  insoluble  form. 

CoLUMBiUM  (Ta=184). 

This  metal,  called  also  Tantalum,  was  discovered  in  1801,  in  a  mineral 
from  North  America  (Columbia).  It  was  afterwards  found  in  the  minerals 
called  tantalite,  yttro-tantalite,  and  Fergusonite.  Columbiura  has  been  obtained 
by  heating  potassium  with  the  potassio-fliwride  of  columbium,  and  washing 
the  reduced  mass  with  water.  It  remains  in  the  form  of  a  black  powder ; 
by  pressure  it  acquires  the  lustre  and  color  of  iron  ;  it  burns  at  a  red  heat 
into  whitish  oxide.  It  is  insoluble  or  nearly  so,  in  most  acids.  Heated  to 
redness,  it  burns  into  columbic  acid. 

Oxide  of  Columbium  ;  Tantalous  Acid  (TaO^).— When  columbic  acid  is 
intensely  heated  in  a  charcoal  crucible,  it  is  superficially  reduced  to  a  metallic 
state,  but  the  interior  portion  is  a  dark-gray  oxide,  becoming  brown  when 
pulverized  ;  it  is  insoluble  in  the  acids,  but  may  be  peroxidized  by  fusion 
with  potassa. 

Columbic  Acid  ;  Tantalic  Acid  (TaOg)  is  obtained  by  fusing  finely- 
powdered  tantalite  with  caustic  potassa ;  a  soluble  columbate  of  potassa  is 
formed,  from  which  columbic  acid  may  be  precipitated,  as  a  white  hydrate, 
by  acids.  After  having  been  ignited,  it  is  nearly  insoluble  in  acids,  but  solu- 
ble in  potassa.     The  hydrated    acid  (Ta03,3HO)  dissolves  in  potassa,  in 


OXIDES    OF    MOLYBDENUxM.  451 

nitric,  hydrochloric,  hydrofluoric,  sulphuric,  tartaric,  citric,  and  oxalic  acids. 
It  is  dissolved  by  a  solution  of  birioxalate  of  potassa,  but  scarcely  at  all  by 
bitartrateof  potassa.  It  is  ap:ain  precipitated  from  its  acid  solutions  by  alka- 
line carbonates.  Ferrocyanide  of  potassium  produces  a  yellow  ;  infusion  of 
galls  an  orange;  and  the  hydrosulphates  a  white  precipitate  in  the  oxalic 
solution.  Tantalic  acid  is  precipitated  by  water  from  its  solution  in  sul- 
phuric acid,  and  when  this  precipitate  is  dissolved  by  diluted  hydrochloric 
acid,  and  a  bar  of  zinc  is  introduced,  the  liquid  at  first  acquires  a  blue  color, 
and  afterwards  becomes  brown.     (Will  ) 

Niobium.  Ilmenium.  Norium.  Pelopium. — Among  these  rare  metals, 
the  two  first-mentioned  have  been  announced  as  associated  with  colurabium 
in  some  varieties  of  tantalite,  but  their  distinctive  characters  have  been  as  yet 
very  imperfectly  ascertained.  Niobium  is  considered  by  some  chemists  to  be 
columbium,  while  the  metal  pelopium  has  no  independent  existence,  the  pe- 
lopic  and  niobic  acids  being  identical.  Yon  Kobell  has  announced  another 
metal  of  this  series,  to  which  he  has  given  the  name  of  Dianium.  He  states 
tiiat  it  exists  in  the  columbite  of  Tammela,  in  euxenite,  and  other  minerals. 
Rose  and  St.  Clair  Deville,  who  have  examined  these  minerals,  affirm  that 
the  supposed  dianic  acid  is  hyponiobic  acid.  Dianium,  therefore,  is  identical 
with  Pelopium  and  Columbium  {Cosmos,  Janvier,  1862,  p.  28). 
• 

Molybdenum  (Mo=48). 

This  metal  derives  its  name  from  the  Greek  fio-Kv^^atva  (a  mass  of  lead), 
owing  to  the  res'emblance  of  the  native  bisulphide  to  lead.  It  was  discovered 
in  1782.  The  bisulphide  is  its  principal  ore;  there  is  also  a  native  molyh- 
date  of  lead.  To  procure  molybdenum,  the  pulverized  native  sulphide  is 
roasted  in  a  muffle,  so  as  to  burn  off  the  sulphur ;  a  gray  powder  remains, 
which  is  digested  in  ammonia,  and  the  solution  filtered  and  evaporated  to 
dryness :  the  dry  residue  is  then  dissolved  in  nitric  acid,  and  again  evapo- 
rated to  dryness,  when  pure  molybdic  acid  is  left.  If  this  be  made  into  a 
paste  with  oil  and  charcoal,  and  intensely  heated,  the  metal  remains.  It 
may  also  be  obtained  by  passing  hydrogen  over  molybdic  acid  at  a  red  heat 
in  a  porcelain  tube. 

Molybdenum  is  a  whitish,  brittle,  and  very  difficultly-fusible  metal ;  when 
intensely  heated  in  the  air,  it  produces  a  white  crystalline  sublimate  of  mo- 
lybdic acid.  It  forms  three  compounds  with  oxygen,  two  of  which  are  sali- 
fiable, and  the  third  an  oxide. 

Protoxide  of  Molybdenum  (MoO)  is  obtained  by  dissolving  molybdic 
acid  in  hydrochloric  acid,  and  putting  a  piece  of  zinc  into  the  solution  :  the 
liquid  changes  to  blue,  red,  and  black  ;  excess  of  ammonia  is  then  added,  by 
which  protoxide  of  molybdenum  is  thrown  down  in  the  form  of  a  black 
hydrate,  whilst  the  oxide  of  zinc  is  retained  in  solution.  In  the  state  of 
hydrate,  this  oxide  is  soluble  in  the  acids,  but  when  anhydrous,  it  is  almost 
insoluble.  It  is  not  dissolved  by  the  caustic  and  carbonated  alkalies,  but 
the  recently-precipitated  hydrate  is  soluble  in  carbonate  of  ammonia. 

Deutoxide  of  Molybdenum  (MoOJ. — This  oxide  is  obtained  by  heating 
a  mixture  of  sal-ammoniac  and  molybdate  of  soda  in  a  platinum  cruoible 
until  the  fumes  cease:  the  residue  is  well  washed,  digested  in  caustic  potassa 
to  separate  any  molybdic  acid,  and  again  washed  with  boiling  water.  The 
oxide  remains  in  the  form  of  a  black  powder,  becoming  dark-brown  when 
dry,  and  purple  when  exposed  to  the  sun's  rays.  Although  zinc  reduces 
molybdic  acid  to  the  state  of  protoxide,  copper  only  brings  it  down  to  deut- 
oxide; if  therefore,  copper,  molybdic  acid,  and  hydrochloric  acid  are  put 
together,  the  molybdic  acid  disappears,  and  the  liquid,  which  contains  the 
chlorides  of  copper  and  molybdenum,  acquires  a  deep-red  tint.     When  au 


452  MOLYBDIC    ACID.      MOLYBDATES. 

excess  of  ammonia  is  added  to  the  liquid,  the  dentoxide  of  molybdenum  is 
thrown  down,  and  the  oxide  of  copper  is  retained  in  solution ;  the  precipi- 
tate is  cleansed  by  washing  with  solution  of  ammonia,  and  when  carefully 
dried  in  vacuo  over  sulphuric  acid,  is  the  hydrated  deutoxide.  It  is  brown, 
slightly  soluble  in  water,  and  insoluble  in  saline  solutions  and  in  caustic 
alkalies,  but  soluble  in  their  carbonates.  When  heated  in  vacuo,  it  becomes 
dark  brown,  and  loses  its  solubility. 

Molyhdous  Acid. — When  metallic  molybdenum  and  molybdic  acid  are 
boiled  together  in  water,  a  blue  solution  is  formed,  which  has  sometimes 
been  termed  molyhdous  acid,  and  regarded  as  a  distinct  stage  of  oxidation, 
but  which  appears  to  be  a  compound  of  molybdic  acid  with  the  deutoxide, 
and  consequently  a  molybdate  of  oxide  of  molybdenum  =Mo02,  +  Mo03. 
When  a  current  of  hydrogen  is  passed  over  molybdic  acid  at  a  dull  red  heat, 
it  acquires  a  blue  color,  and  becomes  converted  into  molyhdous  acid.  Tliis 
compound  is  soluble  in  water,  and  yields  a  rich  blue  solution,  which  becomes 
colorless  on  moderate  dilution:  it  is  insoluble  in  a  solution  of  sal-ammoniac; 
it  is  immediately  converted  into  molybdic  acid  by  nitric  acid  and  chlorine; 
and,  on  the  other  hand,  deoxidizing  agents,  such  as  protochloride  of  tin,  or 
tin  filings  and  hydrochloric  acid,  convert  molybdic  acid  into  this  blue  com- 
pound. 

Molybdic  Acid  (M0O3) The  production  of  this  acid  has  alreai^r  been 

described.  It  is  a  white,  difl&cultly-soluble  powder.  Heated  to  redness  in 
an  open  vessel,  it  slowly  sublimes,  and  condenses  in  yellowish  scales.  It 
dissolves  in  hot  sulphuric  acid,  forming  a  solution  which  is  colorless  while 
hot,  but  on  cooling  acquires  a  blue  color,  which  is  heightened  by  the  addi- 
tion of  soda.  Its  hydrochloric  solution  is  pale  yellowish-green,  but  becomes 
blue  when  neutralized  by  potassa.  It  dissolves  in  the  alkalies,  forming  solu- 
tions which  are  colorless,  and  from  which  the  molybdic  acid  is  at  first  pre- 
cipitated, but  afterwards  dissolved,  by  the  stronger  acids.  It  unites  with 
bases  and  forms  neutral  and  acid  salts.  The  molybdic  acid  has  been  lately 
recommended  by  F.  Frohde  as  a  more  reliable  test  for  morphia  than  nitric 
acid.  The  molybdic  acid  is  dissolved  in  strong  'sulphuric  acid,  and  a  drop 
of  this  solution  is  added  to  morphia  or  any  of  its  salts  (in  a  dry  state),  when 
a  violet  color  is  produced;  this  passes  to  a  blue,  aud  afterwards  to  a  dingy 
green,  leaving  a  nearly  colorless  spot. 

Molybdate  of  Ammonia  (NHp,Mo03). — This  salt  is  obtained  by  dis- 
solving molybdic  acid  in  excess  of  ammonia,  and  leaving  it  to  spontaneous 
crystallization  :  it  forms  square  prisms,  of  a  pungent  metallic  taste.  When 
the  ammoniacal  solution  is  boiled  down,  it  atfords,  on  cooling,  a  crystalline 
mass  of  himolyhdate  of  ammonia,  which,  by  spontaneous  evaporation,  may  be 
obtained  in  rhombic  crystals  of  a  pale  bluish-green  color,  and  difficultly  solu- 
ble in  water.  A  solution  of  this  salt  is  occasionally  employed  as  a  test  for 
phosphoric  acid.  The  suspected  solution  of  phosphate  is  acidulated  with 
nitric  acid,  and  the  molybdate  is  then  added.  If  a  phosphate  is  present 
the  liquid  becomes  yellow,  and  in  boiling  it  a  yellow  crystalline  precipitate 
is  obtained,  the  insoluble  phospho-molybdate  of  ammonia.  The  phospho- 
molybdic  acid  is  used  as  a  precipitant  for  the  alkaloids,  but  it  has  no  advan- 
tage over  the  iodo-hydrargyrate  of  potash,  which  does  not  form  an  insoluble 
compound  with  ammonia,  or  precipitate  that  alkali. 

Protochloride  of  Molybdenum  (MoCl).— When  the  vapor  of  bichloride 
of  molybdenum  is  passed  over  molybdenum  heated  nearly  to  redness,  a  deep 
red  compound  is  obtained,  which  yields  a  crystalline  sublimate  when  heated 
in  an  open  tube  :  it  is  insoluble  in  water,  but  is  decomposed  by  a  solution  of 
potassa,  yielding  hydrated  protoxide  of  molybdenum.  This  chloride  forms 
double  salts  with  sal-ammouiac  and  with  chloride  of  potassium. 


•  TESTS    FOR    TFIE    SALTS    OF    MOLYBDENUM.      URANIUM.  453 

Bichloride  of  Molybdenum  (MoClo)  is  formed  by  heatin/?  metallic  mo- 
lybdenum in  dry  chlorine;  the  metal  burns,  and  a  red  vapor  fills  the  retort, 
which  condenses  into  crystals  resembling  iodine ;  they  are  fusible,  volatile, 
and  in  the  air  first  fume,  and  then  deliquesce  into  a  black  liquid,  which 
changes  color  in  proportion  to  the  water  it  absorbs,  becoming  blue-green, 
green-yellow,  dark  red,  rose-colored,  and  lastly,  yellow.  This  chloride  forms 
a  double  ammonio-chloride  of  molybdenum  with  sal-ammoniac,  but  does  not 
combine  with  the  chlorides  of  potassium  or  sodium. 

Chloromolyhdic  Acid. — When  a  current  of  chlorine  is  passed  over  gently- 
heated  binoxide  of  molybdenum,  a  yellowish  crystalline  sublimate  is  formed, 
and  molybdic  acid  remains  in  the  tube:  this  compound  is  less  volatile  than 
the  bichloride.  It  readily  dissolves  in  water,  and  alcohol.  It  is  a  com- 
pound of  molybdic  acid  with  perchloride  of  molybdenum  =MoCl3,2Mo03. 

There  are  three  Sulphides  of  Molybdenum,  two  of  which  correspond 
with  the  deutoxide  and  with  molybdic  acid,  and  the  third  contains  4  equiva- 
lents of  sulphur ;  no  protosulphide  corresponding  with  the  protoxide  has 
been  formed. — Bisulphide  of  molybdenum  (MoS^)  is  produced  artificially  by 
intensely  heating  a  mixture  of  molybdic  acid  and  sulphur,  out  of  the  contact 
of  air.  It  forms  the  native  sulphide.  —  Tersulphide  of  Molybdenum  (M0S3)  is 
obtained  by  saturating  a  strong  solution  of  a  molybdic  salt  with  sulphuretted 
hydrogen,  and  then  adding  hydrochloric  acid;  a  dark-brown  precipitate 
falls,  which  becomes  black  on  drying,  and  which,  when  heated  in  close 
vessels,  gives  off  sulphur,  and  becomes  bisulphide.  The  sulphide  combines 
with  the  sulphides  of  the  alkaline  bases,  and  produces  a  class  of  sulphur- 
salts,  which  may  be  called  molybdo-tersulphides,  some  of  which  form  beautiful 
iridescent  crystals. — Persulphide  of  Molybdenum  (MoS^)  is  obtained  by  satu- 
rating bimolybdate  of  potassa  with  sulphuretted  hydrogen,  and  boiling  the 
solution  for  some  hours  in  a  retort :  when  it  cools,  a  black  powder  and  red 
scales  are  deposited,  which  must  be  separated  as  far  as  possible  :  the  red 
deposit  is  then  washed  upon  a  filter  with  water,  till  the  washings  no  longer 
afford  a  red  (not  a  brown)  precipitate  with  hydrochloric  acid ;  the  residue 
upon  the  filter  is  then  treated  by  boiling  water,  and  the  dark-red  solution 
which  filters  through  is  decomposed  by  excess  of  hydrochloric  acid  :  a  brown 
precipitate  falls,  which,  when  washed  and  dried,  is  the  quadrisulphide. 

Tests  for  the  Salts  of  Molybdenum. — 1.  The  protosalts  give  brown 
precipitates  with  the  alkalies  and  their  carbonates,  soluble  in  excess  of  car- 
bonate of  ammonia,  but  not  of  the  alkali.  2.  Sulphuretted  hydrogen  gives 
a  brown  precipitate,  soluble  in  hydrosulphate  of  ammonia.  3.  The  salts  of 
the  deutoxide  give  brown  precipitates  with  ammonia,  and  with  ferrocyanide 
of  potassium.  4.  The  molybdates  are  characterized  by  the  blue  color  pro- 
duced on  the  addition  of  a  few  drops  of  protochloride  of  tin,  and  by  the  blue 
color  produced  by  zinc  in  their  solutions,  when  acidulated  with  hydrochloric 
acid.  This,  after  a  time,  becomes  green,  and  ultimately  black.  When  a 
mineral  containing  molybdenum  is  fused  with  carbonate  of  soda  and  nitre,  a 
soluble  molybdate  of  the  alkali  is  obtained.  Molybdic  acid  is  precipitated 
from  its  solutions  by  a  mineral  acid,  but  the  precipitate  is  soluble  in  an  ex- 
cess of  the  acid.  This  forms  a  distinction  between  the  molybdic  and  tungstic 
acids.  The  oxides  of  molybdenum  give  to  microcosmic  salt  in  the  inner 
flame  of  the  blowpipe  a  green  color,  and  to  borax  a  brown-red  color. 

Uranium  (XJ==60). 

Uranium  (named  from  the  planet  Uranus)  was  discovered  in  1789,  in  a 
mineral  called  pitchblende,  which  is  an  impure  oxide,  and  from  which  the 
metal  and  its  compounds  are  almost  exclusively  obtained.  It  also  occurs,  in 
the  form  of  a  double  phosphate  of  lime  and  uranium,  in  uranite,  a  rare  mica- 


454  SALTS    OF    URANIUM. 

ceons  mineral ;  and  in  a  similar  mineral  of  a  green  color,  called  chalcolite,  in 
which  the  lime  is  replaced  by  oxide  of  copper. 

Uranium  is  obtained  by  the  decomposition  of  its  chloride  by  sodium,  the 
process  being  similar  to  that  by  which  majGrnesium  is  obtained  :  it  is  white, 
slightly  malleable,  and  unchanged  by  air  and  water  at  common  temperatures; 
when  heated  in  air,  it  undergoes  combustion  and  is  converted  into  an  oxide. 

Oxides  of  Uranium. — Uranium  forms  four  oxides — namely,  a  protoxide, 
a  sesquioxide,  and  two  intermediate  oxides. — Protoxide  of  Uranium  (^0) 
is  formed  by  heating  the  peroxalate  out  of  contact  of  air :  it  is  brown,  and, 
when  in  the  state  of  hydrate,  dissolves  in  the  acids,  forming  green  salts. 
"When  heated  to  redness,  and  suddenly  cooled,  it  becomes  the  hlack  oxide 
(U4OJ,  which  is  used  in  porcelain  painting  for  the  production  of  an  intense 
black.  —  Green  Oxide  of  Uranium  (U3O4)  is  obtained  by  evaporating  an 
ethereal  solution  of  nitrate  of  uranium,  and  exposing  the  residue  to  a  red 
heat. — Per  or  Sesquioxide  of  Uranium  (U2O3).  Uranium  and  its  inferior 
oxides  pass  into  peroxide  when  acted  upon  by  nitric  acid,  forming  a  yellow 
solution,  from  which  the  alkalies  throw  down  compounds  of  the  peroxide 
with  the  precipitants.  A  pure  hydrate  of  the  peroxide  nray,  however,  be 
obtained  by  evaporating  the  alcoholic  solution  of  the  pernitrate  until  it 
effervesces  in  consequence  of  the  escape  of  nitrous  ether;  the  yellow  residue, 
washed  first  with  cold  and  then  with  hot  water,  leaves  the  hydrate,  assuming, 
when  dried  at  212°,  the  form  of  a  yellow  powder  =UyO.„HO,  but  if  dried  in 
vacuo  =U20o,2HO.  At  a  high  temperature  (about  570°)  it  becomes  anhy- 
drous, and  afterwards  loses  oxygen,  and  leaves  a  brown  mixture  of  protoxide 
and  green  oxide  :  in  its  anhydrous  state  it  is  red. 

The  salts  of  the  peroxide  of  uranium  are  best  formed  by  the  action  of 
nitric  acid  upon  the  salts  of  the  lower  oxides.  They  are  yellow,  and  mostly 
soluble  in  water,  and  are  reduced  to  protosalts  by  sulphuretted  hydrogen, 
and  by  alcohol  and  ether  under  the  influence  of  solar  light.  Peroxide  of 
uranium  unites  to  bases  ^oxxnmg  uranates ;  those  of  the  alkalies  are  obtained 
by  precipitating  the  uranic  salts  with  them.  The  uranates  of  baryta,  lime, 
and  magnesia  are  formed  by  mixing  their  salts  with  those  of  the  uranic  oxide, 
and  adding  ammonia,  but  a  portion  of  uranate  of  ammonia  in  these  cases 
goes  down  with  them.     They  are  yellow  or  orange-colored  compounds. 

Nitrate  of  Uranium  (U203,N05,6H0). — This  is  the  common  crystallized 
nitrate  of  uranium  obtained  by  evaporating  the  nitric  solution  of  any  of  the 
oxides:  it  forms  yellow  prisms,  efflorescing  in  a  warm  atmosphere  into  a  ter- 
hydrate.  When  heated  it  fuses  in  its  water  of  crystallization,  becoming 
orange-colored  ;  and  at  a  red  heat  leaves  green  oxide.  It  is  very  soluble  in 
water,  alcohol,  and  ether.  When  its  alcoholic  solution  is  gently  heated,  it 
effervesces  and  evolves  nitrous  ether,  depositing  hydrated  peroxide.  Its 
ethereal  solution,  exposed  to  the  sun's  rays,  deposits  green  oxide,  nitrous 
ether,  and  a  green  solution  of  protoxide  being  at  the  same  time  formed. 
When  crystallized  nitrate  of  uranium  is  carefully  heated  until  it  becomes 
orange-colored,  a  yellow  insoluble  subnitrate  separates :  this,  at  a  red  heat, 
passes  first  into  UgO^,  and  then  into  UyOg.  This  solution  sometimes  con- 
tains lead  as  an  impurity;  this  will  affect  the  action  of  tests.  The  ammonio- 
nitrate  of  uranium  is  of  a  golden-yellow  color,  soluble  in  boiling  water  with 
loss  of  ammonia,  but  not  very  soluble  in  cold  water.  It  is  easily  dissolved 
by  diluted  nitric  acid  when  heated.  The  solution  is  rendered  pale  by  an 
excess  of  acid. 

The  nitrate  of  uranium  has  been  employed,  under  the  name  of  Wothlytype, 
for  taking  photographic  drawings.  Paper  impregnated  with  a  strong  solu- 
tion of  this  salt  (I  part  to  5  parts  of  distilled  water)  is  dried  and  exposed  in 
the  usual  manner.     After  several  minutes'  exposure  in  direct  sunlight,  a  not 


TESTS    FOR    THE    SALTS    OF    URANIUM  455 

very  vigorous  imajye  is  obtained.  Tt  is  subsequently  developed  by  the  use  of 
a  silver  or  gold  developer,  and  fixed  by  simply  washing  the  drawing  in 
water.  The  advantages  of  this  process  are  said  to  be  that  it  dispenses  with 
the  use  of  hyposulphite  of  soda  or  any  chemical  fixing  agent.  It  is  to  be 
observed,  however,  that  either  silver  or  gold  is  employed  for  the  necessary 
purpose  of  developing  the  images,  and  it  is  well  known  to  be  extremely 
difficult  to  remove  these  metals  entirely  from  the  tissue  of  paper  except  by 
the  aid  of  some  chemical  solvent. 

pROTOCHLORTDE  OF  Uranium  (UCl)  IS  obtained  by  passing  dry  chlorine 
over  a  mixture  of  oxide  of  uranium  with  one-fourth  its  weight  of  carbon 
heated  to  redness  in  a  porcelain  tube  :  red  vapors  of  the  chloride  are  formed, 
which  condense  into  dark-green  crystals  :  they  dissolve  rapidly  in  water, 
furnishing  a  dark-green  solution,  and,  when  exposed  to  air,  evolve  fumes  of 
hydrochloric  acid. 

Sulphates  of  Uranium. — A  sulphate  of  protoxide  of  uranium  (UO.SOg) 
is  formed  by  adding  sulphuric  acid  to  the  concentrated  aqueous  solution  of 
the  protochloride  :  it  forms  green  hydrated  crystals,  which  do  not  become 
anhydrous  till  so  highly  heated  as  to  begin  to  lose  acid,  and  which,  in  a  large 
quantity  of  water,  are  resolved  into  a  green  acid  solution,  and  a  deposit  of 
basic  sulphate  =2(XJO),S03,2HO,  when  dried  in  vacuo.  This  salt  forms  a 
crystallizable  double  sulphate  with  sulphate  of  ammonia  =NH^0,S03,+ 
U0,S03.  Sulphate  of  green  oxide  of  uranium  is  formed  by  dissolving  the 
green  oxide  in  sulphuric  acid,  and  expelling  the  excess  of  acid  by  heat :  it  is 
a  pale-green  mass  =1X30^,2803.  When  heated  to  redness  it  evolves  sulphu- 
rous acid,  and  leaves  a  pale  yellow  sulphate  of  the  peroxide  :  2(1X30^,2803) 
^8(1X203,803) +  80^.  Sulphate  of  peroxide  of  uranium  (1X303,803)  is  ob- 
tained by  oxidizing  the  solution  of  the  green  oxide  in  sulphuric  acid  by  nitric 
acid,  or  by  adding  sulphuric  acid  to  a  solution  of  the  nitrate,  evaporating  to 
dryness,  so  as  to  expel  the  excess  of  acid,  dissolving  the  residue  in  water, 
and  concentrating  the  solution  by  evaporation  to  the  consistency  of  syrup;  it 
is  slowly  and  difficultly  crystallizable  in  small  yellow  prisms  =IX,^03S03,3HO: 
dried  at  212°,  they  lose  2  atoms  of  water,  and  become  anhydrous  at  600°. 
A  phosphate  and  carbonate  of  the  peroxide  of  uranium  may  be  obtained  by 
double  decomposition.  There  is  also  an  ammonio-phosphate,  which  is  very 
insoluble. 

Tests  for  the  Salts  of  Franium The  salts  of  the  peroxide  form  yellow 

solutions ;  an  excess  of  acid  renders  them  pale.  1.  Sulphuretted  hydrogen 
produces  no  precipitate.  2.  Hydrosulphate  of  ammonia  throws  down  a  dark- 
brown  sulphide.  3.  Potassa  or  ammonia  throws  down  an  orange-yellow: 
uranate,  insoluble  in  an  excess  of  the  reagent,  and  in  hydrochlorate  of 
ammonia.  4.  Alkaline  carbonates  (soda  and  potassa)  give  a  pale  yellowish- 
green  precipitate,  not  soluble  in  an  excess.  The  precipitate  is  dissolved  by 
alkaline  bicarbonates,  and  by  carbonate  of  ammonia,  but  is  re-deposited  on 
boiling  the  liquid.  5.  Ferrocyanide  of  potassium  gives  a  deep  red-brown 
precipitate,  or  color :  ammonia  destroys  this  color,  forming  a  nearly  colorless 
liquid.  The  color  of  the  precipitate  closely  resembles  that  which  is  produced 
in  a  solution  of  copper ;  but  the  ferrocyanide  of  copper,  dissolved  by  am- 
monia, produces  a  blue  liquid.  This  furnishes  a  sufficient  distinction  between 
the  two  metals.  The  carbonate  of  an  alkaline  earth  (baryta)  precipitates 
the  sesquioxide  of  uranium  from  its  solutions  as  it  does  the  sesquioxide  of 
iron.  With  borax  the  oxide  gives,  under  the  blowpipe,  a  bead  which  is 
green  in  the  inner  and  yellow  in  the  outer  flame.  With  microcosmic  salt  the 
color  from  the  outer  flame  is  yellow-green. 

Peroxide  of  uranium  is  used  to  give  a  yellow  or  a  greenish  yellow  color 
to  glass.     The  green  oxide  is  employed  to  produce  a  black  color  on  porce- 


456  TELLURIUM    AND    ITS    COMPOUNDS    WITH    OXYGEN. 

lain.     The  protosalts  of  urauium  are  green,  and  are  rapidly  converted  into 
yellow  persalts  either  by  exposure  to  air,  or  by  the  action  of  nitric  acid. 

Tellurium  (Te=G4). 

Tellurium  was  discovered  in  1T82.  It  derives  its  name  from  tellus,  the 
earth.  Its  ores  are  rare,  and  generally  contain  it  in  combination  with  other 
metals,  especially  with  gold,  silver,  lead,  copper,  and  bismuth. 

Tellurium  is  of  an  iron-gray  color,  hard,  brittle,  fusible  at  a  temperature 
a  little  above  melting  lead,  and  volatile  at  a  full  red  heat,  its  vapor  condens- 
ing in  metallic-looking  opaque  globules  in- the  cold  part  of  the  tube.  The 
vapor  is  yellow,  resembling  that  of  selenium.  It  is  partially  oxidized  and 
converted  into  a  white  uncrystalline  oxide,  which  is  deposited  around  the 
condensed  globules  of  the  metal.  It  gives  a  metallic  ring  resembling  some- 
what that  of  arsenic  ;  but  it  is  so  much  less  volatile  than  arsenic,  that  it  re- 
quires for  its  volatilization,  the  full  heat  of  Bunsen's  jet.  Its  oxide  is  not 
deposited  in  transparent  octahedral  crystals.  When  warmed  with  sulphuric 
acid,  it  imparts  to  that  liquid  a  splendid  amethyst-red  color,  which  is  not 
permanent.  If  heated  on  platinum  it  rapidly  melts,  combines  with,  and  de- 
stroys that  metal,  forming  a  very  fusible  crystalline  alloy.  When  heated  on 
mica,  it  melts  and  burns  with  a  bluish  flame,  having  a  greenish  margin,  and 
it  evolves  a  thick  white  acid  smoke.  The  color  of  the  flame  resembles  that 
of  selenium,  but  has  a  greenish  tint.  It  traverses  a  solution  of  indigo,  giving 
a  pale  blue  light.  Although  closely  resembling  selenium,  yet  it  difters  in 
readily  forming  a  fusible  alloy  with  platinum,  and  in  evolving  no  reddish- 
colored  fumes  when  heated  in  air.  Its  sp.  gr.  is  6*2  to  6*8.  It  is  crystalli^ 
able,  and,  for  a  metal,  it  appears  to  be  a  bad  conductor  of  heat  and  electricity  : 
indeed,  it  may  be  said,  in  some  respects,  to  form  a  connecting  link  between 
sulphur  or  selenium  and  the  metals.  By  some  chemists  it  is  placed  among 
the  metalloids,  between  selenium  and  phosphorus. 

BiNOXiDE  OF  Tellurium  ;  Tellurous  Acid  (TeOg). — Exposed  to  heat  and 
air,  tellurium  fuses  and  burns,  exhaling  a  peculiar  sour  odor,  and  forming  a 
white  oxide.  This  oxide  is  thrown  down  as  a  white  hydrate  when  a  recently 
made  solution  of  tellurium  in  nitric  acid  is  poured  into  water.  In  its  anhy- 
drous state  it  is  difficultly  soluble,  but  when  hydrated,  it  readily  dissolves  in 
most  of  the  acids,  forming  colorless  solutions  of  a  nauseous  'metallic  taste  : 
they  afford  metallic  tellurium  in  a  black  powder  when  acted  on  by  phospho- 
rous acid,  or  sulphurous  acid,  as  well  as  by  zinc,  iron,  tin,  lead,  copper,  and 
some  other  metals.  Most  of  the  solutions  of  this  oxide  in  the  mineral  acids 
are  decomposed  by  copious  dilution  with  water,  provided  there  is  no  great 
excess  of  acid;  with  the  alkalies  and  their  carbonates  they  give  precipitates 
of  hydrated  oxide  soluble  in  excess  of  the  precipitant,  especially  when  aided 
by  heat:  they  are  precipitated  white  by  phosphate  of  soda;  dark-brown  by 
sulphuretted  hydrogen  and  alkaline  hydrosulphates  ;  and  yellow  by  tincture 
of  gall ;  they  are  not  affected  by  ferrocyanide  of  potassium,  nor  by  oxalic 
acid.  The  basic  combinations  of  tellurous  acid,  or  tellurites,  are  obtained  : 
1.  by  dissolving  the  hydrated  acid  in  the  alkalies;  2.  by  double  decomposi- 
tion ;  or  3.  by  fusion.  The  alkaline  tellurites  are  soluble  in  water  :  those  of 
baryta,  lime,  and  strontia  with  difficulty ;  most  of  the  other  compounds  are 
insoluble  in  water;  but  they  are  nearly  all  soluble  in  hydrochloric  acid. 

Peroxide  of  Tellurium  ;  Telluric  Acid  (TeOg)  may  be  obtained  by  pass- 
ing chlorine  through  the  solution  of  tellurous  acid  in  excess  of  potassa  till 
it  is  fully  saturated,  and  the  first  precipitate  is  redissolved.  The  filtered 
liquor  is  then  neutralized  by  ammonia,  and  chloride  of  barium  added,  which 
occasions  a  precipitate  of  tellurate  of  baryta;  this,  digested  with  a  fourth  of 
its  weight  of  sulphuric  acid  (diluted  with  water),  yields  a  solution,  which, 


TESTS  FOR  THE  SALTS  OF  TELLURIUM.  457 

when  filtered  and  carefully  evaporated,  affords  crystallized  hydrated  telliirio 
acid  =TeO.„3IiO,  from  which  adherin<^  sulphuric  acid  may  be  removed  by 
alcohol.  This  hydrate  loses  its  water  by  heat,  and  the  anhydrous  ncid,  of  a 
lemon-yellow  color,  remains.  This  acid  is  readily  procured  as  a  tellurate  by 
fusinj::^  tellurium  with  nitre,  and  when  this  is  calcined  with  charcoal  and  car- 
bonate of  potassa,  telluride  of  potassium  is  obtained.  Anhydrous  telluric 
acid  is  insoluble  in  water  ;  but  the  crystallized  acid  dissolves  in  boiling  water. 
When  boiled  with  hydrochloric  acid  it  forms  tellurous  acid,  and  like  selenic 
acid,  sets  free  chlorine  (p.  232).  Dried  at  320°,  the  crystals  lose  2  atoms  of 
water,  and  become  anhydrous  at  a  temperature  a  little  below  redness.  The 
tellurates  of  the  alkalies  are  moderately  soluble  in  water  ;  those  of  the  alkaline 
earths  are  sparingly  soluble;  and  many  of  the  other  tellurates  are  insoluble. 
When  tellurium  is  heated  in  chlorine  it  burns,  forming  a  dark  liquid,  which 
by  an  excess  of  chlorine  becomes  yellow,  and  concretes  on  cooling  into  a 
white  deliquescent  crystalline  bichloride,  =TeCl3.  If  this  is  heated  witjj 
pulverized  tellurium,  a  dark  purple  protochloride  is  formed,  =TeCl,  more 
volatile  than  the  bichloride,  and  giving  a  vapor  resembling  that  of  iodine. 

Telluretted  Hydrogen  (TeH). — When  an  alloy  of  tellurium  and  tin,  or 
zinc  is  acted  on  by  hydrochloric  acid,  telluretted  hydrogen  gas  is  evolved  ;  it 
reddens  litmus,  dissolves  in  water,  and  possesses  the  general  properties  of 
sulphuretted  hydrogen,  which  it  also  resembles  io  odor.     Its  sp.  gr.  is  4*48. 

There  appear  to  be  two  sulphides,  which  act  as  sulphur  acids  ;  they  are 
obtained  by  the  decomposition  of  tellurous  and  telluric  acids  by  sulphuretted 
hydrogen. 

.  Tests  for  the  Compounds  op  Tellurium The  solutions  of  tellurium  in 

mineral  acids  are  decomposed  by  the  immersion  of  zinc,  tin,  lead,  copper,  or 
cadmium,  and  the  metal  is  precipitated  in  the  form  of  a  black  powder.  Tel- 
lurous acid  and  its  salts  are  decomposed  when  an  excess  of  hydrochloric 
acid  is  present,  by  boiling  them  with  sulphurous  acid,  or  alkaline  sulphites, 
by  protosulphate  of  iron,  and  protochloride  of  tin,  which  occasion  a  brown 
or  black  flocculent  precipitate  of  tellurium.  Sulphuretted  hydrogen  throws 
down  a  black  bisulphide  of  tellurium,  which  is  soluble  in  hydrosulphate  of 
ammonia.  The  telluride  of  potassium  procured  by  the  method  above  de- 
scribed blackens  silver  and  evolves  telluretted  hydrogen  when  treated  with 
acids. 

Titanium  (Ti=24). 

Titanium  was  first  detected  in  a  mineral,  found  in  the  form  of  a  black  sand, 
in  the  vale  of  Menachan,  in  Cornwall,  consisting  of  the  oxides  of  titanium 
and  iron.  In  the  state  of  titanic  acid  it  exists  in  the  minerals  called  Rutilite, 
Anatase,  and  Oysanite.  Titanite  is  a  silicate  of  titanium  and  lime  :  it  occurs 
in  quartz  and  granite,  and  it  sometimes  transverses  rock-crystal  in  brown 
hair-like  filaments.  Titanium,  as  titanic  acid,  is  frequently  found  in  clays 
and  sands,  associated  with  silica  and  oxide  of  iron.  It  is  also  found  in  the 
slags  of  some  iron  furnaces ;  they  contain  small  copper-colored  cubic  crys- 
tals, of  a  sp.  gr.  of  5'3 ;  insoluble  in  the  acids,  but  oxidized  by  fusion  with 
nitre.  They  appear  to  be  a  combination  of  nitride  with  cyanide  of  titanium, 
and  contain  about  18  per  cent,  of  nitrogen  and  4  of  carbon.  Another 
nitride  is  obtained  in  form  of  copper-colored  scales  by  passing  ammonia 
over  the  ammonio-chloride  of  titanium  heated  to  redness.  These  nitrides 
were  formerly  regarded  as  pure  titanium.  To  obtain  titanium,  the  potassio- 
fluoride  is  decomposed  by  potassium,  when  the  metal  remains  in  the  form  of 
gray  particles,  which  burn  brilliantly  if  heated  in  oxygen. 

Protoxide  of  Titanium  (TiO). — When  titanic  acid  is  subjected  to  a 
white  heat  in  a  charcoal  crucible,  it  is  superficially  reduced:  but  the  interior 


458  TITANIUM    AND    ITS    COMPOUNDS    WITH    OXYGEN. 

is  in  the  state  of  a  black  powder,  which  is  the  protoxide.  When  a  plate  of 
zinc  is  immersed  in  a  solution  of  chloride  of  titaiiinm,  a  purple  powder  is 
obtained,  which  is  a  hydrated  sesquioxide  (Ti.^O^.HO). 

Peroxide  of  Titanium  ;  Titanic  Acid  (TiOg)  may  be  obtained  from  riiti- 
lite,  by  fusing  it,  in  fine  powder,  in  a  platinum  crucible,  with  thrice  its  weight 
of  carbonate  of  potassa  :  a  gray  mass  is  obtained,  which,  after  having  been 
washed  with  water,  is  dissolved  in  hydrochloric  acid,  and  on  diluting  with 
water,  and  boiling  the  solution,  the  greater  part  of  the  titanic  acid  is  pre- 
cipitated;  it  may  be  collected  and  washed  with  very  dilute  hydrochloric  acid. 
The  acid  is  more  perfectly  precipitated  by  adding  sulphite  of  soda  and 
boiling  the  liquid.  Titanic  acid  is  white,  infusible,  and  very  difficult  of 
reduction  :  its  sp.  gr.  is  3  93.  When  calcined  it  becomes  yellow,  and  is  then 
dissolved  only  by  concentrated  hydrofluoric  or  sulphuric  acid.  When  recently 
precipitated,  it  dissolves  in  some  of  the  acids,  but  becomes  nearly  insoluble 
aJ'ter  it  has  been  ignited ;  and  like  oxide  of  tin,  it  is  susceptible  of  two  iso- 
meric modifications.  When  its  solution  in  hydrochloric  acid  is  heated  to  the 
boiling-point,  a  part  of  the  titanic  acid  is  thrown  down  ;  but  by  slow  evapo- 
ration a  soluble  chloride  remains.  It  is  precipitated  by  the  pure  and  carbo- 
nated alkalies,  including  ammonia  and  its  carbonate,  in  a  gelatinous  form  : 
infusion  of  galls  and  ferrocyanide  of  potassium  throw  it  down  of  a  charac- 
teristic red-brown  color,  and  the  precipitate  is  soluble  in  an  excess  of  the 
solution  of  the  ferrocyanide.  Sulphuretted  hydrogen  produces  no  precipi- 
tate in  the  hydrochloric  solution.  Titanic  acid  which  has  been  rendered 
yellow  by  ignition  is  sometimes  used  in  enamel  and  porcelain  painting,  to 
give  a  yellow  color.  Titanic  acid  is  thrown  down  from  its  solution  in  hydro- 
chloric acid,  by  alkalies  arid  the  alkaline  carbonates,  and  the  precipitates  are 
insoluble  in  an  excess  of  the  reagents.  The  precipitates  are,  however,  dis- 
solved by  strong  acids. 

Bichloride  of  Titanium  (TiCl.^)  is  obtained  bypassing  dry  chlorine  over 
metallic  titanium,  or  over  a  mixture  of  titanic  acid  and  charcoal  heated  to 
redness.  It  is  a  dense,  transparent,  and  colorless  fluid,  fuming  when  exposed 
to  air.  It  boils  at  277^  ;  the  density  of  its  vapor  is  6'836.  With  a  small 
quantity  of  water  it  forms  a  crystalline  hydrate,  which,  by  the  further  addi- 
tion of  water,  deposits  titanic  acid. 

BiFLuoRiDE  OF  TiTANiuM  (TiFg). — Titanic  acid  readily  dissolvcs  in  hydro- 
chloric  acid.  When  this  solution  is  saturated  with  potassa  and  evaporated, 
a  titanofiuoride  of  potassium  is  the  result. 

Bisulphide  of  Titanium  (TiS^)  is  obtained  by  passing  the  vapor  of  sul- 
phide of  carbon  over  ignited  titanic  acid.  It  has  a  dark-green  or  bronze 
color,  and  a  metallic  lustre. 

None  of  the  other  metals  appear  so  to  combine  with  titanium  as  to  form 
definite  alloys  ;  but  when  it  is  blended  with  some  of  them  by  fusion,  it  is 
susceptible  of  oxidation,  and  is  then  soluble  in  acids  which  do  not  otherwise 
act  upon  it. 

Tests  for  the  Salts  of  Titanium. — Titanium  is  not  thrown  down  in  the 
metallic  state  by  any  other  metal.  The  orange-red  precipitate,  which  its 
solutions  afford  with  infusion  of  galls  and  with  ferrocyanide  of  potassium, 
is  very  characteristic.  When  titanic  acid  is  fused  on  charcoal  with  carbonate 
of  soda  and  cyanide  of  potassium,  it  does  not,  like  tin,  yield  any  metallic 
globule.  In  ordinary  analyses  of  silicates,  titanic  acid  is  liable  to  be  pre- 
cipitated with,  and  estimated  as,  oxide  of  iron,  or  to  be  weighed  as  silica. 
The  best  method  of  separation  is  probably  the  following  :  Fuse  the  mineral 
containing  titanic  acid  with  four  times  its  weight  of  carbonate  of  soda,  and 
remove  all  that  can  be  dissolved  by  cold  water.  The  residue  will  be  a 
titanate  of  the  alkali  and  oxide  of  iron.     Digest  this  in  concentrated  hydro- 


ANTIMONY    AND    ITS    COMPOUNDS    WITH    OXYGEN.  459 

chloric  acid,  by  which  the  iron  and  titanic  acid  are  dissolved  ;  then  boil  the 
sohition,  diluted  with  water,  with  sulphite  of  soda — titanic  acid  alone  is  pre- 
cipitated. This  may  be  redissolved  in  hydrochloric  acid,  and  a  bar  of  zinc 
introduced  into  the  liquid.  If  titanic  acid  is  present,  it  is  reduced  to  the 
8tate  of  sesquioxide,  which  is  dissolved,  and  p^ives  a  blue  color  to  the  liquid. 
By  a  continuance  of  the  action  it  is  still  further  reduced,  and  the  oxide  of 
titanium  is  precipitated  as  a  violet-colored  powder. 


CHAPTEE    XXXV. 

Antimony  (Sb  =  129). 

Antimony,  or  stibmm,  was  first  made  known  towards  the  end  of  the  fif- 
teenth century.  It  is  found  native,  but  its  principal  ore  is  the  sulphide,  the 
stibium  of  the  ancients.  Antimony  is  obtained  from  the  sulphide  by  mixing 
8  parts  of  it  in  fine  powder,  with  6  of  tartar,  and  3  of  nitre,  and  pro- 
jectiuf^  it  by  spoonfuls  into  a  red-hot  crucible.  The  sulphur  is  oxidized  by 
the  nitre,  and  the  metal  collects  at  the  bottom.  If  the  metal  is  required 
perfectly  pure,  the  p-ure  oxide  must  be  reduced  by  charcoal. 

Antimony  is  of  a  bluish-white  color,  brittle,  and  crystalline,  so  that  when 
broken  it  exhibits  splendid  facets,  and  the  surface  of  the  ing;ot  as  it  has 
cooled  in  the  crucible  is  often  stellated.  It  fuses  at  about  1160^,  or  at  a  dull 
red  heat :  it  is  slowly  volatile  at  a  white-heat  and  in  the  absence  of  air,  but 
in  a  stream  of  hydrop:en  it'may  be  distilled.  Itssp.  gr.  is  6-7.  Placed  upon 
ignited  charcoal,  under  a  current  of  oxygen,  antimony  burns  with  great  bril- 
liancy, throwing  off  a  dense  yellow  smoke  ;  and  if  a  globule  of  the  intensely- 
heated  metal  be  thrown  upon  the  floor,  or  upon  a  black  board,  it  subdivides 
into  numerous  smaller  globules,  which  burn  as  they  roll  along,  and  leave  a 
series  of  white  or  yellowish  lines  of  oxide.  The  metal  is  not  dissolved  by- 
hydrochloric  acid,  but  readily  by  nitrohydrochloric  acid.  It  is  oxidized 
when  heated  with  nitric  acid,  leaving  a  white  residue,  insoluble  in  nitric  but 
soluble  in  tartaric  acid. 

Antimony  and  Oxygen. — There  are  two  well-defined  compounds  of  anti- 
mony with  oxygen,  a  ternxide,  SbOg,  and  antimonic  acid,  SbOg.  A  third 
oxide  is  sometimes  described  under  the  name  of  antimonioits  acid,  SbO^,  but 
it  should  rather  be  regarded  as  an  antimoniate  of  oxide  of  antimony  (SbOg, 
SbO,). 

Teroxide  of  Antimony  (SbOg)  is  formed  by  heating  the  metal  in  air  to 
its  point  of  combustion,  when  the  vapor  burns  with  a  bluish  flame  ;  and  by 
placing  the  crucible  in  an  inclined  position,  acicular  crystals  of  the  oxide 
are  deposited  in  its.  upper  part,  fornaing  ih^fiores  antimonii  And  nix  stihii  of 
the  older  chemists.  It  may  also  be  formed  by  adding  50  parts  of  finely- 
powdered  metallic  antimony  to  200  of  sulphuric  acid,  boiling  the  mixture  to 
dryness,  and  washing  the  dry  mass,  first  in  water,  and  then  in  a  weak  solution 
of  carbonate  of  soda :  a  white  powder  remains,  which,  when  thoroughly 
washed  with  hot  water,  is  the  teroxide.  Teroxide,  or,  as  it  is  sometimes 
called,  protoxide  of  antimony,  is  white,  fusible,  and  volatile  at  a  high  red 
heat,  undergoing  no  change  in  close  vessels,  but  condensing  in  acicular  and 
octahedral  crystals  ;  after  fusion  it  concretes  into  a  silky  crystalline  mass  : 
if  air  be  present,  it  burns  like  tinder,  and  passes  into  a  higher  state  of  oxida- 
tion.    It  is  soluble  in   hydrochloric  and  tartaric   acids,  and  it  forms  emetic 


# 

460  ANTIMONIOUS    AND    ANTIMONTC    ACIDS, 

tartar  when  boiled  with  a  solution  of  bitartrate  of  potassa.     It  occurs  native^ 
forming:  the  white  ore  of  antimony. 

Teroxide  of  antimony  forms  compounds  with  many  bases,  and  in  various 
atomic  proportions  :  most  of  them  are  decomposed  by  water,  which  becomes 
milky  from  the  deposition  of  a  subsalt.  These  compounds  have  been  termed 
antimonites.  The  teroxide  is  precipitated  from  its  solution  in  hydrochloric 
acid  by  potassa  as  a  white  hydrate,  which  is  dissolved  by  an  excess  of  the 
alkali.  If  to  this  alkaline  liquid,  nitrate  of  silver  is  added,  a  black  antimo- 
nide  of  silver  (Agg.Sb),  quite  insoluble  in  ammonia,  isthrovyn  down.  When 
chloride  of  gold  is  added,  there  is  a  dark  purple  precipitate  of  reduced  gold. 
The  teroxide,  when  heated  in  a  reduction  tube,  melts  into  a  yellow  liquid, 
and  is  only  partially  volatilized  in  octahedra  by  the  heat  of  a  spirit-lamp. 
The  analogous  compound  of  arsenic  is  entirely  volatilized  in  brilliant  octa- 
hedral crystals  without  melting. 

Antimonious  Acid,  or  Antimoniate  of  Antimony  (SbOgSbOj,  or  2Sb04), 
is  the  result  of  the  above-mentioned  combustion  of  the  protoxide  :  it  is  also 
obtained  by  exposing  antiraonic  acid  to  a  red  heat.  It  is  white  in  its  ordi- 
nary state  ;  and  it  is  fixed  and  infusible  in  the  fire.  It  is  thus  distinguished 
from  the  teroxide.  It  also  differs  from  this  oxide  in  being  less  soluble  in 
hydrochloric  acid.  Antimonious  acid  differs  from  antimonic  acid  by  its  re- 
mainiug  white  when  heated  in  a  close  vessel  or  tube,  and  by  its  not  evolving 
oxygen  under  these  circumstances. 

Antimonic  Acid  ;  Peroxide  of  Antimony  (SbOj)  is  procured  by  acting 
for  a  considerable  time  upon  the  finely-powdered  metal  by  an  excess  of  hot 
nitric  acid,  and  exposing  the  product  to  a  heat  not  exceeding  500^.  It  is 
of  a  pale  yellow  color,  tasteless,  and  insoluble  in  water.  It  neither  fuses  nor 
volatilizes  at  a  bright  red  heat,  but  loses  oxygen,  and  becomes  antimonious 
acid.  It  does  not  decompose  the  alkaline  carbonates  in  the  humid  way,  but 
at  a  red  heat  it  expels  their  carbonic  acid,  and  combines  with  the  base.  It 
dissolves,  but  not  readily,  in  a  boiling  solution  of  caustic  potassa,  from  which 
it  is  thrown  down  by  an  acid  in  the  form  of  a  white  hydrate,  SbOs,4HO. 
In  this  state  it  reddens  litmus  and  dissolves  in  hydrochloric  acid,  and  in  the 
alkalies.  In  the  anhydrous  state  it  is  only  partially  dissolved  by  hydro- 
chloric acid.  An  acid  solution  of  this  oxide  is  precipitated  by  a  current  of 
sulphuretted  hydrogen,  as  an  orange-yellow  pentasulphide  of  antimony.  No 
precipitate  is  produced  by  this  gas  in  an  alkaline  solution  of  hydrated  anti- 
monic acid  ;  and  if  free  from  teroxide  it  does  not  reduce  the  salts  of  silver 
and  gold. 

Antimoniates. — Antimonic  acid  in  combination  with  bases  forms  neutral 
and  acid  salts.  Antimoniate  of  potassa  is  formed  by  heating  1  part  of  pow- 
dered metallic  antimony  with  4  of  nitre,  in  an  earthen  crucible,  and  washing 
the  pulverized  product  with  water.  Its  formula  is  2(KO),Sb05.  When  this 
salt  is  boiled  for  some  hours  in  water,  it  is  partly  converted  into  a  soluble 
hydrated  antimoniate,  and  an  insoluble  hiantimoniate  =KO,2Sb05.  A  solu- 
ble biantimoniate,  supposed  to  contain  a  modified  acid  {metantimonic  acid), 
is  obtained  by  deflagrating  antimony  with  nitre,  washing,  and  boiling  the 
product  so  as  to  convert  it  into  the  state  of  soluble  antimoniate,  and  evapo- 
rating this  solution  in  a  silver  basin  to  the  consistence  of  syrup  :  caustic 
potassa  is  then  added,  and  the  evaporation  is  continued  till  a  drop  of  the 
solution,  placed  upon  a  cold  piece  of  glass,  crystallizes  ;  it  is  then  set  aside 
to  cool,  and  the  crystallized  salt  dried  upon  a  porous  tile.  This  himetanti- 
moniate  of  potassa  has  the  formula  KO,HO,Sb03=6Aq.  It  has  been  used 
as  a  test  for  soda,  with  which  it  furnishes  an  insoluble  precipitate  ;  but  its 
indications  are  very  uncertain,  and  the  test  itself,  when  kept  for  a  few  days  in 
solution,  passes  into  the  neutral  antimoniate,  which  does  not  precipitate  soda. 


ANTIMONIURETTED  HYDROGEN.  4G1 

The  insoluble  himetnntimoniate  of  sodaH  represented  as  ]S'aO,HO,Sb03,(>Aq. 
Considerable  uncertainty  hangs  over  the  nature  of  these  modifications  of  the 
antimonic  acid  and  the  antimoniates,  the  difference  in  their  properties  pro- 
bably depending  upon  peculiarities  of  molecular  constitution,  which  confer 
distinct  characters  upon  compounds  similarly  constituted. 

Antimony  and  Hydrogen. — Antimonurettedhydrogen  yas  (SbHg)  is  formed 
by  the  action  of  dilute  sulphuric  or  hydrochloric  acid  on  an  alloy  of  zinc  and 
antimony;  or  by  adding  an  acid  solution  of  oxide  of  antimony  to  zinc.  The 
gas  is  colorless,  nearly  inodorous  (if  free  from  arsenic),  and  is  decomposed 
when  passed  through  a  tube  heated  to  dull  redness,  depositing  a  brilliant 
coat  of  metallic  antimony.  It  burns  in  the  air  with  a  pale  greenish-white 
flame,  producing  a  white  smoke  consisting  of  oxide  of  antimony,  and  if  the 
flame  be  in  contact  with  glass  or  porcelain,  metallic  spots  are  formed  some- 
what resembling  those  produced  by  a  similar  combustion  of  arseniuretted 
hydrogen.  It  instantly  decomposes  the  salts  of  silver,  precipitating  a  black 
antimonide  of  silver  (SbIl3+3AgO=Ag3Sb-|-3HO),  but  it  produces  no 
change  of  color  in  paper  impregnated  with  a  solution  of  a  salt  of  lead.  In 
contact  with  water  the  gas  rapidly  undergoes  decomposition,  and  deposits 
metallic  antimony  in  the  form  of  a  black  powder.  {See  Arsenuretted  Hy- 
drogen, p.  472.) 

Antimony  and  Chlorine  ;  Terohloride  op  Antimony  (SbClg). — Anti- 
mony takes  fire  when  thrown  in  fine  powder  into  gaseous  chlorine,  and  a 
mixed  chloride  is  formed  with  combustion.  The  terchloride  is  usually  ob- 
tained by  the  distillation  of  3  parts  of  powdered  metallic  antimony  with  8  of 
corrosive  sublimate  (Sb  +  3HgCl  =  SbCl3,-|-3Hg),  or  by  dissolving  oxide  of 
antimony  in  hydrochloric  acid,  and  evaporating  to  dryness  out  of  the  contact 
of  air.  It  is  a  soft  solid  at  common  temperatures,  but  becomes  liquid  by  a 
gentle  heat,  and  crystallizes  as  it  cools.  It  is  the  butter  of  antimony  of  old 
writers.  It  deliquesces  by  exposure  to  air.  When  water  is  added  to  it  a 
mutual  decomposition  ensues,  and  hydrated  oxychloridc  of  antimony  and 
hydrochloric  acid  result  (6SbCl34-15HO=15HCl  +  SbCl3,5Sb03).  This 
white  basic  compound  resembles  that  of  bismuth  in  its  mode  of  production 
and  insolubility.  It  is  distinguished  from  the  bismuthic  precipitate  by  its 
being  entirely  dissolved  by  tartaric  acid. 

Perchloride  of  Antimony  ;  Pentachloride  of  Antimony  (SbClg),  is 
formed  by  passing  dry  chlorine  over  heated  antimony,  or  by  exposing  the 
terchloride  to  a  stream  of  dry  chlorine.  It  is  a  volatile  transparent  liquid, 
which  emits  fumes  when  exposed  to  air.  When  heated  it  becomes  terchlo- 
ride by  the  evolution  of  chlorine.  By  exposure  to  air  it  becomes  a  crystalline 
hydrated  perchloride,  vi\nQ\i\%  deliquescent  and  soluble  without  decomposition 
in  hydrochloric  acid. — Oxychloride.  When  chloride  of  antimony  is  mixed 
with  a  large  quantity  of  water,  a  precipitate  falls,  (5(Sb03)SbCl3)  which  was 
formerly  used  as  an  emetic,  under  the  name  of  AlgarottVs  poivder,  or  Mercu^ 
rius  vitae.  The  same  compound  is  formed  on  diluting  a  solution  of  antimony 
in  nitro-hydrochloric  acid.  When  first  thrown  down  it  is  white  and  curdy, 
but  afterwards  assumes  a  yellowish-gray  color  and  becomes  pulverulent  or 
crystalline.  By  continued  washing  with  hot  water,  and  by  the  action  of 
alkaline  carbonates,  it  leaves  the  oxide  of  the  metal.  Antimony  combines 
with  bromine  and  iodine,  forming  compounds  analogous  to  the  chlorides. 

Tersulphide  of  Antimony  (SbSg). — This  compound  may  be  formed  by 
fusing  the  metal  with  sulphur.  Its  color  is  dark-gray  and  metallic ;  its 
specific  gravity  4*66  :  it  closely  resembles  the  native  sulphide.  When  exposed 
under  a  muffle  to  a  dull  red  heat,  it  gradually  loses  sulphur,  aud  absorbs 
oxygen,  being  converted  into  a  gray  powder,  which  consists  of  a  mixture  of 
oxide  and  sulphide.     If  the  heat  be  increased,  this  fuses  into  a  transparent 


462  SULPHIDES    OF    ANTIMONY. 

substance  formerly  called  Glass  of  antimony.  Compounds  of  the  oxide  with 
larger  quantities  of  the  sulphide,  have  been  termed  Saffron  of  antimony  or 
Crocus  metallorum,  and  Liver  of  antimony. 

Hydrated  tersulphide  of  antimony  h  thrown  down  in  the  form  of  a  reddish- 
brown  or  orange-colored  precipitate,  when  sulphuretted  hydrogen  is  passed 
through  antimonial  solutions,  and  when  carefully  dried  it  retains  its  color, 
but  if  it  be  heated  it  darkens,  and  becoming  anhydrous,  assumes  a  metallic 
appearance.  It  dissolves  in  solutions  of  the  sulphides  of  the  all<aline  metals, 
which  take  it  up  largely  when  heated,  and  deposit  a  portion  of  it  on  cooling; 
it  is  thrown  down  from  these  solutions  by  acids.  Hydrochloric  acid  dis- 
solves it  with  evolution  of  sulphuretted  hydrogen,  producing  a  colorless  ter- 
chloride.  A  hot  solution  of  sulphide  of  antimony  in  caustic  or  carbonate  of 
potassa,  deposits  a  brown  powder  on  cooling,  formerly  called  Kermes  mineral; 
it  is  sulphide  mixed  with  oxide  of  antimony,  retaining  a  little  of  the  alkali. 
If  hydrochloric  acid  be  added  to  the  filtrate,  after  the  deposition  of  the 
Kermes,  sulphuretted  hydrogen  escapes,  and  the  remaining  sulphide  of  anti- 
mony is  thrown  down,  with  some  excess  of  sulphur,  and  a  variable  proportion 
of  oxide  of  antimony.  This  compound  is  the  golden  sulphide  of  antimony  of 
pharmacy,  but,  like  Kermes,  it  is  .of  uncertain  composition.  The  red  ore  of 
antimony  is  a  native  oxysulphide,  =2SbS3-j-Sb03. 

Native  sulphide  is  by  far  the  commonest  ore  of  antimony.  It  occurs  in 
prismatic  and  acicular  crystals.  It  was  known  to  the  ancients,  and  used  by 
the  Asiatic  and  Greek  ladies  as  a  pigment  for  the  eyelashes  :  it  was  called 
stimmi  {atiixfxi)  and  stibium  (art/St).  It  is  known  in  commerce  as  crude  anti- 
mony, and  is  usually  met  with  in  conical  masses  or  loaves,  presenting  a 
dark-gray  crystalline  fracture;  its  powder  is  nearly  black,  and  its  melting- 
point  somewhat  above  that  of  the  pure  metal :  it  is  seldom  pure,  frequently 
containing  the  sulphides  of  lead,  iron,  copper,  and  arsenic,  the  arsenical 
impurity  forming  sometimes  1-33  per  cent, 

Pentasulphide  of  Antimony  ;  Sulphantimonic  Acid  (SbSg)  is  formed 
by  passing  sulphuretted  hydrogen  through  pentachloride  of  antimony  dis- 
solved in  aqueous  tartaric  acid.  It  is  an  orange-colored  powder,  which 
when  heated  out  of  contact  of  air,  loses  2  atoms  of  sulphur ;  it  dissolves  in 
warm  aqueous  ammonia,  and  in  potassa  and  soda,  and  combines  with  the 
basic  sulphides,  forming  compounds  which  have  been  called  sulphantimo- 
niates.  One  of  the  most  remarkable  of  these  is  the  tribasic  suljihantimoniate 
of  sodium,  (3NaS,SbS5+ I8Aq)  :  it  is  obtained  by  mixing  18  parts  of  finely- 
powdered  tersulphide  of  antimony,  22  of  dry  carbonate  of  soda,  13  of  quick- 
lime, and  3  5  of  sulphur,  triturating  this  mixture  with.a  little  water,  and  then 
putting  it  into  a  well-closed  bottle  filled  with  water,  and  allowing  it  to  digest, 
with  frequent  agitation,  for  twenty-four  hours  ;  the  clear  liquor  is  then  filtered 
and  evaporated  m  vacuo  over  sulphuric  acid  ;  it  crystallizes  in  transparent 
tetrahedra.  , 

Alloys  of  Antimony. — With  potassium  and  sodium  antimony  forms  white 
brittle  compounds.  The  alloy  of  potassium  and  antimony  may  be  procured 
by  heating  to  redness  in  a  covered  crucible  a  mixture  of  equal  parts  of  finely- 
powdered  antimony  and  tartar  for  about  three  hours.  By  substituting  tar- 
trate of  soda  for  common  tartar,  the  alloy  of  sodium  and  antimony  may  be 
obtained  ;  and  a  mixture  of  soda-tartrate  of  potassa  and  powdered  antimony 
yields  the  triple  alloy  of  antimony,  potassium,  and  sodium.  When  these 
alloys  are  reduced  to  powder,  and  exposed  to  air,  they  heat,  and  take  fire 
like  pyrophori  (p.  41),  and  if  blended  with  excess  of  carbon  they  burst  into 
sudden  ignition  on  exposure,  especially  on  the  addition  of  a  few  drops  of 
water.  Antimony  and  iron  combine  by  fusion,  and  form  a  white  alloy  :  2 
parts  of  sulphide  of  antimony  fused  with  1  of  iron,  yield  a  slag  of  sulphide 


TESTS    FOR    THE    COMPOUNDS    OP    ANTIMONY.  463 

of  iron,  and  an  alloy  formerly  called  Martial  regulus.  This  alloy  may  be 
recognized  by  its  magnetic  properties.  Zhic  and  antimony  form  a  hard 
brittle  alloy.  Antimony  and  tht  may  be  fused  together  in  various  propor- 
tions :  an  alloy  of  1  atom  of  each  is  brittle  and  pnlverizable  :  1  part  of  anti- 
mony and  10  parts  of  tin  form  a  ductile  compound,  which  a  little  lead  renders 
brittle.  A  fine  pewter  is  said  to  consist  of  12  parts  of  tin  and  1  of  antimony, 
with  a  small  addition  of  copper.  An  alloy  of  1  of  antimony  and  3  of  copper 
is  lamellar  and  brittle,  but  takes  a  good  polish.  When  there  is  excess  of 
antimony  the  alloy  is  white.  Type  metal  is  a  compound  of  4  parts  of  lead 
and  1  of  antimony  ;  its  hardness  is  such  as  to  resist  the  pressure  to  which  in 
the  printing  press  the  type  is  necessarily  subjected  :  it  is  readily  fusible,  and 
takes  a  very  sharp  impression  from  the  matrix  or  mould  in  which  the  letter 
or  stereotype  plate  is  cast.  A  good  white  metal,  used  for  spoons  and  tea- 
pots, called  Britannia  metal,  is  composed  of  100  tin,  8  antimony,  2  bismuth, 
and  2  copper.  Antimony  readily  combines  and  forms  a  fusible  alloy  with 
platinum. 

Tests  for  the  Compounds  of  Antimony. — 1.  The  compounds  of  anti- 
mony, when  dissolved  in  water,  or  in  an  acid,  are  decomposed  by  the  immer- 
sion of  a  plate  of  zinc ;  the  metal  is  thrown  down  in  the  form  of  a  black 
powder,  and  when  hydrogen  is  evolved  a  portion  of  antimony  escapes  with 
this  gas.  2.  iSulphuretted  hydrogen  produces  a  distinctive  brownish-red  or 
dark  orange  precipitate  in  salts  of  antimony  with  excess  of  acid,  but  if 
they  are  neutral,  their  color  is  only  changed,  and  the  precipitate  does  not 
ensue  until  an  acid  (tartaric)  is  added.  3.  The  alkaline  hydrosulphates  pro- 
duce a  similar  precipitate,  which  is  soluble  in  an  excess  of  the  precipitant, 
especially  when  aided  by  heat.  The  precipitate  is  insoluble  in  ammonia, 
but  is  dissolved  by  potassa.  4.  Many  of  the  combinations  of  antimony  are 
decomposed  when  largely  diluted  with  water,  and  a  basic  salt  is  thrown  down  : 
this  decomposition  is  prevented  by  the  presence  of  an  excess  of  tartaric  acid. 
{Distinction  from  Bismuth,  see  p.  43y.)  5.  Ammonia  and  the  carbonate  of 
ammonia  throw  down  teroxide  of  antimony  completely  from  its  solutions  as 
a  white  precipitate,  insoluble  in  an  excess  of  either  precipitant.  6.  Potassa 
throws  down  a  white  hydrated  oxide,  soluble  in  an  excess  of  the  alkaline 
liquid.  Nitrate  of  silver  added  to  this  alkaline  solution  of  the  oxide,  pro- 
duces a  black  precipitate,  insoluble  in  ammonia  ;  and  chloride  of  gold  pro- 
duces in  it  a  purple-black  precipitate.  7.  Ferrocyanide  of  potassium  gives  a 
white  precipitate,  having  frequently  a  bluish  tint  from  the  presence  of  iron. 

These  results  are  not  obtained  in  a  solution  of  tartar  emetic,  or  the  double 
tartrate  of  antimony  and  potassa.  1.  Sulphuric,  nitric,  and  hydrochloric 
acids  produce  white  precipitates  (basic  salts)  in  a  solution  of  the  double 
tartrate.  These  precipitates  are  readily  dissolved  by  an  excess  of  tartaric  or 
hydrochloric  acid.  2.  The  alkalies  and  alkaline  carbonates  do  not  precipitate 
the  solution  except  at  a  boiling  temperature.  3.  It  is  not  precipitated  by 
ferrocyanide  of  potassium.  4.  It  is  not  readily  precipitated  by  sulphuretted 
hydrogen  until  an  acid  is  added,  and  for  this  purpose  the  tartaric  acid  is  pre- 
ferable :  an  orange-red  precipitate,  characteristic  of  oxide  of  antimony,  is 
thrown  down.  This  precipitate  is  distinguished  from  many  other  sulphides 
by  its  solubility  in  sulphide  of  ammonium,  and  in  solution  of  potassa — as 
well  as  by  its  insolubility  in  ammonia.  If  collected  and  dried,  it  may  be  dis- 
solved by  heat  in  a  small  quantity  of  strong  hydrochloric  acid  ;  and  when  all 
the  sulphuretted  hydrogen  has  escaped,  it  will  be  found  that,  on  adding  this 
solution  to  water,  a  white  oxychloride  of  antimony  is  precipitated,  possessing 
the  characters  elsewhere  described  (p,  461).  A  portion  of  the  sulphide,  dis- 
solved in  hydrochloric  acid  may  be  introduced  with  zinc  and  sulphuric  acid 
into  Marsh's  apparatus.     The  gas  which  escapes  at  the  jet  produces  a  deep 


464  ANALYSIS    IN    CASES    OP    POISONING. 

black  deposit  on  paper  impregnated  with  a  solution  of  nitrate  of  silver  ;  bnt 
unless  sulphur  is  present  it  produces  no  change  on  paper  impregnated  with  a 
salt  of  lead.  When  ignited  the  gas  burns  with  a  pale  yellowish-white  flame, 
producing  white  fumes  of  teroxide  of  antimony  (p.  461).  Porcelain,  or 
glass,  depressed  on  the  flame  receives  a  black  deposit  of  finely-reduced  metallic 
antimony,  with  grayish-colored  layers  of  oxide  at  the  circumference.  There 
is  no  metallic  lustre,  such  as  is  produced  by  arsenic  under  similar  circum- 
stances ;  but  on  examining  the  reverse  side  of  the  glass,  a  metallic  lustre 
will  be  perceptible.  If  a  current  of  the  gas  is  heated  to  redness  in  a  tube, 
a  ring  of  metallic  antimony  of  a  tin-like  lustre  will  be  deposited  close  to  the 
heated  spot.  This  is  much  more  fixed  than  the  deposit  of  arsenic,  and  can- 
not, like  it,  be  resolved  into  a  white  sublimate  of  transparent  octahedral 
crystals.  If  the  gas  is  made  to  pass  through  a  small  quantity  of  fuming 
nitric  acid  containing  nitrous  acid,  it  is  decomposed,  the  antimony  is  per- 
oxidized,  and  may  be  obtained  as  a  white,  insoluble  residue,  on  evaporation. 
A  solution  of  nitrate  of  silver  produces  no  change  in  this  deposit;  but  if 
one  or  two  drops  of  ammonia  are  added,  there  is  a  black  deposit  of  anti- 
monide  of  silver  (AggSb).  Compounds  of  antimony  heated  with  carbo- 
nate of  soda  or  cyanide  of  potassium  in  the  reducing  flame  of  the  blowpipe, 
yield  globules  of  metal,  surrounded  by  a  white  incrustation  on  the  charcoal. 

Analysis  in  Cases  of  Poisoning. — The  suspected  liquid,  if  clear,  may 
be  acidulated  with  tartaric  acid,  and  a  current  of  sulphuretted  hydrogen 
passed  into  it.  The  precipitated  sulphide  may  be  easily  identified  by  the 
characters  above  described.  The  contents  of  the  stomach,  or  the  coats  of 
the  organ,  may  be  boiled  in  hydrochloric  or  tartaric  acid,  and  the  filtered 
liquid  subsequently  decomposed  by  the  gas. 

The  following  method  of  detecting  antimony,  when  dissolved  in  any  organic 
liquid,  is  based  upon  the  principle  by  which  copper  and  other  metals  may 
be  detected  under  similar  circumstances  (page  427).  Acidulate  a  portion 
of  the  suspected  liquid  with  hydrochloric  acid,  and  place  it  in  a  shallow  pla- 
tinum capsule.  Touch  the  platinum,  through  the  acid  liquid,  with  a  piece 
of  pure  zinc  foil.  Wherever  the  metals  come  in  contact,  metallic  antimony 
in  the  state  of  a  black  powder,  is  deposited  upon  the  surface  of  the  platinum. 
The  liquid  should  be  poured  off,  and  the  capsule  thoroughly  washed  with 
distilled  water.  This  may  be  effected  without  disturbing  the  deposit.  A 
small  quantity  of  hydrosulphate  of  ammonia  poured  on  the  black  deposit 
speedily  dissolves  it  (if  antimony)  by  the  aid  of  heat,  and  on  evaporation,  an 
orange-red  sulphide  of  antimony  remains.  This  may  be  dissolved  by  a  few 
drops  of  strong  hydrochloric  acid,  and  on  adding  the  acid  liquid  to  water, 
hydrated  oxychloride  of  antimony  is  precipitated.  By  this  process  antimony 
in  small  quantity  may  be  detected  in  any  liquid  containing  organic  matter. 
Some  portion  of  the  metal  escapes  with  the  hydrogen.  The  quantity  of  anti- 
mony may,  however,  be  so  small,  or  the  metal  may  be  so  ditfused  through 
the  animal  substance  (in  the  tissues),  that  this  process  will  yield  no  evidence 
of  the  presence  of  antimony.  The  parts  should  then  be  finely  cut  up,  and 
boiled  in  a  mixture  of  one  part  of  hydrochloric  acid,  and  five  parts  of  water. 
After  some  time,  the  liquid  may  be  tested  by  introducing  into  it  a  slip  of 
polished  copper  foil  free  from  antimony.  If  antimony  is  present  in  small 
quantity,  the  copper  will  acquire  a  violet-colored  deposit  on  its  surface  :  if 
in  large  quantity,  the  deposit  will  be  gray  with  a  metallic  lustre,  or  sometimes 
in  the  state  of  a  black  powder.  When  the  copper  with  the  deposit  is  heated 
in  a  reduction  tube,  no  crystalline  deposit  can  be  obtained  from  it  as  in  the 
case  of  arsenic.  Having  obtained  deposits  on  several  slips  of  copper  foil, 
these  may  be  washed,  dried,  and  heated  in  a  strong  solution  of  potassa  (free 
from  lead),  with  occasional*  exposure  to  air,  until  the  metallic  deposit  is  re- 


ARSENIC.       ITS    DIFFUSION.  465 

moved.  The  antimony  is  thereby  oxidized  and  dissolved  by  the  potassa. 
A  current  of  sulphuretted  hydrogen  gas  may  then  be  passed  into  the  alkaline 
liquid.  This  will  throw  down  any  lead  tliat  may  be  accidentally  present. 
Filter  the  alkaline  liquid  and  acidulate  with  hydrochloric  acid:  the  orange 
sulphide  of  antimony  is  deposited,  and  may  be  collected  and  examined  by 
the  methods  above  described. 

Zinc  separates  metallic  antimony,  in  the  form  of  a  black  powder,  from  the 
acid  solutions  of  its  oxides.  This  is  one  of  the  difficulties  attendant  on  the 
use  of  Marsh's  process  for  the  detection  of  antimony.  The  greater  part  of 
the  metal  is  deposited  in  the  tube  as  a  black  flaky  precipitate,  and  in  the 
course  of  a  short  time,  barely  a  trace  of  antimony  will  be  found  issuing  with 
the  hydrogen  from  the  jet.  Tin  also  separates  antimony  under  certain  cir- 
cumstances, and  it  may  be  usefully  employed  in  qualitative  testing.  Any 
liquid  suspected  to  contain  antimony  should  be  concentrated  by  evaporation 
to  the  smallest  possible  bulk,  and  one-tenth  part  by  volume  of  pure  hydro- 
chloric acid  should  then  be  added  to  it.  A  slip  of  pure  tin-foil  half  an  inch  long 
and  one-eighth  of  an  inch  wide  may  be  immersed  in  the  suspected  liquid  and 
allowed  to  remain  for  24  hours.  If  antimony  is  present  the  tin  will  have 
acquired  a  black  deposit  which  is  quite  soluble  in  a  solution  of  sulphide  of 
ammonium.  If  there  is  no  deposit  it  may  be  concluded  that  no  antimony  is 
present.     Under  similar  circumstances  arsenic  is  not  deposited  on  tin. 

The  following  method  admits  of  the  se[)aration  of  antimony  from  organic 
substances  when  the  metal  is  in  mere  traces.  Coil  a  portion  of  pure  zinc 
foil  round  a  portion  of  clean  platinum  foil,  and  introduce  the  two  metals 
into  the  hydrochloric-acid  decoction  of  the  tissues,  sufficiently  diluted  to 
prevent  too  violent  an  action  on  the  zinc.  Warm  the  organic  liquid,  and 
suspend  the  coils  in  it.  Sooner  or  later,  according  to  the  quantity  of  anti- 
mony present,  the  platinum  as  well  as  the  zinc  will  bs  coated  with  an  adher- 
ing black  powder  of  metallic  antimony.  Wash  the  platinum  foil,  and  digest 
in  strong  nitric  acid.  So  soon  as  the  antimony  is  dissolved  from  its  surface, 
the  platinum  may  be  removed.  Add  a  few  drops  of  hydrochloric  acid,  and 
evaporate  the  acid  liquid  to  dryness.  The  residue,  redissolved  in  hydro- 
chloric acid,  and  the  solution  diluted  and  treated  with  a  current  of  sulphu- 
retted hydrogen,  will  yield  an  orange-red  sulphide  of  antimony.  The  black 
deposit  is  readily  dissolved  by  sulphide  of  ammonium,  yielding  an  orange- 
red  sulphide  of  antimony,  and  it  is  also  soluble  in  nitrohydrochloric  acid,  but 
not  in  hydrochloric  acid  alone.  When  kept  for  a  few  days  in  contact  with 
water  and  air,  the  black  metallic  deposit  is  converted  into  white  oxide  of  anti- 
mony. Magnesium  may  be  employed  with  advantage  in  this  experiment  in. 
place  of  zinc.  In  this  case  the  liquid  need  not  be  so  strongly  acidulated. 
The  magnesium,  as  it  dissolves,  does  not  impart  to  the  liquid  any  substaoae 
which  can  be  precipitated  by  sulphuretted  hydrogen. 


CHAPTER    XXXVI. 

Arsenic  (As='75). 

The  distinct  metallic  characters  of  arsenic  were  fir&t  noticed  in  17t3,  but 
some  of  its  combinations  (the  sulphides)  were  known  before  the  Christian  era. 
Its  name  is  derived  from  the  Greek  apaevixov  (orpiment).     Its  chemical  rela- 
tions are  such  as  to  place  it  rather  among  the  simple  acidifiable  substances  than 
30 


r 


466  CHEMICAL    PROPERTIES    OP    ARSENIC. 

among  the  metals  :  it,  however,  has  the  lustre  and  opacity  of  a  metal,  and 
conducts  electricity.  It  occurs  native,  and  in  form  of  native  oxide  ;  and  there 
are  many  native  arsenates :  it  also  occurs  as  a  sulphide,  and  is  frequently 
found  in  combination  with  other  sulphides,  especially  with  sulphide  of  iron, 
constituting  arsenical  pyrites  =Y^'^^,YqA^.  It  is  owing  to  its  presence  in 
pyrites  that  arsenic  is  found  in  coal  and  lignite.  It  has  been  detected  in  the 
coal  of  Northumberland  and  Nottingham.  The  coal  of  Sarrebriick  was 
found  to  contain  0  003  per  cent,  of  arsenic,  and  in  a  variety  of  French  coal 
from  Ville,  as  much  as  0*0415  per  cent,  of  arsenic  was  detected  (Percy's 
Metallurgy,  p.  106).  During  the  roasting  of  the  arseniferous  sulphides  of 
copper,  iron,  cobalt,  and  nickel,  large  quantities  of  oxide  of  arsenic  are 
formed,  and  from  such  sources,  commercial  demands  are  supplied.  The 
amount  of  white  arsenic  obtained  in  Cornwall  in  1865,  and  separated  from 
other  metallic  ores  was  826  tons. 

Traces  of  arsenic  are  found  in  many  minerals,  and  consequently  in  some 
of  their  products,  as  in  sulphur  and  sulphuric  a«id,  in  zinc,  in  sulphide  of 
antimony,  and  occasionally  in  phosphorus.  It  w^as  at  one  time  supposed 
that  arsenic  entered  into  the  composition  of  the  flesh  and  bones  of  animals 
as  a  normal  constituent,  but  it  has  been  clearly  proved  that  it  is  never  found 
in  the  tissues,  either  of  animals  or  vegetables,  except  when  it  has  been  intro- 
duced into  them  by  accident  or  design.  It  is  thus  remarkably  contrasted 
with  phosphorus,  which  is  an  essential  constituent  of  organic  matter.  On 
the  other  hand,  the  chemical  analogies  between  these  elements  are  in  some 
respects  striking.  In  vapor,  they  have  a  similar  odor  :  they  form  solid  acids 
with  oxygen,  similar  in  composition  (AsOg,  POg  and  AsO,,  PO5),  and 
similar  gaseous  compounds  with  hydrogen  (AsHg,  PH3).  Their  volume 
equivalents  are  the  same,  the  atomic  weight  of  each  element  being  represented 
by  half  a  volume  of  vapor. 

Arsenic  may  be  obtained  from  the  purified  white  arsenic  of  commerce,  by 
mixing  it  with  its  weight  of  black  flux,  and  introducing  the  mixture  into  a 
flask  or  small  retort,  gradually  raised  to  a  red  heat :  a  brilliant  metallic 
sublimate  of  arsenic  collects  in  the  upper  part  of  the  flask  or  retort.  The 
volatility  of  white  arsenic  pr.events  its  easy  reduction  by  charcoal  alone  ; 
but  the  potassa  in  the  flux  enables  it  to  acquire  a  temperature  sufficient  for 
its  reduction.  Dried  ferrocyanide  of  potassium  is  a  good  reducing  agent 
in  all  cases  where  it  is  desired  to  obtain  the  metal  from  arsenious  acid. 
Arsenic  may  also  be  obtained  by  heating  the  ore  called  native  arsenic 
in  coarse  powder  in  a  retort ;  the  metal  sublimes,  leaving  the  impurities 
behind. 

Properties. — Arsenic  is  of  a  steel-gray  color,  crystalline  texture,  and  very 
brittle.  Its  sp.  gr.  is  5-75.  It  volatilizes  when  heated,  and  in  close  vessels 
may  be  sublimed  at  a  temperature  lower  than  its  fusing  point;  this  is 
generally  stated  to  be  about  400,  but  according  to  Fischer  it  does  not  rise 
in  vapor  below  a  dull  red  heat.  The  density  of  arsenic-vapor  is  about  10*39. 
Metallic  arsenic  tarnishes  on  exposure  to  air,  falling  to  a  grayish-black 
powder  (suboxide  ?).  It  gives  off  no  vapor.  It  does  not  decompose  water, 
and  is  not  dissolved  by  that  liquid,  although  it  is  slowly  oxidized  by  air  and 
w^ater.  It  has  no  taste  and  no  odor  at  ordinary  temperatures ;  but  in  the 
state  of  metallic  vapor,  as  it  is  liberated  by  heating  its  oxide  with  carbon, 
it  has  an  odor  resembling  that  of  garlic.  When  boiled  in  water  with  a 
Btrong  solution  of  potassa,  arsenite  of  potassa  is  formed  and  hydrogen  is 
jJUfiliberated.  It  is  not  soluble  in  strong  hydrochloric  acid  :  but  it  is  rapidly 
^■^  oxidized  and  converted  into  arsenic  acid  by  nitric  and  nitrohydrochloric 
acids.  Diluted  nitric  acid  transforms  it  into  arsenious  acid.  It  combines 
directly  with  chlorine,  iodine,  bromine,  and  other  elementary  bodies.     It  is 


ARSENIOUS    ACID.  467 

rapidly  oxidized  by  an  ozonized  atmosphere,  and  is  converted  into  arsenic 
acid  (p.  112).  When  heated  in  a  close  tube,  it  sublimes  unchanged  :  but 
when  heated  in  air,  it  is  oxidized  and  converted  into  arsenious  acid,  which 
is  deposited  in  octahedral  crystals. 

Native  arsenic  usually  occurs  in  rounded  masses,  or  nodules,  of  a  foliated 
lamellar  texture,  and  is  often  associated  with  the  ores  of  silver,  cobalt,  lead 
and  nickel.  Its  color  in  the  fresh  fracture  is  nearly  tin-white,  but  it  speedily 
tarnishes. 

Arsenic  and  Oxygen. — There  are  two  compounds  of  arsenic  and  oxygen, 
namely,  arsenious  acid  and  arsenic  acid. 

Arsenious  Acid  (AsOa) ;  White  Arsenic;  White  Oxide  of  Arsenic. — 
This  is  the  best  known,  and  most  commonly  occurring  compound  of  arsenic. 
It  is  formed  by  the  combustion  of  the  metal ;  but  is  generally  procured  by 
the  joint  action  of  heat  and  air  on  certain  arseniferous  ores.  Arsenious  acid 
occurs  in  white  translucent  vitreous  masses,  often  of  a  slight  buff  tint,  and 
occasionally  transparent,  especially  when  first  removed  from  the  subliming 
vessel  :  on  breaking  the  more  opaque  pieces,  a  translucent  glassy  nucleus  is 
often  found  within  them.  When  slowly  sublimed  in  a  current  of  air,  as  in  a 
tube  open  at  both  ends,  the  vapor  condenses  in  regular  octahedral  crystals  ; 
but  if  rapidly  sublimed  it  forms  a  white  powder,  which,  however,  under  the 
microscope,  is  evidently  crystalline.  The  massive  arsenious  acid  of  com- 
merce is  generally  pure,  but  when  in  powder  it  is  sometimes  adulterated  with 
the  sulphate  of  baryta  or  lime.  The  temperature  at  which  arsenious  acid  rises 
in  vapor  is  below  that  at  which  it  fuses,  and  appears  to  be  about  360°.  The 
density  of  its  vapor  is  13*85,  and  it  is  inodorous.  When  heated  under  pres- 
sure, or  when  suddenly  and  highly  heated,  it  fuses,  and  concretes  on  cooling 
into  an  amorphous  vitreous  solid.  Arsenious  acid  is  almost  tasteless.  In 
fine  powder  it  has  been  described  as  having  a  rough  or  astringent  taste. 
The  specific  gravity  of  the  opaque  arsenious  acid  is  about  3  6,  that  of  the 
transparent  vitreous  and  fused  acid  is  about  3  8.  The  solubility  of  arsenious 
acid  in  water  has  been  variously  stated,  and  it  appears  in  some  measure  to 
be  dependent  upon  its  isomeric  modifications  ;  100  parts  of  water  at  60°  dis- 
solving 0*96  of  the  vitreous,  and  1-25  of  the  opaque  acid  ;  and  at  212°,  9  68 
of  the  former  and  11-47  of  the  latter.  When  these  solutions  are  cooled 
down  to  60°,  r78  of  the  vitreous  and  2-9  of  the  opaque  are  retained. 

We  have  found  by  experiment  that  hot  water  cooling  from  212°  on  the 
opaque  variety  in  fine  powder,  does  not  dissolve  more  than  l-400th  part  of 
its  weight.  Water  boiled  for  an  hour  and  allowed  to  cool,  will  hold  dis- 
solved l-40th  part  of  its  weight,  or  twelve  grains  to  an  ounce.  If  boiled  for 
a  shorter  time  not  more  than  l-80th  part  is  retained  in  the  cold  solution. 
Cold  water  does  not  dissolve  more  than  from  l-400th  to  1-1 000th  of  its 
weight.  When  mixed  with  water  the  powder  partly  floats,  forming  a  film 
on  the  surface.  A  saturated  solution  of  arsenious  acid  has  a  slightly  acid 
reaction  on  litmus-paper.  It  is  dissolved  by  alcohol  and  oils,  but  only  to  a 
slight  extent.  When  a  concentrated  solution  of  the  vitreous  acid  in  boiling 
hydrochloric  acid  is  suffered  to  cool,  the  crystals  which  it  deposits  have  the 
properties  of  the  opaque  acid,  and  this  transition  from  the  one  aliotropic 
modification  to  the  other  is  attended  by  the  evolution  of  light ;  but  if  the 
opaque  acid  is  used,  or  if  the  deposited  crystals  are  redissolved,  those  which 
are  subsequently  deposited  from  the  hydrochloric  solution  are  formed  without 
any  luminous  appearance.  ^^ 

Arsenious  acid  is  decomposed  at  a  dull  red  heat  by  hydrogen,  and  many  ^B 
of  the  metals.     Its  aqueous  solution  is  rendered  yellow  by  a  current  of  sul-  ^^ 
phuretted  hydrogen,  and  when  the  solution  is  acidulated  by  hydrochloric 
acid  a  yellow  precipitate  of  tsrsulphide  of  arsenic  falls;  AsOg, +  3113  = 


468  CHEMICAL    PROPERTIES    OF    ARSENIOUS    ACID. 

AsSg+SHO  :  a  yellow  tint  is  observed,  even  when  only  a  10,000th  part  of 
arsenious  acid  is  dissolved.  Hydrosulphate  of  ammonia  does  not  precipitate 
a  solution  of  arsenious  acid  unless  an  acid  is  added,  when  the  tersulphide 
falls.  Sulphate  of  copper  and  nitrate  of  silver  give  no  precipitates  in  the 
solution  until  an  alkali  is  added,  when  the  former  produces  a  green,  and  the 
latter  a  yellow  precipitate.  For  the  further  action  of  tests  upon  this  com- 
pound in  the  solid  as  well  as  in  the  dissolved  state,  see  page  476. 

Hydrochloric  acid  is  a  powerful  solvent  of  arsenious  acid,  but  by  the  con- 
tinued application  of  heat  much  of  the  arsenic  escapes  as  chloride.  A  copper 
wire  introduced  into  this  acid  solution,  moderately  heated,  is  instantly  coated 
with  a  layer  of  metallic  arsenic  of  an  iron-gray  color.  (As03+3HCl4-3Cu  = 
As-fSHO-fSCuCl).  On  this  reaction  Behisch^s  process  for  the  detection  of 
arsenic  is  based  (page  477).  When  placed  in  contact  with  nascent  hydro- 
gen, as  by  adding  zinc  or  magnesium  to  the  hydrochloric  acid  solution,  or 
any  soluble  compound  of  arsenic  to  zinc  or  magnesium  and  sulphuric  acid, 
water  and  arsenuretted  hydrogen  are  produced  (As03  +  6H=AsH3-j-3HO). 
On  this  reaction,  Marshes  process  for  the  separation  of  arsenic  is  founded 
(page  477).  Unlike  antimony,  the  metal  is  not  separated  from  its  solutions 
by  tin.  Thus  a  strip  oi  pure  tin-foil,  placed  in  a  solution  of  arsenious  acid 
containing  one-tenth  of  its  volume  of  hydrochloric  acid,  remains  untarnished: 
no  metallic  arsenic  is  deposited.  In  a  solution  containing  antimony,  this 
metal  under  similar  circumstances  is  rapidly  separated  in  the  cold,  and  is  de- 
posited on  the  tin  in  the  form  of  a  black  powder.  A  boiling  solution  of 
potassa  readily  dissolves  arsenious  acid  without  change.  If  a  strong  alkaline 
solution  is  employed  in  excess,  and  pure  zinc  is  added  to  the  liquid,  arsenu- 
retted hydrogen  escapes  (K0  +  6Zn-f 3HO+As03=AsH3H-KO,(5ZnO). 
Fleitmann  has  recommended  this  process  for  the  detection  of  arsenious  acid 
when  mixed  with  organic  matter. 

When  arsenious  acid  is  mixed  with  rather  more  than  its  bulk  of  dry  acetate 
of  potassa  or  soda,  and  the  mixture  is  strongly  heated  in  a  closed  tube,  it 
undergoes  fusion,  a  portion  of  metallic  arsenic  is  sublimed,  and  the  oxide  of 
the  compound  radical  cacodyle,  recognized  by  its  offensive  odor,  is  set  free 
(2C4H303-i-As03=C4H60,As+4CO,).  It  is  decomposed  by  carbon  and 
all  carbonaceous  flues,  the  metal  being  volatilized  (As03  +  3C=As-l-3CO). 
The  cyanide  of  potassium,  mixed  with  a  little  carbonate  of  soda  to  prevent 
fusion,  and  the  ferrocyanide  of  potassium,  heated  with  arsenious  acid, 
decompose  it,  and  metallic  arsenic  is  sublimed:  2As03-f  3KCy=2As-f  3K0, 
CyO.  Powdered  metallic  magnesium  also  acts  as  a  good  reducing  agent 
(AsOg-|-3Mg=As  +  3MgO).  Arsenious  acid  operates  as  a  deoxidizer. 
When  boiled  with  a  solution  of  chromate  of  potassa,  green  oxide  of  chromium 
is  produced.  It  decolorizes  a  solution  of  permanganate  of  potassa,  reduces 
chloride  of  gold  to  the  metallic  state,  and  reduces  the  black  oxide,  of  copper 
to  red  oxide,  when  a  few  drops  of  the  sulphate  are  added  to  a  solution  of 
arsenious  acid  in  caustic  potassa,  and  the  liquid  is  boiled.  Chlorine,  or  a 
mixture  of  hydrochloric  acid  with  chlorate  of  potassa,  as  well  as  an  alkaline 
nitrate  or  chlorate,  by  fusion,  convert  it  into  arsenic  acid  and  arsenate  of 


Traces  of  arsenious  acid  are  not  unfrequent  in  various  chemical  and  phar- 
maceutical preparations  :  it  has  been  detected  in  sulphuric,  hydrochloric, 
nitric,  acetic,  and  phosphoric  acids,  in  phosphate  of  soda,  and  in  emetic  tar- 
tar. The  preparations  of  bismuth  and  copper  frequently  contain  it ;  and  it 
is  sometimes  found  associated  with  the  hydrated  oxide  of  iron,  in  the  ochreous 
sediments  of  spring  and  river  waters  (page  150).  This  acid  is  used  in  many 
of  the  arts,  especially  in  color-making,  dyeing,  and  calico-printing ;  it  is  also 
used  in  medicine,  and  in  a  variety  of  preparations  for  the  destruction  of  ver- 


ARSENITES.      SCHEELE'S    GREEN.  469 

min.  It  is  much  em[)loyed  in  the  steeping  of  seed-corn  for  the  purpose  of 
destroyini]^  the  spores  of  fungi.  In  the  small  quantities  in  which  it  is  com- 
monly sold  to  the  public  it  is  directed  to  be  colored  with  indigo  or  soot,  a 
circumstance  which  must  be  borne  in  mind  in  searching  for  it  in  cases  of 
poisoning.  It  is  a  powerful  irritant  poison,  and  has  destroyed  the  life  of 
an  adult  in  the  small  dose  of  two  grains.  It  is  rapidly  absorbed  into  the 
blood,  and  is  equally  fatal  whether  it  is  taken  by  the  mouth  or  applied  to  a 
wound. 

Arsenites. — These  salts,  when  strongly  heated,  either  evolve  arsenious 
acid  or  metallic  arsenic  :  in  the  latter  case  they  are  converted  into  arsenates; 
thus,  5(AsOj=3(AsOJ-}-2As:  when  heated  with  charcoal,  or  cyanide  of 
potassium,  metallic  arsenic  sublimes.  The  alkaline  arsenites,  when  in  solu- 
tion, are  decomposed  by  lime  and  the  salts  of  lime,  and  a  white  precipitate 
of  arsenite  of  lime  falls,  2(CaO)As03:  they  are  precipitated  green  by  solu- 
tions of  copper,  2(CuO)As03,  and  yellow  by  nitrate  of  silver,  2(AgO)As03. 
They  are  not  precipitated  by  sulphuretted  hydrogen,  except  when  an  excess 
of  a  stronger  acid  is  present :  in  this  way  the  hydrochloric  solutions  of  those 
arsenites,  which  are  insoluble  in  water,  may  also  be  .decomposed.  The 
arsenites  of  ammonia,  potassa,  and  soda,  are  easily  soluble,  but  are  uncrys- 
tallizable  :  they  are  formed  by  dissolving  the  acid  in  the  respective  alkaline 
solutions.  The  supposed  crystals  of  arsenite  of  ammonia  deposited  by  the 
solution  of  arsenious  acid  in  ammonia  are  quite  destitute  of  ammonia,  and 
consist  only  of  arsenious  acid.  When  arsenious  acid  is  dissolved  in  the 
alkaline  carbonates,  it  is  deposited  unaltered  by  evaporating  the  solution,  so 
that  it  has  been  doubted  whether  this  acid  expels  carbonic  acid  in  the  humid 
way. 

The  arsenites  of  lime,  baryta,  strontia,  and  magnesia,  are  with  difiBculty 
soluble  in  water,  but  readily  soluble  in  hydrochloric  acid  :  there  are  two 
arsenites  of  lime — one  basic,  =2(CaO)As03;  the  other  neutral,  CaO,As03. 
Arsenite  of  potassa  is  the  active  ingredient  in  the  Liquor  arsenicalis  of  the 
Pharmacopoeia,  and  in  Fowlerh  mineral  solution,  or  tasteless  ague-drop.  A 
mixture  of  arsenious  acid  with  carbonate  of  potassa,  or  soft-soap,  is  used  as 
a  wash  for  killing  the  fly  in  sheep.  Another  mixture,  used  by  naturalists  for 
preserving  animals,  consists  of  32  parts  of  white  soap,  32  of  arsenious  acid, 
12  of  dried  carbonate  of  potassa,  and  4  of  powdered  quicklime,  with  1  part 
of  camphor.  Arsenuretted  hydrogen  is  said  to  be  slowly  evolved  from  this 
composition. 

Arsenite  op  Copper,  2(CuO)  AsOg,  Scheele^s  green  ;  Aceto- Arsenite  op 
Copper,  SchweinfUrth  green  3(CuO,As03)  +  (CuO,C^H303)  are  green  pig- 
ments much  used  in  the  arts.  The  latter,  known  also  by  the  name  of  Emer- 
ald green,  from  its  rich  green  color,  containing  59  per  cent,  of  arsenious 
acid.  It  is  much  employed  in  the  coloring  of  paper-hangings  and  various 
articles  of  dress,  as  well  as  in  the  coloring  of  confectionery.  When  an  alka- 
line arsenite  is  mixed  with  a  solution  of  sulphate  of  copper,  a  precipitate  of 
an  apple-green  color  falls  (Scheele^s  green),  used  as  a  pigment :  it  is  prepared 
by  dissolving  2  parts  of  sulphate  of  copper  in  44  of  hot  water,  and  gradually 
adding  it  to  a  solution  of  2  parts  of  carbonate  of  potassa  and  1  of  arsenious 
acid  in  44  of  hot  water,  the  whole  being  well  stirred  during  mixture  :  the 
arsenite  of  copper,  in  the  form  of  a  fine  green  powder,  is  gradually  deposited, 
and  is  to  be  washed  and  dried  at  212^.  A  similar  preparation,  known  under 
the  name  of  SchweinfUrth  green,  is  made  as  follows :  50  lbs.  of  sulphate  of 
copper  and  10  of  lime  are  dissolved  in  20  gallons  of  vinegar,  and  a  boiling- 
hot  aqueous  soljition  of  50  lbs.  of  arsenious  acid  quickly  stirred  into  it ;  the 
precipitate  is  dried  and  reduced  to  a  fine  powder.  This  green  pigment,  by 
reason  of  its  being  very  loosely  laid  on  paper-hangings  is  liable  to  be  diffused 


470  CHEMICAL    PROPERTIES    OP    ARSENIC    ACID. 

in  the  air  of  a  room,  and  under  these  circumstances  it  has  in  some  cases  given 
rise  to  the  usual  well-marked  symptoms  of  chronic  poisoning.  Its  employ- 
ment on  articles  of  dress  and  confectionery  has  been  attended  with  more 
serious  consequences.  The  following  is  a  simple  method  of  detecting  arsenic 
in  the  colored  substance.  Cover  a  portion  of  the  green  paper  with  a  solu- 
tion of  ammonia.  The  green  pigment  is  dissolved  and  forms  a  blue  solution 
with  the  ammonia,  owing  to  the  oxide  of  copper  with  which  the  arsenic  is 
combined.  Place  a  few  crystals  of  nitrate  of  silver  in  a  porcelain  capsule, 
and  pour  upon  them  a  few  drops  of  ammoniacal  solution.  If  arsenic  is 
present,  the  crystals  will  acquire  a  superficial  yellow  color  by  the  production 
of  yellow  arsenite  of  silver  (see  page  476).  A  small  portion  of  the  green 
powder,  when  heated  in  a  reduction-tube,  yields  a  sublimate  of  octahedral 
crystals,  which  may  be  easily  identified  as  arsenious  acid. 

In  the  solutions  of  lead,  antimony,  and  bismuth,  arsenite  of  potassa  forms 
white  precipitates;  added  to  nitrate  of  cobalt,  it  forms  a  pink  precipitate  ; 
and  bright  yellow,  with  nitrate  of  uranium.  With  nitrate  of  silver  it  forms 
a  yellow  precipitate,  very  soluble  in  ammonia.  All  these  precipitates  are 
probably  arsemtes  of  the  respective  metals,  and,  heated  by  a  blowpipe  on 
charcoal,  they  exhale  the  smell  of  arsenic.  They  are  decomposed  when 
boiled  in  solution  of  carbonate  of  potassa  or  of  soda  ;  they  are  mostly  soluble 
in  an  excess  of  arsenious  acid,  and  are  readily  dissolved  by  nitric  acid,  and 
such  other  acids  as  form  soluble  compounds  with  their  bases.  Native  arse- 
nite of  lead  is  found  in  France,  Spain,  a!id  Siberia,  and  the  mineral  called 
Condurrite  appears  to  be  an  arsenite  of  copper. 

Arsenic  Acid  (AsOg)  is  obtained  by  distilling  a  mixture  of  1  part  of  hy- 
drochloric, 12  parts  of  nitric,  and  4  parts  of  arsenious  acid  :  nitric  oxide  gas 
is  given  oif,  and  when  the  contents  of  the  retort  have  acquired  the  consist- 
ency of  a  thin  syrup,  they  are  poured  into  a  porcelain  dish,  and  evaporated 
by  a  moderate  heat ;  suddenly,  the  arsenic  acid  (which  is  anhydrous)  con- 
cretes into  an  opaque  white  mass,  which  should  be  put,  whilst  warm,  into  a 
well-stopped  phial.  The  hydrochloric  acid  is  only  useful  in  promoting  the 
solution  of  the  white  arsenic,  which  otherwise  adheres  to  the  retort,  and 
occasions  irregular  ebullition. 

Arsenic  acid  is  a  white  deliquescent  compound  ;  it  forms  several  crystalli- 
zable  hydrates  :  it  fuses  in  close  vessels  at  a  heat  approaching  to  redness,  and 
concretes  on  cooling  into  a  vitreous  mass ;  at  a  higher  temperature  it  is 
decomposed,  oxygen  is  evolved,  and  arsenious  acid  sublimes  (As05=As03-f 
20).  Its  specific  gravity  is  about  3 '7.  It  requires  for  solution  6  parts  of 
cold  and  2  of  boiling  water ;  its  solution  reddens  vegetable  blues,  and  has 
an  acid  and  metallic  taste.  When  water  is  poured  upon  the  solid  acid,  part 
only  is  immediately  dissolved,  and  another  portion,  as  is  the  case  with  phos- 
phoric acid,  remains  undissolved,  but  after  a  time,  upon  agitating  the  solution, 
the  whole  is  taken  up.  Arsenic  acid  gives  with  lime-water  a  white  precipi- 
tate, and  with  ammonio-sulphate  of  copper  a  pale  greenish-blue  precipitate. 
It  is  converted  by  sulphurous  acid  into  arsenious  acid,  and  by  the  bisulphite 
or  hyposulphite  of  soda  into  arsenite  of  soda  (AsOg-f  2SOa=As03-f  2SO3). 
It^exerts  no  reducing  action  on  chloride  of  gold,  permanganate  of  potassa, 
or  the  salts  of  copper  and  chromium.  When  the  solid  acid  is  boiled  with 
aniline  in  certain  proportions,  it  produces  a  purple  dye.  When  heated  with 
hydrochloric  acid,  and  copper  is  introduced  into  the  liquid,  metallic  arsenic  is 
only  slowly  deposited  ;  and  there  is  no  deposit  unless  the  arsenic  acid  is  in  com- 
paratively large  proportion.  Sulphuretted  hydrogen  very  slowly  affects  it,  and 
throws  down  after  a  time  a  pale  yellow  pentasulphide  (As03-t-5HS  =  AsSg-f 
HO).  To  effect  its  complete  precipitation,  it  should  be  firs?  converted  into 
arsenious  acid  by  warming  the  solution  with  sulphurous  acid.  Another  method 


CHEMICAL    CHARACTER    OF    THE    ARSENATES.  4U 

consists  in  acidulating  the  liquid  with  hydrochloric  acid,  then  adding  a  solu- 
lution  of  hyposulphite  of  soda,  and  boiling  the  mixture.  Tersulphide  of 
arsenic  is  precipitated  (AsS.,).  With  nitrate  as  well  as  with  the  amraonio- 
nitrate  of  silver,  arsenic  acid  gives  at  once  a  red-brown  precipitate.  It  is 
decomposed  by  nascent  hydrogen  like  arsenious  acid,  and  yields  arsenuretted 
hydrogen.  When  the  solid  acid  is  heated  to  redness  with  carbon  or  cyanide 
of  potassium,  the  arsenic  is  reduced  to  the  metallic  state,  and  is  sublimed. 

Arsenates  are  produced  by  the  union  of  this  acid  with  metallic  oxides  ; 
those  which  are  insoluble  may  be  formed  by  adding  arsenate  of  potassa  to 
their  respective  solutions.  The  normal  arsenates  are  constituted  like  the 
phosphates,  of  1  atom  of  acid  with  3  of  base,  and  there  are  also  salts  with 
1  and  2  atoms  of  basic  oxide,  in  which  the  deficient  base  is  replaced  by  1 
and  2  atoms  of  water ;  but  there  appear  to  be  no  modifications  correspond- 
ing to  the  pyrophosphates  and  metaphosphates.  The  arsenates  which  are 
insoluble  in  water,  are  soluble  in  dilute  nitric  acid  and  in  such  other  acids  as 
do  not  form  insoluble  compounds  with  their  bases:  ammonia,  precipitates 
them  from  these  solutions.  They  are  readily  decomposed  by  charcoal  at  a 
red-heat ;  but  many  of  them,  when  heated  alone,  are  unchanged  even  at  a 
higher  temperature.  They  are  decomposed  when  boiled  in  solutions  of  the 
fixed  alkaline  carbonates.  The  soluble  arsenates  generally  give  a  white  pre- 
cipitate with  lime-water  2(CaO)HO,AsO-;  they  are  not  immediately  preci- 
pitated by  a  solution  of  sulphuretted  hydrogen  :  with  protosulphate  of  iron 
they  give  a  white  precipitate  (or  yellowish  if  arsenious  acid  be  at  the  same 
time  present).  They  give  white  precipitates  with  solutions  of  lead  and  zinc  ; 
yellow  with  the  persalts  of  uranium  and  mercury  ;  red  with  the  solutions  of 
salts  of  cobalt;  green  with  those  of  nickel ;  pale  greenish-blue  with  those  of 
copper  2(CuO)HO,AsO„  and  reddish-brown  with  those  of  silver  3(AgO) 
AsO..  The  last  reaction  is  the  most  characteristic:  hence  nitrate  of  silver 
is  alone  sufficient  for  the  detection  of  an  arsenate.  These  precipitates  are 
mostly  soluble  in  hydrochloric  acid,  and  in  solutions  of  ammoniacal  salts. 
Arsenate  of  potassa  gives  a  yellow  precipitate  with  persulphate  of  uranium 
when  the  solution  is  so  diluted  as  to  contain  only  a  10,000th  part  of  arsenic 
acid  ;  and  with  protosulphate  of  iron  a  white  cloud  is  perceptible  under  the 
same  state  of  dilution.  All  the  arsenates,  when  dissolved  in  water  or  la 
dilute  nitric  acid,  give  a  white  precipitate  with  acetate  of  lead,  which  fuses 
and  emits  arsenical  fumes  when  heated  on  charcoal  before  the  blowpipe. 

The  salt  commonly  called  Binarsenate  of  potassa  =K0,As03,  may  be 
formed  either  by  adding  excess  of  arsenic  acid  to  a  solution  of  potassa,  and 
evaporating  ;  or  by  heating  to  redness,  in  a  Florence  flask,  a  mixture  of  equal 
parts  of  nitre  and  white  arsenic.  During  the  latter  operation  much  nitrous 
gas  is  evolved,  and  on  dissolving  the  residue  in  water,  filtering,  and  evapo- 
rating, prismatic  crystals  are  obtained,  resembling  those  of  the  corresponding 
phosphates  of  ammonia  and  potassa;  they  are  soluble  in  5-3  parts  of  water 
at  40^,  and  insoluble  in  alcohol;  their  formula  is  KO,2(HO),As05.  Mac- 
quer  was  the  first  who  procured  this  salt ;  hence  it  is  termed  Macquerh  Ar- 
senical salt.  «It  is  not  easily  decomposed  by  heat  alone,  and  may  be  fused 
and  kept  red-hot  without  undergoing  other  change  than  losing  a  little  water  ; 
but  when  mixed  with  about  an  eighth  of  charcoal  powder  and  distilled, 
metallic  arsenic  rises,  and  carbonate  of  potassa,  mixed  with  a  part  of  the 
charcoal,  remains  in  the  body  of  the  retort.  This  salt  as  well  as  the  arsenite, 
is  used  in  medicine.  It  is  a  delicate  test  of  the  presence  of  silver,  in  solu- 
tions of  which  it  occasions  a  red-brown  precipitate  ;  it  is  also  sometimes 
used  to  separate  iron  from  manganese ;  it  produces  in  the  persalts  of  iron  a 
white  precipita'te,  whilst  the  arsenate  of  manganese  remains  in  solution.  Ar- 
senate  of  soda  is  extensively  used  in  calico-printing.     When  dissolved  iu 


4Y2  ARSENATES    OF    IRON.      ARSENURETTED    HYDROGEN, 

water  and  mixed  with  sugar,  it  is  sometimes  employed  as  a  fly-poison.  Paper 
impregnated  with  this  liquid,  and  dried,  is  sold  under  the  name  of  Papier 
Moure.  The  arsenates  of  the  alkaline  earths  are  not  soluble  in  water.  When 
a  solution  of  an  arsenate  is  acidulated  with  hydrochloric  acid,  and  boiled 
with  hyposulphite  of  soda,  tersulphide  of  arsenic  is  precipitated.  {See  p. 
4n.) 

Arsenic  acid  forms  a  nearly  insoluble  compound  salt  with  ammonia  and 
magnesia,  resembling  the  ammonio-magnesian  phosphate.  When  phosphoric 
acid  or  a  phosphate  is  not  present,  arsenic  may  be  thus  separated,  and  its 
quantity  determined.  If  a  solution  of  sulphate  of  magnesia  is  mixed  with 
a  solution  of  arsenic  acid;  and  if  ammonia,  with  chloride  of  ammonium,  is 
then  added,  an  insoluble  crystalline  precipitate  of  arsenate  of  ammonia  and 
magnesia  is  slowly  produced.  This  is  not  only  a  test  for  arsenic  acid,  but 
it  serves  to  distinguish  it  from  arsenious  acid,  as  this  forms  no  similar  com- 
pound salt.  The  precipitate,  when  dried  at  212°,  has  the  composition  NH,, 
HO,2(MgO)AsO.,HO.  It  contains  62*9  per  cent,  of  arsenic  acid.  It  does 
not,  like  the  corresponding  phosphate,  admit  of  calcination,  as  a  portion  of 
arsenic  would  be  expelled  at  a  high  temperature. 

Arsenates  op  Iron. — The  protosalts  of  iron  give  a  white  precipitate  with 
arsenate  of  ammonia,  which  gradually  becomes  green  on  exposure  to  air; 
it  appears  from  Chenevix's  analysis  to  be  3(FeO),As05,6HO.  When  solu- 
tions of  perchloride  of  iron  and  bibasic  arsenate  of  soda  are  mixed,  a  white 
perarsenate  of  iron  falls  :  2Fe,Cl3-f  3[2NaO,  As05]  =  2Fe203,3As05-f  6NaCl. 
This  salt,  when  dried  at  common  temperatures,  retains  about  18  per  cent,  of 
water  (=12  atoms)  which  it  loses  when  heated,  and  becomes  red,  and  at 
higher  temperatures  it  glows  and  acquires  a  yellow  color.  It  is  insoluble  in 
water;  hence  hydrated  peroxide  of  iron  has  been  used  as  a  chemical  anti- 
dote in  poisoning  by  arsenic.  This  oxide  precipitates  both  arsenious  and 
arsenic  acid  when  these  are  in  solutioti  in  water.  The  arsenates  of  the  other 
metallic  oxides  call  for  no  special  notice. 

Arsenic  and  Hydrogen  ;  Arsenuretted  Hydrogen  Gas.  Hydride  of 
Arsenic  (AsHg). — When  nascent  hydrogen  comes  into  contact  with  arsenic, 
or  any  of  its  soluble  compounds,  a  portion  of  the  metal  is  carried  over  in  a 
state  of  combination  with  the  hydrogen.  If  arsenious  acid  is  added  to 
dilute  sulphuric  acid,  and  magnesium  or  zinc  is  dissolved  in  the  mixture,  the 
liberated  hydrogen  is  rich  in  arsenic  ;  but  free  hydrogen  is  also  evolved. 
Pure  arsenuretted  hydrogen  is  best  obtained  by  the  action  of  hydrochloric 
acid  upon  a  pulverized  alloy  of  zinc  and  arsenic,  obtained  by  fusing  together 
equal  parts  of  these  metals.  This  gas  is  colorless :  it  has  a  nauseous  odor 
resembling  garlic,  and  is  so  poisonous  that  extreme  caution  must  be  observed 
in  dealing  with  it.  It  has  proved  fatal  to  three  chemists,  who  were  engaged 
in  experiments  upon  it.  The  gas  blackens  paper  impregnated  with  nitrate 
of  silver,  but  it  produces  no  change  of  color  on  paper  impregnated  with  a 
salt  of  lead. 

Arsenuretted  hydrogen  may  be  collected  and  retained  over  water,  which, 
however,  absorbs  it  to  the  amount  of  about  one-fifth  of  its  volnme,  and,  if  it 
contain  air,  a  dark-colored  film  of  arsenic  is  gradually  deposited  ;  it  is  not 
absorbed  by  alkaline  solutions,  nor  by  alcohol  or  ether,  but  oil  of  turpentine 
absorbs  it  largely.  It  is  liquefied,  under  atmospheric  pressure,  when  cooled 
down  to  — 40°.  Faraday  could  not  solidify  it  at  166°  below  0°.  Arsenu- 
retted hydrogen  is  decomposed  at  a  full  red  heat,  arsenic  is  deposited,  and  2 
volumes  of  the  gas  afford  3  volumes  of  hydrogen.  When  mixed  with  an 
insufficient  quantity  of  air  or  oxygen  for  its  perfect  combustion  it  deposits 
metallic  arsenic  in  burning;  but  with  excess  of  oxygen  it  explodes  with 
violence,  and  forms  water  and  arsenious  acid.     It  burns  in  contact  with  air 


CHLORIDE    OF    ARSENIC.  473 

with  a  pale  blue  frame,  forminnr  water  and  arsetiions  acid,  and  depositing 
arsenious  acid  upon  the  sides  of  the  jar  as  the  flame  descends  (AsH^  +  ^Oss 
3H04-AsO.J.  These  are  the  products  of  its  combustion  when  burnt  from  a 
jet.  If  a  clean  glass  plate,  or  a  surface  of  porcelain,  is  held  above  the  point 
of  the  flame,  arsenious  acid  and  water  only  are  deposited  ;  if  held  so  as  to 
bisect  the  flame  a  deposit  is  obtained,  consisting  of  metallic  arsenic  in  the 
centre,  and  of  white  arsenioVis  acid  at  the  circumference.  When  deposited 
on  glass  the  central  portion  is  opaque  if  viewed  by  transmitted  light,  but  by 
reflected  light  it  has  a  strong  metallic  lustre.  The  deposit  is  of  a  hair-brown 
color  at  the  circumference.  It  possesses  the  following  additional  chemical 
characters:  1.  It  is  entirely  dissolved  by  fuming  nitric  acid,  and  leaves,  on 
evaporation,  arsenic  acid.  2.  It  is  readily  dissolved  by  a  fresh  solution  of 
chloride  of  lime,  and  leaves,  on  evaporation,  some  arsenate  of  lime  mixed 
with  chloride.  3.  It  is  not  readily  dissolved  by  hydrosulphate  of  ammonia  ; 
on  evaporation  it  leaves  a  yellow  residue  of  sulphide  of  arsenic.  The  anti- 
monuretted  hydrogen,  produced  under  similar  circumstances,  has  widely 
different  properties.  In  addition  to  those  elsewhere  described  (page  461) 
the  following  may  be  noticed  in  contrast  with  the  characters  of  an  arsenical 
deposit :  1.  It  is  not  dissolved  by  a  solution  of  chloride  of  lime.  2.  It  is 
readily  dissolved  by  hydrosulphate  of  ammonia,  leaving,  on  evaporation,  an 
orange-red  sulphide  of  antimony. 

The  sp.  gr.  of  arsenic  in  vapor  is  10*39,  and  the  sp.  gr.  of  arsenuretted 
hydrogen  is  2'695.  As  in  the  analogous  compound  of  phosphorus — half  a 
volume  of  the  vapor  of  arsenic  =75,  is  combined  with  three  volumes  of 
hydrogen  =3,  the  3z  volumes  being  condensed  into  2  volumes  of  the  gas 
(pp.  72  and  245). 

Atoms.    Weights.     Per  cent.  "Vols.  Sp.  Gr. 

Arsenic         .         .     1     ...     75     ...     96-15     ...       J     ...*     5-195 
Hydrogen    .         .     3     ...       3     ...       3-85     ...     3       ...     0-207 

1  78  100-00  2  5-402 

The  sum  of.  the  sp.  gr.  of  the  constituents,  divided  by  2  (5*402 -r  2),  is 
equal  to  2'701,  which  is  but  little  in  excess  of  the  sp.  gr.  determined  by 
Dumas.  Compared  with  hydrogen,  the  sp.  gr.  is  one-half  of  the  equivalent 
weight,  namely,  39.  The  observation  occurs  with  this  as  with  respect  to  the 
phosphorus-compound  :  one  volume  of  the  vapor  of  arsenic  is  equivalent  to 
two  atoms  of  this  elementary  substance. 

Arsenuretted  hydrogen  gas  is  instantly  decomposed  by  chlorine ;  and  if 
chlorine  is  suffered  to  ascend  into  a  jar  containing  it,  while  standing  over 
water,  each  bubble  inflames,  producing  hydrochloric  acid,  whilq  brown  fumes 
of  arsenic  are  produced  and  deposited  ;  if  the  arsenuretted  hydrogen  is  sent 
up  in  the  same  way  into  chlorine,  when  this  gas  is  in  great  excess  hydro- 
chloric and  arsenious  acids  are  immediately  formed.  The  gas  is  similarly 
decomposed  by  iodine  and  bromine.  Agitated  with  a  solution  of  sulphate 
of  copper,  the  gas  is  absorbed,  and  arsenide  of  copper  and  water  are  formed. 
3(CuO,S03)-f  AsH3=Cu3As4-3HO  +  3S03.  This  action  furnishes  a  means 
of  testing  the  purity  of  the  gas,  for  any  uncombined  hydrogen  remains  un- 
absorbed.  It  reduces  the  salts  of  silver,  gold,  platinum,  and  rhodium,  to 
the  metallic  state,  and  arsenious  acid  remains  in  solution  :  thus,  with  nitrate 
of  silver,  the  results  are  silver,  arsenious  acid,  water,  and  nitric  acid.  6(AgO, 
NOJ-f AsH3=6Ag-f As03-h3HO-f6N05.  We  find  by  experiment  that 
there  are  no  liquids  which  so  completely  arrest  and  decompose  this  gas  as  a 
saturated  solution  of  nitrate  of  silver  and  fuming  nitric  acid. 

Arsenic  and  Chlorine  ;  Terchloride  of  Arsenic  (AsClg). — This  com- 
pound may  be  formed  :    1.  By  throwing  finely-powdered  arsenic  into  chlo- 


474  SULPHIDES    OF    ARSENIC.      REALGAR. 

rine  ;  the  metal  burns  and  produces  a  volatile  liquid  ;  or  by  passinj^  dry 
chlorine  over  arsenic  placed  in  a  tube,  and  gently  heated  :  the  resulting  vapor 
of  the  chloride  should  be  condensed  in  a  receiver  cooled  by  ice,  and  may  be 
purified  by  redistilling  it  with  a  little  powdered  arsenic.  2.  Distil  6  parts 
of  corrosive  sublimate  with  1  of  powdered  arsenic  ;  the  chloride  passes  into 
the  receiver  in  the  form  of  an  unctuous  fluid,  formerly  called  butter  of  arsenic. 
3.  1  part  of  arsenious  acid  with  10  parts  of  sulphuric  acid,  are  put  into  a 
tubulated  retort,  and  the  temperature  raised  to  about  212°.  Fragments  of 
fused  common  salt  are  then  thrown  in  by  the  tubulature ;  by  continuing  the 
heat,  and  successively  adding  the  salt,  chloride  of  arsenic  is  obtained  ;  it 
distils  over,  and  may  be  condensed  in  cold  vessels.  Yery  little  hydrochloric 
acid  is  disengaged,  but  towards  the  end  of  the  operation,  a  portion  of 
hydrated  chloride  of  arsenic  is  produced,  which  floats  upon  the  pure 
chloride,  and  appears  more  viscid  and  colorless.  Mixed  with  a  large  quan- 
tity of  w^ater,  the  chloride  of  arsenic  is  decomposed,  and  arsenious  acid  is 
formed,  hydrochloric  acid  being  at  the  same  time  produced.  On  this  reaction 
Schneider,  in  1852,  founded  a  process  for  procuring  arsenic  by  distillation  in 
cases  of  poisoning.  When  fused  chloride  of  sodiuiu  is  employed,  this  should 
always  be  kept  in  excess,  as  if  the  sulphuric  acid  is  in  excess,  the  arsenious 
acid  will  be  retained  by  it  in  the  retort.  If  the  mixture  of  arsenious  and 
hydrochloric  acids  is  saturated  with  chlorine,  or  chlorate  of  potassa,  the 
arsenic  is  converted  into  arsenic  acid,  and  barely  a  trace  passes  over  as 
chloride. 

Chloride  of  arsenic,  when  concentrated,  is  a  dense  oleaginous  transparent 
liquid  :  it  does  not  freeze  at  0°;  it  boils  at  about  270°,  the  density  of  its 
vapor  being  6'3  :  it  exhales  vapor  when  exposed  at  common  temperatures  to 
the  air.  With  a  small  quantity  of  water  it  forms  what  has  been  termed 
hydrated  chloride  of  arsenic :  this  is  probably  a  hydrochloric  solution  of 
arsenious  acid  ;  [AsCl34-3HO  =  As03  +  3HCl],  and  when  more  largely 
diluted,  arsenious  acid  is  deposited  ;  but  when  a  solution  of  arsenious  acid 
in  excess  of  hydrochloric  acid  is  heated,  the  whole  is  volatilized,  and  there 
is  no  residue ;  so  that  when  hydrochloric  acid  containing  arsenious  acid  is 
distilled,  the  product  which  passes  over  is  always  arseniferous ;  and  when 
any  arseniferous  acid  acts  upon  common  salt,  the  hydrochloric  acid  which  is 
evolved  carries  arsenic  with  it.  On  this  reaction  is  based  a  method  of  sepa- 
rating arsenic  from  mineral  and  organic  substances  [see  page  465).  A  diluted 
solution  of  chloride  of  arsenic  reduces  a  solution  of  gold  to  the  metallic 
state.  When  heated  with  metallic  copper,  arsenic  is  deposited  on  the  metal ; 
and  when  a  rod  of  zinc  or  magnesium  is  introduced  into  the  liquid,  the  arse- 
nic rapidly  escapes  as  arsenuretted  hydrogen. 

There  is  no  pentachloride  of  arsenic;  ^.  e.,  no  chloride  corresponding  to 
arsenic  acid.  When  arsenic  acid  is  distilled  with  hydrochloric  acid,  terchlo- 
ride  only  appears  to  be  produced  to  a  limited,  extent.  The  greater  part  of 
the  arsenic  acid  remains  unchanged  in  the  retort.  The  chloride  of  arsenic 
is  a  powerful  poison,  as  it  is  very  readily  absorbed.  A  quantity  equivalent 
to  the  tenth  part  of  a  grain  has  produced  serious  symptoms. 

A.RSENIC  AND  Sulphur.  Bisulphide  of  Arsenic.  •  Red  Sulphide  of  Ar- 
senic. Realgar  (AsS^). — By  slowly  fusing  a  mixture  of  metallic  arsenic 
and  sulphur,  or  by  heating  15  parts  of  arsenious  acid  with  8  parts  of  sulphur, 
a  red  sulphide  of  arsenic  is  obtained.  It  is  crystallizable,  and  of  a  vitreous 
fracture  :  its  specific  gravity  is  34  to  3-5.  It  is  easily  fusible,  and  may  be 
sublimed  unaltered  in  close  vessels.  It  is  usually  known  under  the  name 
of  Realgar,  and  occurs  native.  It  is  used  in  the  preparation  of  the  pyro- 
technical  compound,  called  White  Indian  Fire,  which  consists  of  24  parts 
of  saltpetre,  7  of  sulphur,  and  2  of  realgar,  finely  powdered  and  well  mixed. 
The  mixture  burns  with  a  splendid  white  flame  of  great  brilliancy. 


ORPIMENT.      ALLOYS    OF    ARSENIC.  4t5 

Tersulphide  of  Arsenic.      Orpimeyit.     Sulpharsenious  Acid  (AsSg) 

When  snlphnretted  hydrofj^en  is  passed  through  a  solution  of  arsenious  acid 
in  dilute  hydrochloric  acid,  this  sulphide  is  formed.  It  is  also  procured  by 
subliming  a  mixture  of  sulphur  and  arsenious  acid,  or  arsenic,  in  proper 
proportions.  It  is  fusible,  and  sublimes  in  close  vessels  without  change  :  it 
has  a  rich  golden-yellow  color,  and  assumes  a  lamellar  texture  on  cooling. 
Heated  in  air,  it  burns  with  a  pale-blue  flame,  producing  fumes  of  sulphurous 
and  arsenious  acids.  Its  specific  gravity  is  3*45.  It  is  soluble  in  caustic 
alkaline  solutions  ;  it  is  insoluble  in  diluted  acids,  but  is  decomposed  by 
nitric  and  nitro-hydrochloric  acids,  forming  arsenic  and  sulphuric  acids. 
These  sulphides  are  decomposed  by  fusion  with  potassa ;  sulphide  of  potas- 
sium and  metallic  arsenic  in  the  form  of  a  sublimate,  are  the  results. 

As  this  sulphide  is  commonly  met  with,  it  contains  undecomposed  arse- 
nious acid  in  variable  proportions.  This  may  be  separated  by  boiling  the 
compound  in  water,  in  which  the  sulphide  is  insoluble.  Although  the  sul- 
phide is  not  very  soluble  in  strong  hydrochloric  acid,  yet  under  continued 
heaj;,  chloride  of  arsenic  and  arsenuretted  hydrogen  are  produced.  It  is 
only  the  hydrated  precipitated  sulphide  that  is  readily  dissolved  by  strong 
solutions  of  potassa,  soda,  or  ammonia.  By  its  solubility  in  ammonia  sul- 
phide .of  arsenic  may  be  separated  from  sulphide  of  antimony.  For  the 
complete  reduction  of  this  sulphide.  Otto  recommends  that  it  should  be 
heated  with  ten  parts  of  a  mixture  consisting  of  1  part  of  cyanide  of  potas- 
sium, and  3  parts  of  carbonate  of  soda,  finely-powdered  and  well-dried  : 
Bulphocyanide  of  potassium  is  formed  and  metallic  arsenic  is  sublimed  (2As 
S3+3KCy=3KCyS,+  2As). 

An  ammoniacal  solution  of  this  sulphide  has  been  employed  as  a  dye-stufif. 
Orpiment  is  the  basis  of  a  pigment  called  King^s  Yellow.  Native  Orpiment 
(the  auripigmentum  of  the  ancients)  is  of  a  bright  lemon  or  golden  color.  It 
is  generally  massive  and  lamellar.  This,  and  the  preceding  sulphide,  act  as 
sulphur  acids,  and  form  salts  (Arsenio-sulphides),  with  sulphur  bases. 

Persulphide  of  Arsenic.  Sulpharsenic  Acid  (AsS,). — When  sulphuret- 
ted hydrogen  is  passed  through  a  concentrated  solution  of  arsenic  acid,  a 
pale  yellow  precipitate  very  slowly  falls,  which  may  be  sublimed,  without 
change,  in  close  vessels.  It  is  fusible,  and  soluble  in  alkaline  solutions,  but 
insoluble  in  boiling  water.  The  same  compound  is  obtained  when  sulphu- 
retted hydrogen  is  passed  through  a  concentrated  solution  of  arsenate  of 
potassa,  and  the  resulting  sulpho-salt  is  decomposed  by  hydrochloric  acid 
(p.^  4T0).  This  compound  reddens  litmus-paper.  Its  reactions  are  those  of 
a  sulphur  acid.  Thus,  it  combines  with  alkaline  and  metallic  sulphides  to 
form  sulphur  salts,  and  it  expels  carbonic  acid  from  the  carbonates.  The 
sulphides  of  arsenic  are  poisonous,  but  in  a  less  degree  than  arsenious  acid. 
Common  orpiment,  owing  to  its  containing  arsenious  acid,  is  a  virulent 
poison. 

There  is  a  native  sulphide  of  arsenic  and  iron  diffused  with  ordinary  py- 
rites (FeAs,FeSjj).  It  is  of  a  more  silvery  color  than  common  pyrites. 
When  heated,  it  exhales  an  odor  of  arsenic.  It  is  called  arsenical  pyrites, 
or  mispickel.  It  is  an  abundant  source  of  arsenious  acid.  By  the  decora- 
position  of  arsenical  pyrites,  under  exposure  to  air  and  moisture,  insoluble 
compounds  of  the  acids  of  arsenic  and  oxide  of  iron  are  diffused  through 
certain  soils,  and  are  contained  in  the  sediments  of  spring  and  river  waters. 

Alloys  of  Arsenic  ;  Arsenides. — Arsenic  unites  with  most  of  the  metals, 
forming  compounds  which  are  generally  brittle  and  comparatively  fusible. 
Arsenic  and  iron  form  compounds  which  are  more  brittle,  hard,  and  fusible 
tlian  iron  :  iron  containing  only  2  or  3  per  cent,  of  arsenic  becomes  very 
brittle  when  heated.     Native  arsenide  of  cobalt  occurs  in  cubic,  octahedral, 


476  TESTS    FOR    ARSENIOUS    ACID. 

• 

and  dodecahedral  crystals,  sp.  s^r.  6*78,  of  a  tin  white  color;  it  contains 
about  20  per  cent,  of  cobalt  and  80  of  arsenic,  and  is  therefore  Co^ASg.  The 
ore  known  in  Germany  as  speiskohalt  is  an  arsenide  of  cobalt,  iron,  and 
nickel.  Arsenide  of  nickel  is  gray  and  brittle.  Kupfermckel  is  a  native 
arsenide  ^ AsNij ;  and  the  white  arsenical  nickel,  or  nickel  pyrites,  is  AsNi. 
When  copper  is  heated  to  redness  with  excess  of  arsenic,  a  gray  arsenide  is 
formed  ;  it  has  been  called  lohite  tomhac.  Arsenide  of  lead  is  obtained  by 
heating  lead  with  excess  of  arsenic  or  of  arsenions  acid  ;  it  is  of  a  gray,  crys- 
talline, brittle  compound.  A  very  minute  quantity  of  arsenic  (less  than  1 
per  cent.)  is  always  contained  in  common  lead  shot;  it  gives  the  lead  the 
property  of  spherical  granulation  when  the  fused  metal  is  passed  through  a 
sieve  and  suffered  to  fall  through  the  air  till  it  solidifies.  Arsenide  of  anti- 
mony is  brittle,  hard,  and  very  fusible  :  it  occurs  native^  containing  about  36 
per  cent,  of  antimony  ;  this  ore  therefore  is  SbASg. 

Tests  for  Arsenic  ;  Analysis  in  Cases  of  Poisoning. — Arsenious  acid, 
or  arsenic,  as  it  is  commonly  called,  is  a  white  crystalline  powder.  1.  When 
heated  on  platinum  foil,  or  mica,  it  is  entirely  volatile  at  a  moderate  heat, 
without  undergoing  fusion.     It  escapes  in  a  white  smoke,  which  has  no  odor. 

2.  When  gently  heated  in  a  small  reduction-tube,  closed  at  one  end,  it  sub- 
limes without  fusing,  in  well-defined  transparent  octahedral  crystals,  or  deri- 
vatives of  the  octahedron,  sometimes  visible  without  the  aid  of  a  microscope. 

3.  A  small  portion  on  a  loop  of  platinum-wire  introduced  into  a  Bnnsen's 
jet,  burns  with  a  pale  blue  flame,  emitting  dense  white  fumes.  4.  When  a 
solution  of  hydrosulphate  of  ammonia  is  poured  upon  the  powder  it  under- 
goes no  immediate  change  of  color  ;*but  by  exposure  to  heat,  or  by  sponta- 
neous evaporation  of  the  liquid,  it  is  converted  into  an  orange-yellow  sul- 
phide of  arsenic,  which  is  dissolved  by  ammonia,  but  not  by  hydrochloric 
acid.  5.  The  powder  is  not  easily  dissolved  by  water,  ^ven  at  a  boiling 
temperature.  It  is,  however,  readily  dissolved  by  potassa  without  change,  and 
by  hydrochloric  acid  which  converts  it  into  volatile  chloride  of  arsenic.  A 
small  quantity  of  hydrochloric  acid  in  water  renders  arsenious  acid  much 
more  soluble.  6.  When  heated  with  3  or  4  parts  of  soda-flux  (prepared  by 
calcining  acetate  of  soda  in  a  close  platinum-crucible)  it  yields  a  dark  iron- 
gray  sublimate  of  metallic  arsenic.  In  the  absence  of  soda-flux,  powdered 
ferrocyanide  of  potassium  may  be  used  as  a  reducing  agent.  The  sublimate 
of  metallic  arsenic  may  be  identified  by  the  following  characters.  When 
the  glass  with  the  metal  is  gently  heated  in  a  larger  tube,  the  metal  is 
oxidized  and  volatilized  in  the  form  of  a  white  crystalline  sublimate  of  ar- 
senious acid.  When  treated  with  strong  nitric  acid  containing  nitrous  acid, 
and  evaporated  to  dryness,  it  leaves  a  residue  of  arsenic  acid,'  which  is  known 
by  the  brick-red  color,  or  stain  produced  on  the  addition  of  a  few  drops  of 
nitrate  of  silver.  Cadmium,  tellurium,  selenium,  and  mercury  produce  sub- 
limates ;  but  when  heated,  or  acted  on,  by  nitric  acid,  the  results  are  wholly 
different. 

A  solution  of  arsenious  acid  in  water  is  tasteless,  and  feebly  acid  to  litmus- 
paper.  1.  Ammonio-nitrate  of  silver  produces  with  it  a  yellow  precipitate 
of  arsenite  of  silver.  2.  Ammonio-sulphate  of  copper  givesagreen.precipi- 
tate.  This  precipitate,  when  collected,  dried,  and  heated  in  a  tube,  yields  a 
sublimate  of  arsenious  acid  in  octahedral  crystals.  The  green  precipitate, 
dissolved  in  a  few  drops  of  solution  of  ammonia,  and  treated  with  a  crystal 
of  nitrate  of  silver,  produces  on  the  surface  of  the  crystal  a  layer  of  yellow 
arsenite  of  silver.  3.  A  current  of  sulphuretted  hydrogen  produces  a  yellow 
precipitate,  which  is  completely  thrown  down  on  acidulating  the  liquid  with 
a  few  drops  of  diluted  hydrochloric  acid.  This  yellow  precipitate  (sulphide 
of  arsenic)  is  known  from  all  others  of  a  similar  color.  I.  By  its  insolubil- 
ity in  hydrochloric  acid  ;  2.  By  its  dissolving  in  ammonia,  forming  a  pale 


ANALYSIS    IN    CASE    OF    POISONING.  477 

colorless  solution  ;  and  3.  By  its  yielding  a  sublimate  of  metallic  arsenic 
when  heated  with  2  or  3  parts  of  powdered  ferrocyanide  of  potassium. 

Arsenic  Acid. — This  compound  is  easily  recognized.  1.  By  its  fixedness 
when  heated.  2.  By  its  great  solubility  in  water,  and  the  strong  acid  reac- 
tion which  it  imparts  to  water.  3.  By  the  color  of  the  precipitate  given  by 
a  solution  of  nitrate  or  ammonio-nitrate  of  silver.  When  the  arsenic  acid 
is  in  a  very  diluted  state,  the  precipitate  is  of  a  pale  brownish  color,  becom- 
ing of  a  deeper  and  browner  red  in  proportion  to  the  quantity  present. 
Metallic  arsenic  and  arsenious  acid  may  be  readily  identified  by  these  pro- 
perties when  converted  into  arsenic  acid  by  the  action  of  fuming  nitric  acid. 

When  arsenic  is  contained  in  organic  liquids  it  may  sometimes  be  separated 
in  lumps,  or  powder,  by  washing  ;  or  if  dissolved,  it  may  be  precipitated  as 
sulphide  by  sulphuretted  hydrogen,  and  this  may  be  tested  in  the  manner 
above  described.  i^mzscA's  jorocess  furnishes  a  useful  trial  test  under  these 
circumstances.  The  suspected  liquid,  which  should  not  contain  nitric  acid, 
or  any  chlorate  or  nitrate,  must  be  acidulated  with  pure  hydrochloric  acid 
(its  purity  having  been  previously  determined)  in  the  proportion  of  1  part 
of  acid  to  6  or  7  parts  of  the  liquid.  The  acid  liquid  is  then  brought  to  the 
boiling  point,  and  a  slip  of  bright  copper-wire,  or  foil  (free  from  arsenic)  is 
introduced.  If  the  quantity  of  arsenic  is  minute,  the  copper  will  acquire  a 
metallic  deposit  of  a  bluish  or  purple  color,  passing  to  gray  or  iron-gray,  in 
proportion  to  the  quantity  of  arsenic  present.  The  coated  copper,  washed 
and  dried,  will,  when  heated  in  a  small  reduction  tube,  yield  a  sublimate  of 
octahedral  crystals  of  arsenious  acid.  If  there  is  no  tarnish  or  deposit  on 
the  copper  after  some  minutes'  boiling,  it  may  be  inferred  that  arsenic  is 
either  not  present,  or  that  the  proportion  is  exceedingly  small.  On  the  other 
hand,  there  may  be  a  deposit,  but  insufficient  to  yield  crystals  of  arsenious 
acid.     In  this  case  the  following  process  may  be  resorted  to  : — 

The  solid  or  tissue,  previously  dried  and  divided  into  small  portions,  or 
an  extract  of  the  suspected  liquid,  may  be  placed  in  a  flask  or  retort  with  a 
sufficient  quantity  of  pure  and  concentrated  hydrochloric  acid  to  render  the 
mass  quite  liquid.  The  receiver  should  contain  a  small  quantity  of  distilled 
water.  If  a  globular  flask  is  used,  this  may  be  connected  with  the  receiver 
by  means  of  a  long  narrow  tube,  kept  cool  by  wetted  blotting-paper  folded 
round  it.  The  distillation  should  take  place  slowly,  by  means  of  a  sand- 
bath,  and  be  carried  nearly  to  dryness.  A  distillate  is  thus  obtained  con- 
taining either  the  chloride  of  arsenic,  or  a  mixture  of  hydrochloric  and 
arsenious  acids.  If  this  is  colored,  or  mixed  with  organic  matter,  it  should 
be  submitted  to  a  second  distillation.  When  any  oily  matter  has  distilled 
over,  this  should  be  separated  by  passing  it  through  a  wet  filter.  In  some 
cases,  as  where  the  substance  has  not  been  thoroughly  dried,  a  second  dis- 
tillation, with  a  fresh  portion  of  hydrochloric  acid,  may  be  required  to  remove 
the  whole  of  the  arsenic  ;  but  with  ordinary  care  this  is  not  necessary.  One- 
third  of  the  liquid  distillate  (diluted  with  water  if  too  acid)  may  now  be 
heated  with  a  slip  of  polished  copper  foil  (^Reinsch^s  process).  If  ar- 
senic is  present,  even  to  the  l-4000th  of  a  grain,  the  copper  will  indicate 
this  by  a  change  of  color — the  metallic  lustre  being  retained.  By  using 
other  portions  of  copper  successively,  the  whole  of  the  arsenic  may  be  ex- 
tracted. The  remaining  two-thirds  of  the  liquid  should  then  be  submitted 
to  Marsh'' s  process  with  the  following  modifications.  The  distillate,  if  very 
acid,  should  be  so  diluted  that  its  action  on  zinc  may  not  be  too  violent. 
The  most  convenient  form  of  apparatus  is  a  tube,  about  an  inch  in  width  and 
six  or  eight  inches  in  height,  provided  with  a  well-fitted  cork,  through  which 
passes  a  safety-funnel  tube  on  one  side,  and  an  exit  or  delivery-tube,  bent  at 
a  right  angle,  on   the  other  side.     The  exit-tube  should  be  connected  by 


478  DETECTION    OF    ARSENIC    IN    CASES    OF    POISONING. 

corks  with  a  short  wide  tube,  containing  fragments  of  fused  chloride  of  cal- 
cium, for  the  purpose  of  drying  the  gas.  To  the  other  end  of  the  drying- 
tube  there  should  be  fitted  a  long  tube  of  hard  glass  (free  from  lead),  about 
one-quarter  of  an  inch  in  diameter,  and  provided  with  two  or  three  capillary 
contractions.  This  tube  should  be  bent  at  a  right  angle,  so  that  the  end  of 
it  may  dip  into  a  solution  of  nitrate  of  silver. 

Pure  zinc  or  magnesium  having  been  placed  in  the  apparatus,  the  acid  dis- 
tillate is  poured  upon  it  through  the  funnel.  After  a  short  time,  if  arsenic  is 
present,  the  bubbles  of  hydrogen,  as  they  escape,  will  darken  the  solution 
of  nitrate  of  silver.  The  liquid  will  first  become  of  a  pale  brown  color, 
gradually  deepening  to  black,  according  to  the  amount  of  arsenic  present. 
When  the  silver  solution  has  undergone  this  change,  the  horizontal  glass 
tube  may  be  heated  to  redness,  about  an  inch  before  each  capillary  contrac- 
tion. The  arsenuretted  hydrogen  will  be  thereby  decomposed,  and  a  dark 
mirror  of  metallic  arsenic,  in  the  form  of  a  ring,  will  be  deposited  in  the  con- 
tracted portion  of  the  tube.  By  this  arrangement,  three  or  more  metallic 
deposits  of  arsenic,  corresponding  to  each  contraction,  may  be  procured. 
When  the  gas  has  spent  itself  in  the  silver  solution,  this  may  be  removed. 
The  end  of  the  delivery  tube  should  then  be  washed,  and  allowed  to  dip  into 
a  small  quantity  of  fuming  nitric  acid  containing  nitrous  acid.  This  com- 
pletely arrests  and  decomposes  the  arsenuretted  hydrogen. 

The  chemist  has  now  before  him  all  that  is  necessary  to  identify  the  sub- 
stance as  arsenic.  The  glass  tube  is  detached  from  the  apparatus,  and  the 
metallic  sublimates  are  obtained  separately  by  melting  the  glass  in  the  con- 
tracted portions.  One  may  be  sealed  up  and  preserved  ;  one  may  be  tested 
by  applying  a  gentle  heat  to  the  metallic  deposit,  when  a  brilliant  ring  of 
colorless  octahedral  crystals  may  be  obtained,  plainly  visible  under  the  micro- 
scope. With  respect  to  the  other  tube,  the  portion  of  glass  containing  the 
metallic  deposit  may  be  separated  by  a  file,  broken  into  fragments,  and  di- 
gested in  a  small  porcelain  capsule,  in  a  few  drops  of  fuming  nitric  acid. 
On  evaporating  to  dryness  and  adding  a  solution  of  nitrate  of  silver,  a  red- 
dish-colored precipitate,  entirely  soluble  in  ammonia,  indicates  that  arsenic 
acid  was  present,  and  that  the  metallic  deposit  was  arsenic.  It  is  here 
assumed  that  the  chemist  is  obliged  to  rely  exclusively  upon  the  results 
obtained  by  decomposing  the  arsenuretted  hydrogen  gas  by  heat.  In  gen- 
eral, however,  it  will  be  found  that  the  silver  solution  and  the  nitric  acid 
which  have  been  employed  to  receive  the  surplus  gas,  will  yield  satisfactory 
evidence,  and  render  a  special  analysis  of  the  metallic  deposits  unnecessary. 

1.  The  darkened  solution  of  nitrate  of  silver  is  filtered,  in  order  to  sepa- 
rate the  metallic  silver.  The  filtrate  contains  arsenic  in  the  state  of  arseni- 
ous  acid,  mixed  with  nitrate  of  silver  undecomposed.  The  addition  of  ammo- 
nia to  this  liquid  produces  immediately  a  yellow  precipitate  of  arsenite  of 
silver. 

2.  The  fuming  nitric  acid  into  which  the  gas  has  been  passed,  may  be 
evaporated  to  dryness  on  a  sand-bath  in  a  clean  porcelain  capsule.  A  white 
deliquescent  acid  residue  is  thus  obtained.  On  adding  to  this  residue  a 
few  drops  of  nitrate,  or  of  ammonio-nitrate  of  silver,  a  brick-red  precipitate 
of  arsenate  of  silver  is  immediately  produced.  (For  the  further  details  of  this 
process  see  Guyh  Hospital  Reports,  Oct.  1860,  p.  253.)  It  will  be  per- 
ceived that  by  this  method,  arsenic  if  present  is  obtained  in  the  state  of 
metal  and  of  its  two  oxides  arsenioas  and  arsenic  acids.  Hence  no  further 
demonstration  is  required. 

The  usual  method  of  detecting  arsenic  in  the  tissues  or  organs  of  the  body, 
consists  in  rendering  the  arsenic  soluble  in  the  midst  of  a  large  quantity  of 
carbonized  organic  matter,  which,  in  spite  of  every  care,  will  more  or  less 


MERCURY.  479 

accompany  it.  By  the  process  of  distillation  as  originally  sn«?p^ested  by 
Schneider,  the  arsenic  is  removed  from  the  organic  matter,  and  thus  sepa- 
rated from  a  large  number  of  metals  which  do  not  form  volatile  chlorides  at 
a  low  temperature.  The  residue  in  the  retort,  after  the  complete  separation 
of  arsenic,  may  be  analyzed  for  mercury,  antimony,  and  other  metals.  "This 
process  does  not  interfere  with  the  carbonization  of  the  residue  by  sulphuric 
acid,  if  necessary.  In  the  state  of  chloride,  arsenic  is  distingui*shed  from  all 
metals  excepting  antimony,  by  its  ready  conversion  into  a  gaseous  hydride, 
and  by  the  entire  decomposition  of  this  hydride  by  heat.  Lastly,  by  means 
of  the  hydride  the  arsenic  may  be  reproduced,  1st,  as  metal ;  2d,  as  arsenious 
acid  ;  and  3d,  as  arsenic  acid,  beyond  which  it  is  unnecessary  to  carry  the 
analysis.  The  processes  of  Marsh  and  Reinsch  are  not  here  resorted  to  until 
after  the  arsenic  has  been  separated  from  other  substances  by  distillation. 
These  processes  should  corroborate  each  other  ;  and  the  only  caution  required, 
is  that  pure  zinc  and  copper,  as  well  as  pure  hydrochloric  and  nitric  acids, 
should  be  employed.  These  substances  should  each  be  separately  tested  in 
the  apparatus  on  a  sufficient  scale,  before  the  analysis  is  commenced.  Mag- 
nesium is  preferable  to  zinc,  from  its  absolute  purity. 

In  reference  to  antimony,  there  are  characteristic  differences,  which  have 
been  already  described  (p.  465).  The  only  method  by  which  the  quantity  of 
arsenic  can  be  approximately  determined  in  these  researches,  is  by  condensing 
the  whole  of  the  arsenic  obtained  from  a  given  weight  of  the  material,  in 
fuming  nitric  acid,  and  precipitating  the  arsenic  so  obtained  as  arsenate  of 
ammonia  and  magnesia  (p.  472).  A  hundred  parts  of  this  precipitate,  dried 
at  212°,  are  equivalent  to  54 -14  of  arsenious  acid. 

If  the  organic  substance  submitted  to  examination,  should  be  in  a  state  of 
putrefaction,  sulphuretted  hydrogen  may  be  found  in  the  distillate.  This 
may  be  removed  by  the  addition  of  chlorine,  and  heating  the  liquid,  or  by 
exposing  the  liquid  to  air- for  24  hours.  Sulphur  is  deposited  and  may  be 
separated  by  filtration.  If  the  quantity  is  small,  the  sulphuretted  hydrogen 
may  be  stopped  by  placing  lead-paper  in  the  first  portion  of  the  drying-tube. 
When  sulphuretted  hydrogen  comes  over  with  arsenuretted  hydrogen,  the 
metallic  deposit,  obtained  by  heating  the  current  of  gas  is,  in  part  at  least, 
converted  into  yellow  sulphide  of  arsenic.  If  arsenic  acid  is  present,  this 
should  be  converted  into  arsenious  acid  by  sulphurous  acid  before  submitting 
it  to  distillation.  If  sulphide  of  arsenic  or  orpiment  is  present,  this  should 
be  converted  into  arsenic  acid  by  fuming  nitric  acid,  and  then  submitted  to 
distillation  as  above  described.  By  the  process  above  described,  minute 
traces  of  arsenic  have  been  separated  from  Thames  mud,  the  ochreous  deposits 
of  rivers,  and  from  the  salts  of  copper  as  well  as  from  animal  solids  and  fluids 
of  various  kinds  iu  cases  of  poisoning. 


CHAPTEE    XXXVII. 

Mercury  (Hg=100). 

The  principal  ore  of  this  metal  is  the  sulphide  or  natii'>e  cinnabar,  from 
which  mercury  is  separated  by  distillation,  either  with  quick-lime  or  iron- 
filings,  or  by  simply  burning  off  the  sulphur.  Mercury  occurs  native,  in  small 
globules,  generally  dispersed  through  the  sulphide.     It  is  also  found  as  a 


I 


4B0  OXIDES    OP    MERCURY. 

chloride,  iodide,  and  selenide,  but  these  are  rare  ores:  in  combination  witji 
silver  it  constitutes  native  amalgam. 

Mercury  is  a  brilliant  silvery-white  fluid-metal,  whence  the  terms  hydrar- 
gyrum (liScop  apyvpoj)  and  quicksilver.  It  has  been  known  from  remote  ag:es. 
It  is  liquid  at  all  common  temperatures,  solid  at  — 40^,  and  contracts  at  the 
moment  of  congelation.  Its  characters,  when  frozen,  vary  with  the  tempera- 
ture, being  flexible  when  verging  towards  liquefaction,  but  brittle  at  lower 
temperatures.  It  boils  at  about  660*^.  It  emits  vapor  at  all  temperatures 
above  40^,  but  no  api)arent  spontaneous  evaporation  goes  on  from  it  when 
below  that  temperature.  Its  great  lustre  and  opacity  may  be  well  seen  by 
compressing  a  globule  between  two  clean  glass  plates.  If  pure,  it  assumes 
when  placed  on  surfaces  of  glass  or  porcelain  a  rounded  spherical  form  capa- 
ble of  subdivision  by  pressure  into  minute  and  scarcely  visible  globules.  It 
flows  also  readily  as  a  globule  over  the  surface  :  when  mixed  with  lead,  tin, 
or  other  metals,  it  coheres  to  surfaces,  and  the  globular  form  is  no  longer 
seen.  It  may  be  deprived  of  these  impurities  by  careful  distillation,  but  it 
has  been  found  better  before  distilling  the  impure  mercury,  to  add  to  it  about 
one-twelfth  of  its  weight  of  nitric  acid,  allowing  a  slight  digestion  in  the 
cold  and  then  applying  a  moderate  heat.  The  mercury  is  decanted  and  dis- 
tilled. The  nitrates  formed  by  the  action  of  the  acid  may  be  evaporated 
to  dryness,  and  the  dry  residue  distilled  with  the  mercury  (Lacassin).  Its 
sp.  gr.  at  60°  is  13  56,  but  in  the  solid  state  it  exceeds  14.  The  specific 
gravity  of  mercurial  vapor  is  6  97 6.  When  mercury  is  pure,  it  is  not  affected 
by  agitation  in  contact  with  air  ;  but  when  impure,  it  becomes  covered  with 
a  gray  powder,  which  is  a  mixture  of  the  foreign  metallic  oxide  and  finely- 
divided  mercury.  When  pure  mercury  is  shaken  with  water,  ether,  sulphu- 
ric acid,  or  oil  of  turpentine,  or  rubbed  with  sugar,  chalk,  lard,  conserve  of 
roses,  &c.,  it  is  reduced  to  a  gray  powder,  which  consists  of  minute  mercu- 
rial globules,  blended  with  the  foreign  body;  and  when  this  is  abstracted 
they  again  unite  into  running  mercury.  In  well  made  mercurial  ointment 
these  globules  are  not  discernible  by  the  naked  eye.  The  extent  to  which 
this  division  may  be  carried,  is  well  illustrated  in  the  preparation  termed 
precipitated  mercury  ;  obtained  by  precipitating  a  solution  of  corrosive  subli- 
mate by  protochloride  of  tin  :  the  liberated  mercury  forms  so  fine  a  precipi- 
tate that  it  is  perfectly  black,  and  requires  several  hours  to  subside.  There 
are  two  oxides  of  mercury,  both  of  them  salifiable :  a  dioxide  or  suboxide, 
HggO,  and  an  oxide,  HgO. 

Suboxide  op  Mercury.  Dioxide  of  Mercury  ;  Black  Oxide  of  Mercury ; 
Mercurious  Oxide  (Hg^O). — This  oxide  (formerly  termed  protoxide)  is 
obtained  when  finely-levigated  dichloride  of  mercury  -(calomel)  is  triturated 
with  excess  of  lime-water ;  it  must  be  carefully  washed  with  cold  water,  and 
dried  at  common  temperatures,  under  exclusion  of  light.  It  is  a  black  or 
brownish-black  powder,  sp.  gr.  10  6,  easily  resolved  by  light,  or  by  heat  into 
metal  and  oxide.  The  salts  of  this  oxide  are  generally  obtained  either  by 
its  direct  solution,  or  by  digesting  excess  of  mercury  with  the  acids,  or  with 
the  salts  of  the  red  oxide,  or  by  double  decomposition  :  they  are  usually 
yellow  when  basic,  but  otherwise  colorless,  soluble  in  water,  redden  litmus, 
and  taste  metallic  ;  some  of  them  are  resolved  by  the  action  of  water  into  an 
insoluble  basic,  and  a  soluble  acid  salt.  They  give  black  precipitates,  with 
the  caustic  alkalies.  With  carbonate  of  potassa  they  afford  a  brownish- 
yellow,  and  with  bicarbonate  a  yellowish-white  precipitate,  sparingly  soluble 
in  an  excess  of  the  bicarbonate,  and  becoming  black  and  losing  carbonic  acid 
when  boiled.  With  carbonate  of  ammonia  the  precipitate  is  at  first  white, 
but  blackens  on  adding  it  in  excess.  With  hydrochloric  acid  and  soluble 
chlorides  these   salts  give  a  white  precipitate   of  subchloride  of  mercury, 


SUBCHLORTDE  OF  MERCURY.   CALOMEL.  481 

which  is  immediately  blackened  by  the  alkalies.  With  sulphuretted  hydro- 
gen, and  the  hydrosulphates,  the  precipitate  is  black  ;  with  phosphate  of 
soda,  white ;  with  iodide  of  potassium,  greenish-yellow,  darkened  by  an 
excess  of  the  precipitant ;  with  hydrocyanic  acid,  mercury  is  precipitated, 
and  a  cyanide  of  mercury  formed  :  Hg,,0  +  HCy=Hg-fHgCyH-HO. 

Oxide  of  Mercury.  Red  Oxide  ;  Peroxide  ;  Mercuric  Oxide  (HgO). — 
This  oxide  is  produced  by  heating  mercury  in  a  long-necked  flask,  open  to 
the  air,  nearly  to  its  boiling-point.  It  becomes  slowly  coated  with  reddish- 
brown  scales  and  crystals,  and  is  ultimately  converted  into  a  red  crystalline 
substance,  called  in  old  pharmaceutical  wovV^,,  precipitatum  per  se,  or  calcined 
mercury.  It  may  also  be  obtained  by  heating  nitrate  of  mercury,  so  long  as 
fumes  of  nitrous  acid  are  evolved  ;  the  resulting  oxide  is  in  the  form  of  an 
orange-red  crystalline  powder.  This  oxide  is  also  thrown  down  in  the  form 
of  a  yellow  powder,  when  potassa  of  soda  is  added  to  a  solution  of  corrosive 
sublimate,  or  of  nitrate  of  mercury.  In  this  precipitated  state  it  possesses 
certain  properties  in  regard  to  solvents,  which  distinguish  it  from  the  crystal- 
line oxide,  of  which  it  is  considered  an  allotropic  modification.  Oxide  of 
mercury  has  a  metallic  taste,  and  is  poisonous  ;  it  is  slightly  soluble  in  water, 
and  the  solution,  which  is  feebly  alkaline,  when  exposed  to  air  becomes 
gradually  covered  with  a  brilliant  film.  Its  specific  gravity  is  11 '0^4.  When 
heated,  it  blackens,  but  becomes  again  red  on  cooling;  at  a  red  heat  it 
evolves  oxygen,  and  is  reduced  to  the  metallic  state;  it  was  thus  that 
Priestley  first  obtained  oxygen  gas.  When  long  exposed  to  light  it  becomes 
black  upon  the  surface.  It  should  be  entirely  volatilized  when  placed  upon 
a  red-hot  iron,  for  it  is  sometimes  adulterated  with  red  lead.  This  oxide  of 
mercury  is  decomposed  by  sulphur,  phosphorus,  and  several  of  the  metals  : 
when  mixed  with  sulphur  and  heated,  it  explodes  ;  and  with  phosphorus  it 
explodes  by  the  blow  of  a  hammer.  It  combines  with  acids,  and  like  the 
suboxide  forms  compounds,  several  of  which  are  resolvable  into  salts  with 
excess  of  base,  and  salts  with  excess  of  acid.  There  is  also  a  great  tendency 
to  the  formation  of  double  salts  among  the  haloid  mercurial  compounds. 
The  salts  of  the  red  oxide  are,  generally  speaking,  more  active  and  poisonous 
than  those  of  the  black  oxide;  they  mostly  redden  litmus,  and  are  reduced 
first  to  the  state  of  salts  of  suboxide,  and  then  to  metal,  by  several  deoxi- 
dizing agents,  such  as  phosphorous  and  sulphurous  acids,  protochloride  of 
tin  and  sugar. 

Mercury  and  Chlorine  combine  in  two  proportions,  and  form  a  sub- 
chloride  or  dichloride,  and  a  chloride  or  perchloride  of  mercury,  compounds 
corresponding  with  the  oxides,  and  formerly  called  protochloride  and  bichlo- 
ride ;  the  old  terms  calomel  and  corrosive  sublimate  applied  to  these  chlorides 
are  distinctively  convenient,  and  are  not  liable  to  cause  mistakes  in  dispensing 
mercurial  preparations. 

SUBCHLORIDE  OF  Mercury;  Dichloride  of  Mercury.  Mercurious  Chloride. 
Calomel  (Hg3,CI). — This  compound  is  first  mentioned  by  Crollius  early  in 
the  seventeenth  century.  The  first  directions  for  its  preparation  are  given 
by  Beguin  in  1608.  There  are  several  processes  by  which  calomel  may  be 
obtained:  one  of  these  consists  in  triturating  4  parts  of  corrosive  Sublimate 
with  3  of  mercury  (and  a  little  water  to  prevent  the  dust  rising),  till  the 
whole  forms  a  gray  powder,  which  is  introduced  into  a  proper  subliming 
vessel,  gradually  raised  to  a  red  heat :  the  subchloride  sublimes,  mixed  with 
a  little  of  the  chloride,  which  may  be  separated  by  reducing  the  whole  to  fine 
powder,  and  washing  it  in  large  quantities  of  hot  distilled  water.  In  this 
process  the  chloride  is  reduced  to  the  subchloride  by  the  addition  of  mer- 
cury (HgCl  +  Hg,  =  Hg2,Cl).  Subchloride  of  mercury  may  also  be  formed 
by  precipitating  a  soFution  of  subnitrate  of  mercury  by  a  solution  of  common 
31 


482  CALOMEL  AND  CORROSIVE  SUBLIMATE. 

salt:  Hg20,N054-NaCl=Hg:2Cl,-f  NaO,N05.  Calomel  is  generally  manu- 
factured upon  the  large  scale,  for  pharmaceutical  purposes,  by  sublimation, 
from  a  mixture  of  the  sulphate  of  the  suboxide  with  common  salt :  (Hg^O, 
S03,-|-NaCl,  =  IIgaCl  +  NaO,S03).  The  calomel  vapor  is  received  into  a 
capacious  condenser,  in  which  it  is  deposited  in  a  pulverulent  form  :  it  is 
afterwards  most  carefully  triturated,  levigated,  and  washed  in  large  quanti- 
ties of  distilled  water,  till  it  becomes  perfectly  tasteless,  and  till  the  water 
filtered  from  the  washed  powder  is  not  discolored  by  sulphuretted  hydrogen. 

The  form  in  which  calomel  sublimes  depends  much  upon  the  dimensions 
and  temperature  of  the  vessel  in  which  its  vapor  is  condensed.  In  small 
vessels  it  generally  condenses  in  a  crystalline  cake,  the  interior  surface  of 
which  is  often  covered  with  prismatic  crystals  :  in  this  state  it  acquires,  by 
rubbing  into  powder,  a  pale  buff  tint.  If,  on  the  contrary,  it  is  sublimed 
into  a  capacious  and  cold  receiver,  it  falls  in  an  impalpable  white  powder. 
By  a  modification  of  the  process,  it  may  be  suffered,  as  it  sublimes,  to  fall 
into  water.  But  in  whatever  way  calomel  is  obtained,  it  requires  cafeful 
washing,  and  extreme  care  as  to  its  state  of  minute  mechanical  division.  To 
detect  corrosive  sublimate  in  calomel,  we  may  digest  the  calomel  in  warm 
ether  for  a  few  hours,  pour  off  the  liquid  or  filter  it  and  evaporate  to  dryness. 
Any  corrosive  sublimate  will  be  kft  in  prismatic  crystals,  which  will  acquire 
a  red  color  when  moistened  with  a  solution  of  iodide  of  potassium. 

Calomel  is  tasteless,  and  insoluble  in  water.  Its  sp.  gr.  is  7 '14.  At  a 
beat  somewhat  below  redness,  it  rises  in  vapor,  without  previous  fusion  ;  but 
it  fuses  when  heated  under  pressure.  The  density  of  its  vapor  is  8 -2.  By 
hot  hydrochloric  acid  it  is  resolved  into  mercury  and  corrosive  sublimate; 
but  when  boiled  in  dilute  hydrochloric  acid  a  portion  is  dissolved  without 
decomposition.  By  nitric  acid  it  is  converted  into  corrosive  sublimate  and 
pernitrate,  with  the  evolution  of  nitric  oxide  (3Hg2CI  +  4N05=3HgCl-h3 
[HgOj^^Ogj  +  NOg).  Sulphur,  phosphorus,  and  several  of  the  metals  de- 
compose it.  Boiled  with  copper  and  water,  chloride  of  copper  and  metallic 
mercury  are  procured.  Triturated  with  iodine  and  water,  corrosive  subli- 
mate and  iodide  of  mercury  are  formed  :  Hg2ClH-I=HgCl  +  HgI.  With 
aqueous  hydrocyanic  acid  calomel  yields  metallic  mercury,  and  cyanide  of 
mercury  and  hydrochloric  acid  are  found  in  solution  ;  HggCl-|-HCy=Hg-|- 
HgCy  +  HCl.  Native  Suhchloride  of  Mercury  or  Mercurial  Horn  Ore,  has 
been  found  crystallized,  and  sometimes  incrusting  and  massive  :  it  is  rare. 

Chloride  of  Mercury.  Perchloride.  Bichloride.  Mercuric  Chloride. 
Oxymuriate  of  Mercury ;  Corrosive  Sublimate  (HgCl). — When  mercury  is 
boiled  and  introduced  into  chlorine,  it  burns  with  a  pale  flame,  and  a  white 
volatile  substance  rises,  which  is  this  chloride.  When  oxide  of  mercury  is 
heated  in  a  current  of  chlorine,  oxygen  is  expelled  ;  HgO  +  Cl=HgCl4-0  : 
and  when  the  oxide  is  gently  heated  in  hydrochloric  acid  gas,  water  and  the 
chloride  are  the  results;  HgO-f  HCl  =  HgCl  +  HO.  The  ordinary  process 
for  making  corrosive  sublimate  consists  in  exposing  a  mixture  of  chloride  of 
sodium  and  sulphate  of  mercury  to  heat  in  a  proper  subliming  vessel ;  corro- 
sive sublimate  rises,  and  sulphate  of  soda  is  the  residue :  HgO,S03+NaCl= 
NaO,S03wMIgCl. 

Chloride  of  mercury  has  an  acrid  nauseous  taste,  leaving  a  permanent 
metallic  and  astringent  flavor  upon  the  tongue  :  it  is  a  powerful  corrosive 
poison.  It  evaporates  to  a  small  extent  at  common  temperatures.  Its  spe- 
cific gravity  is  5'4.  It  is  usually  met  with  either  in  the  form  of  heavy  white 
semi-transparent  and  imperfectly  crystallized  masses,  or  in  powder.  It  fre- 
quently exhibits  prismatic  crystals  upon  the  inner  surfaces  of  the  sublimed 
cakes.  It  is  soluble  in  about  16  parts  of  cold,  and  3  of  boiling  water;  and 
as  the  solution  cools,  it  deposits  quadrangular  prismatic  crystals.     It  dis- 


CHLORIDES  OP  MERCURY.  483 

solves  in  3  parts  of  alcohol  and  in  4  of  ether.  "When  heated,  it  fuses,  boils, 
and  entirely  evaporates  in  the  form  of  a  dense  white  vapor,  powerfully 
afifecting  the  nose  an(\  mouth  :  the  density  of  this  vapor  is  9*4  :  it  is  condensed 
in  prismatic  crystals  on  cold  surfaces  in  tubes.  Corrosive  sublimate  is  nearly 
insoluble  in  concentrated  nitric  and  sulphuric  acids.  Hydrochloric  acid  of 
the  specific  gravity  1"158,  at  the  temperature  of  60°,  dissolves  about  its  own 
weight,  and  the  solution,  when  cooled  to  about  40°,  concretes  into  a  mass 
of  crystals;  there  appear  to  be  two  or  three  of  these  hydro  chlorates  of  chloride 
of  mercury  ;  they  are  partially  decomposed  when  added  to  a  great  excess  of 
water,  and  resolved  into  free  hydrochloric  acid  and  chloride.  Corrosive 
sublimate  is  either  decomposed  by,  or  combines  with,  many  organic  bodies  ; 
some  of  them  convert  it  into  calomel,  others  enter  into  combination  with  it, 
forming  permanent  compounds.  The  applications  of  it  to  the  preservation 
of  anatomical  preparations,  and  to  the  prevention  of  dry  rot,  illustrate  these 
actions.  The  efiBcacy  of  a  mixture  of  white  of  ^.gg  and  water,  in  preventing 
or  mitigating  the  poisonous  effects  of  this  substance,  depends  upon  its  direct 
combination  with  albumen. 

Oxichlorides  of  Mercury. — There  are  three  of  these  compounds  produced 
by  the  action  of  corrosive  sublimate  on  bicarbonate  of  potassa  ;  and  each 
of  them  is  said  to  be  susceptible  of  allotropic  modifications.  If  a  saturated 
solution  of  the  bicarbonate  is  added  to  8  times  its  bulk  of  a  saturated  solution 
of  the  chloride,  a  red  precipitate  falls,  which  is  2(HgO)HgCl ;  but  with  one 
volume  of  the  alkaline  solution,  and  two  of  the  sublimate,  the  precipitate  is 
black  and  crystalline,  but  of  the  same  composition.  When  the  solutions  are 
mixed  in  equal  volumes,  the  precipitate,  which  is  at  first  yellow,  is  3(HgO) 
HgCl ;  and  when  the  solution  of  sublimate  is  added  to  a  large  excess  of  that 
of  the  bicarbonate,  carbonic  acid  is  evolved,  and  brown  crystalline  crusts  are 
deposited,  which  are  4(HgO)HgCl. 

Action  of  Ammonia  on  Chloride  of  Mercury. — When  corrosive  sub- 
limate is  heated  in  a  stream  of  ammonia,  a  white  crystalline,  volatile,  and 
fusible  compound  is  obtained,  which  is  not  soluble  in  water  without  decom- 
position :  it  is  an  ammonio- chloride  =NH3,2HgCI.  A  solution  containing 
1  atom  of  sal-ammoniac  and  1  of  corrosive  sublimate  in  a  small  quantity  of 
water,  yields  rhombic  prisms,  permanent  in  the  air,  but  which,  when  dried 
at  212°,  become  opaque,  and  lose  about  5*5  per  cent,  of  water.  They  con- 
stitute the  sal  alemhroth  of  the  old  chemist  =NH4Cl,HgCl.  When  1  atom 
of  sal-ammoniac  and  2  of  corrosive  sublimate  are  mixed  and  heated,  a  com- 
pound =  NH^Cl  +  2HgCl  sublimes:  when  the  same  salts  are  dissolved  in  water, 
the  solution  yields,  on  evaporation,  silky  crystals  =NH4C1 -f-2HgCl-f  HO. 

Amidochloride  of  Mercury  ;  White  Precipitate  (HgNH3,HgCl)  is  ob- 
tained by  adding  a  slight  excess  of  ammonia  to  a  solution  of  corrosive 
sublimate,  washing  the  precipitate  with  cold  water,  and  drying  it  by  a  gentle 
heat:  2HgCl  +  2NH3=HgNH„HgCl-f NH.Cl.  It  is  a  white  powder, 
which,  when  boiled  in  water,  is  partly  converted  into  sal-ammoniac,  which  is 
dissolved,  and  partly  into  an  almost  insoluble  yellow  powder,  which  is  a  com- 
pound of  amidide,  chloride,  and  oxide  of  mercury  :  2(HgNH2HgCl)-f  2H0 
=  NH,Cl  +  (HgNH3  4-HgCl  +  2HgO).  When  white  precipitate  is  highly 
heated,  a  red  crystalline  compound  remains,  which  is  represented  by  the 
formula  2(HgCl)HgN.  White  precipitate  is  more  chalky-looking  than 
calomel,  and  not  so  heavy.  Like  calomel  it  is  insoluble  in  water;  but  while 
alkalies  turn  calomel  black,  they  produce  no  change  of  color  in  this  compound. 
When  boiled  in  a  solution  of  potash,  white  precipitate  gives  off  ammonia, 
and  the  residue  becomes  yellow.  Calomel  is  blackened  and  evolves  no 
ammonia.  White  precipitate,  owing  to  imperfect  washing,  generally  con- 
tains  some  corrosive  sublimate.       This  may  be  detected  by  the  process 


484  IODIDES    OF    MERCURY. 

recommended  for  its  detection  in  calomel.     Ammonio-chloride  of  mercury  is 
an  active  poison.     In  medicine  it  is  used  only  for  external  application. 

Hydrargochlorides. — Chloride  of  mercury  forms  a  numerous  series  of 
double  salts  with  chlorides  of  the  other  metals,  which  are  obtained  by  dis- 
solving the  salts  in  proper  proportions,  and  allowing  them  to  crystallize. 

Iodides  of  Mercury. — There  are  two  iodides  of  mercury,  corresponding 
to  the  chlorides. 

SuBioDiDE  (HgJ)  is  obtained,  1.  By  triturating  together  200  parts  of 
mercury  and  128  parts  of  iodine,  moistened  with  alcohol.  2.  By  adding 
iodide  of  potassium  to  a  very  dilute  solution  of  acetate  or  nitrate  of  suboxide 
of  mercury  :  Hg20,N05+KI  =  Hg2l-fK0,N05.  3.  By  digesting  in  boiling 
water  236  parts  of  calomel  with  166  of  iodide  of  potassium  :  Hg2Cl  +  KI= 
Hggl-f  KCl.  4.  By  triturating  together  1  equivalent  of  mercury  with  1  of 
iodide  of  mercury,  moistened  with  alcohol.  Subiodide  of  mercury  is  a  dingy 
greenish-yellow  powder  :  specific  gravity  7  "7  :  it  is  nearly  insoluble  in  water, 
and  insoluble  in  alcohol.  When  rapidly  heated  in  a  glass  tube  it  fuses,  and 
sublimes  unaltered  :  gently  heated,  or  long  exposed  to  light,  it  is  resolved 
into  mercury  and  iodide. 

Iodide. — Periodide  of  Mercury  (Hgl)  is  obtained,  1.  By  triturating  1 
equivalent  of  mercury  with  1  of  iodine  (100  mercury  and  127  iodine) 
moistened  with  a  little  water  or  alcohol.  2.  By  the  mutual  decomposition 
of  corrosive  sublimate  and  iodide  of  potassium  :  HgCl4-KI=HgI  +  KCl. 
When  a  strong  solution  of  iodide  of  potassium  is  gradually  added  to  one  of 
corrosive  sublimate,  a  red  precipitate  forms,  which  redissolves  on  agitation  ; 
forming  a  soluble  compound  of  chloride  and  iodide  of  mercury  ;  on  the 
further  addition  of  iodide  of  potassium  a  pale  reddish  and  permanent  pre- 
cipitate is  obtained,  which  is  also  a  compound  of  chloride  and  iodide, 
containing,  however,  more  of  the  latter ;  this  precipitate,  on  continuing  the 
addition  of  the  iodide  of  potassium,  becomes  of  a  brilliant  scarlet,  and  this 
is  iodide  of  mercury,  but  if  excess  of  iodide  is  added,  it  disappears,  and  a 
colorless  solution  of  hydrargoiodide  of  potassium  is  formed ;  so  that  to 
obtain  a  pure  iodide  of  mercury  the  relative  atomic  equivalents  must  be 
strictly  preserved.  When  heated  it  becomes  yellow,  and  fuses  into  an  amber- 
colored  fluid,  giving  off  vapor  which  condenses  in  yellow  rhombic  plates; 
these,  if  scratched  or  ruptured,  resume  a  scarlet  color  (p.  36).  Crystalliza- 
ble  double  salts  {hydrargoiodides  or  iodo-hydrargyrates)  are  formed  by  the 
combination  of  iodide  of  mercury  with  the  alkaline  iodides.  The  iodide  is 
soluble  in  the  chlorides  of  the  metals  of  the  alkalies,  but  does  not  form 
crystallizable  compounds  with  them.  When  a  hot  solution  of  corrosive  sub- 
limate is  saturated  with  iodide  of  mercury,  it  deposits  crystals  on  cooling 
=HgI,2HgCl.  A  combination  of  this  kind  forms  a  useful  precipitant  of 
the  alkaloids,  producing  with  the  true  alkaloids,  when  the  solution  is  not  too 
acid,  an  insoluble  white  compound  containing  an  insoluble  hydriodate  of  the 
alkaloid.  This  test  is  made  by  dissolving  16  grains  of  corrosive  sublimate 
and  60  grains  of  iodide  of  potassium  in  4  ounces  of  water.  Small  quantities 
of  morphia,  veratria,  and  strychnia  are  thus  easily  detected  in  mixtures  which 
do  not  contain  much  alcohol  or  acid  (acetic).  If  no  precipitate  is  produced, 
the  absence  of  an  alkaloid  may  be  fairly  inferred.  Albumen  gives  a  pre- 
cipitate with  the  test,  but  this  organic  principle  may  be  separated  by  boiling 
the  liquid  and  filtering  it  before  adding  the  test.  It  is  not  affected  by 
ammonia,  but  gives  a  precipitate  of  yellow  oxide  of  mercury  with  potash  or 
soda. 

Subbromide  of  Mercury  (Hg^Br)  is  obtained  when  1  atom  of  mercury 
and  1  of  bromide  of  mercury  are  mixed  and  heated ;  it  forms  a  crystalline 


BROMIDES.       SUBNiTRATES    OF    MERCURY.  485 

sublimate  of  a  pale  yellow  color:  it  is  also  thrown  down  in  the  form  of  a 
white  powder,  on  mixing^solutions  of  bromide  of  potassium  and  nitrate  of 
suboxide  of  mercury.  It  is  insoluble  in  water,  fusible,  and  volatile  at  a  dull 
red  heat. 

Bromide 'OF  Mercury  (llgBr)  is  formed  by  triturating  mercury  with  bro- 
mine, or  when  bromine  and  mercury  are  shaken  together  in  water.  It  is 
deposited  from  its  aqueous  solution  in  lamellar  crystals,  fusible  and  volatile. 
It  is  soluble  in  100  parts  of  cold  water,  and  in  4  or  5  of  boiling  water.  It 
is  very  soluble  in  alcohol  and  in  ether.  An  oxyhromide  of  mercury  =HgBr, 
3HgO,  is  formed  by  boiling  bromide  and  oxide  of  mercury  together  in  water  ; 
it  is  a  yellow  crystalline  powder,  sparingly  soluble  in  boiling  water.  There 
are  several  compounds  of  bromide  of  mercury  with  basic  bromides  (Jiydrar- 
gobromides),  some  of  which  are  crystallizable. 

Mercury  and  Nitrogen.  Xitride  of  Mercury  (IlggN). — This  com- 
pound is  formed  by  passing  ammonia  over  oxide  of  mercury  till  saturated  ; 
it  is  then  heated  to  300°,  and  the  current  of  ammonia  continued  as  long  as 
water  is  formed:  3HgO -f  NH3=Hg3N,-|-3HO.  The  product  is  always 
contaminated  by  a  little  metallic  mercury,  which  may  be  abstracted  by  cold 
dilute  nitric  acid.  Nitride  of  mercury  is  a  brown  powder,  which  explodes 
when  struck  with  a  hammer,  or  when  suddenly  heated. 

Mercury  and  Nitric  Acid.  Nitrates  of  Mercury. — There  appear  to 
be  three  nitrates  of  the  suboxide  of  mercury — namely,  a  neutral  and  two 
basic  salts.  1.  The  neutral  Nitrate  of  suboxide  of  Mercury  =HggO,N05,  is 
formed  by  digesting  excess  of  mercury  in  cold  dilute  nitric  acid  till  short 
prismatic  crystals  are  formed,  which  include  2  atoms  of  water.  (If  these  are 
left  in  the  solution  they  gradually  give  place  to  larger  crystals  of  a  sesqui- 
salt.)  They  are  entirely  soluble  in  a  small  quantity  of  warm  water  ;  by  a 
large  quantity  of  water  they  are  resolved  into  an  acid  and  basic  salt :  the 
acid  salt  is  at  once  obtained  by  dissolving  this,  or  the  subnitrates,  in  dilute 
nitric  acid.  This  salt  is  resolved  by  heat  into  red  oxide  {Hydrargyri nitrico- 
oxidum),  a,nd  nitrous  acid;  (Hg30,NOg=2E[gO  +  N04).  2.  Sesquinitrate 
of  suboxide  of  Mercury  (3IIg30,2N03). — When  the  first  formed  crystals  of 
the  preceding  salt  are  left  in  the  mother-liquor,  they  gradually  dissolve,  and 
are  replaced  by  large  transparent  prisms  having  the  formula  3B[g20,2N05, 
3H0.  They  are  soluble  without  decomposition  in  a  little  water ;  in  much 
water  they  pass  into  a  yellowish  subsalt  and  a  soluble  supersalt. — 3.  Bibasic 
nitrate  of  suboxide  of  Mercury  (2(Hg20)N05)  is  formed  by  repeatedly 
washing  either  of  the  preceding  salts  with  cold  water  :  it  remains  as  a  yellow 
crystalline  powder. 

Nitrates  of  the  red  oxide  of  Mercury  ;  Pernitrates  of  Mercury. — 1.  There 
is  no  crystallizable  monobasic  tiitrate  of  red  oxide  of  Mercury  =HgO,N05. 
When  peroxide  of  mercury  is  dissolved  in  nitric  acid,  or  when  mercury  is 
boiled  in  strong  nitric  acid,  a  dense  liquor  is  obtained  on  evaporation,  which 
stains  the  cuticle  brown  ;  on  further,  evaporation  acid  escapes,  and  crystals 
of  dipernitrate  are  formed.  2.  Bibasic  nitrate  of  red  oxide  of  Mercury. 
Dipernitrate  of  Mercury  2(HgO)N05.  This  salt,  which  crystallizes  out  of 
the  preceding  solution,  is  deliquescent,  decomposed  by  water,  but  soluble 
without  change  in  water  acidulated  by  nitric  acid :  its  crystals  are  2(HgO) 
N05,2HO.  3.  Tribasic  nitrate  of  the  red  oxide  of  Mercury  =(3HgO)N05, 
HO,  remains  in  the  form  of  a  yellow  hydrated  powder  when  the  preceding 
salt  is  drenched  with  cold  water  as  long  as  it  runs  off  sour. — Sexbasic  nitrate 
of  red  oxide  of  Mercury,  6(HgO)N05,  is  formed  by  the  continuous  action  of 
boiling  water  on  the  yellow  tribasic  salt.  The  nitrates  of  mercury  are  some- 
times used  for  the  purpose  of  dressing  the  fur  on  the  skins  of  animals  such 


486  NITRATES    OF    MERCURY        SULPHIDES. 

as  hares  and  rabbits.  Workmen  engaged  in  this  occupation  have  suffered 
from  the  usual  symptonas  of  mercurial  poisoning. 

Action  of  ammonia  on  the  Nitrates  of  Mercury.  1.  Ammonio-nitrate  of 
suboxide  of  Mercury.  Hahnemannh  Soluble  Mercury  (3Hg.^0,H-NH^d, 
NO5). — This  compound  is  obtained  by  precipitating  a  very  dilute  cold  aqueous 
solution  of  nitrate  of  suboxide  of  mercury  by  a  weak  solution  of  ammonia; 
the  mixture  should  be  constantly  stirred,  the  ammonia  not  added  in  excess, 
and  the  precipitate  washed  as  quickly  as  possible  upon  a  filter,  and  dried  in 
the  shade  at  ordinary  temperature.  It  is  a  grayish-black  powder. — 2.  Nitrate 
of  ammonia  and  of  suboxide  of  Mercury.  By  evaporating  a  mixed  solution 
of  nitrate  of  suboxide  of  mercury  and  nitrate  of  ammonia,  prismatic  crystals 
are  formed,  the  aqueous  solution  of  which  gives  a  gray  precipitate  both  with 
ammonia  and  with  carbonate  of  potassa. — 3.  Basic  a.  mi  do -nitrate  of  Mer- 
cury (HgNHg-f  5(HgO)N05).  Tliis  compound  appears  to  be  sometimes 
formed  when  excess  of  ammonia  is  added  to  a  concentrated  nitrate  of  per- 
oxide of  mercury  :  it  is  a  pale  yellow  powder  containing  about  85  per  cent, 
of  mercury. 

Mercury  and  Sulphur.  Subsulphide  of  Mercury  ;  Disulphide  of  Mer- 
cury (HgaS). — When  1  part  of  mercury  is  triturated  for  some  time  with  3 
of  sulphur,  a  black  tasteless  compound  is  obtained,  which  was  called  in  old 
pharmacy,  Ethiops  mineral ;  when  boiled  in  solution  of  potassa,  sulphur  is 
taken  up,  and  sulphide,  (HgS)  remains,  so  that  it  is  probably  a  mixture  of 
sulphur  and  sulphide.  When  sulphuretted  hydrogen  is  passed  through  a 
dilute  solution  of  nitrate  of  suboxide  of  mercury,  or  through  a  mixture  of 
very  finely  divided  calomel  and  water,  a  black  powder  is  thrown  down,  which 
is  a  true  subsulphide. 

Sulphide  OF  Mercury  ;  Bisulphide;  Vermilion;  Cinnabar  (HgS). — This 
sulphide  is  obtained  anhydrous  and  of  a  red  color  by  the  following  process : 
6  parts  of  mercury  are  mixed  in  an  iron  pot  with  1  of  sulphur,  and  made  to 
combine  by  a  moderate  heat,  and  constant  stirring  :  the  mixture  is  then 
transferred  to  a  subliming-vessel,  and  heated  to  redness  in  a  sand-bath. 
Mercury  and  sulphur  evaporate,  and  a  steel-gray  sublimate  forms,  which  is 
removed,  and  rubbed  or  levigated  into  a  very  fine  powder  (vermilion).  If 
mercury  and  sulphur  are  heated  together  in  large  quantities,  the  action  is  so 
intense  at  the  moment  of  their  combination,  as  to  occasion  an  explosive 
ignition.  When  solution  of  corrosive  sublimate  is  decomposed  by  the  pro- 
longed action  of  an  excess  of  sulphuretted  hydrogen,  or  of  an  alkaline 
sulphide,  the  precipitate  which  falls  is  hydrated  sulphide  of  mercury  :  it  is 
black,  until  warmed  in  the  sulphuretted  liquor,  when  it  gradually  reddens,  as 
a  result  of  dehydration.  The  principal  points  to  attend  to  in  procuring  this 
pigment  of  its  most  perfect  hue,  are  in  the  first  place  the  careful  selection 
and  cleansing  of  the  first  crystalline  gray  sublimate,  so  that  there  may  not 
be  the  smallest  remaining  admixture  of  the  black  pulverulent  amorphous 
compound;  ajid  secondly,  the  perfection  of  the  pulverization  and  elutriation, 
so  as  to  render  the  powder  as  impalpable  as  possible.  Cinnabar  is  not 
altered  by  exposure  to  air  or  moisture ;  when  heated  to  a  dull  redness  in  an 
open  vessel,  the  sulphur  forms  sulphurous  acid,  and  the  mercury  escapes  in 
vapor.  The  metal  is  thus  procured  from  its  ores  (p.  479).  In  close  vessels 
it  sublimes  before  it  fuses.  It  is  decomposed  by  distillation  with  fixed  alka- 
lies, lime,  and  baryta,  and  by  several  of  the  metals.  When  adulterated  with 
red  lead  or  with  colcothar,  it  is  not  entirely  volatile.  It  is  insoluble  in  caustic 
alkaline  solutions,  and  in  nitric  and  hydrochloric  acids;  but  nitrohydrochloric 
acid  acts  upon,  and  decomposes  it,  even  in  the  cold.  Boiled  in  sulphuric 
acid,  sulphurous  acid  is  evolved,  and  a  sulphate  of  mercury  is  formed.  Native 
Cinnabar  is  the  principal  ore  of  mercury  :  it  occurs  massive  and  crystallized. 


SULPHATES    OF    MERCURY.  4S7 

It  is  of  various  colors,  sometimes  appearine^  steel-prray,  at  otliers  bright-red. 
Native  mercury,  and  native  amalg:nm  of  silver,  sometimes  accompany  it. 

Chlorosulphide  of  Mercury  (2(rigS)IIgCl). — AViien  sulphuretted  hy- 
drogen is  passed  through  a  solution  of  corrosive  sublimate  a  white  precipitate 
is  first  formed  ;  if  the  action  of  the  gas  is  continued,  this  white  compound 
blackens  and  becomes  hydrated  sulphide  of  mercury.  The  same  white  com- 
pound is  formed  by  digesting  moist  and  recently  precipitated  sulphide  of 
mercury,  in  a  solution  of  corrosive  sublimate.  It  may  be  washed  and  dried 
without  decomposition.  Corresponding  compounds  of  the  sulphide  have 
been  obtained  with  iodide  and  bromide  of  mercury.  Sulphide  of  mercury 
also  combines  with  other  metallic  sulphides. 

Sulphide  of  Suboxide  of  Mercury  (Hg.,0,S03). — When  1  part  of  mer- 
.cury  is  digested  in  a  moderate  heat  with  \^  of  sulphuric  acid,  sulphurous 
acid  gas  is  evolved,  and  a  white  mass  is  obtained,  which,  washed  with  cold 
water,  affords  a  difficultly  soluble  white  salt,  which  is  a  sulphate  of  suboxide 
of  mercury.  The  same  salt  is  thrown  down,  when  sulphuric  acid  is  added  to 
a  solution  of  nitrate  of  suboxide  of  mercury  :  it  is  also  formed  by  triturating 
equivalent  proportions  of  mercury  and  persulphate,  and  heating  the  mixture. 
In  this  way  it  is  prepared  for  the  manufacture  of  calomel.  Sulphate  of  sub- 
oxide of  mercury  requires  500  parts  of  cold,  and  300  of  boiling  water  for 
its  solution  :  it  crystallizes  in  prisms. 

Sulphate  of  Peroxide  of  Mercury;  Persulphate  of  Mercury  (HgO, 
SO3). — This  salt  is  formed  when  two  parts  of  mercury  and  three  of  sulphuric 
acid  are  boiled  down  to  dryness.  Sulphurous  acid  escapes  in  consequence 
of  the  decomposition  of  a  portion  of  the  acid  (Hg  +  2S03=HgO,S03+SOjj). 
Thi«  sulphate  is  decomposed  in  the  humid  way  by  the  hydracids,  and  free 
sulphuric  acid  is  found  in  solution.  It  is  resolved  by  water  into  a  soluble 
acid  salt  and  an  insoluble  basic  salt:  the  former  may  be  obtained  in  white 
deliquescent  acicular  crystals. — Tribasio  Sulphate  of  Peroxide  of  Mer- 
cury ;  Subsulphate  of  Mercury  (3(HgO)S03).  This  sa-k,  long  known 
under  the  name  of  Turpeth  mineral  (so  called  from  a  similarity  in  its  medi- 
cinal effects  to  those  of  the  root  of  the  Convolvulus  Terpethum,  which  is 
cathartic  and  emetic),  is  obtained  in  the  form  of  an  almost  insoluble  yellow 
powder  by  the  action  of  boiling  water  upon  the  preceding  sulphate ;  when 
gently  heated,  its  color  gradually  deepens  to  orange,  but  reverts  to  lemon- 
yellow  as  it  cools.  Sulphate  of  Mercury  forms  a  double  salt  with  sulphate 
of  ammonia  =NH^0,S03-f  HgOjSOg,  which  is  difficultly  soluble,  and  falls 
in  the  form  of  a  white  powder  on  mixing  solutions  of  the  component  sul- 
phates. 

Phosphates  of  Mercury. — When  solution  of  common  phosphate  of  so"da 
is  dropped  into  a  solution  of  suboxide  of  mercury,  a  white  crystalline  pre- 
cipitate falls  (2(Hg30)HO,PO.)  ;  when  the  solution  of  the  phosphate  is 
added  to  pernitrate  of  mercury,  a  dense  white  insoluble  powder  is  thrown 
down=2(HgO)HO,P05. 

Carbonates  op  Mercury. — Carhonate  of  Suboxide  of  Mercury  (Hg^O, 
CO^)  is  thrown  down  when  solution  of  carbonate  of  soda  is  dropped  into 
solution  of  nitrate  of  suboxide  of  mercury,  in  the  form  of  yellow  powder. 
Carbonate  of  Peroxide  of  Mercury  (4(  HgO)  CO  J. — Solution  'of  nitrate  of 
mercury  affords  a  reddish-brown  precipitate  with  carbonate  of  soda,  which 
is  slightly  soluble  in  excess  of  the  alkaline  solution,  and  in  aqueous  car- 
bonic acid. 

Mercury  and  Cyanogen.  Cyanide  of  Mercury  (HgCy). — There  are 
several  processes  for  obtaining  this  compound.  (I.)  By  boiling  1  part  of 
finely-powdered  peroxide  of  mercury  with  2  of  Prussian  blue  in  8  of  water, 
a  solution  is  obtained,  which  if  filtered  while  hot,  deposits  crystals  of  the 


488  FULMINATING    MERCURY. 

cyanide.  (2.)  When  peroxide  of  mercury  is  brought  into  contact  with  the 
vapor  of  hydrocyanic  acid  they  act  intensely  upon  each  other,  and  water  and 
cyanide  of  mercury  are  formed.  (3  )  Peroxide  of  mercury  may  be  digested 
in  aqueous  hydrocyanic  acid.  (4.)  To  a  solution  of  2  parts  of  ferrocyanide 
of  potassium  in  15  of  boiling  water,  add  3  parts  of  dry  persulphate  of  mer- 
cury ;  boil  for  15  minutes  and  filter  off  the  clear  liquid  whilst  hot ;  as  it  cools 
cyanide  of  mercury  crystallizes,  which  must  be  purified  by  a  second  crystalliza- 
tion; (K,FeCy3+3(HgO,S03)=3HgCy-f2KO,S03,  +  FeO,S03).  Cyanide 
of  mercury  forms  anhydrous  prismatic  crystals,  nearly  colorless,  or  of  a  pale 
buff  color,  at  first  transparent,  permanent  in  the  air,  poisonous,  and  of  a 
nauseous  metallic  taste ;  they  dissolve  in  8  parts  of  water  at  60°,  and  are 
sparingly  soluble  in  alcohol.  This  salt  is  decomposed  by  heat,  as  in  the 
process  for  obtaining  cyanogen,  and  a  brown  or  black  matter  remains  in  the 
retort,  which  \s>  paracyanogen  (p.  218)  If  distilled  with  hydrochloric  acid, 
hydrocyanic  acid  and  chloride  of  mercury  are  produced:  it  is  also  decomposed 
by  hydriodic  acid  and  by  sulphuretted  hydrogen,  an  iodide  and  a  sulphide  of 
mercury,  and  hydrocyanic  acid,  being  formed  (p.  282).  Nitric  acid  dis- 
solves it  without  decomposition.  It  is  decomposed  when  heated  with  sul- 
phuric acid.     The  alkalies  do  not  act  upon  this  cyanide. 

Fulminating  Mercury  ;  Fulminate  of  Mercury  ;  (2(Hg30)Cy202). — 
This  compound  is  prepared  by  dissolving  100  grains  of  mercury  in  a  measured 
ounce  and  a  half  of  nitric  acid,  aided  by  heat.  This  solution  is  to  be  poured, 
when  cool,  into  two  measured  ounces  of  alcohol  in  a  porcelain  basin,  and 
gently  warmed  :  it  soon  effervesces  and  evolves  ethereal  vapor,  and  if  the 
action  is  too  violent,  it  must  be  quelled  by  cooling  the  vessel,  or  by  the 
addition  of  a  little  cold  alcohol.  During  this  action  a  gray  precipitate 
falls,  which  is  to  be  immediately  separated  by  decantation  and  filtration, 
washed  with  small  quantities  of  distilled  water,  and  carefully  dried  at  a  heat 
not  exceeding  100°.  The  above  quantity  of  mercury  should  yield  about  120 
grains  of  the  powder.  If  the  product  is  mixed  with  metallic  mercury,  it 
may  be  purified  by  solution  in  boiling  water,  from  which  it  is  deposited  in 
silky  acicular  crystals.  This  dangerous  compound  is  now  in  considerable 
demand  for  the  manufacture  of  percussion  caps.  It  is  introduced  into  the 
caps,  closely  compressed,  moistened  with  a  resinous  varnish,  and  subsequently 
carefully  dried.  When  fulminating  mercury  is  heated  to  about  300°,  it 
explodes  suddenly  with  a  bright  flame  :  it  also  detonates  by  friction  or  per- 
cussion, especially  when  placed  in  contact  with  particles  of  sand  or  glass  ; 
by  the  electric  spark,  and  by  contact  of  concentrated  sulphuric  and  nitric 
acids ;  the  gases  evolved  by  its  explosions  are  carbonic  acids,  nitrogen,  and 
the  vapor  of  mercury. 

Alloys  of  Mercury.  Amalgams. — Mercury  combines  with  most  of  the 
other  metals,  forming  a  class  of  compounds  which  are  called  amalgams. 
Many  of  these  are  definite  and  crystallizable,  and  may  be  separated,  by 
gentle  pressure,  from  the  excess  of  mercury  in  which  the  definite  compound 
is  suspended  or  dissolved.  They  are  generally  brittle  or  soft.  The  extra- 
ordinary phenomena  connected  with  the  amalgam  of  ammonium,  and  the 
probable  nature  of  that  substance,  have  already  been  discussed  (p.  183). 
An  amalgam  of  sodium  is  now  in  great  demand  for  procuring  gold  and  silver, 
as  well  as  for  many  useful  purposes  in  chemistry  and  the  arts.  One  part  of 
potassium  with  70  of  mercury  produces  a  hard  brittle  compound.  If  mer- 
cury is  added  to  the  liquid  alloy  o^  potassium  and  sodium,  an  instant  solidi- 
fication ensues,  and  heat  enough  to  inflame  the  latter  metals  is  evolved. 
Iron  and  mercury  may  be  combined  by  triturating  together  clean  iron  filings 
and  zinc-amalgam,  and  adding  a  solution  of  perchloride  of  iron  ;  by  rubbing 
and  heating  this  mixture,  the  iron  and   mercury  form  a  bright  amalgam. 


AMALGAMS    OF    MERCURY.  489 

Under  common  circumstances,  iron  resists  the  action  of  mercnry  so  perfectly, 
that  tiie  latter  metal  is  usually  kept  in  iron  bottles;  and  mercurial  troughs 
and  barometer  cisterns  are  made  of  iron.  An  amalg:am  of  zinc  is  used  for 
the  excitation  of  electrical  machines.  8  parts  of  mercury  and  1  of  zinc  form 
a  white  brittle  compound  ;  5  of  mercury  and  2  of  zinc  form  a  crystal  I  izable 
amalgam.  Amalgam  of  tin  is  easily  formed  by  triturating  the  metals  to- 
gether, or  by  fusion  at  a  gentle  heat :  it  is  largely  used  for  silvering  looking- 
glasses.  This  beautiful  process  is  performed  as  follows  :  A  single  and  perfect 
sheet  of  pure  tinfoil,  of  proper  thickness,  and  somewhat  larger  than  the  plate 
of  glass,  is  spread  upon  a  perfectly  plane  table  of  slate  or  stone  :  mercury  is 
then  poured  upon  it,  and  rubbed  upon  its  surface  by  a  hare's  foot,  or  a  ball 
of  flannel  or  cotton,  so  as  to  form  a  clean  and  bright  amalgam;  upon  this, 
an  excess  of  mercury  is  poured,  until  the  metal  has  a  tendency  to  run  off. 
The  plate  of  glass,  previously  made  quite  clean,  is  now  brought  horizontally 
towards  the  table,  and  its  edge  so  adjusted,  as,  by  gradually  and  steadily 
sliding  it  forward,  to  displace  some  of  the  excess  of  mercury,  and  float  the 
plate  as  it  were  over  the  amalgam,  the  dross  upon  its  surface  being  pushed 
onwards  by  the  edge  of  the  glass,  so  that  the  mercury  appears  beneath  it 
with  a  perfectly  uniform,  clean,  and  brilliant  reflecting  surface.  Square  iron 
weights,  of  10  or  12  lbs.  each,  are  then  placed  side  by  side  upon  the  surface 
of  the  plate,  so  as  entirely  to  cover  it,  and  press  it  down  upon  the  amalga- 
mated surface  of  the  tin  ;  in  this  way  the  excess  of  mercury  is  partly  squeezed 
out,  and  the  amalgam  is  made  to  adhere,  by  crystallization,  firmly  to  the 
glass  (p.  23).  The  mercury,  as  it  runs  off",  is  received  into  a  channel  on  the 
side  of  the  table,  which  is  slightly  inclined  to  facilitate  the  drainage,  and  in 
about  48  hours  the  weights  are  taken  off  and  the  plate  is  carefully  lifted  from 
the  table  and  set  nearly  upright,  by  which  the  adhering  mercury  gradually 
drains  off,  and  the  brilliant  amalgam  remains,  perfectly  and  uniformly  ad- 
hering to  the  glass.  Amalgam  of  copper  may  be  made  as  follows  :  to  a 
hot  solution  of  sulphate  of  copper  add  a  little  hydrochloric  acid  and  a  few 
sticks  of  zinc,  and  boil  the  mixture  for  about  a  minute  ;  the  copper  will  be 
precipitated  in  a  metallic  state,  and  in  a  finely-divided  spongy  form  ;  take 
out  the  zinc,  pour  off  the  liquor,  wash  the  copper  with  hot  water,  and  pour 
upon  it  a  little  dilute  nitrate  of  mercury,  which  will  instantly  cover  every 
particle  of  copper  with  a  coating  of  this  metal  ;  then  add  mercury  to  the 
amount  of  two  or  three  times  the  weight  of  the  copper,  and  a  slight  tritura- 
tion will  so  con>bine  them  that  the  completion  of  the  process  may  be  effected 
by  heating  the  mixture  for  a  few  minutes  in  a  crucible.  Lead  and  mercury 
readily  combine  in  all  proportions  :  3  parts  of  mercury  and  2  of  lead  form  a 
crystallizable  amalgam.  Bismuth  amd  mercury  readily  unite  :  a  mixture  of 
3  parts  of  mercury,  1  of  lead,  and  1  of  bismuth  forms  a  fluid  amalgam  used 
for  silvering  the  inside  of  hollow  glass  spheres.  When  mercury  is  adulterated, 
it  is  with  these  metals  ;  but  the  facility  with  which  it  then  oxidizes,  and  the 
imperfect  fluidity  of  its  small  globules,  render  the  fraud  easy  of  detection. 

Tests  for  the  Salts  of  Mercury. — The  soluble  salts  of  the  suboxide  are 
mostly  white  :  some  of  them,  when  neutral,  are  resolved  by  water  into  basic 
and  acid  salts.  1.  With  phosphorous  and  sulphurous  acids,  and  protochlo- 
ride  of  tin,  they  give  precipitates  of  metallic  mercury  ;  2.  The  caustic  alka- 
lies throw  down  a  black,  and  the  carbonated  alkalies  a  yellow  or  brown  pre- 
cipitate ;  3.  The  alkaline  phosphates,  a  white  precipitate,  even  in  very  dilute 
solutions;  4.  Sulphuretted  hydrogen  and  the  hydrosulphates,  black;  5. 
Hydriodic  acid  and  the  iodides,  dingy  green  or  yellow  in  very  diluted  solu- 
tions ;  6.  Hydrochloric  acid  and  the  chlorides,  white  and  curdy  precipitates; 
the  alkaline  chromates,  red  ;  ferrocyanide  of  potassium,  white  ;  the  oxalates, 
white,  even  when  very  dilute.     The  soluble  salts  of  the  red  or  peroxide  of 


490  TESTS    FOR    THE    SALTS    OF    MERCURY. 

mercury  are  mostly  white  when  neutral,  yellow  when  basic,  and  are  often  re- 
solved by  .water  into  acid  and  basic  salts.  1.  Protochloride  of  tin  gives  a 
black  precipitate,  which,  when  boiled,  thrown  on  a  filter,  and  dried,  runs 
into  small  globules  of  metallic  mercury.  2.  Caustic  alkalies,  when  added 
in  small  quantity,  give  a  reddish-brown,  and  in  large  qnantity,  a  yellow  pre- 
cipitate of  the  hydrated  oxide  of  mercury.  3.  Ammonia  and  carbonate  of 
ammonia  produce  white  precipitates  in  their  solutions.  4.  Iodide  of  potas- 
sium gives  a  red,  and  infusion  of  galls  an  orange  precipitate.  Unless  in  con- 
centrated solutions  they  are  not  affected  by  hydrochloric  or  oxalic  acid.  Me- 
tallic mercury  is  precipitated  from  all  of  its  solutions  by  a  plate  of  clean 
copper,  or  by  the  addition  of  protochloride  often,  and  boiling  the  liquid. 
The  insoluble  mercurial  salts  are  mostly  volatilized  at  a  red  heat ;  and  both 
soluble  and  insoluble  salts  are  decomposed,  with  the  production  of  metallic 
mercury,  when  heated  in  a  glass  tube  with  2  or  3  parts  of  dry  carbonate  of 
soda,  or  of  ferrocyanide  of  potassium. 

Analysis  in  Cases  of  Poisoning. —  Oxide  of  Mercury  may  be  identified 
by  its  red  color,  its  insolubility  in  water,  and  by  its  yielding  a  sublimate  (in 
globules)  of  metallic  mercury,  when  dried  and  heated  in  a  glass  tube.  It  is 
dissolved  by  nitric  acid,  and  the  solution  possesses  the  characters  assigned 
above  to  the  persalts  of  the  metal.  White  precipitate.  This  is  a  white  chalky- 
looking  powder,  not  soluble  in  water,  but  partly  converted  into  a  yellow 
basic  salt  by  boiling  water:  1.  Ammonia  does  not  change  its  color.  2. 
Nitric  acid  readily  dissolves  it  (by  these  two  characters  it  is  distinguished 
from  calomel) ;  in  the  acid  solution,  chlorine  may  be  found  by  the  addition 
of  nitrate  of  silver.  3.  When  boiled  with  a  solution  of  potassa,  ammonia  is 
liberated.  4.  When  digested  with  protochloride  of  tin,  it  is  darkened,  and 
metallic  mercury  is  set  free.  5.  When  heated  with  dry  carbonate  of  soda,  it 
yields  a  sublimate  of  metallic  mercury. 

Corrosive  Sublimate. — This  is  the  principal  poison  of  mercury.  It  is 
usually  seen  in  heavy  crystals,  or  in  the  form  of  a  white  crystalline  powder. 
As  a  solid,  1.  When  the  powder  is  heated  on  a  platinum  foil  or  mica,  it 
melts,  and  is  volatilized  in  a  white  vapor  without  leaving  any  residue.  2. 
When  heated  in  a  close  tube,  it  melts  and  forms  a  sublimate,  consisting  of 
prismatic  crystals  sometimes  stellated.  3.  The  powder  is  changed  in  color 
by  the  following  reagents:  iodide  of  potassium  produces  a  bright  scarlet, 
potassa  a  yellow,  and  hydrosulphate  of  ammonia  a  black  precipitate  ;  ammo- 
nia does  not  alter  it.  4.  The  mercury  and  chlorine  may  be  discovered  by 
one  process.  Mix  the  powder  with  3  parts  of  dry  carbonate  of  soda,  and 
heat  it  until  the  residue  in  the  tube  fuses  and  becomes  white.  A  sublimate 
of  metallic  mercury  in  globules  will  be  obtained.  Detach  by  a  file  the  end 
of  the  tube  containing  the  fused  residue,  which  is  chloride  of  sodium  with 
some  undecomposed  carbonate.  Digest  it  in  water  with  nitric  acid,  and 
apply  heat  until  it  is  entirely  dissolved  :  then  add  to  the  solution,  nitrate  of 
silver.  A  white  precipitate  of  chloride  of  silver,  insoluble  in  nitric  acid  will 
be  at  once  produced.  The  solid  is  thus  proved  to  contain  both  mercury  and 
chlorine,  and  the  only  compound  of  these  elements  soluble  in  water  is  cor- 
rosive sublimate.  In  solution  in  water.  1.  Protochloride  of  tin  added  to  a 
solution  of  corrosive  sublimate,  produces  a  black  precipitate  which,  after  it 
has  been  boiled,  is  resolved  into  globules  of  metallic  mercury.  2.  Sulphu- 
retted hydrogen  and  hydrosulphate  of  ammonia  produce,  after  a  time,  a  black 
sulphide,  not  soluble  in  alkalies  or  diluted  acids.  3.  If  the  liquid  is  acidu- 
lated, and  bright  copper  foil,  wire,  or  gauze,  is  plunged  into  it,  the  copper 
acquires  a  silvery-white  deposit,  even  in  the  cold,  but  more  rapidly  by  heat. 
When  the  copper  with  the  metallic  deposit  is  heated  in  a  tube,  globnles  of 
mercury  are  obtained. 


DETECTION    OF    MERCURY    IN    CASES    OF    POISONING.  491 

In  Organic  Liquids. — The  liquid  should  be  separated  by  filtration  from 
any  insoluble  portion.  The  latter  should  be  pressed,  dried,  and  set  aside 
for  a  separate  analysis.  A  slip  of  bright  copper  foil  or  gauze  may  be  em- 
ployed as  a  trial  test  in  the  manner  above  described.  In  place  of  copper, 
a  small  galvanic  combination,  made  by  twisting  a  layer  of  gold-foil  round  a 
layer  of  zinc  foil,  may  be  introduced.  The  liquid  should  be  slightly  acidu- 
lated with  hydrochloric  acid  and  warmed.  The  metals  may  be  suspended  in 
the  liquid  for  some  hours.  If  the  mercurial  poison  is  present,  the  gold  will 
sooner  or  later  lose  its  color  and  become  silvered  while  the  zinc  will  be  wholly 
or  in  part  dissolved.  The  slip  of  gold  foil  may  be  washed  in  water,  and 
afterwards  in  ether,  and  dried.  It  should  be  divided  into  two  equal  portions. 
One  should  be  submitted  to  heat  in  a  tube,  when  globules  of  mercury  will 
be  obtained  ;  the  other  should  be  heated  in  concentrated  nitric  acid,  until 
the  gold  has  reacquired  its  yellow  color.  On  evaporating  the  excess  of  acid, 
and  adding  a  solution  of  protochloride  of  tin,  a  dark  gray  precipitate  of 
metallic  mercury  is  thrown  down.  It  may  be  remarked  that  sublimed  mercury 
is  wholly  unlike  any  other  volatile  substance.  Globules  of  the  8000th  part 
of  an  inch  in  diameter  may  be  easily  recognized  by  the  aid  of  a  microscope. 
Their  perfect  sphericity,  their  silvery  whiteness  by  reflected,  and  complete 
opacity  by  transmitted  light,  at  once  identify  them  as  metallic  mercury. 

In  the  event  of  a  doubt  existing  respecting  their  mercurial  nature,  the 
following  experiment  will  remove  it.  Cut  off  by  a  file  the  portion  of  glass 
in  wliich  they  are  deposited  :  introduce  this  into  a  wide  short  tube,  with  a 
few  drops  of  hydrochloric,  and  half  the  quantity  of  nitric  acid.  Heat  the 
acid  liquid,  and  carry  it  to  dryness  on  a  sand-bath.  White  prismatic  crys- 
tals of  corrosive  sublimate  will  remain  if  the  sublimate  was  of  a  mercurial 
nature,  and  too  great  a  heat  has  not  been  applied.  On  touching  the  white 
residue  cautiously  with  a  drop  of  solution  of  iodide  of  potassium,  the  crystals 
will  acquire  a  scarlet-red  color. 

Another  method  of  analysis  may  be  sometimes  usefully  resorted  to.  Place 
the  suspected  organic  liquid  in  a  small  golden  capsule.  Acidulate  it  slightly 
with  hydrochloric  acid,  and  touch  the  gold,  through  the  acid  liquid,  with  a 
slip  of  pure  zinc  foil.  Mercury  will  be  deposited  in  a  white  silvery  stain  on 
the  gold,  wherever  the  two  metals  have  come  into  contact.  Wash  out  the 
capsule  with  distilled  water,  and  add  a  few  drops  of  strong  nitric  acid.  Per- 
nitrate  of  mercury  is  thus  obtained,  which  may  be  tested  by  the  processes 
above  described  for  the  detection  of  the  persalts  of  mercury. 

The  insoluble  compounds  of  mercury  may  be  dissolved  by  strong  nitric 
acid,  and  the  solution  tested  for  the  metal.  If  none  is  found,  the  dried  solid, 
mixed  with  dried  carbonate  of  soda  or  ferrocyanide  of  potassium,  may  be 
heated  in  a  tube,  when  mercury,  if  present,  will  be  volatilized.  The  tissues 
may  be  dried  and  dissolved  in  1  part  of  hydrochloric  acid  and  4  parts  of 
water.  The  metal  may  be  separated  from  the  concentrated  liquid,  either  by 
copper-gauze  or  by  gold  and  zinc. 

The  processes  above  described  reveal  only  the  presence  of  mercury.  When 
the  quantity  of  corrosive  sublimate  in  an  organic  liquid  is  moderately  large, 
it  may  be  removed  by  means  of  ether.  Place  the  filtered  liquid  supposed  to 
contain  the  poison,  in  a  stoppered  tube  ;  add  to  it,  its  volume  of  pure  ether, 
and  agitate  the  liquid  at  intervals  for  half  an  hour.  Allow  the  liquid  to 
subside,  pour  off  the  ether  into  a  dial-glass,  and  submit  it  to  spontaneous 
evaporation.  As  the  ether  passes  off,  the  corrosive  sublimate  wMll  be  de- 
posited in  white  silky-looking  prisms.  These  may  be  purified  by  solution  in 
water,  if  necessary,  and  the  solution  again  crystallized.  If  mercury  and 
arsenic  are  associated  in  a  poisonous  mixture,  the  arsenic  may  be  entirely 
separated  by  distillation  (page  479). 


492  PRODUCTION    OF    SILVER    FROM    ITS    ORES. 


CHAPTER    XXXVIII. 

Silver  (Ag=108). 

This  metal,  the  Luna  or  Diana  of  the  alchemists  (D),  was  known  at  a 
very  remote  period  :  it  is  found  native,  and  in  a  variety  of  combination,  the 
most  common  of  which  is  the  sulphide.  Native  Silver  occurs  massive,  arbor- 
escent, capillary,  and,  sometimes,  crystallized.  It  is  seldom  pure,  but  con- 
tains other  metals,  which  affect  its  color  and  ductility. 

Silver  is  not  unfrequently  obtained  in  considerable  quantities  from  argen- 
tiferous sulphide  of  lead,  which  is  reduced  in  the  usual  way,  and  the  argen- 
tiferous lead  is  then  fused  in  a  shallow  dish,  placed  in  a  reverberatory  furnace, 
with  a  current  of  air  constantly  passing  over  its  surface  ;  in  this  way  the  lead 
is  converted  into  oxide  or  litharge,  and  the  silver  is  left  in  the  metallic  state. 
The  litharge  which  results  from  this  operation  is  afterwards  reduced  by 
charcoal,  and  furnishes  lead  which  is  free  from  silver ;  the  ordinary  lead  of 
commerce  generally  contains  a  trace  of  the  latter  metal,  and  is  consequently 
unfit  for  certain  purposes  of  the  arts,  especially  for  the  manufacture  of  white 
lead. 

The  sulphides  of  silver  are  reduced  by  amalgamation.  The  ore,  when 
washed  and  ground,  is  mixed  with  a  portion  of  common  salt,  and  roasted : 
during  this  operation  arsenic  and  antimony  are  expelled,  the  copper  and  the 
iron  are  converted  into  oxides,  chlorides,  and  sulphates,  and  sulphate  of  soda 
and  chloride  of  silver  are  formed.  The  product  is  powdered,  and  agitated 
with  mercury,  water,  and  filings  or  fragments  of  iron  ;  in  this  operation  the 
chloride  of  silver  is  decomposed,  chloride  of  iron  is  formed  which  is  washed 
away,  and  the  silver  and  mercury  combine  into  an  amalgam,  from  which  the 
excesss  of  mercury  is  first  squeezed  out  in  leather  bags,  and  the  remainder 
driven  off  by  distillation.  The  old  process  of  eliquation  is  now  scarcely 
used :  it  consisted  in  fusing  alloys  of  copper  and  silver  with  lead  ;  this  triple 
alloy  was  cast  into  plates  which  were  placed  in  a  proper  furnace  upon  an 
inclined  plane  of  iron  with  a  small  channel  grooved  out,  and  heated  red-hot, 
during  which  the  lead  melted,  and  in  consequence  of  its  attraction  for  silver, 
carried  that  metal  with  it,  the  copper  being  left  behind  in  a  reddish-black 
spongy  mass.  The  separation  of  silver  from  lead  by  the  process  of  crys- 
tallization has  been  already  noticed  (page  26). 

Pure  Silver  may  be  procured  by  dissolving  the  standard  silver  of  com- 
merce in  nitric  acid,  diluted  with  an  equal  measure  of  water.  Immerse  a 
plate  of  clean  copper  in  the  filtered  solution,  which  occasions  a  precipitate 
of  metallic  silver ;  collect  it  upon  a  filter  ;  wash  it  with  a  weak  solution  of 
ammonia,  and  then  with  water,  and  fuse  it  into  a  button.  It  may  also  be 
procured  by  adding  to  the  above  solution  of  standard  silver  a  solution  of 
common  salt ;  collect,  wash,  and  dry  the  precipitate,  and  gradually  add  it 
to  twice  its  weight  of  fused  carbonate  of  potassa  mixed  with  carbonate  of 
soda,  in  a  red-hot  crucible.  Metallic  silver  is  separated,  and  may  be  fused 
into  a  button.  Again  the  chloride  may  be  dissolved  in  ammonia,  and  a  slip 
of  copper  foil  introduced :  or  the  chloride  diffused  in  water  may  be  decom- 
posed by  nascent  hydrogen  derived  from  zinc  and  sulphuric  acid  or  from 
sodium  amalgam.     By  any  of  these  processes  silver  may  be  procured  pure. 


PROPERTIES    OF    SILVER.       OXIDES    OF    SILVER.  493 

Properties. — Silver  is  of  a  more  pure  white  tban  any  other  metal :  it  has 
considerable  brilliancy,  and  takes  a  high  polish.  Its  specific  gravity  varies 
between  10*4,  which  is  the  density  of  cast  silver,  and  10'5  to  10'6,  which  is 
the  density  of  rolled  or  stamped  silver.  It  is  harder  than  gold,  and  after 
gold  the  most  ductile  of  metals.  One  grain  of  the  pure  metal  may  be  drawn 
into  wire  400  feet  in  length,  finer  than  a  human  hair.  It  is  less  malleable 
than  gold,  but  it  may  be  beaten  into  leaves  which  are  not  more  than 
1-150, 000th  of  an  inch  in  thickness.  They  are  not,  however,  so  thin  as  to 
be  translucent.  When  alloyed  with  gold  the  malleability  is  increased,  and 
the  leaves  transmit  a  violet  colored  light.  Silver  is  regarded  among  metals 
as  the  best  conductor  of  heat  and  electricity.  Silver  melts  at  a  bright  red 
heat,  estimated  at  18t3°  of  Fahrenheit's  scale,  and  when  in  fusion  appears 
extremely  brilliant.  It  resists  the  action  of  air  at  high  temperatures  for  a 
long  time,  and  does  not  oxidize,  but  it  is  readily  oxidized  by  a  current  of 
moist  air  containing  ozone.  The  ordinary  tarnish  of  silver  is  occasioned  by 
sulphuretted  hydrogen ;  it  takes  place  very  slowly  upon  the  pure  metal,  but 
more  rapidly  upon  the  alloy  with  copper  used  for  plate,  especially  in  a  damp 
atmosphere.  Pure  water  has  no  effect  upon  the  metal ;  but,  if  the  water 
contains  organic  matter,  it  is  sometimes  slightly  blackened.  If  an  electric 
discharge  is  passed  through  fine  silver-wire,  it  burns  into  a  black  powder. 
In  the  Voltaic  circle  it  burns  with  a  fine  green  light,  and  throws  off  abundant 
fumes.  Exposed  to  an  intense  white-heat  in  the  open  fire  it  boils  and 
evaporates,  but  in  close  vessels  it  is  not  sensibly  volatile.  If  suddenly 
cooled,  it  crystallizes  during  congelation,  often  shooting  out  like  a  cauli- 
flower, and  spirting  or  throwing  small  particles  of  the  metal  out  of  the 
crucible.  This  arises  from  the  escape  of  oxygen,  which  the  metal  absorbs 
and  retains  whilst  fluid,  but  suddenly  gives  off  when  it  solidifies  :  this  curious 
property  of  absorbing  oxygen  is  prevented  by  the  presence  of  a  small  quan- 
tity of  copper. 

Oxides  of  Silver. — There  are  three  oxides  of  this  metal — a  suboxide, 
AgijO  ;  a  protoxide,  AgO  ;  and  a  binoxide,  AgO^.  Of  these,  the  protoxide 
only  forms  permanent  and  definite  saline  combinations.  1.  Suboxide  of 
Silver  (Ag^O).  This  oxide  is  obtained  by  the  action  of  hydrogen  on  citrate 
of  silver,  at  the  temperatcPre  of  212^;  the  protoxide  loses  half  its  oxygen, 
and  the  suboxide  remains  combined  with  half  of  the  acid.  The  solution  in 
water  of  the  suboxide  salt  is  dark-brown,  and  the  suboxide  is  precipitated 
black  from  it  by  potassa  ;  when  the  solution  of  the  subsalt  is  heated,  it  be- 
comes colorless,  and  metallic  silver  appears  in  it.  Some  other  salts  of  silver 
containing  organic  acids,  may  be  substituted  for  the  citrate.  2.  Oxide  of 
Silver  (AgO)  may  be  obtained  by  adding  lime-water  or  a  diluted  solution  of 
soda  to  a  solution  of  nitrate  of  silver,  washing  the  precipitate,  and  drying  it 
at  212°.  It  is  of  a  dark  olive  color,  tasteless,  but  soluble  to  a  small  extent 
in  pure  water ;  and,  like  oxide  of  lead,  it  has  when  in  solution  an  alkaline 
reaction  :  this  solution  is  reddened  by  exposure  to  light,  and  is  rendered 
turbid  by  a  little  carbonic  acid,  but  again  becomes  clear  with  an  excess. 
When  heated  to  dull  redness  this  oxide  is  reduced  to  the  metallic  state  ;  long 
exposure  to  light  also  reduces  it,  converting  it  into  a  black  powder,  which 
is  either  silver  or  its  suboxide.  It  is  reducible  by  hydrogen  at  a  tempera- 
ture of  about  212°  ;  and  also  by  phosphorous  and  sulphurous  acids.  It 
imparts  by  fusion  a  yellow  color  to  glass,  and  is  employed  in  enamel  and 
porcelain  painting.  Oxide  of  silver  dissolves  in  aqueous  ammonia,  forming 
a  colorless  liquid,  which  becomes  coated  with  a  film  of  suboxide  by  exposure 
to  air;  and  when  kept  for  some  months  in  a  stopped  bottle,  acquires  a  film 
of  metallic  silver.  Berthollet's  fulminating  silver  is  also  formed  by  the  action 
of  ammonia  on  the  oxide.    The  best  process  for  preparing  it  is  to  pour  a 


4'&4  CHLORIDE    OP    SILVER. 

small  quantity  of  strong  aqueous  ammonia  upon  the  oxide ;  a  portion  is  dis- 
solved, and  a  black  powder  remains,  which  is  the  deto.nating  compound  ;  it 
should  be  cautiously  dried  on  bibulous  paper.  It  explodes  with  tremendous 
violence  when  gently  rubbed  or  heated  ;  nitrogen  and  water  are  evolved,  and 
the  silver  is  reduced.  It  should  only  be  prepared  in  small  quantities,  and 
handled  with  caution,  for  it  occasionally  explodes  while  wet.  It  is  soluble 
in  an  excess  of  ammonia,  and  this  solution  sometimes  deposits  it  in  small 
brilliant  opaque  crystals.  There  is  some  doubt  respecting  the  real  nature 
of  this  compound :  it  is  probably  a  nitride  of  silver, =Ag3N.  The  composi- 
tion usually  assigned  is  3(AgO)NH3 ;  when  exploded,  it  is  converted  into 
3Ag  +  N-f3HO. 

Peroxide  of  silver  (AgOg). — By  electrolyzing  a  weak  solution  of  silver, 
acicular  crystals  of  this  peroxide  are  formed  at  the  positive  pole.  Ammonia 
energetically  decomposes  it,  and  acids  convert  it  into  the  protoxide.  When 
mixed  with  phosphorus  or  sulphur,  and  struck  with  a  hammer,  it  detonates. 
There  is  reason  to  believe  that  the  second  equivalent  of  oxygen  is  in  the 
state  of  ozone,  and  is  evolved  as  such.  If  introduced  in  a  sealed  tube  into 
a  stoppered  bottle  containing  dry  chlorine,  and  the  tube  is  then  broken  by 
agitating  the  bottle,  it  will  be  found  after  a  short  time  that  the  chlorine  has 
disappeared  and  is  replaced  by  oxygen. 

Chloride  op  Silver  (AgCl). — Silver  does  not  decompose  hydrochloric 
acid  even  on  boiling,  so  that  no  chloride  can  be  formed  by  digesting  the 
metal  in  the  acid.  If  the  surface  of  the  silver  is  tarnished  by  sulphuretted 
hydrogen,  the  sulphuret  is  entirely  decomposed  and  the  discoloration  removed 
by  the  acid.  Silver  and  chlorine  may,  however,  combine  directly  on  contact. 
When  silver  leaf  is  acted  upon  by  gaseous  chlorine  in  a  humid  state,  it  is 
gradually  converted  into  this  compound,  and  if  sufficiently  thin,  a  leaf  of 
white  chloride  of  silver  is  obtained  in  a  few  hours  ;  otherwise  the  action  is 
superficial.  Chloride  of  silver  is  usually  procured  by  adding  a  solution  of 
common  salt  to  a  solution  of  nitrate  of  silver.  It  falls  in  the  form  of  a  white 
curdy  precipitate,  which,  by  exposure  to  light,  becomes  violet-colored,  brown, 
and  ultimately  black.  This  happens  even  in  diffused  daylight;  but  in  sun- 
shine the  change  is  rapid,  especially  if  organic  matter  or  moisture  is  present. 
This  property  of  the  chloride  has  led  to  its  eraifloyment  in  photography. 
When  a  small  quantity  of  subchloride  of  mercury  is  precipitated  along  with 
the  chloride  of  silver,  the  blackening  effect  of  light  is  greatly  diminished. 
Chloride  of  silver  is  so  insoluble  in  water,  that  the  minutest  portion  of  hydro- 
chloric acid,  or  of  any  chloride  in  aqueous  solution,  may  be  detected  by  it. 
It  is  insoluble  in  nitric  acid,  and  in  cold  sulphuric  acid ;  but  when  boiled  in 
sulphuric  acid,  it  is  slowly  decomposed,  with  the  formation  of  sulphate  of 
silver.  It  is  soluble  to  a  small  extent  in  boiling  hydrochloric  acid,  and  in 
strong  solutions  of  the  chlorides  of  the  alkaline  metals,  forming  with  them 
erystallizable  double  salts.  It  is  abundantly  soluble  in  solutions  of  ammonia, 
cyanide  of  potassium,  and  the  alkaline  hyposulphites. 

When  dry  chloride  of  silver  is  heated  to  dull  redness  in  a  silver  crucible, 
it  does  not  lose  weight,  but  fuses,  and,  on  cooling,  concretes  into  a  gray 
semitransparent  substance  (sp.  gr.  5-45),  which  has  been  called  horn  silver^ 
or  luna  cornea.  If  slowly  cooled,  it  has  a  tendency  to  octahedral  crystalli- 
zation. Heated  to  a  bright  red  or  white  heat  in  an  open  vessel,  it  volatilizes 
in  dense  white  fumes.  If  fused  with  potassa  or  soda,  or  their  carbonates, 
chloride  of  silver  is  decomposed,  and  metallic  silver  is  obtained;  (AgCl-|- 
K0=Ag4-KClH-0).  Moist  chloride  of  silver  is  also  decomposed  when 
triturated  with,  and  boiled  in  a  solution  of  caustic  potassa;  a  dense  black 
oxide  is  produced,  and  if  sugar  is  added,  it  is  reduced  to  metallic  silver.  If 
diffused  in  water  acidulated  with  dilute  sulphuric  or  hydrochloric  acid,  and 


IODIDE,    BROMIDE,    AND    NITRATE    OF    SILVER.  495 

a  rod  of  magnesium  or  zinc  is  introduced  into  the  mixture,  hydrogen  is 
liberated  and  the  silver  is  completely  reduced  (AgCl4  H  =  AgH-  HCl).  Tri- 
turated with  fine  zinc  filings,  and  moistened,  the  heat  produced  is  considera- 
ble. The  fused  chloride,  exposed  to  ammonia,  absorbs  a  considerable  portion 
of  the  gas,  which  is  again  given  off  by  heat.  If  the  chloride,  thus  saturated 
with  ammonia,  is  thrown  into  chlorine,  the  ammonia  spontaneously  inflames. 

Chloride  of  silver  is  said  to  require  113,000,000  partsof  water  to  dissolve  it. 
It  may  therefore  be  considered  as  insoluble  in  water.  Hence  a  salt  of  silver 
is  employed  in  quantitative  analysis,  as  a  means  of  determining  the  propor- 
tion of  chlorine.  In  these  cases  some  excess  of  the  precipitant  should  be 
used,  and  the  precipitate  allowed  to  subside  previous  to  separating  it  upon 
the  filter  :  if  the  supernatant  liquor  becomes  perfectly  clear,  the  whole  of  the 
silver  has  fallen  ;  if  it  remains  opalescent,  a  portion  is  probably  still  retained. 
When  the  precipitate  remains  long  suspended,  its  deposition  may  be  accele- 
rated by  heat,  by  agitation,  or  by  adding  a  little  nitric  acid.  The  chloride 
should  be  perfectly  dried  before  weighing  it.  100  parts  of  the  dried  and 
fused  chloride,  are  equivalent  to  24*67  parts  of  chlorine  and  75  33  of  silver. 
Native  Chloride  of  Silver  has  been  found  in  most  of  the  silver-mines :  it  occurs 
massive  and  crystallized. 

Iodide  of  Silver  (Agl). — When  silver-leaf  is  put  into  a  bottle  containing 
a  little  iodine  it  is  speedily  tarnished,  and  in  the  course  of  a  few  days  con- 
verted into  a  film  of  yellow  iodide.  Iodide  of  silver  is  precipitated  upon 
adding  a  soluble  iodide  to  a  solution  of  nitrate  of  silver.  It  is  of  a  yellowish 
color,  insoluble  in  water,  and  decomposed  when  heated  with  potassa. 
Chlorine  also  decomposes  it.  It  is  nearly  insoluble  in  ammonia.  When 
fused  it  acquires  a  red  color.  It  dissolves  in  solutions  of  the  alkaline 
cyanides  and  hyposulphites,  and  in  a  saturated  solution  of  nitrate  of  silver  : 
it  is  also  dissolved  by  iodide  of  potassium  and  other  alkaline  iodides  Native 
Iodide  of  Silver  has  been  found  in  some  of  the  Mexican  ores,  associated  with 
native  silver,  sulphide  of  lead,  and  carbonate  of  lime. 

Bromide  of  Silver  (AgBr)  is  an  insoluble  yellowish  substance,  thrown 
down  upon  the  addition  of  bromine,  or  the  soluble  bromides,  to  nitrate  of 
silver  :  it  dissolves  in  an  excess  of  a  strong  aqueous  solution  of  ammonia, 
and  readily  in  alkaline  cyanides  and  hyposulphites  :  it  is  fusible,  and  con- 
cretes on  cooling  into  a  yellow  corneous  mass.  Chlorine  converts  it  into 
chloride  of  silver  :  it  is  sparingly  soluble  in  solutions  of  bromide  of  potas- 
sium and  sodium,  and  more  abundantly  so  in  a  solution  of  sal-ammoniac  : 
the  compounds  which  it  forms  with  the  alkaline  bromides  are  decomposed 
when  diluted.  Native  bromide  of  silver  has  been  found  in  Mexico  and  Chili, 
in  small  yellowish  cubic  crystals  ;  and  a  native  chlorobromide  (3Ag'Cl,2Ag 
Br)  from  Chili  has  been  described  by  Colonel  Yorke. 

Nitrate  of  Silver  (AgO,N05). — Nitric  acid  diluted  with  3  parts  of 
water  readily  dissolves  silver,  with  the  disengagement  of  nitric  oxide  :  if  the 
silver  contains  copper,  the  solution  is  bluish  ;  or  if  gold,  that  metal  remains 
undissolved  in  the  form  of  a  black  powder.  The  solution  of  nitrate  of  silver 
should  be  clear  and  colorless  ;  it  is  caustic,  and  tinges  animal  substances  at 
first  of  a  yellow  color,  becoming,  by  exposure  to  light,  purple  or  black.  On 
evaporation,  the  solution  yields  anhydrous  tabular  crystals,  which  have  a 
bitter  metallic  taste,  and  are  soluble  in  about  their  own  weight  of  water  at 
60°,  and  in  half  their  weight  at  212°:  they  are  insoluble  in  nitric  acid. 
Alcohol  dissolves  about  one-fourth  its  weight  of  this  salt  at  its  boiling-point, 
but  deposits  nearly  the  whole  as  it  cools.  Nitrate  of  silver,  when  mixed 
with  organic  matters,  blackens  on  exposure  to  light ;  and  when  thus  acted 
upon,  it  is  no  longer  perfectly  soluble  in  water,  owing  to  the  separation  of  a 
portion  of  metallic  silver;   but  if  cautiously  excluded  from  the  contact  of 


0Kk  AMMONIO-NITRATE    OF    SILVER. 

organic  matter,  light  alone  does  not  discolor  it.  When  heated  in  a  silver 
crucible,  it  fuses  into  a  gray  mass,  and  if  cast  into  small  cylinders,  forms  the 
lunar  caustic  of  pharmacy.  It  may  be  fused  at  the  end  of  platinum  wire. 
When  nitrate  of  silver  is  exposed  to  a  red  h-eat,  the  acid  is  partly  evolved 
and  partly  decomposed,  and  metallic  silver  is  obtained.  Sulphur,  phospho- 
rus, charcoal,  hydrogen,  and  several  of  the  metals,  decompose  this  nitrate. 
A  few  grains  mixed  with  a  little  sulphur,  and  struck  upon  an  anvil  with  a 
heavy  hammer,  produce  a  detonation  :  phosphorus  occasions  a  violent  ex- 
plosion when  about  half  a  grain  of  it  is  placed  upon  a  crystal  of  the  nitrate 
and  struck  sharply  with  a  hammer ;  if  heated  with  charcoal  it  deflagrates, 
and  the  metal  is  reduced. 

A  stick  of  phosphorus  or  charcoal  introduced  into  a  weak  solution  of 
nitrate  of  silver,  soon  becomes  incrusted  with  crystals  of  silver.  A  plate  of 
copper  also  occasions  a  precipitation  of  crystalline  silver.  Arborescent 
crystals  of  silver  may  be  produced  on  glass  by  the  following  process :  Coat 
a  glass  plate  with  collodion  in  the  usual  way,  immerse  it  in  the  bath  of  nitrate 
of  silver  to  produce  a  complete  penetration.  Then  lay  it,  with  the  coated 
surface  downwards,  on  a  triangle  or  quadrangle  made  of  fine  copper  wire, 
and  keep  it  in  the  dark.  The  silver  will  be  slowly  reduced  at  each  point  of 
contact  with  the  wire,  and  will  spread  in  a  thin  crystalline  film  over  the 
surface.  When  dried,  the  crystals  may  be  protected  by  another  glass  plate 
placed  over  the  surface.  Mercury  introduced  into  a  solution  of  nitrate  of 
silver  causes  a  crystalline  deposit  of  silver,  called  the  arbor  Diaiice.  Proto- 
sulphate  of  iron  throws  down  metallic  silver  when  added  to  a  solution  of  the 
nitrate  ;  protochloride  of  tin  forms  a  gray  precipitate. 

When  some  of  the  solutions  of  silver  are  reduced  by  certain  essential  oils, 
or  by  grape-sugar,  a  brilliant  film  of  the  metal  may  be  so  thrown  down  upon 
glass  as  to  furnish  a  substitute  for  the  amalgam  of  tin  usually  employed  for 
mirrors:  the  coating  is  not  to  be  depended  upon  for  durability,  but  it  has 
the  advantage  of  being  applicable  to  curved  surfaces  and  the  interior  of 
spherical  vessels.  Pelouze  and  Fremy  describe  the  process  as  follows  :  600 
grains  of  nitrate  of  silver  are  dissolved  in  1200  grains  of  water;  to  this  are 
added,  1st.  75  grains  of  a  solution  composed  of  10  grains  of  sesquicarbonate 
of  ammonia,  10  of  solution  of  ammonia,  sp.  gr.  0980,  and  25  of  distilled 
water  ;  2d.  30  gains  of  solution  of  ammonia,  sp.  gr.  0  980  ;  3d.  1000  grains 
of  alcohol,  sp.  gr.  0-850  :  this  mixture  is  left  at  rest  to  become  clear,  it  is  then 
decanted,  and  a  mixture  of  equal  parts  of  alcohol  and  of  oil  of  cassia  is 
added,  in  the  proportion  of  1  part  of  this  essence  of  cassia  to  15  parts  of  the 
solution  of  silver :  this  mixture  is  shaken  and  left  to  settle  for  some  hours, 
and  then  filtered  :  just  before  applying  it  to  the  glass  to  be  silvered,  it  is 
mixed  with  l-78th  of  its  bulk  of  essence  of  cloves,  cooiposed  of  1  part  of  oil 
<^  cloves  and  3  of  alcohol.  The  glass  to  be  silvered  is  first  thoroughly 
cleansed,  then  covered  with  the  silvering  solution  and  warmed  to  about  100^, 
at  which  temperature  it  is  kept  for  2  or  3  hours:  the  liquid  is  then  decanted 
and  may  be  used  for  other  glasses.  The  deposit  of  silver  is  then  washed, 
dried,  and  varnished. 

Nitrate  of  silver  is  employed  for  writing  upon  linen,  under  the  name  of 
indelible  or  marking  ink :  and  it  is  an  ingredient,  with  gallic  or  pyrogallic 
acid,  in  some  of  the  liquids  sold  for  the  purpose  of  changing  the  color  of 
hair  :  the  black  stain  of  any  of  these  preparations  of  silver  may  be  removed 
by  cyanide  of  potassium.  When  taken  internally,  a  bluish-black  discolora- 
tion of  the  skin  often  ensues,  so  that  the  whole  surface  of  the  body,  and 
especially  the  parts  exposed  to  light,  acquire  a  leaden-gray  color.  Among 
organic  compounds  which  deoxidize  a  solution  of  nitrate  of  silver,  may  be 
noticed  the  freshly-precipitated  resin  of  guaiacum.     This  is  white,  but  on 


SULPHIDE    AND    HYPOSULPHITE    OF    SILVER.  497 

adding  it  to  a  small  quantity  of  nitrate  of  silver  and  warming  the  liquid,  it 
becomes  of  a  deep-blue,  a  result  of  oxidation  of  the  resin.  On  boiling  the 
Cquid  the  color  changes  and  metallic  silver  is  separated  in  the  form  of  a  dark 
powder.  Gallic  acid  slowly  reduces  the  metal  in  the  cold,  but  pyrogallic 
acid  rapidly  decomposes  it,  the  silver  being  precipitated  as  a  black  powder. 

Solution  of  the  nitrate  of  silver  is  a  valuable  test  of  the  presence  of  chlo- 
rine, hydrochloric  acid,  and  the  soluble  chlorides,  with  all  of  which  it  forms 
a  white  cloud  when  very  dilute,  but  a  flaky  precipitate  when  more  concen- 
trated ;  the  precipitate  is  soluble  in  ammonia,  but  insoluble  in  nitric  acid. 
Heat,  agitation,  or  the  addition  of  a  few  drops  of  nitric  acid,  so  as  to  render 
the  liquid  acid,  facilitates  the  deposition  of  the  precipitate.  The  hydriodic, 
hydrobromic,  and  hydrocyanic  acids  also  occasion  in  a  solution  of  nitrate  of 
silver,  precipitates  which  become  slightly  darkened  by  exposure  to  light. 

Ammonio-Nitrate  of  Silver. — Ammonia  is  rapidly  absorbed  by  nitrate 
of  silver,  with  the  production  of  heat  sufficient  to  fuse  the  compound,  which 
consists  of  100  parts  of  the  nitrate,  and  295  parts  of  ammonia.  An  ammo- 
nio-nitrate  of  silver  is  also  obtained  when  ammonia  is  added  to  a  solution  of 
nitrate  of  silver  until  the  first-formed  precipitate  is  redissolved.  This  solu- 
tion when  colored  with  a  little  Indian  ink  forms  a  good  marking  ink,  but  the 
stains  of  all  these  compounds  may  be  removed  by  cyanide  of  potassium  :  or 
by  steeping  the  linen  in  chlorine  water  until  the  stain  is  whitened,  and  then 
applying  ammonia  or  a  solution  of  hyposulphite  of  soda  to  dissolve  and  wash 
out  the  chloride. 

Sulphide  of  Silver  (AgS). — Silver  readily  combines  with  sulphur,  and 
produces  a  gray  crystallizable  compound,  more  fusible  and  softer  than  silver. 
It  may  be  obtained  by  heating  finely-divided  silver,  or  plates  of  silver,  with 
sulphur.  Its  density  is  about  7.  Sulphuretted  hydrogen  and  hydrosulphate 
of  ammonia  occasion  a  copious  black  precipitate  of  sulphide  of  silver  when 
added  to  solutions  of  the  metal  :  sometimes  a  portion  of  the  silver  is  at  the 
same  time  reduced  to  the  metallic  state.  It  is  the  presence  of  sulphur  in  the 
atmosphere  (generally  sulphuretted  hydrogen)  which  occasions  the  tarnish 
upon  silver,  and  which  is  a  great  obstacle  to  many  applications  that  might 
otherwise  be  made  of  this  beautiful  metal. 

Native  Sulphide  of  Silver,  or  vitreous  silver,  is  found  massive  and  crystal- 
lized. It  is  soft  and  sectile.  A  triple  combination  of  silver,  antimo7iy,  and 
«M//?A?/r,  =  3(AgS)SbS3,  constitutes  the  red,  or  ruby  silver-ore  ;  it  is  some- 
times accompanied  by  the  brittle  sulphide,  or  silver  glance,  and  by  antimonial 
silver  (AggSb). 

Hyposulphite  of  Silver  (AgO,S203,5HO)  is  formed  by  dropping  a  weak 
solution  of  nitrate  of  silver  into  a  solution  of  hyposulphite  of  soda  :  a  white 
cloud  is  produced,  which  redissolves  on  agitation  :  on  adding  more  of  the 
precipitant,  the  cloud  reappears  and  aggregates  into  a  gray  precipitate  of 
hyposulphite  of  silver.  When  the  nitrate  is  in  excess,  the  precipitate  rapidly 
changes  from  gray  to  yellow,  brown,  and  black,  being  ultimately  converted 
into  sulphide  of  silver.  Hyposulphite  of  silver  is  also  produced  when  chlo- 
ride of  silver  is  dissolved  in  any  of  the  hyposulphites;  the  solution  has  a 
sweetish  taste.  This  solubility  of  argentine  compounds  in  alkaline  hyposul- 
phites, has  led  to  the  important  application  of  them  to  the  photographic  art. 
{See  Photography,  p.  511.)  Hyposulphite  of  silver  is  very  prone  to  de- 
composition, especially  on  boiling,  being  resolved  into  sulphate  of  oxide  of 
silver,  and  sulphide  of  silver.  Doable  salts  of  the  hyposulphites  of  ammonia, 
potassa,  and  soda,  with  silver,  have  been  formed. 

Sulphite  of  Silver  (AgOjSOg)  is  obtained  in  white  crystalline  grains 
by  adding  an  alkaline  sulphite  to  a  solution  of  silver.     It  produces  double 
salts  witb  the  sulphites  of  the  alkalies. 
32 


498  SULPHATE,    PHOSPHATE,   AND    CYANIDE    OF    SILVER. 

Sulphate  op  Silver  (AgO,S03)  is  deposited  when  sulphate  of  soda  or 
dilute  sulphuric  acid  is  mixed  with  nitrate  of  silver.  It  is  also  produced  by 
boiling  silver  with  its  weight  of  sulphuric  acid.  It  forms  a  white  salt  solu- 
ble in  about  90  parts  of  water  at  60°;  in  boiling  water  it  is  more  soluble, 
and  is  deposited,  as  the  solution  cools,  in  small  anhydrous  crystals :  it  dis- 
solves in  sulphuric  acid,  but  on  moderate  dilution,  the  greater  part  of  the 
salt  again  falls  down.  By  leaving  a  strong  sulphuric  solution  of  silver  in  a 
dark  place,  it  gradually  absorbs  water,  and  octahedral  crystals  of  the  sulphate 
are  deposited.  Upon  the  large  scale,  small  portions  of  gold  are  separated 
from  large  quantities  of  silver,  by  heating  the  finely-granulated  alloy  in  sul- 
phuric acid  :  the  gold  remains  in  the  form  of  a  black  powder,  and  the  sul- 
phate of  silver  may  be  decomposed  by  the  action  of  metallic  copper,  which 
precipitates  metallic  silver,  and  forms  sulphate  of  copper.  Sulphate  of 
silver  absorbs  ammonia,  and  by  saturating  a  strong  and  warm  solution  of 
ammonia  with  sulphate  of  silver,  prismatic  crystals  =2(NH3),AgO,S03,  are 
obtained. 

Phosphate  of  Silver  3(AgO)P05. — When  a  solution  of  common  phos- 
phate of  soda,  2(NaO)HO,P05,  is  added  to  nitrate  of  silver,  a  yellow  anhy- 
drous tribasic  phosphate  of  silver  falls,  and  free  nitric  acid  is  found  in  the 
supernatant  liquor:  3(AgO,N05)-f2(NaO)HO,P05=3AgOP05+2(NaO, 
N05)-fH0,N05).  If  the  solution  of  nitrate  of  silver  is  precipitated  by 
anhydrous  tribasic  phosphate  of  soda,  3(NaO)P05,  the  supernatant  solution 
remains  neutral.  This  phosphate  of  silver  fuses  at  a  red  heat.  It  is  soluble 
in  nitric,  phosphoric,  and  acetic  acids,  as  well  as  in  ammonia  and  carbonate 
of  ammonia. 

Pyrophosphate  op  Silver,  2(AgO)P05,  is  the  white  precipitate  thrown 
down  from  nitrate  of  silver  by  pyrophosphate  of  soda:  in  this  case  the  super- 
natant liquid  remains  neutral  [2(AgO,N05)-f  2(NaO)P03=2(AgO)P05-f- 
2(NaO,N03)]. 

Metaphosphate  of  Silver  (AgO,P05)  is  a  white  gelatinous  precipitate, 
thrown  down  by  a  solution  of  nitrate  of  silver  by  metaphosphate  of  soda  ; 
boiling  water  resolves  it  into  an  acid  and  a  basic  salt. 

Carbonate  of  Silver  (AgOjCOg)  is  precipitated  in  the  form  of  a  pale 
yellow  powder,  by  adding  carbonate  of  potassa  to  nitrate  of  silver.  It 
blackens  by  exposure  to  light,  and  is  easily  decomposed  by  heat.  Moist 
oxide  of  silver  absorbs  carbonic  acid  from  the  air. 

Cyanide  of  Silver  (AgCy). — Hydrocyanic  acid,  or  solution  of  cyanide 
of  potassium,  causes  a  white  precipitate  in  solution  of  nitrate  of  silver,  which 
is  cyanide  of  silver,  and  which,  when  heated,  fuses,  and,  at  a  high  tempera- 
ture, gives  out  cyanogen.  It  is  insoluble  in  water  and  in  fixed  alkalies,  but 
soluble  in  ammonia.  It  is  decomposed  by  hydrochloric  acid,  and  by  sulphu- 
retted hydrogen  ;  nitric  acid  scarcely  acts  upon  it,  unless  concentrated  and 
heated.  Sulphuric  acid,  diluted  with  its  volume  of  water,  decomposes  it 
when  boiling,  with  the  escape  of  hydrocyanic  acid  and  the  formation  of  sul- 
phate of  silver  :  in  this  way  cyanide  may  be  separated  from  chloride  of  silver. 
It  dissolves  in  a  strong  solution  of  nitrate  of  silver,  and  forms  a  compound 
which  is  decomposed  by  water.  It  is  soluble  in  the  alkaline  chlorides,  in 
hyposulphite  of  soda,  and  in  cyanide  of  potassium.  Argento-cyanides. — Cya- 
nides of  the  alkaline  bases  form  soluble  double  salts  with  cyanide  of  silver : 
they  are  insoluble  in  alcohol,  which  throws  them  down  from  their  aqueous 
solutions.  The  argento-cyanide  of  potassium  (KCy,AgCy)  yields  plumose 
colorless  crystals  :  it  produces  precipitates  in  many  of  the  metallic  solutions, 
which  are  insoluble  argento-cyanides.  A  solution  of  oxide  or  chloride  of 
silver  in  cyanide  of  potassium,  forms  a  useful  liquid  for  silvering  metals  by 
immersion,  especially  when   aided  by  electricity.     It  is  thus  employed  in 


FULMINATE    OF    SILVER.  499 

electro-plating :  1  part  of  cyanide  of  potassiam  may  be  dissolved  in  10  parts 
of  water,  and  50  or  60  grains  of  oxide  or  chloride  of  silver  dissolved  in  each 
pint :  the  oxide  and  chloride  should  be  in  a  moist  state.  Cyanide  of  potas- 
sium is  also  useful  for  removing  the  tarnish  from  old^  silver.  It  decomposes 
and  dissolves  the  sulphide. 

Cyanate  of  Silver  (AgO,CyO). — This  monobasic  salt  falls  in  the  form 
of  a  white  powder  when  cyanate  of  potassa  is  added  to  nitrate  of  silver. 

Fulminate  of  Silver;  Fulminating  Silver,  2(AgO)Cya02. — This  dan- 
gerous compound  is  prepared  as  follows  :  100  grains  of  fused  and  finely- 
powdered  nitrate  of  silver  are  added  to  an  ounce  of  warm  alcohol  in  a  large 
basin  ;  an  ounce  of  nitric  acid  is  then  added,  and  presently  effervescence 
ensues  and  a  powder  falls  :  as  soon  as  this  appears  white,  cold  water  is  added, 
and  the  powder  collected  upon  a  filter,  washed,  and  carefully  dried  at  a  tem- 
perature of  100°.  In  collecting  and  handling  this  powder  the  utmost  caution 
is  requisite  ;  it  should  be  made  in  small  quantities  only,  and  not  touched 
with  anything  hard,  for  it  has  exploded  upon  the  contact  of  a  glass  rod  under 
water.  The  feather  of  a  common  quill  serves  to  collect  it ;  and  it  should  be 
kept  either  under  water,  or  if  dry,  in  a  wide-mouthed  vessel  covered  by 
paper,  and  not  in  a  stoppered  or  corked  phial.  Fulminating  silver  is  a  gray 
crystalline  powder  ;  it  acquires  a  dingy  hue  by  exposure  to  light ;  it  dissolves 
in  from  30  to  40  parts  of  boiling  water,  and  as  the  solution  cools,  nearly  the 
whole  is  again  deposited  in  minute  crystals.  It  detonates  with  great  violence 
when  heated,  or  when  touched  by  any  hard  substance ;  placed  upon  a  piece 
of  rock-crystal  and  touched  in  the  slightest  manner  by  another  crystal,  it 
explodes  violently  ;  it  also  detonates  upon  the  contact  of  sulphuric  acid,  and 
by  the  electric  spark.  In  the  formation  of  fulminic  acid,  a  portion  of  the 
alcohol  is  oxidized  so  as  to  form  aldehyde,  and  formic  and  oxalic  acids  :  this 
is  effected  at  the  expense  of  the  oxygen  of  the  nitric  acid,  which  passes  into 
hyponitrous  acid,  and  this,  reacting  upon  another  portion  of  the  alcohol, 
forms  hyponitrous  ether,  fulminic  acid,  and  water  ;  1  atom  of  hyponitrous 
ether  and  1  of  hyponitrous  acid  containing  the  elements  of  1  atom  of  fulminic 
acid  and  6  of  water. 

Hyponitrous  Ether  -f-  Hyponitrous  Acid  =  Fulminic  Acid  +  Water 
'        C^H.OjNOg       '    '  NO3  ""    '~     C4N2O2    ""       5H0 

When  fulminating  silver  (2(AgO)Cy30a)  is  digested  in  a  solution  of 
potassa,  half  of  the  oxide  of  silver  is  precipitated,  and  on  filtering  and 
evaporating  the  solution,  a  crystallizable  salt  is  obtained  =AgO,KO,Cy303. 
It  is  dangerously  explosive.  In  this  salt  one  atom  of  oxide  of  silver  is 
replaced  by  one  atom  of  potassa.  Corresponding  compounds  may  be  ob- 
tained with  other  basic  oxides. 

Cyanurate  of  Silver. — If  nitrate  of  silver  is  added  to  cyanurate  of 
potassa,  a  white  precipitate  is  obtained,  which  consists  of  1  atom  of  cyannric 
acid  combined  with  2  of  oxide  of  silver  and  1  of  water ;  2(AgO)HO,Cyg03. 
This  salt,  heated  in  the  dry  state,  evolves  hydrated  cyanic  acid.  If  a  solution 
of  silver  be  added  to  a  boiling  solution  of  cyanurate  of  ammonia,  containing 
ammonia  in  excess,  the  cyanurate  with  3  atoms  of  oxide  of  silver,  is  formed  : 
3(AgO)Cy303. 

Ausenite  of  Silver,  2(AgO)As03,  is  precipitated  in  the  form  yf  a  pale 
yellow  powder,  soon  becoming  deeper  yellow,  gray,  and  brown,  by  the  addi- 
tion of  arsenite  of  potassa,  to  nitrate  of  silver.  Arsenious  acid  only  produces 
a  white  cloud  in  solution  of  nitrate  of  silver,  but  the  yellow  arsenite  falls  on 
the  subsequent  addition  of  a  small  quantity  of  alkali.  This  salt  retains  its 
yellow  color  when  carefully  dried,  but  becomes  brown  on  exposure  to  light. 


500  SALTS    OF    SILVER.      ALLOYS    OF    SILVER. 

Arsenio -nitrate  of  Stiver. — This  is  obtained  in  solution  by  mixing  one  part 
of  a  saturated  solution  of  nitrate  of  silver  with  five  or  six  parts  of  a  saturated 
solution  of  arsenious  acid.  It  should  give  a  yellow  precipitate  when  a  small 
quantity  of  any  alkali  is  added  to  it.  If  the  precipitate  is  brown  more 
arsenious  acid  must  be  added.  It  is  a  useful  solution  for  the  detection  of 
alkalies  or  alkaline  liquids. 

Arsenate  op  Silver,  3(AgO)As05,  is  thrown  down  from  nitrate  of 
silver  by  arsenic  acid,  and  by  the  soluble  arsenates,  of  a  reddish-brown 
color.  It  is  insoluble  in  water,  but  soluble  in  aqueous  ammonia;  it  dis- 
solves in  nitric  acid,  and  in  acetic  acid. 

Chromate  of  Silver,  AgO.CrOg,  is  precipitated  of  a  crimson-red  color 
by  mixing  solutions  of  chromate  of  potassa  and  nitrate  of  silver.  It  soon 
loses  its  brilliant  tint  and  becomes  brown. 

Bichromate  of  Silver,  AgO,2Cr03  is  precipitated  by  adding  bichromate 
of  potassa  to  an  acid  solution* of  nitrate  of  silver.  When  boiled  in  water  it 
is  resolved  into  dark  green  neutral  chromate,  and  an  acid  solution,  which,  on 
cooling,  again  deposits  crystals  of  bichromate. 

Alloys  of  Silver. — The  compounds  of  silver  with  potassium,  sodium, 
and  other  light  metals,  have  not  been  examined.  When  silver  and  steel  are 
fused  together,  an  alloy  is  formed,  which  appears  perfect  while  in  fusion,  but 
globules  of  silver  exude  from  it  on  cooling,  which  shows  the  weak  attraction 
of  the  metals.  At  a  very  high  temperature,  the  greater  part  of  the  silver 
evaporates,  but  a  portion  equal  to  about  1  in  500  remains,  forming  an  alloy 
known  as  silver-steel,  and  said  to  be  well  adapted  to  the  formation  of  cutting 
instruments,  but  subject  to  rust  from  galvanic  action.  Silver  readily  com- 
bines with  zinc,  producing  a  brittle  bluish-white  granular  alloy.  With  tin 
silver  forms  a  white,  hard,  brittle  alloy.  The  alloy  with  copper  constitutes 
plate  and  coin.  By  the  addition  of  a  small  proportion  of  copper  to  silver, 
the  metal  is  rendered  harder  and  more  sonorous,  while  its  color  is  scarcely 
impaired.  When  the  two  metals  are  in  equal  weights  the  compound  is 
white  :  the  maximum  of  hardness  is  obtained  when  the  copper  amounts  to 
one-fifth  of  the  silver.  The  standard  silver  of  this  country  is  composed  of 
92-5  silver+T"5  copper ;  that  of  France,  of  90  silver -|-10  copper;  and  in 
that  of  Prussia,  the  alloys  amount  to  25  per  cent.  The  specific  gravity  of 
British  standard  silver  is  10"3.  The  silver  coins  of  the  ancients,  and  many 
Oriental  silver  coins,  are  nearly  pure  ;  they  only  contain  traces  of  copper 
and  of  gold.  When  silver  alloyed  by  copper,  such  as  standard  silver,  is 
exposed  to  a  red  heat  in  the  air,  it  becomes  black  from  the  formation  of  a 
superficial  film  of  oxide  of  copper  ;  this  may  be  removed  by  immersion  in  hot 
diluted  sulphuric  acid,  and  a  film  of  pure  silver  then  remains,  of  a  beautiful 
whiteness  :  this  is  called  blanched,  dead,  or  frosted  silver.  The  blanks  for 
coin  are  treated  in  this  way  before  they  are  struck,  whence  the  whiteness  of 
new  coin,  and  the  darker  appearance  of  the  projecting  portions  occasioned 
by  wear,  in  consequence  of  the  alloy  showing  itself  beneath  the  pure  surface  ; 
articles  of  plate  are  often  deadened,  matted,  or  frosted  by  boiling  in  bisul- 
phate  of  potassa  (sal  enixum),  which  acts  in  the  same  way  as  dilute  sul- 
phuric acid.  Lead  and  silver  form  a  very  brittle  dull-colored  alloy,  from 
which  the  lead  is  easily  separated  by  cupellation.  When  fused  lead  con- 
taining silver  is  suffered  to  cool  slowly,  the  lead,  which  first  concretes,  forms 
granular, crystals,  and  is  nearly  pure,  while  almost  the  whole  of  silver  is 
contained  in  the  liquid  portion  ;  in  this  way  the  separation  of  the  two  metals 
may  to  a  certain  extent  be  efi'ected,  especially  upon  the  large  scale  (p  26). 
Antimony  iovm?.  a  brittle  white  alloy.  With  Bismuth,  [he  alloy  is  brittle 
and  lamellar.  When  silver  and  arsenic  are  fused  together,  an  alloy  is  formed, 
which  is  gray,  brittle,  and  granular.     Silver  amalgamates  easily  with  mer- 


ASSAY    OP    SILVER.  501 

cury :  when  red-hot  silver  is  thrown  into  heated  mercury  it  dissolves,  and 
when  8  parts  of  mercury  and  1  of  silver  are  thus  combined,  a  granular 
crystalline  soft  amalgam  is  obtained.  "When  a  solution  of  this  amalgam  in 
liquid  mercury  is  squeezed  through  chamois  leather,  the  excess  of  mercury, 
retaining  only  a  trace  of  silver,  goes  through,  and  the  solid  amalgam  is  left 
behind.  Amalgam  of  silver  is  sometimes  employed  for  plating;  it  is  applied 
to  the  surface  of  copper,  and  the  mercury  being  evaporated  by  heat,  the 
remaining  silver  is  burnished.  The  better  kind  of  plating,  however,  is  per- 
formed by  the  application  of  a  plate  of  silver  to  the  surface  of  the  copper, 
which  is  afterwards  extended  by  rolling.  A  mixture  of  chloride  of  silver, 
chalk,  and  pearlash,  is  employed  for  silvering  brass :  the  metal  is  rendered 
very  clean,  and  the  above  mixture,  moistened  with  water,  rubbed  upon  its 
surface.  Plating  by  metallic  precipitation  from  ammonio-chloride  of  silver 
is  also  frequently  resorted  to,  but  electro-plating  with  cyanide  of  silver,  now 
supersedes  the  other  methods. 

Assay  of  Silver. — The  analysis  of  alloyed  silver  is  in  continual  practice 
by  refiners  and  assayers.  It  may  be  performed  in  the  humid  way  by  dis- 
solving the  alloy  in  nitric  acid,  precipitating  with  hydrochloric  acid  or  chlo- 
ride of  sodium,  and  either  reducing  the  chloride,  or  estimating  the  quantity 
of  silver  which  it  contains ;  every  100  parts  of  the  carefully  dried  chloride 
indicating  75-33  of  silver. 

But  a  modification  of  this  method  is  now  generally  resorted  to,  especiatty 
applicable  in  cases  where  the  quality  of  the  alloy  is  approximately  known  : 
it  depends  upon  the  precipitation  of  the  silver  by  a  standard  solution  of  com- 
mon salt,  each  1000  grains  of  which  contain  a  sufficient  quantity  of  salt  to 
precipitate  10  grains  of  silver;  so  that,  supposing  the  silver  and  the  salt  to 
be  pure,  10  grains  of  silver  dissolved  in  nitric  acid,  would  be  entirely  pre- 
cipitated by  1000  grains  of  the  standard  solution.  To  effect  this,  each  1000 
grains  of  the  standard  solution  must  contain  5  55  grains  of  pure  chloride  of 
sodium  ;  this  is  equivalent  to  388  grains  in  each  gallon  of  such  solution  ;  but 
as  commercial  salt  is  not  absolutely  pure,  the  exact  strength  of  the  standard 
solution  must  be  experimentally  adjusted  by  dissolving  10  grains  of  perfectly 
pure  silver  in  nitric  acid,  precipitating  it  by  1000  grains  of  the  solution,  and 
adding  either  salt  or  water,  as  may  be  required.  Having  thus  prepared  this 
standard  solution  of  salt,  1000  grains  of  it  are  put  into  a  convenient  counter- 
poised burette,  or  dropping-bottle ;  10  grains  of  the  sample  of  silver  to  be 
assayed  are  then  placed  in  a  stoppered  bottle  capable  of  holding  about  6 
ounces  of  water,  and  dissolved  in  about  2  drachms  of  nitric  acid  of  sp.  gr. 
1'25.  Such  portion  of  the  solution  of  salt  is  then  added  as  will  be  required 
to  throw  down  nearly  the  whole  of  the  silver ;  the  bottle  is  then  well  shaken 
for  about  a  minute,  and  the  precipitated  chloride  allowed  to  subside.  When 
the  liquid  above  it  has  become  clear,  a  drop  or  two  more  of  the  standard 
solution  is  added,  and  if  it  occasions  any  precipitate,  the  bottle  is  again 
shaken,  and,  when  clear,  more  of  the  standard  solution  is  very  cautiously 
added,  as  long  as  it  occasions  any  turbidity.  When  no  cloud  is  produced, 
the  weight  of  the  standard  solution  which  has  been  added  is  ascertained  by 
re-weighing  the  burette,  and  the  number  of  grains  so  employed  indicates  the 
quantity  of  pure  silver  in  the  sample  :  if  this  be  of  the  fineness  of  English 
standard  silver,  925  grains  of  the  standard  solution  will  have  been  used, 
indicating  the  composition  of  the  alloy  to  be  9  25  silver  and  0*75  copper  :  if 
the  sample  be  of  the  French  standard,  900  grains  of  the  salt  solution  will 
have  been  required,  indicating  an  alloy  of  9  silver  and  1  copper.  This  pro- 
cess of  humid  assaying  was  introduced  into  the  French  Mint  by  Gay-Lussac, 
who  has  described  it  in  detail,  together  with  the  apparatus  required  for  car- 
rying it  out,  and  the  precautions   necessary  to  insure  accuracy.     A  full 


502  CUPELLATION.      TESTS    FOR    THE    SALTS    OF    SILVER. 

description  of  this  method,  by  Mulder,  will  be  found  in  the  Chemical  News, 
1861,  vol.  2,  pp.  137—204. 

Assayers  generally  determine  the  value  of  silver  bars  by  the  process  of 
cupellation.  Of  the  useful  metals,  three  resist  the  action  of  air  at  high  tem- 
peratures— namely,  silver,  gold,  and  platinum  ;  the  others,  under  the  same 
circumstances,  become  oxidized  ;  it  might,  therefore,  be  supposed,  that  alloys 
of  the  first  three  metals  would  suffer  decomposition  by  mere  exposure  to 
heat  and  air,  and  that  the  oxidizable  metal  would  burn  into  oxide.  This, 
however,  is  not  the  case  :  for  if  the  proportion  of  the  latter  be  small,  it  is 
protected  by  the  former ;  or,  in  other  cases,  a  film  of  infusible  oxide  coats 
the  fused  globule,  and  prevents  the  further  action  of  the  air.  These  diffi- 
culties are  overcome  by  adding  to  the  alloy  some  easily  oxidizable  metal,  the 
oxide  of  which  is  fusible.  Lead  is  usually  selected  for  this  purpose.  Sup- 
posing, therefore,  that  an  alloy  of  silver  and  copper  is  to  be  assayed,  or 
analyzed  by  cupellation,  the  following  is  the  mode  of  proceeding :  A  clean 
piece  of  the  metal  (about  20  grains)  is  laminated,  and  accurately  weighed. 
It  is  then  wrapped  in  the  requisite  quantity  of  pure  sheet-lead,  apportioned 
by  weight  to  the  quality  of  the  alloy,  and  placed  upon  a  small  cupel,  or 
porous  shallow  crucible,  made  of  bone-earth.  The  whole  is  then  placed 
within  the  muffle,  heated  to  bright  redness  :  the  metals  melt,  and,  by  the 
action  of  the  air  which  plays  over  the  hot  surface,  ihe  lead  and  copper  are 
oxidized,  and  their  fused  oxides  are  absorbed  by  the  cupel,  and,  if  the  opera- 
tion has  been  skilfully  conducted,  a  button  of  pure  silver  ultimately  remains, 
the  completion  of  the  process  being  judged  of  by  the  cessation  of  the  oxida- 
tion and  motion  upon  the  surface  of  the  globule,  and  by  the  brilliant  appear- 
ance assumed  by  the  silver  when  the  oxidation  of  its  alloy  ceases.  The 
button  of  pure  silver  is  then  suffered  to  cool  gradually,  and  its  loss  of  weight 
will  be  equivalent  to  the  weight  of  the  alloy  which  has  been  separated  by 
oxidation,  a  certain  allowance  being  made  for  a  small  loss  of  silver,  which 
always  occurs,  partly  by  evaporation,  and  partly  by  the  metal  being  carried 
off  with  the  oxides  which  are  absorbed  by  the  cupel.  To  perform  this  pro- 
cess with  accuracy,  certain  precautions  are  requisite,  which  can  only  be 
learned  by  practice,  so  as  to  enable  the  operator  to  obtain  uniform  results. 

Tests  for  the  Salts  of  Silver. — 1.  The  soluble  salts  of  silver  give  with 
hydrochloric  acid,  and  with  soluble  chlorides,  a  white  curdy  precipitate, 
which  is  readily  soluble  in  ammonia  and  in  hyposulphite  of  soda,  but  insolu- 
ble in  nitric  acid  :  it  darkens  by  exposure  to  light.  2.  With  solutions  of 
potash  and  soda  brown  precipitates  are  produced,  insoluble  in  an  excess  of 
the  alkali.  3.  With  ammonia  the  precipitate  is  also  brown,  but  readily 
redissolves  in  an  excess  of  the  precipitant.  4.  With  sulphuretted  hydrogen 
and  hydrosulphate  of  ammonia,  the  precipitate  is  black  and  insoluble. 
5.  Protosulphate  of  iron  throws  down  metallic  silver.  6.  A  yellow  precipi- 
tate with  common  phosphate  of  soda,  and  arsenite  of  potassa, — a  brick-red 
precipitate  with  arsenate  of  potassa, — a  crimson  with  chromate  of  potassa, 
and  a  white  with  ferrocyanide  of  potassium,  are  further  characteristics.  The 
silver  salts  insoluble  in  water  are  mostly  soluble  iu  ammonia,  and  in  nitric 
acid.  These  salts,  excepting  those  containing  colored  acids,  are  either  white 
or  of  a  pale  yellow  color,  provided  they  have  not  been  exposed  to  light,  to 
sulphuretted  hydrogen,  or  deoxidizing  agents.  Many  of  the  metals,  especially 
copper,  tin,  and  lead,  separate  metallic  silver  when  immersed  in  its  solutions. 
Before  the  blowpipe  the  silver  salts  are  easily  reduced,  especially  when 
mixed  with  carbonate  of  soda. 


PHOTOGRAPHY.  503 


CHAPTER    XXXIX. 

PHOTOGRAPHY   AND    ITS   APPLICATIONS. 

The  Chemistry  of  Light. 

The  art  of  photography  is  based  on  the  chemical  changes  which  the  salts 
of  silver  undergo,  when  exposed  to  light.  Silver  is  not  the  only  metal  which 
is  affected  by  light.  Solutions  of  gold  in  contact  with  organic  matter,  yield 
metallic  gold  of  a  defep  purple  color.  The  compounds  of  mercury,  chromium, 
uranium,  iron,  and  molybdenum,  are  either  reduced  to  a  lower  state  of  oxi- 
dation by  light,  or,  as  in  the  black  oxide  of  mercury,  the  metal  is  set  free. 
But  there  are  no  metallic  salts  which  are  so  favorable  for  the  practice  of 
photography  as  those  of  silver ;  hence  they  are  almost  exclusively  employed 
for  this  purpose. 

In  some  cases,  a  pure  binary  compound  of  the  metal,  Agl,  or  AgBr,  is 
used  on  a  surface  of  metallic  silver,  as  in  the  daguerreotype  process  :  in  others, 
a  binary  salt,  obtained  by  double  decomposition,  associated  with  pyroxyline, 
is  selected,  as  in  the  collodion  process.  The  silver-compound  used  with  dry 
collodion,  is  the  same  as  that  of  the  daguerreotype,  namely,  Agl,  or  AgBr, 
and  is  frequently  a  compound  of  the  two  ;  while  with  the  wet  collodion,  there 
are  not  only  these  two  salts,  but  free  nitrate  of  silver.  In  the  ordinary 
paper  process,  the  chloride  of  silver  (AgCl)  is  employed  ;  but  there  is  asso- 
ciated with  this,  free  nitrate  of  silver ;  and  when  the  surface  of  the  paper  is 
albumenized,  an  organic  compound  of  albuminate  of  silver. 

All  the  salts  of  silver  are  more  or  less  affected  by  light.  In  some  instances 
they  undergo  a  visible  change,  being  rendered  dark  in  proportion  to  the 
intensity  of  the  light  and  the  length  of  exposure.  This  is  well  seen  in  the 
white  chloride  of  silver  when  in  a  humid  state  ;  and  in  the  nitrate  and  am- 
raonio-nitrate  in  contact  with  organic  matter.  It  is  less  apparent  in  the 
sulphocyanide,  the  hyponitrite,  and  pyrophosphate  of  silver,  and  is  scarcely 
visible  in  the  cyanide,  even  after  long  exposure.  The  iodide  and  bromide 
of  silver  do  not  darken  by  exposure  to  light*  but  they  undergo  instantane- 
ously a  remarkable  molecular  change,  which  renders  them  especially  adapted 
for  photography. 

The  conditions  necessary  for  these  changes  are  light  and  moisture.  When 
the  salt  of  silver  is  in  contact  with  albumen  or  gelatine,  the  reduction  is  not 
only  accelerated,  but  it  takes  place  with  greater  uniformity  and  depth.  A 
decomposable  salt  of  silver  in  contact  with  organic  matter,  will  spontaneously 
change  in  the  dark  in  a  humid  atmosphere  ;  and  thus  it  is  well  known  that 
paper  employed  in  photography,  when  once  sensitized,  or  impregnated  with 
a  silver  solution,  cannot  be  preserved  unless  certain  precautions  are  taken. 
The  albuminate  and  chloride  of  the  metal,  formed  upon  the  surface  of  the 
paper  in  the  act  of  sensitizing  it,  are  decomposed,  and  the  paper  is  slowly 
darkened.  The  effect  of  a  dry  atmosphere  in  preserving  the  salts  Of  silver 
from  change  has  been  elsewhere  described  (p.  42).  As  pure  chloride  of 
silver  undergoes  no  change  of  color  when  exposed  to  light  in  an  atmosphere 
artificially  dried  by  chloride  of  calcium,  the  presence  of  water  or  moisture 
appears  to  be  necessary  to  the  change  ;  but  the  presence  of  organic  matter 
is  not  absolutely  necessary.      In  contact  with  water  alone,  the  chloride 


504  ACTION    OF    LIGHT    ON    THE    SALTS    OP    SILVER. 

changes  from  a  snow-white  to  a  pink,  violet,  brown,  and  finally  a  dark 
bronze-black  color ;  and  during  this  conversion,  hydrochloric  acid  is  pro- 
duced. Hence  the  chemical  change  may  be  thus  represented :  AgCl  +  HO 
=Ag-}-HCl-f  O.  According  to  Mitscherlich,  the  precipitated  chloride, 
well  dried,  inclosed  in  a  tube,  and  exposed  to  light,  is  decomposed,  and 
chlorine  only  liberated  :  AgCl=Ag-fCl.  The  darkening  of  a  layer  of  the 
precipitated  chloride  is  superficial ;  if  the  darkened  surface  is  removed,  the 
chloride  beneath  will  be  found  quite  white.  When  the  chloride  is  precipi- 
tated on  paper  for  photographic  purposes,  the  change,  after  long  exposure, 
extends  more  or  less  into  the  substance  of  the  paper.  If  ammonia  is  poured 
upon  the  precipitated  chloride  which  has  been  exposed  to  light,  that  portion 
which  has  not  undergone  the  change,  is  dissolved,  while  the  dark  substance 
(^.  €.,  the  reduced  silver)  remains  undissolved.  If  a  strong  solution  of  chlo- 
rine is  added  to  the  darkened  chloride,  it  is  again  rendered  white,  by  reason 
of  the  metallic  silver  recombining  with  this  element ;  and  the  white  chloride, 
when  covered  with  a  solution  of  chlorine,  does  not  readily  undergo  the 
change.  A  solution  of  common  salt  or  hydrochloric  acid  in  excess,  also 
retards  the  change ;  but  when  the  solution  of  nitrate  of  silver  is  in  excess,  it 
takes  place  with  very  great  rapidity.  We  have  preserved  paper  prepared 
with  chloride  of  silver,  but  containing  an  excess  of  chloride  of  sodium,  for  a 
period  of  twenty-two  years.  Under  strong  solar  light  it  retained,  after  this 
long  interval,  sufficient  unchanged  chloride  to  yield  an  impression  from  a 
collodion  negative. 

Nitrate  of  silver  undergoes  no  change  by  exposure  to  light,  except  wheu 
in  contact  with  organic  matter  :  the  nitric  acid  and  oxygen  are  then  liberated, 
and  the  silver  is  reduced;  AgO,N05=Ag  +  0-fN05.  The  oxygen  is  pro- 
bably taken  by  the  hydrogen  and  carbon  of  the  organic  matter.  The  in- 
soluble chloride,  iodide,  and  bromide  of  silver  are  not  so  readily  decomposed, 
when  in  contact  with  organic  matter  in  the  dark,  as  the  soluble  nitrate,  or 
the  ammonio-nitrate  of  silver.  If  mixed  with  the  nitrate,  however,  they 
rapidly  undergo  a  change :  hence,  for  the  perfect  preservation. of  plates  or 
paper  covered  with  iodide  of  silver,  it  is  necessary  that  every  trace  of  the 
nitrate  of  silver  should  be  removed.  On  this  principle  is  founded  the  dry- 
plate  process  in  photography.  The  dry  and  pure  iodide  of  silver,  free  from 
nitrate,  will  receive  an  impression  on  exposure,  just  as  certainly,  although 
not  so  rapidly,  as  the  wet  iodide  mixed  with  nitrate.  Among  the  facts  which 
prove  that  the  chloride  and  nitrate  of  silver  are  reduced  by  light  to  the 
metallic  state,  are  the  following  :  1.  That  substance  which  has  been  darkened 
by  light  is  insoluble  in  ammonia  and  the  alkaline  hyposulphites ;  while  that 
portion  of  the  salt  of  silver  which  has  not  undergone  the  change,  is  readily 
dissolved  by  these  reagents.  2.  When  the  reduction  of  the  chloride  or 
nitrate  has  taken  place  on  paper,  the  surface  has  been  found  to  conduct 
electricity.  3.  When  paper  which  has  thus  been  darkened  by  light  is  intro- 
duced into  a  weak  solution  of  chloride  of  gold,  rendered  slightly  alkaline, 
metallic  gold  is  slowly  deposited  of  a  dark  purple  color,  in  place  of  the  re- 
duced silver;  an  efi'ect  similar  to  that  produced  by  metallic  silver  when 
immersed  in  a  solution  of  gold.  The  well-known  process  of  toning  photo- 
graphs, depends  on  this  property  of  chemically  replacing  metallic  silver  by 
metallic  gold :  and  there  is  but  little  doubt  that  the  impressions  are  thus 
rendered  much  more  durable.  It  is  an  ascertained  fact,  that  this  replacement, 
or  substitution,  does  not  occur  except  in  those  portions  of  a  drawing,  in 
which  the  silver  has  been  completely  metallized  or  perfectly  reduced  by  light. 

There  is  another  circumstance  connected  with  this  metallization  of  silver, 
under  the  influence  of  light,  which  is  deserving  of  notice.  When  all  other 
conditions  are  favorable,  the  rays  of  the  spectrum  afi'ect  the  salts  of  silver 


EFFECT    OP    COLORED    LIGHT    ON    THE    SALTS    OF    SILVER.       505 

unequally.  If  paper,  containing  the  albuminate  and  chloride  of  silver,  is 
covered  with  plates  of  glass  variously  colored,  and  is  then  exposed  for  an 
equal  time  to  light,  it  will  be  found  that  under  some  of  the  dark-colored 
plates  the  change  has  been  nearly  as  great,  as  if  colorless  glass  had  been 
employed,  while  under  the  lighter-colored  plates,  it  has  been  retarded.  Ex- 
periments of  this  nature  have  clearly  proved  that  the  dark  or  more  refrangi- 
ble rays  of  light,  violet,  indigo,  and  blue,  allow  the  chemical  changes  to  take 
place  rapidly  ;  while  the  less  refrangible  rays,  red,  orange,  and  yellow,  retard 
them.  Of  all  the  colors,  the  blue  produces,  witfein  a  given  time,  the  greatest, 
and  the  red,  the  least  amount  of  chemical  action.  Thus  the  sensitized  paper 
is  intensely  blackened  under  blue  glass,  while  it  remains  nearly  white  under 
red  glass.  The  chemical  rays,  however,  do  not  appear  to  be  completely 
intercepted  ;  for  a  long  exposure  to  light  through  colored  glass  will  slowly 
lead  to  a  change  of  color  in  the  paper.  The  chemical  action  of  light  is 
therefore  determined  by  the  difference  between  the  accelerating  and  retarding 
rays,  of  which  white  light  is  constituted.  Colorless  light,  however,  produces 
caeteris  paribus,  a  more  rapid  and  complete  change  than  the  isolated  blue 
rays  of  a  colored  medium. 

From  these  facts  it  will  be  perceived  that  the  two  ends  of  the  solar  spec- 
trum do  not  neutralize  each  other  in  reference  to  this  force ;  for  the  actinic 
or  chemical  rays  predominate,  and  are  found  to  operate  sooner  or  later 
through  every  color.  Nothing  but  the  absolute  withdrawal  of  light  will 
entirely  arrest  the  chemical  changes.  Hence  the  salts  of  silver  may  be  em- 
ployed for  photometric  observations.  They  serve  to  measure,  not  only  the 
relative  intensity  of  light,  but  by  the  changes  induced  on  sensitized  paper, 
they  are  made  available  for  numerous  important  purposes  in  science  and  the 
arts.  We  have  thus  seen  this  art  successfully  applied  to  the  diurnal  registra- 
tion of  the  amount  of  rain-fall  ;  the  electrical  tension  of  the  atmosphere,  and 
the  force  and  direction  of  the  wind.  It  has  also  furnished  important  evidence 
in  courts  of  law,  and  has  been  usefully  employed  to  illustrate  various  sub- 
jects in  medicine,  natural  history,  archaeology,  ethnology,  and  astronomy. 

Other  conditions  connected  with  these  phenomena  are  worthy  of  notice. 
The  chemical  changes  produced  in  the  salts  of  silver  are  not  in  proportion 
to  the  illuminating  power  of  the  rays  of  the  spectrum.  The  greatest  amount 
of  light  is  in  the  yellow  rays,  and  the  least  amount  in  the  blue  and  violet ; 
but  the  latter  possess  the  chemical  power  in  its  greatest  intensity.  The 
salts  of  silver,  it  is  well  known,  are  decomposable  by  heat :  but  in  reference 
to  these  chemical  changes,  it  is  found  that  the  calorific  rays  (red)  have  the 
least  influence  in  producing  them.  Hence,  this  photochemical  force  is  not 
in  proportion  to  the  light  or  heat  of  the  solar  rays,  but  to  other  rays  which 
are  called  actinic;  and  the  force  itself  is  therefore  called  actinism.  In  refer- 
ence to  the  spectrum,  it  is  at  its  maximum  when  the  violet  and  blue  rays 
predominate,  and  at  its  minimum  when  the  yellow  and  red  rays  are.  most 
abundant.  Hence,  if  red  or  yellow  rays  abound,  as  in  a  glowing  sunset,  or 
occasionally  in  a  foggy  state  of  the  atmosphere,  however  clear  an  image  may 
appear  to  the  eye,  the  actinic  power  is  lost,  and  an  impression  cannot  be 
taken. 

The  salts  of  silver  differ  from  each  other  in  respect  to  the  changes  produced 
by  colored  light :  thus  while  the  maximum  effect  on  the  chloride  paper  is  in 
the  blue  rays,  that  produced  on  the  iodized  paper  is  in  the  extreme  violet, 
while  the  bromized  paper  is  affected  more  or  less  throughout  the  whole  spec- 
trum, even  in  the  yellow  and  red  rays.  These  remarkable  effects  produced 
by  the  colored  rays  of  the  spectrum  have  not  received  any  explanation  on 
the  unduhatory  theory  of  light:  and  it  seems  difficult  to  understand  how  an 
undulation,  or  any  mechanical  vibration,  producing  a  violet  color,  should 


506  PHOTOGRAPHY    ON    SILVER.      DAGUERREOTYPE. 

break  up  ^  the  chemical  composition  of  chloride  of  silver,  while  that  which 
produces  a  yellow  or  red  ray  should  have  little  or  no  effect  upon  this  salt. 

The  colored  rays  of  the  spectrum  are  represented  on  prepared  paper  by 
degrees  of  darkness,  or  a  blackening  of  the  exposed  portions,  and  not  by  the 
reproduction  of  color.  It  has  been  hitherto  found  impossible  to  procure  and 
fix  by  the  chemical  agency  of  light  the  colors  Of  external  objects,  except  to 
a  very  limited  extent.  We  have  in  one  instance  seen  the  iridescent  colors  of 
the  opal  transferred  to  a  surface  of  silver,  by  the  daguerreotype  ;  but  they 
entirely  disappeared  on  the  preservation  of  the  impression.  Further,  the 
unequal  action  of  white  light  as  it  is  reflected  from  white  surfaces,  as  well  as 
from  shadows  and  shades  of  various  degrees,  is  so  great,  that  it  is  difficult, 
if  not  impossible,  to  attain  the  even  gradation  of  tone  which  gives  harmony 
to  all  natural  objects.  White  light  acts  with  such  disproportionate  rapidity, 
and  the  light  of  shadows  so  slowly,  that  the  most  finished  impressions  of 
objects  are  generally  left  with  extremes  of  light  and  shade.  While  the  lights 
are  unnaturally  intense,  the  shadows  are  generally  black,  without  that  grada- 
tion which  in  nature  serves  to  reveal  the  most  minute  details.  There  is  a 
want  of  aerial  perspective.  To  a  certain  extent  this  defect  is,  however, 
remediable  by  art. 

With  a  knowledge  of  the  principles  above  described,  a  chemist  may  pro- 
duce, and  render  permanent,  images  which  have  been  impressed  by  light  on 
a  salt  of  silver.  He  may  select  a  medium  of  metallic  silver,  glass,  or  paper, 
and  he  may  produce  the  image  on  the  prepared  surface,  either  by  refraction 
with  a  camera  obscura,  or  by  superposition  and  simple  exposure  to  dififused 
light.  In  either  case  he  may  obtain,  directly  or  indirectly,  an  image  in 
metallic  silver,  in  those  parts  in  which  the  metal  has  been  reduced ;  while 
the  undecomposed  salt  of  silver  remains  in  those  spots  in  which  there  has 
been  a  deficiency  or  entire  absence  of  light.  A  solvent  is  selected  for  the 
removal  of  the  unchanged  salt,  and  the  drawing  is  thus  preserved. 

The  fact  that  images  of  objects  might  be  impressed  by  light  on  paper,  im- 
pregnated either  with  the  chloride  or  nitrate  of  silver,  had  been  proved 
experimentally  by  Davy  and  Wedgwood  in  1802 ;  but  they  could  discover 
DO  method  of  fixing  or  preserving  them.  It  was  not  until  1816  that  the 
solvent  properties  of  the  alkaline  hyposulphites  on  the  salts  of  silver  were 
first  made  known  by  Herschel ;  but  so  slow  was  the  progress  of  this  subject, 
that  even  in  1839  Mr.  Fox  Talbot,  in  announcing  his  discovery,  could  sug- 
gest no  better  means  for  the  preservation  of  his  drawings  than  the  use  of 
strong  solutions  of  alkaline  chlorides,  iodides,  and  bromides,  which  were 
soon  proved  to  be  quite  inefficient. 

1.  Daguerreotype.  Photography  on  Silver. — This  branch  of  the  art  has 
received  its  name  from  the  discoverer,  Daguerre,  who  first  announced  his 
process  in  the  year  1839.  This  may  be  regarded,  in  a  chemical  point  of 
view,  as  photography  in  its  most  simple,  and  for  delineation  of  details  its 
most  perfect,  form,  A  highly  polished  plate  of  silver  is  exposed  to  the 
diluted  vapor  of  iodine,  in  a  dark  box.  A  colored  film  of  iodide  of  silver 
(Agl)  is  thus  produced  by  direct  combination,  and  this,  at  a  certain  stage, 
is  found  to  possess  a  high  degree  of  sensitiveness  to  light.  The  use  of 
bromine  in  addition  to  iodine  was  suggested  by  Dr.  Goddard  in  1840.  A 
compound  film  of  bromo-iodide  of  silver  was  thus  produced;  and  this  is  found 
to  give  more  satisfactory  results  than  the  iodide  alone.  The  plate  is  then 
transferred  from  the  dark  room  to  a  camera,  and  in  from  five  to  ten  seconds 
it  is  removed.  In  this  stage  nothing  is  visible  on  the  plate.  The  film  has 
the  same  bronze-yellow  color  as  when  it  was  placed  in  the  camera ;  but  a 
molecular  change  may  be  proved  to  have  taken  place.  When  the  plate  is 
exposed  in  a  box,  at  a  moderate  temperature,  to  the  vapor  of  mercury,  an 


PHOTOGRAPHY    ON    GLASS.      COLLODION    PROCESS.  507 

image  will  immediately  appear,  the  metallic  vapor  fixing  itself  closely  (by 
amalgamation)  only  on  those  parts  which  have  received  the  luminous  im- 
pression, the  mercury  lying  loosely  on  the  other  portions  without  entering 
into  chemical  combination.  When  a  strong  solution  of  an  alkaline  hypo- 
sulphite is  poured  over  the  plate,  the  image  appears  in  full  relief,  with  a  con- 
trast of  light  and  shade,  and  with  the  most  delicate  details.  The  portions 
of  bromo-iodide  of  silver  not  acted  on  by  light  are  dissolved  by  an  alkaline 
hyposulphite  ;  and  the  highly  polished  silver  beneath  forms  the  deep  shades, 
which  give  blackness  to  the  picture.  The  mercury  imparts  a  dull  white 
appearance  to  those  parts  of  the  metal  with  which  it  is  chemically  combined 
or  amalgamated,  and  thus  constitutes  the  lights. 

The  action  of  light  on  the  bromo-iodide  of  silver  probably  consists  in 
displacing  the  bromine  and  iodine,  wholly  or  in  part,  and  thus  leaving 
a  metallic  surface  favorable  for  combination  with  the  vapor  of  mercury 
(Ag,Br=Ag-f-Br).  Mercury  does  not  combine  with  the  salts  of  silver: 
hence  the  film  of  undecomposed  bromo-iodide  in  those  parts  which  were  not 
exposed  to  light  is  sufficient  to  prevent  any  direct  union  between  the  mer- 
cury and  the  silver  beneath.  After  the  undecomposed  salt  of  silver  has  been 
removed  by  the  alkaline  hyposulphite,  the  plate  simply  requires  washing. 
A  film  of  gold  may  be  then  spread  over  it  by  heating  upon  its  surface  a 
layer  of  a  very  diluted  solution  of  chloride  of  gold  in  hyposulphite  of  soda; 
and  another  washing  completes  the  operation. 

Owing  to  the  highly  polished  surface  of  the  metal,  the  daguerreotype  is 
admirably  adapted  to  bring  out  the  minutest  details  of  objects.  In  1846  we 
obtained  by  this  process  a  copy  of  the  10,000  letters  of  the  Greek  inscription 
on  the  Rosetta  stone  of  the  British  Museum,  within  the  space  of  two  square 
inches.  The  drawing  is  still  preserved,  and  the  Greek  letters  are  easily 
legible  by  the  aid  of  a  lens.  The  process,  however,  has  these  disadvantages  : 
the  film  is  so  thin  that  the  polish  of  the  silver  prevents  the  image  from  being 
clearly  seen  in  all  lights;  and,  as  with  all  silver-surfaces,  the  plate  is  exposed 
to  tarnishing  by  sulphuration.  These  drawings,  therefore,  can  only  be  pre- 
served by  completely  preventing  the  access  of  air.  The  film  of  sulphide  of 
silver,  which  after  a  time  obscures  the  drawing,  may,  however,  be  removed 
by  washing  the  plate  with  a  weak  solution  of  cyanide  of  potassium. 

2.  The  Collodion  Process.  Photography  on  Glass. — The  application  of 
pyroxyline,  or  gun-cotton,  to  the  purposes  of  photography,  was  discovered 
by  Mr.  Archer,  in  1850.  It  is  used  either  in  the  wet  or  dry  state;  and  as  it 
is  employed  on  glass,  it  may  be  applied  either  for  the  production  of  positive 
images,  with  the  light  and  shade  correct,  or  of  negative  images,  in  which 
the  light  and  shade  are  reversed.  Positive  impressions  on  paper  may  be 
procured  from  the  latter.  Collodion  is  a  solution  of  pyroxyline  in  a  mixture 
of  ether  and  alcohol.  {See  Pyroxyline.)  There  are  several  compounds 
known  under  the  name  of  gun-cotton,  but  one  of  these  only  appears  to  be 
well  fitted  for  photographic  purposes  (p.  174).  It  is  what  is  called  a  substi- 
tution-compound, in  which,  assuming  cotton  to  be  Ga^HgpOjjo,  four  equivalents 
of  nitrous  acid  are  substituted  for  four  of  hydrogen,  thus  bringing  the 
formula  of  photographic  cotton  to  Ca4[H,p4(NOJ]0.^.  The  proportion  of 
cotton  to  the  mixed  solvents  varies  according  to  circumstances.  From  5  to 
6  grains  of  cotton  may  be  used  to  an  ounce  of  a  solvent  consisting  by  measure 
of  one  part  of  alcohol  (sp.  gr.  0830)  and  two  parts  of  ether  (sp.  gr:  0724), 
the  latter  being  diminished,  and  the  former  increased,  in  hot  weather.  When 
the  collodion  is  required  for  use,  it  is  necessary  to  add  to  it  an  alcoholic 
solution  of  an  iodide,  either  of  potassium,  cadmium,  or  ammonium,  or  a 
mixture  of  these.  The  proportion  of  iodide  required  is  from  4  to  6  grains 
to  each  ounce  of  collodion.    Pure  iodide  of  potassium,  free  from  iodate  {see 


508  COLLODION    PROCESS.       CHEMICAL    CHANGES. 

page  318),  is  commonly  selected  for  immediate  use;  and  the  iodide  of  cad- 
mium when  the  liquid  is  required  to  be  preserved.  A  mixture  of  equal  parts 
of  the  two,  i.  e.,  2^  grains  of  each  iodide,  dissolved  in  2  drachms  of  alcohol, 
will  be  found  convenient.  This  quantity  may  be  added  to  6  drachms  of  the 
prepared  collodion.  A  mixture  of  the  iodides  of  potassium,  ammonium,  and 
cadmium  is  frequently  employed  with  advantage ;  and  an  addition  of  the 
bromide  of  either  metal  to  the  iodide  renders  the  film  more  sensitive  to  the 
less  refrangible  rays  of  light  (yellow  and  red)  (page  505).  In  using  a 
bromide,  the  proportion  should  not  exceed  1  to  3  or  4  parts  of  the  iodide. 
Reynaud  advises  for  each  ounce  of  collodion  5*3  grains  of  iodide  to  15 
grains  of  bromide,  as  producing  the  most  sensitive  film.  The  bromides  of 
ammonium  and  cadmium  are,  according  to  him,  preferable  for  this  purpose. 

When  collodion  thus  prepared,  has  been  rendered  perfectly  clear  by  sub- 
sidence, it  is  poured  rapidly  from  a  wide-mouthed  vessel  over  a  freshly 
cleaned  and  dry  surface  of  plate-glass ;  and  as  soon  as  it  is  set  into  a  cohe- 
rent layer,  the  glass  is  plunged  into  a  bath  containing  a  solution  of  nitrate 
of  silver,  in  a  darkened  room. 

This  bath  is  prepared  by  dissolving  480  grains  of  neutral  crystallized 
nitrate  of  silver  in  2  ounces  of  water,  and  adding  to  the  solution  4  grains  of 
iodide  of  cadmium  or  potassium,  dissolved  in  a  small  quantity  of  water. 
Iodide  of  silver  is  thus  formed,  and  dissolved  by  the  concentrated  nitrate. 
The  solution  may  be  then  made  up  to  twelve  fluidounces,  by  the  addition  of 
distilled  water.  After  standing  some  hours,  it  should  be  filtered  to  separate 
the  precipitated  iodide  of  silver.  The  solution,  when  filtered,  should  neither 
be  alkaline  nor  neutral.  If  acid,  a  little  oxide  of  silver  may  be  used  to  cor- 
rect this ;  and  when  corrected,  it  may  be  very  slightly  acidulated,  either 
with  a  few  drops  of  glacial  acetic  acid,  or  of  strong  nitric  acid  (containing 
nitrous  acid)  properly  diluted.  If  the  bath  is  neutral,  the  pictures  are  not 
clear;  if  too  acid,  the  sensitiveness  of  the  film  is  impaired.  To  avoid  a 
"fogging"  of  the  impression,  it  has  been  lately  suggested  that  a  few  drops 
of  an  alcoholic  solution  of  iodine  should  be  added  to  the  bath-liquid,  until 
it  has  acquired  an  orange-yellow  color.  (Reynaud.) 

The  result  of  the  immersion  of  the  plate  in  this  bath  for  a  few  minutes,  or 
until  the  oily  appearance  of  the  film  is  removed,  is  the  production  on  it,  of 
a  primrose-colored  layer  of  iodide  of  silver,  while  nitrate  of  soda  or  cadmium 
is  dissolved  in  the  bath:  (AgCNO^-f KI(CdI)=AgI  +  KO(CdO)N03). 
If,  when  taken  from  the  bath,  the  opaque  yellow  film  is  well  washed  with 
distilled  water,  to  remove  all  traces  of  free  nitrate  of  silver,  it  may  be  dried, 
and  the  dry  plate  preserved  in  a  sensitive  state  in  a  dark  box  (containing 
some  quick-lime)  for  many  weeks,  or  even  months.  We  have  thus  obtained 
impressions  on  dry  plates  after  four  or  five  months'  preservation.  The  ab- 
sence of  moisture  and  the  entire  withdrawal  of  light  are,  however,  essential 
conditions  for  the  preservation  of  the  plates.  Yarious  liquids,  such  as  tannic 
acid,  albumen,  and  a  solution  of  chloride  of  sodium,  have  been  employed  as 
varnishes  for  covering  and  preserving  the  film,  containing  the  precipitated 
iodide  of  silver. 

The  plate  with  the  iodide  of  silver  on  its  surface,  may  be  exposed  in  the 
camera  for  a  few  seconds  if  wet,  and  for  a  longer  period  if  dry.  When 
removed,  no  image  is  perceptible ;  but  on  pouring  over  the  film  of  iodide, 
a  solution  of  a  protosalt  of  iron  mixed  with  a  few  drops  of  a  weak  solution 
of  nitrate  of  silver,  of  gallic  or  pyrogallic  acid,  the  image  will  appear,  slowly 
or  rapidly  according  to  the  nature  and  strength  of  the  developer,  the  degree 
of  exposure,  and  the  intensity  of  light.  We  have  found  the  following  pro- 
portions to  be  well  fitted  for  bringing  out  the  image :  Green  sulphate  of 
iron,  150  grains;  glacial  acetic  acid,  two  fluidrachms  and  a  half;  alcohol, 


DEVELOPMENT  OF  THE  IMAGE.  509 

five  fluidrachms ;  distilled  water,  ten  ounces.  When  all  the  minute  de- 
tails are  visible,  the  surface  of  the  film  should  be  well  washed  with  water  to 
remove  the  whole  of  the  iron  developed.  The  silver  thus  reduced  and 
deposited  in  the  parts  aflFected  by  light,  is  not  sufficiently  dense,  but  its 
density  and  opacity  may  be  increased  by  the  use  of  the  following  (intensify- 
ing) solution  :  Pyrogallic  acid,  40  grains;  citric  acid,  100  grains;  distilled 
water,  8  ounces.  The  plate  having  been  covered  with  this  solution,  a  few 
drops  of  a  solution  of  nitrate  of  silver  (thirty  grains  to  the  ounce)  are  added 
to  it,  and  it  is  again  poured  on  the  plate,  and  moved  about  until  the  dark 
portions  appear  sufficiently  opaque.  If  a  dry  plate  is  used,  this  should  be 
breathed  upon,  or  wetted  with  distilled  water,  before  the  developing  solution 
is  poured  over  it,  in  order  that  the  latter  may  be  readily  diffused  over  the 
whole  surface.  The  illuminated  portions  of  the  picture  will  appear,  under 
the  action  of  the  reducing  liquid,  more  or  less  black,  while  the  shaded  por- 
tions will  retain  the  yellow  color  of  the  iodide.  When  the  details  of  the 
shaded  portions  appear,  the  acid  liquid  is  washed  off,  and  the  development 
is  arrested.  The  surface  of  the  plate  is  then  well  washed,  and  the  plate 
introduced  into  a  bath  containing  a  saturated  solution  of  hyposulphite  of 
soda.  After  a  few  minutes,  it  will  be  found  that  .the  yellow  iodide  of  silver, 
where  it  has  not  been  affected  by  light,  will  be  dissolved ;  and  only  the 
reduced  or  metallized  portions  of  silver  will  remain  :  these  appear  more  or 
less  opaque  when  viewed  by  transmitted  light.  The  plate  now  requires  the 
most  complete  washing  with  water  to  remove  every  trace  of  hyposulphite  of 
soda,  or  the  film  of  reduced  silver  will  be  subsequently  cracked  and  de- 
stroyed by  the  crystallization  of  traces  of  this  salt  beneath. 

The  changes  which  take  place  in  the  production  of  the  image  on  the 
iodide  of  silver,  have  been  variously  explained.  All  agree  that  the  effect  of 
the  impingement  of  light,  is  to  produce  only  a  molecular  change  in  the  com- 
pound. There  is  no  perceptible  alteration  in  the  film  after  exposure  to 
light.  There  is  no  loss  of  iodine,  or  the  iodide  would  be  darkened  like  the 
chloride.  The  film  retains  its  chemical  properties,  and  whether  on  paper  or 
on  silver,  it  is  still  easily  dissolved  by  the  alkaline  hyposulphites.  In  refer- 
ence to  the  Daguerreotype,  a  molecular  change  in  the  iodide,  is  proved  to 
exist,  by  the  vapor  of  mercury  fixing  itself  only  on  those  parts  which  have 
been  exposed  to  light,  excluding  the  iodine  and  combining  directly  with  the 
metallic  silver.  In  regard  to  the  collodio-iodide,  it  may  be  inferred  from 
the  effect  of  reducing  agents,  that  the  changes  consist  in  a  deoxidation  of 
the  nitrate  and  a  deiodization  of  the  iodide  of  silver.  It  is  a  singular  fact, 
that  while  a  molecular  change  is  produced  in  the  iodide  by  the  agency  of 
light  only,  the  actual  production  of  the  image  depends  on  the  presence  of  a 
small  quantity  of  nitrate  of  silver,  either  on  the  plate  itself  in  the  wet  pro- 
cess, or  by  an  addition  of  it  to  the  reducing  liquid  in  the  dry  process. 

The  effects  produced  by  reducing  agents,  such  as  the  gallic  and  pyro- 
gallic acids,  on  the  oxysalts  of  silver,  are  somewhat  remarkable.  Gallic 
acid  reduces  a  solution  of  the  nitrate  very  slowly  at  common  temperatures: 
pyrogallic  acid  reduces  it  instantaneously,  throwing  down  black  metallic 
silver  by  taking  the  oxygen  from  the  oxide:  (AgO,N05+C,3Hg08=Ag-f 
NOg-f-C^gHgOgjO).  A  solution  of  the  sulphate  of  silver  is  scarcely  changed 
in  color  by  the  gallic,  and  is  only  slowly  decomposed  by  the  pyrogallic  acid. 
When  acetic  or  citric  acid  is  mixed  with  the  pyrogallic,  the  reducing  actioa 
is  retarded,  much  more  by  the  citric  than  by  the  acetic  acid.  It  is  in  order 
to  prevent  a  too  rapid  decomposition,  by  which  the  plate  would  be  speedily 
covered  with  precipitated  silver,  and  the  picture  rendered  indistinct,  that 
one  or  other  of  these  acids  is  added  to  the  reducing  liquid.  Either  of  them 
has  the  property  of  lowering  the  reducing  power  of  the  pyrogallic  even  to 


510  CHEMICAL    CHANGES   PRODUCED. 

that  of  the  gallic  acid.  On  the  other  hand,  the  presence  of  any  alkali  leads 
to  the  instantaneous  decomposition  of  a  salt  of  silver.  Thus,  when  pyro- 
gallic  acid  is  added  to  a  solution  of  the  ammonio-nitrate  of  silver,  the  metal 
is  immediately  reduced  and  precipitated.  It  has  been  elsewhere  stated  that 
a  solution  of  pyrogallic  acid  in  potassa  has  the  property  of  entirely  removing 
oxygen  from  air  (p.  154).  Neither  the  gallic  nor  the  pyrogallic  acid 
exerts  any  reducing  action  on  the  chloride,  bromide,  or  iodide  of  silver, 
except  in  the  presence  of  an  excess  of  nitrate,  when  both  the  oxysalt  and 
haloid  compound  are  decomposed.  The  decomposition  appears  in  all  cases 
to  commence  with  the  nitrate  and  to  extend  to  the  iodide  ;  but  unless  the 
iodized  film  has  been  exposed  to  light,  it  resists  the  action  of  pyrogallic  acid, 
even  in  the  presence  of  nitrate  of  silver.  The  proportion  of  nitrate  in  the 
reducing  liquid,  is  commonly  greater  than  that  of  the  pyrogallic  acid  era- 
ployed.  It  is  another  curious  feature  of  these  changes,  that  when  once  the 
silver  has  been  reduced  as  a  result  of  the  impression  of  light,  a  continued 
reduction  of  the  nitrate  of  silver  by  a  further  employment  of  this  salt  mixed 
with  pyrogallic  acid,  does  not  obscure  the  image,  or  produce  a  loose  deposit 
over  the  whole  surface  of  the  plate.  The  fresh  portions  of  silver  as  they  are 
set  free  by  the  pyrogallic  acid,  fix  themselves  upon  the  metal  already  re- 
duced, add  to  its  thickness,  and  thus  increase  the  intensity  of  the  darkened 
portions.  The  fact  is  well  illustrated  in  the  process  of  intensifying  a  nega- 
tive, in  which  the  reduced  metal  forms  a  basis  for  an  increased  deposit  of 
metallic  silver  from  the  nitrate.  This  depends  on  the  well-known  principle, 
that  like  particles  attract  each  other  in  preference  to  unlike.  The  reduced 
silver  coheres  to  the  metallic  silver  of  the  film,  but  not  to  the  layer  of  unde- 
composed  iodide. 

Pyrogallic  acid  rapidly  deoxidizes  strong  nitric  acid,  but  it  has  no  action 
on  it  in  the  very  diluted  state  in  which  the  latter  is  here  liberated ;  and  it 
has  no  tendency  to  decompose  the  iodide  of  silver  alone ;  but  assuming  that 
the  molecular  condition  of  the  iodide  has  been  broken  in  the  parts  which 
have  received  an  impression  from  light,  it  is  probable  that  the  iodine  is 
thereby  placed  in  a  state  for  removal  by  very  slight  causes.  As  the  result 
of  the  application  of  the  reducing  agent  is  the  same,  whether  it  is  employed 
immediately  or  after  eighteen  hours  (if  the  plate  has  been  kept  in  the  dark), 
it  is  clear  that  this  molecular  displacement  of  the  atoms  of  silver  and  iodine 
is  not  of  a  temporary  kind,  or  the  power  of  bringing  out  the  image  would 
be  speedily  lost.  The  iodide  on  the  plate,  in  the  parts  affected  by  light,  may 
be  decomposed  by  the  metallic  silver  which  is  liberated  from  the  nitrate  by 
pyrogallic  acid,  so  that  the  same  compound  may  be  decomposed  by  light, 
and  reformed  by  the  reducing  agent.  If  the  compound  on  the  plate  after 
the  action  of  light  is  represented  by  Agl,  and  the  silver  liberated  from  the 
nitrate  by  the  pyrogallic  acid  be  regarded  as  Ag,  then  the  change  would  be 
as  in  the  following  equation,  AgI^-\^Ag=A^I-\-Ag.  The  iodine  is  removed 
from  the  iodide,  and  it  must  be  removed  either  as  iodide  of  silver  (Agl),  or 
(on  the  assumption  that  water  is  decomposed)  as  hydriodic  acid  (HI),  the 
oxygen  of  an  atom  of  water  being  taken  by  another  portion  of  the  pyrogallic 
acid.  The  last  view  is  entirely  opposed  to  the  fact  that  pyrogallic  acid  with 
water  has  no  decomposing  action  on  the  iodides,  whether  soluble  or  insoluble 
in  water.  A  solution  of  iodide  of  potassium  is  not  decomposed  by  pyrogallic 
acid.  A  solution  of  iodine  in  water  does  not  lose  its  color  by  the  addition 
of  this  acid,  although  it  is  so  changed  that  starch  will  no  longer  render  it 
blue.  Hence,  under  the  most  favorable  circumstances,  water  is  not  decora- 
posed  by  pyrogallic  acid  in  the  presence  of  a  metallic  iodide. 

Mr.  Carey  Lea  has  shown  that  light  acts  on  neutral  iodide  of  silver,  since 
he  produced  an  action  on  silverized  glass  by  merely  covering  it  with  a  sola- 


PRESERVATION    OF    THE    IMAGE    ON    GLASS.  511 

tion  of  iodine,  but  this  fact  had  already  been  established  by  the  results  ob- 
tained in  the  Daguerreotype.  According -to  this  gentleman,  there  are  four 
pictures  or  impressions  on  an  ordinary  negative  :  1st,  by  that  produced  by 
the  physical  action  of  light  on  the  iodide  of  silver;  2d,  by  the  reduction  of 
iodide  to  subiodide,  if  the  exposure  has  been  sufiBciently  long ;  3d,  one  pro- 
duced by  light  in  connection  with  the  organic  matter  of  the  film  ;  and  4th, 
the  reduction  of  the  chloride  and  bromide,  if  present.  With  respect  to  the 
demonstration  of  the  third,  an  ordinary  bromo-iodized  plate  was  treated  with 
pernitrate  of  mercury.  The  bromide  and  iodide  of  silver  were  dissolved, 
and  the  film  left  clear  as  glass.  When  it  had  been  well  washed  and  the 
developer  added,  an  image  appeared. 

The  protosulphate  of  iron  is  now  almost  universally  employed  as  a  re- 
ducing agent  in  place  of  pyrogallic  acid.  The  protosulphate  passes  to  the 
state  of  persulphate  at  the  expense  of  the  oxide  of  silver.  3(FeO,S03)4- 
AgO,N05=Ag+Fe303,3S03+FeO,N05.  It  is  employed  in  the  propor- 
tion of  14  grains  to  the  ounce  of  water,  acetic  acid  and  alcohol  being 
added  in  the  proportions  above  given.  This  reducing  agent  produces  less 
dense  negatives  :  the  reduced  silver  has  a  tendency  to  assume  a  white  crys- 
talline or  frosted  state,  and  the  more  acid  the  sulphate  from  the  presence  of 
free  sulphuric  or  nitric  acid,  the  stronger  is  this  effect.  There  is  another 
evil  attending  its  use — the  silver  is  frequently  reduced  to  a  metallic  film  on 
the  surface  of  the  liquid  ;  this  falls  on  the  collodion-negative,  and  cannot  be 
removed  by  mere  washing.  The  image  is  thus  obscured.  The  sulphuric 
may  be  replaced  by  the  acetic  acid,  as  in  adding  acetate  of  lead  or  acetate 
of  baryta  to  a  solution  of  the  protosulphate  of  iron,  and  filtering  the  liquid. 
Nitrate  of  baryta  has  been  employed  for  a  similar  purpose,  and  in  this  case 
nitric  acid  is  set  free.  The  iron-developer  should  always  be  strongly  acid 
(with  acetic  acid)  in  order  to  prevent  a  too  rapid  reduction  of  the  salt  of 
silver.  •  The  addition  of  acetic  ether  and  hyponitrous  ether  has  been  found 
to  operate  effectually  in  a  similar  manner.  Like  the  pyrogallic  acid,  the 
protosulphate  of  iron  has  no  action  on  the  iodide  of  silver  unless  free  nitrate 
is  present,  and  unless  the  iodide  has  been  exposed  to  light.  It  does  not 
decompose  either  the  soluble  or  insoluble  iodides,  and  it  does  not  discharge 
the  color  of  a  solution  of  iodine,  or  prevent  the  formation  of  the  usual  blue 
compound  on  the  addition  of  a  solution  of  starch. 

The  reduced  silver  on  the'plate  is  insoluble  in  a  solution  of  hyposulphite 
of  soda,  but  the  undecomposed  iodide  is  dissolved  by  it.  It  forms  a  com- 
pound salt  with  the  iodide:  its  action  may  be  thus  represented:  Agl-|-2 
(NaO,S303)=NaI-f  NaO,AgO,2S30a.  The  glass  plate  thus  preserved  may, 
according  to  the  degree  to  which  the  image  has  been  brought  out,  be  em- 
ployed as  2i  positive,  by  placing  it  on  a  dark  background,  in  which  case  those 
portions  that  are  opaque  to  light,  or  in  which  the  silver  is  deposited,  will 
reflect  light,  and  furnish  the  lights  of  the  picture ;  while  those  which  are 
transparent,  and  on  which  the  light  did  not  act,  will  appear  black  from  the 
nature  of  the  background,  and  these  will  represent  the  shadows  of  the  pic- 
ture. In  the  Daguerreotype  the  picture  is  inverted  when  finished,  while  in 
the  collodion  positive  it  appears  non-inverted.  In  a  further  stage  of  devel- 
opment the  image  may  be  so  strongly  defined  that  the  deposited  silver  will 
more  or  less  completely  intercept  the  light,  producing  a  negative  impres- 
sion, from  which  a  non-inverted  image,  or  positive  drawing,  may  be  procured 
on  another  sensitized  surface.  In  order  to  protect  the  film  on  the  plate  from 
injury  it  is  necessary  to  varnish  the  collodion  side  with  amber  or  resinous 
varnish.  The  former  is  preferable,  as  it  is  not  softened  by  solar  heat  in 
taking  a  positive  drawing. 


512  PHOTOGRAPHY    ON    PAPER. 

3.  Photography  on  Paper. — In  1839,  Mr.  Fox  Talbot  first  published  a 
method  of  procuring  images  on  paper  with  the  salts  of  silver,  and  of  so  pre- 
serving them  that  from  the  negatives  positive  drawings  (in  which  the  light 
and  shade  were  correct)  might  be  taken  by  superposition  and  exposure.  He 
used  the  chloride,  iodide,  or  bromide  of  silver;  and  various  saline  solutions 
as  preservatives.  He  gave  to  one  modification  of  his  process  for  producing 
the  image  the  name  of  Calotype.  In  this  the  image  was  received  on  paper 
impregnated  with  iodide  of  silver,  and  afterwards  developed  by  a  mixture  of 
gallic  acid  and  nitrate  of  silver.  It  would  be  impossible  here  to  describe 
the  numerous  modifications  which  the  so-called  paper-process  has  assumed 
since  it  was  first  discovered.  Owing  to  imperfect  methods  of  preservation, 
nearly  all  the  drawings  which  were  taken  at  an  early  period  have  perished. 
Paper  impregnated  with  wax,  with  one  part  of  wax  to  four  parts  of  paraffin, 
with  gelatin,  albumen,  and  other  substances,  has  been  used,  and  admirable 
drawings  of  large  size  have  been  procured  from  transparent  wax-negatives : 
but  the  paper-process  is  now  chiefly  confined  to  the  procuring  of  positive 
impressions  from  collodion  negatives  on  glass  ;  and  the  salt  of  silver  which 
is  preferred  for  this  purpose  is  the  chloride  (AgCl),  with  or  without  albu- 
men, but  always  accompanied  with  free  nitrate  of  silver.  The  chloride, 
although  the  cheapest  and  most  convenient,  is  not  the  most  sensitive  com- 
pound. Experiments  on  this  subject,  performed  by  Mr.  Wright,  have  given 
the  following  results,  in  which  the  action  of  light  on  chloride  of  silver  is 
taken  as  a  standard  : — 


Paper  prepared  with  chloride  of  silver 

.     1-000 

"               "          chloriodide  of  silver   . 

.     1-078 

«               "          bromide  of  silver 

.     2-396 

"               "          chlorobromide  of  silver 

.     4-022 

«               "         bromiodide  of  silver   . 

.     4-060 

Preparation  of  the  Paper. — Paper  manufactured  for  photographic  use 
should  be  floated  for  five  minutes  on  a  solution  containing  from  10  to  12 
grains  of  chloride  of  sodium  or  ammonium  to  an  ounce  of  water.  When 
dried,  it  should  be  floated  in  a  dark  room  for  another  five  minutes,  on  its 
salted  surface,  on  a  solution  of  nitrate  of  silver,  consisting  of  from  60  to  80 
grains  to  the  ounce  of  water.  When  dry,  it  is  fit  for  use.  Paper  prepared 
with  a  surface  of  albumen  and  impregnated  with  chloride  of  sodium  may  be 
readily  procured.  This  may  be  sensitized  in  a  similar  manner.  A  positive 
impression  is  taken  by  placing  the  collodion  side  of  a  negative  plate,  on 
which  there  is  a  fixed  image,  in  contact  with  the  dry  sensitive  side  of  the 
paper,  and  exposing  it  to  light  in  a  pressure-frame  until  the  lights  of  the 
drawing  are  of  a  pale  lilac  hue,  and  the  shades  are  of  a  deep  bronze  color. 
It  is  afterwards  soaked  in  successive  portions  of  tepid  water,  until  the  water 
is  no  longer  rendered  milky  by  the  production  of  chloride  of  silver.  It  is 
then  transferred  to  a  toning  bath,  which  is  thus  prepared :  Acetate  of  soda 
and  bicarbonate  of  soda,  of  each  20  grains  :  dissolve  in  ten  fluidounces  of 
distilled  water,  and  filter  the  solution.  Add,  at  the  time  required,  one 
fluidrachm  of  the  following  solution  :  chloride  of  gold  eight  grains,  distilled 
water  one  ounce.  The  soda  liquid  should  be  kept  in  a  stoppered  bottle 
covered  with  black  paper.  It  may  be  used  any  number  of  times,  the  quan- 
tity lost  being  made  up  by  a  fresh  quantity  of  a  similar  solution  ;  and  as  the 
gold  is  removed  by  each  process  of  toning,  an  additional  quantity  may  be 
added  to  the  soda  liquid.  The  toning  liquid  should  be  prepared  a  few  hours 
before  it  is  used,  and  warmed  to  a  temperature  of  about  70^  or  80°  by 
placing  it  before  a  fire.  As  there  is  occasionally  a  deposit  in  it,  the  solution 
before  use  should  be  poured  off  clear,  or  filtered. 


PHOTOGRAPHY    ON    PAPER.  513 

The  positive  paper  drawings,  before  immersion  in  the  toning  bath,  should 
be  first  well  soaked  in  a  weak  solution  of  acetate  of  soda,  and  afterwards 
^'ashed  in  two  or  three  waters  until  all  traces  of  chloride  of  silver  disappear. 
Under  these  circumstances,  there  is  only  reduced  silver  on  the  surface  of  the 
paper,  and  some  portion  of  chloride  in  the  tissue  of  the  paper.  The  draw- 
ings, which  are  now  reddish-colored,  are  introduced  separately  into  the  toning 
liquid,  the  face  upwards,  and  are  kept  in  motion  until  they  begin  to  darken. 
The  silver  is  replaced  by  gold,  and  the  drawing  passes  through  shades  of 
brown,  purple-black,  blue-black,  and  black,  and,  if  left  too  long,  a  kind  of 
bleacliing  takes  place,  and  the  sharpness  and  delicacy  of  the  drawing  are 
destroyed.  As  a  rule,  they  should  be  removed  when  the  color  is  of  a  deep 
purple-black.  Those  drawings  which  are  feebly  printed  will  not  acquire  any 
depth  of  color;  they  either  become  more  faint,  or  retain  a  brown  color.  In 
fact,  it  is  only  in  those  parts  in  which  the  silver  has  been  completely  reduced 
by  light,  and  has  a  bronze  color  from  overprinting,  that  this  toning  effect 
takes  place.  The  auro-chloride  of  sodium,  in  the  proportion  of  ten  grains 
to  one  ounce  of  distilled  water,  forms  also  a  good  toning  solution,  as  a  sub- 
stitute for  pure  chloride  of  gold.  All  the  operations  above  described,  except 
that  of  salting  the  paper,  must  be  carried  on  in  a  darkened  room.  The 
drawing,  after  toning,  should  be  washed  in  cold  water,  to  remove  any  traces 
of  the  gold-bath,  and  then  plunged  for  a  quarter  of  an  hour  into  a  solution 
of  hy|)Osulphite  of  soda,  containing  one  ounce  of  the  salt  to  eight  ounces  of 
water.  Any  chloride  of  silver  contained  in  the  substance  of  the  paper  is 
thereby  removed,  while  in  a  perfect  drawing  the  color  is  but  little  changed, 
unless  it  is  allowed  to  remain  too  long  in  the  bath.  No  more  of  the  solution 
of  hyposulphite  should  be  employed  than  is  necessary  for  the  number  of 
drawings  to  be  preserved.  The  hyposulphite,  after  use,  should  be  thrown 
away.  If  used  more  than  once,  it  is  liable  to  cause  stains  in  the  drawings 
subsequently  made.  The  drawing  is  now  soaked  in  a  large  quantity  of 
water,  occasionally  renewed,  for  twenty-four  hours,  with  a  view  to  remove  all 
the  compound  hyposulphite  of  soda  and  silver.  The  last  drainings  of  the 
drawing  may  be  tested  for  any  traces  of  hyposulphite,  either  by  a  solution 
of  nitrate  of  silver,  or  of  acid  subnitrate  of  mercury.  If  any  hyposulphite  is 
still  contained  in  the  washings  of  the  drawing,  the  former  will  give  a  brown 
color  to  the  liquid,  and  the  latter  will  produce  a  gray,  or  even  a  black  pre- 
cipitate. Albumenized  paper,  owing  to  the  greater  uniformity  of  chemical 
action,  facility  for  toning  the  smoothness  of  surface,  and  tenacity  which  it 
possesses,  is  now  almost  universally  employed  for  positive  photography.  It 
is,  however,  open  to  this  serious  objection  :  the  albuminate  of  silver  which 
is  formed  on  the  surface  is  not  soluble  in  an  alkaline  hyposulphite,  and  is 
therefore  irremovable.  The  lights  of  the  drawing  therefore  retain  a  quantity 
of  silver  salt,  which  slowly  tarnishes,  not  merely  from  the  sulphur  vapors 
diffused  through  the  atmosphere,  but  by  reason  of  the  sulphur  contained  in 
the  albumen  itself,  and  which,  by  decomposition,  has  a  tendency  to  produce 
brown  sulphide  of  silver  and  cause  a  yellow  or  brown  discoloration  of  the 
drawing.  Attempts  have  been  made  to  correct  this  evil  by  pressing,  rolling, 
ironing,  and  waxing  the  drawings,  but  only  with  partial  success.  These 
objections  do  not  apply  to  the  plain  paper  drawings,  but  it  is  a  matter  of 
great  difficulty  to  procure  paper  of  this  kind  which  will  give  clear  details, 
that  will  resist  the  necessary  processes  of  toning,  treating  with  chemical 
solvents,  and  frequent  washing.  Paper  prepared  with  collodion  in  place  of 
albumen  has  been  employed,  and  with  success,  but  it  is  more  difficult  to 
prepare. 

In  February,  1839,  soon  after  the  announcement  of  Mr.  Fox  Talbot's 
method  of  impregnating  paper  with  chloride  of  silver,  we  found  that  a  solu- 
33 


514  CHEMICAL    CHANGES    IN    THE    PAPER    PROCESS. 

tion  of  ammonio-nitrate  of  silver  gave  greater  certainty  and  uniformity  in 
the  results.  The  solution  then  called  Photogenic  liquid  was  prepared  by 
dissolving  4  drachms  of  nitrate  of  silver  in  6  ounces  of  water.  Strong  am- 
monia wa^  added  to  the  liquid  until  the  oxide  of  silver  at  first  precipitated 
was  entirely  redissolved  ("On  the  Art  of  Photogenic  Drawing,"  Jeffery. 
London,  1840,  p.  6).  The  liquid  was  laid  on  the  paper  with  a  brush,  the 
paper  being  selected  according  to  the  dark  and  even  tone  which  it  acquired 
when  prepared  with  the  silver  solution  and  exposed  to  light.  Drawings 
taken  by  this  process  in  July,  1839,  and  preserved  by  the  hyposulphite  of 
lime,  have  undergone  but  little  change  in  twenty-eight  years.  The  lights 
and  shades  are  still  well  defined,  but  the  color  of  the  shades  is  brown,  as  a 
result  of  the  action  of  hyposulphite  and  the  absence  of  toning.  By  allowing 
the  drawing  to  remain  in  a  very  diluted  solution  of  gold  for  twenty-four 
hours,  the  silver  is  replaced  by  a  purple  deposit  of  gold.  The  lines  of  the 
drawing  at  first  disappear,  and  are  afterwards  restored  in  precipitated  gold. 
The  paper  should  be  well  washed  afterwards,  in  order  to  remove  any  traces 
of  chloride  of  gold.  In  salting  paper  for  the  ammonio-nitrate  of  silver,  the 
quantity  of  chloride  of  ammonium  or  sodium  used  should  be  less  than  that 
employed  for  the  nitrate.  It  was  thought  that  such  a  solution  would  be 
dangerous  for  use,  by  giving  rise  to  the  production  of  fulminating  silver; 
but  an  experience  of  many  years  showed  that  this  was  an  error.  The  addi- 
tion of  a  small  quantity  of  alcohol  and  a  few  drops  of  nitric  acid  to  the  liquid 
has  been  found  to  render  it  adapted  for  albumenized  paper,  the  proportion 
of  nitrate  of  silver  employed  being  about  70  grains  to  an  ounce  of  water. 
The  objection  to  the  use  of  the  ammonio-nitrate  on  plain  paper  is  the  diffi- 
culty of  giving  a  good  permanent  color  by  toning  with  gold.  A  drawing 
may  be  well  taken  on  plain  paper,  but  the  processes  of  toning  and  preserving 
by  hyposulphite  destroys  its  sharpness. 

The  chemical  changes  which  take  place  in  the  various  stages  of  the  paper 
process  may  be  thus  described:  Chloride  of  silver  is  produced  in  sensitizing 
the  paper,  NaCl-hAgO,N05=AgCl  +  NaO,N05.  The  chloride  is  by  this 
method  of  preparation  evenly  precipitated  over  the  surface  of  the  paper;  but 
it  is  always  mixed  with  free  nitrate  of  silver,  which  accelerates  and  increases 
the  chemical  changes.  When  albumenized  paper  is  used,  in  addition  to  the 
two  preceding  salts,  an  organic  salt  (the  albuminate)  is  also  produced.  The 
three  salts  are  decomposed  by  light,  but  in  difl'erent  degrees:  the  nitrate 
produces  a  brown-black,  the  chloride  tends  to  produce  a  purple-black,  and 
the  albuminate  a  reddish-brown  color,  which  is  not  easily  darkened  by  the 
gold-bath.  A  deficiency  of  nitrate  of  silver  in  the  silver-bath  (as  it  is  rapidly 
replaced  by  nitrate  of  soda),  an  undue  proportion  of  chloride  of  sodium  in 
the  paper,  or  too  short  a  contact  with  the  sensitizing  liquid,  will  affect  the 
results.  Exposure  to  light  causes  a  reduction  of  the  silver  in  the  exposed 
parts  to  the  metallic  state:  AgCl  =  AgH-CI,  and  AgO,N05=Ag-f  0-f  NO^; 
but  only  a  very  small  portion  of  the  silver  salts  on  the  paper  is  thus  metal- 
lized. When  the  recent  drawing  is  washed  with  acetate  of  soda  and  placed 
in  water  containing  an  alkaline  chloride,  there  is  an  abundant  milky  deposit, 
owing  to  the  production  of  chloride  of  silver  from  the  undecomposed  nitrate 
in  the  paper.  This  should  be  removed  as  rapidly  as  it  is  formed,  but  the 
body  of  the  paper  will  still  hold  a  quantity,  which  surface-washing  with  water 
will  not  remove.  When  the  drawing  is  now  placed  in  an  alkaline  solution 
of  gold,  the  gold  is  deposited  either  upon  or  in  substitution  of  the  metallic 
silver,  giving  to  it  a  purple-black  in  place  of  the  red-brown  color  (3Ag-}- 
AuCl3=Au-H3AgCl),  and  rendering  it  better  fitted  to  withstand  the  action 
of  the  hyposulphite  of  soda.  A  compound  hyposulphite  of  gold  and  soda, 
which  may  be  made  by  adding  a  weak  solution  of  the  chloride  of  gold  to  a 


GOLD.      DISTRIBUTION    AND    PRODUCTION.  515 

concentrated  solntion  of  the  hyposulphite,  has  been  found  preferable  for  the 
toning  of  drawings  on  plain  salted  paper.  In  this  case  it  is,  however,  pro- 
bable that  the  more  perishable  sulphide  of  silver  still  exists  in  the  drawing, 
with  precipitated  gold.  The  perfect  preservation  of  the  drawing  is  based 
on  two  conditions  :  1.  The  entire  removal  from  the  substance  of  the  paper 
of  any  chloride  of  silver  by  the  hyposulphite  of  soda:  AgCl4-2(NaO,SaOa) 
=NaCl  +  NaO,AgO,2S202.  Hence  the  drawing  should  be  left  sufficiently 
long  in  this  liquid,  and  it  should  be  of  a  sufficient  strength,  but  not  greater 
than  is  required,  for  the  removal  of  the  chloride.  If  very  strong,  it  injures 
the  finer  parts  of  the  impression  by  dissolving  the  reduced  silver.  It  is 
better,  therefore,  to  employ  a  solution  of  the  minimum  strength  for  the 
removal  of  the  chloride.  If  the  solution  is  too  weak,  it  produces  in  the 
substance  of  the  paper  spots  of  brown  sulphide  of  silver.  2.  The  second 
condition  is,  that  the  whole  of  the  compound  hyposulphite  thus  produced 
should  be  removed  from  the  paper,  otherwise  it  will  undergo  spontaneous 
decomposition,  especially  in  a  damp  atmosphere.  Brown  and  yellow  stains 
sooner  or  later  appear  in  the  drawing,  and  thus  destroy  it.  They  arise  from 
the  decomposition  of  the  hyposulphite  of  silver,  which  passes  through  a 
series  of  changes  until  it  is  resolved  into  sulphide  of  silver,  and  ultimately 
this  appears  to  be  itself  resolved  into  sulphate  of  silver  (AgO,S203=AgO, 
S02+S  =  AgS  +  S03).  The  sulphuric  acid  probably  reacts  upon  another 
portion  of  hyposulphite,  forming  sulphate  of  silver,  and  setting  free  sulphur 
and  sulphurous  acid. 

There  are  many  points  connected  with  the  art  of  photography  which  can 
be  acquired  only  by  long  practice.  The  causes  of  failure  in  every  stage  of 
the  process  are  numerous,  and  are  sometimes  difficult  of  explanation. 


CHAPTER    XL. 

GOLD.     PLATINUM. 

Gold  (Au=19t). 

Gold  has  been  known  from  the  remotest  ages  :  it  is  the  Sol  of  the  alche- 
mists, who  represented  it  by  the  circle  O,  the  emblem  of  perfection.  It 
occurs  in  nature  in  a  metallic  state  alloyed  with  silver  or  copper,  and  is  called 
native  gold.  It  is  found  disseminated  in  primitive  or  igneous  rocks,  or  in 
the  beds  of  rivers,  and  in  alluvial  deposits.  The  largest  supplies  have  been 
derived  from  Australia  and  California;  from  Brazil,  Mexico,  and  Peru;  from 
the  Ural  Mountains  ;  and  from  some  parts  of  Africa.  The  rivers  of  Hun- 
gary, Transylvania,  and^Piedraont,  have  also  yielded  the  metal ;  and  it  has 
been  found  in  Cornwall,  Wicklow,  and  North  Wales.  The  gold  quartz  from 
the  Welsh  Hills,  near  Dolgelly,  produced  in  1862,  5299  ounces  of  gold;  in 
1863,  552  ounces  ;  in  1864,  2336  ounces  ;  and  in  1865,  only  1663  ounces. 
Gold  has  also  been  found  in  the  refuse  slags  of  sulphuric  acid  works,  when 
pyrites  has  been  used  as  a  source  of  sulphur.  Although  it  generally  occurs 
in  small  nodules  and  granules,  nuggets  are  sometimes  found  weighing  many 
pounds.  It  is  usually  separated  from  the  matrix  by  grinding  and  washing, 
or  by  amalgamation  with  mercury.  The  latter  process  has  been  to  a  great 
extent  superseded  by  the  employment  of  sodium  amalgam  as  suggested  by 
Mr.  Crookes.     The  product  in  gold  has  been  thereby  increased  threefold. 


516  •    PROPERTIES    or    GOLD. 

Messrs.  Johnson  and  Matthey  found,  by  direct  experiment  on  the  same 
sample  of  California  mineral,  that  while  by  ordinary  amalgamation  a  toQ 
yielded  only  2  oz.  16  dwts  of  gold,  by  the  sodium  amalgam  the  yield  was  a 
few  grains  more  than  t  ozs.,  while  an  assay  of  the  mineral  showed  that  it 
contained  7  ozs.  9  dwts.  per  ton.    (See  Chem.  News,  Oct.  12,  1866,  p.  170  ) 

Gold  may  be  obtained  pure  by  dissolving  standard  gold  in  nitro-hydro- 
chloric  acid,  evaporating  the  solution  to  dryness  (by  a  gentle  heat  towards 
the  end  of  the  process),  redissolving  the  dry  mass  in  distilled  water,  filtering, 
acidulating  with  hydrochloric  acid,  and  adding  a  solution  of  protosulphate  of 
iron.  A  brown  powder  falls,  which,  after  having  been  washed  with  hydro- 
chloric acid  and  distilled  water,  affords  on  fusion  with  a  little  borax  or  other 
suitable  flux,  a  button  of  pure  gold;  (6(FeO,S03)  +  AuCl3=2(Fe203'3S03)  + 
FeaCl^+Au).  If  the  solution  from  which  the  gold  is  precipitated  is  ex- 
tremely dilute,  it  acquires  on  the  first  addition  of  the  salt  of  iron  a  beautiful 
blue  tint,  when  viewed  by  transmitted  light,  and  appears  reddish  by  reflection. 

Properties. — Gold  is  of  a  deep  and  peculiar  reddish-yellow  color.  It  melts 
at  a  bright-red  heat,  equivalent  to  al3out  2016°  of  Fahrenheit's  scale,  and 
when  in  fusion  appears  of  a  greenish  color ;  as  it  solidifies  it  contracts  in 
bulk.  Its  specific  gravity,  in  its  least  dense  state,  after  fusion,  is  192  ;  by 
hammering  and  rolling  it  may  be  brought  up  to  193  or  19'4.  It  is  so 
malleable,  that  it  may  be  beaten  into  leaves  which  do  not  exceed  the 
1-200, 000th  of  an  inch  in  thickness  ;  a  single  grain  may  be  extended  over  56 
square  inches  of  surface.  In  this  state  of  tenacity  the  metal  is  translucent 
and  admits  of  the  passage  of  the  green  rays  of  light.  No  alloy  can  be  thus 
attenuated,  for  the  alloys  of  gold  are  generally  harder  and  less  ductile  and 
malleable  than  pure  gold.  The  green  color  transmitted  by  the  leaf  is  there- 
fore a  test  of  purity.  It  may  be  at  once  observed  by  breathing  on  a  glass 
plate,  or  mica,  and  pressing  it  on  the  leaf.  It  will  readily  cohere.  The 
metal  undergoes  no  change  by  exposure  to  air  or  water  at  any  temperature. 
Pure  gold  never  tarnishes,  but  some  of  its  alloys  are  readily  tarnished  by 
oxidation  or  sulphuration.  The  ductility  of  gold  is  such  that  a  grain  may 
be  drawn  out  into  500  feet  of  wire.  An  inch  of  this  wire  would  weigh  only 
l-6000th  part  of  a  grain. 

Gold  may  be  kept  for  several  hours  in  fusion  without  perceptible  loss  of 
weight;  but  when  subjected  to  an  intense  heat  it  affords  evidence  of  vola- 
tility. The  concentrated  mineral  acids  have  separately  no  action  upon  pure 
gold  ;  neither  has  sulphur  nor  sulphuretted  hydrogen.  Chlorine,  iodine,  and 
bromine,  on  the  contrary,  are  capable  of  acting  upon  it;  the  agent  com- 
monly resorted  to  for  dissolving  it,  is  chlorine,  generally  in  the  form  of  nitro- 
hydrochloric  acid,  or  aqua  regia.  If  a  small  portion  of  leaf-gold  is  added  to 
a  freshly-made  solution  of  chlorine,  and  the  mixture  is  heated,  the  gold  is 
speedily  dissolved,  forming  a  yellow-colored  liquid.  Any  silver  that  may  be 
present,  will  remain  in  dark-colored  particles  undissolved.  Bromine  water 
also  dissolves  gold.  When  gold  is  boiled  with  hydrochloric  acid,  and  a  small 
quantity  either  of  peroxide  of  manganese,  or  of  an  alkaline  seleniate  is  added 
to  the  liquid,  the  metal  is  immediately  dissolved.  Chlorine  is  set  free  in  both 
cases  (pp.  188  and  232).  Hydrofluoric  acid  has  no  action  on  gold.  When 
mixed  with  strong  nitric  acid  and  boiled,  the  gold  immersed  remains  un- 
changed. No  fluoride  is  formed  under  the  circumstances.  Sulphuric  acid 
and  nitric  acid  used  separately  have  no  action  on  the  metal.  Thus  gold-leaf 
boiled  in  strong  sulphuric  acid  remains  unchanged,  but  if  a  drop  of  nitric 
acid  is  added,  the  gold  is  entirely  dissolved.  It  does  not  appear  that  any 
salt  is  formed,  for  when  added  to  water  the  gold  is  precipitated  in  the  metallic 
state  as  a  purple  black  powder.  If  the  sulphuric  solution  is  simply  exposed 
to  air,  the  gold  is  deposited  in  a  similar  state  so  soon  as  the  acid  absorbs 


PERCHLORIDE    OF    GOLD.  517 

water.  The  remarkable  fact  is  that  so  small  a  quantity  of  nitric  acid  should 
confer  this  solvent  property  on  sulphuric  acid.  If  hydrochloric  acid  is  sub- 
stituted for  nitric  acid  in  this  experiment,  the  p^old  is  not  dissolved. 

There  are  two  oxides  of  j?old,  a  protoxide  and  b,  peroxide. 

Protoxide  op  Gold.  Atirous  Oxide  (AuO)  is  obtained  by  precipitating 
a  solution  of  the  protochloride  by  a  weak  solution  of  potassa.  It  is  of  a  dark 
color,  and  is  converted  by  hydrochloric  acid  into  metallic  gold  and  perchlo- 
ride ;  potassa  and  soda  dissolve  a  little  of  it ;  with  ammonia  it  forms  a  de- 
tonating compound. 

Peroxide  of  Gold.  Auric  Oxide  ;  Auric  Acid  (AuOg). — The  best  pro- 
cess for  obtaining  peroxide  of  gold  consists  in  the  decomposition  of  the 
perchloride  by  magnesia  or  oxide  of  zinc  washing  the  precipitate  with  dilute 
nitric  acid,  and  drying  it  at  a  low  heat.  It  is  of  a  brown  color,  and  is  re- 
duced by  the  action  of  light,  or  when  heated  to  480^.  It  dissolves  in  sul- 
phuric and  in  nitric  acids,  but  the  solutions  are  decomposed  by  dilution  with 
water.  It  is  soluble  in  the  hydrochloric  acid,  and  combines,  when  hydrated, 
with  alkaline  bases,  forming  salts  which  have  been  called  Aurates.  It  is  not 
dissolved  by  hydrofluoric  acid.  With  ammonia  it  forms  a  fulminating  com- 
pound.    It  explodes  at  290°. 

Protochloride  of  Gold  (AuCl)  is  obtained  by  exposing  the  perchloride 
to  a  temperature  not  exceeding  350°  :  it  loses  chlorine,  and  is  converted  into 
a  pale-yellow  protochloride,  which  is  very  unstable,  and  is  decomposed  by  the 
action  of  boiling  water. 

Perchloride  of  Gold  (AuClg). — The  common  solvent  of  gold,  for  the 
purpose  of  obtaining  the  chloride,  is  the  nitrohydrochloric  acid.  Six  grains 
of  pure  gold  (dentist's  foil)  may  be  dissolved  in  -J  a  drachm  of  pure  nitric 
and  \\  drachms  of  pure  hydrochloric  acid.  A  gentle  he-at  should  be  em- 
ployed, and  the  acid  liquid  concentrated  by  evaporation  on  a  sand-bath,  until 
it  is  reduced  to  one-third  of  its  bulk.  It  may  then  be  set  aside  for  crystalli- 
zation, or  at  once  mixed  with  a  quantity  of  water,  in  proportion  to  the 
strength  of  the  solution  required.  The  chemical  changes  may  be  thus  repre- 
sented :  (Au-hN05+3HCl=AuCl3  +  3HO  +  NO,).  By  evaporating  a  satu- 
rated solution,  prismatic  crystals  of  a  deep  orange  color  are  obtained.  These 
are  very  deliquescent,  fusible,  and  readily  decomposed  by  heat,  yielding,  at 
first  the  protochloride,  and  ultimately,  pure  gold.  The  solution,  even  when 
much  diluted,  has  a  rich  yellow  color.  It  is  decomposed  by  phosphorus, 
charcoal,  sulphurous  and  gallic  acids,  and  many  of  the  metals  and  their 
compounds.  Even  silver  will  slowly  displace  gold.  Silver  leaf  allowed  to 
remain  in  a  diluted  solution  of  chloride  of  gold,  acquires  a  dark  metallic 
film  upon  the  surface.  ,  In  the  toning  of  photographs  by  immersing  the 
paper  with  reduced  silver  in  a  solution  of  chloride  of  gold,  the  gold  is  de- 
posited either  in  the  place  of  or  in  contact  with  the  reduced  silver.  A  diluted 
solution  of  chloride  spread  over  a  surface  of  clean  [copper  gives  a  good 
bronzing  effect  to  that  metal  by  the  deposition  of  gold.  Leather  washed 
over  the  diluted  chloride,  and  exposed  to  light,  acquires  a  golden-brown  film 
of  the  reduced  metal.  If  a  sheet  of  paper  or  gelatin  is  soaked  in  the  diluted 
chloride  and  exposed  to  light,  the  gold  is  deposited  of  various  shades  of 
green-purple  or  ruby  color.  This  compound  of  gold  has  been  used  for 
photographic  purposes  in  place  of  the  salts  of  silver.  Like  the  latter,  it  is 
only  reduced  by  light  in  the  presence  of  organic  matter.  When  the  solution 
of  chloride,  with  a  small  quantity  of  soda  or  potash,  is  boiled  in  a  liquid 
containing  organic  matter,  the  gold  is  rapidly  reduced  and  precipitated  la 
the  form  of  a  purple  powder.  Protosulphate  of  iron  throws  down  the 
metal  in  a  finely-divided  state,  and  in  this  condition  it  is  used  for  gilding 
porcelain,  and  other  purposes  (p.  516). 


518  PERCHLORIDE  AND  SULPHIDE  OF  GOLD. 

Perchloride  of  gold  dissolves  in  alcohol  and  in  ether :  the  latter  solution 
is  obtained  by  agitating  the  aqueous  solution  of  gold  with  ether,  after  which 
the  mixture  separates  into  two  portions ;  the  superior  is  yellow,  and  is  an 
ethereal  solution  of  chloride  of  gold  *,  the  inferior  is  colorless,  being  water 
and  hydrochloric  acid.  Polished  steel  dipped  into  this  ethereal  solution 
acquires  a  coating  of  gold,  and  it  has  hence  been  employed  for  gilding  deli- 
cate cutting  instruments.  When  long  kept,  it  often  slowly  deposits  films  of 
metallic  gold,  in  arborescent  crystals.  The  ruby  gold  is  here  in  the  metallic 
state  as  in  Bohemian  glass. 

Purple  of  Cassius. — When  a  dilute  mixed  solution  of  protochloride  and 
perchloride  of  tin  is  gradually  added  to  a  dilute  solution  of  perchloride  of 
gold,  this  purple  compound  is  precipitated  ;  and  if  a  piece  of  tinfoil  be  im- 
mersed in  a  dilute  solution  of  the  chloride,  the  same  purple  powder  is  thrown 
down.  The  purple  of  Cassius,  so  called  from  its  discovery  by  Cassius  of 
Leyden,  is  used  in  enamel  and  porcelain  painting,  and  also  for  tinging  glass 
of  a  fine  ruby  tint.  It  retains  its  color  at  a  high  red  heat:  it  is  insoluble 
in  solutions  of  potassa  and  soda;  but  if,  whilst  in  its  hydrated  state,  it  is 
washed  with  ammonia,  a  bright  purple  liquid  is  obtained.  This  compound 
is  regarded  as  a  hydrated  stannate  of  gold  and  tin  (AuO,Sn03+SnO,SnOa4- 
4Aq). 

Auro-Perchlorides. — These  are  compounds  in  which  the  chloride  of 
gold  is  combined  with  certain  electro-positive  chlorides,  such  as  those  of  the 
alkaline  bases,  potash  and  soda ;  they  consist  of  1  atom  of  perchloride  of 
gold,  and  1  atom  of  the  other  chloride,  and  may  be  formed  of  their  respec- 
tive chlorides  in  such  proportions.  Some  of  them  have  been  long  known  : 
they  mostly  form  prismatic  crystals,  and  include  water  of  crystallization.  It 
is  in  consequence  of  the  formation  of  these  soluble  double  salts,  that  a  solu- 
tion of  perchloride  of  gold  in  hydrochloric  acid,  yields  no  precipitates  with 
the  alkalies,  even  when  added  in  excess.  Different  aurochlorides,  obtained 
by  adding  salts  of  potassa,  soda,  ammonia,  and  other  bases,  to  the  chloride, 
are  employed  in  gilding  copper  trinkets,  buttons,  and  other  articles.  It  may 
be  here  observed  that  most  metals  are  readily  deposited  from  acid  solutions 
only.  In  reference  to  gold  the  deposition  of  the  metal  does  not  readily  take 
place  except  from  an  alkalinic  solution. 

Iodides  and  Bromides  of  gold,  corresponding  to  the  chlorides,  have  been 
formed.  They  also  produce  double  salts  with  the  electropositive  iodides  and 
hromides. 

Sulphide  of  Gold  (AuS.AuSg)  is  produced  by  passing  sulphuretted 
hydrogen  through  a  cold  and  diluted  aqueous  solution  of  perchloride  of  gold. 
It  falls  in  the  form  of  a  black  powder,  and  is  resolved  by  heat  into  gold  and 
sulphur.  It  is  soluble  in  alkaline  sulphides.  A  double  sulphide  of  gold  and 
potassium  is  formed,  when  sulphide  of  gold  is  digested  in  a  solution  of  sul- 
phide of  potassium  ;  or  when  gold,  sulphur,  and  potassa  are  fused  together; 
the  compound  is  soluble  in  water.  Sulphide  of  gold  is  used  in  the  Potteries 
as  a  source  of  the  preparation  of  gold  with  which  a  dingy  gilding  is  given 
to  porcelain.  When  sulphuretted  hydrogen  is  passed  through  a  boiling 
solution  of  chloride  of  gold,  the  metal  is  precipitated:  4AuCl3+3HS-f 
9HO=4Au+12HCl  +  3S03. 

Protocyanide  of  Gold  (AuCy)  falls  in  the  form  of  a  yellow  crystalline 
precipitate  on  adding  a  solution  of  cyanide  of  potassium  to  a  dilute  solution 
of  perchloride  of  gold.  Its  most  important  compound  is  that  with  cyanide 
of  potassium,  which  may  be  formed  by  dissolving  either  cyanide  of  gold,  or 
the  compound  obtained  by  precipitating  a  solution  of  perchloride  of  gold  by 
ammonia,  in  a  solution  of  cyanide  of  potassium.     Its  concentrated  solution 


ALLOYS  OF  GOLD   ANALYSIS.  519 

gives  crystals  =KCy,AuCy.     It  is  used  for  gilding  silver  and  copper,  and 
especially  for  electro-plating. 

Percyanide  of  Gold  (AuCy.,)  is  formed  by  mixing  a  solution  of  caustic 
potassa,  to  which  excess  of  hydrocyanic  acid  has  been  added,  with  perchlo- 
ride  of  gold  free  from  uncorabined  acid.  It  yields  crystals  =AuCy3  +  6Aq. 
It  forms  double  salts  with  the  cyanides  of  the  alkaline  bases. 

Alloys  of  Gold. — The  most  important  are  those  with  copper,  mercury, 
and  silver.  With  copper,  gold  forms  a  ductile  alloy  of  a  deeper  color,  harder, 
and  more  fusible  than  pure  gold;  this  alloy,  in  the  proportion  of  11  gold  to 
1  copper,  or  91*67  gold,  8  33  copper,  constitutes  standard  gold;  its  density 
is  17  "157,  being  a  little  below  the  mean.  One  troy  pound  of  this  alloy  is 
coined  into  46|f  sovereigns,  or  20  troy  pounds  into  934  sovereigns  and  a 
half.  The  pound  was  formerly  coined  into  44  guineas  and  a  half.  The 
standard  gold  of  France  consists  of  9  parts  of  gold  and  1  of  copper. 
Standard  gold  is  not  affected  by  nitric  acid  ;  but  the  inferior  alloys  which 
are  made  to  imitate  gold,  consisting  chiefly  of  copper  and  zinc,  immediately 
decompose  this  acid,  and  set  free  deutoxide  of  nitrogen.  Standard  gold 
containing  nearly  9  per  cent,  of  copper  is  not  affected  by  nitric  acid.  The 
inferior  copper  alloys,  as  a  rule,  decompose  the  strong  acid,  and  are  dissolved 
as  nitrates.  There  is  an  alloy  consisting  of  16  parts  of  copper,  7  of  platinum, 
and  1  of  zinc,  which  resists  the  action  of  the  nitric  acid  test,  and  it  has,  at 
the  same  time,  the  color  of  16  carat  gold.  In  testing  small  articles  of  jewelry 
the  following  plan  may  be  adopted.  The  metal  may  be  rubbed  upon  a 
smooth  surface  of  blood-stone  or  jasper,  so  as  to  transfer  a  portion  to  the 
stone.  One  or  two  drops  of  strong  nitric  acid  are  then  placed  on  the 
metallized  surface  of  the  stone.  If  the  article  is  a  base  alloy,  the  metallic 
appearance  is  speedily  destroyed,  and  the  metal  is  dissolved  :  if  gold,  it 
remains  unaffected.  Base  alloys  are  frequently  plated  with  gold,  and  in  this 
case  the  only  method  of  judging  of  the  quality  of  the  metal,  is  by  taking  the 
specific  gravity,  which  should  be  at  least  17  for  standard  gold.  Trinket-gold 
is  seldom  above  15  ;  and  the  so-called  gold  chains  ordinarily  met  with  vary 
from  11  to  13.     Common  gilt  articles  vary  from  7  to  9. 

Mercury  and  gold  combine  readily  on  contact,  especially  when  heated,  the 
mercury  then  taking  up  a  considerable  proportion  of  gold  without  loss  of 
fluidity :  when  rich  in  gold,  the  amalgam  is  of  a  buttery  consistency,  and 
may  be  separated  from  the  more  liquid  portion  by  pressure  through  leather. 
It  consists  of  about  two  parts  of  gold  and  one  of  mercury :  the  amalgam 
used  for  gilding  bronze  contains  about  one-eighth  of  gold.  Silver  and  gold 
mix  readily  in  all  proportions,  when  the  fused  metals  are  stirred  together. 
The  standard  gold  at  present  coined,  is  for  the  most  part  alloyed  with  copper 
only ;  previous  to  the  year  1826,  the  alloy  consisted  in  part  of  silver,  hence 
its  paler  color.  To  separate  the  silver  from  gold,  the  alloy  is  melted  with  a 
great  excess  of  silver,  granulated,  and  boiled  in  sulphuric  acid,  by  which  the 
silver  is  oxidized  and  converted  into  sulphate,  and  the  metallic  gold  remains 
in  the  form  of  a  dark  insoluble  powder,  which  is  afterwards  collected,  washed, 
and  fused  into  a  button  or  ingot.  In  the  same  way,  the  small  quantity  of 
gold  contained  in  silver  coin,  which  used  to  pass  unheeded,  is  extracted  by 
sulphuric  acid;  the  recently  coined  silver  will  accordingly  be  found,  in  most 
cases,  destitute  of  those  traces  of  gold  which  are  contained  in  our  coin  of  a 
date  anterior  to  1826.  When  gold  and  silver  are  parted  by  the  action  of 
nitric  acid,  it  is  necessary,  as  in  the  case  of  sulphuric  acid,  that  the  silver 
should  be  in  great  excess  (three-fourths  of  the  weight  of  the  alloy) ;  it  is 
otherwise  protected  from  the  solvent  power  of  the  acid. 

Assay  of  Gold. — Tiie  quantity  of  standard  or  other  gold  used  for  assay 
is  generally  about  8  grains :  to  this,  about  three  times  its  weight  of  pure 


520        TESTS  FOR  THE  SALTS  OF  GOLD.   PLATINUM. 

silver,  ton^ether  with  the  proper  proportion  of  lead  is  added,  and  the  whole 
subjected  to  cupellation,  as  already  described  (page  502).  The  silver  and 
gold  are  thus  thoroughly  combined,  while  the  oxides  of  lead  and  copper  are 
absorbed  by  the  cupel.  The  auriferous  button  is  then  flattened  under  the 
hammer,  and  after  having  been  annealed,  is  passed  between  a  pair  of  small 
rollers,  so  as  to  extend  it  into  a  thin  ribbon :  it  is  then  again  annealed,  and 
coiled  up  so  as  to  form  what  is  called  a  cornet,  which  is  put  into  a  flask  or 
matrass  containing  about  an  ounce  of  hot  nitric  acid,  sp.  gr.  1-180,  and 
boiled  for  about  ten  minutes,  by  which  the  silver  is  entirely  dissolved,  and 
the  gold,  retaining  the  form  of  the  cornet,  remains  :  this  is  again  boiled  for 
about  twenty  minutes  in  somewhat  stronger  nitric  acid,  and  then  carefully 
washed  and  transferred  to  a  small  crucible,  in  which  it  is  heated  to  redness. 
When  cold,  the  loss  upon  the  original  weight  of  the  sample,  is  carefully 
ascertained.  The  weight  of  the  alloy  operated  upon  is  always  represented 
as  =1000,  and  the  weights  used  are  so  adjusted  as  to  give  the  value  of  the 
alloy  in  thousandths.  In  the  process  of  gold-assaying,  as  in  that  of  silver, 
various  errors  have  to  be  compensated  for,  more  especially  in  reference  to 
the  traces  of  copper,  lead,  and  silver  which  may  have  been  left  in  the  gold. 

Tests  for  the  Salts  of  Gold. — Such  of  these  as  are  soluble  are  distin- 
guished by  the  peculiar  purple  precipitates  which  they  afford  with  the  mixed 
chlorides  of  tin.  All  the  compounds  of  gold  are  decomposed  by  heat,  and 
the  residuary  gold  is  easily  recognized.  The  following  reactions  are  pro- 
duced in  a  diluted  solution  of  chloride  of  gold  by  the  under-mentioned  tests: 

1.  Potash  2Lndi  soda  give  no  precipitate,  but  form  soluble,  double  aurates. 

2.  Protosulphate  of  iron  gives  a  precipitate  which  may  be  blue  or  green, 
with  a  ruddy  appearance  on  the  surface,  from  reduced  gold.  3.  Sulphurous 
acid  throws  down  metallic  gold  slowly. in  the  cold,  rapidly  when  the  mixture 
is   heated.     4.    Oxalic   acid  the    same.       5.    Tincture   of  galls    the   same. 

6.  Arsenious  add.      This  produces,  on   boiling,  a  similar  decomposition. 

7.  Guaiacum  resin,  freshly  precipitated,  produces  a  bluish  green  color. 
On  warming  the  mixture,  metallic  gold  is  precipitated.  Tannic  acid,  gallic 
acids  also,  throw  down  metallic  gold.  The  compounds  of  gold  are  decom- 
posed by  light  in  contact  with  organic  matter,  and  metallic  gold,  of  various 
shades  of  purple  color,  is  deposited. 

Platinum  (Pt=99). 

This  metal  was  first  made  known  in  1741.  Its  name  is  derived  from 
platina,  a  diminutive  of  the  Spanish  word  plata,  silver. 

Platinum  is  found  in  the  metallic  state,  in  small  grains,  confined  to  streams 
and  alluvial  strata,  chiefly  in  Brazil  and  Peru,  and  in  the  Uralian  mountains 
of  Siberia.  The  grains,  besides  platinum,  contain  generally  gold,  iron,  lead, 
palladium,  rhodium,  iridium, 'and  osmium,  and  often  oxide  of  titanium  and 
chromate  of  iron.  Rounded  masses  of  the  metal  occasionally  occur  among 
them  ;  these  are  rarely  larger  than  a  pea  or  a  small  marble,  though  some 
have  been  found  of  the  size  of  a  pigeon's  egg.  The  usual  mode  of  obtaining 
pure  platinum  consists  in  digesting  the  ore  in  nitrohydrochloric  acid,  decant- 
ing the  clear  solution  from  the  black  insoluble  residue,  and  mixing  it  with 
a  solution  of  sal-ammoniac;  a  yellow  double  chloride  of  ammonium  and  pla- 
tinum falls  (NH^CIjPtCy,  which,  when  well  washed  and  heated  to  redness, 
leaves  a  spongy  mass  of  finely-divided  metal ;  this  is  triturated  with  water, 
and  subjected  to  powerful  pressure  in  a  brass  mould,  so  as  to  form  a  porous 
ingot,  which  is  gradually  raised  to  a  white  heat  and  carefully  hammered  at 
its  ends,  until  it  forms  a  coherent  bar. 

Malleable  platinum  has  lately  been  manufactured  by  the  following  process, 
contrived  by  Deville  and  Debray.    The  prepared  ore  is  fused  with  its  weight 


PLATINUM-      ITS    COMPOUNDS    WITH    OXYGEN.  521 

of  sulphite  of  lead  and  half  its  weight  of  metallic  lead  ;  some  of  the  impuri- 
ties are  thus  separated  in  combination  with  sulphur,  while  the  platinum  forms 
an  alloy  with  the  lead,  which  is  freed  from  the  scoriae,  and  subjected  to  the 
joint  action  of  heat  and  air,  until  the  greater  part  of  the  lead  is  oxidized  into 
lithar<re,  so  that  the  residuary  alloy  only  retains  about  5  per  cent,  of  lead. 
It  is  then  subjected  to  the  intense  heat  of  an  oxyhydrogen  flame  in  a  furnace 
of  chalklime,  where  the  rest  of  the  lead  (together  with  any  gold,  copper,  and 
osmium)  is  driven  off  in  fumes  :  the  remaining  platinum  is  cast  into  any 
required  form.  This  process,  which  has  furnished  ingots  of  more  than  50 
pounds  in  weight,  leaves  some  rhodium  and  iridium  in  combination  with  the 
platinum  ;  but  these  metals  do  not  affect  its  useful  applications,  neither  ren- 
dering it  more  fusible  nor  more  liable  to  the  action  of  acids.  In  the  Inter- 
national Exhibition  of  1862,.  Messrs.  Johnson  exhibited  a  mass  of  pure 
platinum,  prepared  by  Deville's  process,  weighing  230  pounds,  and  valued  at 
3840/.  It  had  been  cast  in  a  mould  of  lime.  In  the  production  of  this 
enormous  mass  of  a  metal  hitherto  regarded  as  infusible,  the  operator  was 
nearly  killed  by  the  fumes  of  osmic  acid  evolved. 

The  color  of  platiaum  is  white — between  that  of  iron  and  silver.  When 
pure  it  scarcely  yields  in  malleability  to  gold  and  silver  :  it  is  excessively 
ductile  and  tenacious,  and  takes  a  good  polish  :  it  is  harder  than  copper, 
but  softer  than  iron.  Its  hardness  is  increased  by  the  presence  of  iridium. 
Platinum  is  more  ductile  than  malleable.  It  may  be  drawn  into  the  finest 
wire,  but  cannot  be  beaten  into  such  thin  leaves  as  gold  and  silver.  It 
undergoes  no  change  by  exposure  to  heat,  and  can  only  be  melted  by  the 
oxyhydrogen  jet.  It  cannot  be  oxidized  at  any  temperature.  Its  rate  of 
expansion  and  contraction  by  heat  is  so  similar  to  that  of  glass,  that  it 
admits  of  being  welded  with  or  fused  into  glass.  The  specific  gravity  of 
platinum  fluctuates  between  21  and  22.  Its  extreme  difficulty  of  fusion,  and 
the  perfect  manner  in  which  it  resists  the  action  of  almost  all  acids,  at  a 
boiling  or  even  at  a  red  heat,  render  it  importantly  useful  in  many  of  the 
arts,  and  indispensable  in  the  laboratory.  The  curious  catalytic  action  of 
clean  surfaces  of  platinum  on  wire  and  foil  of  pulverulent  and  spongy  plati- 
num, and  platinum  black,  upon  gaseous  mixtures,  especially  in  determining 
the  combination  of  oxygen  and  hydrogen,  has  rendered  this  metal  useful  in 
gaseous  analyses.  Bibulous  paper,  or  fibres  of  asbestos,  saturated  with  a 
strong  solution  of  chloride  of  platinum,  dried,  and  ignited,  yield  an  ash 
which  exhibits  the  properties  of  a  finely-divided  platinum  in  perfection. 
This  catalytic  action  of  platinum  appears  increased  in  proportion  to  the 
mechanical  division  of  the  metal  and  the  perfect  cleanliness  of  its  surface. 

Platinum- Black. — Platinum-black  may  be  prepared  by  dissolving  proto- 
chloride  of  platinum  in  a  strong  hot  solution  of  caustic  potassa,  and  adding 
alcohol :  the  hot  mixture  is  stirred  till  the  effervescence,  arising  from  the 
escape  of  carbonic  acid  ceases;  this  is  so  violent  as  to  require  the  use  of  a 
capacious  vessel.  The  platinum  falls  in  the  form  of  a  black  powder,  from 
which  the  supernatant  liquor  is  poured  off;  the  powder  is  then  boiled  suc- 
cessively in  alcohol,  in  hydrochloric  acid,  and  in  solution  of  potassa,  and 
lastly,  in  four  or  five  portions  of  distilled  water.  If  the  alcohol  is  not 
entirely  removed,  the  powder  ignites  on  drying,  and  loses  its  catalytic  power. 
It  is  dissolved  by  a  solution  of  chlorine.  When  dry,  it  looks  like  lamp- 
black, but  acquires  a  metallic  aspect  after  having  been  heated  white-hot. 
This  form  of  platinum  is  also  obtained  by  heating  an  aqueous  solution  of 
.4  parts  of  bichloride  of  platinum,  10  of  crystallized  carbonate  of  soda,  and  1 
of  grape-sugar  to  212^,  stirring  the  liquor  till  the  whole  of  the  black  pre- 
cipitate has  fallen,  which  is  then  well  washed  and  dried  :  it  is  improved  by 


522  PROTOXIDE    OF    PLATINUM, 

boiling  it  first  in  nitric  acid,  and  then  in  solution  of  potassa,  and  finally 
washings  and  drying:. 

A  much  more  simple  method  of  procuring  platinum-black  consists  in 
decoraposino^  the  ammonia  or  potash  chloride  of  platinum  by  zinc.  The 
yellow  compound  is  diffused  through  water  acidulated  with  diluted  sulphuric 
acid,  and  a  bar  of  zinc  is  introduced.  As  the  hydrogen  is  evolved  the  pla- 
tinum is  separated  as  a  black  powder,  and  simply  requires  washing.  Mag- 
nesium is  equally  effectual,  and  being  purer  than  zinc,  leaves,  when  dis- 
solved, no  metallic  residue  to  contaminate  the  platinum.  Sodium  amalgam 
also  throws  down  platinum-black  still  more  rapidly.  Pure  mercury  only 
very  slowly  precipitates  a  solution  of  the  chloride.  Iron,  and  some  other 
metals,  throw  down  platinum  in  a  very  finely-divided  state. 

Spongy  Platinum. — Spongy  platinum  is  readily  procured  by  heating,  on 
platinum  foil,  the  dry  ammonio-chloride  of  platinum  until  the  yellow  color 
has  disappeared,  and  nothing  but  a  gray  spongy-looking  metallic  substance 
remains.  Care  should  be  taken  not  to  overheat  it.  It  is  platinum  in  a  less 
finely-divided  state  than  platinum-black.  Its  properties  are  remarkable  : 
these  have  been  elsewhere  described  (see  Catalysis).  It  condenses  certain 
gases  when  they  are  in  contact  with  it,  and  causes  their  union,  although  the 
metal  itself  undergoes  no  change.  That  condensation  is  said  to  be  equal  to 
250  times  the  volume  of  the  platinum.  In  the  presence  of  hydrogen  it  con- 
denses oxygen,  and  vice  versa;  and  produces  water  by  causing  the  combina- 
tion of  the  two.  At  a  moderate  heat  it  condenses  hydrogen  and  deutoxide 
of  nitrogen,  producing  ammonia  and  water.  Although  it  does  not  appear  to 
absorb  or  condense  oxygen  when  alone,  yet  it  acts  upon  the  freshly  precipi- 
tated resin  of  guaiacum  like  the  ozonides,  or  those  bodies  which  easily  part 
with  oxygen  in  the  nascent  state.  It  oxidizes  the  resin,  and  imparts  to  it  a 
blue  color.  During  these  combinations  the  platinum  passes  to  the  state  of 
full  red  heat,  but  undergoes  no  change  of  weight  or  properties. 

Although  pure  platinum  is  infusible  in  an  ordinary  wind  furnace,  it  softens 
so  as  to  admit  of  welding  and  forging.  In  the  arc  of  flame  of  the  voltaic 
current,  and  before  the  oxyhydrogen  blowpipe,  in  a  lime-furnace,  it  not  only 
admits  of  being  fused,  but  when  very  intensely  heated  it  is  said  to  give  off 
vapor.  Platinum  is  insoluble  in  nitric  acid,  yet  when  alloyed  with  certain 
other  metals  soluble  in  this. acid,  it  is  taken  up  ;  as  for  instance,  with  silver. 
It  is  attacked  at  high  temperatures  by  the  alkalies,  especially  by  baryta, 
lithia,  and  potassa,  which  cause  its  oxidation  and  destruction.  Nitre  and 
the  alkaline  persulphides  have  a  similar  action.  Platinum  readily  fuses  with 
phosphorus,  but  it  is  not  affected  by  sulphur  unless  in  the  spongy  state.  It 
combines  with  the  greater  number  of  the  metals,  and  with  many  of  them— 
such  as  lead,  antimony,  and  tin — forms  very  fusible  compounds ;  these  actions 
show  the  necessity  of  caution  as  to  the  substances  which  are  ignited  or  fused 
in  platinum  crucibles,  and  as  to  the  fuel  with  which  they  are  brought  into 
contact. 

The  affinity,  of  platinum  for  oxygen  is,  like  that  of  gold,  extremely  feeble  ; 
it  shows  no  disposition  to  become  an  oxide  by  exposure  to  air  or  oxygen  at 
any  temperature,  and  although  a  strong  electric  discharge,  when  transmitted 
through  a  fine  platinum  wire,  dissipates  it  into  black  dust,  this,  as  in  the 
analogous  case  of  gold,  is  probably  finely-divided  metal,  and  not  the  result 
of  oxidation.     Two  oxides  of  platinum  have  been  satisfactorily  identified. 

Protoxide  of  Platinum  (PtO).— When  protochloride  of  platinum  is 
gently  heated  in  a  solution  of  caustic  potassa,  a  black  oxide  is  formed,  part 
of  which  is  dissolved,  and  part  precipitated:  it  may  be  thrown  down  from  its 
alkaline  solution  by  diluted*  sulphuric  acid.     It  is  easily  reduced  by  heat, 


OXIDES    AND    CHLORIDES    OF    PLATINUM.  523 

and  slowly  dissolves  in  the  acids,  most  of  which  decompose  it,  and  resolve 
it  into  peroxide  and  metal. 

BiNoxiDE  OF  Platinum  ;  Peroxide  of  Platinum  (PtOJ  is  obtained  by- 
decomposing  nitrate  of  platinum  by  carbonate  of  soda,  so  as  to  leave  the 
nitrate  in  excess.  It  falls  in  the  form  of  a  brown  hydrate,  which,  when 
heated,  first  gives  out  water  and  becomes  black  ;  at  a  higher  temperature  it 
evolves  oxygen,  and  is  reduced  :  it  has  a  feeble  attraction  for  the  acids,  but 
combines  with  many  salifiable  bases,  and  dissolves  in  the  caustic  and  car- 
bonated alkalies.  It  forms  a  fulminating  ammoniacal  compound,  similar  to 
fulminating  gold. 

Protochloride  of  Platinum  (PtCl) When  perch! oride  of  platinum  is 

exposed  in  a  porcelain  capsule  to  a  temperature  not  exceeding  that  of  melt- 
ing tin  (about  400°),  and  stirred  so  long  as  it  evolves  chlorine,  it  is  con- 
verted into  a  gray  powder,  insoluble  in  water,  and  not  decomposed  by  sul- 
phuric or  nitric  acid,  but  soluble  in  boiling  hydrochloric  acid.  This  is  the 
protochloride  of  platinum.  It  forms  crystallizable  double  salts  with  the  alka- 
line chlorides.  It  is  decomposed  at  a  red  heat,  leaving  a  residue  of  metallic 
platinum. 

Bichloride  of  Platinum;  Perchloride  of  Platinum  (PtClg). — A  solution 
of  chlorine  has  no  action  on  ordinary  platinum  foil  or  wire,  but  when  in  the 
finely-divided  state  of  sponge  or  as  platinum  black,  chlorine,  especially  by 
the  aid  of  heat,  slowly  combines  with  the  metal  to  form  a  bichloride.  The 
usual  process  for  making  this  salt  consists  in  digesting  fine  platinum  wire  foil  or 
grains  in  one  part  of  nitric  and  three  of  hydrochloric  acid  with  three  parts  of 
water  (to  keep  down  iridium.)  The  solution  is  accelerated  by  heat  and  is 
evaporated  to  two-thirds  of  its  volume  after  saturation  with  platinum.  When 
so  evaporated,  it  affords  a  deep-brown  liquid  which  shoots  into  prismatic  crys- 
tals, consisting  of  hydrated  perchloride  of  platinum  and  hydrochloric  acid  ; 
on  further  evaporation  it  yields  a  brown  saline  mass,  which  becomes  deeper 
colored  upon  the  expulsion  of  its  combined  water.  It  is  then  a  perchloride 
of  platinum,  yielding  a  deep  yellow  solution  in  water,  and  soluble  in  alcohol 
and  in  ether.  If  still  further  heated,  it  loses  all  its  chlorine,  and  metallic 
platinum  remains  as  a  dull  gray  film  which  acquires  a  metallic  lustre  by  bur- 
nishing. It  was  by  this  method  that  earthenware  and  china  were  at  one 
time  platinized.  The  bichloride  of  platinum  combines  with  the  alkaline 
chlorides  forming  an  extensive  class  of  double  salts  known  as  PlatinO' 
chlorides.  More  frequently  the  name  of  the  alkali  is  used  as  a  prefix. 
Among  these  may  be  mentioned  the  compounds  with  potassium,  rubidium, 
coBsium,  ammonium,  and  thallium.  These  are  all  more  or  less  insoluble  in 
water.  The  salts  of  potassium,  rubidium,  caesium  and  ammonium  are  isomor- 
phous  and  crystallize  in  cubes.  The  sodium  salt  is  quite  soluble  in  water 
and  crystallizes  in  prisms. 

The  Ammonio- Bichloride  of  Platinum  (NH^CIH- PtClg)  is  the  yellow 
powder  which  falls  when  solutions  of  bichloride  of  platinum  a"nd  sal-ammoniac 
are  mixed.  When  exposed  to  heat,  it  loses  a  little  water,  and  at  a  red  heat 
it  evolves  nitrogen,  hydrochloric  acid,  and  sal-ammoniac,  without  undergoing 
fusion,  and  the  platinum  remains  in  the  peculiar  state  known  as  spongy  or 
reduced  platinum.  It  requires  150  parts  of  water  at  60^^  and  80  parts  of 
boiling  water  to  dissolve  one  part  of  this  salt.  This  ammonio-chloride  is 
insoluble  in  alcohol  and  in  cold  hydrochloric  acid,  but  it  falls  as  a  crystalline 
powder  from  its  solution  in  hot  hydrochloric  acid.  It  is  almost  entirely  in- 
soluble in  solution  of  sal-ammoniac. 

The  action  of  ammonia  ow  the  two  chlorides  of  platinum  gives  rise  to  a 
series  of  compound  bases  which  have  much  theoretical,  but  little  practical  in- 
terest, and  which  have  hitherto  been  only  imperfectly  examined  as  to  pro- 


524  SALTS    OF    PLATINUM. 

perties  and  preparation.     Any  condensed  notice  of  these,  compatible  with 
the  limits  of  this  work,  would  be  useless  to  the  student. 

Potassio- Bichloride  of  Platinum  (KC],PtCl2)  — This  is  thrown  down  in  the 
form  of  a  yellow  powder,  when  concentrated  solutions  of  chloride  of  potassium 
and  of  bichloride  of  platinum  are  mixed.  It  is  soluble  in  108  parts  of  water  at 
60°  and  in  19  parts  of  boiling  water,  and  is  deposited  from  its  boiling  solu- 
tion in  small  octahedral  crystals.  It  is  insoluble  in  alcohol.  The  difficult 
solubility  of  this  compound  renders  bichloride  of  platinum  a  useful  test  of 
the  presence  of  the  salts  of  potassa,  as  well  as  of  the  salts  of  rubidium  and 
caesium.  The  platino-chlorides  of  these  two  metals,  however,  are  much  less 
sohible  than  the  platino-chloride  of  potassium  :  hence  a  solution  of  the  latter 
gives  a  dense  yellow  precipitate  in  a  salt  of  caesium  or  rubidium.  Sodio- 
Bichloride  of  Platinum  (NaCbPtCl^). — Chloride  of  sodium  occasions  no 
precipitate  with  bichloride  of  platinum,  but  the  mixed  solutions  yield  on 
evaporation  prismatic  crystals,  of  a  deep  orange  color,  soluble  in  water  and 
in  alcohol,  and  which,  when  heated,  lose  6  atoms  of  water  of  crystallization, 
leaving  the  anhydrous  double  salt.  A  variety  of  other  analogous  double 
salts  have  been  described  ;  they  are  generally  made  by  mixing  the  two 
chlorides  in  atomic  proportions.  The  Bihromide  and  Biniodide  of  platinum 
are  sparingly  soluble  in  water,  and  are  obtained  by  the  decomposition  of  the 
bichloride,  by  bromide  and  iodide  of  potassium. 

Protosulphide  of  Platinum  (PtS)  may  be  formed  by  heating  finely- 
divided  platinum  with  sulphur,  or  by  the  decomposition  of  protochloride  of 
platinum  by  sulphuretted  hydrogen.  It  is  a  gray  or  black  powder,  unaltered 
by  air  or  water,  scarcely  attacked  by  the  boiling  acids,  but  decomposed  when 
heated  in  the  air.  Bisulphide  of  Platinum  (PtSj  falls  in  the  form  of  a 
brownish  powder,  when  the  sodio-bichloride  of  platinum  is  precipitated  by 
sulphuretted  hydrogen  :  at  a  red  heat  it  is  decomposed,  and  leaves  metallic 
platinum. 

Protosulphate  of  Platinum  (PtOjSOa)  is  obtained  when  a  solution  of 
protoxide  of  platinum  in  caustic  potassa  is  saturated  with  sulphuric  acid,  the 
liquid  poured  off,  and  the  precipitate  dissolved  in  diluted  sulphuric  acid  ; 
the  concentrated  solution  is  black  ;  diluted  with  water  it  becomes  red,  and 
passes  into  persulphate.  Persidphate  of  Platinum  (Pt03,2S03)  is  obtained 
hy  acidifying  the  sulphur  of  the  sulphides  of  platinum  by  nitric  acid.  It  is 
deep  brown,  and  soluble  in  water,  alcohol,  and  ether;  with  soda,  potassa, 
and  ammonia,  it  forms  double  salts. 

Cyanide  of  Platinum  forms  a  series  of  double  cyanides,  some  of  which  are 
extremely  beautiful.  The  platino-cyanide  of  potassium  (KCy,PtCy)  or 
(K,PtCy2)  formed  by  dissolving  protochloride  of  platinum  in  a  solution  of 
cyanide  of  potassium,  forms  prismatic  crystals,  yellow  by  transmitted,  and 
blue  by  reflected  light.  They  contain  3  atoms  of  water.  The  platino- 
cyanide  of  magnesium  forms  crystals  which  exhibit  various  shades  of  red, 
blue,  and  green  (p.  33).  When  chlorine  is  passed  through  a  solution  of  the 
platino-cyanide  of  potassium,  crystals  are  deposited  which  are  green  by  trans- 
mitted light,  but  of  a  copper  color  by  reflected  light.  This  salt,  termed 
sesquiplatino-cyanide  of  potassium,  has  the  formula  (K3,Pt2Cy3,6Aq). 

Alloys  of  Platinum. — Iron  and  platinum  in  equal  parts  form  a  crystal- 
line alloy,  which  takes  a  fine  polish.  Platinum  dissolves  in  fused  zinc  ;  the 
alloy  is  bluish-white,  brittle,  and  hard.  Zinc  heated  in  Diatinum-foil  before 
the  blowpipe  burns  vividly  and  even  with  explosion.  Tin  and  platinum 
form  alloys  more  or  less  brittle  and  fusible.  When  tin-foil  and  platinum  are 
wrapped  together  and  heated  by  the  blowpipe,  they  combine  with  incan- 
descence. With  its  weight  of  nickel  platinum  forms  a  pale  yellow  alloy, 
susceptible  of  a  high  polish.     Copper  and  platinum  form  alloys,  the  ductility 


TESTS    FOR    THE    SALTS    OF    PLATINUM,  525 

and  color  of  which  vary  with  the  proportions  :  platinum  easily  destroys  the 
color  of  copper  :  an  alloy  of  1  platinum,  16  copper,  1  zinc,  resembles  gold 
in  color.  Lead  and  platinum  form  brittle  alloys.  Platinum  and  lead-foil 
folded  together  and  heated  before  the  blowpipe,  combine  with  elevation  of 
temperature.  Antimony  and  platinum  readily  enter  into  ignition  in  the 
flame  of  a  spirit  lamp  when  they  combine,  in  the  same  manner  as  tin  and 
zinc.  Arsenic  and  platinum  form  a  dark-gray  brittle  alloy.  When  particles 
of  arsenic  are  placed  upon  red  hot  platinum-leaf,  they  immediately  fuse  a  hole 
in  it.  Mercury  amalgamates  difficultly  with  platinum  :  spongy  platinum 
forms  the  readiest  combination,  especially  when  rubbed  with  the  mercury  in 
a  hot  mortar.  Silver  and  platinum  form  ductile  alloys.  Gold^w^  platinum 
require  a  strong  heat  for  combination,  and  the  color  of  the  gold  is  greatly 
deteriorated. 

The  perfection  with  which  vessels  of  platinum  resist  the  action  of  heat, 
and  of  most  acids,  renders  them  peculiarly  valuable  in  many  of  their  applica- 
tions ;  but  its  high  price  is  against  its  general  adoption.  In  the  employ- 
ment of  platinum-vessels,  the  following  precautions  must  be  attended  to  :  1. 
They  must  not  be  subjected  to  the  action  of  compounds  which  evolve  chlo- 
rine. 2.  Nitre,  and  the  alkalies,  must  not  be  fused  in  them.  3.  No  metallic 
reductions  must  be  performed  in  them  ;  nor  compounds  of  phosphorus  de- 
composed, so  as  to  evolve  that  substance.  4.  When  metallic  oxides  are 
heated  in  a  platinum  crucible,  the  heat  must  not  be  raised  to  redness  if  the 
oxide  is  easily  decomposed.  5.  The  immediate  contact  of  the  fuel  (charcoal 
should  always  be  used)  with  the  crucible  should  be  avoided,  especially  at 
very  high  temperatures ;  for  by  combining  with  silicon  platinum  is  rendered 
brittle  and  unsound. 

Tests  for  the  Salts  of  Platinum. — The  color  and  the  difficult  solubility 
of  the  ammonio  and  potassio-chlorides  of  platinum,  and  the  solubility  of  the 
corresponding  soda-compound,  are  very  characteristic  of  this  metal.  All  the 
metals  which  reduce  the  chloride  of  gold,  with  the  exception  of  palladium, 
act  similarly  upon  chloride  of  platinum,  but  its  complete  separation  in  the 
metallic  state  is  slow  :  iron,  zinc,  cadmium,  and  copper,  are  its  most  eGfective 
precipitants  ;  they  separate  it  as  a  black  powder,  which  sometimes  adheres  in 
films  to  the  glass.  Protosulphate  of  iron,  tincture  of  galls,  oxalic,  sulphur- 
ous, and  arsenious  acids  occasion  no  precipitates  in  a  solution  of  perchloride 
of  platinum,  a  circumstance  which  distinguishes  this  metal  from  gold,  silver, 
and  palladium. 

A  solution  of  a  salt  of  platinum  has  the  following  special  characters:  1. 
Potash  and  ammonia  throw  down  yellow  precipitates.  2.  The  Chlorides  of 
potassium  and  ammonium  also  throw  down  yellow  precipitates  (platino-chlo- 
rides).  3.  The  solution  evaporated  to  dryness,  and  heated,  yields  metallic 
platinum. 

The  chloride  of  ammonium  from  the  insolubility  of  the  platino-chloride 
formed,  has  been  usually  selected  as  the  test  for  this  metal,  the  precipitation 
being  aided  by  the  addition  of  a  little  alcohol  or  diluted  hydrochloric  acid. 
The  discovery  of  the  salts  of  thallium,  however,  by  Dr.  Crookes  has  made 
known  a  still  more  delicate  test  for  the  compounds  of  platinum.  A  solution 
of  nitrate  of  thallium  will  throw  down  a  platino-chloride  of  that  metal,  in  a 
solution  in  which  chloride  of  ammonium  produces  no  change.  The  platino- 
cliloride  of  thallium  requires  15,585  parts  of  water  to  dissolve  it. 

In  a  mixture  of  gold  and  platinum,  the  gold  may  be  precipitated  and  sepa- 
tated  by  boiling  the  solution  with  sulphate  of  iron  or  arsenious  acid,  or  the 
platinum  may  be  precipitated  by  chloride  of  ammonium  or  nitrate  of  thallium, 
rreshly-precipitated  guaiacum  resin,  when  added  to  a  solution  of  gold,  .pro- 


526  SALTS    OF    PALLADIUM. 

duces  a  greenish-blue  color;  with  chloride  of  platinum  it  produces  no  parti- 
cular effect.  On  boiling  the  solutions  the  gold  is  completely  reduced  and 
deposited,  but  the  platinum  solution  remains  unchanged.  The  salts  of  plati- 
num, unlike  those  of  gold  and  silver,  are  not  affected  by  light. 


CHAPTER    XLI. 

PALLADIUM.     RHODIUM.     RUTHENIUM.     OSMIUM,     IRIDIUM. 
Palladium  (Pd=54). 

Palladium  was  discovered  by  Wollaston  in  1803  :  it  is  associated  with 
the  other  metals  mentioned  in  the  last  section  as  constituting  the  ore  of  pla- 
tinum.    It  has  also  been  found  alloyed  with  gold. 

Palladium  is  separated  from  the  ore  of  platinum  by  the  following  process. 
Digest  the  ore  in  nitrohydrochloric  acid,  neutralize  the  redundant  acid  by 
soda,  throw  down  the  platinum  by  sal-ammoniac,  and  filter :  to  the  filtered 
liquor  add  a  solution  of  cyanide  of  mercury  :  a  yellow  flocculent  precipitate 
of  cyanide  of  palladium  is  soon  deposited,  which  yields  palladium  on  expo- 
sure to  heat.  This  metal  has  a  dull-white  color,  is  malleable  and  ductile,  but 
hard.  It  fuses  at  a  temperature  above  that  required  for  the  fusion  of  gold, 
and  when  intensely  heated  by  the  oxyhydrogen  blowpipe,  it  is  dissipated  in 
sparks.  When  heated  over  the  flame  of  a  spirit-lamp,  it  acquires  various 
shades  of  blue  upon  its  surface,  in  consequence  of  superficial  oxidation.  It 
is  acted  on  by  the  greater  number  of  the  acids  when  aided  by  heat,  and  also 
by  potassa  and  nitre  :  it  has  a  strong  affinity  for  cyanogen. 

Protoxide  of  Palladium  (PdO). — This  oxide  is  the  base  of  the  salts  of 
the  metal.  Thus,  when  nitrate  of  palladium  is  precipitated  by  an  alkali,  the 
red  or  dark-orange  powder  which  falls  is  a  hydrated  oxide.  In  this  state,  it 
is  soluble  in  acids,  yielding  red  and  brown  salts  of  an  astringent  taste.  It 
becomes  black  and  anhydrous  at  a  dull  red  heat.  Binoxide  of  Palladium 
(PdOg)  is  obtained  as  a  brown  hydrate,  by  the  action  of  a  solution  of  potassa 
on  the  potassio-chloride  of  palladium. 

Protochloride  op  Palladium  (PdCl)  is  obtained  by  digesting  palladium 
in  hydrochloric  acid  with  a  little  nitric  acid,  and  evaporating  to  dryness  :  it 
forms  a  brown  powder,  which  is  nearly  black  when  anhydrous.  It  forms 
double  salts  with  the  basic  metallic  chlorides,  which  are  soluble  in  water  and 
in  alcohol.  With  ammonia  it  forms  a  series  of  compounds  resembling  those 
of  platinum.  Bichloride  of  Palladium  ;  Perchloride  of  Palladium 
(PdCy  is  only  known  in  solution.  It  forms  red  double  salts  with  the  alka- 
line chlorides. 

Nitrate  of  Palladium. — Palladium,  when  aided  by  heat,  dissolves  slowly 
in  nitric  acid,  forming  a  brown  solution  which  leaves  a  brown  subnitrate  on 
evaporation.  Nitrate  of  protoxide  of  palladium  forms  a  double  salt  with 
ammonia. 

Sulphide  of  Palladium  (PdS)  is  formed  by  .fusing  sulphur  with  palla- 
dium ;  it  is  white,  hard,  and  fusible,  and  when  long  exposed  to  heat  and  air, 
it  loses  its  sulphur.  It  is  thrown  down  in  the  form  of  a  black  powder  by 
the  action  of  sulphuretted  hydrogen  upon  the  salts  palladium. 

Protosulphate  of  Palladium  (PdO,S03)  is  obtained  by  boiling  the  pro- 
tonitrate  to  dryness  with  sulphuric  acid ;  or  by  boiling  the  metal  in  sulphuric 


SALTS    OF    RHODIUM.  52Y 

acid,  when  sulphurous  acid  is  evolved,  and  a  brown  solution  is  obtained, 
which  deposits  the  sulphate  in  red  crystals.  This  salt,  dissolved  in  aqueous 
ammonia,  yields  two  ammonio-sulphates  =:NH3,PdO,S03  and  2(NH3,)PdO, 
SO,. 

Carbide  of  Palladium. — Palladium  acquires  brittleness  when  fused  in 
contact  with  charcoal.  When  a  plate  of  palladium  is  long  held  in  the  flame 
of  alcohol,  carbonaceous  excrescences  gradually  form  upon  it,  which,  when 
burned,  leave  palladium.  This  property  of  precipitating  charcoal  from  flame, 
and  combining  with  it,  is  peculiar  to  palladium  ;  platinum  and  iron  only  show- 
slight  indications  of  it. 

Cyanide  of  Palladium  (PdCy)  is  formed  when  a  solution  of  cyanide  of 
mercury  is  added  to  a  neutral  solution  of  palladium:  it  falls  in  olive-colored 
or  dingy  yellow  flakes;  this  furnishes  a  method  of  separating  palladium  from 
other  metals  which  are  incapable  of  decomposing  the  cyanide  of  mercury. 
It  dissolves  in  cyanide  of  potassium,  and  forms  palladio-cyanide  of  potassium. 
There  is  also  a  corresponding  ammoniacal  salt. 

Tests  for  the  Salts  of  Palladium. — The  fixed  alkalies  throw  down  red 
or  orange  precipitates  from  the  solutions  of  palladium,  sparingly  soluble  in 
excess  of  the  alkali.  Ferrocyanide  of  potassium  gives  an  olive-green  preci- 
pitate ;  and  sulphuretted  hydrogen  one  of  a  dark-brown  color.  Protochloride 
of  tin  occasions  a  brown  precipitate  in  the  neutralized  solutions  of  palladium; 
when  dilute,  the  mixture  becomes  green.  Protosulphate  of  iron  throws  down 
metallic  palladium.  Cyanide  of  mercury  forms  a  precipitate  in  all  the  salts 
of  palladium,  when  the  acid  is  not  in  excess.  Iodide  of  potassium  occasions 
a  black  precipitate  of  iodide  of  palladium  in  very  diluted  solutions.  Chloride 
of  palladium  added  to  a  solution  of  1  part  of  iodide  of  potassium  in  400,000 
of  water  produces  a  brown  tint.  It  is  therefore  a  delicate  test  for  an  alkaline 
iodide. 

As  the  iodide  of  palladium  is  slightly  soluble  in  iodide  of  potassium  the 
latter  must  not  be  in  excess.  Chloride  of  palladium  is  not  only  a  delicate 
test  for  an  alkaline-iodide,  but  it  enables  the  chemist  to  separate  iodide  from 
chlorine  and  bromine.  The  palladium  salt  gives  no  precipitate  in  solutions 
of  an  alkaline-chloride  or  bromide  unless  in  the  latter  case  the  solution  is 
very  concentrated. 

Rhodium  (R=52). 

After  the  platinum  and  palladium  have  been  separated  from  the  nitrohy- 
drochloric  solution  of  the  crude  ore,  by  sal-ammoniac  and  cyanide  of  mercury, 
and  any  excess  of  the  cyanide  has  been  decomposed  by  the  addition  of  hydro- 
chloric acid,  chloride  of  sodium  is  added,  and  the  liquor  evaporated  to  dry- 
ness, the  residue  is  then  digested  in  alcohol,  which  leaves  a  red  insoluble 
double  chloride  of  sodium  and  rhodium.  When  this  is  dissolved  in  water, 
and  a  plate  of  zinc  immersed,  metallic  rhodium  is  thrown  down  ;  or  the 
double  chloride  may  be  at  once  decomposed  by  heating  it  in  a  current  of 
hydrogen.  Rhodium,  discovered  by  Wollaston  in  1108,  is  a  white  metal 
very  difficult  of  fusion,  and  extremely  hard  and  brittle.  When  pure,  the 
acids  do  not  dissolve  it,  but  they  act  upon  several  of  its  alloys.  It  may  be 
oxidized  by  ignition  either  with  nitre  or  with  bisulphate  of  potassa,  and, 
when  heated  with  the  latter,  a  double  sulphate  of  peroxide  of  rhodium  and 
potassa  is  produced.  It  may  be  oxidized  by  the  joint  action  of  heat  and  air, 
but  the  protoxide  =R0,  has  not  been  examined  in  an  isolated  state.  The 
salifiable  oxide  is  R^Og. 

Sesquioxide  of  Rhodium  (RaOg). — This  oxide  is  obtained  by  heating 
finely-divided  rhodium  with  caustic  potassa  and  a  little  nitre  to  redness  in  a 


S9^  COMPOUNDS    OF    RUTHENIUM    AND    OSMIUM. 

silver  crucible,  washing  the  product,  and  digesting  it  in  hydrochloric  acid  : 
a  greenish-gray  hydrated  oxide  remains,  which  is  insoluble  in  acids. 

Protochloride  of  RhodiUxM  (RCl)  is- obtained  by  passing  dry  chlorine 
over  heated  protosulphide  of  rhodium  :  it  is  reduced  when  heated  in  hy- 
drogen. 

Sesquichloride  of  Rhodium  (R^Clg)  is  obtained  by  adding  fluosilicic 
acid  to  an  aqueous  solution  of  rhodiochloride  of  potassium,  filtering,  evapo- 
rating, dissolving  the  residue  in  water,  and  evaporating  again  with  the  addi- 
tion* of  hydrochloric  acid.  This  is  a  dark-brown  compound,  which  deli- 
quesces on  exposure  to  air,  and  forms  a  red  solution  with  water,  and  with 
alcohol.  This  chloride  combines  with  many  other  chlorides  to  form  double 
salts  {Rhodiochlorides),  which  are  of  a  red  color :  hence  the  name  of  the 
metal. 

Rhodiochloride  OP  Ammonium;  Ammonio-sesquichloride  of  Rhodium 
(2(NH^Cl)R2Cl3),  is  obtained  by  evaporating  a  mixed  solution  of  chloride 
of  rhodium  and  sal-ammoniac  :  it  forms  brilliant  garnet-colored  prisms, 
which,  when  decomposed  by  heat,  leave  31  per  cent,  rhodium. 

Protosulphide  of  Rhodium  (RS)  is  obtained  by  heating  the  ammonio- 
chloride  with  sulphur  :  when  heated  in  the  air  it  leaves  spongy  rhodium. 

Sesquichloride  OF  Rhodium  (Rj^Sg)  is  thrown  down  in  the  form  of  a 
brown  hydrate,  by  adding  hydrosulphate  of  ammonia  to  a  hot  solution  of 
rhodio-chloride  of  sodium. 

Characters  of  the  Salts  of  Rhodium. — The  salts  of  the  sesquioxide 
are  mostly  red ;  they  are  reducible  by  hydrogen  and  by  zinc  ;  sulphuretted 
hydrogen  occasions  a  brown,  and  ammonia  a  yellow,  precipitate  in  them.  A 
hydrated  oxide  of  rhodium,  of  a  red-brown  color,  is  thrown  down  by  lime- 
water  from  a  solution  of  the  sesquichloride  of  rhodium  in  hydrochloric  acid. 

Ruthenium  (Ru=62). 

This  is  one  of  the  raetals  remaining  in  that  portion  of  the  ore  of  platinum 
which  resists  the  reaction  of  aqua  regia  :  it  has  been  imperfectly  examined, 
but  is  stated  to  be  hard,  brittle,  infusible  in  the  oxyhydrogen  flame,  but 
readily  oxidized  by  fusion  with  nitre,  and  furnishing  four  oxides.  Of  these, 
the  peroxide,  or  Ruthenic  acid  (RuOg),  is  produced  when  the  other  oxides 
are  heated  with  nitre.  The  sesquioxide  (Ru^Og)  is  obtained  by  heating  the 
metal  in  the  air  :  it  forms  soluble  yellow  salts  with  the  acids,  from  which  the 
alkalies  throw  it  down  in  the  form  of  a  brown  hydrate. 

When  a  solution  of  sesquichloride  of  ruthenium  is  decomposed  by  sulphu- 
retted hydrogen,  a  brown  sulphide  falls,  and  the  supernatant  liquid  retains  a 
protochloride  in  solution,  and  is  of  a  bright  blue  color  :  this  is  the  most 
marked  character  of  the  metal. 

Osmium  (Os=100). 

Osmium  and  iridium,  discovered  by  Tennant  in  1803,  are  also  contained 
in  the  residue  of  the  action  of  nitrohydrochloric  acid  upon  the  ore  of  plati- 
num. This  residue,  when  fused  with  potassa  and  washed,  furnishes  a  yellow 
alkaline  solution  of  oxide  of  osmium,  which,  when  saturated  by  sulphuric 
acid  and  distilled,  yields  a  colorless  solution  of  this  oxide,  from  which  almost 
all  the  other  metals  thfow  down  metallic  osmium.  When  thus  obtained  by 
precipitation,  osmium  is  in  the  form  of  a  black  powder,  which  acquires  a 
metallic  lustre  by  friction.  Osmium  is  the  heaviest  of  all  known  metals ;  its 
specific  gravity  being  21-4.  Lithium,  also  a  metal,  occupies  the  other  end 
of  the  scale  ;  its  sp.  gr.  being  059,  thus  showing  that  in  equal  bulks  osmium 
is  36  times  as  heavy  as  the  lightest  metal.     Osmium  has  not  yet  been  melted. 


COMPOUNDS    OF    OSMIUM.  529 

When  heated  in  the  air  osmium  burns  into  an  oxide,  and  exhales  poison- 
ous fumes  having  a  peculiar  odor,  somewhat  like  that  of  chlorine ;  hence  the 
name  of  the  metal  (from  6(T;u?J,  odor),  and  most  of  its  compounds  may  be  re- 
cognized by  exhaling  this  odor  when  heated  with  a  little  carbonate  of  soda 
before  the  blowpipe.     It  forms  five  oxides. 

Protoxide  of  Osmium  (OsO)  is  obtained  by  the  action  of  pure  alkalies  on 
the  protochloride  :  it  falls  in  the  forms  of  a  nearly  black  hydrate,  obstinately 
retaining  a  portion  of  alkali ;  it  dissolves  slowly  in  the  acids,  forming  deep- 
green  or  greenish  brown  solutions.  Sesquioxide  of  Osmium  (Os^Og)  has 
not  been  isolated,  but  is  produced  when  the  peroxide  is  heated  with  excess 
of  ammonia.  Binoxide  of  Osmium  (OsOy). — When  a  solution  of  bichloride 
of  osmium  is  heated  with  carbonate  of  soda,  the  binoxide  falls  in  the  form  of 
a  dark  gray  powder.  Teroxide  of  Osmium  (OsOg)  is  assumed  to  exist  in 
certain  salts  of  this  metal,  but  it  has  not  been  isolated.  It  has  the  proper- 
ties of  a  weak  acid.  * 

Peroxide  of  Osmium  ;  Osmic  Acid  (OsOJ  is  the  volatile  oxide  above 
adverted  to,  and  is  obtained  by  the  combustion  of  the  metal  in  oxygen,  by 
the  action  of  boiling  nitric  acid,  or  by  the  fusion  of  osmium  with  nitre  or 
with  potassa.  When  osmium  is  heated,  and  a  current  of  oxygen  passed 
over  it,  yellowish  crystals  of  the  anhydrous  peroxide  are  formed :  these  dis- 
solve slowly  in  water,  and  readily  in  alcohol  and  ether  ;  the  solutions  stain  the 
skin  black,  and  gradually  deposit  metallic  osmium.  It  is  reduced  by  sulphu- 
retted hydrogen,  and  sulphide  of  osmium  is  formed.  It  has  no  acid  reaction, 
but  it  combines  with  alkalies,  and  forms  compounds  which  are  permanent  at 
high  temperatures.  When  infusion  of  galls  is  dropped  into  its  aqueous 
solution,  a  characteristic  blue  color  is  produced. 

Chlorides  of  Osmium  — Four  chlorides  of  this  metal  have  been  described. 
When  chlorine  is  transmitted  over  heated  osmium,  a  dark  green  sublimate 
of  protochloride  of  osmium  \^  i\iQ  result.  This  is  succeeded  by  a  red  subli- 
mate, which  is  the  bichloride.  The  sesquichloride  and  perchloride  have  not 
been  obtained  in  a  separate  state,  but  form  double  salts  with  chloride  of 
potassium. 

Sulphides  of  Osmium. — Sulphur  and  osmium  apparently  combine  in 
several  proportions,  for  sulphuretted  hydrogen  precipitates  it  from  all  its 
solutions. 

The  remaining  compounds  of  this  remarkable  metal  have  not  been  minutely 
examined,  but  the  characters  of  its  salts  will  be  sufficiently  obvious  from  the 
preceding  statements. 

Iridium  (Ir=99). 

Iridium  is  found  associated  with  platinum  and  gold.  It  gives  great  hardi- 
ness to  both  metals,  and  its  presence  (alloyed  with  osmium)  in  Californtia  gold 
coined  at  the  United  States  Mint  is  said  to  have  caused  the  destruction  of 
some  valuable  dies,  and  this  led  to  its  detection  and  removal. 

The  alloy  of  Iridium  and  Osmium  remaining  after  the  ore  of  platinum  has 
been  digested  in  aqua  regia,  may  be  decomposed  by  fusing  it  with  chloride 
of  sodium,  and  passing  chlorine  over  the  mixture,  in  a  tube  heated  to  dull 
redness ;  the  resulting  product  is  then  digested  in  boiling  water,  and  the 
filtered  solution  concentrated,  mixed  with  nitric  acid,  and  distilled ;  osmic 
acid  passes  over,  and  iridio- chloride  of  sodium  remains,  which,  by  the  addi- 
tion of  sal-ammoniac,  yields  a  precipitate  of  iridio-chloride  of  ammonium : 
this  double  salt  is  decomposed  by  heat,  and  metallic  iridium  remains. 

Iridium  is  a  hard,  white,  brittle  metal,  extremely  difficult  of  fusion.  It  is 
not  acted  upon  by  acids,  but  its  alloy  with  platinum  is  soluble  in  aqua  regia^. 
34 


530  COMPOUNDS    OF    IRIDIUM. 

and  it  is  oxidized  when  fused  with  nitre.  When  in  a  very  finely-divided 
state,  it  has  properties  resembling  those  of  platinum  black. 

Oxides  of  Iridium. — There  are  three  oxides  of  this  metal,  the  solutions 
of  which  are  of  various  colors  :  hence  the  name  Iridium  (from  Iris,  the  rain- 
bow) applied  to  it.  The  protoxide  is  thrown  down  by  the  action  of  potassa 
on  the  protochloride,  in  the  form  of  a  black  powder,  nearly  insoluble  in  acids, 
but  yielding,  with  potassa,  a  blue  or  purple  solution.  The  sesquioxide  is 
formed  by  fusing  iridium  with  nitre.  In  its  hydrated  state,  it  is  soluble  in 
hydrochloric  acid,  giving  a  blue  solution,  which  becomes  green,  and  brown 
when  heated.  The  hinoxide  falls  as  a  blue  hydrate,  when  a  solution  of  bi- 
chloride of  iridium  is  boiled  with  potassa. 

Chlorides  of  Iridium. — ^\\%  protochloride  h  formed  by  heated  iridium  in 
chlorine  :  it  is  of  a  dark  olive  color,  and  forms  double  salts  with  the  alkaline 
chlorides.  The  sesquichloride,  formed  by  dissolving  the  sesquioxide  in 
hydrochloric  acid,  also  produces  double  salts.  The  bichloride  also  forms 
double  salts  with  other  chlorides,  many  of  which  resemble  the  corresponding 
platinum  compounds.  The  iridio-bi chloride  of  ammonium  is  remarkable  for 
the  intense  brownish-red  color  of  its  solution  :  it  is  said  to  communicate  a 
decided  tint  to  40,000  parts  of  water. 

Alloys  of  Iridium. — The  greater  number  of  these  alloys,  when  digested 
in  nitric  acid,  leave  iridium ;  but  nitrohydrochloric  acid  dissolves  them  when 
the  proportion  of  iridium  is  not  considerable.  The  native  alloy  of  iridium 
and  osmium  forms  small  crystals  of  much  lustre,  harder  than  steel,  and  as 
refractory  as  iridium.  It  has  lately  been  found  in  Canada.  A  fused  alloy 
of  platinum  and  iridium  has  been  employed  by  Messrs.  Johnson  and  Matthey 
for  making  the  touchholes  for  cannon.  One  of  these,  used  in  a  Whitworth 
gun  for  more  than  3000  rounds,  showed  scarcely  any  signs  of  wear.  The 
hardness  and  durability,  as  well  as  infusibility  of  this  alloy,  render  it  better 
fitted  for  vent-pieces  than  any  other  metal  or  metallic  alloy. 

In  consequence  of  the  difficult  fusibility  of  iridium,  and  of  the  native  alloy, 
grains  of  it  are  sometimes  diffused  through  ingots  of  gold,  and  remain  after 
a  number  of  successive  fusions.  In  coined  gold  moneys,  it  occasionally  hap- 
pens that  one  or  more  of  these  grains  may  be  discerned  ;  and  where  large 
quantities  of  gold  are  melted,  they  sink  to  the  bottom  of  the  crucible,  so  that 
dn  great  gold  coinages  at  the  Mint,  it  has  occasionally  happened  that  several 
-ounces  of  the  ore  of  iridium  have  been  thus  accumulated. 

There  are  some  peculiarities  belonging  to  the  six  preceding  metals — 
namely,  platinum  and  its  associates — which  deserve  notice,  in  reference  to 
•their  atomic  weights  and  their  specific  gravities,  and  which  have  led  to  their 
^division  into  two  groups  of  three  each,  as  follows  : — 


Sp.  Gr. 

Atom.  Wt. 

Sp.  Gr. 

Atom.  Wt. 

Platannm  . 

.     21-15 

99 

Palladium  . 

.     11-8 

54 

Iridium     . 

.     21-15 

99 

Rhodium    . 

.     12-0 

52 

Osmium    . 

.     21-40 

100 

Ruthenium 

.     11-3 

52 

It  will  be  observed  that  the  specific  gravities  and  atomic  weights  of  the 
'first  group  are  almost  identical ;  so  also  are  those  of  the  second  group,  the 
specific  gravities  and  atomic  weights  of  which  are  almost  precisely  one-half 
of  those  of  the  first  group. 


QUALITATIVE    ANALYSIS    OF    METALLIC    COMPOUNDS.  531 


CHAPTEH    XLIT. 

QUALITATIVE    ANALYSIS    OF    THE    COMPOUNDS    OF    THE 
PRECEDING    METALS. 

In  giving  a  summary  of  the  methods  of  detecting  the  salts  of  the  metals, 
not  included  in  the  28th  chapter,  we  propose  making  a  selection  of  those 
which  are  more  likely  to  fall  in  the  way  of  a  student.  They  may  be  repre- 
sented by  the  following  eighteen  bodies  :  iron,  manganese,  zinc,  tin,  cadmium, 
lead,  copper,  bismuth,  cobalt,  nickel,  chromium,  uranium,  antimony,  arsenic, 
mercury,  silver,  gold,  and  platinum.  They  are  here  given  in  the  order  in 
which  they  have  been  treated  in  this  volume.  Referring  in  this  place  to  the 
solutions  of  their  salts,  and  to  those  compounds  which  are  soluble,  we  may 
observe  that  many  may  be  at  once  recognized  by  their  peculiar  colors,  even 
when  the  liquids  are  much  diluted.  These  are  the  salts  of  iron,  manganese, 
copper,  cobalt,  nickel,  chromium,  uranium,  gold,  and  platinum. 

The  reagents  which  may  be  selected  for  the  qualitative  analysis  of  these 
metals  are,  sulphuretted  hydrogen,  hydrosulphate  of  ammonia,  iodide  of  po- 
tassium, hydrochloric  acid,  ammonia,  and  ferrocyanide  of  potassium. 

Among  the  general  reagents  employed  in  the  analysis  of  metals,  there  is 
none  so  useful  as  sulphuretted  hydrogen.  The  gas  should  be  washed,  and 
passed  in  a  current  into  the  suspected  liquid,  previously  acidulated  with 
hydrochloric  acid.  It  produces  in  the  liquid  either  a  change  of  color  or  a 
colored  precipitate  (sulphide),  which  may  be  then  easily  identified  by  certain 
special  characters. 

The  following  metallic  oxides  are  precipitated  as  sulphides  from  their  solu- 
tions, of  the  colors  mentioned  below. 

Yellow.  Orange  red. 


AsOg  CdO  SbOg 

AsOj  SnOg  SbOg 

Arsenious  acid  is  precipitated  of  a  golden-yellow  color,  immediately ; 
arsenic  acid  of  a  paler  yellow  color,  slowly ;  oxide  of  cadmium  is  thrown 
down  of  a  sulphur-yellow  color ;  and  a  peroxide  of  tin  of  a  yellowish-brown 
color.  The  two  arsenical  sulphides  are  recognized  by  their  entire  solubility 
in  ammonia,  or  in  its  hydrosulphate,  as  well  as  in  a  solution  of  potassa ;  and 
by  their  insolubility  in  strong  hydrochloric  acid.  The  sulphide  of  cadmium 
is  insoluble  in  ammonia,  potassa,  and  hydrosulphate  of  ammonia,  but  is  dis- 
solved readily  by  strong  hydrochloric  acid.  The  sulphide  of  tin  is  not  soluble 
in  ammonia,  but  is  dissolved  by  the  hydrosulphate,  and  by  hydrochloric  acid. 
The  hydrosulphate  of  ammonia  may  be  at  once  employed  to  divide  the  four 
oxides,  which  produce  yellow  sulphides,  into  two  groups.  For  this  purpose 
no  hydrochloric  acid  should  be  added  to  the  suspected  liquids.  The  hydro- 
sulphate produces  no  precipitate  in  solutions  of  arsenious  and  arsenic  acids, 
but  it  precipitates  at  once  the  oxide  of  cadmium,  and  peroxide  of  tin.  The 
sulphide  of  tin  is  distinguished  from  that  of  cadmium,  not  only  by  a  striking 
difference  of  color,  but  by  the  fact  that  it  is  quite  soluble  in  an  excess  of  the 
hydrosulphate,  while  the  sulphide  of  cadmium  is  insoluble  in  that  liquid. 
The  means  of  distinguishing  arsenious  from  arsenic  acid  have  been  elsewhere 


532  QUALITATIVE    ANALYSIS    OF    METALLIC    COMPOUNDS. 

fully  explained  (pages  416,  ill).  An  orange-red  precipitate  is  peculiar  to 
antimony,  whether  the  oxide  is  combined  with  a  mineral  or  a  vegetable  acid. 
The  precipitated  sulphide  is  insoluble  in  ammonia.  The  antimonial  com- 
pounds are  similarly  precipitated  by  hydrosulphate  of  ammonia,  the  orange- 
red  sulphide  being  soluble  in  an  excess  of  reagent. 

The  acid  solutions  of  the  following  metals  are  precipitated  or  colored  by 
a  current  of  sulphuretted  hydrogen : — 

Precip.  bi-own  or  black  by  Sulphuretted  Hydrogen. 

Hg  0  PbO  SnO 

HggO  CuO  AuOg 

Ag  0  BiOg  PtOg 

The  persalts  of  mercury  are  thrown  down  at  first  of  a  yellowish  color : 
the  precipitate  becomes  black,  only  when  the  sulphuretted  hydrogen  has  been 
passed  into  the  liquid  in  large  excess.  Lead  is  not  readily  precipitated  from 
very  acid  solutions ;  a  solution  of  platinum  is  deepened  in  color  by  the  gas, 
and  only  slowly  precipitated. 

Among  the  metallic  oxides  in  this  list,  a  salt  of  copper  would  be  recog- 
nized by  its  blue  color,  a  compound  of  gold  by  its  rich  yellow,  and  of  pla- 
tinum by  its  red-brown  color.  The  application  of  ammonia,  or  the  ferrocy- 
anide  of  potassium,  would  serve  to  identify  a  cupreous  salt.  {See  Copper, 
page  426.)  A  solution  of  potassa  would  precipitate  platinum,  and  not  gold  ; 
while  a  solution  of  protosulphate  of  iron  would  precipitate  gold  (in  a  metal- 
lic state),  and  would  not  affect  a  solution  of  platinum. 

The  solutions  of  the  remaining  metallic  oxides  are  colorless.  One  of  these 
(bismuth)  may  be  distinguished  by  the  solution  giving  a  white  precipitate 
when  added  to  a  large  quantity  of  distilled  water.  This  precipitate  is  soluble 
in  nitric  acid,  but  it  is  not  dissolved  by  a  solution  of  tartaric  acid.  {See 
Bismuth,  p.  439.) 

The  solutions  of  the  other  metals,  much  diluted,  may  be  treated  with  a 
solution  of  iodide  of  potassium :  they  are  then  precipitated  as  iodides,  of 
the  following  colors  :  Subsalts  of  mercury,  yellow  (insoluble  in  hydrochloric 
acid,  and  in  potassa) ;  persalts  of  mercury,  scarlet  (soluble  in  an  excess  of 
the  reagent)  ;  salts  of  silver,  pale  yellow  (insoluble  in,  but  rendered  white 
by  ammonia)  ;  of  lead,  bright  yellow  (soluble  in  hydrochloric  acid,  and  in 
potassa)  ;  the  salts  of  protoxide  of  tin,  pale  yellow  (soluble  in  hydrochloric 
acid  and  potassa) ;  the  salts  of  bismuth  produce  a  brown  precipitate  soluble 
in  an  excess  of  the  iodide. 

Although  the  solutions  of  copper,  gold,  and  platinum,  have  been  already 
excluded  from  the  group,  by  color  and  their  chemical  properties,  it  may  be 
desirable  to  place  here  the  results  produced  by  the  addition  of  iodide  of 
potassium  to  their  diluted  solutions.  With  a  salt  of  copper,  the  iodide  pro- 
duces a  yellow-brown  precipitate  of  subiodide  of  copper ;  with  gold,  a  yel- 
low-green precipitate,  iodine  being  set  free  ;  and  with  platinum,  a  deep  wine- 
red  colored  liquid,  which,  on  being  heated,  deposits  platinum  in  a  metallic 
state.  The  whole  of  the  metals  in  this  group  are  precipitated  by  hydrosul- 
phate of  ammonia,  as  brown  or  black  sulphides.  Of  these,  three  only,  the 
protoxide  of  tin,  and  the  peroxides  of  gold  and  platinum,  are  dissolved  by 
an  excess  of  the  reagent.  The  sulphide  of  tin  requires  a  large  excess  for 
solution.  Hydrochloric  aaWalso  serves  as  an  eliminating  test  for  the  color- 
less metallic  solutions  of  this  group  : — 

Precipitated  white.  Not  Precipitated. 


HggO  AgO  PbO  HgO  BiOg  SnO 


QUALITATIVE    ANALYSIS    OP    METALLIC    COMPOUNDS.  533 

The  white  precipitate  given  by  lead  is  soluble  in  boiling  water :  it  is  also 
dissolved  with  or  without  the  aid  of  heat,  by  a  solution  of  potassa,  and  by 
strong  hydrochloric  acid.  The  white  precipitates,  given  by  suboxide  of  mer- 
cury and  oxide  of  silver,  are  insoluble  in  water,  potassa,  and  in  hydrochloric 
acid.  The  precipitated  subchloride  from  suboxide  of  mercury  is  not  soluble 
in  ammonia,  but  is  blackened  by  that  alkali.  The  precipitated  chloride  of 
silver  is  quite  soluble  in  ammonia,  forming  a  colorless  solution.  Of  the  three 
not  precipitated  by  the  acid,  a  persalt  of  mercury  is  recognized  by  the  black 
precipitate  of  metallic  mercury  given  on  the  addition  of  a  protosalt  of  tin  ; 
and  a  protosalt  of  tin  by  a  similar  precipitate  being  produced  when  a  per- 
salt of  mercury  is  added  to  its  solution.  Bismuth  may  be  recognized  by  the 
precipitate  which  it  gives  on  the  addition  of  water  (p.  439.) 

We  have  thus  disposed  of  eleven  metals  of  the  selected  group.  The  re- 
maining seven  are  not  precipitated  by  a  current  of  sulphuretted  hydrogen^  in 
solutions  acidulated  with  hydrochloric  acid. 

Not  precipitated  by  Sulpliuretted  Hydrogen. 


Fe  O  NiO  MuO 

FegOg  CoO  U2O3 

Cr  O3  ZnO 


When  sulphuretted  hydrogen  is  passed  into  a  solution  of  peroxide  of  iron, 
the  persalts  are  reduced  to  the  state  of  protosalts,  and  there  is  a  milky- white 
deposit  of  sulphur.  In  the  salts  of  chromic  acid  a  green  color  is  produced 
from  the  production  of  green  oxide  of  chromium,  which  is  dissolved  in  the 
acid  liquid,  and  sulphur  is  separated. 

Hydrosulphate  of  ammonia  precipitates  the  whole  of  these  metallic  solu- 
tions : — 

p.  black  or  brown.  Green.  White.  Reddish-white. 


r- 


Fe  0  CoO  CrOg  ZnO  MnO 

FeA        U2O3 

NiO 

Black  sulphide  of  iron  is  produced  by  this  test  in  gaits  of  the  protoxide 
and  peroxide,  a  small  quantity  being  suspended,  and  giving  a  greenish  color 
to  the  liquid.  When  exposed  to  air,  these  precipitates  are  rapidly  converted 
into  reddish-brown  hydrated  peroxide  of  iron.  In  undergoing  this  rapid 
change  by  exposure  to  air,  they  are  distinguished  from  the  sulphides  of  nickel 
and  cobalt.  These  precipitates  are  not  soluble  in  an  excess  of  the  reagent. 
The  other  three  metallic  oxides  are  sufficiently  characterized  by  the  colors 
of  their  sulphides. 

The  ferrocyanide  mid  ferricyanide  of  potassium  may  be  here  employed  as 
useful  eliminating  reagents.  The  protosalts  of  iron  are  precipitated  white 
or  bluish-white  by  ferrocyanide,  and  deep  blue  by  ferricyanide  of  potassium. 
The  persalts  are  precipitated  of  a  deep  blue  color  by  ferrocyanide,  but  not 
by  ferricyanide  of  potassium ;  this  liquid  merely  imparts  to  them  a  deep 
greenish  tint.  Ferrocyanide  of  potassium  produces  in  the  salts  of  nickel  a 
pale  green  precipitate,  in  the  salts  of  cobalt  a  dingy  olive-green  precipitate, 
and  in  the  salts  of  peroxide  of  uranium,  a  deep  red  color  or  precipitate, 
resembling  that  produced  in  solutions  of  salts  of  copper.  The  cupreous  pre- 
cipitate is  dissolved  by  ammonia  with  the  production  of  a  blue  color,  while 
the  uranium  precipitate  is  dissolved  by  this  alkaline  liquid,  with  the  produc- 
tion of  a  pale  yellow  color.  The  action  of  this  test  upon  the  other  members 
of  this  group  may  be  thus  described.  Oxide  of  zinc  gives  a  white,  and  oxide 
of  manganese  a  reddish-white  precipitate.     The  presence  of  copper  or  iron, 


63  i 


QUALITATIVE    ANALYSIS    OP    METALLIC    COMPOUNDS. 


as  an  impurity,  in  these  liquids,  will  of  course  affect  the  colors  of  the  preci- 
pitates. A  chroraate  is  neither  changed  in  color  nor  precipitated :  a  bichro- 
mate acquires  a  darker  color. 

Ferrocyanide  of  potassium  is  also  useful  as  a  general  test.  We  subjoin  a 
table  of  its  reaction  on  the  eighteen  metals  which  have  been  here  selected 
for  qualitative  analysis.  The  greater  number  of  these  metallic  solutions  are 
precipitated  white,  or  of  shades  of  white :  some  are  not  precipitated  ;  while 
a  few  are  thrown  down  of  peculiar  colors,  by  which  they  may  in  general  be 
identified. 

Not  precipitated  by  ferrocyanide  of  potassium. 


AS03 

ASO5 
Pre 

SbOg 

CrOj 

AUO3 

PtO^ 

With  tartaric  acid.              Emerald  green         Pale  green 

color.                     color. 

cipitated  white  by  ferrocyanide  of  potassium. 

SbOg 

SbOg 

Ago 
Reddish-white. 

HgO 

Hg^O 

PbO 

Claret  red. 
"cuO  U^O^ 

BiOg 

SnO 
SnOg 

Blue. 

FeO 
ZnO 
CdO 

Pale-green. 

MnO 

NiO  CoO 

The  oxides  of  antimony  combined  with  organic  acids  are  not  precipitated 
by  this  test. 

The  insoluble  compounds  of  the  metals  may  be  brought  into  solution  with 
hydrochloric  or  nitric  acid  ;  and  the  solutions,  properly  diluted,  may  then  be 
submitted  to  the  action  of  the  tests  here  described. 

The  object  of  these  rules  is  to  point  out  the  base,  or  oxide  of  the  metal. 
"When  this  has  been  indicated,  the  tests  of  special  kind,  which  are  described 
under  each  metal,  may  then  be  applied. 


ORGANIC    SUBSTANCES.  535 


ORGANIC  CHEMISTRY. 


CHAPTER    XLIII. 

CONSTITUTION  AND  PROPERTIES  OF  ORGANIC 
SUBSTANCES.  PROXIMATE  ANALYSIS. 

Organic  Chemistry  is  that  branch  of  the  Science  which  refers  to  the 
properties  and  composition  of  organized  products,  or  of  substances  which 
have  been  formed  in  vegetables  and  animals,  under  the  influence  of  life. 
These  products  differ  remarkably  in  physical  and  chemical  characters  from 
bodies  which  belong  to  the  Mineral  or  Inorganic  kingdom  ;  and  they  may, 
in  many  cases,  be  at  once  distinguished  by  external  appearance.  In  refer- 
ence to  chemical  composition,  they  are  also  widely  different.  While  they  are 
constituted  of  a  smaller  number  of  elements,  the  atoms  of  each  element  are 
in  general  numerous,  and  are,  at  the  same  time,  grouped  in  more  complex 
forms,  building  up  frequently  intermediate  compounds  or  proximate  princi- 
ples. The  greater  number  of  vegetable  substances  are  constituted  of  only 
three  elements.  Carbon^  Hydrogen,  and  Oxygen,  of  which  carbon  is  the  prin- 
cipal. Some  organic  substances  contain  only  ^2^0  elements,  CH  or  CO,  the 
compounds  of  HO  being  inorganic  ;  but  in  these  cases,  the  atoms  of  each  are 
more  numerous  than  in  the  mineral  compounds  of  the  same  elements.  One 
of  the  most  simple  in  atomic  constitution  among  organic  substances,  is  pro- 
bably anhydrous  oxalic  acid.  It  contains  only  two  elements,  and  but  a 
small  number  of  atoms  of  each,  being  represented  by  the  formula  C3O3.  In 
this  simple  state,  however,  it  includes  an  atom  of  each  of  the  inorganic  com- 
pounds of  the  same  elements,  CO  (carbonic  oxide),  and  COg  (carbonic  acid). 
The  alkaloids,  or  vegetable  alkalies,  are  at  the  other  end  of  the  scale.  The 
most  complex  contain  four  elements,  of  which  nitrogen  is  one ;  and  with  the 
exception  of  this,  the  atoms  of  each  element  are  very  numerous.  Thus  mor- 
phia, one  of  the  alkaloids  of  opium,  is  represented  by  the  following  complex 
formula:  CgsHgoOgN,  and  its  equivalent  or  combining  weight  is  292.  The 
low  saturating  power  of  these  organic  bases  will  account  for  the  high  num- 
bers by  which  they  are  represented.  Thus,  292  parts  of  morphia  are  only 
equivalent  to  41  of  potassa,  31  of  soda,  and  IT  of  ammonia.  Other  bodies, 
such  as  the  neutral  vegetable  organic  principles,  gum,  starch,  and  sugar, 
occupy  an  intermediate  position.  They  consist  of  three  elements,  carbon 
hydrogen,  and  oxygen,  of  which  the  oxygen  and  hydrogen  are  in  the  propor- 
tions to  form  water.  Thus,  cane-sugar  and  gum  are  Oi^^fi^j  and  starch, 
dextrine,  and  cellulose  are  C^gH^jOio  the  differences  among  these  bodies 
consisting  chiefly  in  the  presence  or  absence  of  one  or  more  atoms  of  water. 
This  curious  relationship  of  the  oxygen  to  the  hydrogen  in  these  bodies,  long 
since  attracted  the  notice  of  chemists,  and  it  entered  into  one  of  the  early 
systems  of  classification.     It  is  not,  however,  peculiar  to  neutral  substances, 


536  ISOMERIC    CONDITIONS. 

but  is  found  occasionally  among  vegetable  acids.  Thus  anhydrous  acetic  acid 
is  C4H3O3,  and  pyroffallic  acid  is  C^gHgOg.  It  is  a  mere  accident  of  consti- 
tution to  which  no  importance  can  be  attached,  inasmuch  as  there  is  no  rea- 
son to  suppose  that  these  elements  are  combined  as  water;  and  it  is  quite 
certain  that  the  neutral  properties  of  a  compound  do  not  depend  upon  any 
uniformity  in  the  proportions  of  oxygen  and  hydrogen. 

Isomeric  Conditions. — The  fact  that  two  substances  so  different  in  phy- 
sical and  chemical  properties  as  gum  and  sugar,  are  represented  by  the  same 
number  of  atoms  of  the  three  elements,  C,H,0,  at  once  points  to  a  peculiar 
character  among  organic  products — namely,  the  frequent  occurrence  of  iso- 
merism among  them.  The  meaning  of  this  term  has  elsewhere  been  fully 
explained  (p.  18)  ;  and  illustrations  of  its  two  principal  modifications,  poly- 
merisra  and  metamerism,  have  been  given.  The  word  merely  expresses  the 
fact  of  a  similarity  of  atomic  proportions  among  different  bodies ;  and  the 
reasonable  inference  from  the  existence  of  this  condition  is,  that  the  proper- 
ties of  organic  compounds  are  referable  to  a  different  arrangement  of  their 
atoms, .and  not  to  their  relative  proportions.  The  atoms  of  carbon,  oxygen, 
and  hydrogen  in  gum  are  so  numerous,  that  they  admit  of  being  arranged  in 
a  variety  of  groups ;  and,  according  to  the  order  of  grouping,  so  may  the 
properties  vary.  Analysis  might,  therefore,  show  that  two  substances  were 
identical  in  composition,  while  they  were  at  the  same  time  entirely  different 
in  properties.  We  agree  with  the  observation  of  Pelouze  and  Freray,  that 
in  the  present  state  of  science,  the  molecular  constitution  of  bodies  and  the 
mode  of  arrangement  of  their  elements,  are  problems  yet  unsolved,  even  with 
respect  to  the  most  simple  organic  substances  ;  and  d  fortiori^  unsolvable 
with  regard  to  those  which  are  complex.  {Traite,  de  Ghimie,  1861,  ii.  p. 
463.) 

The  non-oxygenated  oils  of  the  vegetable  kingdom,  present  a  remarkable 
isomeric  series.  In  their  ultimate  constitution  they  consist  of  hydrogen  and 
carbon,  forming  the  series  of  hydrocarbons.  Thus  oil  of  turpentine,  one  of 
the  series,  has  the  formula  CgoHie-  ^^^  ^^^^  ^^  lemons,  oranges,  bergaraot, 
camomile,  cloves,  and  thyme  are  represented  by  the  same  formula  (Cy„Hig) ; 
and  the  differences  existing  among  these  oils  can  only  be  referred  to  a  dif- 
ferent molecular  arrangement  of  the  carbon  and  hydrogen. 

This  complex  atomic  constitution  leads  to  results  which  may  be  regarded 
as  peculiar  to  organic  chemistry — namely,  the  variety  of  artificial  .products 
which  may  be  obtained  from  them  by  different  methods  of  treatment.  Thus, 
in  reference  to  the  effects  o^  heat,  some  are  volatilized  without  decomposition 
(benzoic  acid)  ;  others  are  entirely  decomposed,  as  gum,  starch,  and  sugar, 
yielding  compounds  which  vary  in  their  nature,  according  to  the  temperature 
applied  ;  while  a  third  class,  at  a  heat  below  redness,  are  converted  into  new 
and  stable  compounds,  simply  by  the  loss  of  the  elements  either  of  water  or 
of  carbonic  acid.  When  gallic  acid  is  converted  into  pyrogallic  acid  by 
heating  it  to  about  410^,  carbonic  acid  is  evolved,  and  the  new  acid  is  sub- 
limed in  crystals : — 

Gallic  acid.  Pyrogallic  acid.       Carbonic  acid. 

Again,  when  pyrogallic  acid  itself  is  heated  to  a  still  higher  temperature 
(482°),  it  is  resolved  into  water,  and  a  black  amorphous  insoluble  compound, 
which  is  called  metagallic  or  gallulmic  acid  : — 

C.aHeOe         =        2H0        +         C,2H40, 


Pyrogallic  acid.  Metagallic  a^id. 


ORGANIC    CHEMISTRY.       EDUCTS    AND    PRODUCTS.  53t 

So,  when  malic  acid  is  converted  by  heat  into  maleic  acid,  water  is  evolved. 
Thus— 

jCgHeO.o        =        CgH.Og        +        2H0 

Malic  acid.  Maleic  acid. 

The  organic  acid  is  thus  entirely  transformed,  partly  into  a  new  pyrogenous 
acid,  and  partly  into  water  or  carbonic  acid,  without  leaving,  in  a  carefully 
conducted  experiment,  any  trace  of  carbon  in  the  retort.  (Pelouze.)  The 
influence  of  heat  in  causing  the  re-arrangement  of  the  elements  of  hydrated 
cyanate  of  ammonia,  and  its  conversion  into  a  neutral  organic  base,  urea,  has 
been  already  pointed  out  (p.  18).  The  conversion  of  starch  and  gum  into 
sugar,  and  the  transformation  of  cane-sugar  into  grape-sugar,  when  these 
substances  are  heated,  or  merely  agitated  with  diluted  acids,  furnish  other 
illustrations  of  the  facility  with  which  a  new  arrangement  of  atoms  is  pro- 
duced, and  tend  to  confirm  the  correctness  of  chemical  views  regarding  the 
isomeric  constitution  of  these  bodies.  The  production  of  oxalic  acid  by 
treating  sugar  with  nitric  acid,  or  by  acting  on  sawdust  (woody-fibre)  with 
potassa  at  a  low  temperature,  proves  not  only  the  facility  of  change,  but  the 
very  difl*erent  chemical  methods  by  which  this  change  may  be  brought  about. 
It  would  be  easy  to  multiply  instances  of  this  kind,  by  referring  to  the 
action  of  some  of  the  metalloids,  as  well  as  of  their  compounds,  on  organic 
substances.  The  range  of  organic  chemistry  has  been  of  late  years  almost 
infinitely  extended  to  the  application  of  this  simple  method  of  research. 

Educts  AND  Products. — The  products,  ov  those  substances  which  result 
from  artificial  processes,  are  far  more  numerous  than  the  educts,  or  proximate 
principles  of  which  organic  compounds  are  considered  to  be  formed.  These 
educts,  which,  as  their  name  implies,  may  be  extracted  in  an  unaltered  state, 
are  the  immediate  or  proximate  principles  of  the  vegetable  or  animal  struc- 
ture ;  and  the  means  Of  separating  them,  or  determining  their  proportion, 
constitutes  an  important  branch  of  chemical  research,  known  &8  proocimate 
analysis.  The  elementary  analysis  of  wood  would  merely  indicate  the  pre- 
sence of  carbon,  hydrogen,  and  oxygen  (C,H,0) :  but  its  principal  proximate 
constituents,  or  the  educts,  which  may  be  extracted  from  it  without  change 
of  properties,  are  gum,  resin,  and  woody  fibre,  each  of  which  would  yield 
the  same  elements  as  the  original  wood,  but  in  proportions  varying  slightly 
with  each  substance.  If  we  compare  Boussingault's  analysis  of  the  grain  of 
wheat  and  of  wheat-straw,  we  shall  find  but  little  difference  in  the  proportion 
of  the  elements,  although  the  former  contains  nutritious  principles  in  the 
form  of  starch,  gluten,  dextrine,  and  sugar ;  while  the  latter  consists  chiefly 
of  woody  fibre,  and  contains  but  little  nutrient  matter. 

Grain  of  wheat.  Wheat-straw. 

Carbon 46-10  48-40 

Hydrogen 5-80  5-30 

Oxygen 43-40  38-95 

Nitrogen 2-30  0-35 

Ash .       2-40  7-00 

100-00  100-00 

Educts,  when  separated,  are  possessed  of  peculiar  physical  and  chemical 
properties  by  which  they  may  be  identified,  and  it  is  to  the  accurate  study 
of  these,  as  well  as  a  knowledge  of  their  elementary  composition,  that  we 
owe  the  numerous  additions  which  have  been  made  to  this  branch  of  science. 
To  take  a  simple  illustration,  gum  is  an  educt ;  its  constitution  is  similar  to 
that  of  cane-sugar  (CjaHjiO^J.     When  1  part  of  gum  is  boiled  with  4  parts 


538  CHANGES    PRODUCED    IN    ORGANIC    SUBSTANCES. 

of  nitric  acid  (sp.  gr.  IBS)  and  1  part  of  water,  it  loses  3  atoms  of  hydrogren, 
acquires  3  atoms  of  oxyp^en,  and  is  transformed  into  a  white  uncrystalline 
and  comparatively  insoluble  substance — mucic  acid  (C^3HgOj4,2HO).  This 
compound,  when  moderately  heated,  is  converted,  like  gallic  acid,  into  a 
volatile  pyrogenous  acid,  while  carbonic  acid  and  water  escape. 

+       2CO2       +        6H0 


Mucic  acid.  Pyromucic  acid.        Carbonic  acid.         Water. 

When  the  isomeric  compound,  cane-sugar  (C^Ji^^O^^),  is  similarly  treated — 
t.  c,  when  1  part  of  sugar  is  boiled  in  8^  parts  of  nitric  acid  (sp.  gr.  1*38), 
and  the  liquid  is  concentrated — an  acid  of  a  totally  different  nature  is  ob- 
tained, namely,  the  oxalic  (Cfi^).  Both  gum  and  cane-sugar  are  convertible 
into  grape-sugar,  C^^K^fli^,  or  C^Jl^fi^^2J10,  by  the  same  process,  i.  e.,  by 
beating  them  in  diluted  sulphuric  acid.  In  this  conversion,  three  atoms  of 
water  are  fixed.  From  gum,  therefore,  as  an  educt,  we  may  obtain  mucic 
acid,  pyromucic  acid,  and  grape-sugar,  as  products ;  and  from  cane-sugar, 
oxalic  acid,  and  grape  sugar.  By  slightly  varying  the  methods  of  treatment, 
other  products  may  be  obtained.  Thus  woody  fibre,  or  cellulose  (Ci^H^oOjo), 
when  heated  with  potassa,  is  converted  into  oxalic  acid  ;  but  when  treated 
with  cold  sulphuric  acid  it  is  transformed  into  grape-sugar.  Under  the 
action  of  nitric  acid,  water  is  produced  at  the  expense  of  a  part  of  the  hy- 
drogen ;  and  for  each  atom  of  hydrogen  lost,  one  atom  of  nitrous  acid  (NOJ 
enters  into  combination.  Gun-cotton  is  the  result  of  this  chemical  substitu- 
tion of  nitrous  acid  for  hydrogen. 

Some  bodies  which  exist  naturally  in  the  vegetable  structure,  and  are  re- 
garded as  educts,  may  be  artificially  produced  by  a  reaction  of  mineral  on 
organic  substances.  In  all  cases,  however,  either  an  organic  substance,  or  a 
body  derived  from  the  organic  kingdom,  is  indispensable  to  this  conversion. 
Hydrocyanic  aeid  may  be  regarded  as  an  organic  product.  The  materials 
for  its  production,  on  contact  with  water,  exist  in  the  bitter  almond,  the 
kernels  of  the  peach,  the  seeds  of  the  apple,  and  other  fruits  of  a  similar 
kind,  as  well  as  in  the  root  of  the  plant  from  which  tapioca  is  obtained 
(Jatropha  manihot),  and  in  the  shoots  and  leaves  of  the  laurel  and  bay-trees. 
The  principal  sources  of  hydrocyanic  acid  are,  however,  certain  metallic 
cyanides  (page  282).  But  these  compounds  have  an  organic  origin  :  they 
are  the  products  of  a  reaction  of  organic  upon  inorganic  substances ;  hence 
the  production  of  hydrocyanic  acid  by  their  decomposition  furnishes  no  ex- 
ception to  the  remark  above  made.  Under  this  point  of  view,  the  production 
of  artificial  urea  from  hydrated  cyanate  of  ammonia  is  simply  a  conversion  - 
of  cyanic  acid  (a  derivative  of  an  organic  substance)  into  another  organic 
compound.  By  no  processes  yet  known,  can  gum,  starch,  or  sugar,  be  pro- 
duced from  their  elementary  constituents  (CHO) ;  and,  by  the  production  of 
alcohol  from  a  mixture  of  sulphuric  acid,  oleBant  gas,  and  water,  Berthelot 
has  merely  proved  that  a  hydrocarbon  of  organic  origin,  or  one  derived  from 
organic  matter,  is  capable  of  being  converted  into  another  organic  product. 
Olefiant  gas  is  obtained  by  a  reaction  of  sulphuric  acid  on  alcohol  (page  275), 
and  Berthelot's  ingenious  experiment  proves  that  when  olefiant  gas  is  dis- 
solved in  sulphuric  acid,  and  this  is  mixed  with  water  and  distilled,  alcohol 
is  reproduced.  This  is  a  simple  case  of  synthesis.  Another  source  of  ole- 
fiant gas  is  coal ;  but  of  the  organic  origin  of  this  substance  no  doubt  can 
be  entertained. 

There  appears  to  be  scarcely  a  limit  to  this  power  of  transforming  one 
organic  substance  into  another,  and  thus  producing  compounds  analogous 
to  educts,  or  those  which  are  formed  by  nature.     Oxalic  acid  is  a  natural 


ORGANIC    CHEMISTRY.  539 

coTivStituent  of  the  leaves  of  sorrel  and  of  the  rhubarb  plant  {Rheum  rhapou' 
ticum)  ;  but,  as  above  stated,  it  is  an  artificial  product  of  the  reaction  of 
potassa  on  woody  fibre,  and  of  nitric  acid  on  sugar.  The  formic  acid, 
which  exists  naturally  in  the  body  of  the  red  ant,  and  as  there  is  reason  to 
believe  in  the  poison  of  the  wasp  and  bee,  is  readily  procured  by  the  action 
of  sulphuric  acid  and  peroxide  of  manganese  on  gum,  starch,  sugar,  or  tartaric 
acid.  It  may  also  be  procured  by  a  reaction  of  peroxide  of  lead  on  tartaric 
acid.  Glucose,  or  grape-sugar,  which  exists  in  the  grape  and  other  fruits,  is 
prodnced  in  large  quantity  by  the  reaction  of  diluted  sulphuric  acid  on  starch. 
By  other  processes,  succinic  acid,  which  is  naturally  contained*  in  amber,  is 
produced  by  the  action  of  nitric  acid  on  certain  fatty  substances  :  butyric 
acid  is  a  product  of  the  fermentation  of  grape-sugar ;  and  lactic  acid  is  pro- 
duced by  the  fermentation  of  grape  sugar  and  sugar  of  milk. 

The  instability  which  characterizes  organic  products  seems  in  a  great 
measure  to  arise  out  of  the  peculiarities  of  their  atomic  constitution  ;  and 
accordingly  we  find  that,  under  circumstances  in  which  inorganic  compounds 
remain  unchanged,  organic  substances  are  subject  to  a  variety  of  changes, 
the  tendency  of  these  being  generally  such  as  to  terminate  in  the  production 
of  binary  compounds.  The  complicated  phenomena  of  fermentation,  putre- 
faction, and  decay  (page  98)  will  illustrate  these  tendencies;  and  the  very 
existence  of  organization  is  intimately  dependent  upon  them.  In  these  causes 
several  intermediate  stages  are  often  passed  through,  but  the  principal  ulti- 
mate results  are  the  production  of  carbonic  acid,  water,  and  ammonia. 
These  form  the  chief  food  of  vegetables  ;  and  when  absorbed  either  from  the 
atmosphere  or  from  the  soil,  they  furnish  carbon,  hydrogen,  oxygen,  and 
nitrogen,  again  to  be  elaborated  into  "  proximate  organic  principles"  by  the 
vital  powers  of  the  plant.  It  is  only  under  such  conditions,  that  vegetables 
can  assimilate  the  materials  of  which  their  fabrics  are  built  up  ;  and,  in  fact, 
so  combine  them  as  to  form  the  proximate  components  of  the  animal  frame ; 
while,  on  the  other  hand,  the  animal  functions  work  in  an  opposite  direction, 
and  produce  the  above-mentioned  binary  compounds.  Thus  the  animal  and 
vegetable  kingdoms  are  found  to  work  in  diametrically  opposite  directions. 
Strictly  speaking,  however,  the  two  kingdoms  may  be  regarded  as  supple- 
mentary to  each  other ;  that  which  the  vegetable  ejects,  is  necessary  to 
animal  existence  ;  and  that  which  the  animal  eliminates,  is  necessary  to  the 
vegetable.  No  plant  could  grow  and  thrive  without  carbonic  acid  and  water, 
and  no  animal  could  live  without  oxygen.  The  vegetable,  therefore,  lives 
by  a  process  of  deoxidation,  and  the  animal  by  a  process  of  oxidation.  The 
vegetable  may  be  regarded  as  the  living  chemical  laboratory  which  prepares 
the  food  for  the  animal.  Water  and  chloride  of  sodium  appear  to  be  the 
only  mineral  substances  which  are  employed  as  food  by  animals.  Other  sub- 
stances used  as  food,  are  derived  either  from  plants  or  animals. 

Spontaneous  Changes. — Probably  there  is  no  greater  difference  between 
organic  and  inorganic  substances  than  that  spontaneous  tendency  to  change 
which  is  manifested  by  the  former,  and  to  which  the  term  fermentation  is 
somewhat  loosely  applied.  By  exposure  to  air,  and  at  a  moderate  tempera- 
ture, in  the  presence  of  a  body  which  is  called  2,  ferment,  sugar  is  spontane- 
ously converted  into  alcohol  and  carbonic  acid ;  and  alcohol  into  acetic  acid 
and  water.  There  are  other  remarkable  conversions  of  an  analogous  kind, 
by  which  gallic,  lactic,  butyric,  and  hydrocyanic  acids  are  produced  from 
substances  which  either  do  not  originally  contain  them,  or  contain  them 
only  in  small  quantity.  These  changes  frequently  consist  in  the  simple 
absorption  or  fixation  of  oxygen.  Thus  the  essential  oil  of  bitter  almonds 
is  converted,  by  exposure  to  air,  into  benzoic  acid  (page  94) ;  ether,  from 
being  neutral,  is  partially  changed  into  acetic  acid,  and  acquires  an  acid 


540  METAMORPHOSES.   ACTION  OF  FERMENTS. 

reaction.  The  gallic  and  pyrogallic  acids,  when  dissolved  in  water  and 
exposed  to  air,  rapidly  absorb  oxygen,  and  are  converted  into  dark-brown 
oxidized  compounds.  This  change  takes  place  with  great  rapidity  when 
the  acids  are  mixed  with  an  excess  of  any  alkaline  base.  Chemists  employ 
a  solution  of  this  kind  as  a  ready  method  for  absorbing  oxygen  (page  100). 
When  pyrogallic  acid  is  dissolved  in  neutral  ether,  it  has  no  acid  reaction  if 
kept  from  air ;  but  when  oxygen  has  free  acces  to  it,  litmus-paper  moistened 
with  the  liquid,  becomes  reddened  by  the  absorption  of  this  element,  show- 
ing that  an  acid  is  produced,  although  in  the  absence  of  pyrogallic  acid,  the 
liquid  simply  evaporates  without  reddening  the  paper.  Woody  fibre  is 
transformed  by  oxidation  into  a  brown  insoluble  compound  called  humus, 
and  carbonic  acid  is  evolved,  constituting  that  condition  which  has  been 
described  as  eremacausis  (page  98).  In  place  of  the  oxygen  entering  into 
combination  with  the  new  compound,  or  being  evolved  as  carbonic  acid,  it 
may  operate  by  removing  part  of  the  hydrogen  and  producing  water.  The 
transformation  of  white  to  blue  indigo  by  exposure  to  air,  is  considered  to 
be  dependent  on  a  change  of  this  kind : — 

C.gHAN    +     0    =    HO    +     C.eHAN 


White  indigo.  '  Blue  indigo. 

The  operation  of  the  ferment,  in  some  of  these  metamorphoses,  appears  to 
be  of  a  catalytic  kind  (p.  58).  It  takes  no  absolute  share  in  the  changes, 
but  it  induces  an  altered  molecular  arrangement  in  other  bodies.  In  refer- 
ence to  the  oxidation  of  bodies,  the  ferment  may  even  be  replaced  by  a 
mineral  substance — platinum-black — which  has  the  power,  under  a  moderate 
access  of  air,  of  rapidly  transforming  alcohol  into  water  and  acetic  acid 
{C^^fi^-\-0^=^^0-\-Cfi^O^]  and  of  converting  wood-spirit  into  water 
and  formic  acid  (C2H,02-+-0^=3H0  +  C3H03).  These  facts  show  that  a 
ferment,  in  certain  cases,  operates,  like  platinum-back,  merely  as  a  medium 
for  transferring  oxygen. 

The  living  animal  body  furnishes  numerous  illustrations  of  the  facility  with 
which  certain  organic  sul3stances  pass  and  repass  into  each  other.  Among 
these,  there  is  probably  none  more  striking  than  the  conversion  of  benzoic 
acid  (Cj^HgOg.HO)  into  hippuric  acid  (Cj8Hg05N,H0).  A  small  quantity 
of  benzoic  acid,  when  taken  into  the  system,  is  eliminated  in  the  urine  as 
hippuric  acid.  The  hippuric  acid  naturally  contained  in  the  urine  of  the 
horse  slowly  disappears,  and  is  spontaneously  changed,  by  a  species  of  fer- 
mentation, into  the  benzoic.  The  condition  of  the  animal  appears  to  favor 
the  production  of  one  or  the  other  acid,  according  to  circumstances.  Thus 
when  the  animal  is  kept  at  rest,  hippuric  acid  is  abundant ;  but  when  violently 
exercised,  this  is  replaced  by  the  benzoic.  This  transformation,  whether 
viewed  as  the  result  of  changes  in  the  living  animal,  or  of  fermentation  out 
of  the  body,  is  the  more  remarkable,  inasmuch  as  the  two  acids  have  no 
isomeric  relations,  and  appear  to  have  no  analogous  composition.  In  some 
instances  we  obtain  a  key  to  this  conversion,  and  can  imitate  the  process. 
When  a  mixture  of  gelatinous  starch  is  heated  for  a  few  minutes  to  a  tem- 
perature of  about  90^,  with  a  small  quantity  of  saliva,  or  of  the  vegetable 
principle  diastase,  it  will  be  found  that  the  starch  has  become  partially  con- 
verted into  grape-sugar  by  a  fixation  of  the  elements  of  water.  It  is  worthy 
of  remark  that  sulphurous  acid  and  sulphites  have  a  tendency  to  prevent 
these  changes,  probably  by  absorbing  and  removing  oxygen.  It  has  been 
long  known  that  sulphurous  acid  had  the  power  of  arresting  the  conversion 
of  sugar  into  alcohol,  and  of  alcohol  into  acetic  acid  ;  but  it  operates  with 
equal  effect  in  preventing  the  conversion  of  starch  into  sugar  by  saliva  and 


MINERAL    CONSTITUENTS    OF    VEGETABLES.  541 

diastase.  Some  of  these  spontaneous  changes  are  of  a  complex  character, 
and  take  place  in  close  vessels  irrespective  of  the  absorption  of  oxygen. 
Thus  pyroxyline  (gun-cotton  or  paper)  is  sometimes  resolved,  without  any 
apparent  cause,  into  nitrous  and  hydrocyanic  acids. 

Proximate  Analysts An  organic  substance  frequently  contains  a  cer- 
tain proportion  of  water  as  well  as  of  mineral  matters.  The  leaves  of  plants 
contain  from  80  to  85  per  cent,  of  water,  and  the  soft  animal  tissues  contain 
a  very  large  quantity  (p.  142) :  to  the  presence  of  this  water  their  physical 
properties  are  mainly  due.  The  driest  vegetable  powders  contain  a  certain 
percentage  of  it,  which  must  be  removed  before  a  correct  analysis  can  be 
made.  The  methods  of  removing  water,  and  determining  the  quantity  pre- 
sent, have  been  elsewhere  described  (p.  146). 

The  mineral  substances  are  sometimes  in  large  proportion  in  the  vegetable 
and  animal  structure.     Bone  contains  about  67,  and  the  teeth  70  per  cent. 
of  mineral  matter,  in  the  form  of  phosphate  and  carbonate  of  lime.     Shells, 
and  other  solid  structures  of  the  like  nature,  are  chiefly  constituted  of  car- 
bonate of  lime,  cemented  by  animal  matter.     In  certain  infusoria,  silica  is 
very  abundant :  this  substance  is  also  an  important  constituent  of  the  epi- 
dermis of  the  reeds  and  grasses.     It  forms  from  13  to  50  per  cent,  of  the 
ashes  of  some  species  of  plants  (p.  299).    It  is  associated  with  oxide  of  iron, 
and  sometimes  with  traces  of  manganese.    Certain  salts  of  lime,  potassa,  soda, 
and  magnesia  are  the  principal  mineral  constituents  of  organic  substances. 
The  alkalies  are  generally  found  in  the  ash,  combined  with  carbonic  acid  (a 
product  of  the  combustion  of  organic  acids)  and  with  sulphuric  acid ;  or  in 
the  state  of  chlorides,  iodides,  and  bromides  of  the  respective  metals.     The 
alkaline  earths  are  also  found  as  carbonates,  but  frequently  associated  with 
the  phosphoric,  sulphuric,  and  silicic  acids.     Lime  and  oxide  of  iron  exist 
more  or  less  in  the  ashes  of  all  organic  substances ;  and  the  metals  iron  and 
manganese  (the  latter  rarely)  are  found  in  the  residue  of  combustion,  as 
oxides.    These  mineral  ingredients,  although  generally  small  when  compared 
with  the  weight  of  the  organic  constituents,  appear  to  be  of  essential  im- 
portance to  the  life  of  plants,  and  to  the  structure  of  the  skeleton  in  animals. 
They  serve,  in  the  vegetable  kingdom,  to  build  up  the  cell-walls  for  the 
reception  of  the  organic  principles,  and  they  give  firmness  and  strength  to 
the  vegetable  structure.    Potassa  and  soda  are  found  abundantly  in  succulent 
plants.    These  alkalies  exist  more  or  less  in  combination  with  vegetable  acids 
in  all  plants ;  and  it  is  to  the  presence  of  their  carbonates  that  the  alkaline 
reaction  of  the  ashes  of  vegetables  is  due.     Potassa  is  more  abundant  in 
inland,  and  soda  in  marine  plants ;  certain  vegetables,  such  as  the  Armeria 
maritima,   Gochlearia  officinalis,  and  Plantago  maritima,   produce  chiefly 
potassa  when  they  grow  in  inland  districts,  and  soda  when  near  the  sea-coast. 
It  is  probable  that  soda  is  never  entirely  absent  from  the  ashes  of  vegetables. 
Although  it  cannot  be  detected  by  ordinary  processes  of  analysis  in  the 
ashes  of  many  inland  vegetables,  including  the  foliage  of  trees,  its  presence 
has  been  revealed  in  every  instance  by  the  photo-chemical  process  of  Bunsen 
and  Kirchoflf.     A  quantity  of  sodium,  amounting  to  less  than  the  20,000th 
part  of  the  weight  of  the  ash,  readily  admits  of  detection  by  spectral  analysis. 
Soda  is  the  principal  alkali  of  animal  compounds  :  as  chloride  of  sodium,  it 
is  found  in  the  ashes  of  most  animal  solids  and  liquids.    Lime  in  combination 
with  phosphoric  acid  is  found  in  all  the  cereal  grains,  as  well  as  in  potatoes, 
turnips,  chicory,  and  other  roots.     The  oxalate  and  carbonate  of  lime,  in  a 
crystalline  state,  are  found  sometimes  in  the  cells  of  plants,  constituting 
raphides.     Crystals  of  oxalate  of  lime  are  found  abundantly  in  the  root  of 
rhubarb,  and  in  certain  cactuses.     Iodine  and  bromine  exist  as  iodides  and 


542  MINERAL    COMPOUNDS    IN    ORGANIC    SUBSTANCES. 

broraide8,  not  only  in  marine,  but  in  many  land  plants;  and  fluorine  has  been 
detected  as  a  constituent  of  scurvy-grass  {Cochlearia  officinalis),  and  in  otiier 
plants  growing  near  the  sea.  The  only  vegetables  which,  according  to  Mul- 
der, yield  no  mineral  ash  or  residue,  are  the  mould-plants,  formed  in  saccha- 
rine and  acid  liquids.  They  consist  of  cellulose  with  nitrogenous  substances. 
Like  the  acalephce,  or  jelly-fish,  of  the  animal  kingdom,  they  are  chiefly  con- 
stituted of  water,  and  yield,  on  drying,  merely  a  trace  of  solid  matter.  The 
proportion  of  mineral  matter  contained  in  an  organic  substance  varies  with 
its  nature.  We  have  elsewhere  given  the  proportions  of  ashes  yielded  by 
different  kinds  of  wood  (p.  255).  By  reference  to  the  analysis  of  wheat  and 
straw  (p.  537),  it  will  be  seen  that  the  proportion  in  the  straw  is  threefold 
that  of  the  grain.  Certain  educts,  when  separated  from  the  vegetable  by 
artificial  processes,  may  be  obtained  so  pure  that,  on  incineration,  they  leave 
no  mineral  matter — e.  g.,  starch  and  sugar;  others,  such  as  gum,  are  always 
associated  with  a  large  quantity  of  lime,  as  well  as  oxide  of  iron.  The 
mineral  matters  found  in  vegetables  are  considered  to  have  a  telluric  origin ; 
«.  e.,  they  are  supposed  to  be  derived  from  the  soil.  Sulphur  and  phosphorus, 
in  combination  with  oxygen,  united  to  bases,  as  sulphates  and  phosphates, 
are  found  in  the  earth;  and  chlorine,  combined  with  sodium,  is  present  in  all 
soils  and  in  all  waters.  It  is  probable  that  plants  growing  near  the  seaside 
derive  a  large  portion  of  the  soda  which  they  contain  from  the  diffusion  of 
the  chloride  in  watery  vapor  in  the  atmosphere.  Marine  plants  and  animals 
derive  this  salt,  chloride  of  sodium,  carbonate  of  lime  (as  coral  or  shell),  as 
well  as  the  iodides  and  bromides  of  the  alkaline  metals,  directly  from  sea- 
water.  The  following  list  comprises  the  principal  inorganic  constituents  of 
vegetable  and  animal  substances:  Sl'SO^),  PCPOg),  Si(Si03),  Ca(CaO), 
Mg(MgO),  K(KO),  Na(NaO),  CI,  I,  Br,  F,  Fe(FeA),  and  Mn(xMnO). 

The  chloride  of  rubidium  has  been  detected  by  M.  Grandeau  in  the  saline 
waters  derived  from  beet-root,  associated  in  minute  quantity  with  chloride  of 
potassium.  It  has  also  been  found  in  the  ashes  of  tobacco,  tea,  coffee,  aud 
in  the  crude  tartar  derived  from  the  grape.  The  colza,  cacao,  and  sugar- 
cane, contained  none,  although  some  of  the  ashes  were  rich  in  potassium.  By 
spectral  analysis,  lithium  has  been  detected  in  the  ashes  of  seaweed,  of  the 
vine,  tobacco,  and  of  numerous  other  plants  growing  on  the  granitic  soil  of 
Germany.  It  is  stated  that  it  has  also  been  found  in  the  ashes  of  milk, 
blood,  and  muscular  tissue.  Dr.  Cameron  did  not  detect  it  in  cereal  plants, 
and  in  some  fuci  which  he  examined ;  but  he  found  that  when  lithia  was 
added  to  the  soil,  the  ashes  of  barley  contained  this  alkali,  which  had  been 
apparently  substiti^ted  for  soda  in  the  plant  {Chemical  News,  May  31,  1862). 
It^  is  remarkable  that  alumina  (AlgOg)  which  is  a  large  constituent  of  every 
soil,  is  rarely  found  in  the  ashes  of  vegetables,  except  as  an  accidental 
ingredient.  The  analyses  hitherto  made  show  that  alumina  is  not  an  essen- 
tial constituent  of  plants,  and  that  it  is  very  rarely  present. 

Although  plants  appear  to  have  generally  a  power  of  rejecting  noxious 
ingredients,  yet  in  certain  cases,  substances  of  a  poisonous  nature  are  taken 
from  the  soil  by  the  roots,  and  are  distributed  through  their  tissues.  The 
metals  thus  absorbed,  appear  to  be  deposited  there,  without  injuring  the 
growth  or  vitality  of  the  plant.  We  have  found  by  direct  experiment  that 
the  seeds  of  mustard  and  cress,  grown  on  a  soil  containing  the  disintegrated 
slag  of  old  lead-works,  took  up  a  sufficient  quantity  of  lead  to  allow  its 
presence  to  be  readily  determined  in  the  grown  plants.  We  also  found  lead 
in  the  ashes  of  many  plants  and  shrubs,  and  of  the  grass  growing  on  lead- 
slag,  in  the  valleys  of  the  Mendip  hills.  Care  was  taken  to  remove  any 
particles  of  the  soil  adhering  to  the  plants.  Dr.  Cameron  states  that  he 
invariably  found  lead  in  the  plants  grown  near  lead-smelting  works  at  Bally- 


ESTIMATION    OF    WATER    AND    MINERAL    MATTER.  543 

corns,  county  of  Dublin  {Cliemical  News,  June,  1862,  p.  315).  Dr.  Wilson 
has  made  a  similar  observation  ;  and  further,  that  herbage  thus  impregnated 
with  lead,  may  be  a  cause  of  lead-poisoning  in  cattle  {Edinhurgh  Monthly 
Medical  Journal,  1852,  vol.  xiv.  p.  386).  The  question  has  been  raised 
whether  plants  can  thus  imbibe  arsenic  from  the  soil  ;  and  this  is  of  some 
importance,  inasmuch  as  arsenical  sulphuric  acid  is  largely  employed  in  the 
manufacture  of  certain  manures.  The  only  recorded  instances  of  the 
absorption  of  this  mineral,  are  in  some  observations  made  by  Dr.  Davy  and 
Mr.  Horsley.  They  found  that  turnips  and  other  vegetables  grown  on  soils 
on  which  arsenicated  manures  had  been  placed,  acquired  an  impregnation  of 
arsenic  {Philosophical  Magazine,  August,  1859,  p.  108).  Some  of  the 
lower  kinds  of  plants  (confervae)  readily  grow  in  certain  metallic  solutions, 
which  are  poisonous  to  animals.  A  solution  of  tartar  emetic  exposed  to  air 
becomes  speedily  covered  with  confervoid  growths  of  a  peculiar  kind. 
Mould-plants  are  observed  to  flourish  in  solutions  of  tartaric,  citric,  gallic, 
and  tannic  acids,  and  their  compounds,  but  not  in  a  solution  of  oxalic  acid. 

With  respect  to  the  inorganic  elements  found  in  the  animal  kingdom,  if 
we  except  the  zoophytes  and  marine  mollusca,  these  elements  may  be  traced 
to  the  food  of  the  animal,  and  not  to  the  medium  in  which  they  live.  Thus 
all  terrestrial  animals  derive  their  support  either  from  other  animals  or  from 
vegetables  ;  hence,  except  from  accidental  circumstances,  the  inorganic  com- 
pounds found  in  animals  are  the  same  as  those  which  exist  in  vegetables. 

The  separation  of  mineral  matters  from  an  organic  substance  may  be 
effected  by  burning  a  known  weight  in  a  platinum  crucible.  The  carbon, 
oxygen,  and  hydrogen,  are  thus  removed,  and  the  residue,  which  is  a  light, 
porous,  white,  or  (if  iron  is  present)  reddish-colored  ash,  can  be  readily 
weighed.  It  will  probably  be  found  to  contain  salts,  some  of  which  are  solu- 
ble in  water,  and  others  only  dissolved  by  acids.  The  larger  proportion  of 
the  ash  is  generally  insoluble  in  water.  Thus  of  100  parts  of  the  ashes  of 
the  oak,  only  15  parts  are  dissolved  by  water ;  of  the  ashes  of  the  box,  24 
parts;  and  of  the  ashes  of  the  fir,  17  parts.  The  acids  and  bases  may  be 
sought  for  by  the  rules  laid  down  at  pp.  276  and  531.  It  has  been  suggested 
that  nitric  acid  should  at  once  be  employed  for  the  removal  of  these  mineral 
substances  from  the  vegetable.  In  a  few  cases  this  may  be  resorted  to ;  but 
the  most  certain  method  of  separation  is  that  of  incineration.  The  presence 
of  mineral  matter  in  any  organic  substance  may  be  readily  detected  by  heat- 
ing a  portion  of  it  on  thin  platinum  foil,  or  in  a  platinum  capsule.  If  there 
is  any  difiBculty  in  consuming  the  carbon,  it  may  be  finely  powdered,  mixed 
with  its  weight  of  red  oxide  of  mercury,  and  heated  either  in  a  glass  tube  or 
porcelain  capsule.  The  proportions  of  water,  mineral,  and  organic  matter, 
in  100  parts  of  the  fresh  leaves  of  the  lettuce  and  nettle,  and  of  the  lime, 
ash,  and  elm-trees,  are  derived  from  recent  experiments  : — 


Water 

Mineral  matter  , 

Organic  matter  . 

Lettuce. 
.     96-6     .. 
.       0-6     ., 
.       2-8     .. 

Nettle. 
,.     79-60     . 
,.       2-96     . 
.     17-44     . 

Lime. 
..     80-     .. 
..       2-     .. 
..     18-     .. 

Ash. 

,.     75-83     . 
.       1-66     . 
,.     22-51     . 

Elm. 

..     70- 
..       2- 

..     28- 

100-0  100-00  100-  100-00  100- 

The  water  was  determined  by  spontaneous  desiccatioTi  and  subsequent 
drying  at  212°;  and  the  ash  by  careful  incineration  in  platinum  ;  the  ash  in 
each  case  was  nearly  white.  It  was  more  or  less  alkaline,  and  was  found  to 
contain  carbonic,  sulphuric,  and  traces  of  phosphoric  acid,  chlorine,  potassa, 
lime,  magnesia,  and  oxide  of  iron.  The  elm  and  nettle  leaves  contained  the 
largest,  and  the  lime  and  ash  leaves  the  smallest  proportion  of  lime  and 


544  PROXIMATE    ANALYSIS. 

oxide  of  iron.  The  greatest  amount  of  phosphoric  acid  was  found  in  the 
nettle,  associated  with  lime.  The  color-test  to  flame  gave  not  the  slightest 
indication  of  the  presence  of  soda  in  any  of  the  leaves.  Probably  by  spec- 
tral analysis  both  sodium  and  rubidium  might  have  been  found. 

The  proximate  analysis  of  an  organic  substance  may  be  generally  effected 
by  various  solvents,  such  as  ether,  alcohol,  or  water,  successively  applied  ; 
and  occasionally  sulphide  of  carbon,  benzole,  oil  of  turpentine,  or  chloroform 
may  be  employed  as  substitutes  for  ether.  Ether,  which  should  be  used  first, 
is  a  solvent  of  fatty  and  waxy  substances,  as  well  as  of  resins,  camphor,  and 
some  essential  oils.  Alcohol  is  a  solvent  of  resins,  and  of  a  variety  of  bodies, 
upon  which  ether  has  but  little  action ;  while  water,  either  cold  or  hot,  is  an 
important  solvent  of  many  neutral  vegetable  principles,  such  as  gum,  sugar, 
or  starch.  Vegetable  alkalies  may  be  dissolved  by  diluted  acetic,  hydro- 
chloric, or  sulphuric  acid;  and  are  thus  obtained  in  a  state  for  further 
separation  by  potassa,  ammonia,  or  lime.  Vegetable  acids  admit  of  separa- 
tion by  potassa,  lime,  oxide  of  silver,  or  lead ;  and  from  the  compounds  thus 
produced  the  acid  may  be  procured  by  a  diluted  mineral  acid,  or  by  the 
decomposition  of  a  vegetable  salt  of  lead  by  sulphuretted  hydrogen.  The 
solvents  above  mentioned  often  remove  several  substances  at  one  time. 
Those  which  are  of  a  crystalline  nature  may  be  separated  either  by  cooling 
or  concentrating  the  solution  to  different  degrees,  or  by  varying  the  solvent. 
The  new  process  of  dialysis  may  be  also  employed  for  the  separation  of  salts 
from  organic  matter  diffused  in  water  (pp.  50,  146). 

Fractional  distillation,  as  applied  to  volatile  liquids,  admits  of  a  more  or 
less  perfect  separation  of  these  liquids,  by  collecting  the  products  which  are 
condensed  at  a  fixed  temperature,  or  within  a  range  of  a  few  degrees.  Thus, 
rectified  coal-naphtha  consists  of  a  series  of  volatile  oils  which  boil  at  tem- 
peratures varying  from  1 40*^  to  342*^.  By  condensing  the  vapors  evolved  at 
different  temperatures,  at  which  the  thermometer  remained  fixed,  Mansfield 
found  that  this  liquid  might  be  resolved  into  five  oils,  having  different  boiling- 
points,  and  possessed  of  different  properties.  The  oil  which  boils  at  176°, 
and  is  condensed  below  that  temperature,  is  well  known  as  an  important 
product,  under  the  name  of  benzole  (CjaHg).  To  this  method  of  separation 
we  owe  the  production  of  paraffine  from  the  tarry  oils  obtained  by  the  dis- 
tillation of  coal  or  bituminous  schist  at  a  low  temperature.  These  remarks 
apply  to  the  preliminary  separation  of  substances  for  a  further  analytical 
investigation.  It  would  be  impossible  to  lay  down  any  general  rules  for  the 
qualitative  and  quantitative  examination  of  the  bodies  thus  obtained  in  solu- 
tion, or  as  a  result  of  distillation.  The  properties  of  each  organic  compound 
must  be  separately  studied,  and  the  tests  for  its  detection,  and  the  processes 
required  for  its  separation,  must  be  well  understood,  before  a  successful 
proximate  analysis  can  be  made.  The  difficulties  with  which  a  chemist  has 
to  contend  are,  that  organic  substances  are  liable  to  undergo  changes  by 
mere  contact  with  simple  chemical  reagents,  and  that  the  means  of  perfect 
separation  by  precipitants  are  much  more  limited  than  in  mineral  chemistry. 


ORGANIC    CONSTITUENTS    OF    VEGETABLES.  545 


CHAPTER    XLIV. 

ULTIMATE  OR  ELEMENTARY  ANALYSIS. 

Organic  Constituents. — Assuming  that  the  hygrometric  water  has  been 
removed  from  an  organic  substance,  and  that  the  proportion  of  mineral  mat^r, 
if  present,  has  been  determined,  the  next  stage  is  to  ascertain  the  nature  and 
proportion  of  the  organic  constituents.  These  are,  in  the  vegetable,  chiefly 
three,  represented  by  carbon,  hydrogen,  and  oxygen,  occasionally  associated 
with  nitrogen,  sulphur,  and  phosphorus.  In  the  animal  they  are  commonly 
four — carbon,  nitrogen,  hydrogen,  and  oxygen;  and,  more  frequently  than  in 
the  vegetable,  associated  with  sulphur  and  phosphorus.  Carbon  is  the  only 
element  which  appears  to  be  essential  to  an  organic  compound.  Gmelin  has 
justly  observed  that  each  of  the  other  elements  may  be  absent  from  particular 
compounds;  but  no  compound,  which,  in  all  its  relations,  deserves  the  name 
of  organic,  is  destitute  of  carbon.  Further,  organic  compounds  are  distin- 
guished from  the  carbon  compounds  of  the  inorganic  kingdom,  by  containing 
more  than  one  atom  of  this  element.  The  atoms  of  carbon  in  organic  formulae 
are  in  pairs,  or  in  even  numbers.  The  carbon  is  frequently  in  such  propor- 
tion as  to  be  equal  to  the  combined  weights  of  oxygen  and  hydrogen  :  it  is 
generally  in  large  excess,  and  is  estimated  to  form  from  one-half  to  two-thirds 
of  the  weight  of  dried  organic  matter.  It  constitutes  42  per  cent,  of  sugar, 
52  per  cent,  of  the  weight  of  alcohol,  and  87  per  cent,  of  the  weight  of  oil 
of  turpentine.  The  great  source  of  carbon  to  the  vegetable  is  the  carbonic 
acid  diffused  through  the  atmosphere  (p.  162).  Although  the  proportion 
present  in  air  is  relatively  small,  it  is  very  great  when  the  bulk  of  the 
atmosphere  is  regarded.  This  gas  is  absorbed  by  the  leaves  of  plants,  and^ 
while  carbon  is  partly  retained,  oxygen,  carbonic  oxide,  and  carburetted 
hydrogen  (in  the  proportion  of  1*11  c.  i.  to  100  of  oxygen)  are  eliminated 
(p.  262).  Boussingault  found  that  when  air  was  passed  over  the  fresh  leaves 
of  the  vine,  the  carbonic  acid  was  absorbed.  The  influence  of  light  appears 
to  be  necessary  for  the  elimination  of  these  gases.  The  roots  of  plants  also 
take  up  a  portion  of  carbonic  acid  in  a  state  of  solution  in  water. 

Test  for  an  Organic  Compound. — In  determining  the  question  whether  a 
substance  is  of  an  organic  or  inorganic  nature,  a  chemist  seeks  for  the 
presence  of  carbon.  No  organic  substance  contains  a  sufficient  quantity  of 
oxygen  to  consume  the  whole  of  its  carbon  and  hydrogen  ;  hence,  if  the 
suspected  solid  is  heated  in  a  close  vessel,  so  that  air  can  have  no  access,  a 
black  or  carbonized  residue  will  remain.  The  experiment  may  be  readily 
performed  by  heating  the  substance  in  a  small  glass  tube.  If  organic — e.  g., 
starch — it  will  be  carbonized:  if  inorganic — e.g.,  sulphate  of  lime — it  will 
remain  unchanged.  Volatile  bodies — such  as  the  oxalic  and  benzoic  acids, 
alcohol,  ether,  and  acetic  acid — require  a  different  method  of  treatment. 
Some  are  entirely,  and  others  are  only  partly,  volatile.  Anhydrous  oxalic 
acid,  too,  presents  this  peculiarity :  the  oxygen  is  in  sufficient  quantity  to 
transform  the  carbon  into  carbonic  acid  and  carbonic  oxide,  but  as  an  inde- 
pendent acid  it  always  contains  an  atom  of  water.  No  inorganic  compound 
leaves  a  residue  of  carbon  when  heated  under  similar  circumstances. 

Sulphuric  acid  is  sometimes  employed  as  a  medium  for  testing  the  organic 
35 


546      DETECTION    AND    SEPARATION    OF    CARBON    AND    HYDROGEN. 

natnre  of  an  unknown  solid.  When  the  substance  is  heated  with  an  excess 
of  the  acid,  the  mixture  is  blackened  by  the  liberation  of  the  carbon,  and 
sulphurous  acid  is  .evolved  as  a  result  of  the  decomposition  of  a  part  of  the 
acid  employed.  Sulphuric  acid,  however,  produces  peculiar  effects  with 
many  organic  products;  it  dissolves  indigo,  forming  a  blue  solution;  and 
gallic  acid,  forming  a  rich  crimson-colored  liquid  ;  it  produces  red-colored 
compounds  with  veratria,  certain  resins,  and  oil  of  bitter  almonds  ;  and  while 
it  carbonizes  many  bodies,  it  dissolves  others,  such  as  citric  acid,  with 
scarcely  any  change  of  color.  On  the  whole,  the  effect  of  heating  the  com- 
pound in  a  close  vessel  furnishes  the  most  reliable  evidence  of  its  organic 
nature. 

Carbon. — If  we  have  satisfied  ourselves,  by  the  production  of  a  carbona- 
ceous residue,  that  the  substance  is  organic,  we  may  next  proceed  to  deter- 
mine, by  an  accurate  chemical  method,  not  only  the  presence,  but  the 
proportion  of  carbon  present.  The  substance  well  dried  and  finely  powdered, 
is  mixed  with  dried  chromate  of  lead,  or  black  oxide  of  copper,  and  intro- 
duced into  a  tube  which  is  connected  with  two  balanced  tubes,  the  first 
containing  broken  chloride  of  calcium  for  drying  the  gaseous  products,  and 
the  second  a  strong  solution  of  potassa,  either  by  itself,  or  diffused  through 
dry  pumice  (p.  162).  When  the  mixture  is  strongly  ignited,  the  carbon  of 
the  organic  substance  is  entirely  converted  into  carbonic  acid:  this  is  dried 
by  the  chloride  of  calcium,  and  the  gas  itself  is  absorbed  by  the  potassa. 
The  increase  of  weight  in  the  potassa  indicates  the  amount  of  carbonic  acid 
present.  100  parts  of  carbonic  acid  represent  27  "2  parts  by  weight  of 
carhon  (C).  The  chromate  of  lead  is  preferable  to  the  oxide  of  copper,  as 
at  a  high  temperature  it  fuses  and  incloses  the  organic  matter,  thus  insuring 
the  complete  oxidation  of  the  carbon  present.  The  changes  which  take 
place  will  be  readily  understood.  The  oxide  of  copper  is  simply  deoxidized, 
2CuO  +  C  =  C03-|-2Cu  ;  but  the  chromate  of  lead  is  reduced  to  subchromate 
and  sesquioxide  of  chromium,  4(PbO,Cr03)  =  4PbO,2Cr03+Cr203  4-03. 
The  oxygen  liberated  is  taken  by  the  carbon.  Unlike  the  black  oxide  of 
copper,  this  compound  evolves  oxygen  by  the  mere  effect  of  heat. 

The  oxide  of  copper  or  chromate  of  lead  is  deoxidized,  not  only  by  the 
•carbon,  but  by  the  hydrogen  of  the  organic  matter :  and  carbonic  acid  and 
•water  are  produced.  The  water  is  absorbed  by  the  chloride  of  calcium. 
'The  production  of  carbonic  acid  under  these  circumstances,  furnishes  of  itself 
a  good  test  of  the  presence  of  organic  matter.  Thus,  in  place  of  heating 
the  organic  compound  in  a  close  vessel,  it  may  be  mixed  with  oxide  of  copper 
and  heated  at  once  in  a  small  tube  bent  at  an  angle  and  drawn  out  in  a 
capillary  form  at  the  open  end.  This  may  be  broken  off  and  dipped  into  a 
small  quantity  of  lime-water  contained  in  a  tube  or  watch-glass.  If  carbon 
is  present,  carbonic  acid  is  produced,  a  fact  indicated  by  a  milky  precipitate 
in  the  lime-water.  A  mere  trace  of  carbon  in  a  substance  thus  easily  admits 
of  detection. 

Hydrogen — This  element  is  commonly  in  small  proportion  by  weight ;  but 
there  is  a  large  class  of  organic  compounds  wtiich  are  formed  entirely  of  hy- 
drogen and  carbon,  the  carbon  always  preponderating.  Hydrogen  forms 
about  6  per  cent,  of  sugar,  and  13  per  cent,  of  alcohol  and  oil  of  turpentine, 
the  latter  being  a  pure  hydrocarbon.  There  is  no  direct  test  for  the  pre- 
sence of  this  element  in  organic  matter.  The  proof  of  its  presence  in  a  dried 
organic  substance  is  derived  from  the  production  of  water,  either  by  simply 
heating  the  solid  to  a  certain  temperature,  or  by  igniting  it  in  a  tube  with 
black  oxide  of  copper  or  chromate  of  lead.  In  this  case  the  deoxidation  is 
•effected  by  hydrogen  as  well  as  by  carbon,  and  if  the  substance  has  been 


DETERMINATION    OP    OXYGEN.  547 

properly  dried  at  212°,  and  the  oxide  of  copper  or  chroraate  of  lead  has  beea 
well  dried,  all  the  water  carried  over  and  condensed  in  the  chloride  of  cal- 
cium tube  will  represent  the  amount  of  hydrogen  in  the  organic  substance. 
The  chromate  of  lead,  when  it  has  been  fused  and  powdered,  is  much  less 
absorbent  of  water  than  the  oxide  of  copper  ;  hence  it  gives  more  correct 
results  for  hydrogen. 

Inflammable  liquids  containing  hydrogen,  such  as  alcohol  and  ether, 
produce  a  large  quantity  of  water  by  combustion  in  air.  The  method  of 
determining  the  presence  and  amount  of  hydrogen  has  been  described  above 
under  Carbon,  and  additional  details  will  be  found  at  pp.  125  and  146.  The 
increase  of  weight  in  the  chloride  of  calcium  tube,  which  arrests  the  water, 
divided  by  9,  indicates  the  amount  of  hydrogen  present.  Thus,  100  parts  of 
water  are  equivalent  to  11  "1  H. 

The  hydrogen  existing  in  vegetable  substances  is,  no  doubt,  chiefly  derived 
from  the  deoxidation  of  water,  either  as  it  is  diffused  in  vapor  through  the 
atmosphere,  or  taken  up  from  the  soil.  This  element  is  never  found  in  the 
atmosphere  in  a  free  state,  but  some  of  its  compounds — namely,  ammonia 
and  light  carburetted  hydrogen — have  been  detected  in  air  in  small  quanti- 
ties; and  some  portion  of  the  hydrogen  of  the  vegetable  structure  may  be 
derived  from  these  sources,  the  nitrogen  and  carbon  being  at  the  same  time 
appropriated.  The  vital  power  which  can  separate  hydrogen  from  oxygen 
can  also  separate  this  element  from  nitrogen  and  carbon  :  the  oxygen  elimi- 
nated from  the  decomposed  water  is  supposed  to  be  ozonized,  like  that  which 
is  set  free  by  the  electrolysis  of  water. 

Oxygen. — This  element,  next  to  carbon,  is  the  principal  constituent  by 
weight  of  organic  matter.  In  some  compounds,  as  in  vegetable  acids,  it  is 
in  greater  proportion  than  carbon.  It  constitutes  66  per  cent,  of  anhydrous 
oxalic  acid,  52  per  cent,  of  sugar,  and  34  per  cent,  of  alcohol.  In  the  case 
of  oxalic  acid,  it  is  associated  with  carbon  only  :  but  in  sugar,  alcohol,  and 
the  greater  number  of  vegetable  principles,  it  is  combined  with  hydrogen, 
and  sometimes  with  nitrogen  and  sulphur.  Some  of  the  alkaloids,  acids, 
and  neutral  compounds  contain  none — e.  g.,  nicotina,  aniline,  hydrocyanic 
acid,  and  oil  of  turpentine.  There  is  no  direct  test  for  the  presence  of  oxy- 
gen in  organic  substances,  if  we  except  the  production  of  carbonic  acid  and 
water  by  heating  them  out  of  contact  of  air.  The  oxygen  is  then  consumed 
by  the  hydrogen  of  the  substance,  and  water  is  produced  as  well  as  carbonic 
acid.  The  general  principle  on  which  the  determination  of  the  presence  and 
amount  of  oxygen  is  based  consists  in  the  separation  and  quantitative  esti- 
mation of  the  other  constituents,  and  in  the  deduction  of  the  sum  of  these 
from  the  amount  of  dry  organic  matter  employed  in  the  experiment.  If  the 
substance  examined  was  perfectly  dry  and  pure,  and  the  other  elements  have 
been  accurately  weighed,  this  method  will  give  a  sufficiently  correct  result ; 
but  any  errors  on  these  points  will  add  to  or  diminish  the  amount  of  oxygen. 
When  the  substance  consists  of  carbon,  hydrogen,  and  oxygen  only,  the 
results  are  generally  satisfactory  ;  but  when  nitrogen,  sulphur,  and  phosphates 
are  present,  there  is  greater  difficulty  attending  the  correct  estimation  of  the 
oxygen.  The  oxygen  found  in  organic  substances  is  probably  derived,  not 
only  directly  from  the  atmosphere,  but  indirectly  from  the  oxidized  products 
— carbonic  acid  and  water — which  are  diffused  through  it. 

.  Nitrogen. — This  element,  although  most  abundantly  found  in  animal  sub- 
stances, is  an  important  constituent  of  many  vegetable  compounds.  Albu- 
men, fibrin,  gluten,  and  casein  of  both  kingdoms  contain  it  in  a  large 
proportion.  It  exists  in  the  sap  and  juice  of  vegetables:  it  is  present  in 
many  alkaloids,  in  indigo,  in  bases  such  as  aniline  and  nicotine ;  also  in 
amygdaline,  in  hydrocyanic  and  carbazotic  acids,  and  in  a  great  variety  of 


548  DETECTION    OF    NITROGEN. 

artificial  products.  Compounds  of  nitrogen  and  hydrogen,  or  of  nitrogen 
and  oxygen,  are  not  met  with  among  organic  substances.  Ammonia,  which 
is  constituted  of  nitrogen  and  hydrogen,  is  not  an  organic  substance,  but 
the  product  of  the  decomposition  of  organic  matter.  Nitrogen  is  associated 
with  carbon  in  cyanogen  and  its  compounds,  with  sulphur  in  oil  of  mustard, 
and  with  sulphur  and  phosphorus  in  albumen,  fibrin,  and  other  organic 
principles. 

Organic  substan-ces  which  contain  this  element  and  a  sufficient  quantity  of 
moisture,  undergo  changes  to  which  the  term  putrefaction  is  applied.  One 
of  the  most  abundant  products  is  ammonia,  which  is  derived  from  the  nitro- 
gen uniting  with  hydrogen  in  the  nascent  state. 

The  presence  of  nitrogen  may  in  general  be  determined  by  heating  the 
dried  substance  in  a  close  tube  :  ammonia,  in  combination  with  carbonic  or 
hydrosulphuric  acid,  is  distilled  over  with  water  among  the  first  products. 
The  alkaline  gas  may  be  identified  by  its  pungent  odor,  and  by  its  reaction 
on  test-paper  placed  in  the  mouth  of  the  tube,  or  by  any  of  the  usual  tests. 
The  substance  may  be  heated  in  a  tube,  with  hydrate  of  potassa  or  calcined 
soda-lime,  finely  powdered:  in  either  case  the  nitrogen  present  is  entirely  set 
free  as  ammonia.  The  alkaline  bases  operate  by  fixing  any  acid  that  may 
be  produced.  For  another  method  of  detecting  this  element,  see  p.  156. 
Even  a  diluted  solution  of  potassa,  at  a  moderate  heat,  will  in  some  cases 
destroy  the  substance  and  produce  ammonia.  Among  alkaloids,  strychnia 
and  morphia  resist  the  action  of  a  solution  of  potassa  which  is  sufl[icient  to 
decompose  atropia,  aconitina,  and  hyoscyamia.  Morphia  or  strychnia,  when 
heated  alone,  evolves  ammonia,  showing  that  nitrogen  is  a  constituent  of 
these  alkaloids";  but  their  salts  give  ofi'  no  ammonia  when  heated,  unless  they 
are  mixed  with  4  or  5  parts  of  hydrate  of  potassa  or  dry  soda-lime.  Caout- 
chouc, when  heated  in  a  reduction-tube,  evolves  ammonia  ;  gutta-percha  does 
not.  When  nitrogen  is  absent,  the  organic  solid  commonly  evolves  an  acid 
(acetic),  the  vapor  of  which  reddens  litmus-paper.  Thus  dextrine,  gum,  or 
woody  fibre,  when  heated  strongly  in  close  vessels,  evolves  acetic  acid.  Non- 
nitrogenous  are  thus  distinguished  from  nitrogenous  substances  :  If  we  heat 
in  a  tube  a  small  quantity  of  Russian  isinglass,  ammonia  is  copiously  evolved  ; 
but  if  we  substitute  for  this  the  substance  called  Japanese  isinglass  {Gelidium 
corneum)  an  acid  vapor  escapes.  This  substance  contains  no  nitrogen,  while 
the  Russian  isinglass  contains  it  in  large  proportion.  Another  method  of 
detecting  nitrogen  in  organic  substances  consists  in  converting  it  into  cyan- 
ogen. For  this  purpose  a  fragment  of  sodium  is  heated  with  the  organic 
substance  in  a  tube  of  narrow  bore.  A  black  alkaline  residue  is  obtained, 
which  is  dissolved  in  water.  The  solution  will  contain  free  soda  as  well  as 
carbonate,  and  if  nitrogen  was  present,  cyanide  of  sodium.  The  liquid 
nearly  neutralized  by  a  dilute  acid,  is  treated  with  a  small  quantity  of  a  solu- 
tion of  green  sulphate  of  iron  and  is  well  stirred.  It  was  now  acidulated 
with  diluted  sulphuric  acid — oxide  of  iron  is  dissolved,  and  if  nitrogen  was 
present  in  the  organic  substance  Prussian  blue  will  be  produced.  The  non 
production  of  Prussian  blue,  under  these  circumstances,  shows  that  nitrogen 
is  not  a  constituent  of  the  substance  examined. 

The  vegetable  is  supposed  to  derive  its  nitrogen  chiefly  from  ammonia 
diffused  through  the  atmosphere,  or  carried  by  rain  into  the  soil.  The  very 
small  proportion  of  ammonia  found  in  air  may  appear  to  be  insufficient  as  -a 
source  of  nitrogen  for  plants ;  but  vegetables  have  the  power  of  extracting 
and  appropriating  their  elements,  even  when  diffused  in  such  minute  traces 
as  not  to  be  revealed  by  ordinary  reagents.  Rubidium  has  been  detected 
in  the  salts  obtained  from  beet-root,  but  none  has  hitherto  been  found  in  the 
soil.     A  similar  fact  has  been  noticed  with  regard  to  marine  plants ;  they 


DETECTION    AND    SEPARATION    OF    SULPHUR.  549 

have  a  power  of  accumulating  and  fixing  iodine  in  their  tissues ;  but  iu  the 
sea-water  in  which  they  flourish,  it  is  difl&cult  to  detect,  by  chemical  tests, 
any  traces  of  iodine,  even  when  a  large  quantity  is  made  the  subject  of  ex- 
periment. Although  nitrogen  is  an  alaundant  constituent  of  the  atmosphere, 
there  is  no  evidence  that  vegetables  procure  it  directly  from  this  source.  As 
hyponitrite  or  nitrate  of  ammonia  (the  result  of  the  oxidation  of  the  elements 
of  air  and  aqueous  vapor  by  ozone  or  electricity),  nitrogen  in  a  combined 
state  is  not  only  diffused  in  the  atmosphere,  but  carried  by  rain  into  the  soil. 
•  According  to  Schonbein,  a  plant  in  the  act  of  growth,  by  causing  a  reaction 
of  the  elements  of  air  upon  aqueous  vapor,  is  a  generator  of  nitrate  (hypo- 
nitrite)  of  ammonia,  and  thus  prepares  a  part  of  its  own  nitrogenous  food. 
On  this  theory,  the  nitrogen  of  vegetables  is  derived  indirectly  from  the  con- 
stituents of  the  atmosphere.  The  quantity  of  nitrogen  in  an  organic  com- 
pound, may  be  determined  either  by  separating  the  element  in  the  gaseous 
state,  or  by  converting  it  into  ammonia,  and  precipitating  this  alkali  by 
chloride  of  platinum.     These  methods  will  be  presently  described. 

Sulphur. — Sulphur  is  frequently  associated  with  nitrogen.  The  nitroge- 
nous principles  of  the  animal  and  vegetable  kingdom — albumen,  fibrin,  gluten, 
and  casein — contain  it  abundantly.  Gelatine  and  indigo  contain  nitrogen 
but  no  sulphur;  gutta-percha  contains  a  trace  of  sulphur  but  no  nitrogen  ; 
while  caoutchouc  contains  both.  Sulphur  is  an  important  constituent  of 
certain  essential  oils.  In  dried  organic  solids,  it  may  be  detected  by  heating 
the  substance  in  a  small  tube  :  the  vapor  evolved,  containing  sulphuretted 
hydrogen,  blackens  a  slip  of  glazed  card,  or  of  paper  impregnated  with  a  salt 
of  lead.  Dried  gluten,  bread,  caoutchouc,  flannel,  hair,  horn,  or  feathers, 
evolve  a  quantity  of  a  sulphur  compound  under  these  circumstances.  If  the 
substance  also  contains  nitrogen,  ammonia  is  produced,  and  hydrosulphate 
of  ammonia  comes  over  with  aqueous  vapor.  The  detection  of  the  hy- 
drosulphate and  therefore  of  the  presence  of  nitrogen  and  sulphur,  in  the 
compound,  is  readily  effected  by  one  experiment.  Paper  wetted  with  a 
solution  of  nitro-prusside  of  sodium,  acquires  immediately  a  rich  purple  or 
crimson  color.  Unless  the  sulphur  is  in  combination  with  an  alkali,  this 
change  does  not  take  place. 

There  are  other  methods  of  detecting  sulphur.  The  substance  may  be 
boiled  in  a  solution  of  potassa  containing  a  small  quantity  of  oxide  of  lead 
dissolved ;  if  sulphur  is  present,  the  substance  is  either  blackened  or  the 
liquid  acquir.es  a  dark  color  from  the  production  of  sulphide  of  lead.  A 
portion  of  flannel  or  silk  thus  tested  by  a  potassa-solution  of  oxide  of  lead, 
will  be  completely  blackened ;  but  if  mixed  with  cotton  the  fibres  of  the  latter 
will  remain  white,  as  this  substance  contains  no  sulphur.  A  small  portion 
of  flour  thus  treated  is  also  blackened  by  reason  of  the  gluten  contained  in 
it.  Pure  starch  is  simply  dissolved,  as  this  contains  no  sulphur.  Owing  to 
the  occasional  presence  of  lead  as  an  impurity  in  a  solution  of  potash,  most 
sulphur  compounds,  when  boiled  with  the  alkali,  impart  to  it  a  dark  color. 
Liquid  compounds  of  sulphur  which  are  dissolved  by  potassa  undergo  a 
similar  change.  As  an  alkaline  sulphide  is  produced  by  the  reaction  of  the 
potassa  on  the  sulphur  of  the  organic  matter,  the  nitroprusside  of  sodium 
may  be  made  available  for  the  detection  of  this  element.  If  a  small  quantity 
of  hair,  woollen,  or  silk  is  boiled  in  a  solution  of  potassa,  the  presence  of 
sulphur  will  be  indicated  by  the  alkaline  liquid  acquiring  a  reddish  or  crimson 
tint  when  a  few  drops  of  nitroprusside  of  sodium  are  added.  For  this  pur- 
pose, potassa,  free  from  lead,  should  be  selected.  When  the  organic  sub- 
stance is  dry  the  following  simple  process  will  enable  a  chemist  to  determine 
the  presence  of  sulphur  and  nitrogen  at  one  operation  :  The  substance  is 
heated  iu  a  narrow  tube,  with  a  small  quantity  of  sodium,  and  the  residue 


550  PHOSPHORUS,   CHLORINE,    BROMINE,    AND    IODINE. 

lixiviated.  A  sulphide  of  the  metal  is  formed,  and  the  presence  of  this  may 
be  discovered  by  the  addition  of  nitroprusside  of  sodium,  which  produces  a 
crimson  color,  or  of  acetate  of  lead  when  a  brown  precipitate  results.  Should 
there  be  much  cyanide  present,  white  cyanide  of  lead  is  thrown  down,  and 
this  conceals  to  some  extent  the  dark  sulphide.  A  few  drops  of  diluted 
nitric  acid  removes  the  cyanide,  and  the  characteristic  precipitate  of  sulphide 
of  lead  is  then  seen  of  its  proper  color.  If  we  add  to  another  portion  of  the 
liquid  a  solution  of  persulphate  of  iron,  we  obtain  a  red  precipitate,  the  sul- 
phocyanide  of  iron,  thus  indicating  the  presence  of  sulphur  and  nitrogen  in 
the  substance  treated  with  sodium.  No  sulphocyanogen  could  be  found  unless 
both  of  these  elements  were  present. 

In  some  cases,  the  molecular  condition  of  the  substance  interferes  with  the 
application  of  this  test.  Thus  caoutchouc  contains  much  sulphur,  but  in 
order  to  detect  it,  the  substance  should  either  be  digested  in  strong  nitric 
acid  containing  nitrous  acid,  or  deflagrated  in  a  silver  crucible  with  pure 
hydrate  of  potassa  and  nitre,  until  it  has  become  white.  The  sulphur  is 
oxidized  and  converted  into  sulphuric  acid  or  sulphate  of  potassa,  and  the 
quantity  of  acid  produced  may  be  determined  by  precipitating  a  neutralized 
solution  of  the  residue  in  water,  with  baryta  or  one  of  its  salts. 

Phosphorus. — This  is  not  unfrequently  associated  with  nitrogen  and 
sulphur  in  organic  compounds,  and  exists  sometimes  in  large  proportion  in 
animal  products.  In  the  state  of  phosphoric  acid  combined  with  soda,  lime, 
or  magnesia,  it  is  an  abundant  mineral  constituent  of  animal  and  vegetable 
matter,  and  is  readily  obtained  by  incineration.  Its  presence  and  proportion 
may  be  determined,  by  deflagrating  the  dried  organic  substance  with  a  mix- 
ture of  equal  parts  of  pure  nitrate  of  potassa  and  bicarbonate  of  potassa  in 
fine  powder.  The  experiment  may  be  performed  in  a  platinum  crucible  : 
the  saline  residue  is  dissolved  in  water,  and  the  solution  neutralized  with 
acetic  acid.  Any  soluble  phosphate  that  is  present  may  be  precipitated  by 
the  methods  described  at  pages  243  and  390.  In  the  first  case  aramonio- 
phosphate  of  magnesia  is  produced,  100  parts  of  which  when  dried  and 
ignited,  are  equivalent  to  28 '57  parts  of  phosphorus,  and  in  the  second  an- 
insoluble  perphosphate  of  iron  is  thrown  down. 

The  sulphur  and  phosphorus  of  the  vegetable  kingdom  are  chiefly  derived 
from  a  deoxidation  of  the  sulphates  and  phosphates  contained  in  the  soil. 

Chlorine,  Bromine,  and  Iodine. — In  all  natural  compounds  these  elements 
are  found  associated  with  alkaline  metals,  and  are  readily  separated  by  the 
process  of  incineration.  Artificial  compounds,  containing  them  in  such  a 
form  as  to  yield  no  precipitate  on  the  addition  of  nitrate  of  silver,  may  be 
analyzed  by  passing  the  vapors  through  a  combustion-tube  containing  a 
mixture  of  three  parts  of  hydrate  of  lime  and  one  part  of  hydrate  of  soda, 
the  purity  of  which  has  been  previously  ascertained.  A  chloride,  bromide, 
or  iodide  of  the  alkaline  metal  is  thus  procured.  After  the  tube  has  cooled, 
the  lime  is  dissolved  in  very  diluted  nitric  acid  ;  and  nitrate  of  silver  is  added 
to  the.  filtered  solution.  A  precipitate,  consisting  of  chloride,  bromide,  or 
iodide  of  silver,  or  a  mixture  of  these  salts,  is  thus  obtained,  and  the  propor- 
tion of  each  element  may  be  determined  by  the  process  described  at  page 
208.  Volatile  compounds  of  these  elements  are  introduced  into  the  mixture 
in  small  glass  bulbs. 

When  the  substance  for  analysis  consists  of  carbon  in  combination  with 
hydrogen  or  oxygen,  or  with  both  of  these  elements,  the  proportions  in  100 
parts  may  be  at  once  determined  by  the  use  of  the  Gombustdon-tube. 

The  tubes  used  in  these  analyses  should  be  made  of  green  glass  free  from 
lead,  or  of  hard  Bohemian  glass.  They  are  generally  about  four-tenths  of  an 
inch  in  diameter,  and  from  15  to  18  inches  in  length,  sealed,  and  either  drawn 


ESTIMATION    OF    THE    RESULTS.  551 

into  a  point  or  rounded  at  the  sealed  end;  the  open  extremity  should  be 
smoothed  by  fusion,  so  as  to  receive  a  cork  without  danger  of  cracking.  It 
is  sometimes  necessary  to  protect  the  tube,  by  rolling  a  strip  of  copper-foil 
spirally  round  it,  tied  at  each  end  by  a  piece  of  wire.  The  tube  may  be 
heated,  either  by  a  lamp-furnace  or  over  charcoal,  in  a  trough  of  sheet-iron 
constructed  for  the  purpose. 

When  the  substance  to  be  analyzed  is  solid,  from  3  or  4  to  8  or  10  grains 
of  it,  properly  dried,  are  carefully  mixed  with  about  200  grains  of  the  dried 
oxide  of  copper,  and  introduced  into  the  combustion-tube,  into  the  end  of 
which  is  previously  placed  about  half  an  inch  in  length  of  small  copper- 
shavings  superficially  oxidized.  These  shavings  should  occupy  about  two 
inches  of  the  tube  above  (or,  as  it  lies  horizontally,  before)  the  organic  mix- 
ture, the  object  being  to  keep  the  whole  contents  of  the  tube  in  a  loose  or 
porous  condition,  so  that  the  gaseous  products  may  escape  from  it  without 
impediment.  .The  mixture  of  oxide  of  copper  and  the  organic  substance 
should  be  placed  about  the  centre  of  the  combustion-tube,  some  pure  oxide 
of  copper  being  placed  before  and  behind  it.  If  the  organic  substance  under 
examination  is  a  ternary  compound  of  hydrogen,  carbon,  and  oxygen,  it  is 
obvious  that  the  products  will  be  only  loater  and  carbonic  acid.  In  order  to 
ascertain  the  weight  of  the  former,  and  thence  the  weight  of  the  hydrogen 
required  to  form  it,  the  products,  as  they  escape,  are  carried  through  a  tube 
containing  fragments  of  fused  chloride  of  calcium,  and  accurately  weighed. 
The  vapor  of  water  is  absorbed,  and  the  increase  in  the  weight  of  the  tube 
and  its  contents,  will  indicate  its  quantity.  The  juncture  of  the  combustion- 
tube  with  the  chloride  of  calcium  tube,  should  be  made  air-tight  by  a  per- 
forated cork. 

The  carbonic  acid,  deprived  of  water,  is  conducted  from  the  extremity  of 
the  chloride  of  calcium  tube,  into  a  light  glass  tube  blown  into  five  bulbular 
enlargements,  containing  a  strong  solution  of  caustic  potassa,  and  accurately 
balanced.  The  bulb  apparatus  is  then  connected  with  the  chloride  of  calcium 
tube,  by  short  lengths  of  caoutchouc  piping. 

After  the  abstraction  of  the  water  in  the  chloride  of  calcium  tube,  the  car- 
bonic acid  passes  on  into  the  solution  of  caustic  potassa,  through  which,  by 
properly  inclining  the  bulb  apparatus,  it  may  be  made  to  pass  in  divided 
bubbles,  and  under  some  pressure,  so  as  to  insure  its  total  absorption.  When 
the  experiment  is  completed,  the  apparatus  is  allowed  to  cool,  and  in  order 
to  prevent  any  portion  of  the  alkaline  solution  retrograding  into  the 
chloride  tube,  the  tip  of  the  combustion-tube  is  broken  off,  and  any  residuary 
carbonic  acid  may  then  be  drawn  into  the  alkaline  solution,  by  applying 
gentle  suction  at  the  end,  or  by  the  use  of  an  aspirator.  The  weight  of  the. 
evolved  carbonic  acid,  and  therefore  of  the  carbon,  is  ascertained  by  accu- 
rately determining  the  increase  in  the  weight  of  the  condenser  with  its  alka- 
line solution. 

In  order  to  illustrate  the  mode  of  operation,  we  may  assume  that  10 
grains  of  pure  starch  have  been  thus  decomposed  by  oxide  of  copper  in  the 
combustion-tube,  and  that  the  chloride  of  calcium  tube  has  acquired  an 
increase  of  weight  equal  to  5  94  grains  (water),  and  the  potassa.  apparatus 
has  increased  in  weight  16  24  grains  (carbonic  acid).  As  pure  starch  is 
known  to  contain  only  carbon,  hydrogen,  and  oxygen,  the  proportions  of 
each  element  in  100  parts  may  be  thus  determined.  Hydrogen  forms  one- 
ninth  part  of  water  :  hence  5-94-f-9  =  0  66  H.  In  22  parts,  by  weight,  of 
carbonic  acid,  there  are  6  parts  of  carbon  :  hence  22  :  6  :  :  1624  :  443  C. 
The  oxygen,  if  these  results  are  correct,  may  be  determined  by  deducting 
the  sum  of  the  weights  of  hydrogen  and  carbon  from  the  weight  of  the  starch 


552  SEPARATION    OP    NITROGEN    AS    AMMONIA. 

employed  in  the  experiment,  0'66  +  4'43  =  5*09  :  and  10  — 509  =  4-91  0. 
Hence  these  results  show  that  pure  starch  consists  of: — 

In  10  parts.  la  100  parts. 
Carbon   .         .         .         .         ,     4-43  44-3 

Hydrogen        ....     0*66  6-6 

Oxygen  .         .         .         .         .     4  91  49-1 

10-00  100-0 

When  nitrogen  is  a  constituent  of  the  organic  matter  under  examination, 
the  mixture  with  oxide  of  copper  is  made  as  usual,  but  the  contents  of  the 
fore  part  of  the  combustion-tube  must  now  consist  of  a  mixture  of  shavings 
or  filings  of  metallic  copper  with  the  oxide,  and  great  care  must  be  taken  slowly 
to  conduct  the  evolved  gases  through  this  mixture,  rather  highly  heated,  in 
order  to  effect  the  complete  evolution  of  the  nitrogen,  and  to  decompose  the 
various  compounds  which  that  substance  might  possibly  form  with  the 
oxygen,  carbon,  or  hydrogen.  The  nitrogen  then  escapes  as  a  gas  with  car- 
bonic acid.  The  gases  may  be  collected  in  a  proper  mercurial  apparatus, 
and  the  carbonic  acid  removed  afterwards  by  a  few  fragments  of  fused 
hydrate  of  potassa,  when  the  nitrogen  will  remain,  and  its  weight  may  then 
be  deduced  from  its  volume.  Deutoxide  of  nitrogen  is  an  occasional  product 
of  the  decomposition  of  a  nitrogenous  compound  by  oxide  of  copper.  It  is 
most  readily  formed  when  chromate  of  lead,  or  a  current  of  pure  oxygen,  is 
employed  in  the  combustion-tube.  It  is  produced  in  larger  quantity,  cceteris 
paribus,  when  the  temperature  is  high,  than  when  the  combustion  takes  place 
slowly. 

The  quantitative  determination  of  nitrogen  may  be  more  accurately  ob- 
tained by  converting  it  into  ammonia,  and  in  this  form  combining  it  with 
chloride  of  platinum,  so  as  to  weigh  it  in  the  state  of  ammonio-chloride. 
(Varrentrapp  and  Will,  Ann.  der  Ghem.  und  Pharm.,  39,  257.)  For  this 
purpose  the  azotized  organic  product,  to  the  amount  of  4  or  5  grains,  is 
thoroughly  blended  in  a  warm  mortar  with  a  mixture  of  1  part  of  dry  hydrate 
of  soda,  and  2  of  lime,  in  such  quantity  as  to  fill  the  combustion-tube  to 
within  about  3  inches  of  its  open  end.  Attached  to  the  combustion  tube  is 
a  three-bulbed  apparatus,  containing  pure  hydrochloric  acid  sp.  gr.  1130. 
Heat  is  then  applied  to  the  combustion-tube,  beginning  at  the  anterior 
extremity;  and  when  the  whole  length  has  been  so  heated  that  the  substance 
has  become  quite  white,  air  is  drawn  through  it  as  in  the  case  where  oxide 
of  copper  is  used,  and  the  contents  of  the  bulb-apparatus  poured  into  a  basin, 
the  bulbs  being  afterwards  washed,  first  with  a  mixture  of  alcohol  and  ether, 
and  then  with  water,  from  an  ounce  to  an  ounce  and  a  half  of  liquid  being 
used  for  that  purpose.  A  solution  of  pure  chloride  of  platinum  is  then 
added  in  excess  to  the  mixture  of  the  hydrochloric  solution  and  washings, 
and  the  whole  evaporated  to  dryness :  the  residue  is  treated  with  a  mixture 
of  two  volumes  of  alcohol  and  1  of  ether ;  if  this  affords  a  yellow  solution, 
excess  of  chloride  of  platinum  has  been  added,  and  the  remaining  washed 
ammonio-chloride  of  platinum  may  be  collected  on  a  filter,  dried  at  212°, 
and  weighed.  In  order  to  control  the  weighing,  the  ammonio-chloride  should 
be  calcined,  and  the  resulting  metallic  platinum  also  weighed.  100  parts  of 
the  dried  ammonio-chloride,  are  equivalent  to  6-22  of  nitrogen  and  44  parts 
of  metallic  platinum.  All  substances  containing  nitrogen,  under  these  cir- 
cumstances, evolve  this  element  in  the  form  of  ammonia,  excepting  nitric  acid. 
If  any  soda-lime  is  carried  over  it  does  not  affect  the  result,  as  these  alkalies 
are  not  precipitated  by  chloride  of  platinum.  Any  excess  of  chloride  of 
platinum  is  completely  removed  by  the  mixture  of  alcohol  and  ether. 

The  soda-lime,  before  use,  should  be  ignited  and  finely  powdered.     In  its 


SEPARATION    OP    NITROGEN    AS    AMMONIA.  553 

reaction  on  organic  matter  at  a  high  temperature,  it  is  probable  that  the 
carbon  unites  with  the  oxygen  of  the  water  of  the  hydrates,  forming  carbonic 
acid,  which  unites  to  the  bases,  while  the  hydrogen  which  is  set  free  combines 
with  the  nitrogen  of  the  organic  substance  to  produce  ammonia.  Three 
parts  of  hydrogen  are  sufficient  for  the  entire  conversion  of  fourteen  parts  of 
nitrogen.  If  the  nitrogenous  compound  is  a  liquid,  it  may  be  introduced 
into  bulbs  and  heated  with  soda-lime  in  the  manner  in  which  organic  liquids 
are  heated  with  black  oxide  of  copper.  Some  nitrogenous  organic  substances 
do  not  evolve  ammonia  under  these  circumstances,  but  a  volatile  organic  base 
on  which  soda-lime  has  no  action.  Thus,  indigo  yields  aniline,  and  other 
substances  produce  other  bases  containing  no  oxygen.  They  all  form,  how- 
ever, insoluble  compounds  with  chloride  of  platinum  and  the  amount  of  nitro- 
gen present  admits  of  easy  determination  by  incinerating  the  salt  and  obtain- 
ing the  platinum  in  the  metallic  state.  99  parts  of  platinum  are  equivalent 
to  14  of  nitrogen  or  100  parts  to  14'4. 

If  the  substance  for  analysis  is  a  volatile  organic  liquid  (alcohol),  it  may 
be  collected  in  a  small  balanced  bulb  of  glass,  and  its  weight  accurately  de- 
termined after  sealing  the  capillary  end  of  the  bulb.  It  may  then  be  dropped 
into  the  midst  of  the  oxide  of  copper  in  the  combustion-tube,  the  small  ca- 
pillary end  being  previously  broken.  After  the  oxide  has  become  full  heated 
in  the  fore-part  of  the  tube,  the  portion  containing  the  bulb  is  heated,  and 
as  the  va^or  of  the  liquid  escapes,  it  is  immediately  decomposed  by  the  ig- 
nited oxide  of  copper.  Two  of  these  bulbs,  containing  together  from  6  to  8 
grains  of  the  liquid,  may  be  employed  in  one  operation,  provided  that  several 
inches  of  the  oxide  are  interposed  between  them.  If  the  liquid  has  a  high 
boiling-point  and  is  rich  in  carbon,  it  will  be  found  better  to  subdivide  the 
quantity  among  three  bulbs.  Substances  of  a  viscid  or  fatty  nature  may  be 
introduced  into  the  combustion-tube  in  small  glass  tubes,  or  in  trays  of  pla- 
tinum foil. 

In  the  analysis  of  hydrocarbons,  it  is  sometimes  necessary  to  use  a  current 
of  pure  oxygen,  in  order  to  consume  the  carbon  Completely.  Occasionally 
chlorate  of  potassa  is  mixed  with  oxide  of  copper,  in  order  to  insure  a  copious 
supply  of  oxygen.  Chromate  of  lead,  as  a  source  of  oxygen,  has  some  advan- 
tages over  oxide  of  copper.  After  it  has  been  fused,  it  is  but  little  hygro- 
metric ;  and  if  the  substance  which  is  to  be  analyzed  contains  chlorine  or 
sulphur,  the  lead  retains  these  elements,  while  with  oxide  of  copper  a  volatile 
chloride  of  that  metal  is  formed,  as  well  as  sulphurous  acid.  This  last-men- 
tioned compound  is  not  absorbed  by  chloride  of  calcium,  but  it  readily  com- 
bines with  potassa,  and  thus  adds  to  the  apparent  amount  of  carbon.  In 
order  to  avoid  this  source  of  error,  a  tube  containing  finely-powdered  peroxide 
of  lead,  should  be  placed  between  the  chloride  of  calcium  tube,  and  the 
potassa-apparatus.  This  completely  arrests  any  sulphurous  acid  that  maiy 
be  produced.  With  the  use  of  chromate  of  lead,  however,  the  tube  contain- 
ing peroxide  is  seldom  required. 

Sulphur  can  be  estimated  only  by  the  process  described  at  p.  549.  Nitric 
acid  is  not  always  efficient  in  completely  oxidizing  the  sulphur  of  organic 
compounds.  Liebig  advises  that  the  substance  should  be  gradually  fused  in 
a  silver  crucible  with  an  excess  of  a  mixture  of  8  parts  of  hydrate  of  potassa 
and  1  part  of  nitre.  If  the  mixture  should  not  become  colorless  when  heated, 
a  little  more  nitre  may  be  added.  The  white  residue  is  dissolved  in  water 
acidulated  with  hydrochloric  acid,  and  this  solution  is  precipitated  by  chloride 
of  barium.  The  sulphate,  after  it  has  been  washed,  dried,  and  ignited,  may 
be  weighed  :  100  parts  of  dried  sulphate  of  baryta  are  equivalent  to  13-8  of 
sulphur.     Volatile  organic  liquids  containing  sulphur  may  be  vaporized,  and 


554 


EQUIVALENTS  OP  ORGANIC  SUBSTANCES. 


the  vapor  passed  through  a  tube  containing  a  mixture  of  nitre  and  bicar- 
bonate of  potassa  or  soda,  strongly  heated. 

[For  further  information  on  the  analysis  of  organic  substances,  the  reader 
is  referred  to  Fresenius's  Quantitative  Analysis,  p.  385,  and  Liebig's  Hand- 
hook  of  Organic  Analysis.'] 

Equivalents  of  Organic  Substances.  Formula. — The  results  obtained 
by  the  use  of  the  combustion-tube  merely  represent  the  weights  of  the  ele- 
ments in  100  parts.  There  can  be  no  doubt  that  these  elements  are  com- 
bined in  equivalent  proportions,  and  the  principles  on  which  the  atomic 
weight  of  an  organic  compound  is  calculated,  are  therefore  similar  to  those 
described  for  mineral  substances  (p.  66).  We  may  take  for  illustration  an 
alkaloid,  an  acid,  and  one  or  more  neutral  substances. 

1.  An  Alkaloid. — One  hundred  parts  of  morphia  yield  by  combustion  :  of 
carbon,  71-91;  of  hydrogen,  6  85;  of  oxygen,  16  44;  and  of  nitrogen,  4*80. 
The  hydrochlorate  of  this  base  may  be  readily  obtained  anhydrous,  and  it  is 
found  that  100  grains  of  the  anhydrous  salt  contain  8875  of  morphia  and 
11*25  of  hydrochloric  acid.  Assuming  this  analysis  to  be  correct,  the  atomic 
weight  of  the  alkaloid  will  be  292  (11'25  :  88  75  :  :  37  :  292).  The  weight 
of  each  element  contained  in  this  quantity  of  the  alkaloid  is  easily  deduced 
from  the  elementary  analysis  of  100  parts.     Thus — 


100 

71-91       : 

:      292      : 

209-97  Carbon 

100 

6-85       : 

:       292      ■ 

20-00  Hydrogen 

100 

16-44       : 

:       292 

48  00  Oxygen 

100 

4-80      : 

:       292       . 

14-01  Nitrogen 

If  the  w^eight  of  each  element,  contained  in  an  equivalent  of  morphia,  is 
divided  by  its  atomic  weight,  the  products  will  represent  the  number  of  atoms 
contained  in  each  atom  of  morphia: — 


Parts. 

Equiv. 

Atoms. 

Atoms. 

209-97 

■—       6       == 

34-99 

or     35  of  Carbon 

20-00 

-^  •     1        = 

20-00 

or    20  of  Hydrogen 

48-00 

4-      8       = 

G-00 

or       6  of  Oxygen 

14.00 

-^    14      = 

1.00 

or       1  of  Nitrogen 

The  formula  for  morphia  is,  therefore,  C35H2o06N=292.  When  it  is  required 
to  calculate  the  percentage  composition  of  the  alkaloid  from  its  formula,  we 
adopt  an  inverse  method.     Thus  : — 

Parts. 
210  Carbon 

20  Hydrogen 

48  Oxygen 

14  Nitrogen 

< 
and — 

100      71-91  Carbon 
100    •     6-85  Hydrogen 
100       16-44  Oxygen 
100        4-80  Nitrogen 

Alkaloids  which  form  double  chlorides  by  combining  with  chloride  of  pla- 
tinum, may  have  their  equivalents  determined  by  a  calculation  based,  1st,  on 
the  weight  of  the  platinum  salt  in  the  dry  state,  and  2dly,  on  the  weight  of 
the  metallic  platinum  obtained  as  a  result  of  its  combustion. 

2.  An  Organic  Acid. — For  the  purpose  of  illustration,  we  may  take  Oxalic 
acid.     This  and  other  acids  are  first  combined  with  oxide  of  silver  or  oxide 


Atoms. 

Equ 

35 

X         6 

20 

X         1 

6 

X         8 

1 

X       14 

292 

210 

292 

20 

292 

48 

292 

14 

FORMULiE    OF    ORGANIC    ACIDS.  555 

of  lead,  takinp^  care  that  the  compounds  are  neither  basic  nor  hydrated. 
The  oxalate  of  lead,  dried  at  212°,  consists  of  24*32  of  oxalic  acid,  and 
7568  of  oxide  of  lead,  or  36  parts  of  the  acid  are  required  to  form  a  definite 
salt  with  112  parts  (or  one  equivalent)  of  oxide  of  lead.  This  acid  contains 
no  hydrogen,  so  that  in  burning  the  dry  lead-salt  with  well-dried  oxide  of 
copper,  no  water  is  formed,  and  the  only  product  is  carbonic  acid  :  100  grains 
of  Oxalic  acid,  (0),  are  thus  found  to  contain  33  33  parts  of  carbon  and 


0 

0 

100      : 

;       33-33       : 

:       36       ; 

:       11-99  Carbon 

100 

:       66-67       : 

:       36       : 

;       24-00  Oxygen 

66-61  of  oxygen:  and  11-99^6=1  99,  or  2C,  and  24-^8=30:  hence  anhy- 
drous oxalic  acid  is  represented  by  Cfi^ :  and  from  this  formula,  its  cen- 
tesimal composition  may  be  deduced  as  in  the  case  of  morphia. 

Alkaloids  and  acids  which  either  crystallize,  or  form  crystallizable  salts, 
frequently  combine  with  water  to  form  hydrates.  To  avoid  error  in  this 
respect,  it  is  sometimes  advisable  to  ascertain  the  atomic  weight  of  an  alka- 
loid by  determining,  by  precipitation,  the  proportion  of  acid  (sulphuric  or 
hydrochloric)  contained  in  a  weighed  quantity  of  the  crystallized  salts.  In 
reference  to  crystallizable  acids,  the  amount  of  water  combined  with  the 
crystals  of  Oxalic  acid  may  be  thus  determined  :  63  grains  of  the  acid  dis- 
solved in  water,  and  precipitated  by  acetate  of  lead,  yield  148  grains  of  dry 
oxalate  of  lead.  Deducting  the  weight  of  the  oxide  (148 — 112  =  36),  we 
obtain  the  weight  of  dry  acid  which  has  combined  with  lead.  As  63 
grains  of  crystallized  acid  were  used  in  the  experiment,  then  63 — 36=21, 
or  three  equivalents  of  water  must  have  been  combined  with  them.  Hence 
crystallized  Oxalic  acid  has  the  formula  C303,3HO,  or,  as  it  cannot  exist 
without  an  atom  of  water,  CaOgHO  -f  2H0. 

3.  Neutral  Bodies. — In  reference  to  neutral  substances  which  do  not  enter 
into  combination  with  mineral  compounds  of  which  the  equivalents  are  known, 
there  are  great  difficulties  in  assigning  a  correct  atomic  constitution.  In 
some  cases  they  combine  with  oxide  of  lead,  and  from  this  combination,  a 
formula  may  be  deduced :  gum,  sugar,  and  starch  are  bodies  of  this  kind : 
on  the  other  hand,  some,  such  as  mannite,  enter  into  no  known  combination. 
The  general  rule  regarding  organic  substances  of  this  nature,  is  to  divide 
the  quantity  of  each  element  contained  in  100  parts,  by  its  equivalent.  The 
quotients  thus  show  the  relations  which  the  elements  bear  to  each  other  in 
atoms  or  equivalents,  and  if  fractional,  these  may  be  converted  into  integers 
by  multiplication. 

Cane-sugar  may  be  combined  with  oxide  of  lead  ;  and,  by  analysis,  it  is 
found  that  this  compound  contains  in  100  parts,  59'3  of  oxide  of  lead  and 
40  1  of  sugar.  If  an  atom  of  sugar  were  united  to  an  atom  of  oxide  of  lead, 
then  the  equivalents  would  be  76-81  for  (59  3  :  40-1  :  :  112  :  16-81),  but 
there  is  great  reason  to  believe  that  2  atoms  of  oxide  of  lead  replaced  2 
atoms  of  water  which  are  contained  in  crystallized  sugar ;  and  therefore  that 
the  equivalent  of  anhydrous  sugar  is  153  ;  (16-81x2=153-14).  One  hun- 
dred parts  of  crystallized  cane-sugar  give  by  combustion  : — 

Atoms. 
Carbon      .     41-50      -f-      6      =       6-92  1-064      =      11-7  or  12 

Hydrogen        6-45       -^       1       ==       6-45  0-993       =       10-9  or  11 

Oxygen     .     52-05      -f.      8       =      6-50  1-000      =      11-0  or  11 

The  figures  in  the  fourth  column  are  obtained  by  making  oxygen  the  unit 
and  divisor,— thus,69-2-i-6-50  =  l-064  ;  6-45-f-6-50=0-993;  and  6-50^6-50 
=  1.     The  quotients  multiplied  by  11  give  the  results  in  atoms  at  HI,  109, 


556  CALCULATED    FORMULuE    OF,  SUGAR    AND    MANNITE. 

and  11  respectively,  or,  in  round  numbers,  C^^K^^O^^.  Deducting  the  2 
atoms  of  water  which  are  known  to  exist  in  crystallized  cane-sugar,  the  for- 
mula would  stand  thus  :  C^'gHyOg-f  2H0.  When  sugar  combines  with  oxide 
of  lead,  the  two  atoms  of  water  are  replaced  by  two  of  this  oxide,  so  that 
saccharide  of  lead  would  be  Cj5jHgOg,2PbO,  or  153  parts  of  sugar  (1  atom) 
to  224  parts  of  oxide  of  lead  (2  atoms).  The  formula  here  given  is  well 
adapted  to  explain  the  conversion  of  sugar  into  alcohol,  as  well  as  various 
other  chemical  changes  of  this  compound.  If,  from  the  formula  of  crystal- 
lized cane-sugar  (C,aHijOii),  we  desire  to  calculate  the  centesimal  composi- 
tion, so  as  to  compare  the  theoretical  with  the  ascertained  results,  the  differ- 
ences will  be  no  greater  than  might  be  explained  by  slight  errors  in  analysis. 
This  will  be  evident  from  the  following  figures  : — 

Atoms.                                                       Calculated.  Found. 

Carbon.        .        .     12  x  6  =  72  or      42-11  41-50 

Hydrogen      .         .     11  x  1  =  H  or         6-43  6-45 

Oxygen          .         .     11  X  8  =  88  or       51-46  52-05 

Mannite  is  a  compound  of  three  elements.     In  100  parts  it  consists  of  : — 


Carbon  .  39-54 
Hydrogen  7-73 
Oxygen    .     52-73 


6       =      6-59  1-00       X       Q      =      Q 

1      =      7-73  1-17       X       6      =      7 

8      =      6-59  1-00       X       Q      =      & 


The  atoms  of  carbon,  hydrogen,  and  oxygen,  as  deduced  from  the  cen- 
tesimal composition,  are  as  the  respective  numbers,  659,  773,  659.  If  the 
figures  in  the  third  column  are  divided  by  the  amount  of  oxygen  as  unity, 
quotients  are  obtained  which,  when  multiplied  by  6,  give  a  series  of  atoms  in 
integers,  namely,  CgHyOg.  These  figures,  therefore,  merely  express  the  pro- 
portions of  the  elements  in  reference  to  their  atomic  weights.  They  convey 
a  better  knowledge  of  the  composition  of  bodies  than  the  arithmetical  pro- 
portions in  100  parts  ;  and  are  so  far  convenient  for  use.  At  the  same  time 
formulae  thus  derived,  are  purely  empirical. 

Volatile  Liquids. — When  the  organic  compound  is  a  volatile  liquid,  its 
vapor-density  will  serve  to  control  the  results  of  an  analysis.  In  the  series 
of  isomeric  liquid  hydrocarbons,  it  is  chiefly  by  the  vapor-density  of  each 
liquid,  that  the  number  of  atoms  which  should  enter  into  the  respective 
formulae,  can  be  accurately  determined.  The  degree  of  condensation  of  the 
elements  is  therefore  a  material  point  in  considering  their  atomic  constitu- 
tion, and  in  constructing  their  formulae.  100  parts  of  Alcohol  yield  by  the 
combustion-tube  : — 

Atoms. 
Carbon    .        .     52-65     -j-     6    =      8-92  8-92    -f-    4-30    =    2 

Hydrogen         .     12-90    -^    1     =    12-90  12-90    -^    4-30    =    3 

Oxygen    .        .     84-45     -j-    8    =      4-30  4-30    -i-    4-30    =    1 

The  sp.  gr.  of  the  vapor  of  alcohol  is  1"61  :  hence,  if  this  analysis  be  cor- 
rect the  specific  gravities  of  the  elements  in  these  atomic  proportions  should 
correspond.  With  respect  to  carbon,  the  volume  of  its  vapor,  compared 
with  hydrogen,  cannot  be  determined  experimentally.  It  is  assumed  that 
one  volume  or  atom  is  represented  by  the  sp.  gr.  0*4146.  Oxygen  has  a  sp. 
gr.  of  1-1057,  and  hydrogen  a  sp.  gr.  of  0*0691,  hence  : — 

Atoms.  Sp.  gr. 

Carbon  ...     2  (0-4146  x  2)  =  0-8292 

Hydrogen     ...     3  (0-0691   x  3)  =  0-2073 

Oxygen        ...     1  (1-1057  -r-  2)  =  0-5528 

Sum  of  specific  gravity        .         .         .     1-5893 


CALCULATED    FORMULAE    FROM    VAPOR-DENSITIES.  557 

The  sp.  gr.  of  the  vapor  of  alcohol  is  therefore  nearly  in  accordance  with 
that  which  should  be  found  in  one  volume  of  a  vapor  of  which  the  consti- 
tuents are  2  atoms  (or  volumes)  of  carbon,  3  atoms  (or  volumes)  of  hydro- 
gen, and  1  atom  (or  half  a  volume)  of  oxygen.  The  most  simple  formula 
for  alcohol  would  therefore  be  C^Uft.  Alcohol  has  neither  acid  nor  basic 
properties,  and  forms  no  definite  compounds  with  bodies.  Hence  its  equi- 
valent might  be  taken  at  twice,  three  times,  or  even  four  times  the  numbers 
of  the  atoms  above  given.  The  theory  of  the  production  of  sulphovinic 
acid  and  of  ether  by  there  action  of  sulphuric  acid  on  alcohol,  is  rendered 
much  more  simple  by  doubling  the  numbers  obtained  by  analysis,  and  making 
them  C^HgOg.  In  this  case  the  atom  of  alcohol  would  correspond  to  two 
volumes  of  its  vapor ;  and  its  specific  gravity  compared  with  air  would  be  as 
161  to  I'GO  and  with  hydrogen  as  23  to  1.  The  conversion  of  alcohol  into 
aldehyde  and  acetic  acid  by  processes  of  oxidation,  is  rendered  more  intelli- 
gible by  the  adoption  of  the  formula  above  given. 

Rectified  Oil  of  turpentine  yields  by  analysis  in  100  parts  : — 

Carbon 
Hydrogen 

Its  formula  as  thus  deduced,  would  be,  in  its  most  simple  form,  5  atoms  of 
carbon  and  4  of  hydrogen  (C5HJ.  But  it  might  also  be  C,oHg  or  CgoHjQ. 
The  ascertained  specific  gravity  of  the  vapor  compared  with  air  is  4*76.  A 
constitution  represented  by  C5H4  would  give  for  the  specific  gravity,  only 
one-half  of  this  density,  or  2-35.  C^JI^  would  give  a  density  of  4*70,  re- 
sembling so  closely  that  which  has  been  determined  by  experiment,  that  it  is 
impossible  not  to  conclude  that  10  atoms  of  carbon  and  8  atoms  or  volumes 
of  hydrogen  are  included  in  each  volume  of  the  vapor  of  oil  of  turpentine. 
The  oil,  however,  combines  with  some  of  the  hydracids,  including  the  hydro- 
chloric. With  the  latter  it  forms  a  solid  artificial  camphor,  represented  by 
C^oH,gHCl.  The  formula  for  the  oil  of  turpentine  should  be,  therefore,  Cgo 
H^g,  unless  it  be  supposed  that  2  atoms  of  the  oil  ^iC^oR^)  are  combined 
with  1  of  hydrochloric  acid.  The  former  is  selected  by  reason  of  its  greater 
simplicity  and  its  agreement  with  the  formulae  of  other  hydrocarbons.  One 
atom  of  oil  of  turpentine,  like  one  atom  of  alcohol,  therefore  corresponds  to 
two  volumes  of  vapor:  hence  the  specific  gravity  would  be  about  4 '7  : — 


Atoms. 

88-24    -^    6    =    14-70 

1-25  or  5 

11-76    -7-    1    =    11-76 

1-      or  4 

Atoms,    Vol. 

Carbon    . 

• , 

.     20  or  20    =    0-4146 

X     20     ... 

...     8-292 

Hydrogen 

. 

.     16  or  16     =    0-0691 

X     16     ... 

...     1-105 

9-397 


Vapor-density  of  oil  of  turpentine    ....     4-698 

Chloroform  is  considered  to  have  the  constitution  represented  by  the  for- 
mula C.jH,Cl3.  The  specific  gravity  of  its  vapor  is  4'20.  This  is  in  accord- 
ance with  the  view,  that  each  atom  of  the  compound  corresponds  to  two  vol- 
umes of  the  vapor  : — 


Carbon  . 
Hydrogen 
Chlorine 


Atoms. 
.     2      .. 
.     1      .. 
.     3      .. 

Vol. 

2 

....     1 
....     3 

2 

jhlorofoi 

m 

Sp.  gr. 

0-4146  X  2     ... 
0-0691   X   1     .-. 
2-4876  X  3     ... 

Sp.  gr. 
...     0-8292 
...     0-0691 
...     7-4628 

1 

8-3611 

isity  of  ( 

.     41805 

558  EMPIRICAL    AND    RATIONAL    FORMULA. 

As  a  general  rule  the  vapor-density  shows  the  proportions  in  which  the 
elements  combine,  but  the  atomic  weight  can  be  correctly  determined  only 
by  calculation  from  some  definite  compound.  In  the  case  of  chloroform  no 
such  compound  is  known.  This  and  other  instances  prove  that  in  the  vapors 
of  organic  liquids,  the  gaseous  elements  undergo  an  enormous  condensation. 

When  the  formula  of  an  organic  substance  merely  expresses  the  number 
of  atoms  of  each  element,  as  C^HgOg  (alcohol),  or  C^H^O^  (hydrated  acetic 
acid),  it  is  called  empirical.  It  expresses  the  relative  proportions  of  the 
elements,  without  reference  to  the  mode  in  which  they  are  combined,  or  to 
the  atomic  weight  of  a  body.  A  rational  formula  implies  one  which  pro- 
fesses, upon  certain  hypotheses,  to  define  the  mode  of  union  or  actual  arrange- 
ment of  atoms  in  a  compound,  of  which  the  equivalent  has  been  determined 
by  experiment. 

We  here  necessarily  enter  into  a  region  of  speculation.  Thus,  out  of  an 
atom  of  alcohol  a  variety  of  rational  formula  may  be  constructed,  according 
to  the  hvpothesis  which  the  chemist  may  adopt.  The  empirical  formula  of 
alcohol  '(C.,He03)  may  be  expressed  by  C^H30  +  H0,  or  2C,H,-f2HO,  or 
2CO-f2CH2,  +  H3.  The  empirical  formula  of  hydrated  acetic  acid  (C^H^J 
may,  according  to  the  radical  theory,  be  converted  into  the  rational  formulae 
(C,H303-fHO,  or2(C,H,)-fOJ. 

Compound  Radicals. — In  inorganic  chemistry,  radicals  are  represented,  by 
simple  substances  which  enter  into  combination  with  oxygen,  chlorine,  and 
other  electro-negative  bodies.  Sulphur  (S)  is  the  radical  of  sulphuric  acid 
(SO3),  and  sodium  (Na)  is  the  radical  of  chloride  of  sodium  (NaCl).  In 
order  to  assimilate  organic  to  inorganic  chemistry,  it  has  been  suggested  that 
some  of  the  atoms  of  organic  substances  may  be  so  arranged  as  to  form 
compound  radicals,  which  are  assumed  to  combine  with  the  electro-negative 
elements,  0,  CI,  and  S,  to  form  biliary  compounds,  like  those  met  with  in 
inorganic  chemistry.  Cyanogen  is  a  well  marked  instance  of  a  compound 
radical.  It  is  represented  by  the  formula  C^jN  and  it  acts  in  all  respects 
like  an  element.  It  combines  with  hydrogen  and  all  the  metals  like  an 
electro-negative  body,  and  with  oxygen  and  chlorine  like  an  electro-positive 
body.  A  compound  radical,  therefore,  is  simply  a  body  which  combines, 
like  an  element,  with  other  elementary  bodies.  It  may  also  enter  into  combi- 
nation with  other  compound  radicals.  In  the  cyanide  of  cacodyle  (KdCy, 
or  C^HgAs-fCaN)  we  have  an  instance  of  two  compound  radicals  combining 
like  elements. 

Organic  radicals,  a  few  of  which  have  been  isolated,  while  the  greater 
number  have  only  an  hypothetical  existence,  may  consist  of  two,  three,  or 
more  elements.  When  they  contain  carbon  and  hydrogen  only,  they  generally 
terminate  in  yle,  and  are  represented  by  a  symbol,  like  elements.  Thus,  the 
radical  of  alcohol  (C^H^)  is  called  Ethyle,  and  is  represented  by  the  symbol 
Ae.  Ether  would  therefore  be  an  oxide  of  ethyle  (C^Ht3,0,  or  AeO).  For- 
myle  (Cgll)  (Fo)  is  the  radical  of  formic  acid,  and  this  acid  is  C2H,03,  oxide 
of  formyle,  or  F0O3.  Methyle  (Me)  is  CgHg ;  Acetyle  (Ac)  C JI3.  Cacodyle, 
which  consists  of  carbon,  hydrogen,  and  arsenic,  is  C4H(;As,  and  has  the 
symbol  Kd.  This  view  of  the  constitution  of  organic  compounds  has  been 
generally  adopted.  While  it  is  open  to  some  objections,  there  can  be  no 
doubt  that  it  has  greatly  facilitated  the  study  and  classification  of  organic 
substances. 

Substitutions. — As  in  mineral  chemistry,  one  negative  element  may  be  sub- 
stituted for  another,  HO  becoming  HCl  by  the  substitution  of  chlorine  for 
oxygen,  so  in  reference  to  organic  radicals,  a  similar  change  may  be  observed. 
Formic  acid  is  converted  into  chloroform  by  the  substitution  of  three  atoms 
of  chlorine  for  three  atoms  of  oxygen,  the  radical  remaining  the  same  :  thus 


COMPOUND    RADICALS.      SUBSTITUTION- COMPOUNDS.  559 

C3H+O3  becomes  C^H-f  CI3;  and  whole  series  of  compounds  may  be  thus 
constructed,  in  which  one  negative  element  simply  replaces  another  negative 
element,  according  to  the  usual  laws  of  equivalent  proportions.  There  is, 
however,  anotlier  remarkable  character  in  organic  compounds,  to  which  the 
term  substitution  is  specially  applied — namely,  where  the  electro-negative  may 
take  the  place  of  an  electro-positive  body,  the  compound  remaining  unaltered 
in  its  type ;  ?'.  e.,  the  elements  being  otherwise  in  the  same  number,  propor- 
tion, and,  as  it  is  supposed,  molecular  arrangement,  differing  in  fact  only  in 
equivalent  weight.  Hydrated  acetic  acid  (C4H303,HO)  may  have  its  hydro- 
gen replaced  by  chlorine,  to  form  chloracetic  acid  (C^ClgOgjHO),  the  electro- 
negative chlorine  being  substituted  for  the  electro-positive  hydrogen.  A 
similar  substitution  is  observed  in  the  conversion  of  chloride  of  methyle  into 
chloroform  by  chlorine:  C,H3C1  +  4C1  =  C3H,C13  +  2HC1. 

In  the  production  of  pyroxyline  from  cellulose  (p.  607),  a  certain  number 
of  atoms  of  nitrous  acid  (NOJ  are  substituted  for  an  equal  number  of  atoms 
of  hydrogen,  the  other  constituents  remaining  unchanged.  Benzole  (Ci^Hg) 
is  in  like  mann-er  converted  by  nitric  acid  into  nitro-benzole  (Ci3H5[NOJ), 
by  the  removal,  of  an  atom  of  hydrogen,  and  the  substitution  of  an  atom  of 
nitrous  acid,  as  in  the  following  equation  : — 

C.^HsH        -f        NO5        =        C,2H,(N0,)         -f-        HO 


Benzole.  Nitric  acid.  Nitrobenzole.  Water.  ^ 

Water  is  a  product  of  this  reaction  :  and,  when  we  compare  the  chemical 
and  physical  properties  of  benzole  with  those  of  nitrobenzole,  there  is  pro- 
bably no  more  remarkable  change  in  organic  chemistry,  than  that  which  this 
substitution  effects. 

Nitrobenzole  admits  of  a  still  further  change,  by  a  removal  of  its  oxygen, 
and  the  addition  of  two  atoms  of  hydrogen  :  it  is  thereby  transformed  into 
Aniliiie,  and  becomes  the  source  of  an  extensive  series  of  most  valuable 
dyes  : — 

C,2H5(N04)        4-        2H0    -f     4Fe     =    C.^R^^    +     2PeA 

Nitrobenzole.  Water.  Iron.  Aniline.       Sesquioxide 

of  iron. 

By  simple  distillation  with  water  and  metallic  iron,  this  remarkable  meta- 
morphosis is  brought  about ;  and  by  assuming  that  aniline  contains  an  atom 
of  the  compound  radical,  Phenyle  (C13H3),  this  base  is  frequently  described 
as  a  compound  ammonia,  in  which  one  atom  of  phenyle  is  substituted  for  one 
atom  of  hydrogen.  Thus  ammonia  being  NH3,  aniline  (Ci3Hy,N)  may  have 
its  atoms  thus  arranged  on  the  type  of  ammonia  (C13H5)  NH^.  It  is  ques- 
tionable how  far  the  application  of  the  names  of  well-known  chemical  sub- 
stances, possessed  of  entirely  different  properties,  to  compounds  of  this 
nature,  is  beneficial  to  science.  It  rests  entirely  on  assumption ;  for  the 
atomic  arrangement  of  the  elements  is  insusceptible  of  proof;  and  although 
the  doctrine  of  substitutions  affords  some  ground  for  the  view,  it  tends  to 
produce  in  the  mind  of  a  student  a  confusion  of  hypothesis  with  fact.  The 
terra  ammonia  is  in  these  cases  employed 'in  an  entirely  new  sense:  it  is 
intended  to  signify,  not  the  well-known  gaseoUs  compound  of  nitrogen  and 
hydrogen,  of  defined  properties  and  composition,  but  a  substance  wholly  dif- 
ferent, and  having  only  an  hypothetical  resemblance  to  it  in  chemical  consti- 
tution. Thus,  a  body  which  contains  one  atom  of  nitrogen,  associated  with 
one  or  more  atoms  of  hydrogen,  and  a  group  of  atoms  which  is  supposed  to 
replace  the  deficient  hydrogen,  is  designated  an  ''  ammonia. ^^  This  may  be 
better  illustrated  by  the  following  table,  in  which  the  composition  of  ammonia 


560  PROXIMATE    ORGANIC    PRINCIPLES. 

is  given,  and  the  atomic  constitution  of  the  radical,  substituted  for  the  hy- 
drogen, is  also  represented.  It  should  be  observed  that  Phenyle  (Cj^Hj) 
has  only  an  hypothetical  existence,  while  Methyle  (C3H3)  and  Ethyle  (C^H^) 
have  been  isolated. 

Radical  substitute  for  1  atom 
of  hydrogen. 

Ammonia    .         .         .     N  H  H  H  

Methylamiue       .         .     N  H  H  Me  Me        =         C^Hg 

Ethylamine         .         .     N  H  H  Ae  Ae         =         C^'H. 

Diethylamine      .         .     N  H  Ae  Ae  2Ae         =         CgHjQ 

Triethylamine     .         .     NAeAeAe         3Ae         =        ^vi^ts 

Aniline       .         .         .     N  H  H  Ph  Ph         =         C.^H^ 

These  are  all  considered  to  be  ammonias,  or  substitution-compounds  of 
ammonia.  They  agree  in  constitution,  in  having  1  atom  of  nitrogen,  asso- 
ciated with  3  atoms  of  hydrogen,  or  with  1,  2,  or  3  atoms  of  the  compound 
radical.  In  accordance  with  this  hypothesis  it  has  been  proposed  to  call 
aniline  Phenylamine  ;  but  there  appears  to  be  no  good  reason  for  changing 
a  universally  received  name  upon  purely  hypothetical  grounds.  Ammonia 
itself  might,  with  an  equal  disregard  of  custom  and  utility,  be  called  Nitra- 
mine,  just  as  arsenuretted  and  antimonuretted  hydrogen  have  been  recently 
designated  Arsenamine  and  Stibamine.  The  latter  are  described  as  "  ammo- 
nias" of  arsenic  and  antimony,  because  they  happen  to  be  constituted  of  one 
atom  of  a  metallic  radical  (replacing  nitrogen),  and  three  atoms  of  hydrogen. 
The  terms  alcohol,  aldehyde,  ether,  urea,  &c.,  hitherto  restricted  to  well-known 
special  bodies,  have  been  thus  vaguely  applied  by  some  chemists  to  com- 
pounds presenting  certain  hypothetical  resemblances  of  constitution.  As 
nothing  is  really  known  of  the  atomic  constitution  of  compounds,  such  a 
system  of  nomenclature,  if  recognized,  must  necessarily  lead  to  perpetual 
changes,  and  to  endless  confusion.  Aniline  has  already  borne  the  names  of 
Kyanol,  Phenylamide,  Phenylia,  and  Benzidam.  Its  present  designation 
points  to  its  original  source  from  indigo.  It  involves  no  hypothesis  of  con- 
stitution, and  is  therefore  not  liable  to  be  changed  by  the  progress  of  dis- 
covery. While  there  can  be  no  objection  to  any  new  organic  compound 
being  designated  according  to  the  fancy  of  its  discoverer,  there  is  a  serious 
objection  to  the  application  of  old  and  well-known  names  to  new  substances, 
or  to  the  use  of  such  names  in  a  sense  entirely  different  from  that  in  which 
they  have  been  hitherto  universally  accepted. 


CHAPTEE    XLV. 

PROXIMATE  ORGANIC    PRINCIPLES.      STARCH.     DEXTRINE 
INULINE.     GUM.     PECTOSE.     GELOSE.     SUGAR. 

The  proximate  principles  of  the  vegetable  and  animal  kingdoms  often 
bear  a  close  resemblance  to  each  other.  Thus  sugar,  oil,  albumen,  and 
coloring  matter,  are  found  in  both.  Gum  appears  to  be  of  purely  vegetable 
origin,  but  starch,  which  has  been  hitherto  considered  to  be  vegetable,  has 
been  found,  according  to  some  authorities,  in  a  modified  condition  in  the 
organs  of  animals.  Urea  is  peculiar  to  the  animal  kingdom.  In  this  and 
the  following  chapters  we  shall  group  together  those  substances  which 
possess  analogous  properties,  whether  of  vegetable  or  animal  origin. 


STARCH. 


561 


Rice          .... 

70-85 

Beans    . 

Dried  potatoes 

83-8 

Maize     . 

Wheat      .... 

.  60-80 

Potatoes 

Aerated  bread  . 

68 

Turnips 

Barley      .... 

60 

Beet- root 

Fermented  bread 

53-3 

Parsnips 

Oats          .... 

50 

Carrots  . 

Peas         .... 

42-6 

Starch  (C.^'R.fiJ, 

Starch  (Fecula  amylum)  is  an  organized  substance  most  extensively 
diffused  in  the  vegetable  kingdom.  It  is  found  in  the  seeds,  tubers,  roots,  and 
woody  portions  of  plants,  and  is  generally  associated  with  gum,  sugar, 
woody  fibre,  and  other  vegetable  principles.  It  is  especially  abundant  in 
the  seeds  of  the  cerealia.  Wheat  and  rice  contain  the  largest  proportions. 
It  is  contained  in  solid  granules  in  the  cells  of  the  seed,  and  is  separated  by 
a  simple  mechanical  process.  The  proportions  contained  in  100  parts  of 
different  seeds  and  roots,  is  as  follows  : — 

42 

28.4 

15-20 

15 

13-14 

9 

3 

Starch  is  usually  seen  as  a  white,  and  especially  in  the  seeds  of  the  cerealia, 
somewhat  glistening  powder,  of  a  specific  gravity  of  about  1*5,  which,  when 
pressed,  produces  a  peculiar  cracking  sound,  and  feels  somewhat  elastic. 
Under  the  microscope  it  is  seen  to  consist  of  small  spheroidal  granules, 
differing  in  size  and  shape ;  the  largest,  and  those  best  adapted  to  micro- 
scopical examination,  are  obtained  from  the  rhizome  of  the  Canna  coccinea, 
known  under  the  name  of  Tous  les  Mois :  they  are  about  one-260th  of  an 
inch  diameter  ;  they  appear  wrinkled,  and  as  if  made  up  of  concentric  layers, 
and  a  fissure  (htlum)  may  generally  be  observed  upon  some  part  of  the  grains, 
which  has  been  regarded  as  the  spot  where  they  adhered  to  the  cell  contain- 
ing them.  Examined  by  polarized  light,  these  granules  present  a  black 
cross,  the  centre  of  which  appears  to  correspond  with  the  hilura.  In  wheat 
starch  this  cross  is  not  easily  observed,  but  in  potato-starch  it  is  distinct,  so 
that  it  has  been  resorted  to  as  a  means  of  detecting  the  adulteration  of 
wheat  starch  with  the  cheaper  varieties.  The  granules  of  potato-starch  are 
remarkable  for  their  large  size  and  peculiar  shape.  Some  of  them  have  a 
diameter  of  one-250th  of  an  inch,  and  have  a  clam-shell  shape,  the  lines  or 
workings  spreading  in  zones  around  the  hilum,  which  is  at  the  smaller  end. 
The  granules  of  wheat-starch  have  about  the  1- 1000th  of  an  inch  in  diameter, 
and  are  of  an  irregularly  rounded  form.  These  granules  are  accompanied 
by  others,  which  are  much  smaller.  The  granules  of  rice-starch  are  small 
and  irregular  ;  they  have  about  the  l-3000th  of  an  inch  in  diameter.  The 
granules  of  starch  are  contained  in  cells,  and  are  separated  mechanically  by 
breaking  up  these  cells  in  cold  water.  Starch  is  chiefly  procured  from  wheat 
and  the  tubers  of  potatoes,  by  simple  maceration  of  the  pulp  in  cold  water — 
the  acetic  acid  produced  by  fermentation  of  the  aqueous  liquid  removing  the 
gluten.  It  is  procured  from  rice  by  dissolving  the  gluten,  by  means  of  a 
weak  alkaline  solution  of  soda.  100  parts  of  rice  yield  from  70  to  80  parts  ; 
100  parts  of  wheat,  from  33  to  45  parts  ;  and  100  parts  of  fresh  potatoes, 
from  10  to  12  parts  of  starch. 

Starch  is  generally  represented  as  insoluble  in  cold  water  ;  and  indeed  the 
usual  mode  of  obtaining  it,  which  consists  in  diffusing  the  rasped  or  ground 
vegetable  in  cold  water,  and  washing  and  collecting  the  deposit,  seems  to 
justify  such  a  conclusion  ;  but  if  potato-starch  is  triturated  with  water  at 
60^,  and  the  mixture  poured  upon  a  filter,  the  filtrate  contains  starch  :  and 
if  a  dilute  solution  of  starch  in  hot  water  is  cooled  to  60°  and  filtered,  there 
is  starch  in  the  filtered  liquid,  but  it  is  probably  in  a  state  of  fine  suspen- 
36 


562  STARCH, 

sion.  As  starch  is  an  organized  substance,  and  cannot  be  obtained  in  that 
state  of  purity  which  belongs  to  crystallized  products,  and,  as  it  is  easily 
convertible  into  gum  and  sugar,  it  may  be  doubted  how  far  some  of  the 
properties  ascribed  to  starch  actually  belong  to  this  body  in  its  pure  form. 

Starch  is  rapidly  disintegrated  by  hot  water :  when  1  part  of  it  is  gradu- 
ally heated  in  15  parts  of  water  to  about  130°,  it  begins  to  change  its  appear- 
ance, and  at  140°  or  150°  the  whole  acquires  a  pasty  consistence,  and  the 
microscope  shows  that  in  this  state  the  granules  are  swollen  and  broken  :  if 
the  paste  is  dififused  through  water,  a  large  portion  of  them  subsides,  and  the 
supernatant  fluid  retains  some  starch,  in  a  modified  state,  but  this  appears 
to  be  after  a  time  deposited.  Dialysis  shows  that  this  substance  is  not  really 
soluble  in  water :  it  will  not  traverse  the  dialysing  septum.  We  have  found 
that  5000  parts  of  water  will  not  dissolve  one  part  of  starch.  It  may  be  for 
a  longer  or  shorter  time  suspended  in  a  transparent  form  in  water,  but  even 
when  aided  by  long  boiling  the  starch  appears  to  be  only  mechanically  dif- 
fused through  the  water,  and  not  perfectly  dissolved.  Various  salts  dis- 
solved in  water,  facilitate  this  deposition  of  starch.  If  starch-paste  is  sub- 
jected, under  pressure,  to  a  temperature  of  about  300°,  a  solution  is  obtained 
which,  on  cooling,  deposits  minute  spherical  granules  of  about  one-4000th 
of  an  inch  diameter,  and  having  the  leading  chemical  characters  of  the  origi- 
nal starch  ;  so  that  in  this  way  the  varieties  of  starch  may  be  brought  to  the 
same  physical  condition. — (Jacquelain.)  Starch  is  insoluble  in  alcohol  and 
ether.  It  forms  a  tenacious  paste  with  weak  solutions  of  potassa  or  soda, 
but  not  with  ammonia. 

With  iodine  it  forms  a  characteristic  blue  compound,  which,  provided  the 
iodine  is  not  in  excess,  loses  color  when  heated  to  about  160°,  but  regains  it 
on  cooling ;  it  is  also  decolored,  with  the  production  of  hydriodic  acid,  by 
exposure  to  light.  This  property  renders  iodine  a  valuable  test  for  starch, 
and  starch  for  iodine,  but  it  is  open  to  many  fallacies.  In  a  warm  solution 
no  color  is  produced,  and  the  blue  color  formed  in  a  cold  solution  of  starch 
is  destroyed  by  chlorine  and  bromine,  by  corrosive  sublimate,  by  all  alkalies, 
by  sulphurous  acid  and  arsenious  acid,  and  by  all  bodies  which  can  enter 
into  combination  with  free  iodine.  When  iodine  is  in  a  combined  state,  it 
has  no  action  on  starch.  Thus  iodide  of  potassium  has  no  effect  until  nitric 
acid,  chlorine,  or  some  oxidizing  agent  is  added  ;  and  iodic  acid  produces  no 
change  in  starch  until  some  deoxidizing  substance  is  added,  e.  g.,  sulphurous 
acid.  Vegetable  acids  (acetic,  oxalic,  and  tartaric)  have  no  effect  upon  the 
compounds  of  starch  and  iodine,  but  gallic  acid  or  tannic  acid  in  excess 
prevent  its  production  and  destroy  the  blue  color  when  produced.  Paper 
imbued  with  a  mixed  solution  of  starch  and  iodide  of  potassium  is  imme- 
diately blued  by  free  chlorine  and  bromine,  and  ia  paper  of  this  kind  is  used 
as  a  test  for  atmospheric  ozone  (p.  115). 

The  ultimate  elements  of  pure  wheat-starch,  dried  at  212°,  are  represented 
as  CigHinOio,  but  when  in  combination  with  oxide  of  lead  the  compound 
appears  to  be  C^aHgOgjPbO,  so  that  the  more  correct  formula  for  starch  is 
CigHgOg+HO  ;  but  starch,  in  its  ordinary  state,  retains  a  larger  propor- 
tion of  water,  and  it  varies  in  the  different  varieties  of  starch.  When  1  part 
of  starch  is  dissolved  in  150  of  boiling  water,  and  precipitated  by  ammoni- 
acal  acetate  of  lead,  the  composition  of  the  precipitate  is  CiaHg09+2PbO. 
This  compound,  which  is  called  the  Amylate  of  lead,  is  also  produced  by 
the  addition  of  subacetate  of  lead  added  to  starch,  in  a  state  of  suspension  or 
solution  in  water.  Starch  mixes  readily  with  a  solution  of  sulphate  of  copper, 
but  on  adding  an  alkali  the  oxide  is  precipitated  in  combination  with  starch. 
It  is  not  redissolved  by  adding  an  excess  of  alkali,  and  no  suboxide  is  pre- 
cipitated on  boiling.     Starch,  when  gelatinized  by  weak  solutions  of  potassa 


USES    OF    STARCH.  563 

or  of  soda,  may  be  thrown  down  from  these  alkaline  liquors  by  neutralizing 
them  with  acetic  acid,  and  then  adding  alcohol.  A  cold  solution  of  starch 
is  precipitated  by  tannic  acid  or  infusion  of  galls,  and  starch  may  be  thus 
separated  from  gum.  The  tannate  of  starch  is  redissolved  at  a  boiling  tem- 
perature. The  mineral  acids  have  a  peculiar  effect  upon  starch,  according 
to  their  degree  of  concentration  and  the  proportion  in  which  they  are  used. 
Strong  nitric  acid  heated  with  starch,  oxidizes  it  and  converts  it  into  oxalic 
acid.  Diluted  nitric  acid  converts  it  into  dextrine.  Strong  sulphuric  acid, 
in  the  cold  produces  slowly  with  starch  a  pink  color,  but  when  heated  the 
mixture  is  carbonized.  Diluted  sulphuric  acid  produces  various  changes  in 
this  principle.  When  starch  is  mixed  with  hot  water  and  sulphuric  acid  is 
added  to  the  mixture  in  the  proportion  of  a  few  thousandths  of  its  weight, 
the  globules  swell  and  burst,  and  the  more  soluble  portions  are  transformed 
into  what  is  called  soluble  starch,  the  liquid  not  having  its  usual  opacity, 
but  being  more  or  less  transparent.  The  article  called  Glenjield  starch 
appears  to  have  undergone  this  change.  It  is  employed  for  stiffening  net 
and  fine  fabrics  generally,  and  it  does  this  without  rendering  them  opaque. 
If  the  proportion  of  acid  is  slightly  increased  and  the  heat  is  continued  for 
a  short  time,  the  starch  undergoes  another  molecular  change  :  the  liquid 
becomes  of  a  pale  yellow  color,  and  now  gives  a  wine-red  in  place  of  a  bright 
blue  color  with  iodine.  The  starch  is  converted  into  dextrine.  If  the  liquid 
with  the  acid  is  boiled  for  some  hours,  it  produces  no  change  of  color  with 
iodine,  but  is  converted  into  starch  sugar,  a  variety  of  glucose  (p.  569). 
The  Greenfield  starch  occasionally  undergoes  transformation  to  this  extent, 
for  we  have  found  it  to  possess  the  property,  like  glucose,  of  reducing  the 
oxide  of  copper  in  a  solution  of  potash. 

The  principal  commercial  varieties  of  starch  are,  1.  Wheat-starch  ;  2. 
Potato-starch ;  3.  Rice-starch ;  4.  Arrowroot-starch,  obtained  from  the 
tubers  of  the  Maranta  arundinacea;  5.  Sago,  from  the  stems  of  certain  palms, 
and  which  is  usually  granulated  ;  6.  Tapioca,  the  starch  of  the  Jatropha 
manihot;  t.  Tons  les  raois,  from  the  rhizome  of  the  Canna  coccinea ;  8. 
Otaheite  arrowroot,  from  Canna  pinnatifida ;  9.  Portland  arrowroot,  from 
the  tubers  of  Arum  maculatum. 

Uses  of  Starch. — Starch  is  not  only  largely  consumed  in  the  manufacture 
of  dextrine,  but  is  in  common  use  for  stiffening  various  fabrics  and  articles 
of  wearing  apparel ;  and  for  this  purpose  a  slight  blue  tinge  is  generally 
given  to  it  by  a  little  artificial  ultramarine.  Thin  and  cheap  calicoes  are 
often  largely  imbued  with  starch  and  sulphate  of  soda  or  magnesia  to  make 
them  appear  of  greater  substance  than  they  really  are.  Lozenges,  and 
various  articles  of  confectionery,  consist  partly  of  starch.  Cheap  sugar- 
plums are  composed  of  refuse  starch,  with  chalk,  gypsum,  and  other  trash : 
a  spurious  refined  liquorice  is  also  made  upon  the  same  principle.  Stone- 
blue  is  a  compound  of  indigo,  or  Prussian  blue,  and  the  inferior  kinds  of 
starch.  Among  the  substances  used  to  adulterate  starch,  porcelain-clay  was 
at  one  time  prevalent.  Considered  as  an  article  of  food,  as  a  part  of  the 
diet  of  children  and  of  invalids,  and  as  a  component  of  our  most  nutritious 
vegetables,  starch  is  very  important.  Bu-t,  although  eminently  adapted  to 
form  part  of  our  food,  it  is  not  fitted  for  exclusive  nutriment ;  and  this  is  the 
case  with  all  vegetables  deficient  in  nitrogen. 

When  starch  is  carefully  heated  to  about  300°  it  becomes  anhydrous,  and 
at  about  400°  it  darkens  in  color  and  is  converted  into  a  substance  called 
torrefied  starch,  British  gum,  or  Dextrine,  It  is  now  soluble  in  cold  water, 
forming  a  brown  gummy  solution,  the  properties  of  which  will  be  hereafter 
described.     If  the  heat  is  carried  still  higher  the  starch  becomes  carbonized, 


564  DEXTRINE. 

and  in  the  air  it  undergoes  combustion.  It  leaves  a  carbonaceous  residue, 
but  this  may  be  entirely  burnt  away,  if  the  starch  is  pure.  Smalt  or  mineral 
blue  is  sometimes  used  to  give  a  slight  color  to  starch,  and  in  this  c4se  the 
coloring  matter  will  be  left  as  a  residue. 

Dextrine  (C^^H.^OJ. 

This  may  be  regarded  as  an  isomeric  condition  of  starch.  It  differs,  how- 
ever, remarkably  in  its  properties.  The  term  dextrine  has  been  given  to 
this  substance  from  the  property  which  its  solution  possesses  of  turning  the 
plane  of  polarization  to  the  right  when  acting  on  polarized  light,  while  gum, 
which  it  resembles  in  chemical  properties,  turns  the  plane  of  polarization  to 
the  left.  A  solution  of  starch  also  rotates  the  plane  to  the  right,  but  not  iu 
such  a  marked  degree  as  a  solution  of  dextrine.  According  to  Roscoe,  the 
deviation  produced  by  dextrine  is  equal  to  -f  138°  7'.  It  has  been  stated 
that  starch  is  easily  convertible  into  dextrine  by  a  heat  of  about  400°  ;  but 
there  are  other  means  of  effecting  this  change  ;  amongst  which  the  most  re- 
markable is  that  produced  by  a  peculiar  azotized  principle  called  diastase 
(from  8uatt]fii,  to  separate),  and  which  is  formed  in  germinating  seeds  and 
growing  buds.  It  occasions  the  change  of  the  amylaceous  part  of  the  seed 
into  gum  and  sugar,  during  a  certain  period  of  its  growth  ;  and  it  is  in  con- 
sequence of  its  presence  in  malt  that  the  brewers'  sweet  worts  are  produced, 
and  that  the  addition  of  a  little  malt  to  unmalted  grain  changes  a  large  pro- 
portion of  its  starch  into  saccharine  or  fermentable  matter.  It  is  a  remarka- 
ble fact  that  saliva  has  also  the  property  of  converting  starch  into  sugar.  If 
a  small  quantity  of  starch  in  water  is  gently  warmed  with  saliva,  and  a  few 
drops  of  a  solution  of  sulphate  of  copper  with  an  excess  of  potash  are  added 
and  the  liquid  is  boiled,  a  precipitate  of  suboxide  of  copper  is  produced,  as 
with  grape-sugar.  Hence  starchy  matters  are  more  or  less  saccharined 
during  the  process  of  mastication. 

Diastase  may  be  obtained  from  carefully  prepared  malt,  by  bruising  and 
digesting  it  in  water  at  70°  to  80°  :  the  pasty  mixture  is  then  pressed,  and 
the  liquor  which  runs  from  it  filtered,  heated  to  about  170°,  and  again 
filtered  :  this  filtrate  retains  the  diastase,  and  may  be  used  for  many  purposes 
as  a  solution  of  that  substance,  but  it  also  retains  other  matters  which  may 
be  separated  by  absolute  alcohol :  this  throws  down  the  diastase.  It  is  a 
white  flocculent  substance,  soluble  in  water,  insoluble  in  alcohol,  tasteless, 
and  easily  decomposed  :  its  effects  upon  starch  are  destroyed  at  a  boiling 
heat :  its  ultimate  composition  has  not  been  determined,  but  as  certain  other 
organic  products  effect  similar  changes  upon  starch,  such  as  gastric  juice, 
animal  membrane,  yeast,  &c.,  its  claims  to  be  considered  a  distinct  principle 
have  been  doubted.  Its  power  of  changing  starch  into  dextrine  and  sugar 
is  such  that  1  part  of  it  is  capable  of  thus  modifying  2000  parts  of  starch  : 
its  effect  may  be  well  shown  by  adding  a  little  of  it  to  a  thick  starch  paste, 
heated  to  about  180° ;  it  immediately  becomes  fluid,  gummy,  and  sweet. 

When  starch-paste  is  warmed  with  water  acidulated  by  sulphuric  acid,  it 
also  passes  into  dextrine.  The  same  change  may  be  effected  by  very  dilute 
nitric  acid  :  Payen's  method  consists  in  moistening  10  parts  of  starch  with  3 
of  water,  containing  one-150th  part  of  nitric  acid,  and  drying  it  in  thin  lay- 
ers in  a  stove  heated  to  about  240°.  In  two  hours  the  conversion  is  com- 
plete. 

Dextrinfe  is  a  brownish  colored  powder,  nearly  tasteless,  uncrystallizable, 
soluble  in  water,  hot  or  cold,  insoluble  in  alcohol,  and  of  the  same  composi- 
tion as  starch  and  gum  ;  it  is  not  blued  but  reddened  by  iodine,  and  differs 
from  gum  in  forming  a  deep  blue  liquor  with  a  solution  of  sulphate  of  cop- 
per, which  deposits  suboxide  of  copper  when  boiled.     With  acetate  of  lead 


INULINE.      LICHENINE.      GUM.  565 

and  ammonia  it  gives  a  precipitate  =C^Jl^fi^(,'2iFhO.  Tannic  acid  produces 
with  the  solution  in  water  a  slight  turbidness.  Unlike  gum,  it  does  not  form  a 
gelatinous  compound  with  the  persalt  of  iron.  It  is  most  easily  convertible 
into  sugar  on  boiling  it  with  a  dilute  acid,  and  it  appears  to  be  the  transi- 
tion stage  between  starch  and  sugar.  When  heated  with  nitric  acid  it  pro- 
duces oxalic  and  not  mucic  acid. 

An  aqueous  solution  leaves  by  drying  a  shining  streak  on  paper  resembling 
gum  in  appearance,  but  differing  from  it  in  the  red  color  produced  by  the 
addition  of  iodine  water.  It  is  this  substance  which  is  used  as  the  adhesive 
material  for  postage  stamps.  It  is  used  also  for  adhesive  bandages,  as  a 
local  application  in  burns  and  scalds,  and  in  fixing  colors  in  calico  printing. 

Although  dextrine  has  been  here  treated  chiefly  as  an  artificial  compound, 
it  appears  to  exist  in  certain  grains  or  seeds  and  roots  as  well  as  in  the 
shoots  of  young  plants.  In  these  cases  it  is  probably  starch  partially  con- 
verted by  natural  processes. 

Inuline  (C^B.^ft2i)' 

This  principle  is  seen  in  the  form  of  a  light  brown  powder,  and  may  be 
obtained  from  the  roots  of  the  Inula  Hellemum,  the  dahlia,  colchicum,  dan- 
delion, and  chicory.  It  is  not  very  soluble  in  cold  water,  but  it  is  dissolved 
by  boiling  water.  It  is  insoluble  in  alcohol.  It  does  not  present  the  form 
of  independent  granules  under  the  microscope.  The  aqueous  solution  is 
neutral.  It  is  not  blued  by  iodine,  but  is  turned  of  a  deeper  yellow  color. 
Tannic  acid  renders  the  solution  slightly  turbid.  A  solution  of  subacetate 
of  lead  gives  with  it  a  dense  precipitate,  and  the  same  is  formed  by  adding 
ammonia  to  a  mixture  of  acetate  of  lead  with  the  solution.  The  lead  com- 
pound has  the  composition  of  Cg^Hg^OgiPbO.  When  heated  with  diluted 
acid  it  is  converted  into  sugar,  and  with  strong  nitric  acid  it  produces 
oxalic  acid,  not  mucic.  Like  gum,  its  solution  turns  the  plane  of  polariza- 
tion to  the  left — it  is  laevorotatory.  From  this  description  it  will  be  seen 
that  the  properties  of  this  substance  are  a  mixture  of  those  of  gum  and 
starch. 

LiCHENINE. 

A  decoction  of  Iceland  moss  contains  a  principle  soluble  in  boiling  water. 
It  resembles  starch  in  being  turned  of  a  dark  purple  by  iodine  water,  and  in 
being  precipitated  in  the  cold  by  a  solution  of  tannic  acid.  The  precipitate 
is  soluble  on  boiling. 

Gum  (C^H,,0,,). 

Several  modifications  of  a  distinct  proximate  principle  of  vegetables  are 
included  under  the  term  gum :  they  are  not  organized,  like  starch,  nor  are 
they  crystal lizable,  like  sugar :  they  either  readily  dissolve  in  water,  hot  or 
cold,  or  swell  up  into  a  viscid  mass  when  moistened  ;  and  they  are  tasteless, 
and  insoluble  in  alcohol  and  in  ether.  They  are  generally  the  inspissated 
juices  of  certain  plants,  and  ooze  naturally  from  the  tree ;  but  in  commercial 
language  the  term  gum  is  loosely  applied  to  substances  which  resemble  it  in 
external  appearance,  such  as  resins.  Caoutchouc  and  gutta  percha  are  also 
sometimes  called  gums.  In  a  chemical  sense  a  gum  is  characterized  by 
solubility  in  cold  water  and  insolubility  in  alcohol :  it  is  -infusible  and  not 
very  combustible.  The  principal  varieties  of  gum  may  be  described  as  Ara- 
bine  and  Bassorine. 

Arahine,  as  represented  by  Gum  Arabic,  is  the  produce  of  various  species 
of  Acacia;  its  sp.  gr.  is  from  1'30  to  1*50.     It  is  soluble  in  water,  hot  or 


666  PECTOSE. 

cold,  and  it  forms  a  viscid,  tasteless  mucilage  with  it,  which,  even  when 
fresh,  slightly  reddens  litmus,  and  leaves  a  transparent  glaze  or  varnish  when 
it  dries.  Alcohol  throws  down  a  white  hydrated  gum  from  its  solution  :  it 
produces  a  rotation  to  the  left  of  a  polarized  ray  of  light.  The  alkalies 
and  alkaline  earths  form  soluble  compounds  with  arabine,  but  with  several 
metallic  oxides  {e.g.^  lead  and  iron)  it  produces  definite,  insoluble  precipi- 
tates, which  have  been  called  Arahi?iates  :  thus,  with  subacetate  of  lead  the 
white  compound  which  falls  is  PbO,C,3HiiOii.  It  is  not  precipitated  by  a 
solution  of  neutral  acetate  of  lead  until  ammonia  is  added,  but  it  is  thrown 
down  by  neutral  persulphate  of  iron,  with  which  it  forms  a  red  jelly,  and 
nitrate  of  mercury.  When  potassa  is  added  to  a  solution  of  gum  and 
sulphate  of  copper,  a  blue  arabinate  falls,  which  is  not  decomposed  by  boil- 
ing :  this  distinguishes  arabine  from  dextrine.  "When  heated  with  concen- 
trated sulphuric  acid,  gum  is  carbonized,  but  when  boiled  with  very  dilute 
sulphuric  acid  it  is  gradually  changed  into  dextrine  and  glucose.  It  absorbs 
chlorine  and  produces  a  peculiar  acid  :  it  also  absorbs  hydrochloric  acid. 
Nitric  acid  converts  it  into  Mucic  acid  {Q^^Jd^fiKO.)  Bromine  and 
iodine  are  without  action  upon  it.  Oxalate  of  ammonia  indicates  the  pre- 
sence of  lime  in  a  solution  of  gum  arable.  When  dried  at  212°,  gum  loses 
from  12  to  It  per  cent,  of  its  weight,  and  it  becomes  hard,  brittle,  and 
pulverizable,  forming  a  white  powder.  When  heated  to  300°  in  air,  it 
swells  up,  but  does  not  melt  or  burn.  At  a  higher  temperature  it  gives  otF 
an  acid  vapor  and  burns,  leaving  an  ash  containing  much  lime. 

An  aqueous  solution  undergoes  no  change  of  color  by  the  addition  of 
iodine,  and  it  is  not  precipitated  by  tannic  acid.  A  good  solution  of  gum 
for  adhesive  purposes  may  be  made  by  dissolving  one  ounce  of  gum  acacia 
in  three  ounces  of  boiling  water,  and  adding  to  the  solution  two  drachms  of 
glycerine  and  a  few  drops  of  a  solution  of  carbolic  acid.  The  latter  pre- 
vents the  production  of  mould.  A  small  portion  of  camphor  may  be  sub- 
stituted for  carbolic  acid. 

Bassorine.  Tragacanthine. — Gum  Tragacanth  may  be  taken  as  the  type 
of  this  modification  of  gum.  It  is  the  produce  of  difi'erent  species  of  Astra- 
galus. When  steeped  in  water  it  swells  into  a  bulky  mucilaginous  mass, 
which,  when  long  boiled,  acquires  the  general  properties  of  arabine.  Cherry- 
tree  gum,  or  Gerasine,  and  the  gum  which  exudes  from  peach  and  apricot 
trees,  and  other  species  of  prunus,  seems  to  be  a  mixture  of  arabine  and 
bassorine.  There  is  also  a  number  of  mucilaginous  substances,  such  as  those 
derived  from  quince-seed,  linseed,  marshmallow  root,  etc.,  which  closely 
resemble  the  varieties  of  gum.  The  term-  mucilage  is  given  to  the  aqueous 
solutions  of  these  seeds.  A  cold  solution  of  bruised  linseed  has  an  acid  re- 
action. It  undergoes  no  change  of  color  on  the  addition  of  iodine,  and  is 
precipitated  by  alcohol,  as  also  by  a  solution  of  subacetate  of  lead. 

Pectose. 

Vegetable  Jelly — A  gelatinous  principle  has  long  been  recognized  as  one 
of  the  proximate  components  of  vegetables :  it  is  derived,  according  to 
Fremy,  from  the  presence  of  Pectose  {rtrjxfbi,  coagulated),  a  substance  usually 
associated  with  the  cellular  tissue,  and  which  is  insoluble  in  water,  alcohol, 
and  ether,  but  which,  under  the  influence  of  acids,  aided  by  a  gentle  heat, 
becomes  converted  into  a  soluble  gelatinous  substance,  Pectine,  represented 
by  the  formula  CfgiH^oOsg.  Pectine  is  found  ready  formed  in  the  juices  of 
ripe  fruits,  in  consequence  of  the  action  of  their  acids  upon  the  original 
pectose.  It  may  be  obtained  from  the  expressed  juice  of  ripe  pears  or  apples 
(after  the  lime  which  it  contains  has  been  precipitated  by  oxalic  acid,  and 
the  albumen  by  a  strong  solution  of  tannin),  by  means  of  alcohol,  which 


PECTIO    ACID.      GELOSE.  50T 

throws  it  down  in  gelatinous  filaments.  When  pure,  it  is  white,  neutral,  not 
crystallizable,  soluble  in  water,  but  insoluble  in  alcohol  and  in  ether :  it  is 
precipitated  by  subacetate,  but  not  by  neutral  acetate  of  lead.  When  its 
aqueous  solution  is  long  boiled,  it  loses  viscosity,  and  is  changed  mto  para- 
pectine,  which  precipitates  neutral  acetate  of  lead  ;  and  if  boiled  with  a  dilute 
acid,  it  is  further  modified  into  metapectine,  which  is  distinguished  by  pre- 
cipitating a  solution  of  chloride  of  barium. 

Pectic  Acid  (C.jgH2o023,2HO). — Pectine  and  its  modifications  are  changed 
into  pectic  acid  by  the  action  of  weak  alkaline  solutions  ;  and  the  soluble 
pectates  thus  formed  may  be  decomposed  by  other  acids.  Pectic  acid  is 
generally  obtained  by  boiling  the  pulp  of  certain  roots,  of  carrots,  for 
instance,  with  a  very  weak  solution  of  an  alkaline  carbonate,  and  precipi- 
tating by  chloride  of  calcium  ;  the  precipitate,  after  having  been  well  washed, 
is  decomposed  by  dilute  hydrochloric  acid,  which  leaves  the  pectic  acid  in 
the  form  of  a  jelly,  insoluble  in  cold  water,  but  which,  when  long  boiled  in 
water,  is  changed  into  parapectic  acid,  which  is  soluble  in  water,  sour,  and 
is  precipitated  from  its  solutions  by  baryta  water :  its  formula  is  (C^^HigO^i, 
2110).  Under  the  influence  of  powerful  acids,  or  alkaline  bases,  pectine 
and  its  modifications  are  further  changed  into  metapectic  acid  (CgH507,2HO), 
which  forms  soluble  salts  with  all  bases. 

Pectic  Fermentation. — Pectose  is  always  associated  with  a  substance 
which  Fremy  calls  Pectase,  having  a  special  action  upon  it  (as  diastase  has 
upon  starch),  and  which  he  represents  as  the  ferment  of  the  gelatinous  pro- 
ducts. It  is  obtained  by  adding  to  fresh  carrot-juice,  alcohol,  which  throws 
it  down  in  an  insoluble  form,  but  it  retains  its  characteristic  properties.  It 
transforms  pectine  (at  a  temperature  between  80°  and  90°)  into  a  substance 
insoluble  in  cold  water  (Pectosic  acid),  and  subsequently  into  Pectic  acid,  as 
above  described.  None  of  these  pectic  compounds  exert  any  rotatory  action 
on  polarized  light. 

Gelose. 

There  are  many  Algae,  Fuci,  and  Lichens,  which  abound  in  a  peculiar 
gelatinizing  principle.  One  of  the  most  remarkable  is  the  Gelideum  cor- 
neum,  from  which  an  article  is  prepared  known  commercially  as  Japan  Isin- 
glass. The  gelideum  corneum  contains  58  per  cent,  of  substances  soluble  in 
boiling  water.  The  dried  gelatinous  compound  obtained  from  it  is  insoluble 
in  cold,  but  soluble  in  hot  water.  It  sets  into  a  firm  jelly  on  cooling,  even 
when  it  forms  only  one-120th  part  of  the  weight  of  the  water.  One  part  of 
isinglass  (animal  gelatin)  produces  a  similar  jelly  with  about  80  parts  of 
w^ater.  The  vegetable  jelly  is  neutral,  tasteless,  and  imputrescible.  It  is 
insoluble  in  alcohol,  ether,  and  weak  acids.  Like  woody  fibre  it  is  con- 
verted into  glucose  by  sulphuric  acid.  Unlike  animal  jelly,  it  is  not  precipi- 
tated in  solution  by  tannic  acid,  and  it  is  not  altered  by  a  solution  of  iodine 
or  subacetate  of  lead.  It  has  been  proposed  to  substitute  it  for  the  varie- 
ties of  animal  gelatine,  but  it  is  destitute  of  nitrogen,  having  the  formula 
C24H21O24  {Eep.  de  Pharm.,  Jan.  1860).  The  edible  birds'-uests,  esteemed 
as  a  delicacy  in  China,  are  constructed  by  a  species  of  swallow,  of  the  Plo- 
caria  Candida.  In  some  of  these  Alg88,  however,  Dr.  Davy  has  found  from 
2  to  4  per  cent,  of  nitrogen,  and  it  is  probable  that  researches  directed  to 
the  use  of  these  allied  vegetables  as  food,  would  greatly  extend  the  number 
of  edible  species.  Many  of  them  abound  also  in  a  modification  of  sugar 
(Majinite),  and  they  are  extensively  used  as  manures  and  as  sources  of 
iodine. 

The  Chondrus  crispus  (Irish,  or  Carrageen  moss)  contains  nearly  80  per 
cent,  of  a  gelatinous  principle  which  has  been  called  Carrageenin  {O^^^q 


St 

568  PROCESS    OF    SUGAR    REFINING. 

O^o)?  ^"^  in  the  Cetraria  Islandica  Berzelius  found  from  40  to  50  per  cent, 
of  a  mucilaginous  matter  which  he  compares  to  starch.  {See  "Stanford  on 
the  Economic  applications  of  Seaweed,"  Journ.  Soc.  of  Arts,  Feb.  1862.) 

Sugar. 

There  are  two  leading  varieties  of  sugar.  Cane-Sugar  (Sucrose)  and 
Grape-Sugar  (Glucose).  To  these  some  writers  have  added  Fruit  Sugar, 
an  uncrystallizable  principle  called  Fructose  or  Levulose. 

Cane-Sugar  (C^^fi^.^HO)  is  chiefly  obtained  from  the  sugar-cane, 
each  gallon  of  its  juice  yielding  about  a  pound  :  it  is  also  derived  from  beet- 
root, which  yields  from  4  to  6  per  cent. ;  from  the  sap  of  the  sweet  maple, 
and  from  some  other  sources,  especially  from  the  stalks  of  Indian  corn  or 
maize,  the  juice  of  which  is  nearly  as  rich  in  sugar  as  that  of  the  cane. 
Several  of  the  palm  tribe,  such  as  the  date  and  cocoa-palm,  are  also  import- 
ant sources  of  this  kind  of  sugar. 

The  general  characters  of  cane-sugar,  and  its  ordinary  commercial  varie- 
ties are  well  known.  Its  sp,  gr.  is  about  1*6  ;  it  dissolves  in  one-third  its 
weight  of  water  at  60°  producing  a  viscid  syrup,  which  affords,  by  sponta- 
neous evaporation,  prismatic  crystals  of  candy.  A  solution  saturated  at 
230°,  concretes  into  a  granular  mass  or  tablet ;  but  when  boiled  down  until 
it  acquires  a  tendency  to  vitreous  fracture  on  cooling,  or  till  a  portion 
thrown  off  from  a  stirrer,  concretes,  or  feathers  as  it  falls,  it  congeals  into  a 
transparent  amorphous  mass  (barley-sugar)  which,  however,  has  a  tendency 
to  become  opaque,  and  pass  into  a  granular  crystalline  texture,  exhibiting*  a 
case  of  dimorphism :  this  change  is  prevented  by  the  addition  of  a  little 
vinegar  or  tartaric  acid.  Absolute  alcohol  dissolves  about  one-80th  of  its 
weight  of  this  sugar  at  its  boiling-point,  nearly  the  whole  of  which  separates 
in  small  crystals  on  cooling.  If  equal  parts  of  strong  syrup  and  of  alcohol 
are  mixed,  a  quantity  of  small  brilliant  crystals  of  sugar  is  soon  deposited. 
Pure  cane-syrup  is  not  prone  to  change ;  but  certain  substances,  when  pre- 
sent only  in  very  minute  proportions,  materially  affect  the  stability  of  the 
solution,  and  lead  to  a  series  of  curious  changes  which  will  be  adverted  to 
under  the  head  of  Fermentation. 

When  a  thin  cane-syrup  is  long-boiled,  it  gradually  grows  less  viscid,  and 
slowly  passing  into  a  modified  state,  ultimately  becomes  brown  and  uncrys- 
tallizable ;  so  that,  where  saccharine  liquids  are  concerned,  the  protracted 
application  of  heat  should  be  avoided ;  and  if  mere  traces  of  acid  or  alkali 
be  present,  these  changes  are  promoted,  and  new  products  result,  some  of 
which  form  insoluble  compounds  with  the  majority  of  basic  bodies,  and  have 
been  termed  melassic  and  melassinic  acids;  others  resemble  ulmic  and  humic 
acid  (sachulmine). 

Refining  of  Sugar. — The  process  of  refining  sugar,  or  of  converting  the 
varieties  of  raw,  brown,  or  Muscovado,  into  white  loaf-sugar,  is  extensively 
carried  on  in  London  and  Liverpool.  The  sugar  is  first  dissolved  in  lime- 
water,  by  the  aid  of  steam,  in  a  metal  tank  called  the  blowing-up  pan,  and 
a  portion  of  bullock's  blood,  technically  termed  sfice,  is  usually  added,  the 
albumen  of  which,  as  it  coagulates,  entangles  many  impurities,  carrying 
them  to  the  surface,  and  so  enabling  them  to  be  skimmed  off,  together  with 
some  insoluble  products  of  the  action  of  the  lime.  The  liquor,  thus  far  cla- 
rified, is  then  transferred  to  a  series  of  cotton  filtering  bags,  till  it  runs 
through  them  quite  bright,  but  still  of  a  dark  color.  To  decolor  it,  it  is 
passed  through  bone-back,  or  other  varieties  of  charcoal,  contained  in  verti- 
cal metallic  cylinders,  the  effect  of  which  is  to  render  the  dark-colored  syrup 
nearly  colorless  and  bright.  In  this  condition,  and  of  proper  strength,  it  is 
transferred  into  the  vacMMW  ^aw,  and  boiled  down  under  diminished  pres- 


GRAPE    SUGAR.  569 

sure,  and  at  a  temperature  of  about  150°,  till  of  sufficient  density  to  be 
drawn  off  into  a  vessel  now  termed  the  heater,  but  which  when,  as  formerly, 
the  syrup  was  boiled  down  over  an  open  fire,  and  at  a  temperature  of  not 
less  than  230°,  was  called  the  cooler.  Here  the  temperature  of  the  syrup, 
now  inclined  to  crystallize,  is  raised  to  about  175°,  under  constant  stirring, 
and  it  becomes  a  kind  of  magma,  which  is  filled  out  into  proper  conical 
moulds  of  copper,  zinced  iron,  or  earthenware,  the  orifice  at  the  apex  of 
each  mould  being  plugged  by  a  paper  stopper.  As  soon  as  this  magma  ha3 
consolidated  upon  the  upper  surface  (or  the  base  of  the  cOne)  it  is  well 
stirred  up  again,  and  in  due  time  the  stoppers  are  removed,  so  as  to  allow 
the  uncrystallized  liquid  to  drain  away  into  vessels  placed  for  its  reception. 
The  loaves  are  now  submitted  to  a  peculiar  washing  or  cleansing  operation, 
sometimes  called  claying,  which  consists  in  the  application  of  a  thick  mortar 
or  magma  of  sugar  and  water  (now  used  instead  of  clay)  to  the  base  of  the 
loaf,  portions  of  the  fluid  from  which  gradually  percolate  the  loaf,  carrying 
the  dark-colored  syrup,  or  treacle,  before  them.  Finally,  an  operation 
termed  liquoring  is  resorted  to  ;  that  is,  a  dense  and  very  pure  syrup  is 
poured  upon  the  base  of  the  loaf,  previously  smoothed  by  a  bottoming  trowel, 
and  as  this  filters  through  the  cone,  it  deposits  a  portion  of  its  sugar  in  its 
way,  and  at  the  same  time  washes  out  the  relics  of  colored  syrup.  When 
this  process  is  completed,  and  all  percolation  has  ceased,  the  loaf  is  knocked 
out  of  the  mould,  and  if  above  16  pounds'  weight,  is  truncated  by  cutting 
off  the  apex,  so  as  to  form  what  is  called  a  lump,  or  titler  ;  or  if  intended  for 
a  loaf  proper,  a  new  apex  is  given  to  it  by  a  conical  cutter  or  nosing  ma- 
chine. Finally,  the  loaves  are  papered,  and  deposited  on  trellised  shelves  in 
a  room  called  the  stove,  heated  to  about  130°,  till  dry  throughout.  By 
another  process,  which  is  now  largely  worked  at  Bristol,  the  crystallizable 
syrup  is  placed  in  a  perforated  cylinder  or  sieve,  which  is  made  to  revolve 
with  great  rapidity  in  another  vessel.  The  treacle  or  fluid  portion  is  by 
this  method  at  once  separated  from  the  small  crystals  of  sugar.  This  is 
known  in  commerce  as  centrifugal  sugar.     It  is  remarkably  pure. 

Grape-Sugar;  Glucose  (C,,H,,0,„  or  C,,H^0,,+2H0).— This  modifi- 
.  cation  of  sugar  abounds  in  grapes,  figs,  plums,  and  other  fruits :  it  is  also 
the  result  of  the  action  of  diastase,  and  of  dilute  acids  upon  starch.  In  good 
seasons  the  expressed  juice  of  grapes  yields  from  30  to  40  per  cent,  of  solid 
matter,  the  greater  part  of  which  is  this  kind  of  sugar.  When  obtained 
from  fruits,  it  is  accompanied  by  more  or  less  of  an  uncrystallizable  sugar 
(Fruit-sugar  or  Fructose,  Q^Jiifit^^  which,  however,  by  assimilating  the 
elements  of  water,  passes  into  the  condition  of  grape-sugar,  or  glucose.  The 
conversion  of  starch  into  this  kind  of  sugar  has  been  adverted  to.  It  is  a 
process  extensively  carried  on  as  a  commercial  manufacture,  especially  in 
France.  (It  is  used  in  the  making  of  beer  and  in  the  adulteration  of  sugar 
and  honey.)  Potato-starch  and  sago  are  principally  used  for  this  purpose  : 
they  are  saccharized  by  the  action  of  dilute  sulphuric  acid  (10  parts  of  acid 
to  1000  of  water  and  500  of  starch).  The  dilute  acid  is  heated  by  steam, 
and  the  starch,  previously  mixed  with  water  of  a  temperature  between  112° 
and  130°,  is  suffered  gradually  to  dribble-in  under  constant  stirring  ;  its  con- 
version into  dextrine  is  immediate  :  in  about  two  hours  and  a  half  the  whole 
of  the  starch  is  added,  and  in  from  15  to  25  minutes  afterwards,  the  sacchari- 
fication  is  complete ;  the  steam  is  then  shut  off,  and  the  liquor  transferred  to 
another  vat,  in  which  the  acid  is  saturated  with  chalk.  When  the  sulphate 
of  lime  has  subsided,  the  clear  liquid  is  drawn  off  and  evaporated  to  the  sp. 
gr.  of  about  1-26.  The  resulting  syrup  is  then  left  to  deposit  the  sulphate 
of  lime  separated  during  evaporation,  and  afterwards  drawn  off  perfectly 
clear.     In  this  state  it  may  be  used  as  a  source  of  alcohol,  or  for  sweeten- 


510  ACTION    OF    BASES    ON    SUGAR. 

ing  colored  liqnors ;  but  it  requires,  for  the  greater  number  of  purposes,  to 
be  deprived  of  color,  which  is  done  by  filtering  it  through  animal  charcoal. 
When  required  in  its  solid  state,  the  syrup  is  evaporated  in  a  steam  vat  till 
of  a  sp.  gr.  of  about  r4  and  then  poured  into  coolers,  where  it  concretes. 

Glucose,  or  grape-sugar,  differs  from  sucrose,  or  cane-sugar,  in  being  less 
soluble  in  water,  and  more  soluble  in  alcohol,  so  that  the  two  may  be  to 
some  extent  separated  by  the  action  of  alcohol.  The  sweetening  power  of 
glucose  is  also  greatly  inferior  to  that  of  sucrose,  2  parts  of  the  latter  being 
in  this  respect  equivalent  to  about  5  of  the  former.  They  both  deoxidize 
and  discharge  the  color  of  a  solution  of  permanganate  of  potash,  but  glucose 
acts  more  rapidly  and  perfectly  than  sucrose.  Sucrose  easily  crystallizes  in 
prisms,  but  glucose  forms  tubercular  concretions,  or  fibrous  acicular  groups, 
=  Ci3H^20,3,2HO.  Both  these  sugars  form  definite  crystallizable  compounds 
with  chloride  of  sodium. 

When  cane-sugar  is  heated  to  about  320°  it  melts,  and  at  about  400°  be- 
comes brown,  deliquescent,  and  slightly  bitter,  losing  water  (2  atoms),  and 
passing  into  Caramel,  =  G^JI^Oq.  In  this  state  it  is  used  for  coloring  wines 
and  spirits :  it  is  soluble  in  water,  but  is  thrown  down  from  its  solution  by 
excess  of  alcohol.  It  combines  with  certain  bases,  such  as  baryta  and  oxide 
of  lead,  forming  insoluble  compounds.  Heated  to  about  500°,  melted  sugar 
bursts  into  flame,  and  leaves  a  porous  mass  of  nearly  pure  charcoal. 

When  grape-sugar  is  heated  to  212°  it  softens,  and  loses  2  atoms  of  water 
becoming  (C^^H^fi^^) ;  at  284°  it  passes  by  further  loss  of  water  into  caramel, 
CigllgOg,  and  at  a  higher  temperature  is  entirely  decomposed.  Solutions  of 
cane  and  of  grape-sugar  produce  a  right-handed  rotation  upon  a  ray  of 
polarized  light. 

Concentrated  sulphuric  acid  acts  energetically  upon  cane-sugar,  evolving 
water,  carbonic  and  formic  agids,  and  charcoal.  It  is  a  striking  experiment 
to  mix  about  equal  bulks  of  oil  of  vitriol  and  strong  syrup  :  the  mixture, 
when  stirred,  becomes  brown  and  black,  then  suddenly  heats,  boils  up,  and 
passes  into  the  state  of  a  bulky  black  magma :  the  acid  appears  suddenly  to 
abstract  the  elements  of  water  from  the  sugar,  leaving  charcoal.  The  action 
of  sulphuric  acid  upon  grape-sugar  is  very  different :  it  merely  renders  it 
brown,  and  a  new  compound,  sulphosaccharic  acid,  is  produced,  characterized 
by  forming  soluble  salts  with  lime  and  baryta. 

Boiled  with  very  dilute  sulphuric,  hydrochloric,  or  tartaric  acid,  cane- 
sugar  becomes  fruit  or  grape-sugar,  by  the  assimilation  of  an  atom  of  water  ; 
and  under  the  influence  of  yeast  {see  Alcoholic  Fermentation)  there  is  a 
similar  transition  of  the  one  species  of  sugar  into  the  other ;  but  the  con- 
verse change,  namely,  that  of  grape  or  fruit-sugar  into  cane-sugar  (glucose 
into  sucrose),  cannot  be  effected.  Nitric  acid  changes  the  varieties  of  sugar 
into  saccharic  and  oxalic  acids.  In  the  presence  of  decomposing  casein  and 
chalk,  sugar  forms  lactic  acid,  and  under  the  influence  of  certain  substances 
occasionally  present  in  raw  sugar,  it  passes  into  a  ropy  mucilage  and  into 
mannite. 

Action  of  bases  upon  Sugar. — When  lime  or  baryta  is  boiled  with  sugar- 
and  water  a  bitter  solution  is  formed,  which  is  said  to  contain  a  definite 
saccharide  (2CaO,  or  2BaO,4-C^s,HgOg).  Freshly  precipitated  oxide  of  lead 
is  similarly  dissolved,  and  on  cooling,  a  white  compound  falls,  which,  after 
having  been  dried  at  212°,  is  =  2PbO-fC,3Hg09.  Alcohol  does  not  pre- 
cipitate sugar  from  its  solution  in  water,  and  tannic  acid  and  iodine  water 
have  no  effect  upon  it.  The  aqueous  solution  gives  no  precipitate  with  a 
salt  of  lead,  but  on  adding  ammonia  the  sugar  combines  with  and  is  precipi- 
tated with  oxide  of  lead.  Many  of  these  compounds  are  soluble  in  excess 
of  alkalies,  and  hence  the  presence  of  sugar  sometimes  prevents  the  precipi- 


TESTS    FOR    SUGAR.  571 

tation  of  metallic  oxides  from  their  salts.  In  other  cases  sugar  tends  to 
reduce  the  oxides.  The  compounds  o^  glucose  with  bases  are  less  stable  than 
the  preceding,  this  sugar  gradually  passing  into  glucic  acid  (C^aHgOgjSHO), 
which  under  the  influence  of  heat  becomes  apoglucic  acid  (CigHQ0g,2H0) : 
and  ultimately  melassic  acid  is  formed.  Grape-sugar  is  distinguished  from 
cane-sugar  by  boiling  it  in  a  solution  of  potassa.  The  former  alone  darkens 
as  the  result  of  the  formation  of  glucic  acid.  This  is  commonly  known  as 
Moor  eh  test. 

Tests  f 07^  Sugar. — The  deoxidizing  property  of  glucose  above  mentioned 
is  the  foundation  of  a  valuable  test  of  its  presence ;  and  inasmuch  as  the 
other  varieties  of  sugar  are  transformed  into  glucose  by  the  joint  action  of 
very  dilute  acids  and  heat,  the  same  mode  of  testing  is  applicable  to  sugar 
generally.  Certain  salts  of  copper  and  of  platinum  are  especially  applicable 
to  these  purposes.  When  a  little  cane-sugar  is  added  to  a  dilute  solution  of 
copper,  and  the  mixture  heated,  little  immediate  change  ensues ;  but  with 
grape-sugar  the  blue  color  of  the  liquor  is  presently  changed  to  green,  it 
then  becomes  yellowish  or  reddish-brown,  and  suboxide  of  copper  or  metallic 
copper  falls:  these  changes  are  more  rapid  when  a  little  alkali  has  been 
added  to  the  solution.  Thus  if  a  few  drops  of  a  very  diluted  solution  of 
sulphate  of  copper  are  added  to  a  solution  of  either  sugar  a  slight  color  is 
imparted.  A  small  quantity  of  a  solution  of  potash  causes  in  the  mixture 
a  precipitate  of  blue  hydrated  oxide  of  copper.  An  excess  of  the  alkaline 
liquid  dissolves  this  precipitate,  forming  a  sapphire-blue  solution.  When 
this  is  heated  the  grape-sugar  causes  rapidly  the  changes  above  mentioned — 
the  yellow  precipitate  formed  being  the  hydrated  suboxide  and  the  red  pre- 
cipitate the  anhydrous  suboxide.  Pure  cane-sugar  thus  treated  does  not 
easily  decompose  the  salt  of  copper.  It  requires  long  boiling  to  produce 
any  decomposition.  With  grape-sugar  it  usually  takes  place  upon  slightly 
warming  the  liquid  and  before  it  has  reached  the  boiling  point.  One  form 
of  the  copper  test  as  it  is  sometimes  employed  for  the  detection  of  sugar  is 
the  soda  tartrate  of  copper,  obtained  by  dissolving  recently  precipitated 
tartrate  of  copper  in  a  solution  of  soda  or  of  carbonate  of  soda  :  it  is  imme- 
diately reduced  when  boiled  with  a  trace  of  glucose ;  used  quantitatively,  it 
will  be  found  that  15  parts  of  the  precipitated  or  red  suboxide  of  copper  are 
equivalent  to  about  5  of  cane-sugar,  and  to  about  5'1  of  grape-sugar.  The 
copper  test  for  sugar  has  been  long  known  under  the  name  of  Trommerh  test. 
Some  precautions  are  required  in  its  employment.  If  sugar  is  not  present 
potash  has  no  solvent  action  on  the  precipitated  oxide  of  copper,  and  on 
boiling  the  colored  liquid,  black  or  anhydrous  oxide  of  copper  only  is 
thrown  down.  On  the  other  hand,  a  solution  of  the  precipitated  oxide  by 
an  excess  of  alkali  does  not  indicate  the  presence  of  sugar.  In  the  presence 
of  albumen,  casein,  glycerine,  mannite,  or  any  alkaline  tartrate,  potash  re- 
dissolves  the  precipitated  oxide,  forming  a  blue  or  purple-blue  liquid  :  but 
on  boiling  the  liquid,  there  is  no  reduction  of  the  oxide  of  copper,  and  no 
red  suboxide  is  produced.  If  chloroform  is  present,  even  in  small  quantity, 
the  oxide  of  copper  is  not  redissolved  by  an  excess  of  potash,  but  it  under- 
goes a  complete  reduction  to  suboxide  on  boiling  it.  Here  the  non-redissolu- 
tion  would  distinguish  chloroform  from  sugar.  On  the  other  hand,  arsenious 
acid  or  an  alkaline  arsenite,  when  present,  forms  a  clear  blue  liquid  with  a 
salt  of  copper  and  an  excess  of  potash  ;  and  on  boiling  the  solution,  the  red 
suboxide  of  copper  is  precipitated  as  if  sugar  were  really  present.  The  test 
when  properly  employed  is  with  proper  precautions  adequate  to  the  detection 
of  sugar  under  all  circumstances.  Although  the  presence  of  pure  cane-sugar 
is  not  readily  indicated  by  the  test,  yet  on  warming  the  solution  for  a  short 


5t2  HONEY.      MANNITE. 

time,  with  a  few  drops  of  tartaric  or  very  dilute  sulphuric  acid,  the  cane  is 
converted  into  grape-sugar,  and  it  will  then  immediately  respond  to  the  test. 

A  hot  solution  of  nitrate  of  suboxide  of  mercury  is  immediately  blackened 
by  glucose,  and  finely-divided  mercury  falls:  in  the  same  way  a  boiling 
solution  of  corrosive  sublimate  deposits  calomel,  which  is  afterwards  partially 
reduced :  red  oxide  of  mercury  is  also  reduced  when  boiled  in  the  saccharine 
solution.  Solutions  of  nitrate  of  silver  and  of  chloride  of  gold,  when  boiled 
with  glucose,  afford  precipitates  of  silver  and  gold  :  when  in  these  cases, 
excess  of  .carbonate  of  soda  is  present,  the  effect  is  more  rapid,  and  in  this 
way  the  chlorides  of  platinum  and  palladium  are  reduced.  A  delicate  test  of 
glucose  is  the  soda-chloride  of  platinum  formed  by  adding  excess  of  a  solution 
of  carbonate  of  soda  to  a  moderately  dilute  solution  of  chloride  of  platinum. 
When  this  solution  is  boiling,  a  small  portion  of  cane-sugar  dropped  into  it 
produces  no  effect,  but  it  is  instantly  discolored,  and  ultimately  blackened, 
by  the  smallest  trace  of  grape-sugar.  Where  these  tests  are  used,  the  absence 
of  other  organic  matters  likely  to  effect  their  decomposition,  must  be  insured. 

The  ultimate  components  of  the  preceding  varieties  of  sugar  are  as  fol- 
lows : — 


SUCROSE, 

GLUCOSE. 

Atoms. 

Equiv. 

Per  cent. 

Atoms, 

Equiv. 

Per  cent. 

C    12 

...       72      .. 

.        42-11 

C  12 

...      72      .. 

.       36-36 

H  11 

...      11      .. 

6-43 

H  14 

...      14      .. 

7-08 

0  11 

...       88      .. 

.       51-46 

0  14 

...     112       .. 

.       56-56 

1-  171  100-00  1-  198  100-00 

Fructose  or  Levulose  exists  chiefly  in  fruits,  but  it  does  not  appear  to  be 
an  independent  sugar,  although  the  formula  0^^^f>^^  is  usually  assigned  to 
it.  It  is  not  crystallizable  :  it  is  quite  soluble  in  alcohol,  and  turns  the  plane 
of  the  polarization  to  the  left :  hence  it  is  sometimes  called  inverted  sugar. 
After  a  time  it  seems  to  be  spontaneously  converted  into  crystallized  grape- 
sugar  or  glucose.  Thus  white  fresh  grapes  contain  fructose,  the  dried  raisins 
contain  glucose. 

Honey. — The  substance  secreted  in  the  nectaries  of  flowers  is  converted 
by  the  bee  into  honey  and  wax :  the  portion  not  required  for  their  food  is 
returned  into  the  combs  in  the  form  of  a  yellow  syrup,  the  qualities  of  which 
differ  according  to  the  flowers  whence  it  has  been  derived.  In  its  original 
liquid  state  it  probably  resembles  uncrystallizable  sugar  of  fruits,  &c.  (Fruc- 
tose, 0^2^130^2) ;  but  when  kept  for  some  time,  a  large  portion  of  it  passes 
into  a  granular  form,  identical  with  glucose  =  C^gHj^O^^.  But  honey  also 
contains  a  little  wax,  gum,  coloring  matter,  and  mannite. 

Diabetic  Sugar,  or  that  which  is  formed  in  a  diseased  state  of  the  animal 
system  (diabetes),  has  all  the  properties  of  grape-sugar  or  glucose.  It  may 
be  separated  from  the  extract  of  diabetic  urine  by  boiling  alcohol. 

Mannite;  Manna-Sugar  (CgH^Og). — This  substance  is  most  abundant  in 
manna,  but  it  is  also  found  in  the  beetroot,  celery,  asparagus,  onions,  and 
probably  in  other  sweet  plants  :  it  is  also  contained  in  the  sap  of  the  larch,  and 
other  species  of  pinus  (Manna  Brigantina).  It  has  been  detected  by  Dr. 
Stenhouse  in  Laminaria  Saccharina,  and  some  other  fuci.  Manna  exudes 
from  several  species  of  ash,  especially  from  the  Fraxinus  ornus  and  rotundi- 
folia.  Mannite  is  obtained  by  boiling  manna  in  alcohol,  from  which  it 
crystallizes  on  cooling  in  acicular  prisms.  It  forms  about  four-fifths  of  the 
best  manna;  the  residue  being  chiefly  common  sugar,  and  a  peculiar  ex- 
tractive matter,  in  which  the  aperient  quality  of  the  manna  is  said  to  reside. 
Mannite  is  also  an  occasional  product  of  the  viscous  fermentation. 

Mannite  is  very  soluble  in  water,  but  is  not  susceptible  of  vinous  fermen- 


FERMENTATION.  513 

tation,  so  that  it  may  in  this  way  be  separated  from  the  other  varieties  of 
sugar ;  for,  when  mixed  with  them,  it  remains  undecomposed  in  that  process. 
Nitric  acid  converts  it  into  saccharic  and  oxalic  acids,  without  any  trace  of 
mucic  acid.  Its  aqueous  solution  precipitates  basic  acetate  of  lead,  forming 
a  compound  in  which  2  equivalents  of  water  are  replaced  by  two  of  oxide  of 
lead,  =  CaIl50^,2PbO.  It  reduces  chloride  of  gold  and  nitrate  of  silver. 
With  precipitated  oxide  of  copper  it  forms  a  clear  blue  liquid  on  the  addition 
of  an  excess  of  alkali,  but  there  is  no  decomposition  or  reduction  on  boiling. 
When  a  solution  of  mannite  is  boiled  with  an  excess  of  a  solution  of  potash 
DO  glucic  acid  is  produced,  and  the  liquid  does  not  darken.  When  heated 
with  diluted  acids,  mineral  or  vegetable,  it  is  not  converted  into  glucose.  It 
combines  with  Sulphuric  acid,  forming  sulphomannitic  acid,  =^CqB.^O^,  2SO3. 

Glycyrrhizine  {Q^^^fi^^  is  the  sweet  principle  of  Uquorice-root :  it  forms 
with  many  acids  and  bases  compounds  which  are  not  very  soluble,  and  it  is 
not  susceptible  of  vinous  fermentation. 

There  are  some  other  substances  allied  to  these  modifications  of  sugar, 
which  do  not  require  detailed  notice,  such  as  Melitose  and  Eucalyn,  the  pro- 
duce of  the  Eucalyptus  munnifera  ;  Sorbine,  from  the  berries  of  the  mountain- 
ash  ;  Quercite,  from  acorns. 


CHAPTER    XLVI. 

ALCOHOLIC    OR   VINOUS  FERMENTATION.      ALCOHOLIC 

LIQUIDS. 

By  fermentation,  we  are  to  understand  the  conversion  of  an  organic 
substance  into  one  or  more  new  compounds,  in  presence  of  a  body  called 
a  ferment.  ,  Hence  there  are  various  kinds  of  fermentation,  designated 
according  to  their  products — vinous  or  alcoholic,  lactic,  butyric,  acetous,  &c. 
In  vinous  fermentation  su^ar  is  resolved  into  alcohol  and  carbonic  acid. 
Sugar  itself  is  not  absolutely  necessary  to  the  process ;  for  starch,  dextrine, 
or  any  substance  capable  of  being  easily  converted  into  sugar,  under  the 
circumstances,  may  be  substituted,  and  similar  products  obtained.  The 
conversion  of  the  substance  into  sugar  appears  to  be,  however,  an  essential 
preliminary  condition  for  the  establishment  of  the  process.  It  is  well  known 
that  a  portion  of  malt  or  saccharized  barley,  mixed  with  unmalted  grain,  will 
produce  alcohol — the  starch  and  dextrine  of  the  unmalted  grain  being  con- 
verted into  sugar  during  the  process.  In  the  same  way  alcohol  may  be  pro- 
duced in  large  quantity,  by  the  mixture  of  the  starchy  pulp  of  the  potato  with 
a  portion  of  treacle.  The  fermentation  of  dough  in  the  making  of  bread 
appears  to  depend  on  similar  principles  ;  apportion  of  the  starch  is  converted 
into  sugar,  and,  in  the  presence  of  a  ferment,  the  sugar  is  immediately 
resolved  into  alcohol  and  carbonic  acid. 

Pure  sugar,  extracted  from  the  vegetable  and  dissolved  in  water,  has  no 
tendency  to  undergo  this  remarkable  change.  A  solution  of  pure  cane- 
sugar  is  slowly  converted  into  grape-sugar,  but  there  the  change  stops  :  no 
alcohol  is  produced.  The  saccharine  juices  of  vegetables,  however,  readily 
ferment,  owing  to  the  presence  of  a  nitrogenous  principle  with  which  they 
are  usually  associated.     This  is  called  o,  ferment    It  is  an  organic  compound 


574  FERMENTATION.      PRODUCTION    OF    FERMENTS. 

containing  nitrogen,  and  is  readily  susceptible  of  change  by  simple  exposure  to 
air.  In  this  state  it  possesses  the  property  of  rapidly  inducing  changes  in  any 
saccharine  liquid.  Gay-Lussac  observed  long  since,  that  when  fresh  grape- 
juice  was  collected  in  a  vessel  containing  carbonic  acid,  and  placed  over 
mercury,  no  fermentation  took  place,  although  all  other  circumstances,  were 
favorable  to  this  process.  When  the  juice  was  exposed  to  air  and  a  proper 
temperature,  it  rapidly  fermented,  and  when  once  this  fermentation  had  com- 
menced, it  continued  until  the  saccharine  matter  was  entirely  decomposed. 
If  to  the  nnfermented  juice,  placed  over  mercury,  a  few  bubbles  of  air  or 
oxygen  were  admitted,  the  same  change  took  place,  and  continued  until  the 
sugar  was  exhausted,  a  large  quantity  of  carbonic  acid  being  at  the  same 
time  evolved,  while  the  liquid  was  found  to  have  lost  its  saccharine,  and  to 
•have  acquired  a  spirituous  or  alcoholic  flavor.  These  facts  prove  that  there 
is  present  in  grape-juice  a  substance  which,  by  contact  with  oxygen,  under- 
goes a  change,  and  becomes  a  ferment ;  and  further,  that  the  saccharine 
juices  of  fruits  do  not  ferment,  because  the  access  of  free  oxygen  is  cut  oflf  by 
the  epidermis  of  the  fruit. 

A  saccharine  solution  of  malt,  called  wort,  will  undergo  similar  changes, 
by  reason  of  the  nitrogenous  principles  contained  in  the  grain.  The  custom 
is,  however,  to  add  to  the  liquid,  for  the  purpose  of  accelerating  the  change, 
a  quantity  of  a  nitrogenous  compound  called  yeast,  or  harm,  derived  from  a 
previous  fermentation.  This  constitutes  the  ferment.  It  produces  a  rapid 
conversion  of  the  saccharine  matter  into  alcohol  and  carbonic  acid  ;  and  at 
the  same  time  causes  the  separation  of  the  nitrogenous  principles  of  the  wort 
in  the  form  of  additional  ferment  or  yeast.  The  quantity  of  new  yeast  thus 
procured,  amounts  to  seven  or  eight  times  the  quantity  of  that  which  has 
been  added  to  the  wort. 

It  has  been  shown  by  Mitscherlich  {Poggend.  Ann.,  iv.  224),  that  the 
actual  contact  of  the  particles  of  the  yeast  with  the  dissolved  sugar  is 
essential.  He  suspended  a  wide  glass  tube,  the  bottom  of  which  was  closed 
with  bibulous  paper,  in  a  jar  of  a  solution  of  sugar,  the  tube  being  itself  filled 
with  the  same  solution.  Some  yeast  was  then  put  into  the  syrup  contained 
in  the  tube,  where  it  soon  induced  fermentation,  and  the  alcohol  there  formed, 
passed  through  the  pervious  bottom,  and,  together  with  carbonic  acid, 
diffused  itself  in  the  surrounding  liquor :  but  the  actual  phenomena  of  fer- 
mentation— namely,  the  decomposition  of  the  sugar  and  the  formation  of 
alcohol  and  of  carbonic  acid — were  limited  to  the  syrup  in  the  tube  contain- 
ing the  ferment,  and  the  sugar  in  the  outer  vessel  remained  unchanged. 
Quevenne  found  that  yeast  which  had  been  deprived  of  all  matter  soluble  in 
water,  still  retained  its  power  of  exciting  fermentation.  The  active  part  of 
yeast  is  composed  of  minute  vesicles,  or  globules,  and  during  fermentation 
these  germinate  in  the  saccharine  liquor,  producing  a  microscopic  fungus,  the 
Torvla  or  Mycoderma  cerevisise.  The  plant,  according  to  one  theory  of  the 
process,  is  supposed  to  grow  at  the  expense  of  the  sugar,  giving  out  carbonic 
acid,  and  leaving  alcohol.  According  to  Andral  and  Gavarret  {Ann.  Gh.  et 
Ph.,  Seme  ser.,  viii.  399),  there  are  two  species  of  vegetable  seeds  contained 
in  yeast,  which  may  be  separated  by  diluting  it  with  water :  in  a  few  days 
globules  fall  to  the  bottom  of  the  vessel,  forming  a  gray  pulverulent  deposit 
which  is  extremely  active  in  producing  alcoholic  fermentation  when  added  to 
saccharine  solutions ;  but  at  the  same  time  a  film  forms  upon  the  surface  of 
the  liquid,  which  consists  of  germs  (of  Penicidlum  glaucum)  having  no 
power  to  excite  fermentation  :  these  latter  germs  make  their  appearance  in 
all  acid  albuminous  liquids,  and  h^comQ  jilamentous,  while  the  true  producer 
of  alcoholic  fermentation  always  retains  its  globular  form.     According  to 


CONDITIONS    WHICH    INFLUENCE    FERMENTATIONS.  515 

Mitscherlich,  the  active  part  of  yeast  which  remains  after  it  has  been  washed 
with  water,  consists  of; 


Before  fermentation. 

After  fermentation. 

Carbon   . 

.    47-0 

47-6 

Hydrogen 

...       6-6 

7-2 

Nitrogen 

.     10-0 

5. 

Oxygen  . 

.     35-8 

Sulphur 

.       ..       0-6 

Of  this  yeast  (in  the  dry  state)  from  2  to  3  parts  are  required  for  the 
decomposition  of  100  parts  of  sugar:  and  if  there  is  excess  of  sugar,  it 
remains  unchanged  after  the  fermentation.  That  portion  of  the  yeast  which 
remains  in  the  form  of  a  deposit  after  fermentation  is  over,  is  inefficient  as  a 
ferment ;  it  appears,  when  examined  under  the  microscope,  to  consist  of  the 
ruptured  cells,  and  is  not  susceptible  of  vegetation  ;  so  that  during  the 
fermentation  of  sugar,  a  certain  portion  of  the  yeast-plant  dies,  and  is  decom- 
posed, the  living  plant  being  required  to  sustain  the  fermentative  process. 
If  more  yeast  be  present  than  is  required  for  the  decomposition  of  a  certain 
quantity  of  sugar,  the  deposit  which  is  in  that  case  formed,  consists  partly 
of  broken  and  partly  of  entire  cells,  and  the  latter  retain  their  power  of 
inducing  fermentation.  It  further  appears  that  that  portion  of  the  yeast 
which  has  become  inert  as  a  ferment,  has  lost  the  greater  part,  if  not  the 
whole,  of  its  nitrogen  ;  and  certainly,  one  of  the  results  of  the  changes  which 
ensue  during  saccharine  fermentation,  appears  to  be  the  formation  of  ammo- 
nia, which  may,  although  so  small  in  quantity  as  generally  to  elude  observation, 
be  easily  detected  amongst  the  gaseous  products. 

For  the  formation  of  artificial  yeast  or  ferment,  the  requisites  appear  to 
be  the  presence  of  sugar,  of  an  azotized  principle,  water,  and  exposure  to 
air  at  a  moderate  temperature.  Any  nitrogenous  substance  partly  decom- 
posed may  act  as  a  ferment.  Thus  gluten,  albumen,  casein,  or  fibrin,  of  the 
vegetable  or  animal  kingdom,  provided  it  be  in  a  state  of  change  or  partial 
decomposition,  may  act  as  a  ferment  to  saccharine  liquids.  To  obtain  a 
ferment,  in  the  first  instance,  a  quantity  of  ground  malt  may  be  made  into  a 
thick  paste  by  the  addition  of  some  concentrated  wort,  at  a  temperature  of 
about  70°  to  75°,  so  as  to  convert  the  starch  into  sugar ;  a  little  alcohol  is 
then  added,  and  after  a  few  days,  when  the  violence  of  the  fermentation  has 
subsided,  a  deposit  of  ferment  is  formed.  An  artificial  yeast  may  be  thus 
prepared  :  A  small  handful  of  ordinary  wheat  flour  is  made  into  a  thick  paste 
with  cold  water,  covered  with  paper,  and  left  seven  days  in  a  warm  room, 
being  occasionally  stirred  (Fownes). 

The  yeast-cells,  when  treated  with  an  aqueous  solution  of  iodine,  are  found 
to  consist  of  a  colorless  envelope,  of  the  nature  of  cellulose,  containing  a 
fluid  which  acquires  a  brown  color  from  the  iodine.  If  yeast  is  dried  in 
vacuo,  or  at  a  low  temperature,  it  is  converted  into  a  hard,  hOrny,  translucent 
substance.  It  reacquires  its  property  of  exciting  fermentation  when  digested 
for  some  time  in  cold  water.  German  yeast  appears  to  be  a  partially  dried 
mass  of  cells.  It  has  undergone  washing  to  free  it  from  the  impurities  of 
the  fermented  liquid,  and  is  then  dried  at  a  low  temperature.  This  yeast 
is  chiefly  obtained  from  the  distilleries  of  Holland,  and  is  now  largely 
imported  into  England.  Boiling  water  destroys  the  fermenting  properties 
of  yeast ;  but  unless  boiled  so  long  as  to  have  its  chemical  nature  entirely 
changed,  it  reacquires  a  fermenting  power  on  exposure  to  air.  As  the 
yeast-cells  are  composed  of  a  cellulose  envelope,  containing  an  albuminous 
liquid,  these  properties  are  destroyed  by  chemical  reagents;  thus  alcohol, 
common  salt,  strong  acids  and  alkalies,  destroy  its  fermenting  power.  Weak 
vegetable  acids  appear  to  accelerate  fermentation.     Yeast  is  generally  acid, 


5Y6  ALCOHOLIC    FERMENTATION.      CHEMICAL   CHANGES. 

and  this  state  of  acidity  probably  operates  favorably  by  converting  any 
cane-sugar  present  in  the  fermenting  liquid,  into  grape  or  fruit-sugar,  which 
more  easily  undergoes  fermentation. 

The  temperature  which  is  found  to  be  most  favorable  for  vinous  fermenta- 
tion is  about  70°,  but  it  will  take  place  at  all  temperatures  between  40^  and 
80°.  The  lower  the  temperature  the  slower  the  process.  At  a  high  tem- 
perature the  alcoholic  rapidly  passes  into  the  acetous  fermentation.  The 
process  appears  to  be  so  identified  with  sugar,  that  it  has  been  employed  as 
a  test  for  this  principle ;  and  the  amount  of  carbonic  acid  obtained  has  been 
employed  as  a  measurer  of  the  quantity  of  the  sugar  present.  A  strong 
solution  of  sugar  will  not,  however,  ferment ;  it  requires  a  certain  state  of 
dilution  with  water,  in  order  that  the  process  should  take  place.  Further, 
sugars  differ  among  each  other  in  the  readiness  with  which  they  take  on  this 
property.  Pure  cane-sugar  {sucrose,  Q^fi^fi^^  does  not  readily  ferment : 
grape-sugar  {glucose,  C^^^fi^^  is  easily  fermented,  but  the  process  takes 
place  most  readily  in  fruit-sugar  {fructose),  represented  by  G^Jl^S)^^.  The 
examination  of  the  solutions  of  these  sugars  by  polarized  light,  during  fer- 
mentation, renders  it  highly  probable  that  both  cane  and  grape-sugar  are 
converted  into  fruit-sugar  before  they  undergo  the  change.  These  two 
sugars  belong  to  the  crystallizable  variety,  and  their  aqueous  solutions  are 
dextrogyrate  under  polarized  light — ^.  e.,  they  turn  the  polarized  ray  from 
left  to  right.  The  fruit-sugar,  which  is  uncrystallizable,  is  Isevogyrate, 
turning  the  rays  from  right  to  left.  Cane-sugar  ferments  slowly,  because 
some  time  elapses  before  it  is  perfectly  converted  into  fruit-sugar  by  the 
acids  contained  in  the  ferment.  In  this  stage  its  rotatory  power  on  polarized 
light  is  inverted.  Cane-sugar  also  requires  for  its  conversion  a  much  larger- 
quantity  of  ferment  than  other  sugars.  When  fermentation  is  complete, 
100  parts  of  fruit-sugar  are  resolved  into  51 '12  of  alcohol  and  4888  of 
carbonic  acid,  so  that  the  ferment  adds  nothing  to  and  removes  nothing  from 
the  elements  of  sugar.  In  fact,  it  appears,  by  a  catalytic  action,  simply  to 
resolve  the  sugar  into  these  two  compounds.  The  changes  may  be  thus 
expressed : — 


C,2H„0„ 

+ 

HO       = 

Water. 
C,2H,20,2 

Fruit-sugar. 

C  13^12^12 

Cane-sugar. 
C,2H„0,4     • 

Fruit-sugar, 
-f        2H0 

Grape-sugar. 

Water. 

An  atom  of  cane-sugar  combines  with  the  elements  of  water  to  produce 
fruit-sugar,  while  an  atom  of  grape-sugar,  by  losing  two  atoms  of  water, 
becomes  at  once  converted  into  fruit-sugar.  1  atom  of  this  compound  is 
resolved  by  fermentation  into  4  atoms  of  carbonic  acid,  and  2  atoms  of 
alcohol : — 


Fruit-sugar.  Carbonic  acid.  Alcohol. 

How  does  the  ferment  operate  to  effect  this  remarkable  change  ?  Yital, 
chemical,  and  dynamical  theories  have  been  suggested  in  order  to  explain 
the  phenomena.  The  vital  theory  assigns  the  cause  to  the  growth  of  a 
fungus  derived  from  the  yeast-cells.  This  is  said  to  become  developed  at 
the  expense  of  the  sugar ;  but  the  objection  to  this  view  is,  that  the  ele- 
ments of  the  sugar  are  not  removed  by  the  fungus  :  they  merely  assume  a 
new  arrangement.  Since  the  discovery  of  the  fact  that  the  ferment  practi- 
cally takes  no  direct  share  in  the  changes,  no  chemical  theory  has  been  sug- 


PRODUCTS    OF    FERMENTATION.  5Yt 

gested,  which  can  adequately  explain  this  conversion.  The  dynamical 
theory,  advocated  by  Liebig,  involves  the  assumption  that  the  molecules  of 
the  ferment  are  in  a  state  of  motion,  arising  from  their  partial  decomposi- 
tion ;  and  that  this  motion  is  mechanically  communicated  to  the  atoms  of 
sugar,  which  thenceforth  arrange  themselves  in  the  form  of  more  stable 
compounds.  This  hypothesis,  however,  fails  to  explain  why  the  particular 
compounds  in  question  are  invariably  produced,  or  how  the  motion  of  atoms 
(if  it  exists)  can  bring  about  such  remarkable  chemical  changes. 

The  phenomena  of  fermentation  may  be  experimentally  demonstrated  by 
dissolving  in  a  quart  of  water  at  a  temperature  of  70^,  half  a  pound  of  trea- 
cle and  half  a  pound  of  brown  sugar,  adding  to  the  solution  one  pound  and 
a  half  of  bruised  raisins,  and  a  pint  of  fresh  yeast.  This  mixture  may  be 
placed  in  a  capacious  glass  globe,  provided  with  a  cork,  and  exposed  to  a 
temperature  of  from  70°  to  80°.  In  about  an  hour  fermentation  will  com- 
mence :  the  liquid  will  appear  to  be  in  continual  motion,  by  reason  of  the 
bubbles  of  carbonic  acid,  as  they  are  evolved,  rising  to  the  surface,  and  car- 
rying with  them  portions  of  the  yeast  and  the  husks  of  the  raisins.  The  gas 
there  escapes,  and  as  the  solids  again  sink  they  gradually  acquire  a  fresh 
coating  of  bubbles,  which  they  carry  up  as  before  ;  and  in  this  way  that 
motion  of  the  whole  mass  of  liquor  is  produced  which  is  so  characteristic  of 
active  fermentation,  and  which,  provided  a  sufficiency  of  ferment  be  present, 
is  maintained  so  long  as  any  sugar  remains  to  be  decomposed.  The  process 
is  attended  by  a  considerable  elevation  of  temperature,  and  when  complete, 
the  liquor  clears,  the  yeast  falls  to  the  bottom,  the  sugar  has  vanished,  and 
is  replaced  by  alcohol.  A  trace  of  ammonia  also  at  the  same  time  makes  its 
appearance. 

Air  or  oxygen  is  not  necessary  to  these  changes  :  they  go  on  readily  in  a 
close  vessel.  Too  free  an  exposure  of  the  liquid  to  air  would  cause  a  loss 
of  alcohol,  or  the  conversion  of  a  part  of  this  product  into  acetic  acid. 
Although  the  ferment  takes  no  direct  part  in  the  changes,  a  portion  of  it, 
equivalent  to  about  2  per  cent,  of  the  weight  of  the  sugar,  invariably  disap- 
pears during  the  process.  There  is  a  certain  relation  between  the  propor- 
tions of  sugar  and  ferment,  which  must  be  observed,  in  order  to  obtain  the 
most  satisfactory  results.  Kegnault  found  that  4  parts  of  cane-sugar  dis- 
solved in  16  parts  of  water,  required  for  their  complete  fermentation  1  part 
of  fresh  yeast.  If  the  proportion  of  yeast  Is  too  small,  it  is  decomposed 
before  the  entire  conversion  of  the  sugar,  a  portion  of  which  remains 
unchanged  in  the  liquid.  If,  on  the  other  hand,  the  yeast  is  in  too  large  a 
quantity,  the  sugar  is  entirely  decomposed,  and  the  residuary  ferment  after- 
wards undergoes  the  usual  spontaneous  changes.  If  more  sugar  be  added, 
this  will  be  converted  into  alcohol  and  carbonic  acid  until  the  ferment  is 
exhausted.  If  in  any  case  the  sugar  is  in  too  large  a  proportion,  the  pro- 
cess is  less  active  :  and  in  a  saturated  solution  of  sugar,  fermentation  is  alto- 
gether arrested.  It  was  formerly  believed  that  the  ferment  itself  was  not 
decomposed,  but  experiment  has  shown  that  there  is  invariably  a  consump- 
tion of  it,  although  this  is  small  in  proportion  to  the  sugar  which  is  decom- 
posed by  it. 

The  properties  of  the  products  thus  obtained  from  sugar  may  be  easily 
demonstrated.  If  a  lighted  taper  is  introduced  into  the  globular  vessel 
when  fermentation  is  complete,  it  will  be  extinguished :  if  a  portion  of  the 
gaseous  contents  of  the  vessel  is  poured  into  a  jar  containing  lime-water, 
and  the  vessel  agitated,  the  liquid  will  become  white  from  thfe  production  of 
carbonate  of  lime.  If  the  gas  is  poured  from  the  globe  into  another  jar 
containing  a  solution  of  chloride  of  lime  colored  blue  by  litmus,  the  color 
will  be  destroyed  on  agitation,  thus  showing  the  presence  of  a  gaseous  acid.. 
37 


678  WINE.      CHEMICAL    PROPERTIES    OF    VINOUS    LIQUIDS. 

If  during  fermentation  the  aperture  of  the  vessel  is  made  air-tight,  and  con- 
nected by  a  bent  glass  tube  with  a  jar  full  of  water,  and  inverted  over  a 
water-bath,  the  carbonic  acid  may  be  collected  as  it  issues  in  bubbles.  The 
quantity  which  escapes  is  very  large  :  it  amounts  to  nearly  half  the  weight 
of  the  sugar,  180  parts  of  fruit-sugar  are  converted  into  92  parts  of  alcohol, 
and  88  of  carbonic  acid.  Three  drachms  of  fruit-sugar,  when  completely 
fermented,  yield  187  cubic  inches  of  this  gas.  One  grain  of  fruit-sugar  thus 
produces  rather  more  than  a  cubic  inch.  In  order  to  produce  these  quanti- 
ties of  alcohol  and  carbonic  acid,  there  are  required  of  grape-sugar  198 
parts,  and  of  cane-sugar  171  parts.  When  the  sugar  is  derived  from  malted 
grains,  the  liquid  product  of  fermentation  is  called  beer;  when  from  the  juice 
of  the  grape,  it  is  called  wine. 

Beer. — This  liquid  consists  chiefly  of  water  and  alcohol,  with  sugar,  dex- 
trine, coloring  matter,  essential  oil,  carbonic  acid,  and  saline  matters.  Hop% 
impart  to  it,  as  a  result  of  the  volatile  oil  and  other  principles  contained  in 
them,  an  aromatic  bitter  flavor,  and  an  agreeable  odor.  They  also  diminish 
the  tendency  to  subsequent  fermentation.  The  color  of  beer  depends  on  the 
temperature  to  which  the  malt  has  been  exposed.  Pale  malt,  i.  e.,  malt  which 
has  not  been  exposed  to  a  temperature  above  140^,  is  in  the  best  condition 
for  the  production  of  beer ;  but  more  color  and  flavor  are  imparted  by  malt 
which  has  been  dried  at  a  higher  temperature.  To  a  good  beer  brewed  from 
pale  malt,  any  depth  of  tint  may  be  imparted  by  a  careful  use  of  roasted 
malt.  Caramel  or  burnt  sugar  is  sometimes  employed  as  a  coloring  sub- 
stance. The  average  amount  of  absolute  alcohol,  by  measure,  in  the  varie- 
ties of  ale,  is  from  6  to  9  per  cent. ;  less  than  six  in  common  ale  ;  in  porter 
about  5  per  cent. ;  and  in  small  beer  1  to  2  per  cent.  Some  of  the  stronger 
ale  contains  as  much  as  9  per  cent.  The  method  of  determining  the  propor- 
tion will  be  described  hereafter. 

Wine. — The  grape-sugar,  or  glucose,  contained  in  the  ripe  grape,  the 
juice  of  which  is  called  must,  is  the  source  of  the  alcohol  of  wine.  Besides 
water  and  alcohol,  the  fermented  juice  contains  sugar,  gum,  coloring  matter, 
malic  and  tannic  acids,  the  bitartrate  of  potassa,  tartrate  of  lime,  and  other 
salts,  as  well  as  volatile  oil  and  oenanthic  ether.  Red  wines  contain  much  red 
coloring  matter,  which  is  derived  chiefly  from  the  red  husks  of  the  grapes. 
The  husks  also  impart  tannic  acid,  which  gives  astringency  to  port  and  simi- 
lar red  wines.  The  pale  yellow  or  brown  color  of  white  wines  arises  from 
the  fermentation  of  the  juice  only,  or  from  fermentation  over  nearly  colorless 
husks.  The  deep  brown  color  of  some  wines  (Tent  wine)  is  more  commonly 
produced  artificially  by  the  addition  of  caramelized  grape-sugar.  The  dark- 
colored  varieties  of  sherry  frequently  owe  their  tint  to  burnt  sugar,  or  caramel. 

All  wines  have  an  acid  reaction,  arising  from  the  presence  of  the  acid  tar- 
trate of  potassa  or  lime,  as  well  as  of  acetic  acid,  derived  from  a  partial 
oxidation  of  the  alcohol  after  the  vinous  fermentation  is  completed.  In 
sparkling  wines  the  acidity  is  partly  due  to  carbonic  acid.  Malic  acid  is 
frequently  present ;  and  sulphuric  acid,  derived  from  the  sulphuring  of  the 
juice  to  arrest  fermentation,  is  also  a  cause  of  acidity.  This  may  be  found 
in  comparatively  large  proportion  in  most  sherry  wines.  The  amount  of  acid 
in  wines  may  be  determined  volumetrically  by  the  use  of  a  standard  diluted 
solution  of  ammonia,  and  a  graduated  burette.  Some  portion  of  the  acid  is 
volatile,  and  may  be  separated  by  distillation. 

In  all  wines  there  is  more  or  less  of  an  odorous  principle,  partly  derived 
directly  from  th'e  grape,  and  partly  formed  during  fermentation ;  it  has  the 
characters  of  an  essential  oil ;  it  constitutes  the  perfume  or  bouquet  of  the 
wine,  and  in  some  wines  is  evanescent  and  small  in  quantity,  in  others  more 
persistent  and  abundant.     It  does  not  exceed  the  forty-thousandth  part  of 


DETERMINATION    OP    ALCOHOL    IN    WINES.  579 

the  wine.  This  odorous  substance,  which  is  formed  in  the  process  of  fer- 
mentation, is  represented  by  Pelouze  and  Liebig  (Ann.  Ck.  et  Ph.,  liii.  115, 
and  Ixii.  439)  as  a  true  ether,  that  is,  as  a  combination  of  oxide  of  ethyle 
with  oenanthio  acid.  The  formula  Ci^HjgOa  is  represented  as  that  of  oenan- 
thic  acid,  which  4-C4H50  gives  CigH^gOa  as  the  composition  of  cenanthic 
ether.  Deleschamps  first  separated  this  ether  from  the  wines  of  Burgundy, 
and  it  was  afterwards  recognized,  together  with  amylic  alcohol  (potato-spirit 
oil),  in  the  products  of  the  distillation  of  the  grapestalks  of  Montpellier. 

(Enanthic  ether  (from  ohoi,  wine),  which  is  considered  to  be  identical  with 
pelargonic  ether,  may  be  obtained  by  agitating  the  oil  derived  from  brandy 
or  from  grain-spirit  (Weinfuselol),  which  is  a  mixture  of  cenanthic  acid  and 
cenanthic  ether,  with  a  solution  of  carbonate  of  soda,  till  the  free  acid  is  neu- 
tralized ;  heat  is  then  applied,  and  the  cenanthic  ether  separates  upon  the 
surface,  and  may  be  dehydrated  by  chloride  of  calcium. 

According  to  some,  this  ether  exists  ready  formed  in  unfermented  grape- 
juice.  It  is  a  colorless  oily  liquid,  of  a  strong  vinous  odor,  sp.  gr.  0-862, 
boiling  at  440*^,  soluble  in  alcohol  and  ether,  but  insoluble  in  water.  A 
small  quantity,  however,  passes  over  with  the  vapor  of  water  during  distilla- 
tion. It  has  a  strong  taste  and  odor,  as  well  as  intoxicating  properties.  It 
imparts  a  powerful  aroma,  which  is  very  persistent  in  any  bottle  or  vessel 
that  has  contained  wine  :  the  odor  is  soon  perceived  over  a  very  large  apart- 
ment. Butyric,  caprylic,  acetic,  and  other  ethers,  are  sometimes  associated 
in  wine  with  the  cenanthic.  The  bouquet  or  perfume  of  wine  is  much  affected 
by  age.  In  some  wines  there  is  a  fixed  non-nitrogenous  principle  which  has 
been  called  cenanthin. 

During  fermentation  the  acid  tartrate  of  potassa  becomes  less  soluble,  by 
reason  of  the  production  of  alcohol ;  and  the  acidity  of  the  wine,  if  dependent 
on  the  presence  of  this  salt,  diminishes,  while  its  strength  increases.  This  is 
deposited  in  the  cask  or  bottle,  either  colored  or  colorless,  according  to  the 
nature  of  the  wine.  It  is  well,  known  under  the  name  of  crude  tartar,  or 
argol.  Some  wines  which  contain  much  sugar  are  observed,  after  a  certain 
period,  to  become  viscid  or  ropy.  This  has  been  called  the  viscous  fermen- 
tation.  It  appears  to  arise  from  a  spontaneous  conversion  of  grape-sugar 
into  an  isomeric  mucilaginous  or  gummy  compound.  Mannite  is  said  to  be 
a  product,  and  hydrogen  is  evolved  under  these  circumstances.  Wines  which 
contain  much  tannic  acid  are  not  liable  to  this  change ;  and  this  acid,  when 
added  to  wine  thus  affected,  precipitates  the  mucilaginous  compound.  We 
have  observed  this  change  to  take  place  in  ale,  arising  probably  from  an 
excess  of  sugar  and  a  deficiency  of  tannic  acid  in  the  hops. 

Wines  which  are  bottled  before  alcoholic  fermentation  is  completed  undergo 
this  process  still  further ;  the  carbonic  acid  accumulates  in  the  liquid,  and 
gives  to  the  wine  a  sparkling  character.  An  albuminous  compound  in  the 
husk  of  the  grape  serves  as  a  natural  ferment  to  the  juice.  If  the  fruit-sugar 
is  in  excess,  the  wine  will  remain  sweet  after  fermentation  (Liqueur  wines). 
If  the  ferment  is  in  excess,  the  whole  of  the  sugar  will  be  decomposed  and 
the  wine  will  be  slightly  acid  (Rhenish  wines).  If  the  sugar  and  ferment 
are  equal,  the  wine  is  neither  acid  nor  sweet  (Burgundy).  {Mulder  on  Wine, 
139.)  When  the  sugar  and  ferment  are  thus  equally  balanced,  the  sugar 
almost  entirely  disappears,  and  a  dry  wine  is  the  result.  If,  during  fermen- 
tation, the  alcohol  reaches  about  20  per  cent,  of  the  wine,  the  process  is 
arrested,  and  any  undecomposed  sugar  remains.  In  some  of  the  Rhenish 
wines  Fischern  found  the  sugar  so  completely  removed  that,  while  it  amounted 
to  21  7  per  cent,  of  the  grape-juice,  it  constituted  only  01  per  cent,  of  the 
wine  (Liebfrauenmilch),  the  alcohol  amounting  to  9*9  per  cent,  and  the  dry 
extract  to  4*1. 


580  COMPOSITION    OP    WINE. 

The  quantity  of  alcohol  contained  in  different  wines  is  variable  ;  the  best 
mode  of  determining  it  consists  in  carefully  distilling  four  ounces  of  the  wine, 
until  from  one-half  to  three-fourths  have  passed  over,  having  previously  neu- 
tralized the  acid  of  the  wine  by  a  little  soda,  potassa,  or  lime,  A  quantity 
of  distilled  water  is  then  added  to  the  portion  of  the  alcoholic  liquid  which 
has  gone  over,  so  as  accurately  to  make  up  the  original  volume  of  the  wine  : 
the  mixture  is  well  shaken  and  set  aside  for  a  day  or  two  in  a  stoppered 
bottle,  so  that  it  may  obtain  its  maximum  density.  Its  specific  gravity  may 
then  be  taken  in  the  usual  way  at  60°,  and  from  this  datum  the  proportion 
of  alcohol  may  be  determined  by  reference  to  tables  which  show  the  quantity 
of  absolute  alcohol  contained  in  diluted  alcohol  of  different  densities  {see  p. 
586).  There  is,  of  course,  no  direct  relation  between  the  original  density  of 
the  wine  and  its  alcoholic  contents,  inasmuch  as  some  of  the  most  alcoholic 
wines  are  also  those  which  have  the  highest  specific  gravity,  in  consequence 
of  the  sugar,  extract,  and  other  substances  which  they  hold  in  solution. 
Thus  we  have  found  some  very  strong  wines  to  have  a  greater  sp.  gr.  than 
water,  the  solid  contents  of  the  wine  being  in  larger  proportion. 

Another  method  consists  in  gently  distilling  the  wine  until  one-half  is 
obtained  in  the  receiver.  The  sp.  gr.  of  the  distillate  may  be  at  once  taken 
without  admixture  with  water.  In  this  case,  as  there  is  only  half  of  the  ori- 
ginal quantity,  the  distilled  spirit  will  have  twice  the  strength :  hence  the 
proportion  of  alcohol  is  determined  by  dividing  the  quantity  per  cent,  by  2. 
Thus,  four  ounces  of  sherry  yield  two  ounces  of  spirit,  which,  when  mixed 
with  two  ounces  of  water,  will  have  a  sp.  gr.  of  0-9753  =  l'r  per  cent,  of 
alcohol.  The  distiUed  spirit,  before  the  addition  of  its  bulk  of  water,  has  a 
sp.  gr.  of  0-9511=34  per  cent,  of  alcohol,  and  34-^2=17  per  cent,  of  alco- 
hol contained  in  the  wine.  These  methods  of  determining  the  alcoholic 
strength  of  wines  are  applicable  to  ale,  beer,  and  other  weak  alcoholic  liquids. 

Independently  of  the  proportion  of  alcohol,  the  analysis  of  wine  is  directed 
to  the  amount  of  dry  extract,  the  quantity  of  mineral  matter,  and  the  nature 
of  the  inorganic  salts.  The  presence  of  tannic  acid,  grape-sugar,  and  other 
inorganic  ingredients,  may  be  determined  by  their  appropriate  tests.  The 
following  represents  the  analysis  of  a  sample  of  dry  sherry.  The  sp.  gr.  of 
the  entire  wine  was  0*994.  The  alcohol,  obtained  by  distillation  from  a 
measured  quantity,  when  made  up  to  its  original  bulk  with  distilled  water, 
had  a  sp.  gr.  of  0*978  at  60°.  According  to  the  tables,  this  is  equivalent 
to  15  per  cent,  by  weight  of  absolute  alcohol.  The  dry  extract  obtained  by 
the  evaporation  of  the  wine  amounted  to  3*75  per  cent,  of  its  weight.  This 
consisted  chiefly  of  grape-sugar,  coloring  matter,  acid  tartrate  of  potassa,  and 
tartrate  of  lime.  The  dry  extract,  when  incinerated,  left  a  white  ash,  which 
weighed  0*45  grains.  The  ash  was  slightly  alkaline :  it  contained  potassa, 
soda,  lime,  and  a  trace  of  alumina,  with  carbonic  and  sulphuric  acids.  In 
the  entire  wine,  besides  grape-sugar  and  coloring  matter,  tartaric,  tannic, 
and  sulphuric  acids  were  found — the  latter  in  comparatively  large  proportion, 
owing  to  the  use  of  burning  sulphur,  for  checking  undue  fermentation  in  the 
wine-manufacture.  The  constitution  of  this  wine  would  therefore  be,  in  100 
parts,  as  follows  : — 

Sp.  gr.  in  the  entire  state 0-994 


Alcohol 15-00 

Dry  saccharine  extract 3-30 

Mineral  ash '  .  0*45 

Water,  oil,  ether,  and  volatile  products        .        .  81-25 


100-00 


ANALYSIS    OP    WINES.  581 

• 

The  comparison  of  weight  with  measure  may  be  thus  made.  The  sp.  gr. 
represents  in  grains  ihe  weiglit  of  eighteen  fluidrachms  of  the  wine  at  68°, 
namely,  994  grains,  the  same  volume  of  water  weighing  nearly  1000  grains 
at  this  temperature.  The  mixture  of  the  distillate  with  the  residue  in  the 
retort,  however  carefully  the  distillation  may  have  been  conducted,  will  not 
reproduce  the  wine  with  its  original  odor  and  flavor.  This  is  owing  to  the 
loss  or  decomposition  of  the  volatile  oily  matters  and  oenanthic  ether  during 
distillation. 

The  quality  of  wine,  although  for  financial  purposes  estimated  by  its  alco- 
holic strength,  does  not  depend  on  the  amount  of  alcohol,  or  of  dry  residue 
in  one  hundred  parts,  although  the  finest  wines  contain,  generally  speaking, 
a  large  proportion  of  solid  matter.  It  depends  chiefly  upon  the  peculiar 
flavor  imparted  by  the  grape  during  fermentation,  and  the  effects  of  age  in 
improving  and  heightening  this  flavor.  The  amount  of  alcohol  will  depend 
on  the  quantity  of  fruit-sugar  in  the  grape-juice,  on  the  addition  of  starch- 
sugar,  or  glucose,  to  the  must  during  fermentation,  or  of  brandy  after  that 
process.  The  solid  contents  are  generally  small,  except  in  sweet  wines.  Dr. 
Christison  states,  from  his  observation,  that  in  Port  and  Sherry,  when  fit  for 
drinking,  the  solid  seldom  exceeds  three  per  cent,  in  Bordeaux  wine  they 
amount  to  about  two  and  a  half,  and  in  Hock  and  Moselle  to  two  per  cent, 
only. 

Te  results  of  analysis  will  be  affected  by  the  age  of  the  wine,  the  degree 
to  which  fermentation  has  taken  place,  and  other  circumstances.  The  fol- 
lowing table  represents,  chiefly  as  the  result  of  recent  analyses,  the  constitu- 
tion of  many  wines  which  are  now  consumed  in  this  country.  The  alcoholic 
strength  is  given  by  weight  in  absolute  alcohol  (sp.  gr.  •'794  at  60°).  At 
this  temperature  and  specific  gravity,  49  parts  of  alcohol  by  weight  are 
equivalent  to  100  parts  of  proof  spirit,  by  weight  (sp.  gr.  '920),  or  to  102*57 
parts  by  measure.  The  alcoholic  strength  of  vinous  liquids  is  sometimes 
calculated  in  alcohol  of  a  sp.  gr.  of  '825.  At  this  sp.  gr.,  however,  alcohol 
is  combined  with  11  per  cent,  of  water. 

TABLE   OF   ANALYSIS  OF  WINES. 


Specific 

Alcohol  in 

Dry  extract  in 

Ash  in  100 

' 

gravity. 

100  by  weiglit 

.    100  by  weight. 

by  weight. 

Port,  1820  (Muspratt) 

.     0-9945 

...       18-01 

...      5-14      ... 

Port,  1844  . 

.     0-9977 

...       17-00 

...       6-20       ... 

0-30 

Sherry 

.     0-9960 

...       17-30 

...      5-70      ... 

0-70 

Sherrj  (dry) 

.     0-9940 

...       15-00 

...      3-75       ... 

0-45 

Tarragona  . 

.     1-0154 

...       16-00 

...     10-80       ... 

0.50 

Gelopiga     , 

.     1-0547 

...       15-00 

...     20-70       ... 

0-20 

Bucellas     . 

.     0-9934 

...       16-00 

...      3-30      ... 

0-40 

St.  Estephe 

.     0-9930 

...       10-00 

...       2-00       ... 

0-30 

11 

.     0-9933 

...       10-00 

...      2-47      ... 

0-23 

Haut.  Brion 

.     0-9940 

9-00 

...      2-30       ... 

0-25 

St.  Emilion 

.     0-9960 

9-00 

...       2-44      ... 

0-32 

Beaujolais 

.     0-9930 

...       10-00 

...       2-00       ... 

0-20 

Sauterne     . 

.     0-9955 

7-50 

...       1-32      ... 

0-10 

Chablis       . 

.     0-9212 

9-00 

...       1-60      ... 

0-10 

Roussillon  . 

.     1-0076 

...       13-00 

...       7-10       ... 

0-40 

Steinberg    \ /^ei^er^ 
Riidesheim  /  ^^^^S^^) 

.     1-0025 
.     1-0025 

...      10-87 
...       12-65 

...       9-94      ... 
...       5-39       ... 

Tokay  (Richter) 

.     1-0201 

...       12-10 

...     10-60      ... 

Malaga  (Mayer) 

.    1-0570 

...       12-24 

...     18-40       ... 

Tent  wine  . 

.     1-1150 

7-00 

...     32-60      ... 

O'Aiy 

Champagne 

.     1-0290 

...      11-70 

...       0-30      ... 

traces 

In  comparing  the  bulk  of  the  wine  with  the  weight,  it  may  be  observed 
that  the  sp.  gr.  represents  the  weight  in  grains  and  tenths  of  grains,  of  18 
fluidrachms,  or  65  cubic  centimetres.     Thus,  this  quantity  of  port  wine 


582  STRENGTH    OF    SPIRITUOUS    LIQUIDS. 

(1820)  weighed  994*5  grains,  the  same  volume  of  water  weigTiing  1000 
grains.  In  calculating  the  percentage  of  alcohol  as  proof  spirit  at  918,  the 
amount  in  absolute  alcohol  should  be  doubled.  Thus,  18  01  absolute  alcohol 
in  port  wine  (1820)  are  equivalent  to  36  75  of  proof  spirit  per  cent. 

Spirituous  Liquids. — Brandy,  rum,  gin,  and  whiskey  are  spirituous  liquids 
which  contain  about  half  their  weight  of  alcohol,  and  are  therefore  nearly  in 
the  condition  of  proof-spirit.  They  are  obtained  by  distilling  various  fer- 
mented liquors.  They  chiefly  consist  of  alcohol  and  water,  with  a  very  small 
proportion  of  solid  matter :  they  owe  their  peculiar  odors  and  flavors  to  the 
presence  of  certain  oily  and  ethereal  products  of  fermentation.  When  genuine, 
they  are  neutral,  and  leave  only  a  slight  residue  on  evaporation.  Brandy  is 
the  result  of  the  distillation  of  wine ;  and  its  qualities  vary  with  the  kind  of 
wine  from  which  it  is  obtained,  and  the  precautions  with  which  it  is  distilled. 
It  is  frequently  strongly  colored  with  caramel. — Rum  is  distilled  in  the  East 
and  West  Indies  from  a  fermented  mixture  of  molasses  and  water,  with  the 
skimmings  of  the  sugar  boilers,  and  the  lees  or  spirit-wash  of  former  distil- 
lations—  Gin,  or  Geneva,  is  prepared  from  difi'erent  kinds  of  corn-spirit:  it 
was  originally  largely  imported  from  Holland,  and  was  known  as  Holland  or 
Hollands'  gin.  Its  flavor  is  derived  from  juniper-berries,  or  from  the  essen- 
tial oil  of  juniper,  which  contributes  to  its  diuretic  quality.  Calamus  aro- 
maticus,  or  sweet  flag,  and  other  flavoring  articles,  are  occasionally  used  in 
its  manufacture.  The  great  gin-distillers  sell  it  to  the  trade  at  about  20  per 
cent,  over  proof,  but  the  retailers  afterwards  dilute  and  generally  sweeten  it. 
Yarious  chemical  substances  are  employed  in  its  adulteration. —  Whiskey  (a 
term  said  to  be  derived  from  the  Irish  usquebaugh^  is  also  a  corn-spirit,  and, 
when  genuine,  derives  its  characteristic  flavor  from  the  malt  used  in  its  manu- 
facture having  been  dried  over  peat  or  turf  fires ;  but  this  odor  and  flavor 
of  burned  turf,  or  peat-reek,  is  frequently  given  to  raw  corn-spirit  by  im- 
pregnating it  with  peat-smoke. — Arrack,  or  Rack,  is  a  spirituous  liquor 
prepared  in  various  parts  of  India  from  the  fermented  juice  of  the  cocoa-nut, 
and  also  from  fermented  infusion  of  rice.  It  has  a  peculiar  flavor  and  odor, 
but  in  other  respects  closely  approaches  in  its  characters  to  rum.  It  is  said 
that  a  genuine  arrack  may  be  very  well  imitated  by  dissolving  10  grains  of 
benzoic  acid  in  a  pint  of  rum. 

There  are  many  other  alcoholic  liquors,  the  preparation  of  which  is  pecu- 
liar to  diJBferent  places — Kirschwasser  is  obtained  in  Switzerland,  and  in 
some  parts  of  France,  from  bruised  black  cherries,  fermented  and  distilled. 
— Maraschino  is  a  similar  liqueur  prepared  also  from  a  peculiar  kind  of  cherry 
growing  in  Dalmatia — Noyau  and  several  analogous  liqueurs  are  flavored  with 
an  essential  oil  containing  more  or  less  hydrocyanic  acid,  and  often  with  that 
derived  from  bitter  almonds,  the  kernels  of  peaches,  apricots,  &c.,  or  from 
the  leaves  of  laurels.  Some  of  these  compounds  come  under  the  denomina- 
tion of  tinctures;  such,  for  instance,  as  Curagoa,  which  is  prepared  by  digest- 
ing orange-berries  (the  immature  fruit)  and  bitter  orange-peel  with  cloves 
and  cinnamon  in  brandy  :  when  this  tincture  is  distilled,  and  afterwards 
sweetened,  it  constitutes  white  Curagoa.  These  compounds  are  frequently 
called  Ratafias,  a  term  derived,  like  the  word  ratify,  from  ratum  and  fio,  to 
make  firm,  or  confirm.  By  ratafia,  therefore,  was  originally  meant  a  liquid 
drunk  at  the  ratification  of  an  agreement. 

In  the  analysis  of  these  spirituous  liquids  the  distillation  for  the  separa- 
tion of  alcohol  must  be  carried  on  at  a  low  temperature  until  nearly  the  whole 
of  the  liquid  has  passed  over.  The  following  table  represents  the  results  of 
recent  analyses,  the  alcohol  being  estimated  by  weight  and  volume  as  abso- 
lute. 


ALCOHOL. 

Alcohol  in 

Dry  extract  in 

Ash  in  100 

Name. 

Sp.  grav. 

100  by  weight. 

100 

by  weight. 

by  weight. 

Whiskey    . 

.     0-9208 

...       50-00 

... 

0-10       .. 

trace 

Gin     . 

.     0-9440 

...       45-00 

0-20       .. 

.       0-10 

Brandy,  Cognac 

.     0-9300 

...       46-00 

... 

1-40       . 

.       0-20 

"       common 

.     0-9483 

...       36-00 

... 

0-60 

.       0-05 

Rum   . 

.     0-9260 

...       48-00 

... 

0-90       . 

.       0-10 

583 


^  But  two  of  these  compound  are  introduced  into  pharmacy,  whiskey,  Spi- 
ritus  Frumenti  (U.  S.  P.),  and  brandy  under  the  classical  name  of  Spiritus 


Vini  Gallici. 


CHAPTER    XLVII. 

ALCOHOL.     ALDEHYDE.     CHLOROFORM.     METHYLIC, 
AMYLIC,    AND    OTHER   ALCOHOLS. 

Alcohol.     Ethylic  Alcohol  {Q^fi^. 

The  word  alcohol  signifies  in  Arabic  a  liquid  or  solid  brought  to  its  utmost 
perfection.  By  the  careful  distillation  of  any  of  the  spirituous  fermented 
liquids  described  in  the  preceding  chapter,  the  alcoholic  portion  may  be  sepa- 
rated from  the  less  volatile  matters,  and  the  product  is  known  in  commerce 
as  Rectified  Spirit  of  Wine.  Its  sp.  gr.  is  usually  about  0*840  to  0  850, 
and  it  consists  of  alcohol  combined  with  about  from  It  to  20  per  cent,  of 
water  :  it  generally  contains  traces  of  oily  matters,  and  of  some  other  impuri- 
ties. The  distillers  commonly  prepare  a  liquor  called  wash,  for  the  express 
purpose  of  producing  from  it  rectified  spirits.  Instead  of  using  pure  malt, 
they  employ  chiefly  raw  grain,  mixed  with  a  small  quantity  only  of  malted 
grain.  The  water  employed  in  the  mash-tub  is  generally  at  a  lower  tempe- 
rature than  that  adopted  in  brewing  beer,  and  the  mashing  is  longer  con- 
tinued. The  wort  is  afterwards  fermented  with  yeast,  and  then  distilled  for 
the  production  of  proof- spirit  and  alcohol.  In  this  state  the  product  is  called 
malt-spirit.  Its  specific  gravity  is  from  '914  to  '936,  and  it  contains  about 
half  its  weight  of  alcohol.  The  oily  products  which  are  combined  with  the 
spirit  and  render  it  impure,  are  mostly  less  volatile  than  alcohol,  so  that  when 
the  process  of  rectification  is  carefully  performed,  they  remain  with  the  resi- 
duary water  in  the  still  or  retort.  Many  precautions  are  requisite,  both  in 
conducting  the  distillation,  and  in  the  management  and  construction  of  the 
stills,  so  as  to  produce  what  is  techanically  known  as  clean  spirit.  Rectified 
spirit  thus  obtained,  varies  in  sp.  gr.  from  "835  to  '884,  and  contains  from  85 
to  65  per  cent,  of  alcohol. 

To  obtain  pure  or  absolute  alcohol,  rectified  spirit  is  usually  dehydrated, 
by  distilling  it  with  certain  substances  which  have  a  strong  affinity  for  water. 
Although  the  boiling  points  of  alcohol  and  water  greatly  differ,  it  is  impos- 
sible to  separate  the  water  from  aqueous  alcohol  by  distillation  at  a  low  tem- 
perature. The  vapors  of  both  pass  over  and  are  condensed  together  so  soon 
as  the  liquid  reaches  a  sp.  gr.  of  0-825.  Among  the  substances  used  for 
dehydration,  are  carbonate  of  potassa,  chloride  of  calcium,  quicklime,  and 
anhydrous  sulphate  of  copper. 

When  common  spirit  of  wine  is  employed,  the  first  portions  of  water  may 
be  abstracted  by  adding  to  it  dry  carbonate  of  potassa  until  that  salt  ceases 
to  be  dissolved ;  the  mixture  is  then  frequently  shaken,  and  when  allowed  to 


684  RECTIFIED    SPIRIT. 

stand  at  rest,  it  soon  separates  into  two  portions,  the  uppermost  being  alco- 
hol (of  sp.  gr.  0'825)  and  the  lowermost  an  aqueous  solution  of  the  car- 
bonate. The  former  is  drawn  oflF  and  poured  upon  a  quantity  of  powdered 
quicklime,  amounting  to  about  half  the  weight  of  the  alcohol,  and  previously 
introduced  into  a  tubulated  retort.  This  mixture  may  be  left  to  digest  for 
a  day  or  two,  and  then  slowly  distilled  in  a  water-bath,  at  a  temperature  of 
about  200°.  Fresh-burnt  lime  alone  may  be  used  without  the  previous 
employment  of  carbonate  of  potassa,  the  water  being  then  absorbed  and 
retained  by  the  lime  as  hydrate.  In  place  of  lime  an  equal  weight  of  fused 
chloride  of  calcium  may  be  employed.  Any  color  or  odor  possessed  by  the 
rectified  spirit  may  be  removed  by  the  use  of  finely-powdered  animal  char- 
coal. 

Properties  of  Alcohol. — Alcohol  is  a  limpid  colorless  neutral  liquid  of  an 
agreeable  odor,  and  a  strong  pungent  taste.  It  is  quite  neutral,  and  is  not 
liable  to  undergo  any  change  by  keeping.  The  specific  gravity  of  absolute 
alcohol  is  0  794  at  60°.  When  spirit  of  wine  is  as  far  as  possible  dehydrated 
by  simple  distillation,  its  specific  gravity  is  0-825  at  60°  (  =  89  per  cent,  of 
alcohol).  The  rectified  spirit  of  the  Pharmacopoeia  is  directed  to  have  a  sp. 
gr.  0*838.  It  contains  16  per  cent,  of  water,  and  is  employed  for  making 
certain  tinctures.  The  quantity  of  absolute  alcohol  contained  in  these  and 
other  commercial  forms  of  alcohol  and  spirit  of  wine,  will  be  seen  by  refer- 
ence to  the  table  given  at  p.  542.  According  to  Despretz,  the  specific  heat 
of  alcohol  is  0  52.  Alcohol  has  never  been  frozen.  Faraday  exposed  it  to 
a  temperature  of  166°  below  0°;  it  thickened  considerably,  but  did  not  con- 
geal {Phil  Trans.,  1845,  p.  158).  According  to  Mitchell,  alcohol  of  0-798 
becomes  oily  at  — 130°,  and  at  — 146°  flows  like  melted  wax  ;  and  alcohol 
of  sp.  gr.  0-820  entirely  congeals  in  a  bath  of  solid  carbonic  acid  and  ether 
(—166°).  The  boiling-point  of  alcohol  of  sp.  gr.  0-7947  is  173°  (Barom. 
29-5).  When  of  the  sp.  gr.  0-825  it  boils  at  a  temperature  of  176°  under 
the  same  pressure.  In  the  vacuum  of  an  air-pump,  alcohol  boils  at  common 
temperatures.  The  specific  gravity  of  the  vapor  of  alcohol  (in  reference  to 
air  =  1-000)  was  experimentally  found  by  Gay-Lussac  to  be  1-6133:  this 
nearly  corresponds  to  its  calculated  specific  gravity.  The  latent  heat  of  the 
vapor  of  alcohol  is  to  that  of  the  vapor  of  water  as  332  to  531  (Despretz). 

Absolute  alcohol  has  so  strong  an  affinity  for  water  as  to  absorb  it  from 
the  atmosphere ;  it  requires,  therefore,  to  be  kept  in  well-stopped  bottles,  as, 
after  exposure,  it  undergoes  a  sensible  increase  of  specific  gravity ;  it  is 
even  apt  to  absorb  a  small  quantity  of  water  during  its  distillation.  Anhy- 
drous sulphate  of  copper  is  not  rendered  blue  by  strong  alcohol,  and  potas- 
sium decomposes  it  without  combustion  and  without  imparting  to  it  a  dark 
color.  Alcohol  does  not  appear  to  form  any  definite  hydrate :  for  even  the 
water,  which  passes  over  with  it  by  distillation  at  a  sp.  gr.  of  0*825,  may  be 
entirely  separated  by  lime,  carbonate  of  potassa,  or  any  substance  which 
combines  with  or  dissolves  in  water.  It  may  be  mixed,  in  all  proportions, 
with  water  without  change,  and  while  heat  is  evolved,  a  diminution  of  bulk 
(or  increase  of  specific  gravity)  ensues.  When  alcohol  and  snow  are  mixed, 
there  is,  on  the  other  hand,  a  diminution  of  temperature,  as  a  result  of  the 
sudden  liquefaction  of  the  snow.  The  contraction  in  volume  which  ensues 
on  mixing  alcohol  with  water  has  been  already  described  (p.  50) :  it  is 
always  attended  with  an  increase  of  temperature.  Thus  equal  measures  of 
alcohol  (sp.  gr.  0*825)  and  water,  each  at  50°,  afford,  when  suddenly  mixed, 
a  temperature  of  70°  ;  and  equal  measures  of  proof  spirit  and  water,  each  at 
50°,  give,  under  similar  circumstances,  a  mixture  of  the  temperature  of  60°. 
The  greatest  amount  of  heat  and  condensation  is  produced  by  the  admixture 


PROOF    SPIRIT. 


585 


of  1  equivalent  (53-74  parts)  of  alcohol  and  6  equivalents  (49*84)  of  water. 
The  mixture  is  reduced  on  cooling  to  100  parts,  and  has  a  sp.  gr.  of  0-227. 
Proof  Spirit. — This  is  a  weaker  form  of  alcohol  than  rectified  spirit.  It 
is  employed  in  reference  to  Excise  regulations,  and  in  pharmacy  {Spiritus 
tenuior).  In  the  latter,  the  sp.  gr.  is  fixed  at  0  920.  It  consists  by  weight 
at  60°  of  49  parts  of  alcohol  and  51  parts  of  water.  The  British  Pharma- 
copoeia directs  that  it  should  be  made  by  mixing  five  pints  of  rectified  spirit 
(0*838)  with  three  pints  of  distilled  water.  It  is  employed  for  making  the 
greater  number  of  medicinal  tinctures.  The  sp.  gr.  of  Excise  proof-spirit 
at  60^  is  0*916.  This  corresponds  nearly  to  equal  parts  by  weight  of  alco- 
hol and  water.  Such  a  mixture,  according  to  Gilpin's  tables,  should  have 
a  sp.  gr.  of  0*917.  The  term  proof,  appears  to  be  derived  from  the  old 
gunpowder-test.  Spirit  was  poured  over  gunpowder  and  the  vapor  in- 
flamed:  if  it  fired  the  gunpowder  it  was  over-proof;  if  it  burnt  without 
igniting  the  powder,  owing  to  the  residuary  water  rendering  the  powder 
damp,  it  was  said  to  be  under-proof.  The  weakest  spirit  capable  of  firing 
gunpowder  was  the  proof-spirit  of  pharmacy,  sp.  gr.  0*920.  Drinkwater 
gives  the  following  table,  showing  the  results  of  his  experiments  upon  the 
composition  of  proof -spirit. 


Alcohol  and  water. 

Specific  gravity 
at  60°  F. 

Bulk  of  mixture  of  100 
measures  of  alcohol 

By  weight 

By  measure. 

+81-82  water. 

Alcohol.                  Water. 

100    4-     103-09 
or  in  100 
49-24      +      50-76 

Alcohol.                 Water. 
100      4-      81-82 
or  in  100 
54     4-      46 

•91984 

175-25 

The  strength  of  such  spirituous  liquors  as  consist  of  water  and  alcohol,  is 
ascertained  by  their  specific  gravity,  and  for  fiscal  purposes  it  is  determined 
by  the  hydrometer ;  but  the  only  correct  mode  of  ascertaining  the  specific 
gravity  of  liquids  is  by  weighing  them  in  a  delicate  balance,  against  an 
equal  volume  of  pure  water  of  the  same  temperature.  For  this  purpose  a 
thousand-grain  bottle  may  be  employed.  Small  hydrometers  are  constructed 
to  indicate,  by  flotation,  proof-spirit,  and  a  certain  number  of  degrees  above 
and  below  proof. 

Alcohol  is  extremely  inflammable,  and  burns  with  a  pale  bluish  flame, 
scarcely  visible  in  bright  daylight ;  but  the  heat  of  its  flame  is  very  intense, 
as  may  be  shown  by  suspending  in  it  a  coil  of  fine  platinum  wire,  which 
soon  becomes  white-hot.  It  produces  no  smoky  deposit  upon  cold  sub- 
stances held  over  it.  The  products  of  the  combustion  of  alcohol  are  carbonic 
acid  and  water,  the  weight  of  the  water  considerably  exceeding  that  of  the 
alcohol  consumed.  According  to  Saussure,  jun.,  100  parts  of  alcohol  afl'ord, 
when  burned,  136  parts  of  water,  the  production  of  which  may  be  shown  by 
holding  a  glass-jar  over  the  flame  until  it  is  extinguished.  Water  is  depo- 
sited on  the  sides  of  the  jar,  and  carbonic  acid  is  collected  within  it,  a  fact 
which  may  be  proved  by  the  addition  of  lime-water.  The  flame  of  alcohol 
may  also  be  burned  under  a  condensing-apparatus,  the  exit-tube  at  its  ex- 
tremity being  turned  down  into  a  glass-jar.  It  will  then  be  found  that  a 
current  of  carbonic  acid  passes  out  of  it :  this  may  be  rendered  evident  by 
lime-water,  and  the  extinction  of  a  taper.  When  alcohol  is  burned  at  a 
lower  temperature  than  that  required  for  its  inflammation,  as  by  the  action 
of  spongy  or  finely-divided  platinum,  or  by  a  hot  platinum  wire,  as  described 
at  p.  54,  the  products  of  its  combustion  are  diS'erent ;  the  proportion  of 
carbonic  acid  is  less,  and  aldehydic  and  acetic  compounds  are  formed. 


586 


TABLE  OF  THE  PERCENTAGE  OF  ALCOHOL. 


The  following  table  by  Fownes  represents  the  specific  gravities  of  mix- 
tares  of  alcohol  and  water.  The  proportion  of  absolute  alcohol  is  given  by 
weight. 


Sp.gr. 

Percentage 

Sp.  gr. 

Percentage 

Sp.  gr. 

Percentage 

at  60°. 

of  alcohol. 

at  eo^". 

of  alcohol. 

at  60=. 

of  alcohol. 

•9991 

0-5 

•9511      .. 

34 

•8769 

...       68 

•9981 

1 

•9490      .. 

35 

•8745 

...       69 

•9965 

...        2 

•9470      .. 

36 

•8721 

...      70 

•9947 

...        3 

•9452      .. 

37 

•8696 

...       71 

•9930 

4 

•9434      .. 

38 

•8672 

...       72 

•9914 

5 

•9416      .. 

39 

•8649 

...       73 

•9898 

...        6 

•9396      .. 

40 

•8625 

...       74 

•9884 

...       7 

•9376      .. 

41 

•8603 

...       75 

•9869 

...        8 

•9356      .. 

42 

•8581 

...      76 

•9855 

9 

•9335      .. 

43 

•8557 

...       77 

•9841 

...      10 

•9314      .. 

44 

•8533 

...      78 

•9828 

...      11 

•9292      .. 

45 

•8508 

...       79 

•9815 

...      12 

•9270      .. 

46 

•8483 

...       80 

•9802 

...      13 

•9249      .. 

47 

•8459 

...       81 

•9789 

...      14 

•9228      .. 

48 

•8434 

...       82 

•9778 

...      15 

•9206      .. 

49 

•8408 

...       83 

•9766 

...      16 

•9184      .. 

50 

•8382 

...       84 

•9753 

...      17 

•9160      .. 

51 

•8357 

...       85 

•9741 

...      18 

•9135      .. 

52 

•8331 

...       86 

•9728 

...      19 

•9113      .. 

53 

•8305 

...       87 

•9716 

...      20 

•9090      .. 

.       54 

•8279 

...       88 

•9704 

...      21 

•9069      .. 

55 

•8254 

...       89 

•9691 

...      22 

•9047      .. 

56 

•8228 

...       90 

•9678 

...      23 

•9025      .. 

57 

•8199 

...       91 

•9665 

...      24 

•9001     ... 

.       58 

•8172 

...       92 

•9652 

...      25 

•8979      .. 

59 

•8145 

...       93 

•9638 

...      26 

•8956      .. 

.       60 

•8118 

...       94 

•9623 

...      27 

•8932      .. 

.       61 

•8089 

...       95 

•9609 

...      28 

•8908      .. 

.       62 

•8061 

...       96 

•9593 

...      29 

•8886      .. 

.       63 

•8031 

...       97 

•9578 

...      30 

•8863      .. 

.       64 

•8001 

...       98 

•9560 

...      31 

•8840      .. 

.       65 

•7969 

...       99 

•9544 

...      32 

•8816      .. 

.       QQ 

•7938 

...    100 

•9528 

...      33 

•8793      .. 

.       67 

Bleached  bees-wax  is  sometimes  employed  as  a  test  for  the  strength  of 
spirits.  It  has  a  sp.  gr.  of  '960,  and  in  spirits  of  this  sp.  gr.,  representing 
29  per  cent,  of  absolute  alcohol,  this  substance  indififerentiy  floats  or  sinks. 
If  the  sp.  gr.  is  lower,  and  the  alcohol  is  therefore  in  greater  proportion,  it 
sinks  :  if,  on  the  contrary,  it  is  higher,  and  the  water  is  in  larger  quantity,  the 
wax  floats.  If  a  tube  is  half  filled  with  water,  and  half  with  alcohol,  the 
wax  will  sink  through  the  latter,  and  float  on  the  former,  indicating  its 
level.  The  slow  diffusion  of  these  liquids,  under  such  circumstances,  will 
be  proved  by  the  wax  maintaining  its  level  for  many  weeks  or  months,  pro- 
vided the  contents  of  the  tube  are  not  disturbed. 

Graham  has  shown  that  alcohol  may,  in  some  instances,  be  combined  with 
certain  saline  bodies,  such  as  chloride  of  calcium,  nitrate  of  magnesia,  nitrate 
of  lime,  chloride  of  zinc,  and  chloride  of  manganese.  The  alcohol  appears 
to  be  substituted  for  water  of  crystallization.  Such  combinations  have  been 
called  alcohates.  They  are  obtained  by  dissolving  the  substances  by  heat  in 
absolute  alcohol,  and  the  compounds,  more  or  less  regularly  crystallized,  are 
deposited  as  the  solution  cools.  .  They  appear  to  be  definite  compounds,  and 
in  some  of  them,  the  alcohol  is  retained  h^  an  attraction  so  powerful,  that  it 
is  not  evolved  at  a  temperature  of  400°  or  500°. 

Alcohol  dissolves  nearly  all  the  acids,  mineral  and  organic,  giving  rise  to 
an  important  and  varied  class  of  compounds.     When  a  little  sulphuric  acid 


CHEMICAL   PROPERTIES    OF    ALCOHOL.  58T 

is  mixed  with  alcohol,  the  mixture  has  no  action  upon  any  neutral  carbonate, 
and  yet  it  decomposes  acetate  of  potassa,  evolving  acetic  acid.  A  mixture 
of  alcohol  and  hydrochloric  acid  does  not  act  upon  carbonate  of  potassa,  but 
it  decomposes  the  carbonates  of  soda,  lime,  strontia,  and  magnesia.  A 
mixture  of  alcohol  and  nitric  acid  is  without  action  upon  carbonate  of 
potassa,  but  it  acts  powerfully  on  the  carbonates  of  lime  and  strontia,  and 
slowly  on  the  carbonates  of  soda,  baryta,  and  magnesia.  Alcoholicsolutious 
of  acetic  and  tartaric  acid  decompose  none  of  the  carbonates :  a  similar 
solution  of  citric  acid  decomposes  the  carbonates  of  potassa  and  joagnesia, 
but  not  the  carbonate  of  baryta,  strontia,  or  lime ;  while  an  alcoholic 
solution  of  oxalic  acid  decomposes  carbonates  of  strontia,  lime,  and  mag- 
nesia, but  not  carbonate  of  potassa.  The  addition  of  a  small  quantity  of 
water  does  not  affect  these  mixtures,  for  when  a  saturated  solution  of 
carbonate  of  potassa  is  mixed  with  an  alcoholic  solution  of  acetic  acid,  the 
carbonate  is  precipitated  without  effervescence  (p.  54)  ;  an  alcoholic  solution, 
therefore,  may  appear  neutral  to  certain  tests,  whilst,  in  reality,  it  is  strongly 
acid. 

Alcohol  dissolves  a  small  quantity  of  sulphur,  especially  at  its  boiling 
temperature,  but  the  greater  portion  is  deposited,  on  cooling,  in  small 
brilliant  crystals.  It  also  dissolves  phosphorus,  taking  up  about  a  240th 
part  at  its  boiling-point,  and  retaining  a  320th  part  when  cold.  This 
solution  is  luminous  in  the  dark  on  exposure  to  air,  and  produces  a  beautiful 
pale  bluish  flame,  when  poured  upon  hot  water.  Alcohol  dissolves  sulphide 
of  carbon,  and  the  solution  is  decomposed  by  the  alkalies.  Alcohol  is  an 
important  agent  in  organic  analysis :  it  dissolves  benzole,  chloroform,  ether, 
the  resins,  and  a  large  number  of  the  alkaloids,  the  vegetable  acids,  camphor, 
and  all  the  essential  oils.  It  dissolves  some  of  the  fatty  acids,  but  not 
readily  the  fixed  oils,  excepting  castor  oil.  It  dissolves  grape  and  fruit- 
sugar,  but  does  not  readily  dissolve  cane-sugar,  and  has  no  solvent  action 
on  starch  and  gum.  It  deoxidizes  slowly  a  solution  of  permanganate  of 
potassa,  but  rapidly  when  the  mixture  is  heated,  or  some  hydrochloric  acid 
is  added.  It  has  no  reducing  action  on  the  salts  of  silver  or  gold,  or  on 
precipitated  oxide  of  copper  when  mixed  with  potassa.  It  readily  reduces 
chromic  acid  to  green  oxide  of  chromium,  when  set  free  from  a  chro.mate 
by  an  acid  (hydrochloric),  and  the  mixture  is  heated.  A  solution  of  a 
chromate,  rendered  alkaline  by  potassa,  is  not  reduced  when  heated  with 
alcohol.  As  this  alkaline  solution  is  readily  reduced  by  grape-sugar,  the 
presence  of  grape-sugar  in  an  alcoholic  liquid  may  be  determined  by  this,  as 
well  as  by  the  copper-test. 

Potassium  decomposes  rectified  spirit,  if  much  water  is  present,  with  the 
ordinary  phenomena  of  combustion.  With  strong  spirit  there  is  no  com- 
bustion; and  when  sodium  or  potassium  is  placed  on  anhydrous  alcohol, 
hydrogen  is  given  off,  and  the  metal  disappears  without  combustion.  A 
crystallizable  compound  is  obtained  from  the  liquid,  which  has  been  called 
sodium  or  potassium  alcohol,  or  ethylate  of  soda  or  potassa.  When 
potassium  or  sodium  is  heated  with  alcohol,  carburetted  hydrogen  is  evolved 
among  the  products. 

Potassa  and  soda  are  soluble  in  alcohol,  hence  this  liquid  is  sometimes 
resorted  to  for  the  purification  of  these  alkalies.  After  a  time,  however, 
they  begin  to  act  upon  each  other,  and  complicated  changes  ensue ;  a  car- 
bonate of  the  alkali  is  formed,  and  carbonaceous  matter  is  evolved  on  the 
application  of  heat;  by  their  slow  mutual  action,  acetic  acid,  a  resin,  and  a 
species  of  brown  extractive,  appear  to  be  formed.  Ammonia  and  its 
carbonates  are  soluble  at  common  temperatures  in  alcohol :  it  also  absorbs 
in  various  proportions  several  other  gases.     Lithia,  baryta,  strontia,  and 


588  COMPOSITION    OP    ALCOHOL.      TESTS. 

lime,  are  almost  insoluble  in  alcohol,  even  in  their  hydrated  states ;  so  als® 
are  the  fixed  alkaline  carbonates  :  but  their  sulphides  are  dissolved.  The 
greater  number  of  the  chlorides,  iodides,  and  bromides,  which  are  soluble  in 
water,  are  soluble  also  in  alcohol,  and  with  many  of  them,  the  definite 
alcoholized  compounds  above  mentioned  are  produced  :  but  the  sulphates 
are  almost  all  insoluble  ;  hence  the  use  often  made  in  the  analysis  of  mixtures 
of  salts,  of  the  separative  power  of  alcohol. 

The  uses  of  alcohol  in  the  arts,  and  its  applications  to  various  economical 
purposes,,  are  extremely  numerous  :  to  the  chemist  it  is  a  most  valuable 
species  of  fuel.  Alcohol  coagulates  albumen  and  corrugates  fibrin.  It 
removes  water  from  organic  matter,  and  is  employed  as  an  antiseptic. 

Composition. — When  alcohol-vapor  and  oxygen  are  mixed  in  certain 
proportions,  and  the  mixture  is  fired  by  an  electric  spark,  a  violent  explosion 
ensues,  and  carbonic  acid  and  water  are  the  results  :  2  volumes  of  alcohol- 
vapor,  or  1  equivalent,  require  6  volumes  of  oxygen,  or  12  equivalents,  for 
their  perfect  combustion  ;  and  4  volumes  of  carbonic  acid  and  6  volumes 
of  aqueous  vapor  result  {Q^B.fi^-\-\^0=iQ0^  +  ^110). 

The  analysis  of  absolute  alcohol  by  oxide  of  copper  gives  results  in  ac- 
cordance with  these  experiments.  The  following  is  the  composition  of  this 
liquid : — 


Atoms. 

Equiv. 

Per  cent. 

Dumas. 

Vol. 

Carbon  . 

.     4       .. 

..       24       .. 

,.       52-65        .. 

,.      52-17      . 

..      4 

Hydrogen 

.     6       .. 

6       .. 

.        12-90       .. 

.       13-31       . 

..       6 

Oxygen 

.     2       .. 

.      16      .. 

.       34-45       .. 

.       34-52       . 

..       1 

Anhydrous  alcohol     1  46  100-00  100-00  2 

For  the  calculated  vapor-density  of  alcohol,  see  p.  556. 

The  equivalent  46,  which  is  here  assigned  to  alcohol,  is  generally  adopted 
by  chemical  authorities.  Some  have  proposed  to  double  it,  and  others  to 
quadruple  it,  upon  hypothetical  considerations ;  but  no  sufficient  reasons 
have  been  advanced  for  these  changes. 

Tests. — The  chief  adulterating  ingredient  is  water,  the  amount  of  which 
may  be  determined  by  distilling  the  liquid  and  taking  the  sp.  gr.  of  the  dis- 
tillatjB.  Alcohol  is  entirely  volatile,  and  any  residue  will  indicate  the  amount 
of  impurity.  The  odor  and  taste  of  the  liquid  will  enable  a  chemist  to  de- 
termine whether  any  essential  oil,  resin,  or  methylated  spirit,  is  mixed  with 
it.  It  burns  with  a  pale  blue  flame,  and  should  deposit  no  smoke  upon  cold 
surfaces  brought  in  contact  with  it.  Absolute  alcohol  should  not  give  a 
blue  color  to  the  white  anhydrous  sulphate  of  copper,  and  should  yield  no 
precipitate  of  silicic  acid  when  a  current  of  fluosilicic  acid  gas  is  passed 
into  it  {see  p-.  305).  In  cases  of  suspected  poisoning,  the  liquid  should  be 
distilled  by  a  water-bath,  and  the  product  rectified  with  fresh  lime  or  car- 
bonate of  potassa.  The  alcohol,  if  present,  may  be  drawn  off  by  a  few  fibres 
of  asbestos  and  burnt.  If  in  sufficient  quantity,  it  will  be  detected  by  its 
odor,  and  by  its  solvent  power  on  camphor.  If  in  very  small  quantity,  the 
heated  vapor  should  be  conducted  through  a  tube  containing  a  few  fibres  of 
asbestos  moistened  with  a  mixture  of  bichromate  of  potassa  and  strong 
sulphuric  acid.  If  only  a  trace  of  alcohol  is  present,  green  oxide  of  chro- 
mium will  be  precipitated  on  the  asbestos.  Ether  and  pyroxylic  spirit 
produce  a  similar  decomposition ;  but  these  liquids  are  detected  by  their 
peculiar  odors. 

Other  alcohols  are  enumeratd:  the  Propylic  (0^fi,liO)\  the  Butylic 
(C,HaO,HO) ;  the  Caproic  CC^aHj^Oa),  and  the  Caprylic  {Q^.ILJd^).  These 
are  occasional  products  of  the  vinous  fermentation,  but  are  more  abundantly 
produced  in  the  fermentation  of  the  marc  or  residue  of  the  grape.     Like 


ALDEHYDE.  589 

araylic  alcohol,  these  alcohols,  which  are  colorless  volatile  liquids,  do  not 
readily  combine  with  water,  in  which,  among  other  properties,  they  differ 
remarkably  from  ordinary  or  ethylic  alcohol.  They  form  an  homologous 
series  of  compounds :  each  contains  two  equivalents  of  oxygen  ;  and  the 
equivalents  of  hydrogen  always  exceed  by  two,  the  equivalents  of  carbon. 

Aldehyde  (C^H^Og). 

This  compound,  which  is  also  called  Acetic  Aldehyde,  derives  its  name 
from  the  words  alcohol  dehydrogenatus,  inasmuch  as  alcohol  becomes  alde- 
hyde by  the  loss  of  2  atoms  of  hydrogen.  Aldehyde  is  one  of  the  products 
of  the  decomposition  of  alcohol  or  ether,  in  passing  the  respective  vapors 
througha  red-hot  tube,  or  in  burning  mixtures  of  ether  or  alcoholic-vapor 
and  ox/^n,  at  a  comparatively  low  temperature  without  flame. 

C^HgOa        +        02=        C^H.O^        +        2H0 


Alcohol.  Aldehyde. 

It  is  best  obtained  in  its  pure  state  by  the  following  process  (Ltebig, 
A7171.  Ch.  et  Ph.,  lix.  289)  :  a  mixture  of  4  parts  of  alcohol  (sp.  gr.  0*844), 
6  of  oil  of  vitriol,  4  of  water,  and  6  of  pulverized  binoxide  of  manganese,  is 
introduced  into  a  capacious  retort,  and  distilled  through  a  condenser  into  a 
large  receiver  cooled  by  ice.  When  about  6  parts  have  passed  over,  or 
when  the  distillate  has  become  acid,  the  process  is  stopped,  and  the  product 
is  put  into  a  small  retort  with  its  own  weight  of  chloride  of  calcium,  and  re- 
distilled ;  this  process  is  repeated,  so  as  to  yield  about  3  parts  of  dehydrated 
aldehyde.  The  distillate,  however,  still  contains  acetal,  ether,  and  alcohol ; 
to  free  it  from  these,  it  is  mixed  with  about  twice  its  volume  of  ether,  and 
saturated  with  dry  gaseous  ammonia,  when  a  crystalline  compound  of 
aldehyde  and  ammonia  gradually  separates,  which  is  insoluble  in  ether,  and 
which  may  be  dried  in  the  air.  Two  parts  of  this  compound  are  then  dis- 
solved in  their  weight  of  water,  and  the  solution  mixed  with  3  parts  of  sul- 
phuric acid  previously  diluted  with  4  of  water,  and  distilled.  Considerable 
effervescence  ensues  during  the  evolution  of  the  aldehyde,  which  requires  to 
be  passed  through  a  good  condensing  apparatus ;  the  distillate  is  fiualiy  de- 
hydrated by  the  careful  addition  of  a  little  chloride  of  calcium,  and  distilled 
at  a  temperature  of  about  87°. 

Pure  aldehyde  is  a  volatile  colorless  liquid,  of  a  peculiar  ethereal,  and  at 
the  same  time  suffocating  odor :  when  its  concentrated  vapor  is  respired,  it 
produces  spasm  of  the  glottis.  Its  sp.  gr.  is  0*79  at  65°  :  its  boiling  point 
is  68°,  and  the  density  of  its  vapor  is  1-53.  It  mixes  in  all  proportions  with 
water,  alcohol,  and  ether,  and  may  be  separated  from  its  aqueous  solution  by 
means  of  chloride  of  calcium.  It  is  neutral  to  test-paper,  but  acquires 
acidity  on  exposure  to  air,  in  consequence  of  the  absorption  of  oxygen  and 
the  formation  of  acetic  acid,  a  change  which  is  very  rapid  under  the  influence 
of  platinum-black  {C^^fi^-\-0^=G^B.p^,B.O).  Heated  with  dilute  nitric 
acid,  it  is  also  acetified,  and  nitrous  acid  is  formed.  With  another  atom  of 
oxygen,  it  forms  aldehydic  acid  (C^H^Og).  An  aqueous  solution  of  aldehyde 
heated  with  oxide,  or  a  salt  of  silver,  reduces  the  metal  in  the  form  of  a  bril- 
liant film,  and  aldehydate  of  silver  is  found  in  solution  {2AgO-\-C^fifi= 
AgOjC^HPg+Ag).  This  result  and  the  odor  are  the  best  tests  of  its  pre- 
sence. Aldehyde  is  found  in  the  distillation  of  wines  dissolved  in  the  alcohol. 
When  its  vapor  is  passed  over  a  heated  mixture  of  hydrate  of  potassa  and 
quicklime,  acetate  of  potassa  is  formed,  and  hydrogen  gas  disengaged.  The 
term  aldehyde  is  now  applied  to  analogous  compounds  obtained  from  the 
imperfect  combustion  of  other  alcohols.     They  are  named  after  the  acids 


590  CHLORAL.      CHLOROFORM. 

which  they  produce,  as  the  result  of  the  absorption  of  2  atoms  of  oxygen ; 
hence  the  compound  above  described  is  sometimes  called  acetic  adelhyde. 

Chloral  (C^ClgHOJ 

Is  a  transparent,  colorless,  oily  liquid,  obtained  by  the  reaction  of  dry 
chlorine  on  anhydrous  alcohol  and  by  subsequent  distillation.  Its  sp.  gr.  is 
1-5;  its  boiling  point  206°,  and  the  density  of  its  vapor  is  5.  It  has  an 
irritating  odor,  is  soluble  in  water,  and  its  solution  is  not  affected  by  nitrate 
of  silver.  It  is  sometimes  called  chloric  ether,  a  name  which  is  also  applied 
to  hydrochloric  ether,  chloride  of  hydrocarbon,  and  to  a  solution  of  chloro- 
form in  alcohol. 

Chloroform  (C2HCI3).  ^ 

Chloroform  may  be  procured  by  distilling  chloral  with  lime  and  water,  or 
with  solution  of  potassa.  It  is  more  readily  obtained  by  distilling  in  a  capa- 
cious retort,  a  mixture  of  1  part  of  alcohol  with  24  parts  of  water  and  6 
parts  of  dry  chloride  of  lime.  The  temperature  should  not  exceed  180°. 
The  distillate  consists  of  water  and  chloroform,  and  the  process  is  arrested 
when  about  two  parts  have  passed  over.  The  chloroform  is  in  the  lowest 
stratum.  It  is  separated  from  the  water,  shaken  with  sulphuric  acid  to  purify 
it,  and  rectified  by  a  second  distillation.  In  addition  to  chloroform,  the  pro- 
ducts of  this  reaction  are  formate  of  lime,  chloride  of  calcium,  and  water. 
The  process  recommended  in  the  British  Pharmacopoeia  is  as  follows : 
Chloride  of  lime  10  pounds,  rectified  spirit  30  fluidounces,  water  3  gallons, 
slaked  lime  a  sufficiency.  The  water  and  spirit  are  mixed  and  brought  to  a 
temperature  of  100°  in  a  large  retort.  The  chloride  of  lime  mixed  with  five 
pounds  of  the  slaked  lime  is  then  added.  A  heat  sufficient  to  cause  distilla- 
tion is  applied,  the  product  being  condensed  in  the  usual  way.  So  soon  as 
distillation  is  well  established,  the  heat  is  withdrawn  and  the  process  is 
stopped,  when  the  product  in  the  receiver  amounts  to  50  ounces.  This  is 
well  washed  in  successive  quantities  of  water,  agitated  with  an  equal  volume 
of  sulphuric  acid,  and  afterwards  by  a  water-bath  distilled  off  2  ounces  of 
chloride  of  calcium  mixed  with  half  an  ounce  of  slaked  linie,  which  should  be 
perfectly  dry.  The  product,  which  is  pure  chloroform,  should  be  preserved 
in  a  cool  place  in  a  well-stopped  bottle.  Wood-spirit  may  be  employed 
instead  of  alcohol,  but  the  product  is  not  so  pure. 

Properties. — Chloroform  is  a  colorless,  transparent,  heavy,  neutral  liquid, 
having,  when  its  vapor  is  diluted,  a  pleasant  odor  resembling  that  of  apples. 
It  has  a  sweet  taste,  slightly  pungent.  Its  sp.  gr. ,  when  pure,  is  1  -5  :  it 
boils  at  140°,  and  the  density  of  its  vapor  is  4  2.  It  is  not  readily  inflam- 
mable, but  it  may  be  burnt  on  bibulous  paper,  producing  a  greenish  colored 
smoky  flame.  When  its  vapor  is  respired,  more  or  less  diluted  with  air,  it 
soon  induces  insensibility,  in  the  same  way  as,  but  more  rapidly  and  effec- 
tually than  ether-vapor ;  hence  its  use  in  the  performance  of  surgical  opera- 
tions and  in  obstetric  practice  as  originally  suggested  by  Dr.  Simpson,  of 
Edinburgh.  {Pharm.  Journ.,  vii.  277  and  313.)  When  a  few  drops  of 
chloroform  are  placed  upon  the  hand,  it  speedily  evaporates,  and  produces  a 
great  degree  of  cold.  If  pure,  it  leaves  no  residue  and  no  unpleasant  odor. 
When  poured  upon  water,  the  greater  part  of  the  liquid  sinks  in  globules, 
which  are  of  a  milk-white  appearance  if  the  chloroform  is  not  perfectly  free 
from  alcohol.  Chloroform  is  so  little  soluble  in  water,  that  three  drops 
added  to  nine  ounces  of  distilled  water,  and  well  shaken,  did  not  wholly  dis- 
appear, although  they  imparted  a  strong  odor  to  the  liquid.  With  alcohol 
and  ether  it  readily  forms  transparent  solutions,  which  burn  with  a  yellow 
smoky  flame.     Water  added  to  the  alcoholic  solution  causes  a  separation  of 


CHLOROFORM.  591 

the  chloroform,  which  falls  to  the  bottom  of  the  vessel.  If  to  the  alcoholic 
solution  potash  is  added,  and  the  mixture  boiled,  the  chloroform  is  resolved 
into  chloride  of  potassium  and  formate  of  potash. 

Chloroform  readily  combines  with  oil  of  turpentine,  and  with  sulphide  of 
carbon.  It  easily  dissolves  camphor,  and  the  solution  burns  with  a  yellow 
smoky  flame,  having  a  green  edge  or  border.  It  speedily  softens  and  dis- 
solves caoutchouc.  It  dissolves  wax,  cantharidine,  amber,  copal,  and  all  the 
common  resins.  With  red  or  black  sealing-wax  it  makes  a  strong  varnish. 
It  has  but  a  slight  solvent  action  on  sulphur  and  phosphorus.  It  dissolves 
iodine  and  bromine,  forming  deep  red  solutions.  A  few  drops  of  chloroform 
shaken  with  an  aqueous  solution  of  iodine  or  bromine  will  remove  either  of 
these  bodies,  and  the  chloroform  falls  to  the  bottom  of  the  vessel,  acquiring 
a  red  color,  the  depth  of  which  is  proportioned  to  the  quantity  of  either  sub- 
stance present.  Chloroform  is  usefully  employed  either  alone  or  in  combi- 
nation with  ether,  as  a  solvent  for  many  alkaloids.  100  parts  of  chloroform 
dissolve  of  veratria,  58*49  parts:  quina,  57'47:  brucia,  56"70:  atropia,  51*19: 
narcotina,  31-17  :  strychnia,  2019  :  cinchonia,  4*31,  and  of  morphia,  0-57. 

Chloroform  floats  on  concentrated  sulphuric  acid,  which  is  only  darkened 
by  it  at  a  boiling  temperature,  when  the  chloroform  is  rapidly  dissipated  in 
vapor.  It  slowly  decomposes  nitric  acid  in  the  cold,  but  at  a  high  tempera- 
ture deoxidation  is  rapid,  and  nitrous  acid  is  abundantly  evolved.  It  scarcely 
afi'ects  a  solution  of  iodic  acid,  which  acquires,  after  a  time,  only  a  faint  pink 
color.  It  has  no  bleaching  properties :  it  does  not  decompose  iodide  of 
potassium,  nor  does  it  dissolve  gold,  either  by  itself  or  when  boiled  with 
concentrated  nitric  acid.  When  nitrate  of  silver  is  added  to  it,  there  is  no 
precipitate,  the  chloroform  merely  acquiring  that  milky  opacity  which  it  has 
when  dropped  into  distilled  water.  The  chlorine  is  therefore  not  in  the  same 
state  of  combination  as  in  the  soluble  chlorides  of  mineral  compounds. 
Chloroform  has  no  action  on  a  salt  of  copper  until  a  solution  of  potash  is 
added  in  excess  and  the  liquid  is  boiled.  The  copper  is  then  reduced  to  the 
state  of  suboxide,  as  if  glucose  was  present.  There  is,  however,  this  marked 
difference :  in  the  presence  of  chloroform  potash  does  not  redissolve  the  pre- 
cipitated oxide  of  copper,  so  as  to  form  the  clear  blue  solution  which  is  pro- 
duced when  grape-sugar  is  present. 

The  alkaline  metals  potassium  and  sodium  have  no  action  upon  pure 
chloroform.  It  may  be  distilled  over  them  without  undergoing  any  change. 
If,  however,  to  a  mixture  of  chloroform  and  sodium  a  small  quantity  of 
water  is  added,  the  nascent  hydrogen  produced  brings  about  a  chemical 
change.  The  temperature  rises,  the  sodium  burns,  and,  after  a  short  time, 
with  explosive  violence,  a  large  amount  of  carbon  being  set  free.  The 
liquid,  which  is  blackened  by  the  amorphous  carbon,  is  strongly  alkaline 
from  the  presence  of  soda,  and  is  copiously  precipitated  by  nitrate  of  silver, 
showing  the  production  of  a  soluble  chloride  of  the  metal — the  oxide  being 
readily  separated  from  it  by  nitric  acid.  Two  of  the  constituents  of  chloro- 
form— chlorine  and  carbon — are  thus  proved  to  be  present  in  this  liquid. 

Chloroform  is  occasionally  observed  to  undergo  spontaneous  changes — 
chlorine  and  hydrochloric  acid  being  set  free.  It  appears  that  a  free  ex- 
posure to  light  favors  this  decomposition.  It  also  takes  place  more  readily 
when  a  little  moisture  is  present  than  when  it  is  quite  free  from  water. 
Alcohol  added  to  it  in  small  quantity  tends,  on  the  other  hand,  to  preserve  it. 

When  the  vapor  of  chloroform  is  passed  over  copper  or  iron,  heated  to 
redness,  it  is  decomposed,  a  metallic  chloride  results,  and  carbon  is  deposited ; 
but,  according  to  Liebig,  no  inflammable  gas  is  evolved.  When  the  vapor 
of  chloroform  is  passed  through  a  glass  tube  heated  to  full  redness,  it  is  re- 


593  PYROXYLIC    SPIRIT    OR    METHYLIC    ALCOHOL 

solved  into  chlorine  and  hydrochloric  acid,  but  no  carbon  is  deposited.     On 
this  is  founded  a  process  for  its  detection  in  the  blood  and  other  liquids. 

Chloroform  is  represented  by  the  formula  CgHClg,  and  is  considered  to  be 
a  terchloride  of  the  compound  radical  formyle  (C^H).  When  the  3  atoms 
of  chlorine  are  replaced  by  3  of  oxygen,  formic  acid  is  produced :  hence  the 
name  chloroform.  The  liquid  contains  89  per  cent,  of  chlorine,  but,  unlike 
an  ordinary  chloride,  it  gives  not  the  slightest  indication  of  the  presence  of 
this  element  by  the  usual  test. 

Methylic  Alcohol  (C^Hfi^). 

This  compound  has  been  long  known  under  the  name  of  Wood-spirit, 
Wood-naphtha,  or  Pyroxylic  spirit.  It  derives  its  present  name  from  vidv, 
wine,  and  v-kti,  wood. 

It  is  not  a  product  of  fermentation,  but  it  is  produced  in  the  destructive 
distillation  of  wood.  In  this  process  there  is  formed,  besides  tar,  acetic 
acid,  and  other  products,  a  variable  portion,  but  not  amounting  on  an 
average  to  more  than  about  1  per  cent,  of  an  inflammable  and  volatile 
liquid.  This  may  be  separated,  to  a  certain  extent,  from  the  water  and 
acetic  acid,  by  distillation  and  separation  of  the  first  products ;  these,  redis- 
tilled and  rectified  over  quicklime,  afford  the  pyroxylic  spirit,  or  methylic 
alcohol  of  commerce.  If  it  contain  ammonia,  it  should  be  neutralized,  by 
sulphuric  acid,  previous  to  its  last  rectification. 

To  obtain  perfectly  pure  pyroxylic  spirit,  an  excess  of  chloride  of  calcium 
is  added,  and  the  mixture  is  distilled  in  a  water-bath  so  long  as  any  volatile 
matter  goes  over.  A  compound  of  wood-spirit  with  chloride  of  calcium  re- 
mains in  the  retort,  to  which  a  quantity  of  water,  equal  to  that  of  the  original 
spirit,  is  added,  and  the  distillation  is  then  continued.  The  product  which 
is  now  obtained,  and  which  is  pure  pyroxylic  spirit  diluted  with  a  little 
water,  may  be  dehydrated  by  a  final  distillation  off  quicklime,  or  anhydrous 
sulphate  of  copper. 

Properties. — Pyroxylic  spirit  is  the  alcohol  of  the  methylic  series.  When 
pure  it  is  a  limpid  colorless  liquid,  of  a  penetrating  odor,  partaking  of  that 
of  alcohol  and  acetic  ether,  with  an  aromatic  taint  which  has  been  compared 
to  peppermint.  Its  taste  is  hot  and  pungent.  Its  sp.  gr.  at  60^  is  0*838. 
It  is  highly  inflammable,  and  burns  with  a  pale  flame  resembling  that  of 
alcohol.  Its  vapor  will  take  fire  at  some  distance  from  the  liquid,  and  the 
flame  spreads  with  great  rapidity.  It  boils  at  about  150° ;  if  heated  in  a 
retort,  even  in  a  water-bath,  the  sudden  escape  of  its  vapor  is  troublesome  : 
this  may  be  prevented  by  the  presence  of  a  little  mercury,  which  equalizes 
the  distribution  of  heat.  The  density  of  its  vapor  is  1'125  (1*20  at  212°). 
When  pure  it  is  not  altered  by  exposure  to  air  or  light,  but  when  subjected 
to  the  slow  action  of  platinum-black,  it  yields,  together  with  other  products, 
formic  acid  ;  not  acetic  acid,  as  is  the  case  with  alcohol.  If  pure  it  is  quite 
neutral,  and  mixes  in  all  proportions  with  water,  alcohol,  and  ether,  without 
becoming  turbid  ;  it  does  not  form  a  black  precipitate  with  protonitrate  of 
mercury.  Like  alcohol,  it  is  a  powerful  solvent  for  resins,  and  is  now  much 
used  in  the  form  of  methylated  spirit.  The  odor  of  its  vapor  is  disagreeable, 
and*when  breathed  it  produces  nausea  and  headache.  It  rapidly  deoxidizes 
a- solution  of  permanganate  of  potash  and  of  chromic  acid,  producing  in  the 
latter  case  green  oxide  of  chromium.  When  potassium  or  sodium  is  placed 
on  it,  it  undergoes  decomposition,  hydrogen  is  evolved  without  combustion, 
and  the  liquid  is  rendered  alkaline.  When  methylic  alcohol  is  mixed  and 
distilled  with  four  parts  by  weight  of  sulphuric  acid,  decomposition  takes 
place,  and  methylic  ether,  water,  and  carbonic  and-  sulphurous  acid  are 
among  the  products.     It  is  strikingly  distinguished  from  ethylic  alcohol  by 


METHYLATED    SPIRIT.      AMYLIC    ALCOHOL.  593 

the  fact  that  a  compound  homologous  to  olefiant  gas  has  not  been  produced 
by  the  action  of  sulphuric  acid  upon  it. 

Chlorine  acts  less  powerfully  on  pyroxylic  spirit  than  on  alcohol,  and  accord- 
ing to  Dumas  and  Peligot,  heat  is  required  to  accelerate  their  mutual  action  : 
it  then  gives  rise  to  the  production  of  two  liquids  of  very  different  degrees 
of  volatility ;  that  which  is  least  volatile  forms  a  crystallizable  compound 
with  ammonia.  According  to  Kane,  the  action  of  chlorine  on  this  spirit, 
under  the  influence  of  light,  is  violent,  and  even  attended  by  inflammation  ; 
in  the  absence  of  light,  the  gas  is  quietly  absorbed  under  the  abundant  pro- 
duction of  hydrochloric  acid,  and  a  thick  liquid  is  formed,  composed  of 
CflHgOgCla.  Chloride  of  lime  acts  upon  pyroxylic  spirit  as  it  does  upon 
alcohol,  and  methylic  chloroform  is  one  of  the  products.  Its  solvent  powers, 
in  regard  to  salts  closely  resemble  those  of  alcohol,  and  it  has  been  stated 
that  it  may  be  substituted  for  alcohol  in  the  preparation  of  fulminating 
silver,  although  the  action  is  less  violent,  and  the  product  smaller  in  quantity; 
but  according  to  Dumas  and  Peligot,  the  product  is  really  oxalate,  and  not 
fulminate  of  silver  ;  so  also  it  converts  nitrate  into  oxalate  of  mercury.  Sul- 
phur and  phosphorus  are  to  a  small  extent  soluble  in  it.  It  dissolves  the 
resins,  and  may  be  used  as  an  excellent  substitute  for  alcohol  in  almost  all 
varnishes ;  indeed,  its  superior  volatility  renders  it  preferable  ;  but  its  offen- 
sive odor  is  objectionable.  It  is  a  powerful  antiseptic,  and  has  been  found 
an  effectual  preservative  of  animal  matter.  Pyroxylic  spirit  has  the  formula 
of  C,H,Oa,  or  as  hydrated  oxide  of  raethyle  of  C,H30,H0,  or  MeO,HO. 

Methylated  Spirit. — A  mixture  of  90  per  cent,  of  alcohol  and  10  per  cent, 
of  methylic  alcohol,  is  much  used  in  the  arts  and  manufactures,  as  well  as  in 
medicine  and  chemistry,  as  a  substitute  for  rectified  spirit. 

Methyle  Me(C2H3)  is  a  gaseous  body  of  a  sp.  gr.  of  r036.  It  is  produced 
by  decomposing  iodide  of  methyl  with  zinc.  It  forms  an  oxide  analogous 
to  ether  in  composition. — Methylic  ether,  CgHgO.  This  oxide  is  a  colorless 
gas  of  an  ethereal  odor,  and  has  a  sp.  gr.  of  1'59.  It  burns  with  a  pale  blue 
flame.  In  elementary  composition  it  is  isomeric  with  alcohol,  for  2(C3H30) 
are  equal  to  C^HgOg.  Methylic  ether  is  procured  by  distilling  1  part  of 
wood-spirit  with  4  parts  of  sulphuric  acid.  The  gas  may  be  collected  over 
mercury,  and  the  carbonic  and  sulphurous  acids  mixed  with  it,  may  be 
removed  by  potassa.  Methyle  forms  a  chloride,  iodide,  and  bromide,  as  well 
as  various  other  compounds,  with  the  oxacids,  analogous  to  those  of  ethyle. 

Pyroxanthine  (CgiHgO^)  is  a  yellow  crystalline  solid,  which  was  dis^ 
covered  by  the  late  Mr.  Scanlan,  as  a  product  of  the  reaction  of  potassa  on 
wood-spirit.  It  is  insoluble  in  water,  but  is  dissolved  by  boiling  alcohoh 
The  crystals  melt  at  291°.  Its  most  remarkable  property  is  that  of  forming 
a  rich  purple  compound  with  strong  sulphuric  acid,  which  slowly  becomes 
blue  and  black. 

Amylic  Alcohol  {O^^^fiy) 

Amylic  Alcohol,  or  Hydrated  Oxide  of  Amyle  (C,oHjj,04-HO  ;  or  AylO) 
has  long  been  known  under  the  name  of  oil  of  potato-spirit;  it  is  i\\Q fusel- 
oil  of  the  Germans.  It  is  now  considered  to  be  the  alcohol  of  the  amylic 
series,  the  base  of  which  is  amyle  (C,oH,i).  It  has  hitherto  been  exclusively 
obtained  as  a  product  of  fermentation,  especially  from  potato-brandy. 
Balard  {Erdmann  and  Marchand^s  Journ.,  xxxiv.  123)  found  it,  accompa- 
nying cenanthic  ether,  in  the  volatile  oil  obtained  from  brandy ;  it  has  also 
been  detected  in  the  spirit  afforded  by  the  fermentation  of  beet-root  treacle. 
It>  is  abundantly  obtained  from  corn-spirit,  in  the  process  of  its  rectification 
upon  the  large  scale  (Medlock,  Journ.  Chem.  Soc,  i.  368).  It  is  chiefly 
produced  during  fermentation  iu  neutral  or  alkaline  liquids,  not  in  acid. 
3» 


594  •  AMTLE.      AMYLENE. 

liquids :  it  is  formed  by  the  decomposition  of  the  starch — hence  its  name, 
amyJic  alcohol.  In  wines  containing  tartaric  and  citric  acids,  or  acid  salts, 
it  is  not  readily  formed.  The  presence  of  hops  also  prevents  its  production, 
since  it  is  not  found  in  ale  or  beer.  The  high  temperature  at  which  it  boils 
renders  it  easy  to  separate  other  volatile  liquids  from  it. 

When  potato-brandy  is  distilled,  and  after  the  greater  part  of  the  alcohol 
has  passed  over,  a  milky  liquid  is  obtained,  which  deposits  the  crude  potato- 
oil.  It  is  similarly  obtained  among  the  less  volatile  products  of  the  distilla- 
tion of  corn-spirit  of  all  kinds.  This  crude  oil  is  purified  by  washing  it 
with  water,  then  drying  it  by  means  of  chloride  of  calcium,  and  redistilling  it; 
the  portion  which  passes  over  at  about  268°  or  270°,  is  pure  amylic  alcohol 

It  is  a  colorless  liquid  of  a  peculiar,  nauseous,  suffocating,  and  most  per- 
sistent odor.  It  has  an  acrid,  hot  taste ;  it  burns  with  a  blue  flame,  but  is 
not  very  easily  inflammable,  differing  strikingly  from  ethylic  alcohol  in  this 
respect.  Its  sp.  gr.  is  OSIS  at  70°;  it  boils  at  270°;  the  density  of  its 
vapor  is  3-14.  At  4°  it  forms  a  crystalline  solid.  It  is  sparingly  soluble 
in  water,  floating  upon  it  like  an  oil,  but  dissolving  in  all  proportions  in 
alcohol,  ether,  and  in  fixed  and  volatile  oils.  It  dissolves  iodine,  sulphur, 
and  phosphorus.  It  is  a  good  solvent  of  the  alkaloid  morphia,  and  deposits 
it  from  a  hot  solution  in  well-defined  prismatic  crystals.  It  separates  mor- 
phia, when  uncombined,  from  an  aqueous  solution.  When  acted  upon  by 
oxidizing  agents  it  yields  Valeric  or  Valerianic  acid.  According  to  Ca- 
hours,  it  is  resolved  when  exposed  to  air,  under  the  influence  of  platinum- 
black,  into  this  acid  and  water.  Its  formula  is  Q^^H^Jd^,  or  CjoHj^O-f  HO. 
When  amylic  alcohol  is  heated  with  sulphuric  acid,  it  does  not  yield  an 
ether  like  ethylic  alcohol.  If  it  is  decomposed,  the  mixture  blackens,  and 
sulphurous  and  carbonic  acids  are  evolved.  When  treated  with  a  larger 
proportion  of  sulphuric  acid  it  does  not  produce  a  gas  homologous  with 
defiant  gas.  It  also  differs  from  ethylic  alcohol  in  its  action  on  the  ray  of 
polarized  light.  It  exerts  a  rotatory  power  to  the  left,  while  alcohol  does 
not  alter  the  position  of  the  ray.  It  very  rapidly  discharges  the  color  of 
permanganate  of  potash  by  deoxidizing  the  permanganic  acid.  When  so- 
dium or  potassium  is  placed  upon  it,  hydrogen  is  evolved  without  combus- 
tion, and  the  liquid  which  becomes  alkaline,  is  speedily  darkened  on  ex- 
posure to  air. 

Amyle,  Ayl  (CjoH,,),  has  been  isolated  by  Frankland  {Journ.  Chem.  Soc, 
iii.  30).  He  obtained  it  by  the  action  of  zinc-amalgam  upon  iodide  of 
amyle,  under  pressure.  Amyle  is  a  colorless  pellucid  liquid  of  an  ethereal 
odor  and  burning  taste;  cooled  down  to  18°  it  becomes  thick  and  oily,  but 
does  not  solidify:  its  sp.  gr.  at  52°  is  0-7704:  the  density  of  its  vapor  is 
4-9062  (=  5  vols,  carbon  vapor,  4-1461 ;  +  11  vols,  hydrogen,  0-7601).  It 
boils  at  310°.  It  does  not  ignite  at  ordinary  temperatures,  but  on  being 
heated  its  vapor  burns  with  a  white  smoky  flame.  It  is  insoluble  in  water, 
but  mixes  in  all  proportions  with  alcohol  and  ether.  It  is  not  affected  by 
fuming  sulphuric  acid,  but  is  slowly  oxidized  by  fuming  nitric  acid,  or  by  a 
mixture  of  nitric  and  sulphuric  acids,  when  it  acquires  the  odor  of  Valerianic 
acid.     Amyle  forms  a  hydride  (C,oHjjH). 

Amylene  (CjoHjo). — When  amylic  alcohol  is  distilled  with  anhydrous 
phosphoric  acid,  amylene  passes  over  as  a  colorless  oily  liquid.  It  is  lighter 
than  water;  its  boiling-point  is  about  102°.  It  is  a  hydrocarbon,  isomeric 
with  olefiant  gas  and  etherine ;  but  the  density  of  its  vapor  is  5*5,  which  is 
5  times  that  of  olefiant  gas  ;  each  volume  of  it  therefore  contains  10  volumes 
of  hydrogen  in  combination  with  10  atoms  of  carbon.  Its  vapor  has  been 
used,  but  unsuccessfully,  as  a  substitute  for  chloroform  in  anaesthetic  surgery  ; 
it  has  caused  death  in  several  instances. 


ETHER.      ITS    PRODUCTION.  695 


CHAPTER    XLVIII. 

ETHER.     OIL   OF   WINE.     COMPOUND   AND   DOUBLE   lETHERS. 

Ether  (CJlfl).    Ethylic  or  Yinic  Ether. 

The  term  Ether  is  applied  to  a  highly  volatile  liquid  obtained  by  the 
action  of  sulphuric  acid  upon  alcohol  This  liquid  is  usually  procured  either 
by  distilling  a  mixture  of  sulphuric  acid  and  alcohol,  or  by  allowing  alcohol 
to  drop  gradually  into  the  heated,  and  somewhat  diluted  acid. 

Sulphuric  acid,  water,  and  alcohol,  at  a  certain  temperature,  are  necessary 
for  the  production  of  ether.  Concentrated  sulphuric  acid  mixed  with  diluted 
alcohol,  or  diluted  sulphuric  acid  mixed  with  absolute  alcohol,  will  equally 
produce  ether,  provided  certain  proportions  are  observed,  and  a  certain 
temperature  is  maintained.  The  following  process  has  been  found  to  yield 
satisfactory  results  :  A  mixture  of  8  parts  by  weight  of  concentrated  sul- 
phuric acid,  and  5  parts  of  rectified  spirit  of  wine  of  sp.  gr.  0'834,  is  intro- 
duced into  a  large  flask,  connected  with  a  proper  condensing  apparatus  and 
receiver,  and  the  mixture  is  heated  by  means  of  a  lamp  until  it  attains  a 
temperature  of  300°.  The  rectified  spirit  is  then  allowed  to  drop  into  the 
heated  mixture  through  a  long  funnel,  and  by  adjusting  its  quantity  on  the 
one  hand,  and  regulating  the  degree  of  heat  on  the  other,  the  temperature 
of  300°  is  maintained  as  steadily  as  possible,  taking  care  at  the  same  time 
that  the  liquid  in  the  flask  is  kept  in  rapid  ebullition.  Under  these  circum- 
stances the  bulk  of  this  liquid  may  be  maintained  unchanged  for  several 
hours,  and  every  drop  of  alcohol  which  falls  into  it  is  instantly  converted 
into  ether  and  water,  the  mixed  vapors  of  which  pass  through  a  tifce  into  a 
condenser.  The  receiver  is  ultimately  filled  with  water  and  ether,  the  latter 
floating  upon  the  former. 

The  principal  point  to  be  attended  to  in  this  process,  is  the  maintenance 
of  a  steady  temperature  at  or  about  300°,  and  of  rapid  or  even  violent  ebul- 
lition. The  limits  of  the  ether-producing  temperature  are  between  260° 
and  310°,  and  the  success  of  the  operation  is  well  insured  by  the  use  of  oil 
of  vitriol  and  spirit  of  wine,  in  the  above  proportions  and  of  the  described 
strength.  If  more  alcohol,  or  a  weaker  acid  be  used,  so  as  to  occasion  the 
boiling-point  to  fall  below  260°,  little  else  than  unchanged  alcohol  distils 
over  ;  and  if,  by  the  employment  of  too  much  oil  of  vitriol,  the  boiling-point 
rises  up  to  or  above  320°,  in  place  of  ether,  oil  of  wine  and  olefiaut  gas  are 
generated,  together  with  variable  quantities  of  other  products. 

The  proportions  recommended  by  Mitscherlich  are,  100  parts  of  concen- 
trated sulphuric  acid  (which  already  contains  18-5  of  water)  diluted  with 
20  parts  of  water,  and  mixed  with  anhydrous  alcohol,  in  the  proportion  of 
50  parts  to  every  100  of  concentrated  acid.  To  this  mixture  heat  is  ap- 
plied, and  it  is  kept  boiling  until  the  thermometer  within  the  flask  indicates 
284° :  two  strips  of  paper  are  then  pasted  upon  opposite  sides  of  the  flask 
containing  the  mixture,  to  indicate  exactly  the  bulk  of  its  contents,  by 
showing  the  level  of  the  liquid  within  it ;  alcohol  is  then  allowed  to  flovv  in 
by  a  funnel-tube,  the  supply  being  so  regulated  as  to  maintain  the  boiling- 
point  at  284°.  The  temperature  for  etherification,  according  to  Mitscher- 
lich, is  between  284°  and  302°      The  distillate  obtained   by  this  process, 


CM  RECTIFICATION 'OP    ETHER.      WASHED    ETHER. 

separates  into  two  parts,  the  lighter  stratnm  being  ether  with  a  little  alcohol 
and  water ;  and  the  heavier,  water  with  a  little  alcohol,  and  ether.  If  the 
process  has  been  carefully  conducted,  the  weights  of  the  water  and  ether 
exactly  correspond  to  that  of  the  alcohol  consumed.  In  an  experiment  on 
a  large  scale,  the  proportions  obtained  in  the  distillate  were  65  ether,  18 
alcohol,  and  17  water.  Careful  manufacturers  obtain  from  100  parts  of  rec- 
tified spirit,  containing  76  parts,  by  weight,  of  absolute  alcohol,  60  parts  of 
ether,  of  the  sp.  gr.  0  727  ;  according  to  calculation,  they  should  obtain 
58  parts  of  ether  of  0 '724. 

The  ether  of  commerce  almost  always  contains  alcohol,  which  materially 
affects  its  density ;  sometimes  it  also  contains  water,  which  is  the  case  with 
what  is  termed  washed  ether  ;  and  if  ether  has  been  long  prepared,  it  is  often 
slightly  acid,  and  leaves  a  peculiar  odor  when  rubbed  upon  the  hand.  In 
order  to  procure  from  the  distillate  perfectly  pure  ether,  it  must  be  well  shaken 
in  a  close  vessel  with  about  twice  its  bulk  of  water,  and  allowed  to  separate 
npon  the  surface  of  the  mixture  ;  it  is  then  poured  off,  and  a  suflScient  quan- 
tity of  well-burned  lime  added  to  it,  by  which  the  water  which  it  had 
acquired  by  the  agitation,  is  abstracted.  The  mixture  of  ether  and  lime  is 
then  distilled  by  a  water-bath,  care  being  taken  to  prevent  all  escape  of 
vapor,  and  to  keep  the  condensing-receivers  cold  :  the  first  third  that  distils 
over  may  be  considered  as  pure  ether,  free  from  alcohol  and  water.  Com- 
mercial ether  may  be  purified  by  agitating  it  with  milk  of  lime,  and  then 
distilling  it  from  a  water-bath  by  a  gentle  heat ;  the  first  distillate  is  then 
shaken  with  water  to  separate  alcohol,  and  the  resulting  aqueous  either  sub- 
sequently dehydrated  by  distilling  it  off  quicklime,  chloride  of  calcium,  or 
anhydrous  sulphate  of  copper. 

The  chemical  changes  which  take  place  in  the  production  of  ether  have 
been  variously  described.  The  alcohol  is  entirely  resolved  into  ether  and 
water  {GJifi^=Gfifi-{-HO),  but  sulphuric  acid  does  not  operate  by  sim- 
ply abstracting  the  elements  of  water,  since  ether  is  equally  produced  at  the 
proper  temperature  (284°  to  302*^)  by  the  reaction  of  diluted  sulphuric  acid 
on  absolute  alcohol.  One  theory  assumes  that  by  the  admixture  of  sulphuric 
acid  and  alcohol  in  certain  proportions,  Sulphovinic  acid  is  produced  ;  and 
that  at  a  certain  temperature,  this  acid  is  simply  resolved  into  ether  and  a 
mixture  of  sulphuric  acid  and  water.  Sulphovinic  acid  has  been  regarded 
by  Liebig  as  a  bisulphate  of  alcohol  (C4Hg022S03),  and  by  Regnault  as  a 
bisulphate  of  ether  with  2  atoms  of  water  (C,H50,2S03  +  2HO).  Which- 
ever view  is  adopted,  it  is  obvious  that  this  compound  contains  all  the  ele- 
ments necessary  to  the  production  of  ether,  when  the  mixture  is  exposed  to 
the  temperature  required  for  its  decomposition.  The  researches  of  Graham 
have,  however,  proved  that  the  production  of  sulphovinic  acid  is  not  neces- 
sary to  the  formation  of  ether.  When  a  mixture  of  oil  of  vitriol  and  alcohol 
is  exposed  in  a  sealed  tube  to  a  temperature  ranging  from  284°  to  302°,  no 
charring  occurs,  but  the  liquid  divides  itself  into  a  light  stratum  which  is 
nearly  pure  ether,  and  a  heavy  stratum  consisting  of  alcohol,  water,  and  sul- 
phuric acid  {Journ.  Chem.  *Soc.,iii.  p.  24).  These  results  confirm  the  origi- 
nal view  of  Mitscherlich,  that  alcohol  is,  under  certain  fixed  conditions, 
simply  resolved  into  ether  and  water  by  a  catalytic,  or  polymerizing,  action 
of  sulphuric  acid.  The  acid  which  remains  in  the  retort  is  unchanged  in 
properties,  and  unaltered  in  quality.  A  certain  proportion  of  acid  is  neces- 
sary in  the  process,  in  order  to  maintain  the  liquid  in  the  retort  or  flask  at 
the  requisite  temperature.  Sulphuric  acid  exerts  a  similar  catalytic  action 
on  oil  of  turpentine  :  it  splits  this  oil  into  two  other  hydrocarbons — terebene 
andcolophene — one  of  which  has  a  higher  boiling  point  and  a  greater  vapor 
density  than  oil  of  turpentine.     This  product,  as  in  the  case  of  ether,  does 


PROPERTIES    OP    ETHER.  597 

not  form  any  combination  with  the  acid.  As  an  additional  proof  that  ether 
is  produced  independently  of  the  conversion  of  alcohol  into  sulphovinic  acid, 
it  may  be  stated  that  the  proportions  of  alcohol  and  sulphuric  acid,  which 
yield  the  greatest  amount  of  sulphovinic  acid,  do  not  yield  the  largest  pro- 
portion of  ether.  One  part  of  sulphuric  acid  to  6  or  8  parts  of  alcohol, 
yields  the  largest  quantity  of  ether  and  but  little  sulphovinic  acid  :  the  pro- 
portion of  sulphuric  acid  must  be  greatly  increased,  in  order  to  produce  sul- 
phovinic acid. 

Other  acids  act  in  a  similar  manner.  Thus,  .when  alcohol  is  heated  to  a 
high  temperature  with  a  concentrated  solution  of  phosphoric  acid,  it  is  split 
into  water  and  ether.  In  this  case  the  water  is  retained  by  the  acid,  and 
when  this  is  sufficiently  hydrated,  its  decomposing  action  on  alcohol  ceases. 
Certain  chlorides  and  fluorides  also  produce  this  conversion.  The  anhy- 
drous chloride  of  zinc  dissolves  to  a  great  extent  in  alcohol.  When  this 
solution  is  distilled,  alcohol  first  passes  over,  and  as  the  temperature  rises, 
ether  and  water  are  obtained  as  products  in  the  receiver. 

Properties. — Ether  is  a  highly  volatile,  transparent,  colorless,  limpid  liquid, 
of  a  peculiar  penetrating  odor,  and  a  pungent  and  sweetish  taste.  It  is 
highly  exhilarating,  and  produces  a  remarkable  species  of  intoxication  when 
its  vapor  is  respired  mixed  with  air ;  by  the  proper  management  of  the  in- 
halation, a  continuous  insensibility  to  pain  may  be  maintained.  This  appli- 
cation of  ethereal  vapor  was  at  one  time  resorted  to  in  the  performance  of 
surgical  operations  ;  but  as  an  anaesthetic  for  breathing,  the  vapor  of  chlo- 
form  is  now  preferred.  In  the  form  of  a  fine  spray,  ether  has  been  lately 
much  used  as  a  local  anaesthetic.  Thus  a  jet  of  finely-divided  ether  directed 
against  a  portion  of  the  skin  annuls  sensibility  so  much  that  severe  surgical 
operations  may  be  performed  without  causing  pain.  Ether  is  neither  acid 
nor  alkaline ;  it  has  a  highly  refractive  power  in  regard  to  light,  and  is  a 
non-conductor  of  electricity.  It  should  not  redden  litmus  when  pure.  The 
evaporation  of  this  liquid  produces  intense  cold.  When  a  few  drops  of 
ether  covering  a  drop  of  water  are  blown  upon  by  a  blowpipe  the  water 
freezes,  in  consequence  of  the  rapid  evaporation  of  the  ether.  The  vapor 
has  been  employed  for  the  artificial  production  of  ice  on  a  large  scale,  the 
evaporation  of  the  liquid  being  accelerated  by  means  of  an  air  pump.  In 
vacuo  this  liquid  boils  at  the  lowest  temperature.  A  mixture  of  it  with 
solid  carbonic  acid  causes  the  thermometer  to  sink  to  — 166°.  The  sp.  gr. 
of  ether  varies  greatly  with  the  temperature.  We  found,  at  a  temperature 
of  60°,  that  absolute  ether,  washed  and  distilled  over  quicklime,  had  a  sp. 
gr.  of  0-113.  It  is  more  commonly  met  with  of  a  sp.  gr.  of  0720.  This 
liquid  is  so  affected  in  its  volume  by  temperature  that  1000  parts  at  96°  are 
reduced  to  968-2  at  60°,  and  to  948'  at  330. 

At  mean  pressure,  ether  boils,  according  to  Gay-Lussac,  at  96  5.  Ether 
of  the  sp.  gr.  of  'T20  may  be  said  to  boil,  under  a  pressure  of  30  inches,  at 
98°.  Upon  this  subject,  however,  authorities  vary  a  little,  in  consequence 
of  variations  in  the  density  of  the  ether,  and  also  of  barometical  pressure, 
circumstances  which  easily  influence  the  boiling-point  of  this  liquid.  Pure 
anhydrous  ether  does  not  freeze.  Faraday  failed  in  congealing  this  liquid, 
although  he  exposed  it  to  a  temperature  of  166°  below  zero.  {Phil.  Trans., 
1845,  p.  158.)  The  extreme  volatility  of  ether  renders  it  impossible  to  pour 
it  from  one  vessel  to  another  without  losing  a  portion  by  evaporation,  and 
its  vapor,  in  consequence  of  its  density,  may  be  seen  to  fall  from  the  liquid  : 
it  is  this  which  renders  it  so  dangerous  to  expose  ether  near  to,  and  espe- 
cially above,  the  flame  of  a  candle.  The  sp.  gr.  of  the  vapor,  at  mean  pres- 
sure and  temperature,  is  25860  in  reference  to  air  as=l.  At  the  tempera- 
ture of  21^o,  1  volume  of  ether  gives  212  volumes  of  vapor.     The  density  of 


598  PROPERTIES    OF    ETHER. 

the  vapor  may  be  well  shown  by  clipping  a  §ock  of  cotton  into  ether,  and 
placing  it  within  a  glass  tube  of  about  an  inch  diameter,  and  18  or  20  inches 
long ;  the  vapor  will  descend  and  escape  from  the  lower  end  of  the  tube, 
where  it  may  be  inflamed  by  a  lighted  taper,  but  none  rises  to  the  upper  end 
of  the  tube.  If  the  lower  end  of  the  tube  be  drawn  into  a  point  and  bent 
upwards,  the  ether  vapor  may  there  be  burned  in  the  manner  of  a  gas-light. 
The  vapor  of  ether,  poured  from  a  wide-mouthed  bottle  through  a  long 
funnel,  will  readily  fall,  and,  when  ignited,  burn  at  the  end  of  the  funnel.  If 
two  or  three  drachms  of  eth^r  are  placed  in  a  quilled  receiver  on  a  stand, 
and  the  vessel  is  slightly  inclined,  the  ether  vapor  will  fall  out  of  the  long 
narrow  tube,  and  may  be  burnt  like  a  jet  of  gas.  Its  density  is  shown  by 
depressing  the  tube,  when  the  flame  will  be  much  increased.  If  raised,  the 
flame  is  diminished,  and  ultimately  extinguished.  This  proves  the  gravi- 
tating power  of  the  vapor.  The  elastic  force  of  the  vapor  may  be  shown  by 
letting  a  drop  or  two  of  ether  pass  into  the  vacuum  of  a  barometer,  when  it 
instantly  depresses  the  mercury  several  inches,  more  or  less  according  to  the 
temperature  :  hence  also,  when  thrown  up  into  gases  standing  over  mercury, 
it  greatly  augments  their  bulk.  The  great  inflammability  of  the  vapor  may 
be  shown  by  boiling  two  or  three  drachms  of  ether  violently  in  a  Florence 
flask,  and  igniting  the  vapor  as  it  issues.  It  burns  in  a  large  column  of 
flame,  with  a  light  like  that  of  coal-gas.  Ether  may  be  poured  upon  a  large 
surface  of  water,  and  its  vapor  burnt  on  this  liquid  in  a  sheet  of  flame. 

When  ether  is  inflamed  it  burns  with  a  bright  and  slightly  sooty  flame, 
leaving  no  residue,  and  producing  carbonic  acid  and  water  (C4lI.O-fl20.= 
4CO2+5HO).  These  products  may  be  collected  by  holding  the  mouth  of  a 
clean  jar  over  a  flame  of  burning  ether.  Water  is  condensed  on  the  sides  of 
the  jar,  and  carbonic  acid  is  collected  in  the  interior.  When  lime-water  is 
poured  into  the  jar  the  presence  of  carbonic  acid  is  proved  by  the  liquid 
becoming  milky  white.  Aldehyde  and  water,  as  well  as  acetic  acid,  are 
among  the  products  of  combustion  at  a  low  temperature  (C4H5O  +  2O  — 
C4H4O3+HO).  By  passing  ether  into  a  jar  or  bladder  supplied  with  a  jet 
and  stopcock,  placed  in  warm  water,  its  vapor  may  be  burned  at  the  jet. 
If  its  vapor  is  mixed  with  about  10  volumes  of  oxygen,  it  explodes  violently 
by  an  electric  spark ;  but  with  smaller  quantities  of  oxygen,  or  with  air,  this 
combustion  is  only  imperfect.  If  a  little  ether  is  poured  into  a  bladder  full 
of  air,  supplied  with  a  stopcock  and  jet,  the  mixture  of  air  and  ether  vapor 
may  be  burned  at  the  jet  with  a  brilliant  flame,  without  risk  of  explosion. 

Exposed  to  air  and  light,  as  in  bottles  which  are  frequently  opened,  ether 
absorbs  oxygen  as  strong  ozone :  it  acquires  bleaching  properties,  and  is 
less  capable  of  dissolving  fixed  oils.  As  one  of  the  results  of  this  absorp- 
tion of  oxygen,  acetic  acid  is  produced.  The  presence  of  this  acid  is  not  at 
first  apparent,  because  it  forms  acetic  ether,  but  it  gives  to  the  ether  a 
peculiar  odor,  and  in  time  it  becomes  acid  to  tests.  Ozonized,  or,  more 
correctly,  antozonized  ether  may  also  be  produced  by  pouring  a  quantity  of 
liquid  ether  into  a  glass  jar,  and  when  the  vapor  is  thoroughly  diffused  with 
air  at  the  mouth  of  the  jar,  introducing  a  bar  of  iron  at  a  black  heat  and 
moving  it  about  for  a  short  time.  The  temperature  of  the  metal  should  not 
be  sufficiently  high  to  inflame  the  vapor.  Ozone  is  produced  which  is  readily 
detected  in  the  air  and  escapes  with  it,  while  antozone  enters  into  combina- 
tion with  the  ether.  Ozone  is  not  soluble  in  ether,  and  the  name  given  to 
this  liquid  should  therefore  be  antozonized  ether.  Besides  its  bleaching 
properties,  it  oxidizes  and  destroys  offensive  effluvia,  and  is  in  this  respect 
a  useful  deodorizer.  It  sets  free  iodine  from  the  iodide  of  potassium,  but  it 
does  not,  like  ozone,  render  precipitated  guaiacum  resin  blue.  When  added 
to  chromic  acid,  or  to  an  acid  solution  of  diluted  bichromate  of.potash,  it 


PROPERTIES    or    ETHER.  59,9 

bring^s  out  a  beautiful  blue  color  from  the  formation  of  perchromie  aoid, 
which  is  dissolved  by  the  ether,  and  this  liquid  floats  with  it,  forminj^  a  blue 
stratum  on  the  surface.  Ether  not  containing  antozone  slowly  reduces  the 
acid  chromate,  forming  green  oxide  of  chromium.  The  decomposition  is 
accelerated  by  heat.  Bodies  containing  ozone  only  do  not  produce  per- 
chromie acid  under  the  circumstances.  Another  difference  has  also  been 
pointed  out.  It  is  well  known  that  peroxide  of  manganese  added  to  an 
antozonide  causes  the  evolution  of  ordinary  oxygen,  and  the  properties  of 
ozonide  and  antozonide  are  destroyed.  A  small  quantity  of  peroxide  of 
manganese  added  to  what  is  called  ozonized  ether,  destroys  its  peculiar 
properties,  thus  proving  that  it  contains  antozone,  or  positive  oxygen.  Dr. 
John  Day,  of  Geelong,  Australia,  and  Dr.  B.  W.  Richardson,  have  intro- 
duced the  antozonized  ether  as  a  valuable  agent  in  medical  practice.  Ether 
long  kept  in  a  bottle  containing  air  generally  acquires  the  properties  of  an- 
tozone. When  added  to  permanganate  of  potash  the  pink  color  is  only 
slowly  discharged  by  pure  and  fresh  ether;  but  if  it  contains  antozone  the 
permanganate  is  very  rapidly  deoxodized  and  loses  its  color. 

If  ether  vapor  is  passed  over  red-hot  platinum  wire,  or  if  red-hot  platinum 
wire  is  plunged  into  a  bottle  of  air  containing  a  little  ether  vapor  diffused  in 
it,  the  metal  continues  to  glow,  and  acetic  and  aldehydic  acids  are  produced. 
When  a  stout  rod  of  platinum,  copper,  iron,  or  glass,  is  heated  short  of 
redness,  and  introduced  into  the  mixture,  ozone  and  antozone  are  produced 
at  the  expense  of  a  part  of  the  oxygen. 

The  best  method  of  preserving  ether  is  to  keep  it  in  well-stopped  bottles, 
quite  full,  and  in  a  dark  place.  In  contact  with  alkaline  bases,  this  conver- 
sion of  ether  into  acetic  acid  takes  place  more  rapidly.  Ether  is  soluble  in 
alcohol  and  chloroform  in  all  its  proportions,  but  has  only  a  limited  solubility 
in  water.  Nine  parts  of  water  dissolve  one  part  of  ether.  On  this  difference 
is  based  the  separation  of  alcohel  from  ether,  as  well  as  the  detection  of  that 
liquid  in  commercial  samples.  When  a  mixture  of  alcohol  and  ether  is 
shaken  with  water  the  mixture  separates  into  two  layers,  each  of  which  con- 
tains the  three  liquids.  The  upper  layer  contains  a  large  excess  of  ether, 
the  lower  a  large  excess  of  water,  with  the  greater  part  of  the  alcohol  with 
which  the  ether  was  mixed.  By  repeated  washing,  the  whole  of  the  alcohol 
may  be  removed.  Ether  which  has  thus  been  washed  retains  about  a  tenth  part 
of  water ;  or,  according  to  Liebig,  36  parts  of  pure  ether  dissolve  one  part 
of  water.  From  this  it  may  be  freed  by  distillation  with  quicklime,  anhydrous 
sulphate  of  copper  or  dry  chloride  of  calcium.  A  mixture  of  alcohol,  ether, 
and  ethereal  oil  is  known  under  the  name  of  Hoffmannh  anodyne  liquor,  or 
spirit  of  ether.  Such  a  mixture  is  employed  in  photography  as  a  solvent  for 
pyroxyline. 

Ether  dissolves  a  small  quantity  of  sulphur  (l-80th),  which  is  not  thrown 
down  by  the  addition  of  a  little  water;  the  solution  smells  of  sulphuretted 
hydrogen,  and  by  slow  evaporation  deposits  regular  crystals  of  sulphur. 
Ether  dissolves  n;iore  than  2  per  cent,  of  phosphorus  (l-37th);  the  solution 
when  concentrated  by  evaporation,  deposits  crystals  of  phosphorus :  it  is 
luminous  in  the  dark  when  in  contact  of  air,  and  if  poured  upon  hot  water 
produces  a  brilliant  column  of  luminous  vapor.  Exposed  to  air,  this  solu- 
tion becomes  acid,  and  phosphorus  is  precipitated  when  it  is  mixed  with 
water  or  alcohol ;  i^  gradually  deposits  red  phosphorus  when  exposed  to 
light.     Ether  does  not  dissolve  potassa  or  soda,  or  their  carbonates. 

The  fixed  and  volatile  oils,  many  of  the  resins,  caoutchouc,  various  forms 
of  extractive,  the  alkaloids,  and  some  other  vegetable  principles,  are  more 
or  less  soluble  in  ether ;  hence  ether  is  often  employed  in  the  analysis  of 
organic. products,  as  a  means  of  separating  their  proximate  principles  from 


6.00  CONSTITUTION  OF  ETHER.   ETHYLE. 

each  other.  When  mixed  with  chloroform,  its  solvent  power  on  certain 
alkaloids  is  much  increased.  Such  a  mixture  is  employed  as  a  solvent  for 
strychnia.  Many  metallic  salts  are  soluble  in  ether,  and  especially  the 
chlorides  of  gold,  platinum,  iron,  and  uranium  ;  the  property  which  ether 
has  of  abstracting  these  salts  from  their  aqueous  solutions,  has  been  adverted 
to  under  the  history  of  the  respective  metals.  Potassium  and  sodinra  are 
converted  into  potassa  and  soda  by  contact  with  ether,  and  hydrogen  is 
disengaged  without  combustion,  the  metals  floating  in  the  liquid. 

A  small  quantity  of  sulphuric  acid  added  to  ether  produces  no  effect,  but 
a  mixture  of  equal  parts  of  ether  and  the  acid  blackens,  and  yields,  on  dis- 
tillation, oil  of  wine,  olefiant  gas,  acetic  and  sulphurous  acids,  and  water  ;  it 
leaves  a  resinous  matter  and  charcoal.  Anhydrous  sulphuric  acid  decom- 
poses ether,  and  produces,  according  to  Liebig,  "  isethionic  and  althionic 
acids,  oil  of  wine,  and  sulphate  and  bisulphate  of  oxide  of  ethyle ;  if  heat 
be  used,  these  products  are  decomposed,  and  sulphate  of  oxide  of  ethyle,  oil 
of  wine,  water,  and  ether,  together  with  acetic,  formic,  and  sulphurous  acids, 
carbonic  oxide,  and  olefiant  gas,  pass  over."  Heated  with  nitric  acid,  ether 
yields,  according  to  Liebig,  carbonate,  acetic,  formic,  and  oxalic  acids,  as 
well  as  aldehyde. 

When  a  little  ether  is  introduced  into  chlorine,  the  gas  is  absorbed,  and 
peculiar  compounds  result.  When  bubbles  of  chlorine  are  passed  into  ether, 
they  often  cause  inflammation,  and  when  a  small  quantity  of  ether  is  poured 
into  a  jar  of  gaseous  chlorine,  and  a  lighted  taper  is  applied,  hydrochloric 
acid  is  formed,  and  carbon  is  set  free,  sometimes  with  explosion.  Iodine 
and  bromine  are  soluble  in  ether,  and  gradually  react  upon  and  decompose 
it.  The  solution  of  iodine  in  ether  is  dark  brown,  and  soon  gives  rise  to 
the  production  of  hydriodic  acid.  When  ether  is  saturated  with  bromine, 
and  the  mixture  is  left  for  ten  or  twelve  days,  it  is  entirely  decomposed;  the 
products  are,  1,  formic  acid(?);  2,  hydrobromic  acid  ;  3,  hydrobromic  ether; 
4,  heavy  bromic  ether  ;  5,  bromal.  The  first  four  products  may  be  separated 
by  distillation,  and  the  bromal  remains  (C^HOjjBrg) :  it  may  be  purified  by 
mixture  with  water,  and  in  the  course  of  twenty-four  hours  crystals  of  hy- 
drate of  bromal  are  formed.  When  this  hydrate  is  boiled  with  an  alkaline 
solution,  2  atoms  are  resolved  into  2  atoms  of  formic  acid,  2  of  bromoform, 
and  6  of  water. 

Composition. — The  vapor  of  ether,  when  passed  through  a  red-hot  tube, 
is  decomposed :  carbon  is  deposited,  and  water  and  aldehyde  are  among  the 
products.  When  the  vapor  is  analyzed  by  passing  it  through  red-hot  oxide 
of  copper,  the  results  furnish  the  following  elementary  composition : — 

Carbon 
Hydrogen  . 
Oxygen 

Ether  ...     1  37  100-00  1^  2-5567 

The  specific  gravity  of  ether  vapor  compared  with  air  is  2  5573,  and  its 
calculated  density  is  in  accordance  with  this  result.  Compared  with  hydro- 
gen, the  sp.  gr.  of  ether  vapor  is  37  ;  its  volume  equivalent  is  1.  If  oxygen 
is  assumed  to  be  16,  the  equivalent  of  ether  must  be  doubled.  Its  relations 
to  alcohol  and  other  bodies  would  thus  be  disturbed,  and  the  formulae  for  the 
various  ethers  would  be  rendered  unnecessarily  complex. 

Tests. — Ether  may  be  identified  by  its  odor  and  inflammability,  as  well  as 
by  the  color  of  its  flame  and  the  products  of  combustion. 

Ethyle. — Ether  is  commonly  regarded  as  an  oxide  of  the  compound  radical 
Ethyle  (C^HJ.    With  an  atom  of  water  it  forms  alcohol,  which  is  therefore  a, 


Atoms. 

Weights. 

Per  cent. 

Vols. 

Sp.  gr. 

.    4 

...      24      .. 

.       64-87       . 

..      4      .. 

.       1-6584 

.     5 

5       .. 

.       13-51       . 

..       5       .. 

.      ^-3455 

.     1 

8      .. 

.       21-62       . 

..         h     - 

.       0-5528 

HEAVY    OIL    OP    WINE.       NITRIC    ETHER.  601 

hydrated  oxide  of  ethyle.  Ethyle  combines  with  the  halogens  and  ether,  as 
its  oxide  combines  with  the  oxacids.  Dr.  Frankland  isolated  this  radical 
by  the  action  of  zinc  on  iodide  of  ethyle.  {Journ.  of  Chem.  Set.,  ii.  p.  263.) 
He  describes  it  as  a  colorless  gas,  of  a  slightly  ethereal  odor,  burning  with 
a  brilliant  white  flame,  and  of  a  sp.  gr.  =200394.  It  is  not  liquefied  at  0°, 
under  atmospheric  pressure,  but  under  a  pressure  =225  atmospheres,  at 
37°,  it  becomes  a  colorless,  transparent,  mobile  liquid  ;  it  is  absorbed  by 
alcohol,  which  evolves  it  again  on  dilution.  In  Frankland's  experiments, 
the  theoretical  result  of  the  decomposition  of  the  iodide  of  ethyle,  namely, 
C4H5l4-Zn  =  ZnI  +  C4H„  was  never  attained,  but  a  portion  of  the  ethyle 
was  always  resolved  into  elayle  and  methyle,  CJH^^C^H^+C^B.^',  so  that 
the  action  of  the  zinc  upon  the  iodide  of  ethyle,  at  the  temperature  required 
for  its  decomposition,  namely  302°,  may  be  represented  as  follows : — 

2[C,H3l]  +  2Zn,  =  2ZnI,  +  C,H,+  CA+C,H3. 

The  anhydrous  does  not  readily  pass  to  the  state  of  hydrated  oxide  of 
ethyle.  Thus,  ether  may  be  shaken  with  water,  and  kept  long  in  contact 
with  this  liquid,  without  producing  alcohol.  The  dehydration  of  the  oxide 
(alcohol)  is  also  effected  in  a  remarkable  manner  by  sulphuric  acid,  and  this 
acid  does  not  combine  with  the  oxide  as  it  is  produced.  The  anhydrous 
oxide  and  water  are  distilled  over  together. 

Heavy  Oil  op  Wine.  Sulphatic  Ether.  Oleum  ^thereum. — When  the 
distillation  of  a  mixture  of  sulphuric  acid  and  alcohol  is  carried  beyond  the 
point  at  which  ether  ceases  to  come  over,  a  liquid,  looking  like  oil,  is  ob- 
tained, to  which  the  above  names  have  been  applied ;  when  washed,  it  has  a 
bitter  aromatic  flavor.  It  has  long  been  known  under  the  name  of  oil  of  wine, 
and  was  formerly  regarded  as  analogous  in  composition  to  the  volatile  oils. 

It  may  be  prepared  by  distilling  a  mixture  of  1  part  of  alcohol  and  2-5 
parts  of  concentrated  sulphuric  acid.  The  oil  in  the  distillate  is  separated 
from  the  water,  and  is  purified  by  placing  it  in  vacuo  with  two  vessels,  the 
one  containing  hydrate  of  potassa,  and  the  other  strong  sulphuric  acid.  Its 
formula  is  C^HjOjSOg.  It  is  therefore,  in  constitution,  a  sulphate  of  the 
o^ide  of  ethyle,  or  sulphuric  ether.  The  oil  is  of  a  yellow  color,  has  a  pene- 
trating aromatic  odor,  and  a  sp.  gr.  of  1133  ;  it  is  soluble  in  alcohol  and 
ether,  but  not  in  water.  It  cannot  be  distilled  without  decomposition ;  at 
270°  it  is  converted  into  alcohol,  sulphurous  acid,  and  olefiant  gas.  When 
long  boiled  with  water,  it  is  converted  into  sulphovinic  acid  and  alcohol, 
and  an  oily  hydrocarbon  which  floats  on  water.  This  is  light  oil  of  wine,  or 
etherole;  it  resembles  olive  oil,  and  has  a  sp.  gr.  of  0-920. 

Numerous  ethers  are  produced  by  the  action  of  a  variety  of  acids  upon 
alcohol.     These  are  called  compound  ethers. 

Hyponitrous  Ether.— iWVroMS  Ether  (C^HPjNOg).— This  is  procured 
by  mixing  and  carefully  distilling,  at  a  gentle  heat,  equal  weights  of  alcohol 
(0-820)  and  of  nitric  acid  (1*30).  One  hundred  parts  of  this  mixture  yield 
10  parts  of  rectified  ether.  It  is  a  highly  volatile  inflammable  liquid,  sp.  gr. 
0-947  at  60°  :  it  boils  at  70°,  and  its  vapor  has  a  sp.  gr.  of  2  627.  It  is 
neutral,  but  by  exposure  to  light,  in  contact  with  water,  it  becomes  acid. 

Nitric  Ether  (C^H^O.NOs).— A  mixture  of  nitric  acid  and  alcohol,  when 
heated,  or  even  allowed  to  stand,  invariably  produces  hyponitrous  ether,  with 
a  violent  action.  In  order  to  prevent  the  formation  of  hyponitrous  acid, 
about  one  per  cent,  of  nitrate  of  urea  is  added  to  equal  weights  of  nitric 
acid  (1-4)  and  alcohol  (0  842).  The  mixture  is  gently  heated,  and  seven- 
eighths  are  distilled  over.  The  nitrate  of  urea  is  unchanged,  and  may  be 
repeatedly  used.    The  rectified  product  has  an  agreeable  odor,  distinct  from 


602  ACETIC,    HYDROCHLORIC,   AND    HYDRIODIC    ETHERS. 

that  of  hyponitrous  ether.  It  has  a  sweet  and  slightly  bitter  taste  :  its  sp. 
gr.  is  ril2,  and  it  boils  at  185°.  It  is  insoluble  in  water,  but  soluble  in 
alcohol,  from  which  it  is  again  precipitated  by  water. 

Acetic  Ether  (CJlfl,Ac). — When  an  acid  does  not  directly  resolve 
alcohol  into  water  and  ether,  the  conversion  may  be  effected,  and  a  new  ether 
produced  by  distilling  one  of  the  salts  of  the  acid  with  alcohol  and  sulphuric 
acid.  Thus  three  parts  of  acetate  of  potassa,  three  of  absolute  alcohol,  and 
two  of  sulphuric  acid,  distilled  to  dryness,  yield  a  product  which,  when 
rectified  by  redistillation  with  sulphuric  acid  and  by  the  action  of  lime  and 
chloride  of  calcium,  is  called  acetic  ether.  This  liquid  boils  at  about  165°. 
Its  sp.  gr.  is  0'89,  and  the  density  of  its  vapor  is  3  03.  It  has  a  peculiarly 
agreeable  odor,  and  appears  to  exist  in  and  contribute  to  the  odor  and  flavor 
of  certain  wines.  It  burns  with  a  yellowish  flame,  and  acetic  acid  is  de- 
veloped by  its  combustion.  Water  dissolves  about  one-seventh  of  its  weight 
of  this  ether,  and  the  solution  is  decomposed  by  potassa,  giving  rise  to  an 
acetate  and  to  alcohol.  Ammonia  has  no  action  upon  it.  It  is  soluble  in 
all  proportions  in  alcohol  and  in  ether. 

Hydrochloric  Ether  (C^H^CI). — Muriatic  Ether.  Chloride  of  Ethyle. — 
This  may  be  obtained  by  subjecting  to  careful  distillation  a  concentrated 
solution  of  hydrochloric  acid  gas  in  alcohol ;  or  a  mixture  of  1  part  of 
alcohol,  1  of  sulphuric  acid,  and  2  of  fused  and  finely-powdered  chloride  of 
sodium.  In  all  these  cases  the  ether  passes  over :  it  should  first  be  trans- 
mitted into  warm  water,  by  which  its  adhering  acid  and  alcohol  are  abstracted, 
and  its  vapor  may  then  be  condensed  by  conducting  it  through  a  cold  tube, 
and  receiving  it  in  a  bottle  surrounded  by  ice  and  salt.  Hydrochloric  ether 
is  a  limpid,  neutral,  colorless  liquid,  of  a  peculiar  penetrating  odor,  and  a 
sweetish  acrid  taste.  Its  specific  gravity  is  0-874  at  42°;  it  boils  at  about 
60°;  and  the  specific  gravity  of  its  vapor  is  2'219.  When  cooled  down  to 
— 10°;  it  crystallizes  in  cubes.  It  is  soluble  in  about  50  parts  of  water,  and 
in  all  proportions  in  alcohol  and  ether.  It  dissolves  sulphur  and  phosphorus, 
as  well  as  the  fixed  and  volatile  oils. 

Iodine  and  Bromine  produce  with  alcohol,  ethers  analogous  to  the  hydro- 
chloric.    They  have  the  formula  C4H5I  and  C^H^Br. 

Hydriodic  Ether,  or  Iodide  of  Ethyle,  is  obtained  by  the  distillation  of  a 
mixture  of  alcohol,  iodine,  and  phosphorus.  It  is  a  colorless  liquid  of  a 
penetrating  ethereal  odor,  of  a  sp.  gr.  of  1*94  at  61°.  It  boils  at  148°  ;  the 
sp.  gr.  of  its  vapor  is  5 '4.  It  is  not  inflammable,  but  when  dropped  on  red- 
hot  charcoal  it  gives  off  a  purple  vapor.  It  is  decomposed  at  a  red  heat. 
It  is  dissolved  by  alcohol,  but  not  readily  by  water.  This  liquid  possesses 
an  interest  as  being  the  source  of  the  compound  radical  ethyle.  Hydrohromic 
Ether  is  prepared  by  a  similar  process.  Fluorine,  cyanogen,  sulphocyanogen, 
and  even  sulphur,  form  compounds  with  ethyle  of  the  nature  of  ethers.  These 
are  obtained  by  various  complex  processes.  Hydrosulphuric  Ether  or  Mer- 
captan  (C^H^S-f  HS),  is  procured  by  distilling  a  concentrated  solution  of 
hydrosulphate  of  sulphide  of  barium  with  sulphovinate  of  baryta.  It  is  a 
colorless  liquid,  of  a  strong  odor,  resembling  that  of  garlic.  It  is  not  very 
soluble  in  water,  but  is  dissolved  by  ether  and  alcohol  in  all  proportions. 
Its  sp.  gr.  is  0*832  :  it  boils  at  97°,  and  the  density  of  its  vapor  is  2"14. 
It  has  a  powerful  affinity  for  mercury :  it  decomposes  corrosive  sublimate, 
forming  mercaptide  of  mercury  :  hence  the  name  mercaptan  (mercurium 
captans). 

Other  ethers  are  formed  by  the  combination  of  oxide  of  ethyle  with  many 
anhydrous  acids — e.  g.,  the  perchloric,  silicic,  boracic,  oxalic,  carbonic, 
arsenic,  cyanic,  hydrocyanic,  formic,  benzoic,  succinic,  tartaric,  and  citric 
acids.     These  aye  for  the  most  part  procured  by  distilling  a  mixture  of 


CELLULOSE.       WOODY    FIBRE,    OR    LIGNINE.  G03 

alcohol  and  hydrochloric  or  sulphuric  acid  with  the  respective  acids  of  their 
salts. 

Double  ethers  are  those  in  which  the  elements  of  ordinary  ether  are  com- 
bined with  the  ethers  of  the  amylic  or  methylic  series. 

Compound  ethers  are  found  ready  formed  in  plants  and  fruits,  and  to  the 
presence  of  these,  their  odors  and  flavors  are  frequently  due.  They  may  he 
artificially  imitated.  When  dissolved  in  a  large  quantity  of  alcohol,  these 
ethers  lose  their  offensive  odor,  and  form  various  essences  for  giving  perfume 
and  flavor.  l^h\i%  pine- apple  oil  is  butyric  ether,  041130,0811703.  It  may  be 
produced  by  agitating  two  parts  of  alcohol  and  two  parts  of  butyric  acid 
with  one  part  of  sulphuric  acid  diluted  with  its  bulk  of  water.  On  standing, 
the  butyric  ether  rises  to  the  surface  and  may  be  purified  by  agitating  it 
with  water  in  which  it  is  almost  insoluble.  It  is  afterwards  deprived  of  any 
water  by  chloride  of  calcium.  It  is  the  alcoholic  solution  of  the  ether  which 
forms  what  is  called  pine-apple  oil.  It  is  also  a  product  of  the  reaction  of 
alcohol  on  impure  glycerine.  Essence  of  melons  is  ether  combined  with  one 
of  the  acids  of  cocoa-nut  oil,  and  essence  of  quinces  is  pelargonic  ether, 
O^HgOjOjgH^^Oa.  This  is  considered  to  be  identical  with  oenanthic  ether, 
which  gives  the  bouquet  to  wine  (page  579).  Pear-oil  is  an  alcoholic  solu- 
tion of  the  acetate  of  amyl,  OjoHj^O.C^HgOg,  and  apple-oil  is  the  valerianate 
of  the  same  radical,  0^oH„0,Cj^Hg03.  The  oil  of  winter-green  is  the  sali- 
cylate of  methyl,  C2H30,C,,HA- 


CHAPTER   XLIX. 

CELLULOSE.    PYROXYLINE.    WOOD.   COAL.    BITUMEN.    PRO- 
DUCTS   OF   THE  DECOMPOSITION  OF  WOOD  AND  COAL. 

Woody  Fibre.     Cellulose.     Lignine. 

The  term  cellulose  has  been  applied  to  the  pure  base  of  woody  fibre. 
The  varieties  of  woody  matter  differ  in  color,  texture,  and  hardness  or 
toughness ;  but  when  freed  from  various  foreign  matters,  they  leave  a  white 
translucent  residue,  insoluble  in  water,  alcohol,  and  ether,  and  convertible, 
by  sulphuric  acid,  into  a  substance  having  some  of  the  characters  of  starch, 
and  then  into  dextrine  or  sugar.  Oertain  piths,  linen,  cotton,  filtering 
paper,  and  some  other  allied  substances,  are  nearly  pure  cellulose.  Weak 
acids  and  aliialine  liquids,  and  a  weak  solution  of  chlorine,  have  scarcely 
any  action  on  this  principle,  but  they  change,  combine  with,  or  decompose 
it  when  concentrated,  and  some  of  these  reactions  are  very  important :  when, 
for  instance,  clean  linen  or  cotton  rags  are  acted  on  by  cold  sulphuric  acid, 
a  magma  is  formed,  which  if  immediately  saturated  by  carbonate  of  baryta, 
or  lead,  yields  insoluble  sulphates,  together  with  soluble  sulpholignates. 
These  salts  appear  identical  with  those  of  the  sulphoglucic  or  sulphosaccharic 
acid,  derived  from  the  action  of  sulphuric  acid  on  glucose.  This  magma  is 
also  blued  by  iodine.  If  it  be  much  diluted  and  boiled,  it  yields  dextrine, 
and  ultimately  glucose.  By  this  action  of  sulphuric  acid  upon  paper,  a  useful 
material  now  known  as  vegetable  parchment,  is  obtained.  It  is  prepared  by 
steeping  thick  unsized  paper  in  a  mixture  of  equal  parts  of  sulphuric  acid 
and  water,  at  a  temperature  of  BO'^y  then  washing  it  well  in  cold  water  and 
drying  it.     It  is  translucent,  tough,  and  nearly  impermeable  to  water,  form- 


604  PYROXYLINE.      GUN-COTTON. 

ing  a  useful  substitute  for  common  parchment  or  vellum.  The  following  is 
another  method  of  preparing  this  parchment :  two  parts,  by  measure,  of  the 
strongest  sulphuric  acid  are  mixed  with  one  part  of  water.  These  propor- 
tions are  material  :  if  the  acid  is  weaker,  the  fibre  of  the  paper  is  converted 
into  gum,  if  stronger  it  is  corroded.  White  blotting-paper  is  thoroughly 
soaked  in  the  mixed  acid  and  water,  and  immediately  removed.  It  is  then 
transferred  to  a  large  quantity  of  water  containing  a  little  ammonia,  and 
after  thorough  washing  it  is  dried.  In  this  conversion  the  fibre  undergoes 
no  chemical  change.  The  molecular  condition  of  the  paper  is  simply  altered 
by  the  pores  being  filled  up.  The  influence  of  a  slight  increase  in  the  water 
may  be  thus  shown.  If  the  unsized  paper  is  wetted  in  spots  before  it  is 
immersed  in  the  acid  mixture,  the  wetted  parts  are  destroyed  while  the 
remainder  of  the  paper  is  parchmented.  The  substance  is  now  put  to  many 
important  uses  in  the  arts. 

Pyroxyline.     Gun-  Cotton. 

This  remarkable  substance,  discovered  in  1846  by  Schoenbein,  is  prepared 
by  dipping  clean  carded  cotton,  well  dried,  into  a  mixture  of  3  volumes  of 
nitric  acid  (sp.  gr.  1-5)  with  5  of  sulphuric  acid.  The  concentrated  com- 
mercial acids  answer  the  purpose :  the  mixture  is  allowed  to  cool,  and  small 
portions  of  cotton  should  be  used  at  a  time,  and  completely  immersed,  so  as 
to  avoid  elevation  of  temperature :  in  10  or  20  minutes  the  cotton  may  be 
withdrawn  (the  excess  of  acid  pressed  out),  and  thoroughly  washed  in  water 
containing  a  little  ammonia;  it  is  then  cautiously  dried,  at  a  temperature 
not  exceeding  200^.  100  parts  of  cotton  thus  treated  yield  about  170  of 
dry  gun-cotton.  Clean  paper,  the  purer  varieties  of  sawdust,  and  other 
forms  of  ligneous  matter,  produce  similar  compounds.  Pyroxylic  paper  is 
remarkable  for  the  intensity  of  its  electricity  when  slightly  rubbed.  Well 
prepared  pyroxyline  resembles  the  original  cotton  in  appearance,  but  is  more 
harsh  and  brittle  to  the  touch,  and  highly  electric ;  its  extreme  combusti- 
bility is  remarkable ;  inflamed  in  the  open  air  it  flashes  off  without  smoke, 
smell,  or  residue  ;  it  takes  fire  at  about  325°,  which  is  about  200°  below  the 
temperature  required  for  the  ignition  of  gunpowder,  and  its  combustion  is 
more  rapid.  In  consequence  of  its  whiteness  it  is  not  so  easily  inflamed  by 
a  solar  lens  as  gunpowder,  unless  it  is  tinged  with  indigo  or  carmine,  or 
covered  with  a  little  charcoal.  Burned  in  a  tube  it  produces  red  fumes, 
having  the  odor  of  nitrous  acid.  When  substituted  for  gunpowder  in  fire- 
arms, the  extreme  suddenness  of  its  explosion  is  apt  to  burst  the  barrel,  but 
it  is  a  powerful  projectile  agent.  For  mining  purposes  it  is  preferable  to 
gunpowder,  in  producing  less  noxious  fumes  ;  and  it  is  not  deteriorated  in 
damp  air,  or  even  (when  subsequently  dried)  by  immersion  in  water ;  and , 
weight  for  weight,  its  explosive  force  is  between  3  and  4  times  greater  than 
that  of  gunpowder.  The  extreme  rapidity  of  its  combustion  is  well  shown 
by  placing  a  flock  of  it  upon  a  small  heap  of  gunpowder,  where  it  may  be 
exploded  by  a  hot  wire  without  kindling  the  powder.  Exclusive  of  the  traces 
of  nitrous  acid  above  adverted  to,  prussic  acid,  aqueous  vapor,  carbonic 
acid,  and  nitrogen,  are  the  products  of  its  combustion.  Pyroxyline,  as 
above  prepared,  is  insoluble  in  dilute  acids ;  it  dissolves  in  methylic  and 
acetic  ethers,  and  in  acetone.  It  is  very  slightly  soluble  in  mixtures  of  ether 
and  alcohol. 

Gun-cotton  for  medical  purposes  is  prepared  by  keeping  the  cotton  for 
about  two  hours  in  a  mixture  of  2  parts  of  powdered  nitre,  and  3  of  sulphuric 
acid  ;  after  washing  and  drying,  it  is  digested  in  a  mixture  of  about  90  parts 
of  ether,  and  10  of  alcohol  {Collodion).  Spread  upon  silk  this  solution  fur- 
nishes a  good  sticking-plaster.     A  solution  of  potassa  dissolves  and  decom- 


GUN  cotton:  manufacture,  properties.  605 

poses  gnn-cotton  ;  ammonia  also  dissolves  it,  and  leaves  it,  on  evaporation, 
in  a  pulverulent  form.  Sulphuric  acid  dissolves  pure  gun-cotton  and  is  not 
discolored  by  it,  unless  it  contains  portions  of  unchanged  cotton.  It  is 
scarcely  affected  by  cold  nitric  acid,  but,  if  heated,  nitrous  acid  vapor  is 
evolved  ;  and  on  adding  water,  a  white  inflammable  powder  falls,  which  re- 
sembles that  obtained  by  a  similar  process  from  a  nitric  solution  of  starch — 
called  xyloidine. 

The  production  of  nitrous  acid  by  the  combustion  of  pyroxyline  may  be 
shown  by  exploding  a  portion  on  blue  litmus-paper,  or  on  starch-paper,  im- 
pregnated with  a  solution  of  iodide  of  potassium.  The  former  is  reddened, 
and  the  latter  acquires  a  deep-blue  color.  The  production  of  prussic  acid, 
or  a  cyanogen  compound,  is  shown  by  exploding  a  portion  in  a  jar,  and  then 
inverting  over  its  mouth  a  watch  glass  moistened  with  a  few  drops  of  a  solu- 
tion of  nitrate  of  silver.  White  cyanide  of  silver  is  speedily  produced.  Gun- 
cotton  is  liable,  when  long  kept,  to  spontaneous  changes ;  it  becomes  soft 
and  pasty,  contracts  greatly  in  volume,  and  the  red  vapors  of  nitrous  acid 
as  well  as  the  vapors  of  prussic  acid  are  evolved.  The  solid  residue  con- 
tains a  principle  which  like  glucose  reduces  oxide  of  copper  in  a  solution 
of  potash.  This  has  been  ascribed  by  some  chemists  to  the  presence  of  pec- 
tose.  According  to  M.  Abel  the  presence  of  a  small  quantity  of  carbonate 
of  soda  in  gun-cotton  prevents  these  spontaneous  changes  in  it. 

The  pyroxyline  used  in  photography  requires  many  precautions  for  its  pre- 
paration. Its  qualities  are  materially  affected  by  the  proportions  of  the 
acids;  their  sp.  gr.,  the  temperature  of  the  mixture,  and  the  period  of  time 
during  which  the  cotton  is  immersed.  Mr.  Nicol  recommends  the  following 
formula:  Ten  ounces,  by  measure,  of  sulphuric  acid  (1*840),  and  5  ounces, 
by  measure,  of  nitric  acid  (1'370),  are  to  be  well  mixed,  and  2  fluidrachms 
of  water  added.  When  the  mixture  has  cooled  to  about  130°,  place  in  it, 
tuft  by  tuft,  well  pulled  out,  5  drachms  of  clean  cotton.  Each  tuft  should 
be  penetrated  by  the  acid,  as  it  is  immersed.  The  cotton  should  be  kept 
immersed  ten  minutes,  then  removed,  washed,  and  dried.  If  it  appear  to 
dissolve  while  immersed  in  the  acids,  this  may  be  prevented  by  pressing  the 
cotton  together  with  glass  rods.  We  have  found  this  compound  to  be  very 
soluble  in  a  mixture  of  alcohol  and  ether.  It  leaves,  on  evaporation,  a  smooth 
transparent  film.  It  is  not  very  explosive,  but  completely  combustible.  Thei 
following  is  another  formula :  Powdered  nitre,  925  grains,  sulphuric  acid 
(1-8),  1389  grains.  When  the  nitre  is  entirely  dissolved  in  the  acid,  plunge 
in,  by  separate  portions,  62  grains  of  clean  cotton.  Immerse  for  ten  minutes, 
then  remove  and  wash  the  product.  Generally  speaking,  the  longer  the 
cotton  is  left  in  the  acid  mixture,  the  less  soluble  it  becomes.  A  sample  of 
gun-cotton  prepared  according  to  this  formula,  was  preserved  for  five  years  in 
a  perfect  state.  It  was  very  combustible  and  explosive  when  dry,  and  very 
soluble  in  a  mixture  of  ether  and  alcohol,  forming  a  good  collodion. 

The  composition  of  pyroxyline  no  doubt  varies,  according  to  the  mode  in 
which  it  is  prepared.  There  are  at  least  four  varieties  known.  In  all  cases 
it  must  be  regarded  as  the  nitrite  of  an  organic  base.  The  formula  for 
photographic  cotton  is  (C^Hie(NOJ,0.^).  It  is  a  substitution-compound  in 
which  4  atoms  of  hydrogen  are  replaced  by  4  atoms  of  nitroUs  acid.  Accord- 
ing to  Pelouze  and  Fr^my  {Chim.  Organ.,  vol.  i.  p.  950),  the  formation  of 
pyroxyline  is  as  follows  : — 

2(C,2H,oO,o)     -f     5(N0,H0)     =     lOHO    -f     (^mH^O.s^SNO^) 
Cellulose.  Pyroxyline. 

The  composition  of  cellulose,  or  pure  woody  fibre,  might  be  represented  as 


606  LIGNINE.      WOOD.       DRY    ROT. 

CgHsOg :  but  a  higher  equivalent  is  better  adapted  to  its  combinations,  and 
its  most  convenient  formula  is  C^ll.^0^ 

LiGNiNE.  Wood. — The  varieties  of  wood  have  cellulose,  as  their  basis, 
with  other  substances  superadded,  giving  special  characters  to  the  several 
varieties.  In  some  of  the  hard  and  white  woods,  these  foreign  matters  are 
nnimportant;  but  in  others,  as  in  the  resinous,  colored,  and  astringent  woods 
and  barks,  they  materially  affect  their  durability  and  uses.  The  average  sp. 
gr.  of  wood  is  1-5,  but  it  generally  floats,  in  consequence  of  theair  it  includes, 
though  there  are  a  few  woods — such  as  guaiacum,  ebony,  and  box — which 
sink  in  water.  Green  wood  includes  from  30  to  40  per  cent,  of  water;  in  its 
ordinary  state  of  dryness,  it  retains  about  25  per  cent.  :  but  when  artificially 
dried,  as  when  used  for  fuel,  in.  which  case  its  humidity  greatly  diminishes 
its  heating  powers,  it  should  not  retain  more  than  10  or  12  per  cent. 

The  durability  of  woods  depends  upon  their  state  of  hardness,  and  upon 
the  extraneous  matters,  such  as  resin  and  tannin,  which  they  contain ;  but  by 
long  exposure  to  air  and  moisture,  they  are  all  more  or  less  liable  to  decay 
{dry  rot)  in  consequence  chiefly  of  the  presence  of  a  nitrogenous  principle 
which  seems  to  act  as  a  ferment ;  the  attacks  of  insects  and  the  growth  of 
fungi  and  lichens  also  contribute  to  these  changes.  This  decay  may  be  to  a 
great  extent  prevented,  by  imbuing  the  timber  with  certain  oils,  tars,  oxides, 
and  salts,  but  especially  with  carbolic  acid;  and  ropes,  sailcloth,  &c.,  may  be 
similarly  treated.  Alum,  sulphate,  and  pyrolignate  of  iron,  sulphate  of 
copper,  corrosive  sublimate,  and  chloride  of  zinc  are  some  of  the  substances 
which  have  been  thus  applied  as  preservatives;  they  act  by  combining  with 
the  wood  or  fibre  ;  but  when  large  dense  pieces  of  timber  are  operated  on, 
there  is  a  difficulty  in  causing  them  to  be  permeated  by  the  solution.  In 
some  cases  this  has  been  efl"ected  by  placing  the  wood  and  preservative  liquor 
in  a  vessel  admitting  of  being  exhausted,  so  that  the  interstitial  air  of  the 
wood  has  been  pumped  out,  and  the  metallic  solution  forced  in  on  restoring 
the  air's  pressure.  Another  mode  of  effecting  a  more  entire  penetration,  con- 
sists in  rendering  the  natural  functions  of  the  tree  available  :  the  force  with 
which  the  sap  rises  from  the  roots  to  the  leaves,  is  well  known,  and  accord- 
ingly, if  a  tree  in  full  leaf  be  cut  through  just  above  the  root,  and  the  cut 
surface  immersed  in  the  metallic  solution,  this  will  be  carried  upwards  and 
transmitted  even  to  the  smaller  branches.  Even  a  hole  bored  into  the  body 
of  the  tree,  or  a  section  into  it  by  a  saw,  may  be  resorted  to  as  means  of  pre- 
senting an  absorptive  surface  to  which  the  protective  liquor  may  be  applied. 
It  has  also  been  proposed  to  apply  this  system  to  coloring  and  perfuming 
woods,  by  causing  them  to  absorb  colored  liquors,  or  metallic  solutions, 
which  by  reacting  upon  each  other  would  cause  the  deposition  of  colored 
precipitates :  Prussian  blue,  chromate  of  lead,  tannate  of  iron,  ferrocyanide 
of  copper,  and  other  similar  metallic  colors,  have  thus  been  formed  by  double 
decomposition  in  the  ligneous  texture,  and  it  has  been  similarly  pervaded  by 
certain  essential  oils.  (Boucrerie,  Ann.  Ch.  et  Ph.,  Ixxiv.  113.)  Silicious 
solutions,  and  solutions  of  certain  phosphates,  have  also  been  thus  employed, 
with  the  twofold  object  of  preservation  from  decay  and  protection  from  fire. 

Products  of  the  Decay  of  Wood. — When  wood  is  kept  dry,  or  when  sub- 
merged in  deep  water,  it  is  little  prone  to  change.  In  dry  mummy-cases,  in 
the  roofs  of  some  old  buildings,  in  the  piles  of  bridges  and  in  submerged 
forests,  wood  has  remained  for  centuries  in  good  condition  ;  but  under  the 
protracted  influence  of  air  and  moisture  it  undergoes  a  series  of  changes,  the 
rapidity  of  which,  as  well  as  the  results,  will  depend  upon  the  texture  of 
the  wood  and  the  quantity  and  nature  of  the  foreign  matters  associated  with 
it.  Some  of  these  promote  and  others  retard  decay ;  among  the  former, 
certain  azotized  or  albuminous  matters  are  apparently  most  active.     Car- 


BITUMINOUS    COAL.      LIGNITE    AND    ANTHRACITE.  60T 

bonic  acid  and  water  are  always  evolved  during  the  decay  of  wood,  and 
a  variety  of  intermediate  compounds  are  among  the  solid  products,  more 
especially  the  brown  matter  found  in  soils  or  mould,  and  to  which  the  terms 
geine,  humus,  and  ulmine,  have  been  applied.  These  or  analogous  com- 
pounds are  obtained  by  the  action  of  alkalies  upon  several  organic  principles 
including  wood.  They  are  compounds  of  carbon,  hydrogen,  and  oxygen  in 
various  proportions,  and  may  be  regarded  as  so  many  steps  in  those  processes 
of  decomposition  in  which  wood,  by  the  loss  of  water  and  carbonic  acid  gradu- 
ally passes  into  the  modification  of  coal.  These  brown  extractive  matters 
combine  with  alkalies,  and  have  been  described  as  geic  acid  (C^oHj^OjJ, 
humic  acid  (C^oHj^O,.^),  and  ulmic  acid  (C^oH^^O^.^).  The  dark  brown  exuda- 
tion on  the  barks  of  certain  trees,  and  especially  of  the  elm,  contains  a  similar 
substance,  combined  with  potassa,  and  allied  products  have  been  found  in 
the  ferruginous  deposits  of  certain  mineral  waters,  and  have  been  termed 
Crenic  and  Apocrenic  acids. 

Coal. — Pit  coal  and  many  of  its  allied  products  are  obviously  of  veget-able 
origin ;  but  the  circumstances  under  which  they  have  been  formed,  and 
deposited  in  their  present  localities,  are  very  imperfectly  understood. 

Lignite,  as  its  name  imports,  generally  retains  its  ligneous  structure;  some- 
times it  resembles  indurated  peat,  and  contains  brown  extractive  matter  and 
resin.  When  heated,  it  exhaleaw,  bituminous  odor,  and  burns  with  a  bright 
flame.     It  is  found  in  tertiary  strata. 

Bituminous  coal  constitutes  our  common  fuel ;  but  there  are  many  varie- 
ties of  it,  differing  in  color  and  structure,  in  their  manner  of  burning,  and  in 
the  quality  and  quantity  of  the  gas  and  coke  which  they  yield  on  distillation 
(see  p.  271).  The  geological  position  in  which  this  coal  occurs,  is  between 
the  New  and  the  Old  Red  Sandstones,  forming  the  coal-measures. 

Cannel  coal  and  Parrot  coal  are  distinguished  by  their  slaty  and  conchoidal 
fracture,  their  clean  dull  surface,  and  by  their  yielding  a  large  proportion  of 
gas  of  high  illuminating  power,  and  leaving  about  half  their  weight  of  coke. 
There  is  a  variety  of  coal  intermediate  between  that  which  is  highly  bitumi- 
nous and  the  anthracites,  called  steam  coal  and  Welsh  coal:  it  burns  well, 
does  not  cake,  gives  little  smoke,  and  yields  a  porous  coke.  It  is  a  useful 
fuel  for  many  closed  stoves,  when  the  draught  is  insufficient  for  the  combus- 
tion of  anthracite. 

Anthracite  (av^pal,  coal)  is  more  difficult  of  combustion,  yields  little  vola- 
tile matter,  and  therefore  burns  without  flame.  Some  of  its  varieties  are 
very  compact,  and  split  into  small  fragments  when  heated. 

The  essential  ultimate  constituents  of  coal  are  carbon  and  hydrogen  ;  but 
it  also  includes  oxygen,  nitrogen,  sulphur,  and  various  mineral  matters,  con- 
stituting the  incombustible  residue  or  ash,  which  is  chiefly  composed  of  sili- 
cious  matter  and  unburnt  charcoal,  with  carbonate  of  lime  and  oxide  of  iron. 
100  parts  of  several  varieties  of  coal,  previously  dried  at  212°,  gave  the  fol- 
lowing results.     (Yaux,  Journ.  Chem.  Soc,  i.  328.) 


Carbon 
Hydrogen  . 
Oxygen 
Nitrogen    . 
Sulphur     . 
Ash 

Newcastle. 
.     81-41 
.       5-83 
.       7-89 
.       2-05 
.       0-75 
.       2-07 

Staffordshire. 

...  78-57 
5-23 

...  12.88 
1-84 
0-89 
1-03 

Wigan  Cannel. 
...       80-07      ... 
5-53       ... 
8-09       ... 
2-12       ... 
1-50       ... 
2-70       ... 

1-276     ... 

Anthracite. 
90-89 
3-28 
2-97 
0-83 
0-91 
1-61 

Specific  gravity . 

.       1-276 

1-278 

1-392 

Approximate  formula    C27H,,02 

C26H.0O3 

C^oHgO 

608  BITUMEN.      ASPHALT.      PETROLEUM.       ROCK-OIL. 

Bitumen,  Asphalt,  Petroleum. — These,  and  several  allied  substances, 
are  closely  connected  with  coal,  in  reference  especially  to  the  products  of 
their  destructive  distillation.  Many  of  the  varieties  of  coal  may  be  regarded 
as  carbonaceous  matters  impregnated  with  bitumen,  and  the  Bituminous 
Schists  are  earthy  compounds,  chieiy  alumino-silicious,  similarly  impreg- 
nated. The  bituminous  shales  of  Dorsetshire,  and  of  Bathgate,  near  Edin- 
burgh {the  Torhane  Mineral),  leave  little  carbonaceons  matter,  and  nothing 
in  the  form  of  coke,  but  from  20  to  25  per  cent,  of  earthy  matter  or  ash. 
When  distilled  in  close  vessels,  their  volatile  products,  on  the  other  hand, 
are  very  abundant,  and  vary  in  character  and  composition  with  the  tempera- 
ture to  which  they  are  subjected.  If  rapidly  distilled  at  a  high  temperature, 
gases  of  high  illuminating  power  abound;  if  at  a  lower  temperature,  liquid 
oily  hydrocarbons  in  great  variety  are  obtained,  and  among  these,  paraffine 
and  its  congeners. 

Asphalt,  or  Mineral  Pitch,  in  its  purest  form,  may  be  taken  as  the  type 
of  the  Bitumens :  it  occurs  on  the  shores  of  the  Dead  Sea  (the  Asphaltic 
Lake^,  in  Barbadoes  and  Trinidad,  in  Albania,  and  nearly  pure  at  Coxitarabo 
in  South  America.  It  formed  a  leading  ingredient  in  the  celebrated  Greek 
fire  of  the  middle  ages.  Pure  asphalt  is  black,  or  dark  brown,  has  a  slight 
bituminous  odor,  a  resinous  fracture;  sp.  gr.  1  to  TI ;  it  softens  when 
heated,  and  burns  with  a  smoky  flame.  Itois  insoluble  in  water,  sparingly 
so  in  alcohol,  but  abundantly  in  ether  and  in  benzole.  Asphalts  and  bitu- 
mens of  various  degrees  of  purity,  and  from  various  sources,  are  used  in 
combination  with  lime,  chalk,  sand,  &c.,  for  pavements  and  cements.  Two 
of  the  proximate  components  of  asphalt  have  been  termed  Asphaltene 
(0«H3,0«)  and  Petrolene  (C,oH,,). 

Petroleum,  Naphtha.  Rock- Oil.  Mineral  Tar.  (Cj^H^^). — Inflammable 
oily  bodies,  issuing  often  in  large  quantities  from  fissures  in  connection  with 
coal  strata,  and  in  other  localities,  have  been  long  known.  The  purer  varie- 
ties are  nearly  colorless,  and  burn  without  residuum  {native  naphtha).  Others 
are  brown,  and  leave  asphalt  when  distilled.  The  Burmese  petroleum  or 
naphtha  has  long  been  celebrated :  it  issues  from  a  sandy  loam  resting  upon 
bituminous  shale  and  coal  strata :  it  is  used  in  lamps,  and  mixed  with  earth 
for  fuel.  Enormous  quantities  of  rock-oil  have  been  lately  imported  from 
the  United  States  and  Canada.  In  the  former  country,  according  to  Mr. 
Hunt,  the  wells  are  chiefly  found  in  New  York,  Pennsylvania,  and  Ohio. 
Those  of  Mecca  (Ohio)  have  been  sunk  from  30  to  200  feet  in  a  sandstone, 
which  is  saturated  with  the  oil.  Of  200  wells  which  have  been  sunk,  a  dozen 
or  more  yield  from  five  to  twenty  barrels  of  oil  daily.  The  wells  of  Pennsyl- 
vania vary  in  depth  from  70  to  300  feet,  and  the  petroleum,  or  rock-oil,  is 
met  with  throughout.  The  oil  varies  considerably  in  color  and  thickness. 
Its  sp.  gr.  is  from  0"830  to  0'890.  The  oil-wells  in  the  United  States  are 
for  the  most  part  sunk  in  the  sandstones  of  the  Devonian  series ;  but  those 
of  western  Virginia  and  southern  Ohio  rise  through  the  coal-measures  which 
overlie  the  Devonian  strata.  In  Canada  the  oil  is  found  in  shales  and  lime- 
stones. At  one  of  the  Canadian  wells  the  oil  rises  from  a  depth  of  234  feet 
at  the  rate  of  25  barrels,  or  about  1000  gallons,  per  hour,  and  much  of  it  is 
allowed  to  run  to  waste  from  the  inadequacy  of  the  supply  of  barrels,  and 
of  other  means  to  store  it.  At  another  well  the  supply  is  alleged  to  have 
poured  forth  about  70,000  gallons  a  day  uninterruptedly,  except  when  the 
opening  was  plugged,  for  several  months.  A  third  well  exists  of  similar  capa- 
city;  and  the  other  wells  which  require  labor  or  machinery  for  pumping  are 
innumerable.     The  American  rock-oil  may  be  regarded  as  a  compound  of 


COAL-TAR.      NAPHTHA        NAPHTHALINE.  609 

various  hydrocarbons  boiling:  at  different  temperatures,  and  possessing  differ- 
ent degrees  of  inflammability.  Some  of  these  oils  evolve  a  vapor  which  is 
exceedingly  inflammable  and  dangerously  explosive  when  mixed  with  air. 
An  act  of  the  legislature  prevents  the  storage  of  petroleum,  except  in  limited 
quantities,  where  it  is  proved  that  it  is  liable  to  give  off  a  vapor  at  or  below 
100°,  which  will  ignite  on  the  application  of  flame  and  produce  combustion 
of  the  liquid.  This  kind  of  inflammable  oil  has  been  sold  for  the  purposes  of 
burning  in  lamps,  and  owing  to  the  evolution  of  inflammable  vapor  has  led 
to  fatal  accidents.  An  oil  is  easily  tested  by  placing  a  portion  in  a  beaker 
immersed  for  a  few  minutes  in  water,  at  a  temperature  of  100°,  and  bring- 
ing a  lighted  taper  near  the  mouth  of  the  beaker.  If  the  vapor  should 
ignite,  and  cause  the  ignition  of  the  liquid  oil,  it  is  exceedingly  dangerous, 
and  it  can  hardly  be  regarded  as  reasonably  safe,  if  it  evolves  an  inflammable 
vapor  at  this  temperature,  although  the  flame  may  not  be  communicated 
to  the  liquid  oil  below.  As  a  rule,  all  oils  intended  for  burning  should  only 
be  capable  of  burning  by  the  aid  of  a  wick.  All  these  mineral  oils,  when 
subjected  to  fractional  distillation,  yield  products  more  or  less  resembling 
those  similarly  obtained  from  coal  naphtha,  and  are  available  for  similar  com- 
mercial purposes.  A  heavy  inflammable  liquid  distilled  from  Petroleum  is 
known  under  the  name  of  Kerosine. 

Coal-tar,  as  produced  in  the  gas-factories,  is  a  very  complex  substance  : 
it  is  always  alkaline,  from  the  presence  of  ammonia :  it  contains  aniline  and 
numerous  other  bases,  as  well  as  carbolic  and  acetic  acids.  When  distilled, 
fetid  ammoniacal  compounds  pass  over,  and  a  hght  oil  {Coal  naphtha),  suc- 
ceeded by  small  portions  of  a  heavier  oil  (dead  oil),  containing  a  little 
paraffine,  and  by  naphthaline :  the  residuary  pitch,  or  asphalt,  is  used  for 
common  black  varnishes.  By  a  careful  fractional  distillation  of  the  rectified 
naphtha,  the  following  products  are  obtained — 1,  An  oil  of  an  alliaceous 
odor,  boiling  between  150°  and  160°;  2,  an  oil  boiling  at  170°,  identical 
with  benzole,  CjaHg ;  3,  an  oil  consisting  chiefly  of  toluole,  C„Hg,  boiling  at 
240° ;  4,  an  oil  boiling  between  240°  and  290°,  having  the  proportions  of 
Cumole,  C,sHj2 ;  and  5,  an  oil  between  330°  and  340°,  and  resembling 
Cymole,  CgoHj^  (Mansfield,  Quarterly  Journ.  Chem.  Soc./\.  252).  Naphtha 
therefore  is  a  mixture  of  several  apparently  definite  hydrocarbons.  Amongst 
them  benzole  is  the  most  important. 

Naphthaline  (CgoHg). — In  a  pure  state  this  is  a  white  substance  in  lami- 
nated crystals,  obtained  by  subjecting  coal-tar  to  distillation.  It  passes 
over  after  the  coal-oils,  and  is  produced  when  the  vapors  of  coal-tar  are  passed 
through  a  red-hot  tube.  It  may  be  purified  by  sublimation  with  powdered 
charcoal.  Naphthaline  has  a  faint  odor,  which  has  been  compared  to  that 
of  the  narcissus,  and  a  slightly  aromatic  taste;  its  sp.  gr.  is  1*05;  it  is 
unctuous  to  the  touch,  and  evaporates  slowly  at  common  temperatures ;  it 
fuses  at  about  176°,  and  crystallizes  as  it  cools;  it  boils  at  420°;  the  sp. 
gr.  of  its  vapor  is  4*5.  It  burns  with  a  lurid  smoky  flame.  It  is  insoluble 
in  water,  but  alcohol,  ether,  and  some  of  the  oils  dissolve  it  readily  ;  it  is 
deposited  from  its  alcoholic  solution  in  lamellar  iridescent  crystals.  Tbe 
alkalies  have  no  action  upon  it. 

When  gently  heated  with  sulphuric  acid  it  produces  a  red  crystalline  com- 
pound which  when  saturated  with  carbonate  of  baryta,  yields  insoluble  sul- 
phate, and  a  soluble  sulphonaphthalate  of  baryta.  The  formula  of  sulpho- 
naphthalic  acid  is  supposed  to  be  HO,C2oH7S,05-  Naphthaline  combines 
with  chlorine,  producing  two  chlorides,  Cj^HgCl.,,  and  CaoH^Cl,.  the  properties 
and  reactions  of  which  have  been  studied  by  Laurent :  it  also  combines  with 
39 


610  BENZOLE.   CARBOLIC  ACID  OR  PHENOL. 

bromine.  From  these  chlorides  and  bromides  a  numerous  series  of  substitu- 
tion-compounds have  been  derived.  By  the  protracted  action  of  nitric  acid 
on  naphthaline,  naphthalic  or  pthalic  acid  is  formed  ^{'2{M0),C^^lfi^), 
which  when  distilled  with  lime  yields  benzole  and  carbonate  of  lime.  This 
acid  is  also  one  of  the  products  of  the  action  of  nitric  acid  on  alizarine. 

Paranaphthaline. — Under  this  terra  Dumas  and  Laurent  {Ann.  Gh.  et 
Ph.,  1,  187)  have  described  a  hydrocarbon  resembling?  naphthaline,  but  yield- 
ing a  vapor  having  the  density  of  6*78.  Paranaphthaline  is  less  volatile 
than  naphthaline,  and,  therefore,  when  coal-tar  is  distilled,  it  is  among  the 
latter  products.  According  to  Reichenbach  {Poggend.  Ann.,  xxviii.  484), 
paranaphthaline  is  a  mixture  of  naphthaline  and  paraffine.  The  term  anthra- 
cene has  been  applied  to  paranaphthalilie,  and  it  has  been  represented  as 
CgoHjg.  Among  the  last  portions  of  the  distillation  of  coal-tar,  a  yellow 
crystalline  solid  is  found,  fusing  at  455°,  and  insoluble  in  most  liquids  ;  it 
has  been  termed  chrysene,  and  its  formula  is  said  to  be  CiaH^ :  it  is  accompa- 
nied by  a  more  fusible  substance,  pyrene  =C3oH^. 

Benzole  (Ci^Hg) ;  Benzine. — Benzole  was  first  discovered  by  Faraday,  in 
the  products  of  the  destructive  distillation  of  whale-oil ;  and  Mitscherlich 
obtained  it  by  heating  benzoic  acid  with  excess  of  hydrate  of  lime ;  but  it  is 
now  procured  from  coal  naphtha,  the  more  volatile  products  of  which  when 
cooled  to  32°,  deposit  it  in  a  solid  form.  It  fuses  at  40°,  boils  at  170°,  and 
burns  with  a  very  smoky  flame.  It  is  insoluble  in  water,  but  soluble  in  alcohol 
and  in  ether ;  it  dissolves  fats  and  oils,  and  is  a  useful  solvent  of  wax, 
caoutchouc,  gutta  percha,  sulphur,  and  numerous  resins. 

When  benzole  is  exposed  to  sunlight  in  contact  with  chlorine,  it  produces 
a  crystalline  chlorobenzole,  =Cj2HgClg;  and  a  hromohenzole,  =Ci4HgBrg,  may 
be  similarly  obtained.  With  anhydrous  sulphuric  acid  benzole  produces  a 
crystallizable  compound,  which,  acted  upon  by  water,  yields  sulphobenzide, 
=013113803,  in  which  therefore  an  atom  of  hydrogen  is  replaced  by  an  atom 
of  sulphurous  acid  :  suJphobenzolic  acid,  =012115803 -f  HO, SO3  is  at  the  same 
time  formed  :  but  amongst  these  reactions,  those  with  nitric  acid  are  the  most 
interesting.  If  benzole  is  gradually  added  to  red  fuming  nitric  acid,  gently 
heated,  there  is  a  considerable  action,  and  on  diluting  the  product,  a  heavy 
yellow  oil  separates,  which  is  nitrobenzole,  =(j^^fi^  \  it  boils  at  415°,  and 
may  be  distilled  without  decomposition  ;  it  smells  like  bitter-almond  oil,  tastes 
sweet,  and  is  used  by  perfumers  and  confectioners  under  the  name  of  essence 
of  Mirbane,  or  bitter  almonds.  When  an  alcoholic  solution  of  nitrobenzole 
is  mixed  with  caustic  potassa,  and  distilled,  a  red  oily  liquid  passes  over, 
which  deposits  crystals  of- azobenzole  (O^^H^N)  ;  the  liquid  contains  aniline. 
By  the  action  of  a  mixture  of  nitric  and  sulphuric  acids  upon  benzole,  a 
crystalline  product,  binitrobenzole,  is  obtained,  =:C^fifiJl^ci.  I"  these 
derivatives  of  benzole,  one  and  two  atoms  of  its  constituent  hydrogen  are 
respectively  replaced  by  one  and  two  atoms  of  NO^  (p.  559).  M.  Berthelot 
has  succeeded  in  producing  benzole  synthetically  from  acetylene  (O^Hj, 
with  which  it  is  isomeric.  In  passing  acetylene  through  a  red-hot  tube,  he 
obtained,  by  condensation,  a  yellowish-colored  liquid,  more  than  one-half  of 
which  was  benzole.  He  therefore  regards  benzole  as  triacetylene  3C^H2= 
CjaHg.  The  fact  is  interesting,  inasmuch  as  acetylene  may  be  produced  by 
the  direct  union  of  carbon  and  hydrogen. 

Carbolic  Acid.  Phenol,  Phenyh'c,  or  Phenic  Acid  {C^^I{QO^,='RO,G^,^ 
H^O)  — When  those  portions  of  the  acid  of  coal-tar  which  distil  over  between 
.300°  and  400°,  are  mixed  with  a  strong  and  hot  solution  of  caustic  potassa. 


PARAFPINE.  611 

a  crystalline  mass  is  obtained,  which  is  resolved  by  the  action  of  water  into 
a  light  oil,  and  a  heavy  alkaline  liquid  ;  when  the  latter  is  neutralized  by 
hydrochloric  acid,  the  impure  carbolic  acid  separates  in  the  form  of  a  light 
oil :  it  requires  to  be  distilled  off  chloride  of  calcium,  exposed  to  a  low  tem- 
perature, and  freed  from  the  remaining  liquid.  The  pure  acid  forms  a  color- 
less deliquescent  crystalline  mass,  which  fuses  at  95°,  and  passes  into  vapor 
at  37 0°.  It  has  a  smoky  odor,  an  acrid  taste,  and  the  antiseptic  properties 
of  kreasote.  It  is  much  used  as  a  deodorizer.  It  does  not  redden  litmus, 
but  produces  a  transient  greasy  stain  upon  the  paper.  Its  sp.  gr.  is  1062. 
When  heated  in  a  sealed  tube  with  ammonia  it  yields  aniline  and  water : 
CiA02+NH3=C,,H,N  +  2HO).  When  carbolic  acid  is  distilled  with 
perchloride  of  phosphorus,  one  of  the  results  is  chloride  of  phenyle  (C^^Hfil), 
a  fragrant  liquid,  boiling  at  277°,  and  a  crystallizable  phosphate  of  phenyle 
is  at  the  same  time  formed.  A  numerous  class  of  substitutional  phenylic 
compounds,  in  which  chlorine,  bromine,  and  nitrous  acid  replace  one  or 
more  of  the  hydrogen  atoms,  has  also  been  formed  ;  they  mostly  constitute 
monobasic  acids,  and  many  of  their  salts  are  of  a  definite  character. 

Paraffine  (CH)  (parum  affinis)  was  originally  discovered  by  Reicben- 
bach,  among  the  products  of  the  distillation  of  wood-tar,  but  it  has  more 
recently  been  abundantly  obtained  from  the  oils  derived  from  the  distillation 
of  bituminous  schists,  and  other  bituminiferous  minerals :  it  exists  in  large 
proportion  in  some  petroleums,  in  that  of  Rangoon  :  it  is  also  contained,  in 
small  qantities,  in  common  coal-tar.  It  is  a  crystalline  solid,  without  taste, 
smell,  or  color.  It  is  not  greasy ;  its  sp.  gr.  is  about  0*87  ;  it  melts  at  112°, 
and  may  be  distilled. over  unchanged  at  a  higher  heat.  Its  name  is  derived 
from  its  inertness,  or  want  of  affinity,  for  it  resists  the  action  of  acids,  alkalies, 
and  chlorine  ;  but  it  unites  by  fusion  with  stearine,  stearic  acid,  cetine,  wax, 
and  resin,  and  it  dissolves  in  naphtha,  benzole,  oil  of  turpentine,  and  chloro- 
form :  it  is  soluble  in  hot  ether,  but  the  solution  concretes  on  cooling ;  it 
also  separates  in  crystalline  flakes  from  its  solution  in  hot  alcohol.  The 
density  of  its  vapor  and  its  true  composition  have  not  been  satisfactorily 
determined,  but  it  is  a  hydrocarbon  of  the  olefiant  type.  The  substance 
known  as  Fossil  wax^  and  tallow,  Ozohei^te,  and  Hacheiine^  which  occur  in 
the  coal-formations,  closely  resemble  paraffine. 

The  product  known  as  Paraffine  Oil  is  one  of  the  associated  hydrocarbons 
contained  in  the  least  volatile  portions  of  the  bituminous  oils.  Together 
with  paraffine  it  is  largely  obtained  from  the  bituminous  schists  accompanying 
the  coal-measures  at  Bathgate,  near  Edinburgh,  and  known  under  the  name 
of  Boghead  Cannel  mineral.  This  valuable  substance  yields  nearly  three- 
fourths  its  weight  of  volatile  matters,  leaving  an  aluminous  ash,  and  some- 
times not  more  than  6  per  cent,  of  carbon  ;  and  no  real  coke,  in  which  respect 
it  is  eminently  distinguished  from  ordinary  coal,  which  yields  from  50  to  60 
per  cent,  of  porous  coke,  and  only  from  1  to  2  per  cent,  of  an  ash  contain- 
ing little  or  no  alumina.  When  wetted,  the  mineral  has  the  well-known 
earthy  smell  of  ordinary  clays,  and  any  hard  substance  produces  on  it  a 
brown  streak. 

The  sp.  gr.  of  the  Boghead  mineral  is  from  1  199  to  1*32.  When  dis- 
tilled at  a  high  temperature  it  produces  a  large  quantity  of  highly  illumi- 
nating gas,  and  it  is  largely  employed  for  the  making  of  gas.  When 
distilled  at  a  low  temperature  (a  low  red  heat),  it  produces  solid  and  liquid 
hydrocarbons,  and  a  smaller  proportion  of  gas.  The  following  results  were 
obtained  as  an  average  :     From  100  parts  of  the  mineral — 


612  WOOD    TAR.      KREASOTE.      EUPION. 


"^ater,  3-0  )  ^^i,.M^   > 

Oils  and  Tar,  45-9  \  Zf^^^};^,,  }  59-11 

Gas,  10-2  )  products  ; 

Coke  or  Carbon,  16*8  ^         ,.,     v 


100-0  100-00 

From  one  ton  of  this  earthy  mineral,  about  eighty  gallons  of  crude  oil  are 
obtained,  and  from  this,  57  gallons  of  refined  oil,  yielding  by  a  cooling 
process  16  pounds  of  paraffine,  and  13  pounds  of  pitch  and  tar.  The  57 
gallons  of  refined  oil,  by  further  distillation,  yield  38  gallons  of  light  oil 
fitted  for  burning,  and  19  gallons  of  a  thick  viscid  oil  employed  as  a  lubri- 
cant for  machinery. 

The  melting  point  of  paraflQne  is  so  low  that  it  too  readily  fuses,  and  it 
burns  with  a  very  smoky  flame.  It  is  not  materially  improved  in  these  re- 
spects, by  mixing  it  with  less  fusible  fat  or  wax,  for  beyond  a  certain  pro- 
portion the  compound  becomes  more  fusible  than  the  mean  would  represent. 
The  oil  requires  a  peculiar  lamp  for  its  combustion.  I^ike  other  hydrocarbon 
oils,  paraffine  oil  cannot  be  employed  for  the  manufacture  of  soap.  It  will 
not  combine  with  alkalies. 

Wood  Tar. — When  wood  is  subjected  to  destructive  distillation  as  in  the 
process  for  the  manufacture  of  gunpowder,  and  of  pyroligneous  acid,  a  large 
quantity  of  tar  is  among  the  products,  from  which,  as  well  as  from  common 
Stockholm  tar^  a  variety  of  hydrocarbons  and  oxyhydrocarbons  may  be  ob- 
tained. The  processes,  by  which  these  are  separated  and  purified,  are  mostly 
tedious  and  complicated  ;  they  have-  been  especially  de*scribed  by  Reichen- 
bach.  Paraffine  is  amongst  them  ;  but  he  has  also  discovered  several  other 
definite  compounds,  such  as  kreasote,  eupion,  tapnomor,  pittacal,  picamar^ 
and  cedriret. 

Kreasote  (xpcaj,  fleshy  aca^a,  to  preserve)  appears  to  be  the  principal 
source  of  the  peculiar  odor  and  of  the  antiseptic  and  preservative  qualities 
of  wood-smoke.  When  properly  purified  it  is  a  colorless  oily-looking  liquid 
of  great  refractive  and  dispersive  power,  of  a  penetrating  smoky  odor  and  a 
burning  taste:  itssp.gr.  is  about  1*04;  it  remains  fluid  at  17^^;  it  burns 
with  a  sooty  flame  ;  is  sparingly  soluble  in  water,  and  is  neutral  to  test-paper. 
It  dissolves  readily  in  alcohol,  ether,  benzole,  and  acetic  acid ;  and  forms  a 
crystalline  compound  with  potassa.  It  coagulates  albumen  ;  and  a  solution 
of  it,  containing  not  more  than  1  per  cent.,  preserves  meat  from  putrefac- 
tion. The  efficacy  of  crude  pyroligneous  acid,  as  a  preservative  of  provi- 
sions, and  the  peculiar  smoky  flavor  which  it  confers  upon  them,  appear  to 
be  due  to  kreasote.  It  is  an  irritant  poison  when  undiluted,  but  when  largely 
diluted  it  has  been  found  effectual  in  checking  vomiting,  and  as  an  appli- 
cation in  toothache  for  the  destruction  of  the  nerve.  It  appears  to  be  closely 
related  to  phenic  (carbolic)  acid,  and  the  formula  C^eHioOa  has  been  assigned 
to  it. 

EuPiON  is  a  light  oil  of  a  peculiar  greasy  character  (fv,  and  ftiutv,  greasy) 
resembling  paraffine  oil.  It  has  the  formula  CJIq,  and  is  regarded  by  Frank- 
land  as  hydride  of  amyl,  C^oHj^.H.  Kapnomor  (xanvbi,  smoke,  fioipa  part) 
is  a  pungent  oil,  sp.  gr.  0*9.  The  formula  CgoH^^Og  has  been  assigned  to 
it.  Pittacal  is  characterized  by  affording  a  blue  color  with  baryta-water. 
Picamar  appears  to  be  the  hitter  principle  of  wood  tar,  and  is  contained  in 
the  heavy  oil.  Cedriret  is  a  crystallizable  product,  soluble  in  kreasote,  but 
insoluble  in  water  and  alcohol. 


ESSENTIAL    OILS.      THEIR    USES.  613 

Picric  Acid.  Carhazotic  Acid  (Ci3Ha(N0,)30,H0).— This  is  a  solid 
crystalline,  and  of  an  intensely  bitter  taste.  It  was  formerly  procured  by 
the  action  of  nitric  acid  upon  indigo,  and  it  is  also  a  product  of  the  reaction 
of  that  acid  on  silk,  salicine,  and  some  resinous  substances.  It  is  now  manu- 
factured chiefly  by  boiling  carbolic  acid  in  strong  nitric  acid.  The  crystals 
are  deposited  from  the  solution  on  cooling.  They  are  of  a  pale  yellow  color, 
in  the  form  of  prisms  with  a  rhomboidal  base.  When  slowly  heated,  the 
crystals  swell,  and  the  acid  is  partly  sublimed  without  change.  If  heated 
in  air,  it  kindles  without  explosion  and  burns,  leaving  a  carbonaceous 
residue ;  when  quickly  heated  it  detonates.  Hydrochloric,  nitric,  and  sul- 
phuric acids  have  no  action  upon  it.  The  acid  is  soluble  in  alcohol,  ether, 
and  benzole.     Ether  appears  to  be  the  best  solvent. 

The  crystals  are  not  very  soluble  in  water,  requiring  80  parts  of  cold 
water  for  their  solution.  They  nevertheless  give  to  the  water  an  intense 
yellow  color,  even  when  much  diluted.  The  acid  has  remarkable  tinctorial 
properties,  and  is  used  as  a  yellow  dye.  It  stains  all  nitrogenous  organic 
matter  yellow,  and  is  thus  employed  as  a  dye  for  silk  or  woUen.  It  does  not 
give  a  permanent  color  to  cotton  or  flax ;  and  it  thus  serves  to  detect  the  admix- 
ture of  cotton  with  silk.  The  article  is  plunged  into  a  strong  and  hot  solu- 
tion of  the  acid,  and  is  afterwards  washed  in  water.  The  silk  only  retains 
the  color.  The  picrate  of  potash  is  very  sparingly  soluble  in  cold  water, 
so  that  the  acid  is  sometimes  used  as  a  test  for  that  alkali. 


CHAPTER  L. 


ESSENTIAL  OILS.     CAMPHOR.     RESINS.     AMBER.     CAOUT- 
CHOUC.   aUTTA  PERCHA. 

Essential  Oils. 

The  essential  or  volatile  oils  may  be  regarded  as  the  odorous  principles  of 
vegetables,  and  are  generally  obtained  by  distilling  the  plant  with  water, 
either  in  its  fresh,  salted,  or  dried  state.  In  some  cases  the  oils  are  pressed 
out  of  the  cellular  structure,  as  from  orange  and  lemon  peel.  They  are 
obtained  from  all  parts  of  plants,  though  usually  most  abundant  in  the  leaves 
and  flowers ;  and  they  sometimes  differ  in  different  parts  of  the  same  plant ; 
thus,  with  regard  to  the  orange-tree,  the  leaves,  flowers,  and  fruit,  each  yield 
a  distinct  oil.  Some  of  them  are  so  delicate  and  evanescent  as  to  require  a 
peculiar  mode  of  treatment,  such  as  those  of  the  flowers  of  jasmine,  tuberose, 
narcissus  and  mignonette  :  these  flowers  are  stratified  with  layers  of  cotton, 
or  wool,  imbued  with  some  inodorous  fixed  oil,  which  by  slight  pressure 
absorbs  the  perfume  of  the  flowers.  When  the  oil  is  saturated  with  the 
essence,  it  is  digested  in  alcohol,  which  abstracts  the  essential  from  the  fixed 
oil,  and  an  odoriferous  essence  is  obtained.  Sometimes  the  cotton  is  distilled 
with  water  or  alcohol  to  separate  the  odorous  essence,  but  the  fragrance  is 
always  more  or  less  impaired  by  these  processes.     {See  Piesse,  On  Perfumes.) 

The  essential  oils  are  applied  to  many  useful  purposes ;  some  in  the  manu- 
facture of  paints  and  varnishes,  some  for  burning  in  lamps  ;  others  in  pharmacy 
and  medicine,  and  others  in  perfumery.  They  are  mostly  ready  formed  in 
the  plant,  but  they  are  in  some  cases  generated  by  the  action  of  water  upon 
peculiar  principles,  as  in  the  production  of  bitter-almond  oil  j  and  there  are 


614  ADULTERATIONS.      CLASSIFICATION. 

a  few  instances  of  their  artificial  production,  as  in  that  of  oil  of  spircea  by 
the  oxidation  of  salicine.  When  fresh  and  pure,  these  oils  are  mostly  colorless, 
or  nearly  so  ;  a  few  are  green  or  blue,  and  some,  after  having  acquired  color, 
lose  it  under  the  influence  of  li^ht.  Their  odors  resemble  those  of  the  plants 
yielding  them,  but  are  less  agreeable,  partly  in  consequence  of  concentration, 
for  they  become  more  pleasant  when  diffused  in  the  air,  or  attenuated  by 
solution  in  some  inodorous  vehicle.  Their  odors  arS  also  influenced  by  their 
chemical  relations  to  air  and  water :  there  are  some,  such  as  those  of  turpen- 
tine, lemons,  and  juniper,  which,  when  distilled  off  quicklime,  out  of  contact 
of  air  are  nearly  inodorous,  but  which  acquire  their  characteristic  odors 
when  spread  upon  paper. 

The  sp.  gr.  of  the  essential  oils  fluctuates  between  0*840  and  1-100,  and 
when  subjected  to  a  careful  fractional  distillation,  they  are  mostly  resolvable 
into  products  differing  in  sp.  gr.  and  in  composition  ;  one  of  which  is 
frequently  a  hydrocarbon,  and  the  other  an  oxyhydrocarhon,  which  is  some- 
times concrete,  constituting  a  species  of  camphor.  The  terras  elaioptene 
and  stearoptene  have  been  applied  to  these  liquid  and  solid  products  (from 
fXatov,  oil,  or  atiap,  fat,  and  Titfjvhe,  volatile).  Their  boiling  points  are  very 
variable,  and  so  are  the  temperatures  at  which  they  congeal,  these  being 
often  dependent  upon  the  relative  proportions  of  their  component  oils. 
They  are  sparingly  soluble  in  water,  to  which,  as  in  the  medicated  waters 
of  the  Pharmacopoeia,  they  communicate  odor  and  flavor  ;  most  of  them  are 
copiously  soluble  in  absolute  alcohol  and  in  ether,  and  in  fixed  oils  and 
liquid  hydrocarbons.  In  consequence  of  the  high  price  of  many  of  these 
oils,  they  are  sometimes  adulterated  with  alcohol,  with  fixed  oils,  or  with 
cheaper  essential  oils.  Alcohol  may  generally  be  separated  by  shaking  the 
adulterated  oil  with  water,  and  its  quantity  determined  by  the  diminution 
in  the  bulk  of  the  original  oil ;  it  may  also  be  abstracted  by  fused  chloride 
of  calcium.  Moreover  the  pure  volatile  oils  dissolve,  for  the  most  part,  in 
the  fixed  oils,  without  interfering  with  their  transparency ;  but  when  adul- 
terated with  alcohol  they  produce  turbidness.  The  admixture  of  a  Jixed  oil 
is  shown  by  the  greasy  stain  which  remains  on  evaporating  a  drop  of  the  oil 
before  the  fire,  from  a  piece  of  blotting-paper :  some  of  the  genuine  oils 
leave  a  stain,  but  it  is  rather  resinous  than  greasy,  and  admits  of  being  written 
upon  with  a  pen  and  ink,  or  removed  by  alcohol ;  the  feel  of  the  fixed  oil 
between  the  finger  and  thumb  is  also  greasy,  and  when  it  is  distilled  with 
water,  the  fixed  oil  remains  in  the  retort.  The  adulteration  of  a  high  priced 
with  a  cheap  essential  oil  is  often  difficult  of  detection,  and  requires  experi- 
ence in  the  odor  and  qualities  of  the  genuine  article.  When  oil  of  turpentine 
is  so  used,  its  characteristic  odor  is  often  covered,  until  the  adulterated  oil 
is  dissolved  in  a  little  alcohol,  and  water,  added,  when  the  odor  and  flavor 
of  the  turpentine  are  manifest.  The  taste  of  the  oil  in  these  cases  is  often 
a  good  guide ;  oil  of  lemons  is  frequently  adulterated  with  turpentine,  but 
its  taste  is  very  different  from  that  of  the  genuine  oil.  The  difference 
between  the  indices  of  refraction  of  the  adulterated  and  genuine  oils  has 
been  proposed  as  a  means  of  detecting  falsifications,  and  Dr.  Wollaston 
suggested  an  instrument  for  the  purpose  (Phil.  Trans.,  1802);  but  the 
refractive  power  of  the  genuine  oil  varies  too  much  to  render  this  method 
satisfactorily  available. 

The  action  of  chlorine,  bromine,  and  iodine  upon  the  essential  oils,  gives 
rise  to  an  infinity  of  new  compounds,  resulting  from  the  substitution  of  one 
or  more  atoms  of  these  elements,  for  a  corresponding  number  of  the  hydro- 
gen atoms  of  the  oil ;  and  in  some  cases,  direct  combinations  ensue.  With 
some  of  them  iodine  causes  fulraination.  Nitric  acid  acts  violently  upon 
most  of  them ;  they  are  more  quietly  decomposed  by  sulphuric  acid.     They 


ESSENTIAL    OILS.      OX YH YDROCARBONS.  '615 

are  not  saponifiable  by  the  alkalies.  When  their  vapors  are  passed  over 
heated  potassa,  or  soda,  hydrogen  is  sometimes  evolved,  and  an  acid  cora- 
poand  with  the  base  is  formed. 

For  the  purpose  of  chemical  description,  the  essential  oils  may  be  arranjred 
under  three  divisions:  1,  Those  composed  of  carbon  and  hydrogen;  2,  of 
carbon,  hydrogen,  and  oxygen;  3,  those  containing  sulphur. 

1.  Hydrocarbons. — The  elementary  composition  of  this  group  may  be 
represented  by  C^H^ :  it  includes  many  isomeric  compounds  of  which  oil  of 
turpentine  may  be  assumed  as  the  type.  Oil  of  turpentine,  G^K^^  {camphene  ; 
camphyle),  is  obtained  by  distilling  the  turpentine  of  commerce  with  water. 
There  are  many  varieties  of  turpentine ;  but  that  principally  resorted  to  as 
a  source  of  the  oil,  is  derived  from  different  species  of  pinus,  and  chiefly 
imported  from  North  America.  The  first  product  is  purified  by  redistilla- 
tion. The  original  turpentine  is  thus  resolved  into  the  volatile  oil,  and  into 
residuary  resin  ;  which,  when  retaining  a  portion  of  water,  is  known  as  yellow 
rosin;  or,  as  colophony,  after  fusion  at  a  higher  temperature. 

Oil  of  turpentine,  or  turps,  as  the  common  oil  is  usually  called,  is  a  color- 
less and  very  mobile  liquid;  sp.  gr.  0*8()5,  boiling  at  312°,  and  yielding  a 
vapor  of  the  density  of  4'764  (p.  557).  It  has  a  characteristic  odor,  a  hot 
pungent  taste,  and  burns  with  a  large  sooty  flame :  it  is  almost  insoluble  in 
water,  but  soluble  to  some  extent  in  alcohol  and  in  ether.  Under  the  name 
of  Camphene  it  was  at  one  time  largely  used  as  a  source  of  light,  and  when 
carefully  burned  in  a  properly  constructed  lamp,  gives  a  brilliant  light;  but 
if  the  oil  is  not  fresh,  and  h^s  been  exposed  to  air,  it  clogs  the  wick,  and 
smokes.  Its  use  has  lately  been  superseded  by  rock-oil  and  other  modifica- 
tions of  naphtha.  When  oil  of  turpentine  which  has  been  agitated  with 
water  is  kept  for  some  time  at  a  temperature  of  120°,  it  deposits  crystals 
^CaoHjg-f  HO.  When  the  oil  and  water  are  left  together  at  common 
temperatures,  another  hydrate,  =C2„H^6,6HO,  is  produced.  A  crystalline 
compound  of  hydrochloric  acid  and  oil  of  turpentine  has  long  been  known 
under  the  name  of  artificial  camphor  =G,^B.^q-\-11CI  Corresponding  hydro- 
bromates  and  hydriodates  have  also  been  formed.  The  decomposition  of 
these,  and  other  terebinthic  compounds,  has  led  to  the  discovery  of  several 
isomeric  hydrocarbons,  principally  distinguished  by  their  action  on  polarized 
light,  some  causing  left-handed  and  others  right-handed  rotation  of  the  ray. 
Oil  of  turpentine  is  a  great  solvent  of  ozone.  When  exposed  to  air  it 
absorbs  oxygen  and  acquires  some  of  the  properties  of  ozone.  Thus  it  will 
bleach  organic  colors  and  oxidize  iodide  of  potassium,  setting  free  iodine. 

The  oils  of  lemon,  hergamot,  orange  Juniper,  and  many  others,  are  isomeric 
with  turpentine  oil. 

2.  OxYHYDROCARBONS. — The  essential  oils  containing  oxygen  are  very 
numerous,  and  include  Camphor  and  its  modifications.  Bitter-almond  oil 
and  Spircea  oil  are  elsewhere  noticed,  and  there  are  others  which  have  been 
the  subjects  of  minute  investigation.  Some  of  these,  when  distilled,  are 
separable  into  a  more  volatile  hydrocarbon  and  a  less  volatile  oxyhydro- 
carbon,  but  the  nomenclature  applied  to  these  compounds  is  often  confused 
and  unsatisfactory  ;  in  some  cases  a  hydrocarbon,  and  in  others  an  oxyhydro- 
carbon,  having  been  assumed  as  the  radical  of  the  series. 

Oil  of  Cumin,  for  instance,  may  be  resolved  into  a  hydrocarbon  =2oHi4, 
which  has  been  called  Cymol,  and  an  oxyhydrocarbon  =^G.^^B.,p.,  called 
Cuminol  But  cuminol  has  also  been  represented  by  the  formula  C^oH,, 
O  -f-H,  and  has  been  described  as  a  hydride  of  a  radical  called  Cumyle,  C,o 
H  O  .     Oil  of  Aniseed  is  similarly  separable  into  a  hydrocarbon,  isomeric 


616  ESSENTIAL    OILS    CONTAINING    SULPHUR. 

with  oil  of  turpentine,  and  an  oxyhydrocarbon  (the  concrete  portion  of  the 
oil),  C20HJ2O2;  but  this  is  sometimes  represented  as  containing  a  radical 
=  CjgH70^,  to  which  the  terra  anisyl  has  been  applied,  and  from  which  a 
Toluminous  series  of  substitution  and  other  compounds  has  been  obtained. 

Analogous  radicals  or  bases  have  been  obtained  from  many  of  the  other 
essential  oils,  or  have  been  assumed  as  existing  in  them  ;  and  it  has  often 
been  found  convenient,  in  theory,  to  represent  the  oils  as  hydrides  of  these 
radicals ;  thus,  oil  of  cinnamon  is  represented  as  a  hydride  of  chinamyl, 
by  the  formula  CisHyOg+H,  another  of  its  products,  cinnamic  acid,  being 

Camphor  (CgoH^gOJ. — Common  camphor  is  the  produce  of  the  Laums 
Camphora  of  Japan,  China,  and  Java.  It  is  extracted,  by  distillation  with 
water,  from  the  roots  and  wood  of  the  tree,  and  refined  by  sublimation.  It 
is  tough,  white,  translucent,  of  a  peculiar  odor  and  flavor,  and  evaporates  at 
ordinary  temperatures,  gradually  subliming  in  close  vessels,  and  attaching 
itself,  in  hexahedral  and  prismatic  crystals,  to  the  surface  most  exposed  to 
cooling.  Its  sp.  gr.  is  0*987  to  0'996*,  but  after  long  immersion  in  water, 
this  is  so  affected  by  changes  of  temperature,  that  this  substance  floats  on 
water  above  50°,  but  sinks  at  a  lower  temperature.  It  fuses  at  370°,  and 
boils  at  400°,  when  it  may  be  distilled  without  decomposition.  When  a  clean 
fragment  of  camphor  is  placed  upon  water,  it  acquires  a  rotatory  motion, 
which  is  rapid  in  proportion  to  its  smallness.  This  appears  to  depend  upon 
the  evolution  of  vapor,  and  the  reaction  of  this  upon  the  water.  The  light- 
ness of  the  camphor  and  the  absence  of  all  friction  favor  this  motion.  It 
does  not  take  place  on  water  already  saturated'with  camphor,  nor  when  any 
good  solvent  of  camphor  is  added  to  the  water.  Thus  the  motions  of  the 
fragments  are  immediately  arrested  by  the  addition  of  oil  of  turpentine  to 
the  water.  Camphor  is  so  little  soluble  in  water  that  it  requires  about  1000 
parts  for  its  solution,  but  is  very  soluble  in  alcohol,  ether,  chloroform,  acetone, 
acetic  acid,  and  sulphide  of  carbon.  It  burns  with  a  white  smoky  flame, 
depositing  much  carbon.  By  the  protracted  action  of  hot  nitric  acid  cam- 
phor is  converted  into  camphoric  acid,  CgoHj^Og  or  2(HO)CaoHj408,  which 
crystallizes  in  acicular  prisms,  rendered  anhydrous  by  sublimation,  and 
sparingly  soluble  in  water. 

A  variety  of  camphor,  known  as  Borneo  camphor,  the  produce  of  the 
Dryahalanops  Camphora,  contains  two  equivalents  more  of  hydrogen  than 
common  camphor:  it  is  associated  with  a  hydrocarbon  {Borneen)  =  Q^H^^, 
identical,  therefore,  with  oil  of  turpentine.  Camphor  is  contained  in  several 
of  the  essential  oils ;  and  substances  resembling  it  are  found  in  the  Inula 
Helenium,  in  Assarabacca,  and  in  some  of  the  Anemones. 

3.  Essential  Oils  containing  Sulphur, — There  are  several  essential  oils 
which  contain  nitrogen  and  sulphur,  amongst  which  the  oil  of  black  mustard- 
seed,  garlic,  assafcetida,  and  horseradish  are  the  most  remarkable. 

Oil  of  Black  Mustard-seed. — To  obtain  this  oil,  the  cake  of  the  seed,  after 
the  fixed  oil  has  been  expressed,  is  made  into  a  paste  with  water,  which  after 
some  hours  is  subjected  to  distillation,  in  the  same  way  as  bitter-almond  oil 
is  distilled  from  the  almond-cake.  As  in  that  case  the  oil  is  formed  by  the 
action  of  emulsine  upon  amygdaline  in  the  presence  of  water,  so  in  this 
instance  the  volatile  and  pungent  mustard-oil  is  formed  by  the  action  of  a 
substance  analogous  to  emulsine,  which  has  been  termed  myrosine,  upon  a 
peculiar  substance  existing  in  the  black  mustard-seed,  and  which  has  been 
termed  xnyronic  add,  sulphosinapisine,  and  sinapine.  The  oil  which  first 
passes  over,  when  dehydrated  by  means  of  fused  chloride  of  calcium,  is  an 
acrid,  colorless  liquid,  soluble  in  alcohol  and  ether :  it  boils  at  290°,  and  the 


RESINS    AND    GUM    RESINS.  61t 

density  of  its  vapor  is  3"44.  Its  altimate  elements  are  CgHgNSg;  so  that  it  has 
been  regarded  as  the  sulphocyanide  of  a  hydrocarbon,  =  C6H3,  to  which  the 
terra  Allyl  has  been  applied,  and  which  has  been  isolated  by  the  action  of 
sodium  upon  iodide  of  allyl  (CgH^I).  This  iodide,  under  the  name  of  iodized 
propylene,  was  obtained  by  Berthelot  {Ann.  Ch.  et  Ph.,  xliii.  257)  as  a  result 
of  the  action  of  biniodide  of  phosphorus  upon  glycerine :  it  has  been  assumed 
as  the  basis  of  numerous  derivatives,  included  in  what  has  been  termed  the 
allyle  series. 

Oil  of  Garlic  is  a  fetid  sulphuretted  product,  which  appears  to  consist  of 
oxide  and  sulphide  of  allyle  (CeHsO  +  CgH^S),  both  of  which  have  been 
isolated. 

Kesins. 

These  substances  are  found  as  proximate  constituents  of  many  plants  : 
those  which  have  been  principally  examined  are  such  as  either  flow  naturally 
from  fissures  in  the  bark  or  wood,  or  are  obtained  from  incisions  in  the  trees 
and  shrubs  which  produce  them.  They  are  almost  always  in  the  first  instance 
mixed  with  variable  proportions  of  essential  oil,  which  either  evaporates  on 
exposure  to  air,  or  becomes  resinified  by  the  action  of  oxygen.  Mixtures 
of  essential  oil  in  large  proportion  with  resin  are  called  balsams:  although, 
strictly  speaking,  this  term  is  applied  to  those  mixtures  of  essential  oil  and 
resin  which  contain  benzoic  or  cinnamic  acid,  as  the  balsams  of  benzoin,  tolu, 
storax,  and  Peru.  Balsams  of  copaiba  and  Canada  are  resins  mixed  with  an 
essential  oil  which  is  isomeric  with  oil  of  turpentine.  The  so-called  Canada 
balsam  is  the  nearly  colorless  liquid  resin  of  the  Pinus  halsamea. 

Resins  are  generally  soluble  in  alcohol,  benzole,  and  chloroform.  Some 
are  soluble  in  ether.  The  alcoholic  solution,  when  mixed  with  water,  gives 
a  whitish  precipitate,  which  has  frequently  an  acid  reaction.  This  is  the 
pure  resin  in  the  state  of  hydrate.  If  an  alcoholic  solution  of  a  resin  is 
poured  upon  a  surface  of  glass,  an  opaque  layer  of  resin  is  left  upon  drying : 
if  the  glass  is  first  heated,  the  resin  is  deposited  in  a  transparent  form,  and 
closely  adheres  to  the  surface.  Many  resins  are  dissolved  when  heated  in  a 
solution  of  potash  or  soda.  They  form  in  this  case  a  species  of  soap,  and 
give  frothiness  to  the  water  when  agitated. 

Resins,  when  pure,  are  inodorous  ;  a  few  of  them  are  crystallizable  ;  they 
are  usually  of  a  pale  yellow  or  brown  color,  opaque  or  transparent.  They 
become  electric  by  friction.  The  greater  number  of  them  are  heavier  than, 
and  insoluble  in  water,  and  have  little  taste.  They  are  generally  softened, 
or  even  fused,  when  boiled  in  water.  In  the  air  they  melt  and  burn  .with  a 
sooty  flame.  They  are  thus  distinguished  from  gums.  When  subjected  to 
dry  distillation,  they  yield  resin-oil,  volatile  liquids,  and  inflammable  gases. 
Many  of  the  natural  resins  are  mixtures  of  two  or  more  resinous  substances, 
separable  by  the  action  of  alcohol.  There  are  many  of  them  which,  when 
in  alcoholic  solution,  redden  litmus,  and  combine  with  alkalies;  others  are 
indifferent,  and  some  have  been  regarded  as  basic. 

Gum-resins  are  natural  mixtures  of  gum  and  resin  in  variable  proportions. 
They  sometimes  contain  an  essential  oil  which  gives  to  them  a  powerful  odor. 
They  are  the  milky  juices  of  plants  solidified  by  exposure.  While  a  pure 
gum  is  insoluble  in  alcohol,  and  a  pure  resin  is  insoluble  in  water,  a  gum- 
resin  is  characterized  by  its  forming  a  milky  emulsion  with  water,  the  solution 
of  the  gum  suspending  the  fine  particles  of  resin  with  which  it  is  associated. 
Ammonium,  Myrrh,  Gamboge,  and  Assafoetida  are  gum-resins. 

There  are  a  few  of  the  resins,  and  their  allied  substances,  which  require 
especial  notice.  ,     -n    •        <•  * 

Colophony;  Common  i?o5iw.— This  is  the  residue  of  the  distillation  ot  tur- 


618  SILVIO    AND    PINIC    ACIDS.      GUAIACUM. 

pentine  (p.  615).  It  is  brittle,  tasteless,  of  a  smooth  shining  resinous  frac- 
ture; sp.  ^r.  1  080;  softens  at  about  180°,  and  fuses  at  275°.  According  to 
Unverdorben,  it  includes  two  distinct  acid  resins,  which  he  designates  pinic 
acid  and  silvic  acid,  the  former  preponderating.  As  respects  the  composi- 
tion of  these  acids,  it  appears  that  they  are  isomeric,  and  have  the  formula 
ascribed  to  colophony  {Q^Jl^fi.^,'RO). 

Silvic  acid  is  obtained  by  mixing  an  alcoholic  solution  of  colophony  with 
an  alcoholic  solution  of  oxide  of  copper,  drying  the  precipitate,  and  digest- 
ing it  in  alcohol,  which  dissolves  the  silvate,  but  leaves  the  pinate  of  copper. 
Sulphuric  acid  is  added  to  the  alcoholic  solution,  and  it  is  then  precipitated 
by  water,  which  throws  down  silvic  acid,  and  which,  dissolved  in  alcohol, 
yields  crystals  on  evaporation. 

Pinic  Acid. — When  pinate  of  copper  is  dissolved  in  boiling  alcohol  acidu- 
lated by  hydrochloric  acid,  and  water  is  added  to  the  mixture,  pinic  acid  is 
precipitated  in  the  form  of  a  colorless  resin.  This  substance  is  not  crystal- 
lizable,  but  in  other  respects  resembles  silvic  acid.  The  pinates  are  less 
soluble  in  ether  than  the  silvates,  and  pinate  of  magnesia  is  insoluble  in 
alcohol,  whereas  the  silvate  is  soluble. 

When  colophony  is  heated  somewhat  above  its  point  of  fusion,  it  acquires 
a  dark  color,  and  is  less  easily  soluble  in  alcohol :  in  this  state  it  has  been 
called  colopholic  acid.  Distilled  over  an  open  fire,  colophony  is  resolved 
into  carbon,  water,  and  colophene;  there  is  also  formed  a  liquid  hydrocarbon 
=  C,„Hg,  having  the  properties  of  terebene.  But  these  products  vary  with 
the  mode  of  distillation,  for  Fremy  represents  them  as  consisting  of  water, 
together  with  a  thick  yellow  oil,  which  he  terms  resineine,  and  represents  as 
=  0^0^2302;  and  by  distilling  in  the  same  way  a  mixture  of  1  part  of  resin 
and  8  of  powdered  quicklime,  he  obtained  two  liquids,  which  he  calls  resi?io?ie, 
=  C,„HyO,  and  resineone,  ssCggllagO,  carbonic  acid  being  at  the  same  time 
formed. 

A  resin  isomeric  with  colophony  is  obtained  from  the  turpentine  of  the 
pinus  maritima,  and  has  been  distinguished  as  pimaric  acid.  All  these 
resins  readily  combine  with  the  alkalies,  and  enter  largely  into  the  composi- 
tion of  common  yellow  soaps.  Elemi,  Anime,  Sandarac,  or  juniper  resin, 
and  Mastic,  each  contain  two  distinct  resins,  separable  to  a  great  extent  by 
the  alternate  action  of  cold  and  hot  alcohol,  and  dififering  slightly  in  compo- 
sition (Johnston,  Phil.  Trans.,  1840). 

Guaiacum. — This  is  a  hard,  brittle,  greenish-brown  resin,  obtained  from 
the  Guaiacum  officinale.  It  is  very  soluble  in  alcohol,  and  its  solution 
gives  a  white  precipitate  with  water,  which  absorbs  oxygen,  and  is  colored  blue 
or  green  according  to  the  quantity  of  resin  and  the  degree  of  exposure.  The 
change  appears  to  be  due  entirely  to  oxidation,  for  the  precipitated  resin, 
inclosed  in  a  hermetically-sealed  glass  tube,  was  unaltered  in  color  after  two 
months'  exposure  to  light.  The  powdered  resin,  exposed  to  air,  slowly 
becomes  green,  and  in  order  to  make  a  pure  tincture  for  experimental  pur- 
poses, the  minor  portions  only  of  the  resin  should  be  taken.  According  to 
Deville,  the  resin  consists  of  two  distinct  resinous  acids,  one  of  which, 
guaiacic  acid,  has  the  following  formula:  HOjCj^HyOg.  Deville  has  pro- 
cured this  from  the  resin  in  a  crystallized  state. 

Chlorine,  bromine,  and  nitric  acid  rapidly  oxidize  the  precipitated  resin, 
turning  it  of  a  green  color.  Nitric  acid  has  the  same  effect  on  the  powdered 
resin  and  on  guaiacum  wood.  Bodies  containing  ozone,  e.  g.,  a  solution  of 
manganate  or  permanganate  of  potash,  or  even  insoluble  peroxide  of  man- 
ganese, give  a  rich  azure-blue  color  to  the  resin — the  last-mentioned  com- 
pound somewhat  slowly.  Peroxide  of  lead  operates  in  a  similar  manner. 
Paper  soaked  in  the  tincture,  and  dried  and  kept  from  air,  has  been  recom- 


RESINS.       LAC.  619 

mended  by  Schonbein  as  a  test  for  ozone.  The  paper  is  bloed  when  ex- 
posed to  an  ozonized  atmosphere,  but  ordinary  oxygen  also  appears  to  have 
a  similar  action  upon  it,  although  a  longer  time  is  required  by  the  produc- 
tion of  the  blue  color.  A  solution  of  a  salt  of  iron,  whether  of  the  prot- 
oxide or  peroxide,  also  produces  a  blue  color  with  the  precipitated  resin. 
This  bluing  takes  place  under  circumstances  which  it  is  not  always  easy  to 
explain.  Thus  the  fresh  pulp  of  potato,  flour,  and  gluten  in  any  form,  pro- 
duce a  similar  change  in  the  resin.  Peroxide  of  hydrogen  does  not  change 
the  color,  and  peroxide  of  barium  only  produces  a  blue  color  with  the  resin 
after  the  addition  of  an  acid  (acetic)  to  the  mixture.  On  this  negative 
action  of  peroxide  of  hydrogen  depends  the  guaiacum  test  for  the  detection 
of  blood. 

Copal,  the  resin  of  the  Hymencea  verrucosa,  is  characterized  by  its  diffi- 
cult solubility  in  alcohol;  but  when  powdered  and  exposed  for  some  months 
to  the  air,  it  becomes  more  soluble.  It  is  the  basis  of  some  excellent  var- 
nishes, and  is  generally  fused  before  it  is  dissolved  in  oils  or  spirit.  Lac  is 
also  a  valuable  ingredient  of  varnishes,  rendering  them,  like  copal,  tough 
and  durable :  its  secretion  appears  to  depend  upon  the  puncture  of  a  small 
insect  (the  Coccus  Jicus) ,  made  for  the  purpose  of  depositing  its  ova  upon 
the  branches  of  several  plants  growing  chiefly  in  India,  more  especially  the 
Mcus  Indica,  Ficus  religiosa,  and  Rhamnus  Jujuba.  The  twig  soon  becomes 
incrusted  with  a  dark  reddish-colored  substance,  constituting  slick-lac,  which, 
when  washed  and  coarsely  pulverized,  forms  seed-lac;  and  this,  formed  into 
thin  plates  by  fusion  at  a  low  temperature,  is  called  shell-lac.  It  consists  of 
about  90  per  cent,  of  a  peculiar  resin,  which  appears  to  be  a  mixture  of 
three  or  four  distinct  resinous  products.  Lac  is  an  important  ingredient  in 
varnishes  and  lacquers,  and  is  largely  used  in  the  manufacture  of  hats,  and 
of  sealing-wax.  The  varnish  commonly  called  lacquer,  employed  for  color- 
ing brass,  and  protecting  it  from  the  oxygen  and  sulphur  of  the  atmosphere, 
is  made  by  mixing  lac  with  half  its  weight  of  sandarach  and  a  small  quantity 
of  Venice  turpentine.  These  are  dissolved  in  ten  or  twelve  parts  of  alcohol. 
Marine  glue  is  a  solution  of  caoutchouc  in  coal-naphtha,  to  which  some 
shell-lac  is  added. 

Red  sealing-wax  is  made  by  carefully  fusing  a  mixture  of  48  parts  of  shell - 
lac,  19  of  Venice  turpentine,  and  1  of  Peru  balsam,  to  which  32  parts  of 
finely-levigated  cinnabar  and  some  sulphate  of  lime  are  afterwards  added. 
In  the  cheaper  kinds  of  red  sealing-wax,  red  lead  is  substituted  for  vermilion, 
and  there  is  a  large  addition  of  common  rosin,  which  causes  the  wax  to  run 
into  thin  drops  when  fused.  Black  sealing-wax  is  made  of  60  parts  of  shell- 
lac,  10  of  Venice  turpentine,  and  8  of  finely-levigated  ivory-black. 

Varnishes. — The  principal  substances  used  in  varnishes  as  solvents  are  the 
oil  of  nuts,  linseed,  and  turpentine,  as  well  as  alcohol,  ether,  chloroform, 
and  benzole.  The  solids  employed  are  amber,  copal,  mastic,  sandarac,  lac, 
dammara,  anime,  benzoin,  and  colophony.  They  are  sometimes  colored  with 
various  vegetable  coloring  principles. 

Asphaltum  is  an  ingredient  in  Japan  or  black  varnish,  and  caoutchouc  in 
those  which  are  required  .to  be  elastic  and  waterproof.  The  best  photo- 
graphic varnish  is  a  solution  of  amber  in  chloroform.  The  characters  of  a 
good  varnish  are,  that  it  should  firmly  adhere  to  the  surface  to  which  it  is 
applied,  that  it  should  not  change  color  or  lose  lustre,  by  exposure  to  light 
and  air ;  and  that  it  should  not  be  long  in  drying.  Varnishes  are  distin- 
guished as  spirit  and  oil  varnishes;  the  former  are  the  most  brilliant,  but 
most  brittle,  the  best  spirit  varnishes  being  those  containing  lac  or  copal. 
The  article  known  as  French  polish  is  an  alcoholic  solution  of  shell-lac,  a 
little  linseed  oil  being  added  at  the  time  of  its  application  :  it  is  laid  ou  by 


620  AMBER.      CAOUTCHOUC. 

a  ball  of  cotton-wool,  and  then  rapidly  rubbed  in  the  direction  of  the  fibres 
of  the  wood  :  it  is  ultimately  finished  off,  after  drying,  by  friction  with  tripoli 
and  oil.  The  varnishes  prepared  with  oil  of  turpentine  (or  benzole)  are  less 
brittle  than  those  in  which  alcohol  only  is  used.  A  common  varnish  for  oil- 
paintings,  and  paper  previously  sized,  is  made  with  24  parts  of  mastic,  3  of 
Yenice  turpentine,  and  1  of  camphor.  These  are  mixed  with  10  parts  of 
pounded  glass,  and  dissolved  in  72  of  rectified  oil  of  turpentine  (Miller). 

Amber. — This  substance,  usually  regarded  as  a  fossil  resin,  is  chiefly 
brought  from  the  southern  coast  of  the  Baltic,  where  it  is  thrown  up  on  the 
beach  ;  it  is  found  on  the  coast  of  Norfolk ;  it  also  occurs  in  beds  of  brown 
coal  or  lignite  in  superficial  strata.  It  has  not  been  found  in  bituminous 
coal  drawn  from  great  depths.  It  is  generally  of  a  peculiar  yellow  color, 
pale  or  deep,  transparent  or  translucent,  slightly  heavier  than  water,  and 
becoming  very  electric  by  friction.  It  is  only  soluble  to  a  small  extent  in 
alcohol  and  in  ether.  Subjected  to  dry  distillation  it  fuses,  giving  off  water, 
oily  matters,  and  succinic  acid ;  the  latter  derived  apparently  from  the  de- 
composition of  that  portion  of  resin  which  is  soluble  in  ether;  and  the  oils, 
from  the  insoluble  and  apparently  bituminous  part.  Sixteen  ounces  of 
amber,  carefully  distilled,  yield  about  an  ounce  of  impure  acid,  three  ounces 
of  oil,  and  ten  of  a  torrefied  resin,  fit  for  the  preparation  of  varnish.  The 
empyreumatic  oil  thus  obtained  by  distillation  is  the  product  of  the  decom- 
position of  the  bituminous  portion  of  amber  which  is  not  soluble  in  alcohol 
or  ether.  Amber  is  dissolved  by  chloroform,  forming  a  useful  varnish.  It 
is  also  dissolved  by  strong  nitric  acid,  and  may  be  crystallized  from  the  solu- 
tion when  it  is  concentrated.  If  the  liquid  portion  is  distilled,  a  substance 
resembling  camphor  passes  over. 

Succinic  acid,  (2HO),C8H^Og,  is  a  product  of  the  action  of  nitric  upon 
stearic  acid.  It  is  also  formed  by  fermentation,  from  asparagine,  and  from 
malic  acid.  It  crystallizes  in  rhombic  plates,  soluble  in  five  parts  of  cold, 
and  two  of  boiling  water  ;  it  may  be  obtained  anhydrous,  by  distillation  with 
anhydrous  phosphoric  acid.  If  the  crystals  are  heated  to  450°,  they  lose  a 
portion  of  their  water,  and  a  monohydrated  acid  sublimes.  The  succinic,  is 
a  very  stable  acid  ;  it  resists  the  action  of  chlorine  and  of  boiling  nitric  acid. 
When  fused  with  caustic  potassa  it  yields  oxalic  acid,  and  an  inflammable 
gas.  The  soluble  succinates  produce  a  bulky  reddish-brown  precipitate  in 
the  neutral  and  basic  salts  of  peroxide  of  iron,  and  they  have  been  used  as 
a  means  of  separating  it  from  oxide  of  manganese.  When  heated  with 
bisulphate  of  potassa,  they  give  a  sublimate  of  succinic  acid. 

Caoutchouc  {Indian  Rubier,  Gum  Elastic)  was  first  brought  to  this 
country  at  the  beginning  of  the  last  century,  moulded  into  the  shape  of  bot- 
tles and  animals,  and  used  for  rubbing  out  pencil  marks :  it  has  since  been 
applied  to  a  variety  of  important  purposes,  and  many  tons  of  it  are  annually 
imported  from  South  America  and  the  East  Indies.  The  trees  which  yield 
it  are  the  Jatropha  and  Urceola  elastica,  and  several  others,  and  it  is  found 
in  small  proportion  in  the  poppy,  lettuce,  euphorbium,  and  other  plants 
having  a  viscid  milky  sap.  The  fresh  juice  of  the  tree  is  a  yellow,  milky 
fluid,  which,  when  exposed  to  warm  air,  forms  an  elastic  deposit,  retaining 
albumen  and  other  impurities  which  are  found  in  the  commercial  article. 
This  is  frequently  of  a  dark  color,  and  has  a  sp.  gr.  varying  from  0"926  to 
0"960.  Pure  caoutchouc  is  a  hydrocarbon,  being,  according  to  Faraday, 
CJIj,  although  other  authorities  give  it  C^H^ ;  thus  making  it  isomeric  with 
oil  of  turpentine.  The  remarkable  elasticity  of  this  substance,  and  its  chemi- 
cal peculiarities,  have  led  to  a  multitude  of  important  applications  of  it  in 


VULCANIZED    RUBBER.      GUTTA    PERCHA.  621 

the  industrial  arts.  (Hancock  on  Caoutchouc,  &c. ;  Muspratt^s  Chemistry, 
Art.  Caoutchouc,  &c.) 

In  its  ordinary  state  it  becomes  hard  at  low  temperatures,  but  never  brit- 
tle ;  it  is  soft  'and  very  elastic  when  warmed ;  and  when  heated  to  about 
260°,  melts  into  a  viscid  mass,  which,  on  cooling,  never  regains  its  former 
characters.  It  burns  with  a  smoky  flame  and  exhales  a  peculiar  odor.  Sub- 
jected to  destructive  distillation,  it  affords  a  mixture  of  various  hydrocarbons, 
gaseous  and  liquid  ;  the  latter,  under  the  name  of  Caoutchine  CgoH^g,  having 
a  peculiarly  penetrating,  greasy,  and  disagreeable  odor.  Caoutchouc  is  in- 
soluble in  water,  alcohol,  dilute  acids,  and  alkalies.  Ether,  chloroform, 
bisulphide  of  carbon,  rectified  oil  of  turpentine,  benzole,  coal-naphtha,  and 
some  other  hydrocarbons,  soften  and  dissolve  it;  some  of  these  solvents 
leaving  it  on  evaporation  in  its  elastic  condition.  In  this  dissolved  state, 
it  is  extensively  used  for  water-proofing  and  other  purposes.  The  processes 
by  which  the  commercial  caoutchouc  is  purified,  kneaded,  moulded  into 
blocks,  cut  into  sheets,  ribbons,  and  thread,  are  almost  exclusively  mechani- 
cal, but  are  necessary  preliminaries  to  its  most  important  applications,  many 
of  which  are  dependent  upon  a  process  which  has  been  termed  Vulcanization, 
and  which  consists  in  subjecting  it,  by  heat  or  solution,  to  the  action  of 
sulphur.  By  this  process  it  becomes  so  far  modified  as  to  resist  the  action 
of  its  ordinary  solvents,  and  of  the  greasy  oils,  and  to  retain  perfect  pliancy 
and  elasticity  at  the  low  temperatures  which  harden,  and  at  the  high  tem- 
peratures which  soften  common  India  rubber.  When  a  sheeti  of  rubber  is 
immersed  in  melted  sulphur,  it  absorbs  a  portion  of  it,  without  any  material 
change ;  but  if  heated  in  this  sulphurized  state,  to  about  300"^,  the  vulcani- 
zation is  effected.  So  also  if  sulphur  is  added  to  the  solution  of  the  rubber 
in  turpentine  or  naphtha,  it  retains  its  ordinary  properties  after  the  evapo- 
ration of  these  solvents^ until  heated  to  the  vulcanizing  temperature  (270° 
to  300°).  Sulphur  is  sometimes  imparted  to  rubber  by  dipping  it  in  thin 
sheets  into  a  solution  of  chloride  of  sulphur.  A  hard  compound  of  sulphur 
and  rubber,  heated  to  a  high  temperature  and  for  a  longer  time,  is  called 
Ebonite, 

The  cause  of  the  change  effected  by  vulcanization  is  not  well  understood  ; 
but  it  is  generally  supposed  that  the  rubber  retains  about  two  per  cent,  of 
sulphur  in  chemical  combination,  inasmuch  as  all  beyond  that  quantity  may 
be  removed  by  appropriate  solvents  (alkaline  sulphites).  It  has  also  been 
surmised  that  the  process  of  vulcanization  has  conferred  an  allotropic  condi- 
tion upon  the  rubber,  and  that  the  Whole  of  the  sulphur  may  be  withdrawn, 
still  leaving  it  in  its  altered  condition.  The  removal  of  sulphur  is  effected 
on  the  large  scale,  by  boiling  the  vulcanized  rubber  in  a  solution  of  sulphite 
of  potassa.  A  large  quantity  of  silicate  of  magnesia,  in  fine  powder,  is 
sometimes  incorporated  with  the  rubber  before  vulcanization,  to  give  it  a 
smooth  and  non-adherent  surface.  An  article  known  as  marine  glue  is  made 
by  dissolving  a  mixture  of  caoutchouc  and  shell-lac  in  coal-naphtha  :  it  is  of 
extreme  adhesiveness. 

GuTTA  Percha  is  closely  allied  to  caoutchouc  in  composition  and  in  its 
general  chemical  characters:  it  was  first  brought  into  notice  in  1846,  and 
has  now  become  an  important  article  of  commerce  :  it  is  the  produce  of  the 
Isonandra  percha,  a  forest  tree  abounding  in  the  islands  of  the  Eastern 
Archipelago.  It  exudes  as  a  milky  juice.  It  is  a  tough,  unyielding,  fibrous 
substance,  generally  met  with  in  black  or  brown  masses.  It  melts  at  250°. 
When  immersed  in  boiling  water,  it  softens,  and  admits  of  moulding  into 
any  requisite  shape,  but  hardens  again  on  cooling,  retaining  the  shape  which 
has  been  given  to  it.     It  becomes  powerfully  electric  by  friction,  and  is  an 


629 


FATS    AND    FIXED    OILS. 


excellent  insulator.  It  is  applied  to  a  variety  of  iisefnl  and  ornamental  pur- 
poses, in  many  of  which  it  is  advantageously  substituted  for  leather.  It  is 
not  elastic  like  caoutchouc,  but  is  much  more  tough.  It  is  insoluble  in 
water  and  alcohol,  but  is  dissolved  by  chloroform,  benzole,  and  sulphide  of 
carbon.  When  heated  in  air,  it  melts,  takes  fire,  and  burns  with  a  smoky 
flame.  It  forms  no  combination  with  sulphur,  like  vulcanized  rubber. 
After  long  exposure  to  air  in  thin  sheets  it  acquires  a  yellow  color,  is  very 
brittle,  and  is  now  soluble  in  alcohol.  It  appears  to  be  resinified  as  a  result 
of  oxidation.     It  rapidly  absorbs  and  removes  ozone. 

Gutta  percha  consists  of  a  distinct  principle,  gutta^  associated  with  two 
resinous  compounds.  The  gutta  is  represented  by  the  formula  C^oHgg,  and 
is  a  pure  hydrocarbon.  The  resins  have  the  same  formula,  with  an  addition 
of  two  and  four  atoms  of  oxygen  respectively.  Gutta  percha  contains  neither 
sulphur  nor  nitrogen. 


CHAPTER    LI. 


FATS    AND    FIXED 
SITION. 


OILS.      PRODUCTS    OF     THEIR    DECOMPO- 
SPERMACETI.      WAX.      SOAPS. 


Fats  and  Fixed  Oils. 

These  substances  are  common  to  animals  and  vegetables ;  they  vary  in 
consistence  from  thin  oil  (olive  oil)  to  hard  fat  (suet).  When  pure,  they 
are  neutral ;  they  leave  a  greasy  spot  upon  paper,  which  does  not  disappear 
when  moderately  heated.  They  are  insoluble  in  water,  but  more  or  less 
soluble  in  alcohol  and  ether,  and  are  insipid  and  inodorous.  In  vegetables 
they  chiefly  occur  in  the  seed,  and  pericarp  of  the  fruit  (olive),  and  are 
generally  obtained  by  pressure,  with  or  without  the  aid  of  heat. 

The  following  table  shows  the  proportion  of  oil  per  cent,  yielded  by  a 
Tarifety  of  seeds  : — 


Walnuts     . 

.     64-8 

Croton  seeds 

.     43-4 

Hazel-nuts 

.     59-4 

Hemp 

.     35-5 

Sweet  almonds  . 

.     55-4 

Mustard 

.     31-8 

Bitter  almonds  . 

.     520 

Laurel  berries 

.     31-8 

Poppy 

.    49-4 

Linseed 

.     29-6 

Cacao 

.    47-4 

Mace 

.     25-5 

Castor 

.     46-0 

Cotton  seed 

.     18-4 

The  residue  left  by  compression  is  well  known  under  the  name  of  oil-cake. 
It  contains,  besides  vegetable  fibre,  various  nitrogenous  principles,  chiefly 
albuminous,  and  it  is  largely  employed  as  food  for  cattle. 

It  has  been  found  that  a  large  quantity  of  oil  is  left  in  these  residues,  and 
as  this  cannot  be  extracted  by  compression,  a  new  plan  has  been  adopted  to 
remove  the  whole  of  the  oil.  Sulphide  of  carbon  is  employed  for  this  pur- 
pose. This  liquid  penetrates  the  cake  of  the  oleaginous  seed  or  the  pulp  of 
the  olive,  and  rapidly  and  completely  extracts  the  residuary  oil,  from  which 
it  is  afterwards  separated  by  distillation.  This  process  is  carried  on  largely 
in  France,  and  it  is  stated  that  from  thirty  to  thirty-five  tons  of  oily  sub- 
stances are  thus  extracted  at  each  operation. 

In  animals  the  oil  is  deposited  in  a  cellular  membrane,  as  in  the  blubber 
of  the  whale.     The  separation  of  the  oil  here  takes  place  by  simply  treating 


8TEARINE.      STEARIC    ACID.  (523 

the  fatty  substance  with  boiling  water.     The  adipose  cells  are  rnptured 

the  oil  escapes  and  collects  upon  the  water  in  which  the  crude  fat  is  boiled. 
The.  melting  points  of  oils  and  fats  vary  from  about  20°  to  140°.  At  high 
temperatures  (500°  to  600°)  they  do  not  distil  unchanged,  but  evolve  acrid 
products,  and  are  resolved,  at  a  red  heat,  into  inflammable  gases  and  vapors, 
of  high  illuminating  power.  Their  specific  gravity,  which  is  below  that  of 
water,  varies  much  with  temperature :  the  sp.  gr.,  for  instance,  of  hog's  lard 
at  60°  is  0-9.38  ;  in  its  fluid  state  at  122°  it  is  0-892  ;  at  155°  it  is  0'881  ; 
and  at  200°,  0'863.  Some  of  these  oils  are  little  aflfected  by  exposure  to  air, 
but  gradually  become  rancid  ;  others  absorb  oxygen,  and  form  a  resinous 
varnish  ;  they  are  known  as  drying  oils ;  and  when  their  surface  is  much 
extended,  as  in  greasy  rags  and  cotton-waste,  this  change  is  sometimes 
attended  by  spontaneous  combustion.  The  drying  quality  of  these  oils  is 
generally  increased  by  heating  them  with  oxide  of  lead  or  manganese. 

When  the  solid  fats  are  subjected  to  pressure  between  folds  of  bibulous 
paper,  they  afford  more  or  less  of  fluid  oil ;  and  when  the  liquid  oils  are 
cooled  to  about  32°,  they  deposit  more  or  less  of  a  concrete  matter.  The 
liquid  portion  is  termed  oleine  or  elaine  (fXuiiov,  oil),  and  the  solid,  stearine 
(otiapjfat),  with  which  a  variable  portion  of  margarine  (fiapyafiov,  a  pearl, 
from  its  pearly  lustre)  is  associated,  each  of  these  being  compounds  of  a 
distinct  fattg  acid,  with  a  sweet  principle,  glycerine  (yxvxvj  sweet).  These 
acids  are  the  oleic,  the  stearic,  and  the  margaric ;  so  that  oleine  is  an  oleate, 
stearine  a  stearate,  and  margarine  a  margarate,  of  glycerine.  Besides  these, 
many  fats  contain  distinct  volatile  acids,  such  as  butyric,  capric,  and  caproic 
acids,  in  butter ;  hircic  acid  in  goat's  fat,  phocenic  acid  in  fish-oil,  etc. 
Oleine  may  be  more  or  less  separated  from  stearine  by  ether  or  oil  of  turpen- 
tine, in  which  liquids  it  is  much  more  soluble  than  stearine. 

In  the  process  of  saponification,  the  fatty  bodies  are  heated  with  hydrated 
alkalies,  generally  with  soda,  by  which  they  are  decomposed,  the  glycerine  is 
set  free,  and  oleates,  stearates,  and  margarates  of  the  alkaline  bases  are 
formed. 


Fat  or  oil 


c,      .  ( Stearic  acid 

Stearme  {(Glycerine 

„  .  ( Marffaric  acid 

Margarine  |  eHyeerine 

^,  .  (  Oleic  acid 

1^  Oleine  |ai^cerine 


These  combinations  (soaps)  are  in  their  turn  decomposed  by  the  greater 
number  of  other  acids,  and  the  fatty  acids  are  separated.  These  acids  are 
insoluble  in  water,  but  soluble  in  alcohol  and  in  ether,  and  are  less  fusible 
than  the  original  fats.  They  are  soluble  in  oil  of  turpentine  and  in  benzole, 
and  when  free  from  volatile  products,  are  insipid  and  inodorous.  The  soaps 
of  alkalies  are  soluble,  but  those  of  the  alkaline  earths,  and  of  most  of  the 
other  metallic  oxides,  are  insoluble  in  water;  hence  it  is  that  hard  waters  are 
unfit  for  washing,  in  consequence  of  the  earthy  salts  which  they  contain,  and 
which  give  rise  to  the  production  of  insoluble  soaps. 

Stearine  (Ci,^H,,oO,b)  {Stearate  of  Glycerine)  is  best  obtained  from  mutton 
suet,  by  boiling  it  in  ether,  and  filtering  the  hot  solution  ;  as  it  cools,  it 
deposits  stearine,  which,  after  having  been  pressed  in  bibulous  paper,  may 
be  purified  by  a  second  solution,  and  cooling.  Its  fusing  point  is  about 
140°.  It  is  insoluble  in  water,  but  soluble  in  boiling  alcohol  and  ether, 
which,  however,  deposit  nearly  the  whole  of  it  as  they  cool. 

Stearic  Acid  (HO,C3eH3,03).— When  stearine  is  saponified,  it  is  resolved 
into  stearic  acid  and  glycerine,  a  change  which  may  be  represented  by  the 
following  equation  : — 


624  STEARATES.      MARGARIC    AND    OLEIC    ACIDS. 

C,„H„oO^    +       6H0,      =  ^^^,0,^  +       3(HO,C3eH3,03) 

Stearine.  Glycerine.  Stearic  acid. 

This  acid  may  be  obtained  by  decomposing  a  soluble  stearine  soap  by  tartaric 
acid,  and  purifying  the  product  by  solution  in  boiling  alcohol,  from  which  it 
separates  in  crystalline  flakes ;  it  may  be  further  purified  by  solution  in  ether. 
It  is  white,  inodorous,  and  tasteless,  but  it  reddens  litmus :  it  fuses  at  about 
160°,  and  may  be  distilled  in  vacuo,  but  when  highly  heated  in  the  air  it 
undergoes  more  or  less  change.  Stearic  acid  may  be  distinguished  from 
stearine  by  its  ready  solubility  in  a  boiling  solution  of  potassa,  by  its  acid 
reaction  and  crystallizing  properties. 

Stearates. — Stearic  acid  forms  monobasic  and  bibasic  salts  (neutral  and 
acid).  The  stearates  of  the  alkalies  are  soluble  in  water,  alcohol,  and  ether ; 
but  when  the  aqueous  solutions  of  the  neutral  compounds  are  largely  diluted, 
they  deposit  flakes  of  the  acid  stearate.  The  stearates  of  the  alkaline  earths 
may  be  obtained  by  double  decomposition,  from  bistearate  of  potassa :  they 
are  insoluble.  Stearate  of  potassa  is  the  basis  of  soft  soap,  and  stearate  of 
soda  of  the  principal  hard  soaps :  these  stearates  are  separated  from  their 
solutions  in  water  by  excess  of  alkali,  and  also  by  chloride  of  sodium  and 
some  other  salts.     Stearate  of  lead  is  the  basis  of  lead-plaster. 

3Iargarine  (CiogHjo^O^g)  {Maryarate  of  Glycerine). — This  substance  is 
found  in  some  animal  fats,  but  it  is  best  obtained  from  olive  oil,  by  cooling 
it  to  32°,  pressing  out  the  oleine,  and  dissolving  the  residue  in  boiling 
alcohol,  from  which  the  margarine  separates  in  pearly  crystals.  It  is  re- 
solved by  the  alkaline  bases  into  glycerine  and  margaric  acid. 

Margaric  Acid  (HO.Cg^HggOg)  is  obtained  by  decomposing  the  soap  of 
olive-oil  and  potassa,  by  acetate  of  lead  or  chloride  of  calcium:  an  insoluble 
margarate  and  oleate  of  lead  or  lime  is  formed,  from  which  the  oleate  may 
be  abstracted  by  cold  ether ;  the  remaining  margarate  may  then  be  decom- 
posed by  dilute  hydrochloric  or  nitric  acid,  when  the  margaric  acid  separates, 
and  may  be  purified  by  crystallization  from  its  alcoholic  solution  :  it  fuses  at 
about  140°;  in  other  respects  it  resembles  stearic  acid,  and  the  margarates 
closely  resemble  the  stearates.  According  to  Heintz,  margarine  is  a  mixture 
of  stearine  and  palmitine  (found  in  palm-oil),  and  consequently  margaric 
acid  is  not  an  independent  acid,  but  a  mixture  of  stearic  and  palmitic  acids. 

Oleine  {G^^Jl^^fi^^  {Oleate  of  Glycerine). — Oleine  is  the  chief  ingredient 
in  the  fat-oils  which  remain  fluid  at  common  temperatures.  It  may  be  pro- 
cured by  separating  the  margarine  and  stearine  from  a  fat  oil,  by  cold  and 
pressure,  dissolving  the  liquid  portion  in  ether,  evaporating,  and  digesting 
the  residue  in  cold  alcohol,  which  dissolves  the  oleine,  and  leaves  margarine 
and  stearine  undissolved.  Oleine  is  colorless,  inodorous,  and  tasteless  ;  its 
sp.  gr.  is  about  0*9.  It  is  insoluble  in  water,  but  abundantly  soluble  in 
alcohol  and  in  ether.     It  remains  fluid  at  and  below  32°. 

Oleic  Add  (CggHggOg)  is  obtained  by  saponifying  almond  oil  with  potassa, 
and  decomposing  the  soap  by  hydrochloric  acid,  which  separates  a  mixture 
of  oleic  and  margaric  acids:  this,  by  digestion  with  oxide  of  lead,  is  con- 
verted into  oleate  and  margarate  of  lead,  and  by  digesting  these  in  ether, 
an  acid  oleate  of  lead  is  dissolved.  The  ethereal  solution  is  mixed  with  its 
bulk  of  water  and  decomposed  by  hydrochloric  acid,  which  throws  down 
chloride  of  lead,  and  leaves  the  oleic  acid  in  solution,  from  which  it  is 
obtained  by  evaporation.  The  crude  oleic  acid,  produced  by  pressure  in 
the  manufacture  of  stearine  candles,  may  be  similarly  purified.  Oleic  acid 
is  colorless,  concretes  at  about  50°,  and  reddens  litmus ;  it  is  insoluble  in 
water,  but  abundantly  soluble  in  alcohol  and  in  alkalies.  The  neutral  oleates 
have  litMe  tendency  to  crystallize.     The  soluble  alkaline  oleates  are  soft 


glycerine:  its  properties.  625 

fusible  compounds,  more  soluble  in  alcohol  than  in  water,  and  are  decom- 
posed, by  excess  of  water,  into  free  alkali  and  acid  compounds.  It  is  a 
solution  of  the  pure  oleate  of  soda  in  the  proportion  of  one  part  to  fifty  parts 
of  water,  mixed  with  two-thirds  of  its  bulk  of  pure  glycerine,  which  forms 
what  is  called  the  glycerine  liquid  for  producing  persistent  soap-bubbles. 
Bubbles  of  large  size  blown  with  this  liquid  will  retain  their  form  for  eighteen 
or  twenty-four  hours.  M.  Plateau  found  that  Marseilles  soap,  in  a  fresh  or 
moist  state,  may  also  be  used  for  this  purpose  in  the  proportion  of  one  part 
dissolved  in  forty  parts  of  distilled  water  at  a  moderate  heat.  When  the 
solution  has  cooled  it  is  filtered,  and  to  three  volumes  of  it  two  volumes  of 
pure  glycerine  are  to  be  added,  and  the  whole  well  shaken  and  allowed  to 
remain  for  several  days.  It  is  then  submitted  to  a  cooling  process,  and  is 
filtered  to  separate  any  deposit.     {Ghem.  News,  Dec.  1866,  p.  291.) 

Glycerine  (CgHgOg)  {y7.vxvi,  sweet). — This  substance  was  discovered  by 
Scheele.  It  is  obtained  by  boiling  equal  parts  of  hydrated  oxide  of  lead 
and  olive  oil  with  water :  the  solution  thus  formed,  freed  from  lead  by  sul- 
phuretted hydrogen,  filtered,  evaporated  to  the  consistency  of  syrup,  and 
then  exposed  in  vacuo  over  sulphuric  acid  until  it  no  longer  loses  weight, 
leaves  the  glycerine.  It  is  now  produced  in  large  quantities  by  soap  and 
candle-makers,  and  has  been  applied  to  many  useful  purposes  in  medicine 
and  the  arts. 

Glycerine  is  a  colorless,  neutral,  inodorous  liquid,  of  a  sweet  taste  and 
syrupy  consistency,  sp.  gr.  1-28,  soluble  in  all  proportions  in  water  and  in 
alcohol,  but  nearly  insoluble  in  ether.  It  does  not  dry  by  exposure  to  air. 
It  is  slightly  volatile  at  212°,  but  when  heated  in  air  to  a  high  temperature, 
it  gives  off  an  inflammable  vapor  and  burns  with  a  luminous  flame.  It  is 
usually  described  as  uncrystallizable,  and  when  pure  and  exposed  to  a  tem- 
perature of  zero,  it  has  not  solidified  but  has  apparently  become  more  viscid. 
A  large  quantity  imported  from  Germany  during  the  severe  winter  of  186(5-7 
was  found  by  Mr.  Crookes  to  have  assumed  a  solid  and  a  crystalline  condition. 
The  original  glycerine  was  of  a  pale  brown  color.  The  solid  glycerine  had 
separated  in*  crystalline  colorless  masses  resembling  sugar  candy.  The 
crystals  were  brilliant  and  apparently  of  an  octahedral  form.  The  liquid 
which  drained  from  them  was  of  a  dark-brown  color.  They  melted  slowly 
retaining  a  temperature  of  45°.  When  fused  the  liquid  had  all  the  proper- 
ties of  pure  glycerine  (Chem.  News,  1867,  i.  26).  It  dissolves  baryta,  lime,, 
oxide  of  lead,  and  many  salts.  When  mixed  with  a  solution  of  caustic 
potassa,  it  readily  dissolves  hydrated  oxide  of  copper,  forming  a  deep  blue 
solution,  which,  however,  produces  no  suboxide  when  boiled.  When  boiled 
with  a  solution  of  potassa,  no  glucic  acid  is  produced,  and  the  liquid  does 
not  become  dark-colored  like  glucose  under  similar  circumstances.  In  order 
to  detect  syrup  in  glycerine  the  liquid  may  be  warmed  with  a  small  quantity 
of  tartaric  acid  and  ther*opper  test  then  applied.  If  cane-sugar  syrup  is 
present  the  red  oxide  of  copper  will  be  formed  and  precipitated.  Sulphuric 
acid  does  not  carbonize  it  in  the  cold  :  it  is  thus  distinguished  from  sucrose.. 
When  heated  in  a  retort,  part  passes  over  and  part  is  decomposed,  producing 
the  pungent  vapors  of  acrolein;  but  it  may  be  distilled  without  decomposi- 
tion in  a  current  of  superheated  steam,  at  a  temperature  between  400°  and. 
500°.  It  is  not  susceptible  of  vinous  fermentation,  but  when  left  for  some 
months  in  a  warm  place,  mixed  with  a  little  yeast,  it  produces  propionic  acid. 
Impure  glycerine  digested  with  alcohol  produces  butyric  ether.  Distilled 
with  dilute  sulphuric  acid  and  peroxide  of  manganese,  it  yields  carbonic  and 
formic  acids.  Mixed  with  twice  its  weight  of  sulphuric  acid  there  is  con- 
siderable elevation  of  temperature,  and  after  the  mixture  has  cooled,  if  it  be 
40 


626  NITRO-GLYCERINE,    NITROLEUM,    AND    GLONOINE. 

diluted,  saturated  by  milk  of  lime,  and  filtered,  it  yields,  on  evaporation, 
crystals  of  a  salt  of  lime  containing  sulphoglyceric  acid,  =Q^fl,-\-'^^0^. 
A  corresponding  Phosphoglyceric  acid  is  said  to  exist  in  the  brain,  and  in 
yelk  of  Ggg. 

In  combination  with  the  fatty  acids,  glycerine  produces  the  various  fats 
and  oils,  but  they  appear  to  combine  in  various  proportions:  assuming  stearic 
acid  as  CggHgjOg,  stearine  will  be  a  terstearate  of  glycerine  : — 

Glycerine.  Stearic  acid.  Stearine. 

and  oleine  a  teroleate  of  glycerine  : — 

^  CeHA        4-         3(C3eH3303)  =         C,^H„^ 

Glycerine.  Oleic  acid.  Oleine. 

and  so  with  regard  to  other  fatty  acids.  Berthelot  has  synthetically  repro- 
duced the  fats  by  the  union  of  their  acids  with  glycerine,  and  has  pointed 
out  the  existence  of  analogous  combinations,  in  which  1  and  2  equivalents 
of  the  respective  acids  are  similarly  combined  with  glycerine,  producing 
distinct  fatty  bodies  {Ann.  Ch.  et  Ph.,  3eme  ser.,  xli.  p.  216). 

Nitro-glycerine,  Nitroleum,  Glonoine,  CeH.(NO^)30f5,  a  substitution  com- 
pound, in  which  three  equivalents  of  the  hydrogen  of  glycerine  are  replaced 
by  three  equivalents  of  nitrous  acid.  It  is  procured  by  adding  glycerine  in 
small  quantities  to  equal  measures  of  the  strongest  nitric  and  sulphuric 
acids,  previously  well  mixed  and  cooled.  If  the  mixture  became  heated,  the 
glycerine  would  be  decomposed,  and  oxalic  and  carbonic  acids  would  be 
produced.  The  combination  is  completed  in  five  or  ten  minutes  :  the  acid 
mixture  is  then  added  to  five  or  six  times  its  volume  of  cold  water  and  well 
agitated :  the  nitroglycerine  is  precipitated  as  a  heavy  oily-looking  liquid, 
so  that  it  may  be  easily  separated  from  the  diluted  acids  by  decantation,  and 
washed.    The  chemical  changes  which  take  place  may  be  thus  represented  : — 

^CeHgOe       +       3(H0,N0,)       =       CeH^CNOJaOe  ^     +       6H0 


Glycerine.  Nitric  acid.  Nitroglycerine.  Water. 

Nitroglycerine  is  an  oily-looking  liquid,  of  a  pale  brownish  color,  becoming 
•Bolid  at  40°,  sp.  gr.  1*6,  not  soluble  in  water,  slightly  soluble  in  alcohol,  but 
easily  dissolved  by  ether  and  wood-spirit.  The  last-named  liquid  is  said  to 
counteract  its  explosive  properties,  and  to  render  its  transport  safe.  It  may 
be  separated  from  these  solutions  by  water.  Although  more  violent  than 
:gunpowder  and  guncotton  in  its  explosive  power,  it  is  not  so  easily  exploded 
by  heat  as  either  of  those  compounds.  When  flame  or  a  red  heat  is  applied 
to  it  openly,  it  burns  without  explosion ;  but  when*  placed  in  a  closed  vessel, 
it  will  explode  at  360°.  It  most  readily  explodes  by  percussion,  as  when 
sharply  struck  in  a  hard  and  resisting  surface.  In  blasting  rockis,  a  fuse 
charged  with  gunpowder  is  employed  for  the  purpose  of  exploding  it :  it  has 
ten  times  the  rending  force  of  an  equal  weight  of  gunpowder.  Like  gun- 
cotton,  it  is  apt  to  undergo  spontaneous  changes,  and  the  evolution  of  gas  as 
a  result  of  decomposition  has  probably  been  the  primary  cause  of  the  serious 
accidents  which  have  occurred  from  the  transport  of  this  liquid.  It  has  a 
sweet  and  aromatic  taste,  and  is  said  to  be  poisonous  both  as  a  liquid  and 
vapor.  When  breathed  in  small  quantities,  it  is  stated  to  have  produced 
violent  headache  and  other  unpleasant  symptoms.  It  has  lately  been  manu- 
factured on  a  large  scale  for  use  in  the  blasting  of  rocks. 


ACTION    or    SULPHURIC    ACID    ON    PATS    AND    OILS.  62*7 

Action  of  Sulphuric  Acid  on  Fats  and  Oils — This  acid  generally  so  com- 
bines with  the  proximate  principles  of  the  fatty  bodies  as  to  form  a  series  of 
distinct  acid  products,  such  as  sidphostearic,  sulphomargaric,  and  sulpholeic 
acids;  the  glycerine  at  the  same  time  yielding  sulphoglyceric  acid;  but  when 
sulphuric  acid  is  heated  with  the  fatty  bodies,  the  glycerine  is  decomposed, 
and  the  fatty  acids  are  set  free.  This  process  is  resorted  to  upon  the  large 
scale,  for  the  production  of  the  fatty  acids  for  the  manufacture  of  candles. 
The  tallow  is  mixed  with  about  a  sixth  part  of  oil  of  vitriol  in  large  copper 
vessels,  and  subjected  to  a  temperature  of  about  350°,  by  means  of  highly 
heated  steam  ;  sulphurous  and  carbonic  acids  are  abundantly  evolved,  in 
consequence  of  the  action  of  the  sulphuric  acid  upon  the  glycerine.  The 
liberated  fatty  acids,  after  having  been  well  washed,  are  distilled  in  a  current 
of  steam,  heated  to  between  500°  and  600°  by  transmission  through  a  red- 
hot  pipe ;  the  fatty  acids  are  carried  over,  leaving  their  impurities  in  the 
form  of  a  black  residue,  and  are  then  subjected  to  pressure,  so  as  to  squeeze 
out  the  more  fluid  oleic  portions,  and  leave  the  stearic  acid  in  a  fit  condition 
for  candle-making.  But  the  decomposition  of  the  fats  by  highly  heated  steam 
only,  has  lately  been  carried  to  such  perfection,  as  not  only  to  yield  the  fatty 
acids,  but  also  the  glycerine,  in  a  very  pure  state,  a  process  which  will  pro- 
bably entirely  supersede  that  by  sulphuric  acid. 

Action  of  Nitric  Acid  on  Fats  and  Oils. — These  products  may  be  divided 
into  two  classes  :  1.  Those  which  are  volatile,  and  pass  over  in  distillation  ; 
and  2.  Those  which  are  comparatively  fixed,  and  remain  in  the  retort ;  they 
are  as  follows  : — 


)latile  acids. 

Volatile  acids. 

Fixed  acids. 

Formic 

(Enanthjlic 

Succinic 

Acetic 

Caprylic 

Adipic 

Butyric 

Pelarganic 

Pimelic 

Valerianio 

Capric 

Suberic 

Caproic 

Sebacic 

These  products  are  obtained  by  gradually  dropping  oleic  acid  into  a  retort 
containing  nitric  acid,  heated  to  about  130° :  violent  action  ensues,  and  the 
distillate  consists  of  water  holding  the  most  volatile  and  soluble  acids  in 
solution,  such  as  formic,  acetic,  and  butyric,  covered  by  an  oily  layer  of  the 
valerianic  and  other  acids.  On  pouring  off  the  oil,  agitating  it  with  baryta- 
water,  and  submitting  the  solution  to  successive  crystallizations,  caproate 
of  baryta  is  first  obtained — then  oenanthylate,  caprylate,  pelargonate,  and 
caprate,  and,  lastly,  valerianate.  The  more  fixed  acids  are  dissolved  in  water, 
and  the  solution  saturated  with  carbonate  of  soda :  on  evaporation,  crystals 
of  acetate  of  soda  separate,  and  on  adding  sulphuric  acid  to  the  mother- 
liquor,  an  oily  layer,  consisting  of  butyric  and  metacetonic  acids  is  formed. 
(Regnault.)  There  are  other  modes  of  obtaining  these  and  the  other  fixed 
acids,  which  are  elsewhere  noticed. 

Suberic  Acid,  CigHj^Og,  is  one  of  the  products  of  the  action  of  nitric 
acid  on  oleic  acid ;  it  was  originally  produced  by  the  action  of  nitric  acid 
upon  cork.  When  pure,  it  is  a  difficultly  soluble  crystalline  powder;  suberates 
of  the  alkaline  bases  are  soluble;  they  give  white  precipitates  with  the  salts 
of  lead  and  silver,  =2,{M0,)G,QB.^fiQ. 

Butyric  Acid  (C3H703,H0).— Butter  includes  several  fatty  bodies  {see 
Milk),  amongst  which  are  butyrin,  caproin,  and  caprylin,  to  which  its  pecu- 
liar smell  and  taste  have  been  referred  :  these  may  be  resolved  by  saponifica- 
tion into  glycerine,  and  butyric,  caproic,  and  caprylic  acids.  Butyric  acid, 
obtained  by  the  decomposition  of  butyrate  of  lime  by  hydrochloric  acid,  is 
a  volatile  oily  body,  sp.  gr.  0963,  and  boiling  at  315°:  it  has  the  odor  of 
rancid  butter,  a  pungent  taste,  and  is  soluble  in  water,  alcohol,  and  ether : 


628  CAPRIC    AND    VALERIANIC    ACIDS. 

its  salts  are  mostly  soluble  and  erystallizable.  It  is  among  the  products  of 
the  action  of  nitric  acid  upon  olein,  and  of  certain  oxidizing  agents  upon 
fibrin  or  casein,  and  is  found  in  some  fruits.  The  readiest  mode  of  obtaining 
it  is  that  of  Pelouze  and  Gelis,  and  is  as  follows:  a  solution  of  sugar  of  the 
sp.  gr.  1*064,  is  mixed  with  powdered  chalk  amounting  to  half  the  weight 
of  the  sugar,  and  to  this  a  portion  of  casein  or  curd  is  added,  equal  to  8  or 
10  parts  for  every  100  of  sugar,  and  the  mixture  kept  at  a  temperature  of 
about  80°;  viscous  and  lactic  fermentations  ensue,  carbonic  acid  and  hydro- 
gen are  evolved,  and  after  some  weeks  hutyrate  of  lime  is  formed  in  the  liquor: 
in  this  case  the  lactic  acid  which  is  first  formed  passes,  by  loss  of  carbonic 
acid  and  hydrogen,  into  butyric  acid. 

2(HO),C„H,oO,p        =     ^  H0,CgH,03        +        4C02+4H 
Lactic  acid.  Butyric  acid. 

This  acid  appears  to  be  formed  in  the  stomach  in  certain  disordered  states 
of  digestion,  and,  by  mixing  with  oily  or  fatty  matters,  to  produce  the  acrid 
liquid  which  gives  rise  to  heartburn  or  cardialgia.  Dr.  Lared  found,  in 
experiments  on  himself,  that  heartburn  could  be  produced  by  swallowing 
butyric  acid.  Pastry  and  substances  of  the  like  nature  contain  butyric  acid 
or  the  elements  required  for  forming  it,  and  these,  it  is  well  known,  produce 
the  disorder  in  question.  The  remedy  consists  in  the  administration  of  a 
mild  alkali,  either  carbonate  of  ammonia  or  soda.  Cod-liver  oil  also  relieves 
it  by  mixing  with  the  butyric  acid  and  dissolving  it. 

Capric  Acid  (CgoH^gOgjHO)  is  among  the  products  of  the  action  of  nitric 
acid  on  oleine,  and  is  one  of  the  results  of  the  saponification  of  butter,  but 
it  is  most  readily  procured  by  the  oxidation  of  the  oil  of  Rue  by  nitric  acid 
(Gerhardt),  and  has  hence  been  termed  Rutic  acid.  It  is  obtained  pure  by 
the  decomposition  of  caprate  of  baryta  by  sulphuric  acid :  it  forms  acicular 
crystals  fusible  at  86°,  of  a  sour  acrid  taste,  and  goat-like  odor. 

Caprylic  Acid  {RO,C^^^fi^  is  liquid  at  temperatures  above  60°,  little 
soluble  in  water,  boils  at  258°,  and  has  a  nauseous  odor. 

Caproic  Acid  (H0,C,gE[jj03)  is  a  liquid  of  a  sour  odor  and  taste,  boiling 
at  390°,  and  sparingly  soluble  in  water. 

Valerianic  Acid  ;  Valeric  acid  (HOjCjoHgOg). — The  volatile  oil,  obtained 
by  distilling  the  root  of  valerian  with  water,  is  a  mixture  of  a  hydrocarbon 
=CioH2,  with  an  oxygenated  oil  convertible  into  valeric  acid.  This  acid  has 
also  been  obtained  from  angelica  root,  and  from  the  berries  and  bark  of  the 
Guelder-rose  (  Viburnum  opulus) :  it  is  an  occasional  product  of  the  oxidation 
of  fatty  bodies,  and  is  artificially  produced  by  the  action  of  oxidizing  agents 
(chromic  acid)  on  amylic  alcohol  {fusel-oil).  It  is  a  colorless  liquid,  smelling 
strongly  of  valerian,  and  of  a  sour  pungent  taste.  It  boils  at  270°,  and  the 
density  of  its  vapor  is  3  55.  It  is  soluble  in  about  30  parts  of  water,  but 
may  contain  20  per  cent,  of  water  without  losing  its  oily  appearance.  The 
Valerianates,  when  pure  and  dry,  are  nearly  inodorous,  but  generally  have  a 
valerianic  odor  and  sweetish  taste ;  they  smell  strongly  of  valerian  when 
moistened  with  a  dilute  acid  ;  some  of  them  have  been  used  medicinally. 
Acted  upon  by  chlorine,  valerianic  acid  furnishes  two  compounds  in  which  3 
and  4  atoms  of  its  hydrogen  are  replaced  by  chlorine,  the  chlorovalerisic  and 
chlorovalerosic  acids ;  and  by  the  protracted  action  of  nitric  acid  a  part  of 
it  is  converted  into  nitrovalerianic  acid,  =HO,CjoHg07N.  The  valerianates 
of  soda  and  zinc  are  used  in  medicine.  They  are  produced  by  replacing  an 
atom  of  water  with  an  atom  of  the  oxide  of  either  metal. 

Valerianate  of  Soda  (XaO,C,oH903). — The  characters  of  this  com- 
pound, as  described  in  the  British  Pharmacopoeia  are,  that  it  is  in  dry  white 


LINSEED    AND    OTHER    FIXED    OILS.  629 

masses  without  any  alkaline  reaction.  It  should  be  entirely  soluble  in  recti- 
fied spirits,  and  give  out  a  powerful  odor  of  valerian  when  moistened  with 
diluted  sulphuric  acid.  The  Valerianate  of  Zinc  (ZnCCjoHgOa)  is  made 
by  double  decomposition,  equal  weights  of  valerianate  of  soda  and  sulphate 
of  zinc  being  dissolved  in  a  sufficiency  of  distilled  water  and  then  mixed. 
This  salt  is  obtained  in  brilliant  white  tabular  crystals  of  a  pearly  lustre. 
They  have  a  slight  odor  of  valerianic  acid,  and  a  metallic  taste.  The  salt 
is  scarcely  soluble  in  cold  water  or  ether,  but  is  dissolved  by  hot  water  or 
alcohol,  and  the  hot  aqueous  solution  is  not  precipitated  by  a  solution  of 
chloride  of  barium.  When  heated  to  redness,  oxide  of  zinc  remains,  which 
when  dissolved  in  diluted  sulphuric  acid  gives  the  usual  reaction  of  that 
metal. 

Fixed  Vegetable  Oils. 

In  adverting  to  the  general  nature  and  properties  of  the  oils  and  fats,  we 
may  select  a  few  more  for  special  notice  ;  taking  linseed-oil  as  a  specimen  of 
the  drying  oils, — olive-oil  of  the  non-drying  or  greasy  oils,  and  palm-oil  of 
the  concrete  oils  or  vegetable  butters.  The  fixed  oils  are  generally  of  a  pale 
yellow  color  :  they  may  be  bleached  by  exposure  to  light.  They  should  be 
neutral,  but  they  frequently  have  an  acid  reaction.  They  are  insoluble  in 
water  and  not  very  soluble  in  alcohol.  They  are  soluble  in  benzole  and 
chloroform.  When  exposed  to  air  they  gradually  assume  resinous  charac- 
ters, as  a  result  of  the  absorption  or  fixation  of  oxygen.  According  to  re- 
cent observations  on  the  drying  of  oils  by  oxidation,  some  volatile  products 
are  given  off,  consisting  chiefly  of  the  formic,  acetic,  butyric,  acrolic,  and 
carbonic  acids,  while  the  fixed  residue  consists  of  margaric  and  oleic  acids 
associated  with  a  resinous  acid.  The  glycerine  also  disappears.  The  greasy 
and  concrete  oils  become  rancid,  principally  in  consequence  of  mucilaginous 
and  albuminous  impurities  which  gradually  react  upon  them.  This  is  espe- 
cially observed  in  olive  oil. 

When  cooled  to  a  low  temperature  the  fixed  oils  thicken  or  solidify, — 
olive  oil  at  about  36° — colza  oil  at  22° — linseed  oil  at  a  temperature  near 
zero,  and  almond  oil  at  some  degrees  below  zero.  They  may  be  heated  to 
about  500°  without  undergoing  decomposition,  but  they  do  not  admit  of 
distillation  without  decomposition  ;  they  are  said  to  boil,  but  are  really  de- 
composed at  about  the  boiling  point  of  mercury  650°.  Owing  to  this  fixed- 
ness at  high  temperatures,  a  fixed  oil  may  be  used  as  a  bath  for  many  useful 
purposes.  Thus  in  the  manufacture  of  vulcanized  rubber,  the  melted  sulphur 
is  kept  heated  to  a  proper  temperature  for  vulcanization  by  means  of  an  oil- 
bath.  The  tempering  of  some  articles  of  hardened  steel  may  also  be  more 
readily  effected  by  employing  heated  oil,  than  in  judging  by  the  color  ac- 
quired by  the  polished  surface  of  the  metal.  Thus  when  the  oil  begins  to 
smoke,  the  temper  is  that  of  a  straw  color,  or  450°.  A  darker  and  more  abun- 
dant smoke  indicates  a  brown  color,  500°.  A  purple  temper,  about  530°, 
is  shown  by  a  still  more  abundant  and  black  smoke.  A  blue  temper  is 
reached  when  the  oil  takes  fire  on  the  application  of  a  flame,  but  ceases  to 
burn  on  its  removal,  a  temperature  of  about  580°.  The  usual  temper  for 
springs  is  found  to  be  when  the  oil  takes  fire  and  continues  to  burn. 

Linseed  oil,  obtained  by  expression  from  the  seeds  of  the  Linu7n  usitatis- 
simum,  or  common  flax,  remains  fluid  until  cooled  down  to  about  0°,  when 
it  gradually  solidifies..  It  is  largely  used  for  paints  and  varnishes,  and  for 
these  purposes  its  drying  quality  is  increased  by  heating  it  with  a  little 
litharge.  It  is  an  important  component  of  Printers^  Ink,  for  which  it  is  first 
heated  and  then  set  fire  to,  and  allowed  to  burn  for  some  time,  when  it  is 
extinguished,  and  the  heating  continued  till  a  film  forms  upon  it }  m  this 


630  OLIVE,    ALMOND,    CASTOR,    AND    PALM    OILS. 

state  it  is  called  varnish,  and  is  easily  raiseible  with  fresh  oil,  or  with  tur- 
pentine, or  other  matters  required  for  thinning  or  tempering  it,  and  about  a 
sixth  or  eighth  part  of  fine  lamp-black  is  then  added.  Silk  and  leather  are 
varnished  and  enamelled  with  similar  preparations  of  linseed-oil.  Walnut, 
hemp,  and  poppy-oil  also  rank  with  the  drying  oils,  but  are  inferior  to  linseed- 
oil. 

Olive-oil,  IS  expressed  from  the  fleshy  part  of  the  fruit  of  the  olive  tree.  It 
varies  in  quality  according  to  the  mode  of  obtaining  it.  What  is  termed 
virgin-oil  is  obtained  by  gentle  pressure  at  common  temperatures  :  it  has  a 
very  slight  nutty  flavor,  and  is  long  in  becoming  rancid.  Its  sp.  gr.  at  60^ 
is  about  0"915.  This  oil  is  unrivalled  for  culinary  use,  and  being  less  apt 
than  most  other  oils  to  thicken  by  exposure  to  air,  it  is  preferred  for  greas- 
ing delicate  machinery,  especially  watch  and  clock-work.  In  order  to  pre- 
pare it  for  this  purpose,  the  finest  and  purest  cold-drawn  oil  is  first  selected  : 
it  is  then  cooled,  and  the  more  liquid  portion  poured  ofl'from  the  fatty  deposit ; 
a  piece  of  sheet-lead  or  some  shot  are  then  immersed  in  it,  and  it  is  exposed 
in  a  corked  phial  to  sunshine  ;  a  white  matter  separates,  after  which  the  oil 
becomes  clear  and  colorless,  and  is  poured  off  for  use. 

Almond-oil  is  prepared  from  sweet  and  bitter  almonds  ;  the  purest  is  cold- 
drawn,  by  gentle  pressure,  from  coarsely-powdered  almonds:  when  hot- 
pressed,  it  has  a  deeper  color,  and  becomes  sooner  rancid. 

Colza  oil  is  an  inodorous  yellowish  oil  obtained  from  cabbage-seed  {Bras- 
sico  oleifera).  It  has  a  sp.  gr.  of  '915.  It  is  most  extensively  used  as  a 
cheap  and  good  burning  oil. 

Oil  of  Ben,  from  the  seeds  of  the  Moringa  aspera,  separates  soon  after 
expression  into  oleine  and  margarine  ;  the  former  is  much  esteemed  for  oil- 
ing watch- work,  as  it  neither  becomes  viscid  nor  rancid  ;  hence  also  its  excel- 
lence for  certain  scented  oils,  as  of  jasmine  and  tuberose  flowers. 

Castor-oil  is  obtained  from  the  seeds  of  the  Ricinus  communis.  This  is 
the  heaviest  of  the  fixed  oils,  its  sp.  gr.  being  0*969.  It  is  a  thick,  viscid, 
colorless  oil ;  when  cooled  to  0^  it  congeals  into  a  transparent  mass.  Although 
not  a  drying  oil,  it  hardens  by  exposure  to  air.  It  dissolves  in  all  propor- 
tions of  alcohol  and  ether,  and  thus  differs  from  other  fixed  oils.  It  forms 
a  thick  tenacious  mass  when  mixed  with  collodion.  This  singular  compound 
has  been  called  Parkapine,  from  its  discoverer,  M.  A.  Parks.  Castor  oil  is 
much  used  as  a  hair  oil,  and  medicinally  as  a  mild  aperient.  The  products 
of  its  saponification  are  peculiar ;  and  when  acted  on  by  nitrous  acid  it  pro- 
duces a  concrete  fatty  substance,  the  palmic  or  ricinelaidic  acid. 

In  the  subjoined  table  we  have  given  the  specific  gravities  of  good  sam- 
ples of  the  principal  fixed  oils  : — 


Sperm  oil 

.     -8750 

Southern  whale 

.     -9225 

Colza 

.     -9156 

Poppy       . 

.     -9254 

Olive  (flask)     . 

.     -9158 

Cod-liver  . 

.     -9285 

Olive  (jar) 

.     -9171 

Linseed    . 

.     -9362 

Olive  (cask) 

.     -9174 

"       boiled  . 

.     -9506 

Almond    , 

.     -9214 

Castor 

.     -9674 

Palm-oil  and  Cocoa-nut  oil  are  good  specimens  of  vegetable  butters.  Palm- 
oil  is  chiefly  produced  from  the  fruit  of  the  Elais  Guineensis ;  it  is  orange- 
colored,  but  admits  of  bleaching,  and  has  the  violet  odor  of  orris-root.  It 
is  used  in  the  manufacture  of  soap,  candles,  and  a  composition  for  greasing 
the  axles  of  railway  carriages,  in  which  it  is  combined  with  soda.  Cocoa- 
nut  oil,  from  the  Cocos  nucifera,  fuses  at  about  70*^  ;  but  its  stearine,  mixed 
with  a  portion  of  the  stearic  acid  of  tallow,  forms  a  good  and  cheap  candle. 
By  saponification  it  afl'ords  several  distinct  acids.  Chocolate-nut  oil,  ex- 
pressed from  the  seed  of  the  Theobroma  Cacao,  gives  greasiness  to  Chocolate, 


MANUFACTURE    OF    SOAPS.  631 

which  is  made  by  torrefying  the  bean,  and  grinding  it  into  a  fine  paste  in  a 
hot  mill  or  mortar.     The  varieties  of  cocoa  are  derived  from  the  same  source. 
Nutmeg  butter,  the  concrete  oil  of  the  nutmeg,  and  Laurel-oil,  the  fat  of  the " 
bay  berry,  belong  also  to  this  class,  and  when  saponified  yield  mynstic  and 
lauric  acids,  and  glycerine. 

^  Animal  fats  are  generally  contained  in  the  adipose  membrane  or  cellular 
tissue,  which  is  chopped  up  and  heated  so  as  to  liquefy  the  fat :  the  remain- 
ing membranes  are  rendered  crisp  by  the  heat,  and  when  the  fat  has  been 
pressed  out  of  them  are  sold  in  the  form  of  flat  cakes,  called  greaves  or  crack- 
lings, used  as  a  coarse  food  for  dogs,  as  a  manure,  and  in  the  manufacture  of 
ferrocyanide  of  potassium.  Whale-oil,  when  saponified,  yields  fatty  acids 
and  glycerine,  and  traces  of  phocenic  acid.  Spermaceti-oil  deposits  the  pecu- 
liar white  fatty  crystalline  matter,  Spermaceti.  The  oil  itself  is  an  oleate  of 
glycerine.  It  is  the  lightest  of  the  fixed  oils,  having  a  sp.  gr.  of  0-878.  It 
is  of  a  yellow  color,  and  when  cooled  to  about  45°  assumes  a  semi-solid 
state.  Spermaceti,  or  Cetine,  when  saponified,  affords  no  glycerine,  but  in 
its  place  a  distinct  base  termed  jEtkal,=G^fl^fi^.  Pure  spermaceti  (C8,H„^0J, 
fuses  at  about  120°  ;  its  sp.  gr.  is  0  940  ;  it  dissolves  in  boiling  anhydrous 
alcohol  and  in  ether,  but  falls  on  cooling.  When  subjected  to  destructive 
distillation  it  is  resolved  into  a  liquid  hydrocarbon,  ce^ewe,  =  Cg^Hg.^,  and  ethalic 
or  palmitic  acid  (CggHg^OaHO).  Ethal  fuses  at  about  118°,  and  is  deposited 
from  its  hot  alcoholic  solution  in  white  flakes.  When  distilled  with  anhy- 
drous phosphoric  acid  it  yields  cetene.  When  oxidized  by  the  protracted 
action  of  boiling  nitric  acid,  spermaceti  yields  succinic,  oenanthylic,  pimelic, 
and  adipic  acids. 

Beeswax  consists,  according  to  Brodie  {Phil.  Trans.,  184T-49),  of  three 
substances  separable  by  boiling  alcohol :  namely,  of  Myricin  (Cg^Hg^Oj, 
which  is  insoluble.;  Cerin  {G^^^fi^,  which  is  deposited  in  crystals  as  the 
solution  cools ;  and  Cerolein,  which  is  retained  in  solution.  Their  relative 
proportions  vary,  but  in  ordinary  beeswax  there  appears  to  be  about  73 
per  cent,  of  myricin,  22  of  cerin,  and  5  of  cerolein.  The  Myrica  cerifera, 
and  some  other  trees,  yield  vegetable  wax.  White  wax  melts  at  140°.  Its 
specific  gravity  is  "960. 

Soaps.  ^ 

Common  hard  soaps  are  chiefly  made  with  tallow  and  soda,  they  are  there- 
fore stearates,  margarates,  and  oleates  of  soda.  The  sp.  gr.  of  the  solution 
of  caustic  soda  is  about  1*15,  and  is  prepared  in  the  usual  way  by  the  action 
of  lime  upon  carbonate  of  soda.  When  the  lye  is  raised  to  its  boiling-point 
the  tallow  is  gradually  added  so  long  as  the  lye  saponifies  it,  and  in  this  way 
a  liquid  is  obtained,  which  holds  the  soap  and  glycerine  in  solution  :  to 
separate  the  former,  common  salt  is  added ;  soap  being  insoluble  in  brine,  is 
thus  brought  to  float  upon  the  surface,  and,  if  the  brine  is  concentrated,  the 
soap  separates  nearly  in  an  anhydrous  state ;  but  as  this  is  not  the  object  of 
the  manufacturer,  the  quantity  of  salt  employed  is  only  such  as  to  effect  the 
separation  of  the  soap  without  dehydrating  it.  New  soap  is  said  to  contain 
about  50  per  cent,  of  water,  and  to  retain  above  30  per  cent,  when  compara- 
tively hard  and  dry.  The  alkali  amounts  to  from  5  to  7  per  cent.  There 
is,  therefore,  a  manifest  advantage  to  the  consumer  in  purchasing  dry  and 
old  soap,  while  the  object  of  the  vendor  is  to  sell  the  soap  as  humid  as 
possible,  and  to  prevent  its  d'esiccation,  which  is  effected  by  keeping  it  in 
damp  cellars.  The  following  analyses  represent  the  comparative  composition 
of  some  well-known  varieties  of  soap  : — 


632  MANUFACTURE    OF    SOAPS. 


BEST  YELLOW. 

BEST  MOTTLED. 

Tallow  acids     . 

.     50-00 

Bone-tallow  acids     . 

.     62-40 

Water       . 

.     31-50 

Water       . 

.     30-00 

Caustic  soda     . 

.       6-50 

Caustic  soda     . 

.       7-60 

Resin 

.     12-00 

MARINE. 

BLUE  MOTTLED. 

Cocoa-oil  acids 

.     23-00 

Palm  and  cocoa-acids 

.     50-00 

Water       . 

.     59-60 

Water       . 

.     41-20 

Caustic  soda     . 

.       2-70 

Caustic  soda     . 

.       7-30 

Chloride  of  sodium 

.     14-70 

Salts 

.       1-80 

{Laboratory,  No.  10,  June,  1867,  p.  176.)  In  the  glycerine  soap  a  large 
proportion  of  glycerine  is  incorporated  with  the  fatty  salts.  Soap  is  some- 
times colored,  mottled,  or  maj*bled,  by  the  addition  of  coloring  matters  :  the 
mottling  is  produced  by  oxide  of  manganese.  Sometimes  a  solution  of 
sulphate  of  iron  is  used,  which  being  decomposed,  causes  the  diffusion  of 
oxide  of  iron  through  the  soap ;  in  these  cases  the  mottling  is  originally 
black,  but  becomes  red  or  brown  or  variegated  upon  the  exterior  of  the  bars 
in  consequence  of  the  action  of  the  air.  A  considerable  quantity  of  common 
rosin  is  added  to  the  yellow  soaps  of  commerce.  There  are  also  other 
additions  made  to  soap,  some  of  which  are  supposed  to  improve  its  detergent 
quality ;  but,  generally  speaking,  they  deteriorate  the  article,  and  are  princi- 
pally resorted  to  as  adding  to  the  weight  of  the  soap  by  the  substitution  of 
cheap  materials ;  sand,  clay,  fuller's  earth,  alkaline  silicates,  sulphate  of  soda, 
Cornish  clay,  aluminate  of  soda,  starch,  flour,  and  many  other  substances, 
have  been  employed.  The  use  of  such  substances  as  these  in  the  manufacture 
of  soap  can  only  be  regarded  as  a  fraud  upon  ihe  public,  often  legalized  by 
the  granting  of  a  patent  to  the  manufacturer  !  Excepting  the  alkaline  sili- 
cates, which  of  course  only  operate  by  their  alkalinity,  the  other  ingredients 
have  no  detergent  action  whatever.  The  presence  of  a  large  percentage  of 
water  artificially  kept  in  the  soap  and  the  addition  of  a  large  quantity  of 
silica  in  the  form  of  silicate  add  greatly  to  the  weight  of  the  soap,  and  'pro 
tanto  reduce  its  value  as  a  detergent  compound.  Silicic  acid  is  not  so 
costly  as  the  fatty  acids ;  hence  the  addition  is  in  favor  of  the  manufacturer. 

Curd  soap  is  usually  manufactured  from  tallow  only,  but  sometimes  lard  or 
olive  oil  is  added.  Common  yellow  soap  is  made  from  tallow,  palm  oil,  and 
common  rosin.  The  latter  being  acid,  combines  with  the  alkali  to  form  a 
saponaceous  compound. 

The  soaps  known  in  commerce  as  Spanish  soap  (Sapo  durus)  and  Marseilles 
soap  are  soda-soaps  of  olive-oil.  Palm-oil  and  cocoa-nut  oil  are  also  largely 
nsed  as  sources  of  soap,  and  mixtures  of  these  with  the  animal  fats  and  bone- 
grease  are  employed  as  the  basis  of  scented  and  other  toilet  soaps.  Bone 
grease  is  manufactured  in  enormous  quantities  by  the  bone-boilers  in  and 
around  London  :  in  addition  to  its  use  in  the  production  of  the  finest  toilet 
soaps,  it  is  employed  in  the  manufacture  of  scented  and  colored  pomatums, 
and  of  an  article  commonly  sold  under  the  name  of  Beards  grease.  Soaps 
are  perfumed  with  various  essential  oils.  Nitro-benzole  under  the  name  of 
Essence  of  Mirhane  is  largely  employed  as  a  cheap  substitute  for  the  essential 
oil  of  bitter  almonds. 

The  soaps  of  potassa  are  distinguished  from  those  of  soda  by  remaining 
soft  (Sapo  mollis).  Common  soft  soap  is  frequently  made  with  fish-oil. 
Naples  soap  is  a  perfumed  potassa-soap  made  with  lard.  Transparent  soap 
is  obtained  by  dissolving  soap  in  alcohol,  which  is  afterwards  distilled  off,  so 
as  to  leave  a  soft  brown  transparent  residue,  which  is  dried  in  moulds  or  balls. 
The  soaps  of  potash,  soda,  and  ammonia  are  soluble  in  water,  but  those  of  the 
alkaline  earths  and  metallic  oxides,  which  are  produced  by  double  decompo- 


MANUFACTURE    OF    SOAPS.      ACROLEINE.  633 

sition,  are  insoluble  in  water,  and  float  upon  it,  forming  a  curd.  A  good 
soda  soap  forms  a  thick  viscid  liquid  with  distilled  water — the  solution  is 
frothy  when  shaken  :  it  has  an  alkaline  taste  and  reaction.  A  solution  of 
pure  oleate  of  soda  with  glycerine  is  remarkable  for  the  tenacity  which  it 
gives  to  water,  and  has  been  much  employed  for  producing  soap-bubbles  of 
large  size  and  remarkable  for  their  preserving  their  form  for  a  long  time. 
Soap  is  soluble  in  alcohol,  but  its  best  solvent  is  a  mixture  of  one  part  of 
water  with  three  parts  of  alcohol.  An  alcoholic  solution  of  soap  is  employed 
as  a  soap-test  for  determining  the  relative  degrees  of  hardness  in  river  or 
spring  water.  For  this  purpose  Castile  or  Spanish  soap  is  preferable,  as 
the  solution  is  less  liable  to  spontaneous  changes.  A  solution  of  soap  is 
decomposed  by  all  acids  and  earthy  salts,  especially  by  the  salts  of  lime  and 
magnesia.  Acids  take  the  alkaline  base  and  set  free  the  fatty  acids  of  the 
soap,  while  the  calcareous  and  magnesian  salts  form  insoluble  white  curdy- 
looking  compounds,  which  float  on  water.  When  heated,  soap  melts  and 
gives  off  a  combustible  vapor,  leaving  an  ash  either  of  soda  or  potash,  and 
sometimes  consisting  of  a  mixture  of  the  alkalies  in  the  state  of  carbonate. 

When  the  fats  and  oils  are  decomposed  by  oxide  of  lead,  the  resulting 
combinations  of  the  fatty  acids  with  that  oxide,  is  known  under  the  name 
of  Lead  plaster.     {Emplastrum  plumhi  ;  Diachylon.) 

AcROLEiNE  (CeH^Og).— When  the  ordinary  fatty  bodies  are  subjected  to 
destructive  distillation,  the  oleic  acid  is  partially  converted  into  sebacic  acid, 
the  stearic  into  margaric  acid,  and  the  glycerine  into  acroleine.  When 
glycerine  is  distilled  with  anhydrous  phosphoric  acid,  water  and  acroleine  are 
the  products,  and  the  latter  may  be  dehydrated  by  rectification  over  chloride 
of  calcium.  Glycerine  contains  the  elements  of  acroleine  with  four  equiva- 
lents of  water,  hence  under  the  dehydrating  action  of  phosphoric  acid,  the 
conversion. is  readily  effected: — 

CeHgOe  =  C^HA  +  4H0 

^ — . '  » — . — '  -—^-'  ^gjgj 

Glycerine.  Acroleine.  Water.  "^^Bl 

Fatty  bodies  which  contain  no  glycerine  do  not  yield  acroleine  by  distillation. 
Thus  while  tallow  produces  it,  stearic  acid  does  not.  Some  have  regarded 
acroleine  as  the  aldehyde  of  glycerine.  Pure  acroleine  is  a  limpid  colorless 
liquid  of  a  highly  irritating  odor,  lighter  than  water,  boiling  at  about  125°, 
and  burning  with  a  bright  flame ;  it  is  soluble  in  alcohol  and  ether,  but  only 
sparingly  so  in  water.  It  soon  undergoes  spontaneous  changes,  depositing 
an  isomeric  white  substance,  disacryle,  and  a  resinoid  body  ;  and  when  ex- 
posed to  air,  or  more  especially  when  oxidized  by  oxide  of  silver,  it  is  con- 
verted into  acrylic  add=(RO,Q^B.^O^),  a  portion  of  the  oxide  being  at  the 
same  time  reduced;  CflH,0,+3AgO,=(AgO,C6H303)+2Ag-|-HO. 


634  VEGETABLE    ACIDS.      TARTARIC    ACID. 


CHAPTER    LII. 

VEGETABLE    ACIDS. 

The  acids  of  the  regetable  kingdom  are  very  numerous  as  a  class.  About 
lYO  are  now  known.  They  are  for  the  most  part  solid  and  colorless,  and 
many  are  crystalline.  They  are  combined  with  potassa,  soda,  or  lime,  and 
are  thus  contained  as  salts  in  the  juices  of  plants.  Some  are  educts,  i.  e., 
they  exist  in  the  vegetable  structure,  and  are  separated  by  simple  processes. 
The  tartaric,  citric,  malic,  gallic,  and  tannic  acids  are  instances  of  this  class. 
Others,  like  the  pyrogallic,  mucic,  and  picric  acids,  are  products  of  art. 
These  are  the  most  numerous,  and  their  number  is  annually  increasing. 
Others,  again,  as  the  oxalic  and  benzoic  acids,  are  both  educts  and  products. 

The  vegetable  acids  are  soluble  in  water  and  in  alcohol :  they  form  with 
bases  various  classes  of  well-defined  crystalline  salts.  By  reason  of  their 
superior  affinity,  they  sometimes  displace  mineral  acids  from  their  saline 
combinations.  Thus  oxalic  acid  separates  lime,  and  the  oxides  of  silver  and 
copper,  from  the  solutions  of  the  salts  of  these  bases ;  and  picric  acid  sepa- 
rates potassa  from  the  salts  of  that  alkali.  Tannic  acid  precipitates  the 
salts  of  lead,  antimony,  and  other  metals.  This  acid  generally  forms  pre- 
cipitates (insoluble  compounds)  with  most  of  the  alkaloids,  and  separates 
them  from  their  mineral  acid  combinations.  Some  of  these  acids  have  a 
simple  constitution,  being  formed  of  three  elements  C  H  O  :  one  (the  oxalic 
acid)  is  formed  of  C  0  only.  Others,  especially  those  of  artificial  origin, 
are  much  more  complex  :  thus  picric,  or  carbazotic  acid,  has  the  composition 
of  (C,2H20(NO^)3,HO).  When  dissolved  in  water,  some,  such  as  the  tartaric, 
citric,  and  gallic  acids,  undergo  decomposition,  and  vegetable  mould  results. 
Others,  such  as  the  oxalic  and  acetic,  show  no  tendency  to  decomposition. 
All  are  decomposed  by  heat  in  close  vessels :  some  are  volatile  when  heated 
to  a  moderate  temperature  in  air  (benzoic,  formic,  acetic)  ;  others  are  fixed, 
and  are  decomposed  when  strongly  heated,  either  being  entirely  burnt,  or 
leaving  a  residue  of  carbon.  When  the  salts  of  these  acids  are  heated  in  close 
vessels,  carbon  and  a  carbonate  of  the  base  result.  The  equivalents  of  these 
acids  are  high :  they  are  easily  determined  by  the  rules  already  explained. 

Tartaric  Acid  (C8H,0,o2HO=T). 

This  acid  is  found  free,  and  in  combination,  in  many  vegetables.  It  is 
found  in  the  grape,  mulberry,  tamarind,  and  pine-apple ;  but  its  principal 
source  is  the  juice  of  the  grape,  in  which  it  exists  in  the  form  of  tartar,  or 
bitartrate  of  potassa  (KO,HO,C8H40io)-  This  salt  is  decomposed  as  follows : 
4  parts  of  it  in  fine  powder,  are  well  mixed  with  one  part  of  powdered  chalk, 
and  the  mixture  thrown,  by  small  portions  at  a  time,  into  10  parts  of  boiling 
water  ;  when  the  effervescence  is  over,  the  whole  is  stirred  and  left  to  subside  ; 
the  liquid,  which  is  a  solution  of  neutral  tartrate  of  potassa,  is  then  poured 
off  the  sediment,  which  is  tartrate  of  lime,  and  a  solution  of  chloride  of 
calcium  is  added  to  it.  This  throws  down  an  additional  portion  of  tartrate 
of  lime,  which  is  mixed  with  the  first,  and  having  been  well  washed,  is  de- 
composed by  dilute  sulphuric  acid  ;  this  forms  sulphate  of  lime,  while  the 
tartaric  acid  remains  in  solution,  and  is  obtained  by  slow  evaporation.     The 


TARTARIC    ACID.      THE    TARTRATES.  635 

first  crystals  require  to  be  redissolved,  and  digested  with  a  little  purified 
animal  charcoal  until  the  liquid  is  colorless ;  it  is  then  again  evaporated  and 
crystallized.  Tartar  may  be  similarly  decomposed  by  carbonate  of  baryta 
and  chloride  of  barium;  the  resulting  sulphate  of  baryta  falls  more  rapidly 
than  the  sulphate  of  lime,  and  may  be  used  for  white  paint. 

Crystallized  tartaric  acid  is  very  sour:  its  sp.  gr.  is  1-74;  it  is  translucent, 
and  of  complicated  forms,  derived  from  an  oblique  rhombic  prism.  It  acquires 
electric  polarity  by  heat.  It  is  permanent  in  a  dry  atmosphere  :  water  dis- 
solves about  1-5  its  weight  at  60°,  and  more  than  twice  its  weight  at  21 2^. 
It  is  also  soluble  in  alcohol.  The  dilute  aqueous  solution  soon  becomes 
mouldy.     It  is  converted  into  oxalic  and  acetic  acids  by  fusion  with  potassa. 

^C8H,0,o,2HO]     +    3  [KO,HO]  =     [KO.C^HgOa]     +    2[KO,C203]     +     6[H0] 

Tartaric  acid.  Potassa.      Acetate  of  potassa.  Oxalate  of  potassa.     Water. 

It  is  transformed  by  the  action  of  peroxide  of  manganese,  or  of  lead,  into 
formic  and  carbonic  acids. 

[C8H,0,o,2HO]     +     eCPbOJ     =    2[PbO,C2H03]     -f    4[PbO,C02]     +    4[H0] 


Tartaric  acid.     Peroxide  of  lead.  Formate  of  lead.        Carb.  of  lead.         Water. 

Tartaric  acid  is  distinguished  by  the  white  granular  precipitate  which  it 
produces  when  added  in  excess  to  solutions  containing  potassa.  If  these 
solutions  are  very  dilute,  the  crystalline  precipitation  is  accelerated  by  the 
addition  of  alcohol.  It  produces  a  white  precipitate,  soluble  in  an  excess  of 
the  acid,  in  lime,  baryta,  and  strontia- water,  and  in  acetate  of  lead.  It  is 
used  in  calico-printing,  and  is  much  employed  as  a  cheap  substitute  for  citric 
acid  in  lemonade  and  in  effervescent  solutions.  In  the  laboratory  it  is  used 
as  a  test  for  the  salts  of  potassa,  and  to  prevent  the  precipitation  of  certain 
oxides,  as  the  oxide  of  antimony,  and  titanic  acid. 

The  tartaric  acid  of  commerce  is  apt  to  be  contaminated  by  traces  of  sul- 
phuric acid  and  of  lead.  To  detect  sulphuric  acid,  chloride  of  barium  may 
be  used  :  if  added  in  excess,  or  if  the  solution  of  tartaric  acid  is  concentrated, 
tartrate  of  baryta  will  fall ;  but  the  presence  of  sulphuric  acid  in  the  precipi- 
tate is  recognized  by  its  insolubility  in  hydrochloric  acid,  which  acid  dissolves 
tartrate  of  baryta.  Sulphuretted  hydrogen  is  the  test  for  the  presence  of  lead. 
If  lead  is  present  this  gives  a  brown  discoloration  to  the  solution.  This 
impurity  is  derived  from  the  leaden  pans  in  which  crystallization  takes  place. 

Pasteur  has  shown  that  there  are  two  modifications  of  crystallized  tartaric 
acid.  The  crystals  of  one  variety,  when  dissolved  in  water,  turn  the  polar- 
ized ray  to  the  right — dextro-tartaric,  or  the  common  tartaric  acid.  Other 
crystals  selected  from  the  same  mass,  when  dissolved  in  water,  turn  the  ray 
to  the  left — Icevo-tartaric  add.  Both  sets  of#rystals  are  unsymmetrical,  but 
the  absence  of  symmetry  is  exactly  in  opposite  directions.  It  is  remarkable 
that  when  equal  parts  of  the  two  acids  are  mixed,  crystals  are  deposited  from 
the  mixture,  which  appear  to  be  identical  in  properties  with  racemic  acid  : 
they  have  no  action  on  a  ray  of  polarized  light.  As  racemic  acid  diflfers  in 
chemical  properties  from  the  tartaric,  these  facts  show  a  singular  relation 
between  the  crystalline  forms  and  the  chemical  and  optical  properties  of 
bodies. 

The  tartrates  are  mostly  crystallizable,  and  are  either  neutral  or  acid.  In 
the  neutral  tartrates  2  atoms  of  base  are  combined  with  1  atom  of  acid,  as  in 
neutral  tartrate  of  potassa,  which  is  2(KO),C8H^O,o,  or  in  tartrate  of  potassa 
and  soda  =KO,NaO,CsH^Oio.  In  the  acid  tartrates  (or  bitartrates)  1  atom 
of  water  replaces  1  of  the  bases,  as  in  bitartrate  of  potassa,  which  is  KO, 


636  METALLIC    TARTRATES. 

HOjCgH^Ojo.  There  is  also  an  important  class  of  tartrates  in  which  one  of 
the  bases  is  a  protoxide  and  the  other  a  teroxide,  the  salt  being  neutral, 
as  in  the  tartrate  of  potassa  and  antimony  (emetic  tartar),  which  is  KO,Sb 
03,C8H^Oio.  Lastly,  there  are  tartrates  in  which  one  of  the  bases  is  replaced 
by  a  weak  acid,  as  in  the  boro-tartrate  of  potassa  =KO,B03,C8H^Oio. 

Tartrate  of  potassa^  2(K0),T,  used  as  an  aperient  under  the  name  of  solu- 
hie  tartar,  forms  prismatic  crystals  of  a  saline  and  bitter  taste,  soluble  in  two 
parts  of  water.  Most  of  the  acids  occasion  a  precipitate  of  the  acid  tartrate 
in  the  aqueous  solution  of  this  salt,  by  abstracting  an  atom  of  potassa. 

Acid  Tartrate.  Bitartrate  of  Potassa.  Tartar  (KO,HO,T). — This  salt 
exists  in  the  juice  of  the  grape,  and  is  deposited  in  wine-casks  in  the  form  of 
a  white  or  red  crystalline  incrustation,  called  argol,  or  crude  tartar.  It  is 
purified  by  dissolving  it  in  boiling  water,  with  one-twentieth  of  its  weight  of 
pipeclay,  which  absorbs  the  coloring  matter,  and  falls  as  a  sediment,  the 
crystals  of  tartar  separating  afterwards  upon  the  surface  of  the  liquor,  and 
upon  the  sides  and  bottom  of  the  boiler;  the  term  cream  of  tartar  was  origi- 
nally applied  to  the  imperfectly  crystallized  superficial  crust.  The  acid  tar- 
trate of  potassa  is  also  formed  by  adding  excess  of  tartaric  acid  to  a  solution 
of  potassa :  the  mixture  presently  deposits  crystalline  grains,  and  furnishes 
an  example  of  diminution  of  solubility  by  increase  of  acid  in  the  salt.  Upon 
this  the  use  of  tartaric  acid  as  a  test  for  potassa  depends ;  for  soda  forms  an 
easily  soluble  supertartrate,  and  affords  no  precipitate. 

The  crystals  of  this  salt,  which  are  rhombic  prisms,  include  one  equivalent 
of  water,  which  is  not  separable  at  a  heat  much  below  that  at  which  the  acid 
of  the  salt  begins  to  be  decomposed.  They  are  hard,  gritty,  and  subacid  ; 
sp.  gr.  1-95.  This  salt  is  soluble  in  184  parts  of  water  at  68° ;  and  in  18 
parts  at  212°.  It  is  rendered  much  more  soluble  by  the  addition  of  boracic 
acid  or  of  borax;  2  parts  of  borax  and  5  of  tartar  are  soluble  in  about  six 
times  their  weight  of  boiling  water;  on  evaporating  the  solution,  the  residue 
concretes  into  Le  Fevreh  soluble  cream  of  tartar,  or  sal-gummosum.  When 
exposed  to  heat  in  a  close  vessel,  tartar  fuses,  blackens,  and  is  decomposed, 
and  carbonate  of  potassa,  mixed  with  charcoal  (black  flux)  remains.  It  is 
an  excellent  flux  in  the  reduction  of  metallic  ores,  upon  a  small  scale,  its 
alkali  promoting  their  fusion,  and  the  carbonaceous  matter  tending  to  reduce 
the  oxides.  Tartar  is  sometimes  adulterated  with  pounded  quartz  or  calca- 
reous spar;  the  former  is  detected  by  its  insolubility,  the  latter  by  efferves- 
cence with  dilute  hydrochloric  acid.  Tartrate  of  lime  is  often  present  in 
purified  tartar ;  it  separates  in  tufts  of  acicular  crystals  from  a  hot  solution 
of  the  salt. 

Tartrate  of  soda  (2(NaO),T+4HO)  forms  acicular  crystals,  soluble  in 
about  their  own  weight  of  w%ter.  When  their  aqueous  solution  is  mixed 
with  half  their  weight  of  tartaric  acid,  it  yields  small  prismatic  crystals  of 
acid  tartrate  of  soda,  =NaO,HO,T,2HO,  of  an  acid  taste,  soluble  in  8  parts 
of  cold  and  1-8  of  boiling  water.  Tartrate  of  soda  is  formed  extempora- 
neously by  dissolving  equal  parts  of  powdered  tartaric  acid  and  of  bicar- 
bonate of  soda,  in  separate  portions  of  water,  and  then  mixing  the  solutions  ; 
it  forms  a  refreshing  saline  and  slightly  aperient  draught. 

Tartrate  of  potassa  and  soda  (KO,NaO,T  +  8HO)  is  prepared  by  satu- 
rating the  excess  of  acid  in  tartar,  with  carbonate  of  soda :  it  is  the  Soda 
tartarizata  of  pharmacy  ;  it  forms  fine  transparent  prismatic  crystals.  This 
salt  has  long  been  used  as  a  mild  aperient,  under  the  name  of  Rochelle  Salt, 
and  Sel  de  Seignette,  having  been  first  prepared  at  Rochelle  by  an  apothecary 
of  the  name  of  Seignette.  The  crystals  are  soluble  in  about  3  parts  of  cold 
water. 


ACTION    OF    HEAT    ON    TARTARIC    ACID.  637 

Tartrate  of  lime  is  often  found  as  a  hard  crystalline  deposit  in  light  white 
wines.  It  falls  on  dropping  tartaric  acid  into  lime-water,  and  is  soluble  in 
excess  of  the  acid. 

Tartrates  of  iron — The  prototartrate  falls  as  a  whitish  crystalline  powder 
on  adding  tartaric  acid  to  protosulphate  of  iron.  When  recently  prepared 
and  moist  peroxide  of  iron  is  dissolved  in  tartaric  acid,  an  uncrystallizable 
salt  is  produced,  which  is  not  precipitated  by  the  alkalies. 

A  pertartrate  of  iron  and  potassa  is  formed  by  digesting  hydrated  peroxide 
of  iron  with  tartar  and  water :  made  into  balls,  and  dried,  it  forms  the 
glohuli  martiales,  or  Boules  de  Nancy,  of  old  pharmacy. 

Tartrate  of  copper  forms  a  bluish  green  crystalline  precipitate  in  a  mixture 
of  tartrate  of  soda  and  sulphate  of  copper :  if  the  solutions  are  very  dilute, 
the  salt  is  long  in  falling,  but  on  striking  the  glass,  or  drawing  lines  upon  it 
with  a  glass  rod,  it  soon  appears.  Dissolved  in  a  solution  of  soda,  this  salt 
forms  a  deep  blue  liquid,  useful  as  a  test  for  grape-sugar. 

7hrtrate  of  lead  is  a  white  crystalline  powder  thrown  down  by  tartaric 
acid,  or  a  tartrate,  from  a  solution  of  nitrate  of  lead.  After  having  been 
heated  in  a  glass  tube  to  dull  redness,  it  leaves  a  pyrophorus,  which  inflames 
when  shaken  out  into  the  air,  in  consequence  of  the  rapid  oxidizement  of 
the  finely-divided  lead. 

Tartrate  of  potassa  and  antimony;  Emetic  tartar  (KO,Sb03,C8H^Ojo,HO), 
is  obtained  by  boiling  any  of  the  forms  of  SbOg  with  tartar  and  water.  It 
is  a  white  salt,  of  a  nauseous  styptic  taste,  slightly  efflorescent,  soluble  in 
about  14  parts  of  cold,  and  in  less  than  2  parts  of  boiling  water.  Its  solu- 
tion is  rendered  turbid  by  hydrochloric,  nitric,  and  sulphuric  acids,  but  not 
by  the  fixed  alkalies :  the  fixed  alkaline  carbonates,  and  lime-water,  decom- 
pose it.  Ammonia  throws  down  oxide  of  antimony,  especially  when  aided  by 
beat.  Infusion  of  galls  and  many  other  vegetable  bitter  and  astringent  infu- 
sions form  a  precipitate  in  a  solution  of  emetic  tartar,  which  is  generally 
said  to  be  inactive,  and  hence  decoction  of  bark  has  been  recommended  as 
an  antidote  to  its  poisonous  effects.  It  is  not  precipitated  by  a  solution  of 
ferrocyanide  of  potassium.  A  solution  of  sulphuretted  hydrogen  precipi- 
tates only  strong  solutions  of  emetic  tartar ;  weaker  solutions  are  merely  red- 
dened by  it :  it  is  also  decomposed  by  hydrosulphate  of  ammonia  ;  in  these 
cases  the  precipitate  is  sulphide  of  antimony.  Heated  to  redness,  out  of  the 
contact  of  air,  it  furnishes  a  highly-pyrophoric  residue,  which  contains  an 
alloy  of  potassium  and  antimony. 

Action  of  Heat  on  Tartaric  Add. — When  common  crystallized  tartaric 
acid  is  heated  to  about  350°,  it  fuses  without  losing  weight,  and  congeals  on 
cooling  into  a  vitreous  mass,  which  has  the  same  saturating  power  as  the 
original  acid,  but  which  produces  salts  differing  in  crystalline  form,  and  more 
soluble  than  the  common  tartrates.  If  the  heat  exceed  360^,  the  acid 
becomes  monobasic,  but  still  without  loss  of  weight,  and  is  represented  by 
CsHgOji.HO:  it  forms*  with  potassa  an  uncrystallizable,  deliquescent  salt. 
These  isomeric  modifications  have  been  designated  metatartaric  and  isotar- 
taric  acids  :  when  solutions  of  their  salts  are  boiled,  they  gradually  revert  to 
common  tartrates.  When  the  common  acid  is  kept  in  fusion  at  about  372°, 
it  loses  half  an  equivalent  of  water,  and  is  changed  into  tartralic  acid.  The 
tartralates  are  quite  distinct  from  the  tartrates :  those  of  lime,  baryta,  and 
strontia  are  soluble  in  water,  and  there  is  no  difficultly  soluble  potassa  salt. 

When  the  temperature  of  the  fused  tartaric  acid  is  raised  to  392^  it  loses 
an  equivalent  of  Vater,  and  becomes  tartrelic  acid:  in  this  state  it  forms  a 
peculiar  syrupy  precipitate  with  the  acetates  of  lime,  baryta,  and  strontia, 


638    .  RACEMIO   ACID.      CITRIC    ACID. 

and  produces  neutral  salts  with  one  equivalent  of  base.  The  tartralates  are 
converted  into  tartrates,  when  boiled  with  water. 

By  carefully  continuing  the  action  of  heat  on  tartaric  acid,  it  may  be  ob- 
tained anhydrous ;  it  is  then  white,  amorphous,  and  insoluble  in  cold  water: 
but  by  the  protracted  action  of  water,  or  by  boiling,  it  reverts  to  its  ordinary 
condition,  by  the  resumption  of  two  atoms  of  water. 

Characters  of  Tartaric  Acid. — 1.  When  heated  on  platinum  foil,  it  melts 
and  burns  with  a  reddish  flame,  evolving  a  peculiar  odor.  It  leaves  a  slight 
residue  of  carbon.  2.  Its  aqueous  solution  is  precipitated  by  lime-water, 
the  white  precipitate  (tartrate  of  lime)  being  dissolved  by  a  slight  excess  of 
acid,  or  by  a  large  quantity  of  water.  3.  A  concentrated  solution  of  the 
acid  is  precipitated  by  a  solution  of  potassa,  provided  the  acid  is  in  excess. 
A  small  quantity  of  alcohol  facilitates  the  precipitation.  4.  Nitrate  of  silver 
produces  no  precipitate  in  a  diluted  solution.  When  the  acid  is  neutralized 
by  potassa,  nitrate  of  silver  throws  down  a  white  precipitate,  which  is  black- 
ened and  decomposed  when  heated  to  212°.  5.  A  few  drops  of  the  acidr 
solution  evaporated  on  a  glass-slide,  leave  prismatic  crystals,  which  assume  a 
plumose  form. 

Racemio  Acid:  Uvic  Acid;  Paratartaric  Acid. — This  acid,  formerly 
considered  as  peculiar  to  the  grapes  of  certain  districts,  has  been  found 
generally  in  the  juice  of  sour  grapes.  It  is  obtained  by  saturating  the  juice 
with  carbonate  of  soda :  the  double  tartrate  is  allowed  to  crystallize,  and 
the  double  racemate,  being  more  soluble,  remains  in  the  mother-liquor ;  it  is 
decomposed  by  carbonate  of  lime,  and  the  racemate  of  lime  (treated  as  the 
tartrate)  affords  crystals  of  racemic  acid,  in  the  form  of  oblique  rhombic 
prisms.  It  may  be  obtained  anhydrous ;  and  in  this  state  as  also  in  the 
intermediate  states  of  hydration,  it  resembles  tartaric  acid,  but  it  is  distin- 
guished by  its  inferior  solubility  in  alcohol,  and  by  furnishing  a  precipitate 
with  nitrate  and  sulphate  of  lime,  as  well  as  with  chloride  of  calcium. 

The  relations  of  the  anhydrous  tartaric  acid  to  its  several  hydrated  modi- 
fications are  as  follows  : — 

Anhydrous  tartaric  acid    ....       CgH^Ojo 

Crystallized  tartaric  acid  ....  CgH^Ojg  2H0 

Metatartaric  acid       .....  CgH^OiQ  2H0 

Isotartaric  acid  .....  Cj^HgO,,    HO 

Tartralic  acid 2(CgH40,o)3HO 

Tartrelic  acid C8H40,o    HO 

Racemic  acid C8H40,o  2H0 

Pyruvic  Acid  ;  Pyrotartaric  Acid. — When  tartaric  acid  is  subjected  to 
distillation  at  about  400*^,  it  furnishes,  among  other  products,  a  liquid  and  a 
crystalline  acid.  The  former  produces  a  characteristic  red  color  with  pro- 
tosalts  of  iron,  and  is  monobasic  :  its  formula  is  HO,CgH305.  The  latter  is 
bibasic  :  it  forms  soluble  salts  with  baryta,  strontia,  and  lime  :  its  formula  is 
2(HO),C,oHeOe. 

Citric  Acid  (C^H50,„3HO=Ci). 

This  acid,  discovered  by  Scheele  in  1784,  is  found  in  several  fruits,  but  is 
especially  abundant  in  lemon-juice.  To  obtain  it,  the  juice,  clarified  by 
heating  it  with  a  little  white  of  Qgg,  is  saturated  with  chalk  added  in  small 
portions,  so  long  as  it  occasions  effervescence :  this  throws  down  citrate  of 
lime ;  but  a  portion  of  acid  citrate  remains  dissolved,  which  may  be  neu- 
tralized by  hydrate  of  lime.  When  the  liquid  no  longer  reddens  litmus,  the 
precipitated  citrate  is  washed,  and  decomposed  by  dilute  sulphuric  acid, 
which  forms  sulphate  of  lime,  and  the  citric  acid  is  retained  in  solution  ;  it 
is  filtered  off  and  evaporated  until  a  crystalline  pellicle  appears  on  the  surface : 


CITRIC    ACID.      ITS    CHEMICAL    PROPERTIES.  639 

crystals  of  citric  acid  are  deposited,  which  are  purified  by  repeated  solntion 
ana  crystallization.  (The  practical  details  of  the  process  are  given  in 
Parks'  Chemical  Essays.)  A  gallon  of  good  lemon-juice  yields  about  10 
ounces  of  pure  acid.  Citric  acid  crystallizes  in  rhoraboidal  prisms,  which 
are  dissolved  by  their  weight  of  cold  water,  and  are  soluble  in  alcohol,  but 
not  in  ether.  It  is  considered  as  tribasic,  the  formula  of  the  ordinary  citrates 
being  3(MO),C,aH50i^.  The  ordinary  crystals  deposited  from  a  hot  saturated 
solution  are  3(HO),Ci2HgO„+HO  ;  but  those  obtained  from  spontaneous 
evaporation,  from  a  cold  solution,  are  3(H0),Cj.^H.0ii-f  2H0.  The  former 
neither  lose  weight  nor  transparency  at  212°,  but  the  latter,  dried  at  212°,  lose 
their  adventitious  water,  and  become  3(H0),Cj.^H.0ii.  Anhydrous  citric  acid 
has  not  been  isolated.  When  the  crystals  are  highly  heated,  inflammable  gas 
and  vapor  are  disengaged,  and  a  yellow  residue  obtained  which  is  aconitic  acid. 
Citric  acid  is  used  in  the  preparation  of  acid  drinks,  and  in  pharmacy,  as  a 
substitute  for  lemon-juice.  When  mixed  with  tartaric  acid,  the  adulteration 
may  be  detected  by  adding  to  the  acid,  dissolved  in  cold  water,  a  solution  of 
acetate  of  potassa,  which  occasions  the  precipitation  of  acid  tartrate  of 
potassa.  When  citric  acid  is  added  to  lime-water,  the  liquid  remains  clear 
until  heated  :  it  then  becomes  turbid,  and  deposits  citrate  of  lime.  This 
character  distinguishes  it  from  several  other  vegetable  acids.  Heated  with 
sulphuric  acid,  citric  acid  is  resolved  into  carbonic  oxide,  carbonic  acid, 
acetic  acid,  and  water.  The  action  of  sulphuric  acid  on  this  acid  and  tar- 
taric acid  is  diflferent.  When  tartaric  acid  is  heated  with  sulphuric,  the 
mixture  is  intensely  blackened ;  when  citric  acid  is  thus  treated,  the  liquid 
acquires  only  a  pale-yellow  color.  The  presence  of  tartaric  acid  in  citric 
would  be  indicated  by  a  considerable  darkening.  The  deoxidizing  or  re- 
ducing powers  of  citric  acid  are  less  than  those  of  tartaric  acid.  Thus  when 
a  tew  drops  of  solutions  of  the  acids  or  their  soluble  salts  are  added  to  a  small 
quantity  of  a  solution  of  green  manganate  of  potash  rendered  strongly  alka- 
line, and  the  liquids  are  heated,  the  color  is  rapidly  discharged  by  tartaric 
acid  as  a  tartrate,  but  not  by  citric  acid  as  a  citrate.  The  dififereuce  is  so 
marked  that  the  manganate  of  potash  may  be  employed  to  detect  the  adulte- 
ration of  citric  with  tartaric  acid.  When  citric  acid  is  decomposed  by  fusion 
with  caustic  potassa,  it  yields  oxalic  and  acetic  acids,  and  water. 

Citrates. — The  citric,  like  other  tribasic  acids,  forms  neutral  and  acid 
salts:  they  are  mostly  soluble  in  water,  and  when  lime-water  is  added  to 
their  solutions,  they  become  turbid  when  boiled,  but  again  clear  on  cooling. 
The  citrates  of  potassa  and  of  soda  are  used  medicinally.  Citrate  of  lime  is 
the  usual  source  of  the  pure  acid. 

Action  of  Heat  on  Citric  Acid. — When  carefully  heated,  citric  acid  loses 
2  atoms  of  water,  and  is  transformed  into  aconitic  acid  (equisetic  or  citricic 
acid),  an  acid  found  in  the  varieties  of  aconite,  and  in  the  equisetums ; — 

Citric  acid.  Aconitic  acid. 


SHOjCjaHgO,,       =       CiaHgOja     +      2H0 

Under  the  continued  influence  of  heat,  aconitic  acid  yields  carbonic  acid, 
and  an  oily  distillate  which  crystallizes  on  cooling,  and  is  a  mixture  of  two 
isomeric  acids,  one  much  less  soluble  than  the  other,  the  itaconic  (pyrocitric 
or  citricic  acid),  and  the  eitraconic  acid;  their  formula  is  '•1)10^^^)1^^. 

Aconitic  acid.  Itacouic  acid. 


C„HeO„        =         C,oH,0,        -f         2C0, 

.     Characters  of  Citric  Acid.^l.  When  heated  on  platinum,  it  melts,  and 
burns  with  a  yellow  flame,  leaving  scarcely  any  carbon.     2.  Its  aqueous  solu- 


646  MALIC    ACID.       TANNIC    ACID. 

tion  is  not  readily  precipitated  by  lime-water  until  it  is  boiled,  when  citrate 
of  lime  is  thrown  down,  3.  A  concentrated  solution  of  the  acid  is  not  pre- 
cipitated by  potassa.  On  this  is  founded  a  method  of  detecting  the  adul- 
teration of  citric  with  tartaric  acid.  Cover  a  glass  plate  with  a  layer  of  solu- 
tion of  potassa,  and  drop  on  the  liquid  the  powdered  acid.  If  pure,  the 
citric  acid  simply  dissolves :  if  tartaric  acid  is  present,  stellated  prisms  of 
acid  tartrate  of  potassa  are  formed  in  groups,  and  remain.  4.  Nitrate  of 
silver  produces  in  the  solution  no  precipitate.  When  the  acid  is  neutralized 
by  potassa,  nitrate  of  silver  throws  down  white  citrate  of  silver,  which  is 
only  slightly  discolored  and  partially  decomposed  when  heated  to  112^^.  5. 
A  few  drops  of  the  acid  evaporated  slowly  on  a  glass  slide,  leave  small  cir- 
cular groups  of  prismatic  crystals  radiating  from  a  centre. 

Malic  Acid.     SorMc  Add  (C8H,08,2H0=Ma). 

The  existence  of  a  distinct  acid  in  apple-juice  was  first  proved  by  Scheele, 
in  1784:  it  was  thence  called  Malic  acid.  In  1815  Donovan  found  it  in 
the  berries  of  the  mountain-ash  (Sorbus  aucuparia).  It  occurs  in  other 
vegetables,  especially  (with  oxalic  acid)  in  the  stalks  of  garden  rhubarb.  It 
is  obtained  from  the  clarified  juice  of  ripe  mountain-ash  berries,  by  adding 
to  it  acetate  of  lead,  washing  the  precipitate  with  cold  water,  then  pouring 
boiling  water  upon  the  filter,  and  allowing  it  to  pass  through  the  precipitate 
into  glass  jars :  after  some  hours,  crystals  of  malate  of  lead  are  deposited, 
which  are  to  be  boiled  with  2-3  times  their  weight  of  dilute  sulphuric  acid, 
sp.  gr.  1'09;  the  clear  liquor  then  poured  off,  and  while  still  hot,  sulphu- 
retted hydrogen  passed  through  it  to  precipitate  the  remaining  lead  ;  the 
liquid,  after  having  been  boiled  and  filtered,  is  a  solution  of  nearly  pure 
malic  acid.  It  crystallizes  with  difficulty  in  deliquescent  prisms.  The  malates 
are  either  acid  or  neutral,  the  acid  being  bibasic.  They  are  mostly  soluble 
in  water,  and  insoluble  in  alcohol.  Lime-water  is  not  rendered  turbid  by 
malic  acid,  but  on  evaporating  the  solution,  crystalline  malate  of  lime  sepa- 
rates, which  is  redissolved  by  boiling.  These  characters  distinguish  malic 
acid  from  oxalic,  tartaric,  racemic,  and  citric  acids.  The  peculiar  and 
brilliant  crystalline  appearance  which  recently  precipitated  malate  of  lead 
assumes  when  left  in  the  liquid,  is  characteristic  of  this  salt.  A  mixture  of 
malate  of  lime  and  water,  with  a  little  yeast,  gradually  ferments  ;  carbonic 
acid  is  given  off,  and  succinic  and  acetic  acids  are  found  in  the  residue. 

Malic  acid.  Succinic  acid.  Acetic  acid. 


3(C8H408,2HO)    =   2(C8H305.3HO)  +    (C,H303,HO)  -f  AGO,  -f  2H0. 

Action  of  Heat  on  Malic  Acid. — When  this  acid  is  heated  up  to  about 
400°,  it  is  resolved  into  water  and  a  crystalline  sublimate  of  Maleic  Acid  (p. 
634);  but  if  the  heat  is  carefully  maintained  between  270°  and  280°,  the 
product  is  Fumaric  or  Paramaleic  Acid,  an  acid  found  in  Fumitory,  and 
isomeric  with  maleic  acid :  it  is  especially  characterized  by  the  insolubility 
of  the  fumarate  of  silver :  according  to  Dessaignes,  a  liquid  containing  one- 
200,000th  of  fumaric  acid,  gives  a  precipitate  with  nitrate  of  silver. 

Tannic  Acid  ;  Tannin  ;  Quercitannic  Acid  ;  Gallotannic  Acid 
(C«H,A4,=Qt)- 
There  are  many  vegetable  substances  containing  a  principle  which  confers 
upon  them  an  astringent  taste,  and  which  has  the  property  of  forming  a  pre- 
cipitate in  a  solution  of  gelatine,  and  of  striking  a  dark-blue  or  black  pre- 
cipitate with  solutions  of  the  persalts  of  iron.     These  properties  are  pos- 


TANNO-GALLATES.      INK.      GALLIC    ACID.  641 

sessed  in  a  remarkable  degree  by  an  infusion  of  gall-nuts — the  excrescences 
which  form  upon  the  branches  and  shoots  of  the  Quermis  infectoria^  being 
produced  by  the  puncture  of  the  female  of  the  Cynips  gallae  tinctorice.  The 
insect  deposits  its  ovum  in  the  puncture,  and  occasions  the  excrescence,  or 
gall,  within  which  the  larva  is  developed,  and  when  the  insect  is  perfect,  it 
eats  its  way  out.  The  best  galls,  known  as  hlack  or  blue  halls,  are  gathered 
before  the  insect  has  escaped  ;  the  white  galls  are  those  from  which  the  insect 
has  departed,  and  are  consequently  perforated  with  a  small  circular  hole. 
To  obtain  tannic  acid,  powdered  galls  are  digested  in  about  an  equal  weight 
of  washed  ether,  containing  about  10  percent,  of  water,  which,  when  poured 
off,  separates  into  two  portions,  the  heavier  of  which,  when  carefully  evapo- 
rated, leaves  tannic  acid.  It  is  an  uncrystallizable  scaly  substance,  of  a  pale 
buff  color,  very  astringent,  and  soluble  in  water,  alcohol,  and  ether :  it  red- 
dens litmus,  and  remains  unchanged  when  dry,  but  when  moist  it  soon 
absorbs  oxygen,  and  passes  into  gallic  acid.  Some  of  the  acids  and  several 
salts  precipitate  its  aqueous  solution  ;  and  when  boiled  with  dilute  hydro- 
chloric or  sulphuric  acid,  it  is  converted  into  gallic  acid  and  sugar. 

C54H22O3,      +       lOHO      =      SCC.^HgO.o)       +      C,2H„0,4 

Tannic  acid  forms  insoluble  compounds  with  the  greater  number  of  bases, 
as  well  as  with  many  organic  substances,  and  especially  the  vegetable  alka- 
loids. Combined  with  gelatin,  it  forms  leather,  and  in  combination  with 
peroxide  of  iron  it  is  the  basis  of  black  dyes  and  writing-ink.  No  immedi- 
ate precipitate  is  occasioned  by  tannic  acid  in  very  dilute  solutions  of  pure 
protosalts  of  iron  :  but  when  the  solutions  are  concentrated,  a  white  gelati- 
nous precipitate  falls.  If  excess  of  tannic  acid  is  added  to  a  solution  of 
persulphate  of  iron,  a  black  precipitate  is  formed  ;  and  a  similar  precipitate 
falls  in  a  solution  of  the  protosulphate  after  due  exposure  to  air. 

The  following,  according  to  Dr.  Miller,  furnishes  a  good  writing-ink : 
Digest  three-quarters  of  a  pound  of  bruised  galls  in  a  gallon  of  cold  water, 
then  add  six  ounces  of  sulphate  of  iron  with  an  equal  weight  of  gum  arable, 
and  a  few  drops  of  creasote.  Let  this  mixture  digest  at  ordinary  tempera- 
tures for  two  or  three  weeks,  with  occasional  agitation,  then  let  it  settle,  and 
decant  for  use.  The  tannoferric  inks  are  liable  to  fade  with  age ;  but  the 
writing  may  generally  be  restored  by  washing  it  with  a  weak  acid,  and  then 
applying  an  infusion  of  galls,  logwood,  or  ferrocyanide  of  potassium. 

Characters  of  Tannic  Acid. — 1.  When  heated  in  air  it  melts,  and  burns- 
like a  resin.  2.  It  is  precipitated  by  a  solution  of  gelatin  or  albumen.  3.. 
It  gives  a  black  precipitate  or  color  in  a  solution  of  a  neutral  persalt  of  iron. 
4.  An  excess  of  lime-water  gives  with  it  a  dirty  blue  precipitate  which 
rapidly  becomes  greenish  colored.  5.  The  acid  has  a  peculiarly  astringent 
taste.  It  may  be  detected  in  all  vegetable  infusions  or  decoctions  by  their 
acquiring  a  dark  color  on  the  addition  of  a  few  drops  of  a  persalt  of  iron. 

Gallic  Acid  (Cj^H^Oio). 

This  acid  was  discovered  in  1786  by  Scheele :  it  is  one  of  the  results  of 
the  decomposition  of  tannic  acid.  It  may  be  obtained  by  mixing  powdered 
galls  into  a  thin  paste  with  water,  and  exposing  it  some  weeks  to  air,  occa- 
sionally adding  water  to  prevent  desiccation  ;  the  powder  swells,  becomes 
mouldy,  and  evolves  carbonic  acid,  in  consequence  of  a  species  of  fermenta- 
tion, during  which  gallic  acid  is  formed.  The  magma  is  then  pressed,  the 
residue  boiled  in  water,  and  the  solution  filtered  while  hot :  on  cooling,  it 
deposits  crystals  of  the  acid,  which  may  be  purified  by  redissolving  and  boil- 
ing them  with  a  little  animal  charcoal,  when  the  filtered  solution  deposits 
white  silky  crystals  of  gallic  acid.  This  acid  is  soluble  in  100  parts  of  cold 
41 


642  CHARACTERS    OF    GALLIC    AND    PYROGALLIC    ACIDS. 

and  in  3  of  boiling  water  ;  readily  soluble  in  alcohol,  and  sparingly  so  in 
ether.  According  to  Strecker,  it  is  a  tribasic  acid,  represented  in  its  anhy- 
drous state  by  C^^H^Oy,  and  forming  3  classes  of  salts,  represented  by  MO, 2 
(H0),C,,H30,,  2(MO),HO,C,,H30,,  and  3(MO),Cj,H30,.  When  1  part  of 
gallic  acid  is  triturated  with  5  of  sulphuric  acid,  gently  heated,  and  dropped 
into  water,  a  red  crystalline  substance  falls  {RufigaUic  aaW,=2(H0),Cj^H^ 
Og),  which  produces  on  mordanted  calico  a  dye  resembling  madder-red. 

Characters  of  Gallic  Acid. — 1.  It  is  white  and  crystalline,  soluble  in  water 
and  alcohol.  When  heated  in  air  it  melts,  and  burns  like  a  resin.  2.  It 
produces  an  inky  blue  color  with  a  persalt  of  iron.  3.  It  is  not  precipitated 
by  nitrate  of  silver  until  boiled,  when  the  silver  salt  is  reduced.  4.  It  gives 
DO  precipitate  with  a  solution  of  gelatin  or  albumen.  5.  With  an  excess  of 
lime-water  it  gives  a  white  precipitate,  which  in  air  rapidly  passes  through 
shades  of  a  blue  and  purple  color.  6.  When  ammonia  is  poured  on  the 
crystals,  they  acquire  a  rich  red  color.  T.  When  the  crystals  are  heated 
with  a  small  quantity  of  sulphuric  acid,  they  produce  a  rich  crimson  com- 
pound. 

Pyrogallic  Acid  (Ci^HgOg). 

This  acid  is  now  largely  manufactured  for  the  purposes  of  photography. 
It  is  obtained  by  sublimation  from  gallic  acid,  which,  at  a  temperature 
between  410^  and  420°,  obtained  by  an  oil-bath,  is  resolved  into  pyrogallic 
and  carbonic  acids. 

Gallic  acid.  Pyrogallic  acid.  Carbonic  acid. 

The  changes  which  this  acid  is  disposed  to  undergo  under  the  influence  of 
a  dry  heat,  account  for  the  great  loss  as  a  result  of  this  process.  Thus  while 
theoretically  74  per  cent,  of  pyrogallic  acid  should  be  obtained,  the  pro- 
duct is  barely  more  than  one-third  of  this,  namely,  25  per  cent.  Hence  the 
costliness  of  this  acid.  By  the  application  of  moist  heat  a  saving  of  50  per 
cent,  has  been  effected.  The  gallic  acid,  with  2  or  3  parts  of  water,  is  sub- 
jected in  a  close  bronze  boiler  to  a  temperature  of  from  392°  to  410°  ;  and 
after  it  has  been  kept  at  this  temperature  for  about  half  an  hour,  the  liquid 
is  allowed  to  cool.  The  pyrogallic  acid  is  treated  with  animal  charcoal, 
filtered  and  evaporated.  The  crystals  are  deposited  on  cooling.  At  a 
higher  temperature  pyrogallic  acid  is  converted  into  water  and  a  brown 
amorphous  product  insoluble  in  water,  but  soluble  in  the  alkalies,  called 
metagallic  acid. 

Pyrogallic  acid  forms  white  acicular  and  lamellar  crystals,  feebly  acid,  of 
an  astringent  bitter  taste.  The  crystals  melt  at  257°,  and  sublime  at  about 
400°.  The  acid  is  very  soluble  in  water,  alcohol,  and  ether.  It  is  perma- 
nent when  dry,  but  in  aqueous  solution  soon  becomes  brown,  as  a  result  of 
oxidation,  and  under  the  influence  of  a  free  alkali,  it  rapidly  absorbs  oxygen. 
It  does  not  precipitate  the  pure  protosalts  of  iron,  but  tinges  them  of  a 
characteristic  blue  ;  it  reduces  most  of  the  salts  of  mercury,  silver,  gold,  and 
platinum.  Dropped  into  milk  of  lime  it  produces  a  purple  tint,  which  soon 
becomes  brown.     It  is  an  important  photographic  agent. 

Characters  of  Pyrogallic  Acid. — These  have  been  described  at  p.  510.  Its 
most  characteristic  property  is  the  instant  reduction  of  silver  to  the  metallic 
state,  from  a  solution  of  the  nitrate.  It  differs  from  gallic  acid  in  many 
respects.  When  the  crystals  are  heated  with  a  small  quantity  of  sulphuric 
acid,  a  black  compound  results  from  some  decomposition  of  the  acid. 


OXALIC    ACID.       MANUFACTURE    FROM    SAWDUST.  643 

Ellagic  Acid  (C^HjO^SHO)  is  produced,  together  with  gallic  acid, 
during  the  exposure  of  moistened  jyalls  to  air  :  it  is  a  gray  crystalline  powder, 
insoluble  in  water  but  soluble  in  the  alkalies,  with  which  it  forms  sparingly 
soluble  salts.  This  acid  has  been  found  in  the  intestinal  concretions  called 
Oriented  Bezoars. 

Oxalic  Acid  (CPaHO). 

This  acid  was  discovered  by  Scheele  in  1776  :  it  is  found  in  some  fruits, 
in  the  juice  of  wood-sorrel'and  of  common  sorrel  (Oxalis  acetosella;  Rumex 
acetosa),  in  the  varieties  of  rhubarb,  especially  the  Rheum  rhaponticum,  or 
pie-plant,  and  in  several  other  plants :  in  these  it  is  generally  combined  with 
potassa  or  lime.  Certain  lichens  growing  upon  calcareous  rocks  contain 
half  their  weight  of  oxalate  of  lime.  It  occasionally  occurs  in  urine,  as  oxa- 
late of  lime,  forming  one  variety  of  urinary  calculus.  The  mineral  called 
Humholdtite  is  a  peroxalate  of  iron.  The  commercial  demands  for  oxalic 
acid  are,  however,  supplied  from  artificial  sources.  When  1  part  of  sugar 
is  mixed  with  4  of  nitric  acid  and  2  of  water,  nitric  oxide  and  carbonic  acid 
are  evolved  ;  after  distilling  off  the  excess  of  nitric  acid,  and  pouring  the 
residue  into  a  shallow  vessel,  crystals  of  oxalic  acid  are  deposited,  and  on 
further  evaporation  of  the  mother-liquor,  a  second  crop  is  obtained.  The 
product  is  purified  by  solution  in  water  and  recrystallization.  According 
to  L.  Thompson  {Pharm.  Journ.,  viii.  117),  one  atom  of  sugar  =C,gHjjOn, 
and  7  atoms  of  nitric  acid  =7N05,  are  thus  resolved  into  7N03,6COa,2HO, 
and  SCCaOgSHO).  These  proportions,  he  observes,  do  not  greatly  differ 
from  those  employed  by  the  wholesale  makers,  who  use  112  lbs.  of  sugar, 
560  lbs.  of  nitrate  of  potassa,  and  280  lbs.  of  oil  of  vitriol,  to  produce  135  lbs. 
of  crystallized  oxalic  acid,  and  490  lbs.  of  sulphate  of  potassa. 

Oxalic  acid  is  now,  however,  chiefly  manufactured  from  sawdust.  It  is 
thus  produced  of  good  quality,  in  large  quantity,  and  at  a  much  cheaper 
rate  than  in  the  process  by  the  action  of  nitric  acid  on  sugar.  It  has  been 
long  known  that  when  woody  fibre  was  heated  to  a  moderate  temperature 
with  caustic  potassa,  the  products  were  ulmic  acid  and  hydrogen.  At  a 
higher  degree  of  heat,  oxalic  acid  replaces  the  ulmic  as  a  product,  and  at  a 
still  higher  degree,  in  which  destructive  distillation  takes  place,  carbonic 
acid  and  hydrogen  result.  The  principle  of  this  new  manufacture,  therefore, 
is  to  heat  the  woody  fibre  with  alkali,  to  a  degree  sufiBcient  to  produce 
oxalic,  and  neither  ulmic  nor  carbonic  acid.  The  sawdust  is  mixed  with  a 
solution  of  two  equivalents  of  hydrate  of  soda  and  one  of  hydrate  of  potassa, 
having  a  sp.  gr.  of  1*25.  Soda  alone  is  not  found  to  answer  the  purpose. 
The  sawdust  acquires  a  dark  brown  color  from  the  action  of  the  alkalies,  and 
is  rendered  soluble  in  water.  The  mixture  is  heated  to  about  400^  in 
shallow  cast-iron  pans  for  some  hours,  care  being  taken  to  avoid  charring. 
The  heat  is  then  cautiously  raised,  and  the  result  is  a  residue,  containing  a 
large  quantity  of  the  mixed  oxalates  of  potassa  and  soda.  A  solution  of 
carbonate  of  soda  passed  through  the  mixed  oxalates  on  a  filter,  transforms 
the  oxalate  of  potassa  to  oxalate  of  soda,  the  carbonate  of  potassa  passing 
through  the  filter.  The  oxalate  of  soda  is  converted  by  lime  to  oxalate  of 
lime,  and  this  compound  is  decomposed  by  an  equivalent  of  sulphuric  acid. 
Oxalic  acid  remains  in  the  liquid,  and  after  two  or  three  crystallizations  is 
obtained  in  a  pure  state  in  large  crystals.  Two  pounds  of  sawdust  thus 
yield  one  pound  of  oxalic  acid.  Messrs.  Dale  and  Roberts,  of  Manchester, 
who  have  perfected  this  process,  manufacture  nine  tons  of  oxalic  acid  weekly 
for  the  purposes  of  calico-printing,  dyeing,  and  bleaching. 

The  ordinary  crystals  of  oxalic  acid  (CA,H0  +  2H0)  are  transparent 
four-sided  prisms.     They  are  intensely  sour,  and  dissolve  in  about  12  parts 


644  OXALATES.      OXAMIDE.* 

of  water  at  60^,  their  solubility  increasing  rapidly  with  the  increase  of 
temperature  ;  at  212°  they  fuse  in  their  water  of  crystallization.  They  are 
less  soluble  in  alcohol  than  in  water,  and  still  less  soluble  in  ether :  at  a 
temperature  of  100°,  they  gradually  fall  into  powder,  and  lose  about  a  third 
of  their  weight :  after  having  been  deprived  of  2  equivalents  of  water,  they 
sublime  when  heated  to  about  320° ;  and  the  sublimate  contains  1  atom  of 
water,  from  which  the  acid  cannot  be  parted  without  being  entirely  decom- 
posed. When  the  ordinary  crystals  are  rapidly  heated  to  about  350°,  water, 
carbonic  acid,  carbonic  oxide,  and  formic  acids  are  the  results.  Unlike  other 
vegetable  acids,  oxalic  acid  is  a  powerful  poison.  A  dose  of  it  has  destroyed 
life  in  ten  minutes.  It  ranks  among  the  most  active  irritant  poisons,  and 
the  resemblance  of  its  crystals  to  those  of  Epsom  salt,  has  given  rise  to  many 
fatal  accidents.     The  antidotes  are  chalk  or  magnesia. 

Hydrochloric  acid  dissolves  oxalic  acid  without  decomposition.  It  is  not 
decomposed  by  dilute  nitric  acid,  but  when  heated  with  concentrated  nitric 
acid,  it  is  converted  into  carbonic  acid.  Mixed  with  about  2  parts  of  sul- 
phuric acid,  and  gently  heated,  it  is  rapidly  resolved  into  equal  volumes  of 
carbonic  acid  and  carbonic  oxide,  whilst  the  water  of  the  crystals  remains 
combined  with  the  sulphuric  acid.  The  intensity  of  the  acidity  of  oxalic 
acid  is  such,  that  1  part  in  200,000  of  water  reddens  litmus.  It  abstracts 
lime  from  sulphuric  acid  when  added  ,to  a  solution  of  sulphate  of  lime,  but 
oxalate  of  lead  is  decomposed  by  sulphuric  acid  ;  so  that  its  affinity  for  bases 
appears  to  be  about  equal  to  that  of  sulphuric  acid.  When  a  solution  of 
oxalic  acid  is  boiled  with  the  peroxides  of  manganese,  lead,  cobalt,  or  nickel, 
or  with  chromic  acid,  these  oxides  are  partially  reduced,  carbonic  acid  is 
evolved,  and  oxalates  are  formed.  When  it  is  boiled  with  chloride  of  gold 
it  throws  down  metallic  gold,  and  carbonic  acid  passes  off. 

Oxalates. — In  the  neutral  oxalates,  the  oxygen  of  the  base  is  to  that  of 
the  acid  as  1  :  3,  their  formula  being  M0,C203 ;  and  if  the  oxygen  of  the 
base  be  added  to  the  acid,  the  result  is  a  metal  and  carbonic  acid,  or 
M,2[C02].  Some  oxalates,  when  heated,  give  this  result :  thus  oxalate  of 
silver  yields,  when  heated,  metallic  silver  and  carbonic  acid  ;  AgO,C203= 
Ag-f2[C03].  Sometimes  carbonic  oxide  and  carbonic  acid  are  given  off, 
leaving  a  protoxide  of  the  metal ;  this  is  the  case  with  oxalate  of  manganese  ; 
MnO,C203=MnO,-fCO-fC02;  and  sometimes  the  carbonic  oxide  thus 
evolved  reacts  on  the  metallic  oxide,  and  reduces  it ;  thus  with  oxalate  of 
cobalt,  CoO-,C203=CoO  +  C04-C02;  and  CoO,  +  CO  =  Co  +  C02.  When 
the  oxalates  are  heated  with  sulphuric  acid,  they  are  decomposed,  and  yield 
carbonic  oxide  and  carbonic  acid.  In  the  acid  oxalates,  the  quantity  of  acid 
is  either  twice,  or  four  times,  that  contained  in  the  neutral  oxalates. 

Oxalate  of  Ammonia  (^^fi,(jfi^,-[-B.O)  is  obtained  by  saturating  a  hot 
solution  of  oxalic  acid  with  carbonate  of  ammonia,  and  crystallizing.  It 
forms  prismatic  crystals,  soluble  in  28  parts  of  cold  water.  They  are  insolu- 
ble in  alcohol.  Added  to  any  soluble  compound  of  lime,  this  salt  produces 
an  insoluble  oxalate  of  lime,  provided  no  excess  of  acid  is  present ;  hence  its 
use  as  a  test  of  the  presence  of  lime.  The  crystals  contain  two  atoms  of 
water.  There  is  a  binoxalate  as  well  as  a  quadroxalate,  but  these  are  unim- 
portant salts. 

Oxamide  (CgO^NHg). — When  oxalate  of  ammonia  is  subjected  to  dry  dis- 
tillation, it  fuses,  boils,  is  decomposed,  and  volatilized,  leaving  a  little  carbon 
behind;  the  liquid  which  passes  over  contains  a  flocculent  substance,  which 
also  lines  the  neck  of  the  retort,  and  to  which  Dumas  gave  the  name  of 
oxamide;  it  may  be  separated  by  washing  and  filtration,  100  parts  of  the 
oxalate  yielding  about  5.  The  other  products  of  the  decomposition  are 
ammonia,  water,  carbonic  acid,  carbonic  oxide,  and  cyanogen.     Oxamide  is 


OXAMIC    ACID.      OXALATES    OP    POTASSA    AND    LIME.  645 

also  formed  by  the  action  of  ammonia  on  oxalic  ether  ;  and  of  boiling  nitric 
acid  upon  ferrocyanide  of  potassium.  Oxamide  forms  a  granulated  powder, 
without  taste  or  smell,  and  having  no  action  on  test-papers.  It  is  volatile 
when  carefully  heated  :  it  is  scarcely  soluble  in  water  at  60°,  and  a  saturated 
solution  at  212°  deposits  it  in  flocculi.  It  is  insoluble  in  alcohol.  Boiled 
with  potassa,  or  soda,  oxamide  evolves  ammonia,  and  the  carbon  and  oxygen 
remain  in  the  state  of  oxalic  acid.  Dilute  sulphuric,  nitric,  and  hydrochloric 
acids  convert  it  into  oxalic  acid,  and  form  ammoniacal  salts.  Boiled  with 
concentrated  sulphuric  acid,  oxamide  affords  sulphate  of  ammonia,  and  equal 
volumes  of  carbonic  acid  and  carbonic  oxide  are  disengaged:  concentrated 
nitric  acid  converts  oxamide  into  nitrate  of  ammonia  and  carbonic  acid. 

Referring  to  the  ultimate  elements  of  oxamide,  Dumas  regards  it  as  an 
amide  of  carbonic  oxide,  or  as  containing  the  hypothetical  radical  amidogen, 
NH,. 

Oxamic  Acid  (C^HgOgN). — This  compound  is  one  of  the  results  of  the 
careful  destructive  distillation  of  binoxalate  of  ammonia,  which  at  a  tempera- 
ture of  about  450°  leaves  a  residue  of  oxamide  and  oxamic  acid  ;  the  latter 
is  soluble  in  water,  and  when  added  to  a  soluble  salt  of  lime  or  baryta,  it 
gives  a  crystalline  precipitate,  which  is  an  oxamate  of  the  base,  and  may  be 
decomposed  by  sulphuric  acid.  Oxamic  acid  is  a  yellowish  powder,  which 
when  boiled  in  water  is  reconverted  into  binoxalate  of  ammonia,  CJIgOgN 
-f2H0,=NHp,CA,H0. 

Oxalates  of  Potassa. — There  are  three  of  these  oxalates  :  the  neutral  salt 
is  with  difficulty  crystallizable.  The  binoxalate  forms  rhombic  prisms,  in- 
cluding 3  atoms  of  water,  one  of  which  is  basic :  it  has  a  very  sour  taste, 
and  is  prepared  in  some  parts  of  Germany  and  Switzerland  from  the  juice  of 
the  wood-sorrel :  it  is  often  used  for  the  removal  of  ink-stains  and  iron- 
moulds  from  linen  under  the  name  of  essential  salt  of  lemons.  The  quadroxa- 
late  is  formed  by  the  action  of  hydrochloric  acid  on  the  binoxalate,  which 
abetracts  half  the  potassa  :  it  crystallizes  in  octahedra. 

Oxalate  of  lime  exists  in  many  plants,  and  is  found  in  such  quantities  in 
some  lichens  (especially  Variolaria  communis^  Indium  corallinum,  Psora 
Candida),  that  the  soil  upon  the  spots  on  which  they  have  grown  and  de- 
cayed, and  trunks  of  trees  upon  which  they  have  flourished,  abound  in  it. 
The  bodies  called  raphides,  found  in  the  cellular  tissue,  and  floating  occa- 
sionally in  the  juices  of  vegetables,  are  composed  of  oxalate  of  lime ;  this 
salt  also  exists  occasionally  in  the  human  urine,  and  forms  calculi,  which, 
from  their  nodular  exterior  and  reddish-brown  color,  are  called  Mulberry 
calculi.  On  adding  oxalate  of  ammonia  to  any  solution  of  lime,  oxalate  of 
lime  is  precipitated  in  octohedral  crystals  :  it  is  insoluble  in  water  in  excess 
of  oxalic  acid,  and  in  acetic  acid,  but  dissolves  in  hydrochloric  and  nitric 
acids :  hence,  in  testing  acid  solutions  for  lime  by  oxalate  of  ammonia,  an 
excess  of  acid  should  be  previously  neutralized.  It  is  decomposed  by  sul- 
phuric acid.  When  oxalate  of  lime  is  digested  in  a  solution  of  a  carbonated 
alkali,*carbonate  of  lime  and  an  alkaline  oxalate  are  formed.  When  rendered 
dry  upon  a  sand-heat,  this  salt  becomes  singularly  electrical  on  friction,  and 
platinum  and  other  metals  rubbed  against  the  powder  become  negative,  the 
powder  positive ;  it  appears  to  stand  at  the  head  of  the  substances  which 
become  positive  by  friction.  (Faraday.)  At  a  red  heat  it  is  converted 
first  into  carbonate  and  then  into  quicklime.  When  well  washed,  and  dried 
at  212°  till  it  ceases  to  lose  weight,  it  is  G2^0,YL0,Cfi^,  and  contains  38'4 
per  cent,  of  lime.  i  ui    • 

Of  the  other  oxalates  those  of  lithia,  strontia,  and  alumina,  are  soluble  m 
water ;  those  of  baryta,  lead,  and  silver,  are  nearly  insoluble  in  water,  but 
are  dissolved  by  a  solution  of  sal-ammoniac.     The  double  oxalate  of  potassa 


646  ACETIC    ACID. 

and  chrominra  forms  crystals  of  an  intense  blue  color.  The  oxalate  of 
copper,  unlike  the  tartrate  and  citrate,  is  not  soluble  in  an  excess  of  potash. 
Characters  of  Oxalic  Acid. — Tests  as  a  poison:  1.  This  acid  crystallizes 
in  well-defined  quadrilateral  prisms.  2.  When  the  crystals  are  heated  on 
platinum,  they  melt,  and  are  volatilized  without  combustion,  and  without 
leaving  a  carbonaceous  residue  :  any  mineral  residue  may  be  regarded  as  im- 
purity. 3.  Lime-water,  or  a  solution  of  sulphate  of  lime,  produces  a  white 
precipitate,  not  soluble  in  any  vegetable  acid,  but  it  is  dissolved  by  nitric 
acid.  4.  A  solution  of  the  acid  gives  a  white  precipitate  with  nitrate  of 
silver  (oxalate  of  silver),  soluble  in  an  excess  of  the  acid.  This  precipitate 
may  be  boiled  without  undergoing  decomposition.  When  collected  in  a  filter, 
washed,  dried,  and  heated,  it  is  decomposed,  with  slight  detonation,  into 
carbonic  acid  and  metallic  silver,  AgO  +  C203=Ag  +  2C02.  The  crystalline 
form  and  volatility,  the  action  of  sulphate  of  lime  and  nitrate  of  silver,  are 
the  most  reliable  tests  in  cases  of  poisoning.  By  reason  of  its  solubility  in 
alcohol,  oxalic  acid  may  be  separated  from  many  organic  substances.  The 
aqueous  solution  of  the  acid,  acidulated  with  acetic  acid,  should  be  precipi- 
tated by  a  solution  of  acetate  of  lead,  rendered  acid  with  acetic  acid :  the 
oxalate  of  lead  collected,  and  this  compound  decomposed  by  a  current  of 
sulphuretted  hydrogen.  By  this  process,  oxalic  acid  may  be  obtained  in  a 
crystalline  state  on  evaporating  the  aqueous  filtrate. 

Acetic  Acid  (C,H,0„  or  C.HgOg.HO). 

There  are  two  principal  sources  of  acetic  acid,  namely,  1.  Acetous  fermen- 
tation, and  2.  The  destructive  distillation  of  wood.  Comparing  the  ultimate 
composition  of  alcohol  with  that  of  acetic  acid,  it  appears  that  1  equivalent 
of  alcohol,  by  taking  4  equivalents  of  oxygen,  is  resolved  into  1  equivalent 
of  acetic  acid  and  2  of  water. 

C4H6O2       -f        O4      =       C^H.O^       4-       2H0. 

Alcohol.  Acetic  acid. 

This  is  the  theory  of  the  formation  of  vinegar  by  the  action  of  air  on 
wine,  beer,  and  similar  fermented  liquors.  The  first  stage  of  conversion, 
however,  is  most  probably  into  aldehyde  : — 

CAO2        -f        O2         =        C.H.O^        4-        2H0. 


Alcohol.  Oxygen.  Aldehyde.  Water, 

oxygen  the  aldehyde  is  co 

20  =  C^H.O^ 


By  taking  two  other  equivalents  of  oxygen  the  aldehyde  is  converted  into 
acetic  acid. 


Aldehyde.  Oxygen.  Acetic  acid. 

Alcohol  itself,  except  in  the  presence  of  oxidizing  agents  (platinum  black), 
does  not  undergo  the  change,  and  a  mixture  of  alcohol  and  water  does  not 
produce  acetic  acid,  unless  some  nitrogenous  substance  as  a  ferment  is  present. 
The  acetic  acid  of  a  previous  fermentation  operates  as  a  ferment  to  convert 
alcohol  into  acetic  acid,  provided  tfie  alcohol  is  diluted  with  a  certain  pro- 
portion of  water,  and  there  is  a  sufficient  access  of  air  to  supply  the  neces- 
sary oxygen. 

Vinegar  (from  vin  aigre),  or  the  dilute  acetic  acid  chiefly  used  for  domestic 
purposes,  varies  in  quality  according  to  the  sources  whence  it  is  obtained. 
The  best  French  vinegar  is  made  by  putting  wine  into  a  cask  already  con- 
taining a  little  vinegar,  and  to  which  air  has  due  access,  the  temperature  of 
the  factory  being  maintained  at  about  80°.     In  this  country,  beer,  or  a  wort 


PROPERTIES  or  VINEGAR.  647 

prepared  for  the  purpose,  is  used  as  a  source  of  vinegar.  A  good  extempo- 
raneous vinegar  may  be*  prepared  by  dissolving  1  part  of  sugar  in  6  of  water, 
with  1  part  of  brandy,  and  a  little  yeast :  this  mixture  is  put  into  a  cask, 
with  the  bunghole  open,  and  kept  at  a  temperature  of  between  70°  and  80^: 
in  from  four  to  six  weeks,  the  clear  vinegar  may  be  drawn  off.  Lieljig  re- 
commends 120  parts  of  water,  12  of  brandy,  4  of  brown  sugar,  1  of  tartar, 
and  ^  of  sour  dough,  left  for  some  weeks  in  a  warm  place,  as  ingredients  for 
the  production  of  a  good  vinegar.  Various  modes  of  accelerating  acetifica- 
tion  have  been  suggested  by  the  extension  of  the  surface  of  the  liquid.  As 
far  back  as  1743,  Boerhaave  recommended  that  a  mixture  of  1  part  of  alcohol 
and  9  of  water  should  be  made  to  trickle  slowly  through  beech-shavings, 
previously  soaked  in  vinegar,  and  lying  loosely  in  a  cask  perforated  with 
holes :  the  best  proportions  are,  1  part  of  alcohol  (sp.  gr.  0848)  with  4  to 
6  of  water,  and  a  thousandth  part  of  ferment,  honey,  or  extract  of  malt. 
This  mixture,  previously  heated  to  about  80°,  is  made  to  trickle  through 
the  shavings  steeped  in  vinegar ;  the  temperature,  as  a  result  of  the  oxida- 
tion of  the  liquid,  soon  rises  to  100°  or  104°,  and  remains  stationary  if  all 
goes  on  favorably.  When  the  liquid  has  been  passed  through  the  shavings 
three  or  four  times,  it  is  completely  acetified  :  this  may  occupy  from  20  to 
36  hours.  If  the  supply  of  air  is  deficient,  part  of  the  alcohol  remains  in 
the  state  of  aldehyde,  which  escapes,  and  occasions  a  loss  of  acetic  acid. 
The  presence  of  essential  oils,  or  of  pyroligneous  acid,  prevents  the  acetifi- 
cation. 

Vinegar  is  apt  to  be  infested  hjjlies  {Musca  cellarus),  and  by  animalcules, 
commonly  termed  eels  (  Vihriones  aceti)  ;  these  may  be  destroyed  by  passing 
the  vinegar  through  a  spiral  tube  immersed  in  boiling  water,  or  by  heating  it 
in  a  hot-water  bath.  When  vinegar  is  exposed  to  air,  it  gradually  becomes 
turbid,  or  mothery,  losing  its  acidity,  and  depositing  a  gelatinous  conferva, 
the  vinegar-plant,  which,  by  reason  of  holding  vinegar  like  a  sponge,  causes 
acetous  fermentation  in  saccharine  liquids.  The  vinegar  becomes  weak  and 
mouldy  as  these  changes  go  on,  and  they  are  rapid  in  proportion  to  its 
weakness. 

The  adulteration  of  vinegar  by  sulphuric  or  by  hydrochloric  acid  may  be 
detected  by  nitrate  of  baryta  and  nitrate  of  silver,  the  precipitates  being 
insoluble  in  nitric  acid;  but  traces  of  sulphuric  acid  are  found  in  all  vinegars 
(from  sulphates  in  the  water),  and  their  presence  must  be  allowed  for  in 
nsing  the  barytic  test.  If  nitric  acid  is  present  in  vinegar,  it  destroys  the 
color  of  an  acid  solution  of  sulphate  of  indigo,  when  boiled  with  it.  In 
order,  as  it  is  said,  to  prevent  vinegar  becoming  mouldy,  it  is  allowed  by  law 
to  contain  one-thousandth  part  of  its  weight  of  sulphuric  acid. 

The  specific  gravity  of  vinegar  depends  more  upon  the  foreign  matters 
which  it  contains,  than  upon  its  actual  strength,  so  that  its  value  cannot  be 
judged  of  by  that  criterion:  the  density  of  the  best  vinegar  is  about  1-020 
to  1-025.  To  ascertain  the  proportion  o^  real  acetic  acid  which  it  contains, 
it  must  be  cautiously  neutralized  by  carbonate  of  soda,  the  quantity  of  this 
salt  requisite  for  the  purpose,  indicating  the  proportion  of  real  acetic  acid 
present,  53  parts  of  dry  carbonate  of  soda  being  equivalent  to  51  of  anhy- 
drous acetic  acid.  The  equivalent  of  carbonate  of  lime,  which  is  50,  .is  so 
near  that  of  acetic  acid,  as  to  furnish  a  ready  mode  of  ascertainmg  the  value 
of  vinegar  or  other  dilute  acetic  acid.  For  this  purpose  a  piece  of  clean 
white  marble  is  selected  and  accurately  weighed  :  it  is  then  suspended  by  a 
thread  in  a  proper  quantity  of  the  vinegar  to  be  examined,  which  is  0(3ca- 
sionally  cautiously  stirred,  so  as  to  mix  its  parts  without  chipping  the  marble ; 
this  when  it  is  no  longer  acted  on,  is  removed,  washed,  dried,  and  weighed ; 
its  loss  in  weight  is  equivalent  to  the  weight  of  acetic  acid  present.    Another 


648  DISTILLED    VINEGAR.      PYROLIGNEOUS    ACID. 

mode  of  ascertaining  the  strength  of  vin^egar  consists  in  neutralizing  it  by 
hydrate  of  lime ;  acetate  of  lime  is  extremely  soluble*,  so  that  the  quantity  of 
acetate  of  lime  formed  and  dissolved,  is  directly  as  the  quantity  of  acid  pre- 
sent, and  the  density  of  the  resulting  solution  of  acetate  of  lime  is  in  the  same 
ratio.  {See  J.  and  P.  Taylor  on  an  Acetometer,  Quart.  Joum.,  vi.)  "An 
ounce  of  good  vinegar  should  saturate  about  30  to  32  grains  of  pure  and  dry 
carbonate  of  potassa  :  such  vinegar  contains  about  5  per  cent,  of  anhydrous 
acetic  acid,  and  its  density  is  from  I'Ol  to  1*03."  (Liebig.) 

Distilled  Vinegar. — When  vinegar  is  carefully  distilled,  the  first  portion 
which  passes  over  usually  contains  a  little  alcohol ;  this  is  followed  by  dilute 
acetic  acid,  which,  towards  the  end  of  the  process,  often  acquires  an  empy- 
reumatic  odor;  the  residue  is  brown,  acid,  and  has  a  burned  flavor.  Accord- 
ing to  R.  Phillips  (on  the  London  Pharmacopoeia),  when  the  best  English 
malt- vinegar,  of  the  specific  gravity  of  1*024  is  distilled,  the  first  eighth  part 
which  passes  over  is  of  the  specific  gravity  0-99712,  so  that  it  contains  a 
little  alcohol ;  a  fluidounce  of  it,  =  0-8047  cubic  inches,  dissolves  from  4*5 
to  5  grains  of  precipitated  carbonate  of  lime  :  the  next  six-eighths  have  the 
specific  gravity  1-0023,  and  a  fluidounce  dissolves  8-12  grains  of  the  carbonate ; 
a  fluidounce  of  the  acid,  of  specific  gravity  TOOT,  dissolves  15  to  16  grains 
of  precipitated  carbonate  of  lime,  or  138  grains  of  marble. 

Distilled  vinegar  is  colorless,  and  it  has  not  the  agreeable  flavor  and  odor 
of  the  original  vinegar ;  it  contains  a  trace  of  alcohol  and  of  acetic  ether, 
and  also  a  peculiar  organic  matter.  When  distilled  from  a  copper-still 
through  a  pewter  worm,  it  becomes  discolored  by  sulphuretted  hydrogen 
from  the  presence  of  traces  of  copper,  lead,  or  tin,  so  that  silver  or  earthen 
condensers  are  used  by  the  wholesale  distillers. 

Pyroligneous  Acid. — The  production  of  vinegar  by  the  destructive  dis- 
tillation of  wood,  was  one  of  the  numerous  discoveries  of  Glauber  ;  and  a 
large  quantity  of  acetic  acids,  of  all  strengths,  is  now  derived  from  this  source. 
The  wood  is  heated  in  iron  retorts,  connected  with  a  proper  condensing 
apparatus,  and  the  inflammable  gaseous  products  are  conducted  into  the  fur- 
nace, so  as  to  serve  as  fuel.  The  hard  woods,  such  as  beech,  oak,  birch,  and 
ash,  are  selected,  and  previously  dried:  The  liquid  products  are  water,  wood- 
spirit  or  naphtha,  tar,  and  acetic  acid :  these  are  drawn  off  from  the  floating 
tar,  and  distilled,  when  the  wood-spirit  first  passes  over,  and  afterwards  the 
acetic  acid,  still,  however,  very  impure  from  the  presence  of  tar  and  other 
matters.  This  impure  acid  is  then  saturated  either  by  soda  or  by  chalk,  and 
the  acetate  so  formed  is  carefully  heated,  so  as  to  decompose  or  expel  the  tarry 
matters  without  decomposing  the  salt,  which  is  then  further  purified  by  solu- 
tion and  crystallization,  and  ultimately  decomposed  by  distillation  with  sul- 
phuric acid  diluted  with  about  half  its  weight  of  water.  The  acetic  acid 
which  passes  over  is  purified  by  redistillation.  The  sulphate  of  soda  resulting 
from  this  process  may  be  used  to  convert  the  crude  acetate  of  lime  to  acetate 
of  soda  and  sulphate  of  lime,  when  chalk  has  been  used  for  the  saturation  of 
the  crude  acid.  The  purest  acetic  acid,  obtained  by  the  decomposition  of  an 
acetate  by  sulphuric  acid,  contains  an  atom  of  water  (HO, Ac),  which  in  the 
formation  of  the  neutral  acetates  is  replaced  by  an  atom  of  base. 

For  our  knowledge  of  the  anhydrous  acid  (C^HgOg),  we  are  indebted  to 
Gerhardt.  It  may  be  obtained  by  distilling  8  parts  of  dry  acetate  of  potassa 
with  3  of  oxychloride  of  phosphorus  ;  the  distillate  is  returned  upon  the  resi- 
due and  redistilled,  and  the  product  again  rectified. 

Anhydrous  acetic  acid,  sometimes  represented  as  the  teroxide  of  the  com- 
pound radical  acetyle  (C^H^),  is  a  colorless  liquid,  of  a  peculiar  odor;  (sp. 
gr.  I'OT);  its  boiling-point  is  280°,  and  the  sp.  gr.  of  its  vapor  is  3  47. 


HYDRATED    ACETIC    ACID.  649 

When  dropped  into  water,  it  falls  to  the  bottom  like  heavy  oil,  but  soon 
dissolves  on  agitation  ;  it  readily  absorbs  moisture  when  exposed  to  air. 
Acted  upon  by  potassium  it  evolves  hydrogen,  and  forms  acetate  of  potassa, 
and  an  oily  product  of  an  agreeable  odor.  It  dissolves  chloride  of  phos- 
phorus, producing  phosphorous  acid  and  oxychloride  of  acetyle. 

Monohydrated  Acetic  Acid,  or  Glacial  Acetic  Acid  (C^H303HO). — This  is 
obtained  by  distilling  1  equivalent  of  fused  acetate  of  soda  with  2  equivalents 
of  sulphuric  acid,  and  placing  the  distillate  in  ice;  the  congealed  product 
is  then  suffered  to  drain,  by  inverting  the  bottle,  and  in  that  frozen  state  it 
is  the  pure  monohydrated  acid.  Its  crystals  are  plates  or  tufts,  which  fuse 
at  about  50°.  It  has  a  strong  pungent  odor,  agreeable  when  diluted,  and  is 
powerfully  acid  and  caustic,  reddening  and  blistering  the  skin.  It  boils  at 
243°,  and  its  vapor  is  inflammable :  it  absorbs  moisture  from  the  air,  and 
dissolves  in  all  proportions  in  water.  The  sp.  gr.  of  the  liquefied  crystal- 
lized acid  is  1-0635  at  62°,  and  this  density  increases  on  dilution,  until  the 
acid  contains  1  equivalent  of  anhydrous  acid  to  3  of  water,  when  it  is  1-073  ; 
on  further  dilution,  its  density  diminishes,  and  when  it  consists  of  about  equal 
weights  of  the  acid  and  water,  its  sp.  gr.  is  1-063,  or  the  same  as  that  of  the 
undiluted  acid.  The  monohydrated  acid  does  not  attack  carbonate  of  lime 
until  it  is  diluted ;  and  when  mixed  with  alcohol,  it  neither  reddens  litmus 
nor  decomposes  many  of  the  carbonates  (p.  585.)  It  is  partially  decomposed 
by  passing  it  through  a  red-hot  porcelain  tube,  yielding  acetone,  carbonic 
acid,  and  water. 

2(C,HA)        =        CeHeO^        +        SCO^        -f        2H0 

Its  entire  decomposition  is  only  effected  at  a  very  high  temperature ;  but 
when  its  vapor  is  passed  over  heated  platinum-black,  it  is  resolved  into  equal 
volumes  of  carbonic  acid  and  light  carburetted  hydrogen  (C^H^O^=s2C02  4- 
2CH2).  Pure  acetic  acid  acts  only  slowly  upon  a  solution  of  permanganate 
of  potash,  but  when  acetic  acid  contains  tarry  matters,  sulphurous  acid  or 
organic  matter,  such  as  is  found  in  vinegar,  the  permanganate  is  rapidly 
decomposed  and  the  color  is  discharged. 

When  chlorine  is  passed  through  a  mixture  of  2  parts  of  glacial  acetic  acid 
and  1  of  water  (taking  care  to  exclude  the  direct  rays  of  the  sun),  it  is  slowly 
absorbed,  and  a  compound  is  formed  which  has  been  termed  chloracetic  acid, 
=HO,C^H203Cl:  it  is  stated  to  produce  definite  salts,  in  which,  when  dilute, 
nitrate  of  silver  gives  no  precipitate.  This  chloracetate  of  silver  forms  shining 
scales,  soluble  in  water,  and  decomposed  by  light. 

When  glacial  acetic  acid  is  exposed  to  the  action  of  gaseous  chlorine, 
under  the  influence  of  the  sun's  rays,  white  deliquescent  flocculi  are  formed 
=110,0^01303.  This  compound  has  been  termed  trichloracetic  acid;  in  it 
the  hydrogen  of  the  anhydrous  acetic  acid  is  replaced  by  chlorine,  but  the 
reaction  is  more  complex,  inasmuch  as  chlorocarbonic,  carbonic,  and  oxalic 
acids  are  at  the  same  time  formed.  This  acid  forms  salts  which  are  soluble 
in  water,  and  which  when  heated,  evolve  chlorocarbonic  acid  and  carbonic 
oxide,  and  leave  a  chloride. 

M0,C,Cl303        =        MCI        -f        2(C0,C1)        -f        2C0 

Sulphacetic  JaU— When  acetic  acid  is  acted  on  by  anhydrous  sulphuric 
acid,  it  loses  2  atoms  of  watei^and  a  new  acid  =C4Ha02,2S08,2HO,  results  : 
it  forms  deliquescent  crystals,^nd  bibasic  salts. 

Acetates.— These  salts  are  very  numerous,  and  many  of  them  of  much 
importance  in  the  arts.  The  neutral  acetates,  =M0,C,H303,  are  all  soluble 
in  water :  acted  on  by  sulphuric  acid  they  evolve  acetic  acid,  recognized  by 


650  ACETATES    OF    COPPER    AND    LEAD, 

its  odor.  They  are  raostly  reddened  by  perchloride  of  iron.  They  are  de- 
composed by  a  red  heat,  some  of  them  giving  off  the  acid  and  leaving  the 
metal,  such  as  the  acetates  of  copper  and  of  silver ;  some  give  off  acetone 
and  leave  a  carbonate,  and  some,  which  require  a  higher  temperature  for 
decomposition,  afford  acetone  and  other  more  complex  products. 

Acetate  of  Ammonia,  obtained  by  neutralizing  distilled  vinegar  by 
ammonia,  has  long  been  used  in  medicine,  under  the  name  of  Spirit  of 
Mindererus.  When  boiled,  ammonia  passes  off  and  a  hinacetate  is  formed. 
These  salts  are  very  soluble  in  water  and  in  alcohol,  and  are  crystallized  with 
difficulty. — Acetate  of  Potassa  is  very  deliquescent;  soluble  in  its  weight  of 
water  at  60°,  and  in  twice  its  weight  of  alcohol.  When  carefully  fused,  it 
concretes  into  a  lamellar  mass  on  cooling,  the  terra  foliata  tartari,  or  febri- 
fuge salt  of  Silvius,  of  old  pharmacy.  It  is  present  in  the  sap  of  many 
vegetables,  and  is  a  source  of  the  carbonate  of  potassa  found  in  their  ashes. 
The  aqueous  solution  of  this  acetate  is  not  decomposed  by  carbonic  acid ; 
but  a  current  of  that  gas  passed  through  its  alcoholic  solution,  precipitates 
carbonate  of  potassa,  and  sets  free  acetic  acid.  Like  the  acetate  of  soda,  it 
is  decomposed  when  heated  with  caustic  potassa  or  lime,  and  resolved  into 
carbonate  of  potassa  and  Marsh  gas.  Acetate  of  soda  is  largely  manufac- 
tured as  a  source  of  acetic  acid,  by  the  action  of  sulphate  of  soda  on  acetate 
of  lime  (NaO,S03,  +  CaO,Ac=NaO,Ac,  +  CaO,S03).  It  crystallizes  in 
rhombic  prisms  with  6  atoms  of  water.  It  bears  a  dull  red  heat  without 
decomposition. — Acetate  of  haryta  forms  efflorescent  crystals  with  1  atom 
of  water,  if  obtained  at  80°,  but  3  if  at  32°.  By  heat  this  salt  is  resolved 
into  carbonate  of  baryta  and  acetone,  2(BaO,C^H303) =2(BaO,  CO^)  -f-  CgHgOa. 
Acetate  of  lime  forms  silky  prisms,  soluble  in  water  and  in  alcohol.  When 
heated  to  about  230°  and  triturated,  it  is  phosphorescent. — Acetates  of  alu- 
mina, prepared  by  decomposing  solutions  of  sulphate  of  alumina  or  of  alura 
by  acetate  of  lead,  are  extensively  used  as  mordants,  by  calico-printers. 
These  acetates  have  been  minutely  examined  by  Mr.  Crum  {Q.  J.  Chem. 
Soc,  vii.) — Protacetate  of  iron,  obtained  by  the  action  of  acetic  acid  on  the 
protosulphide,  out  of  contact  of  air,  forms  white  silky  crystals.  The  pera- 
cetate,  made  by  digesting  iron  turnings  in  the  acid  exposed  to  air,  is  a  deep 
red  solution,  not  crystallizable.     It  is  used  by  dyers  and  calico-printers. 

Acetates  of  Copper These  constitute  the   varieties   of  verdigris.     The 

common  verdigris  of  commerce  is  a  hydrated  dibasic  salt  =2(CuO),Ac, 
3H0 :  it  is  prepared  by  exposing  plates  of  copper  to  the  action  of  acetic 
acid.  The  method  now  practised  consists  in  alternating  plates  of  copper 
with  pieces  of  woollen  cloth  steeped  in  acetic  acid  ;  they  gradually  become 
covered  with  verdigris,  which  is  removed  in  the  form  of  a  blue-green  powder, 
and  the  operation  repeated  as  long  as  the  plate  lasts.  Sometimes  husks  and 
stalks  of  grapes  or  raisins,  in  a  state  of  acetous  fermentation,  are  employed 
to  act  upon  the  copper,  as  is  the  case  with  some  of  the  French  verdigris. 
This  article  is  commonly  packed  in  leather,  and  frequently  adulterated  with 
a  mixture  of  chalk  and  sulphate  of  copper.  Pure  diacetate  of  copper  forms 
small  silky  crystals  of  a  greenish-blue  color,  which  when  heated  to  212°, 
become  green,  and  lose  water :  when  moistened,  this  salt  crumbles,  and  is 
only  partially  soluble  in  water,  by  which  it  is  resolved  into  tribasic  and 
neutral  acetates.  The  neutral  acetate  of  copper  (^crystallized  verdigris)  is 
made  by  dissolving  common  verdigris  in  a^fetic  acid,  and  allowing  it  to 
crystallize  upon  twigs  or  pieces  of  string  :  it  f(frms  blue-green  prisms,  soluble 
in  5  parts  of  boiling  water  and  sparingly  in  alcohol.  When  its  dilute  solu- 
tion is  boiled,  it  deposits  a  tribasic  salt :  if  boiled  with  sugar,  a  crystalline 
precipitate  of  suboxide  of  copper  is  formed.     Acetates  of  lead. — When  oxide 


ACETATES    OF    LEAD.      TESTS    FOR    ACETIC    ACID.  651 

of  lead  is  dissolved  in  excess  of  acetic  acid,  prismatic  crystals  are  obtained 
on  evaporating  the  filtered  solution  =PbO,C^H303,3HO.  This  salt,  known 
as  sugar  of  lead,  generally  occurs  in  the  form  of  a  crystalline  mass,  slightly 
efflorescent,  soluble  in  less  than  two  parts  of  water,  and  in  about  8  parts  of 
alcohol.  When  heated,  it  first  becomes  anhydrous,  then  fuses,  and  at  a 
higher  temperature  is  converted  into  a  subsesquiacetate  =3(PbO),2(C^H3 
Og),  soluble  in  water  and  alcohol,  and  having  an  alkaline  reaction.  When 
7  parts  of  litharge  and  10  of  sugar  of  lead  are  boiled  together  in  30  parts 
of  water,  a  solution  of  a  trihasic  acetate  =3(PbO),C^H303  is  formed, 
known  in  pharmacy  as  Goulard's  extract  of  lead;  this  salt  may  be  obtained 
in  acicular  crystals,  having  an  alkaline  reaction.  Its  decomposition  by  car- 
bonic acid  is  one  of  the  processes  for  making  white  lead,  and  has  been  elsewhere 
noticed.  This  subacetate  is  a  delicate  test  for  the  presence  of  carbonic  acid, 
which  it  absorbs  from  the  atmosphere,  or  from  any  liquid  containing  it : 
even  distilled  water  is  seldom  so  free  from  carbonic  acid  as  not  to  be  rendered 
turbid  by  the  addition  of  a  few  drops  of  this  salt,  and  with  all  spring  and 
river  water  it  forms  a  more  or  less  turbid  white  mixture.  When  excess  of 
minium  is  heated  in  glacial  acetic  acid  to  about  105°,  the  solution  deposits 
prismatic  crystals  on  cooling,  composed  oi  peroxide  and  acetate  of  lead  ;  they 
are  very  unstable,  and  on  attempting  to  dry  them  are  decomposed  into  per- 
oxide of  lead  and  acetic  acid.  Acetate  of  suboxide  of  mercury  (Hg20,Ac,) 
is  formed  by  mixing  solutions  of  acetate  of  potassa  and  nitrate  of  suboxide 
of  mercury  ;  it  forms  micaceous  crystalline  plates  requiring  600  parts  of  cold 
water  for  solution.  The  acetate  of  the  red  oxide  is  readily  soluble.  Acetate 
of  silver  is  deposited  in  lamellar  crystals  when  acetic  acid  is  added  to  a  strong 
solution  of  nitrate  of  silver;  and  it  is  abundantly  precipitated  from  the 
nitrate  by  acetate  of  soda.  This,  and  the  preceding,  are  the  only  neutral 
acetates  not  easily  dissolved  in  water.  Acetate  of  uranium  forms  a  series  of 
double  salts  with  basic  acetates,  which  have  been  described  by  Wertheim. 
{Ann.  Ph.  et  Ch.,  3feme  ser.  xi.  49.) 

Characters  of  Acetic  Acid  and  the  Acetates. — 1.  Acetic  acid  at  ordinary 
temperatures  is  liquid,  and  has  a  powerful  and  peculiar  odor.  2.  It  is 
entirely  volatile  if  pure,  and  the  vapor  of  the  concentrated  acid  is  combusti- 
ble, burning  with  a  pale  reddish  flame.  3.  It  is  not  precipitated  by  lime- 
water,  acetate  of  lead,  or  nitrate  of  baryta  or  silver,  if  free  from  sulphuric 
and  hydrochloric  acids. 

An  acetate  may  be  identified  by  boiling  it  with  sulphuric  acid  :  the  vapor 
of  acetic  acid  is  evolved.  This  may  be  recognized  by  its  odor,  volatility, 
and  acid  reaction.  Acetic  acid  sometimes  contains  lead,  silver,  or  copper, 
as  an  impurity.  The  first  may  be  detected  by  sulphuretted  hydrogen,  pro- 
ducing a  brown  color  :  the  second  by  the  action  of  the  gas,  and  the  produc- 
tion of  a  white  precipitate  by  hydrochloric  acid  :  the  third  by  the  action  of 
ammonia.  Acetate  of  soda  may  be  present  in  the  acid  :  this  is  detected  by 
the  yellow  color  imparted  to  flame. 

Acetone  (CgHgO^). — This  product  is  obtained  when  acetate  of  lime  is 
distilled  with  excess  of  quicklime,  or  when  2  parts  of  acetate  of  lead  and  1 
of  lime,  well  mixed,  are  heated  in  an  iron  retort  connected  with  a  proper 
condensing  apparatus.  The  distillate  is  rectified,  and  finally  redistilled  from 
a  water-bath.  Pure  acetone  is  a  colorless  liquid  of  a  peculiar  aromatic 
odor  and  pungent  taste.  Its  sp.  gr.  0*792  ;  it  boils  at  132°  ;  the  sp.  gr.  of 
its  vapor  is  2-022;  it  dissolves  in  all  proportions  in  water,  alcohol,  and 
ether  ;  but  chloride  of  calcium  and  caustic  potassa  separate  it  from  its  aque- 
ous solution.  It  is  very  inflammable  and  burns  with  a  bright  flame.  _  By 
the  action  of  chlorine  upon  acetone,  three  substitution-products  are  obtained, 
in  which  2,  3,  and  4  atoms  of  its  hydrogen  are  replaced  by  chlorine. 


652  FORMIC    ACID.      FORMATES. 

Formic  Acid  (CaH,03,H0) 

was  first  noticed,  iu  1670,  in  the  body  of  the  red  ant  {Formica  rufa),  and  was 
obtained  by  distilling  the  bruised  insects  with  water.  It  may  be  artificially 
produced  by  many  processes  founded  upon  the  oxidation  of  various  organic 
products.  Dobereiner  procured  it  by  the  distillation  of  10  parts  of  starch, 
3*7  of  peroxide  of  manganese,  30  of  water,  and  30  of  sulphuric  acid,  until  30 
parts  had  passed  over :  or  by  distilling  a  mixture  of  10  parts  tartaric  acid, 
3  of  peroxide  of  manganese,  3  of  sulphuric  acid,  and  3  of  water.  In  these 
cases,  capacious  retorts  must  be  used,  to  allow  of  the  great  effervescence  which 
ensues.  The  acid  distillate,  which  is  very  dilute,  is  saturated  with  carbonate 
of  lead,  and  the  resulting  formate  of  lead  purified  by  crystallization  during 
the  cooling  of  its  solution  in  boiling  water;  it  is  then  decomposed,  either  by 
an  equivalent  of  sulphuric  acid,  or  by  the  action  of  sulphuretted  hydrogen. 
Formic  acid  has  also  been  obtained  by  distilling  a  mixture  of  oxalic  acid  and 
anhydrous  glycerine  at  a  temperature  of  about  212°;  in  this  case,  the  oxalic 
acid  is  resolved  into  formic  and  carbonic  acids. 

2(H0,CA)  =  (H0,C,H03)  +  2(C0,). 

The  reaction  between  the  two  bodies  commences  at  about  127°,  and  attains 
its  maximum  at  194°.  By  distillation,  an  aqueous  fluid  mixed  with  formic 
acid  passes  over  into  the  receiver  and  is  condensed.  The  glycerine  remains 
unchanged,  provided  the  heat  is  not  allowed  to  exceed  220°.  A  fresh  quan- 
tity of  oxalic  acid,  added  to  the  mixture  some  time  after  the  evolution  of 
carbonic  acid  has  ceased,  causes  the  decomposition  to  recommence,  and  a 
fluid  containing  a  larger  proportion  of  formic  acid  is  obtained.  Successive 
additions  of  oxalic  acid  may  thus  be  made.  The  oxalic  acid  yields  more 
than  half  its  weight  of  formic  acid  containing  56  per  cent,  of  the  anhydrous 
acid.  The  action  of  the  glycerine  appears  to  be  of  a  catalytic  kind,  like 
that  of  sulphuric  acid  in  splitting  alcohol  into  ether  and  water..  The 
commencement  and  termination  of  this  process  of  conversion  are  indicated 
by  the  evolution  of  carbonic  acid.  Monohydrated  formic  acid  may  be  pro- 
cured by  this  process  by  heating  formic  acid  of  70  per  cent,  with  anhydrous 
oxalic  acid.    The  decomposition  begins  at  122°. 

There  is  reason  to  believe  that  the  poison  of  the  wasp  and  bee,  as  well  as 
that  of  the  vesicles  surrounding  the  bases  of  the  hairs  on  the  leaf  of  the 
stinging-nettle  ( Urtica  dioica),  is  formic  acid  in  a  concentrated  state. 

Monohydrated  formic  acid  is  a  very  acrid  fuming  liquid,  of  the  sp.  gr. 
1-22;  crystallizable  below  32°,  boiling  at  about  220°,  and  yielding  an  in- 
flammable vapor,  the  density  of  which  is  2'125.  The  anhydrous  acid  has 
not  been  isolated.  It  is  easily  converted  by  oxidation  into  carbonic  acid  and 
water :  when  boiled,  either  with  oxide  of  mercury  or  oxide  of  silver,  this 
oxide  is  reduced,  with  the  escape  of  carbonic  acid  (2AgO,  +  C2H20^,=2Ag, 
-f  2C02,4-2HO).  Chlorine  converts  it  into  carbonic  and  hydrochloric  acids 
(C2H20^,-f2Cl,=2C03-f 2HC1).  Formic  acid  is  frequently  represented  as 
the  teroxide  of  the  compound  radical /ormy/e  (CgH-f  O3).  Its  elements  are 
in  the  proportions  to  form  two  atoms  of  carbonic  oxide  and  one  of  water 
(C,H03=2CO  +  HO). 

Formates. — The  neutral  formates  are  =(MO,C2H03).  They  are  all  soluble: 
when  heated  with  excess  of  sulphuric  acid,  they  yield  carbonic  oxide  and 
water  ;  and  with  caustic  potassa  they  evolve  hydrogen  and  are  changed  into 
carbonates.  Formate  of  ammonia,  when  heated  to  about  400°,  is  resolved 
into  hydrocyanic  acid  and  water,  NH40,C2H03=(C^N,H)4-4HO.  Formate 
of  lead,  when  heated  to  about  375°,  evolves  carbonic  acid  and  hydrogen, 
and  leaves  metallic  lead :  it  requires  40  parts  of  cold  water  for  solution,  but 


PROPERTIES    OP    BENZOIC    ACID.  653 

is  very  soluble  in  boiling  water.    Formate  of  copper  crystallizes  in  lar^e  blue 
prisms  :  it  forms  double  salts  with  the  formates  of  baryta  and  of  strontia. 

Characters  of  Formic  Acid. — This  acid  may  be  identified  by  its  odor,  vola- 
tility, and  its  reducing  power  on  the  salts  of  silver  and  gold. 

Benzoic  Acid  (C,^H503,H0). 

This  substance  is  found  ready  formed  in  benzoin,  the  resinous  exudation 
of  the  Styrax  lenzoin,  a  tree  growing  in  Sumatra,  Borneo,  and  Java.  Tolu 
and  Peru  Balsam  also  contain  it,  in  common  with  Cinnamic  acid;  and  it  is 
a  product  of  the  oxidation  of  hitter-almond  oil.  It  is  found  in  the  pods  of 
the  Vanilla.  It  is  generally  obtained  from  benzoin,  either  by  sublimation, 
or  in  the  humid  way,  by  the  action  of  bases :  the  amount  of  the  product  is 
various,  depending  upon  the  quality  of  the  benzoin,  upon  the  process  selected, 
and  the  care  with  which  it  is  conducted  ;  it  fluctuates  from  4  to  10  per  cent. 
The  process  usually  resorted  to  consists  in  coarsely  pulverizing  the  benzoin, 
and  heating  it  in  a  shallow  vessel,  over  which  a  sheet  of  coarse  blotting-paper 
is  stretched,  surmounted  by  a  cone  of  thick  paper,  or  by  a  wooden  receiver, 
if  the  operation  is  carried  on  upon  the  large  scale.  The  layer  of  benzoin 
should  not  be  more  than  two  or  three  inches  in  thickness,  and  the  heat 
gradually  and  regularly  applied,  so  as  slowly  to  sublime  the  acid,  the  vapor 
of  which,  passing  through  the  bibulous  diaphragm,  condenses  in  a  crystalline 
form  in  the  cone  or  recipient,  empyreumatic  oil  at  the  same  time  evolved,  is 
retained  and  absorbed  by  the  paper.  (Mohr.)  Benzoic  acid  may  also  be 
obtained  by  triturating  benzoin  with  half  its  weight  of  hydrate  of  lime,  and 
adding  10  parts  of  water;  after  the  mixture  has  digested  for  some  hours,  it 
is  boiled  and  filtered  :  the  filtrates  are  then  concentrated,  and  saturated, 
whilst  hot,  by  hydrochloric  acid ;  on  cooling,  benzoic  acid  is  deposited,  which 
must  be  again  dissolved  and  crystallized.     (Scheele.) 

Benzoic  acid  is  inodorous ;  but,  as  it  is  obtained  by  sublimation,  it  has 
an  agreeable  odor,  derived  from  a  trace  of  volatile  oil  j  it  generally  forms 
acicular  crystals.  It  has  a  slightly  sour  and  acrid  taste.  It  melts  at  about 
250°,  and,  on  cooling,  congeals  into  a  crystalline  mass.  At  about  295°  it 
sublimes  :  about  460°  it  boils,  and  forms  an  acrid  vapor,  the  sp.  gr.  of  which 
is  4-26.  This  acid  requires  200  parts  of  water  at  60°,  and  30  parts  at  212°, 
for  its  solution  ;  the  saturated  boiling  solution  concretes  on  cooling  into  a 
crystalline  mass.  It  dissolves  in  about  twice  its  weight  of  alcohol,  and  is 
precipitated  on  dilution  with  water.  It  also  dissolves  in  ether,  and  in  fixed 
and  volatile  oils.  In  its  usual  crystalline  form  it  contains  an  atom  of  water, 
its  equivalent  being  122 ;  that  of  the  anhydrous  acid  is  113. 

It  has  been  found  convenient,  in  reference  to  the  numerous  compounds  of 
the  benzoic  series,  to  regard  them  as  derived  from  a  compound  radical,  to 
which  the  term  Benzoyle  has  been  applied  ;  and  which  has  been  obtained,  in 
the  form  of  an  oil,  by  the  dry  distillation  of  benzoate  of  copper ;  its  formula 
is  C,,H.02,=Bz.  It  is  obvious  that  benzoic  acid  {G^^Rfi^+O)  may  be 
regarded  as  an  oxide,  and  bitter- almond  oil  (C.^H^O^+H)  as  a  hydride  of 
this  radical,  and  that  it  may  be  assumed  as  the  basis  of  the  numerous  deriva- 
tives of  those  bodies.  But  the  term  Benzoyle,  or  Benzule,  is  perhaps  more 
appropriately  confined  to  the  fundamental  hydrocarbon  (Ci^H^)  of  the  series. 

Anhydrous  benzoic  acid  has  been  obtained  by  the  action  of  oxychloride 
of  phosphorus  on  anhydrous  benzoate  of  soda ;  it  is  insoluble  in  water,  but 
soluble  in  boiling  alcohol  and  in  ether :  by  continuous  boiling  in  water  it 
reverts  to  the  ordinary  hydrate. 

Benzoates.^ThQ^Q  salts  are  represented  by  the  general  formula  MU,Oi^ 
H.Og :  they  are  mostly  soluble  in  water  and  in  alcohol.  Benzoate  of  lime 
dissolves  readily  in  boiling  water.     Basic  benzoate  of  peroxide  of  iron  is  so 


654  ESSENTIAL    OIL    OP    BITTER    ALMONDS. 

little  soluble  in  water  that  an  alkaline  benzoate  has  been  used  to  precipitate 
iron,  "and  to  separate  this  metal  from  some  other  oxides. 

Chlorolenzoic  acid  is  the  result  of  the  action  of  the  sun's  rays  on  benzoic 
acid  in  dry  chlorine.  In  it  an  atom  of  hydrogen  is  replaced  by  one  of 
chlorine,  giving  Ci^H^03,Cl.  There  are  also  two  other  of  these  chlorine 
compounds,  in  which  2  or  3  atoms  of  hydrogen  are  displaced  by  a  similar 
number  of  atoms  of  chlorine.  A  similar  bromine  compound  has  also  been 
obtained. 

Sulphohenzoic  acid  is  the  product  of  the  action  of  anhydrous  sulphuric  on 
benzoic  acid  :  it  is  dibasic,  and  is  represented  as  2(HO),Ci4H^S^03. 

Nitrohenzoic  acid  (HOjCi^H^g.NOJ  is  a  compound  in  which  an  atom  of 
hydrogen  is  replaced  by  an  atom  of  nitrous  acid.  The  nitrobenzoates  are 
mostly  crystallizable  and  soluble  in  water  and  alcohol :  when  suddenly 
heated  they  deflagrate. 

Benzamic  acid.  Carhanilic  acid.  Amidobenzoic  acid. — This  is  one  of 
the  results  of  the  action  of  sulphuretted  hydrogen  upon  an  alcoholic  solution 
of  nitrobenzoate  of  ammonia  :  it  is  represented  as  benzoic  acid,  in  which  an 
equivalent  of  hydrogen  is  replaced  by  an  equivalent  of  amidogen  (Ci^H  (N 
H,)03). 

Hydride  op  Benzoyle.  Essential  oil  of  hitter  almonds  (Cj^HgOa-f  H,  or 
C^^HgOg). — Bitter  almond  oil  is  obtained  by  macerating  the  pulverized  bitter- 
almond  cake,  after  the  fixed  oil  has  been  expressed,  in  water  heated  to  about 
100°,  for  24  hours,  and  then  distilling;  it  passes  over  with  the  vapor  of 
water,  and  condenses  in  the  form  of  a  heavy  oil,  the  supernatant  water  hold- 
ing a  portion  of  it  in  solution.  This  oil  is  combined  with  hydrocyanic  acid, 
and  is  therefore,  as  well  as  the  bitter  almond  water,  very  poisonous.  It  may 
be  obtained  also  from  the  peach,  plum,  cherry,  and  apricot  kernels,  from  the 
leaves  and  young  shoots  of  the  laurel  {Prunus  lanrocerasus),  and  from  the 
bark  of  the  wild  cherry  (Prunus  padus).  To  free  it  from  hydrocyanic  acid, 
the  oil  may  be  agitated  with  milk  of  lime  and  a  solution  of  protochloride  of 
iron,  and  redistilled. 

Pure  bitter-almond  oil  is  a  colorless  liquid  of  a  peculiar  and  agreeable 
aromatic  odor  and  a  pungent  flavor.  It  is  not  very  poisonous  when  freed 
from  prussic  acid,  but  as  it  is  much  used  in  confectionery  and  cookery,  care 
should  be  taken  that  for  such  purposes  its  purification  has  been  adequately 
performed.  Its  boiling-point  is  about  350°.  It  is  much  heavier  than  water, 
its  sp.  gr.  being  1*043.  It  is  easily  inflammable,  and  burns  with  a  bright 
sooty  flame.  It  is  soluble  in  about  30  parts  of  water,  and  in  all  proportions 
in  alcohol  and  ether.  Its  alcoholic  solution  constitutes  the  Essence  of  bitter- 
almonds  commonly  sold  for  culinary  purposes;  it  usually  consists  of  one  part 
of  the  oil  dissolved  in  seven  of  alcohol.  When  this  oil  is  exposed  to  air 
it  absorbs  oxygen,  and  is  converted  into  crystallized  benzoic  acid :  C,.HbO„ 
-fO„  =  C,AO, 

Neither  bitter-almond  oil  nor  hydrocyanic  acid  exists  ready  formed,  in  the 
almond  or  sources  whence  they  are  obtained,  but  they  are  produced  by  the 
mutual  agencies  of  certain  azotized  substances,  under  the  influence  of  water 
and  a  due  temperature ;  these  substances  are  amygdaline,  and  emulsin  or 
synaptase. 

Amygdaline  (C^oHgyOgaN)  is  found  in  bitter-almonds,  in  the  leaves  and 
berries  of  the  cherry  laurel,  and  the  bitter  kernels  of  the  species  of  amygdalus 
and  prunus.  To  obtain  it,  the  pulverized  cake  of  bitter-almonds  which  re- 
mains after  the  expression  of  the  fixed  oil,  is  boiled  in  repeated  portions  of 
alcohol  of  sp.  gr.  0-820.  These  alcoholic  liquids  are  then  distilled  in  a 
water-bath,  till  the  residue  acquires  a  syrupy  consistence,  when  it  contains 
little  else  than  amygdaline  and  sugar ;  to  get  rid  of  the  latter,  the  liquor  is 


ACTION    OP    EMULSINE    UPON    AMYQDALINE.  655 

diluted  with  water,  and  a  little  yeast  having  been  added,  it  is  placed  in  a 
warm  situation,  to  ferment;  when  the  fermentation  has  ceased,  the  liquor 
is  filtered,  and  again  evaporated  to  the  consistence  of  syrup  ;  excess  of  cold 
alcohol  is  then  added,  which  throws  down  the  amygdaline  in  the  form  of  a 
white  crystalline  powder.  From  three  to  four  per  cent,  of  the  principle  is 
thus  obtained  from  bitter-almonds.  Amygdaline  is  readily  soluble  in  water, 
and  the  crystals  deposited  from  its  saturated  aqueous  solution  are  transpa- 
rent prisms,  containing  10-57  per  cent,  of  water  (=  6  atoms).  It  is  in- 
odorous and  slightly  sweet  and  bitter.  When  acted  on  by  fixed  alkalies,  it 
evolves  ammonia  and  forms  amygdalic  acid. 

^A-,022^^   +      KO,HO      4-      HO      =      KO,C,oH3,0,,      +      NH, 

Amygdaline.  Amygdalate  of  potassa. 

The  action  of  emulsine  upon  amygdaline  in  the  production  of  bitter 
almond  oil,  was  first  explained  by  Wohler  and  Liebig.  When  a  solution  of 
10  parts  of  amygdaline  in  100  of  water  is  mixed  with  a  solution  of  1  part  of 
emulsine  in  10  of  water,  the  mixture  becomes  opalescent,  acquires  the  odor 
of  bitter  almonds,  and,  when  distilled,  yields  hydride  of  benzoyle  and  hydro- 
cyanic acid  ;  these  changes  ensue  most  rapidly  at  a  temperature  between  85*^ 
and  105°.     Boiling  water  and  boiling  alcohol  destroy  the  action. 

When  expressed  bitter-almonds  are  moistened  and  triturated  with  water, 
the  same  reaction  ensues ;  and  if  water  enough  be  present  to  dissolve  the 
oil  as  it  is  formed,  the  whole  of  their  amygdaline  disappears :  to  obtain  the 
full  proportion  of  oil,  1  part  of  bitter-almond  cake  should  be  macerated  for 
24  hours  in  20  parts  of  water,  at  about  100°,  and  then  subjected  to  distilla- 
tion. Seventeen  grains  of  amygdaline  dissolved  in  an  ounce  of  emulsion  of 
sweet  almonds,  yield  a  solution  containing  1  grain  of  anhydrous  hydrocyanic 
acid. 

In  the  fermentative  changes  which  ensue  during  the  mutual  action  of 
emulsine  and  amygdaline  under  the  conditions  above  stated,  bitter-almond 
oil  and  hydrocyanic  acid  ^re'not  the  only  products;  sugar  and  formic  acid 
are  also  formed.     The  general  result  may  be  represented  as  follows  : — 


1  atom  of  amygdaline, 

C^nHg-OooN 


1  atom  of  hydrocyanic  acid     .  Cg  H 

2  "        hydride  of  benzoyle  CjgHjjO^ 

i      "        sugar   • CgHeOg 

2      "         formio  acid     .     .     .  C4  Hg  Og 

6      "        water H.  0. 


Action  of  Ammonia  on  Hydride  of  Benzoyle.— 'By  agitating  bitter-almond 
oil  with  ammonia  and  heating  the  mixture,  a  crystalline  compound  is  formed, 
hydrohenzamide  (C^H^gNJ ;  it  is  changed  by  the  action  of  potassa  into  an 
isomeric  basic  body,  henzoHne  or  amarine,  the  salts  of  which  are  intensely 
bitter.     Some  other  azotized  compounds  are  similarly  produced. 

When  crude  bitter-almond  oil  (retaining  hydrocyanic  acid)  is  digested 
with  an  alcoholic  solution  of  caustic  potassa,  it  is  converted  into  a  crystal- 
line product,  which  has  been  termed  Benzoine,  represented  as  =0,811^304, 
and  therefore  isomeric  with  the  hydride  of  benzoyle  ;  but  it  is  inodorous  and 
tasteless.  When  its  vapor  is  passed  through  a  red  hot  tube,  it  is  resolved 
into  bitter-almond  oil.  This  curious  product  has  beeb  represented  by  the 
formula  C^^H^.O^H,  as  the  hydride  of  a  radical,  =C^H„0,,  called  5^.%^ 
For  further  details  in  reference  to  these,  and  many  other  compounds  derived 
from  or  connected  with  bitter-almond  oil,  we  must  refer  to  Laurent  (Ann. 
de  Chim.  et  Ph.,  I.  291,  3feme  SQr.)  and  to  Gerhardt  {Chim.  Organ.). 


656-  HIPPURIC    AND    MECONIC    ACIDS 

HippuRic  Acid  (C,3H30,1S',  +  H0). 

This  acid  is  contained  in  a  combined  state  chiefly  in  the  urine  of  herbivo- 
rous maramifera,  forming?  about  TS  per  cent.  It  is  present  in  small  quantity 
in  human  urine,  in  which  it  may  be  produced  artificially  by  the  use  of  ben- 
zoic acid.  Benzoic  acid,  in  passing  through  the  system,  is  converted  into 
hippuric  acid.  It  may  be  obtained  by  adding  milk  of  lime  to  fresh  cow's 
urine,  boiling,  filtering,  neutralizing  the  filtrate  with  hydrochloric  acid,  and 
evaporating  it  to  about  one-eighth  of  its  bulk ;  excess  of  hydrochloric  acid 
is  then  added,  which  throws  down  impure  hippuric  acid.  It  may  be  puri- 
fied by  dissolving  it  in  boiling  alcohol,  which  on  cooling  deposits  it  in  color- 
less, long,  four-sided  prisms  with  pointed  terminations.  It  requires  about 
400  parts  of  water  at  60°  for  its  solution  :  it  is  abundantly  soluble  in  boil- 
ing water  and  in  alcohol,  but  less  so  in  ether.  It  fuses  when  heated,  and 
concretes  into  a  crystalline  mass  on  cooling.  If  distilled  at  a  high  tempera- 
ture it  gives,  among  the  products,  benzoic  and  prussic  acids.  When  long 
boiled  with  dilute  nitric  or  hydrochloric  acid,  it  yields  benzoic  acid  and 
gelatine-sugar  (glycocol  or  glycocine).  When  boiled  for  half  an  hour  in  a 
strong  solution  of  potash,  it  is  converted  into  benzoic  acid,  forming  a  ben- 
zoate  of  the  alkali,  100  parts  of  hippuric  acid  thus  produce  68  parts  of 
benzoic  acid.  This  conversion  also  takes  place  in  the  urine  of  the  horse, 
as  a  result  of  spontaneous  changes  after  it  has  been  voided  ;  and  thus  urine 
which  has  been  long  kept,  yields  benzoic  in  place  of  hippuric  acid.  Boiled 
with  peroxide  of  lead,  carbonic  acid,  benzoic  acid,  and  benzamide  (C^4H5 
OjNHg)  are  formed.  Hippurates. — Those  of  the  alkalies  and  earths  are 
soluble  and  crystallizable ;  they  give  white  precipitates  in  solutions  of  lead, 
mercury,  and  silver,  and  a  brown  precipitate  with  persalts  of  iron. 

Meconic  Acid  (Cj^HO.ijSHO). 

The  existence  of  a  distinct  acid  in  opium  was  announced  by  Seguin  in 
1804,  and  shortly  afterwards  by  Sertuerner,  wlio  gave  it  the  above  name 
(from  ^ijxcov,  poppy).  This  acid  has  not  been  found  in  any  other  plant.  It 
may  be  most  conveniently  extracted  from  the  precipitate  obtained  by  adding 
chloride  of  calcium  to  infusion  of  opium,  in  the  process  for  procuring 
morphia.  This  precipitate  is  washed  first  in  water,  and  then  with  hot 
alcohol,  and  mixed  with  ten  times  its  weight  of  water,  at  195° ;  hydrochloric 
acid  is  then  gradually  added,  so  as  to  dissolve  the  meconate  of  lime  (which 
forms  the  bulk  of  the  precipitate)  and  leave  the  sulphate  of  lime ;  the  solu- 
tion is  filtered,  and  on  cooling  deposits  crystals  of  bimeconate  of  lime:  these 
are  again  dissolved  in  hot  dilute  hydrochloric  acid,  by  which  the  lime  is- 
abstracted,  and  crystals  of  meconic  acid  obtained,  which,  if  pure,  should 
leave  no  residue  when  burned :  they  must  be  redissolved  in  the  acid,  and 
recrystallized,  till  they  are  obtained  in  this  state,  but  care  must  be  taken  to 
keep  the  temperature  of  their  solutions  below  212°. 

Meconic  acid  Crystallizes  in  transparent  and  micaceous  scales  of  an  acid 
taste,  soluble  in  4  parts  of  hot  water,  and  in  alcohol.  The  crystals  are  per- 
manent in  the  air,  but  when  heated  to  212°  they  lose  21  -5  per  cent,  of  water  : 
they  then  sustain  a  temperature  of  240°  without  decomposition  ;  but  if  a 
strong  aqueous  solution  of  the  acid  is  boiled,  it  becomes  dark  colored,  car- 
bonic acid  is  evolved,  and  oxalic  acid  and  comenic  {metameconic)  acid  are 
formed,  together  with  a  brown  product.  Boiled  in  hydrochloric  acid,  me- 
conic acid  is  resolved  into  carbonic  and  comenic  acid. 

One  of  the  principal  characters  of  this  acid  and  of  its  salts,  is  that  of 
forming  a  compound  with  the  peroxide  or  iron  of  an  intensely  red  color, 
very  similar  to  that  of  the  sulphocyanide  of  iron,  but  dififerin^  in  the  fact 


ALKALOIDS    AND    ORGANIC    BASES.  657 

that  a  solution  of  corrosive  sublimate  does  not  destroy  the  red  color ;  hence 
a  persalt  of  iron  is  an  excellent  test  of  its  presence,  and  by  it,  opium  may 
sometimes  be  recognized,  when  the  quantity  is  so  small  as  to  render  the  mor- 
phia very  difficult  of  detection.  The  red  color  is  destroyed  by  heat,  by  sul- 
phurous acid,  and  by  protochloride  of  tin.  Meconic  acid  in  solution  gives 
a  yellowish-white  precipitate  with  acetate  of  lead,  and  this  precipitate  is  not 
dissolved  by  acetic  acid.  The  acid  may  be  detected  in  any  opiate  liquid  by 
adding  to  it  a  mixture  of  a  solution  of  acetate  of  lead  with  acetic  acid,  and 
,  boiling  the  liquid.  The  meconate  of  lead  is  precipitated  in  an  insoluble 
form,  and  may  be  obtained  by  filtration.  When  dry,  this  precipitate,  if 
warmed  with  diluted  sulphuric  acid,  yields  a  solution  of  meconic  acid ;  its 
presence  in  the  filtrate  is  readily  detected  by  the  addition  of  a  persalt  of  iron. 


CHAPTER    LIII. 

ALKALOIDS    AND    ORGANIC    BASES.     SUBSTANCES    ASSO- 
CIATED   WITH    OR    DERIVED    FROM    THEM. 

These  are  for  the  most  part  solid  and  crystallizable  compounds.  Some 
are  volatile :  others  are  fixed,  and  are  readily  decomposed  when  heated,  or 
when  brought  in  contact  with  chemical  reagents.  They  generally  contain  an 
atom  of  nitrogen  as  one  of  their  ultimate  elements ;  they  have  a  bitter  taste, 
are  sparingly  soluble  in  water,  more  soluble  in  alcohol,  but  readily  soluble 
in  most  of  the  dilute  acids  as  well  as  in  ether,  chloroform,  and  benzole.  With 
an  excess  of  iodic  acid,  they  generally  produce  precipitates.  They  are  sali- 
fiable bases,  and  their  compounds  with  the  acids  are- decomposed  and  pre- 
cipitated by  the  alkalies.  The  aqueous  solutions  of  those  which  are  true 
bases,  and  form  crystallizable  salts,  give  white  flocculent  precipitates  with 
solutions  of  tannic  acid;  the  chloriodide  of  potassium  and  mercury,  and  iodide 
of  potassium  with  iodine.  Of  these,  the  chloride  of  potassium  and  mercury, 
or  the  iodo-hydrargyrate  of  potassium,  is  the  most  reliable.  The  liquid 
should  not  be  acid  or  contain  much  alcohol.  Ammonia  is  not  precipitated 
by  this  solution,  but  potash  and  soda  give  a  yellowish  precipitate  with  it. 
The  test  for  alkaloids  is  prepared  by  dissolving  sixteen  grains  of  corrosive 
sublimate,  and  sixty  grains  of  iodide  of  potassium  in  four  ounces  of  water. 
As  it  gives  a  precipitate  with  albumen,  this  when  present  should  be  first  re- 
moved by  boiling  and  filtering  the  liquid  to  be  tested.  Although  this  solu- 
tion precipitates  an  alkaloid  even  when  in  small  quantity,  there  is  no  easy 
process  by  which  the  alkaloid  can  be  extracted  from  the  precipitate  in  a 
pure  state.  Bouchardat  has  proposed  another  precipitant  of  the  alkaloids 
which  is  very  effectual  in  throwing  down  many  of  them  in  an  insoluble  form. 
The  solution  which  he  employs  is  a  strong  solution  of  iodide  of  potassium 
with  iodine.  The  proportions  by  weight  are  5  parts  of  iodide  of  potassium, 
and  1  part  of  iodine,  dissolved  in  20  parts  of  water.  A  small  quantity  of 
this  solution  added  to  a  solution  of  an  alkaloid  throws  down  a  red  brown 
precipitate.  Some  alkaloids  are  effectually  precipitated  by  it,  e.  g.,  strychnia, 
others  only  partially..  The  precipitate  is  quite  insoluble  in  water,  and  admits 
of  frequent  washing  even  in  water  which  is  feebly  acid  without  material  loss. 
The  precipitate  is  diffused  in  water  acidulated  with  dilute  sulphuric  acid, 
and  some  iron  filings  are  added  to  produce  a  slow  evolution  of  hydrogen. 
42 


658  MORPHIA. 

The  precipitate  disappears,  and  the  liquid  becomes  nearly  colorless.  When 
hydrogen  is  no  longer  evolved,  a  solution  of  ammonia  is  added,  and  a  com- 
pound precipitate  of  oxide  of  iron,  and  the  alkaloid  is  thrown  down.  This 
is  well  washed  on  a  filter,  dried,  and  treated  with  alcohol  by  W'hich  the  alka- 
loid is  removed  from  the  oxide  of  iron.  This  process  is  said  to  be  very  effi- 
cacious for  discovering  and  separating  small  quantities  of  some  alkaloids. 
It  would  not  answer  on  the  large  scale.  Other  and  more  simple  methods 
must  here  be  resorted  to. 

The  alkaloids  are  for  the  most  part  crystallizable,  and  are  represented  by 
very  high  equivalent  numbers.  These  solutions  restore  the  blue  color  to 
reddened  litmus.  They  are  found  in  plants  united  to  certain  acids,  and 
usually  forming  neutral  or  acid  salts,  which,  as  well  as  their  artificial  com- 
binations, are  decomposed  in  the  voltaic  circle,  and  the  base  is  evolved  at 
the  negative  pole.  Many  hypotheses  have  been  built  upon  the  ultimate 
composition  of  these  alkaloids,  and  some  curious  analogies  pointed  out 
respecting  them  by  Liebig,  Dumas,  and  others.  In  consequence  of  the 
analogy  that  pervades  these  principles,  one  general  method  of  separating 
them  is  applicable  to  all,  though  each  may  require  peculiar  modifications  of 
it.  The  substance  which  contains  them  is  boiled  in  water  acidulated  by 
an  acid,  the  decoction  is  filtered  and  neutralized  by  ammonia,  lime,  or  mag- 
nesia, when  the  alkaloid  is  precipitated,  and  afterwards  separated  and  puri- 
fied by  alcohol  or  ether.  Much  of  the  history  of  these  bodies  is  connected 
with  Materia  Medica.  We  shall  here  examine  them  simply  in  reference  to 
their  chemical  properties. 

Morphia  (C35H,o06N+2HO=M+2HO). 

In  order  to  procure  this  alkaloid,  a  filtered  solution  of  opium  in  tepid 
water  is  mixed  with  acetate  of  lead  in  excess ;  the  precipitated  meconate  of 
lead  is  separated  by  a  filter,  and  through  the  solution,  containing  acetate  of 
morphia,  now  freed  to  a  considerable  extent  from  color,  a  stream  of  sul- 
phuretted hydrogen  is  passed.  The  filtered,  and  nearly  colorless  liquid, 
from  which  the  lead  has  been  removed,  may  be  warmed  to  expel  the  excess 
of  gas,  once  more  filtered,  and  then  mixed  with  a  slight  excess  of  caustic 
ammonia,  which  throws  down  the  morphia  and  narcotine ;  these  may  be 
separated  by  boiling  ether,  in  which  the  latter  is  soluble.  The  meconate  of 
lead,  well  washed,  suspended  in  water,  and  decomposed  by  sulphuretted 
hydrogen,  yields  solution  of  meconic  acid.  The  quantity  of  morphia 
obtained  from  opium  is  variable  ;  the  produce  is  greatest  from  Turkey  opium, 
and  least  from  the  East  Indian  and  Egyptian.  The  average  is  generally 
estimated  at  about  1  oz.  from  the  pound.  Good  opium  is  considered  to 
contain  ten  per  cent,  of  morphia. 

Morphia^  when  obtained  from  its  alcoholic  solution,  is  in  small  brilliant 
and  colorless  crystals  :  they  are  generally  six-sided  prisms,  with  dihedral 
terminations,  but  their  form  is  a  right  rhombic  prism.  When  gently  heated 
they  become  opaque  and  lose  water :  at  a  higher  temperature  morphia  fuses 
into  a  yellow  liquid,  which  becomes  white  and  crystalline  on  concreting.  In 
the  air  it  burns  with  a  bright  resinous  flame.  When  heated  in  a  close  tube 
it  yields  ammonia.  Morphia,  though  apparently  nearly  insoluble  in  cold 
water,  has  a  bitter  taste  :  boiling  water  dissolves  not  more  than  a  hundredth 
of  its  weight,  but  the  solution  is  alkaline  to  delicate  tests.  It  dissolves  in 
40  parts  of  cold,  and  30  of  boiling  anhydrous  alcohol.  .  It  is  almost  insolu- 
ble in  ether  and  benzole,  and  is  only  sparingly  dissolved  by  chloroform  ; 
hence  one  of  the  methods  of  separating  it  from  narcotina,  which  is  readily 
soluble  in  ether.  Amylic  alcohol  readily  dissolves  morphia  at  a  moderate 
temperature,  and  deposits  it  in  well  marked  crystalline  prisms  on  cooling. 


ALKALOIDS    IN    OPIUM.      CODEIA.  659 

It  also  has  the  property  of  removing  at  least  a  portion  of  morphia  from  au 
aqueous  solution  when  the  alkaloid  is  set  free  by  the  addition  of  ammonia. 
The  amylic  alcohol  also  dissolves  a  portion  of  organic  matter  and  becomes 
colored.  On  drawing  off  the  alcohol  with  a  pipette,  and  allowing  it  to 
evaporate  spontaneously,  a  film  or  crystalline  deposit  may  be  obtained  suffi- 
cient to  give  the  reactions  of  the  tests  for  morphia  as  mentioned  below. 
Morphia  is  soluble  in  potassa  and  soda ;  hence  the  necessity  of  avoiding  the 
use  of  these  alkalies  in  its  precipitation.  Ammonia  dissolves  it  sparingly, 
so  that  this  alkali  ought  not  to  be  used  in  excess. 

The  tests  for  morphia  are:  1.  Nitric  acid,  which  when  dropped  upon 
crystallized  morphia,  forms  a  bright-red  solution.  2.  Neutral  persulphate  of 
iron,  which  produces  a  very  characteristic  blue  color  when  added  to  morphia, 
or  to  its  salts,  provided  the  test  is  neutral  and  the  solutions  are  not  very 
dilute.  3.  Iodic  acid;  when  this  is  added  to  morphia  either  solid  or  in  solu- 
tion of  morphia  it  produces  a  reddish-brown  color,  and  the  odor  of  iodine  is 
immediately  perceptible.  The  minutest  quantity  of  morphia  has  the  property 
of  decomposing  iodic  acid,  but  in  cases  where  very  small  quantities  are  pre- 
sent, a  solution  of  starch  may  be  employed  to  detect  the  free  iodine.  A 
solution  of  iodic  acid  is  decomposed  by  a  great  variety  of  substances ;  its 
chief  use,  therefore,  is  to  distinguish  morphia  from  other  alkaloids  which  do 
not  decompose  it,  rather  than  to  detect  the  presence  of  morphia  in  liquids  of 
unknown  composition.  4.  Sulpho-molyhdic  add,  this  test  for  morphia  has 
been  lately  suggested  by  Frobide.  A  small  quantity  of  molybdic  acid  or  of 
a  raolybdate  is  dissolved  by  heat  in  concentrated  sulphuric  acid.  If  morphia 
or  any  of  its  salts  is  touched  with  a  drop  of  this  compound  acid,  it  produces 
a  beautiful  reddish  violet  color  passing  to  a  deep  sapphire  blue  at  the  margin 
of  the  spot.  The  blue  color  results  from  the  partial  deoxidation  of  the 
molybdic  acid  by  the  morphia,  whereby  a  molybdate  of  molybdenum  or 
molybdous  acid  is  produced.  Many  kinds  of  organic  matter  will  sooner  or 
later  produce  the  blue  compound  tint,  but  the  reddish  violet  or  purple  color 
is  considered  to  be  characteristic  of  morphia.  The  reaction  is  very  delicate 
for  the  smallest  visible  portion  of  morphia  will  be  indicated  by  the  change 
of  color. 

CoDEiA  (CgsHaoO.N-f  2H0). 

This  alkaloid  was  discovered  by  Robiquet,  in  1832,  in  the  hydrochlorate 
of  morphia.  On  dissolving  the  mixed  hydrochlorates  in  water,  and  pre- 
cipitating the  morphia  by  ammonia,  the  codeia  remains  in  solution  and 
crystallizes  by  subsequent  evaporation  :  it  may  be  also  separated  by  ether, 
in  which  it  is  soluble.  According  to  Pelletier,  100  pounds  of  opium  yield 
6  ounces  of  codeia. 

Codeia  crystallizes  in  acicular,  or  flat  prisms,  colorless  and  transparent. 
It  fuses  without  decomposition,  when  heated  in  a  tube  to  about  300°,  and 
the  mass  crystallizes  on  cooling.  In  the  air  it  burns  away  with  a  smoky 
flame.  Water  at  60°  dissolves  1*26  per  cent.,  and  at  212°,  59  per  cent. 
When  it  is  present  in  larger  proportions  than  the  boiling  water  can  dissolve, 
the  excess  fuses,  and  remains  at  the  bottom  of  the  solution.  ^  Its  solution  is 
sensibly  alkaline  to  tests.  Codeia  is  soluble  in  alcohol  and  in  ether,  and  in 
the  dilute  acids,  and  forms  distinct  and  easily  crystallizable  salts.  It  is 
distinguished  from  morphia,  by  its  greater  solubility  in  water  and  in  ether, 
by  its  insolubility  in  fixed  alkalies,  by  its  not  being  reddened  by  nitric  acid, 
nor  blued  by  perchloride  of  iron. 

Narceia  {Q^B.Jd^^^),  Thebaia  (C^H,A^^)»  Papaverine  (C^HatOgN), 
and  Meconine  (CjoH.Oj,  are  other  crystalline  principles  found  in  opium. 


660  NARCOTINA.      CINCHONIA.      QUINIA. 

Narcotina  (C^gHg^OjgN). 

This  well-defined  and  distinct  principle  appears  to  exist  in  opium  in  a  free 
state :  it  may  be  obtained  from  powdered  opium  by  digesting  it  in  warm 
ether,  which  takes  up  little  else  than  narcotina,  and  yields  it  in  crystals. 
When  caustic  potassa  is  added  to  an  aqueous  solution  of  opium,  so  as  just  to 
saturate  the  free  acid,  the  matter  which  falls  consists  chiefly  of  resin  and 
narcotine.  When  all  the  soluble  parts  of  opium  have  been  extracted  by 
water,  as  in  making  extract  of  opium,  and  in  the  preparation  of  morphia, 
the  residue,  digested  in  dilute  hydrochloric  acid,  also  yields  narcotina. 

Narcotina  is  insipid  when  pure.  It  fuses  at  268°,  and  when  slowly  cooled 
concretes  into  a  crystalline  mass.  It  is  deposited  from  its  alcoholic  or  ethe- 
real solution  in  well-defined  rhombic  prisms,  insoluble  in  cold,  and  sparingly 
soluble  in  hot  water;  100  parts  of  boiling  alcohol  (sp.  gr.  0*825)  dissolve 
about  5  parts  of  narcotina,  4  of  which  crystallize  on  cooling :  boiling  ether 
dissolves  about  3  or  4  per  cent.,  of  which  it  deposits  more  than  one-half,  on 
cooling.  It  is  soluble  in  the  volatile  and  fat  oils,  but  insoluble  in  alkaline 
solutions.  It  does  not  render  a  solution  of  a  persalt  of  iron  blue,  nor  is  it 
reddened  by  nitric  acid.  This  acid  turns  it  yellow.  Sulphuric  acid,  con- 
taining a  mere  trace  of  nitric  acid,  immediately  reddens  it  most  intensely : 
but  when  mixed  with  pure  sulphuric  acid,  it  acquires  a  yellow  color.  A 
particle  of  an  alkaline  nitrate  added  to  the  mixture  brings  out  a  blood-red 
color.  It  does  not  decompose  iodic  acid.  Heated  on  paper  over  a  candle, 
it  produces  a  greasy-looking  stain.  As  it  does  not  affect  vegetable  colors, 
it  is  easily  distinguished  from  morphia  and  codeia.  It  is  readily  soluble  in 
dilute  acids,  forming  salts  which  are  very  bitter,  and  with  difficulty  obtained 
in  the  crystalline  state,  for  when  evaporated  they  are  mostly  decomposed  into 
acid  and  narcotina,  and  crystals  of  the  latter  only  separate.  This  is  espe- 
cially the  case  with  the  acetate  of  narcotina,  and  furnishes  a  means  of 
separating  it  from  morphia,  for  the  latter  substance  is  retained  in  permanent 
combination  and  solution. 

+ 
CiNCHONiA.     Cinchonine  (CgoH,30N=Cin). 

This  alkaloid  is  obtained  from  the  principal  varieties  of  pale  or  gray 
Peruvian  bark.  It  is  usually  in  the  form  of  white  semi-transparent  crystals, 
requiring  about  2500  parts  of  water  at  212°  for  their  solution,  and  are 
almost  insoluble  in  cold  water.  They  have  little  taste,  but  become  intensely 
bitter  upon  the  addition  of  almost  any  acid.  They  restore  the  blue  color 
of  reddened  litmus.  They  are  sparingly  soluble  in  cold  alcohol,  ether,  and 
fixed  oils ;  but  more  abundantly  soluble  in  boiling  alcohol :  the  solution 
deposits  crystals  on  cooling,  and  becomes  milky  when  dropped  into  water. 
It  forms  with  acids  a  large  number  of  salts. 

QuiNiA.     Quinine  {QJiiS^^,=(l). 

Quinia  is  generally  obtained  from  yellow  hark.  It  almost  always  contains 
more  or  less  cinchonia :  these  alkaloids  may  be  separated  by  solution  in 
alcohol,  which,  when  duly  evaporated,  deposits  the  cinchona  in  crystals, 
while  the  quinia,  being  more  soluble,  remains  in  solution :  by  one  or  more 
repetitions  of  this  process,  it  may  be  freed  from  cinchonia.  If  they  are  con- 
verted into  sulphates,  the  sulphate  of  quinia,  being  less  soluble  than  the 
sulphate  of  cinchonia,  crystallizes,  and  leaves  the  latter  salt  in  solution. 

Sulphate  of  quinia,  which  is  abundantly  prepared  for  medicinal  use,  is  the 
most  ready  source  of  the  alkaloid :  it  is  obtained  by  adding  ammonia  to  a 
solution  of  that  salt,  when  it  falls  in  white  flakes,  which  unless  very  carefully 


SALTS    OF    QUINIA.       STRYCHNIA.  661 

dried,  are  apt  to  become  brown.  Quinia  is  very  difficult  of  crystallization, 
but  it  has  been  obtained  in  crystals  by  slowly  evaporating  its  alcoholic  solu- 
tion by  exposure  to  dry  cold  air. 

Quinia  has  a  decided  alkaline  action;  it  is  intensely  bitter;  very  sparingly 
soluble,  even  in  boiling  water,  of  which  it  requires  about  200  parts  for  its 
solution.  It  is  readily  soluble  in  boiling  alcohol,  and  the  solution,  when 
evaporated,  leaves  it  in  the  form  of  a  viscid  mass,  which  indurates  and 
acquires  a  resinous  aspect  on  exposure  to  air.  It  is  more  soluble  than  cin- 
chonia  in  chloroform  and  ether.  It  forms  distinct  salts  with  the  acids. 
When  anhydrous  quinia  is  heated  in  a  tube,  it  fuses,  becomes  thick,  viscid, 
and  dark-colored,  an  oily  liquid  evaporates,  ammoniacal  and  hydrocyanic 
vapors  follow,  and  a  bulky  carbonaceous  matter  remains. 

The  Salts  of  quinia  are  for  the  most  part  crystallizable,  and  are  generally 
less  soluble  in  water,  and  more  bitter  than  the  salts  of  cinchonia ;  they  are 
also  soluble  in  alcohol.  The  aqueous  solution  has  a  peculiar  bluish  opaline 
appearance,  as  a  result  of  fluorescence.  They  are  liable  to  acquire  a  yellow 
or  brown  tint  by  long  exposure  to  solar  light.  In  this  altered  state  they 
form  the  substance  called  quinoidine — a  mixture  of  several  basic  compounds, 
including  quinidine  {Q^^Jd^c^-^iB-O),  isomeric  with  quinine.  It  is  ex- 
tracted by  ether.  These  different  bases  of  Peruvian  bark  are  combined  in 
the  plant  with  a  peculiar  crystallizable  acid,  called  the  Cinchonic  or  Kinic 
acid  (CyH^O^HO). 

Strychnia  (C^^Ha^O^NJ. 

The  following  is  Merck's  process  for  the  extraction  of  this  alkaloid.  The 
seeds  of  nux  vomica  are  boiled  for  24  or  36  hours  in  a  closed  boiler,  with 
water  enough  to  cover  them,  acidulated  by  one-eighth  of  its  weight  of  sul- 
phuric acid ;  they  are  then  bruised  and  beaten  into  a  paste,  and  the  liquor 
well  expressed.  Excess  of  caustic  lime  is  then  added  to  it,  and  the  precipi- 
tate, having  bee«i  pressed,  is  boiled  in  alcohol  of  sp.  gr.  -850,  and  filtered 
hot ;  strychnia  and  brucia  are  deposited  together  in  a  colored  and  impure 
state,  and  may  be  separated  by  cold  alcohol,  which  dissolves  the  brucia. 
The  remaining  strychnia  is  then  boiled  in  alcohol  with  a  little  animal  char- 
coal, and  the  solution  filtered  boiling  hot ;  on  cooling,  the  strychnia  crystal- 
lizes.    The  same  process  is  applicable  to  the  Ignatius'  beans. 

Strychnia  is  a  powerful  poison,  de^roying  life  in  the  dose  of  half  a  grain. 
It  is  a  white  crystalline  solid,  neither  fusible  nor  volatile,  but  easily  decom- 
posed by  heat,  yielding  ammonia,  in  close  vessels.  It  requires  7000  parts 
of  cold  and  2500  of  boiling  water  for  solution  :  the  intensity  of  its  bitterness 
is  such,  that  an  aqueous  solution  which  does  not  contain  more  than  a  forty- 
thousandth  of  its  weight  of  strychnia  is  sensibly  bitter.  It  is  soluble  in 
common  alcohol,  especially  at  its  boiling  temperature,  and  readily  crystallizes 
in  quadrangular  prisms  and  octahedra  from  this  solution.  Absolute  alcohol 
and  ether  scarcely  dissolve  it  when  quite  free  from  acid.  It  is  dissolved  by 
chloroform  and  benzole,  and  separated  from  water  by  these  solvents  when  an 
alkali  is  added  to  a  solution  of  a  salt  of  strychnia.  It  is  dissolved  by  the 
acids,  forming  colorless  and  crystallizable  salts.  It  is  not  soluble  in  the 
alkalies.  Nitric  acid  does  not  color  strychnia  or  its  salts,  if  free  from  brucia ; 
but  it  frequently  reddens  them,  owing  to  the  presence  of  traces  of  brucia. 

When  a  minute  quantity  of  strychnia  is  moistened  with  a  drop  of  concen- 
trated sulphuric  acid,  the  strychnia  is  dissolved  without  any  peculiar  color, 
but  if  a  minute  quantity  of  the  peroxide  of  lead  or  manganese,  of  bichromate 
of  potassa,  or  ferricyanide  of  potassium,  is  added,  a  fine  blue  tint  is  developed, 
which  passes  into  violet  and  red,  and  after  some  hours  into  a  pale  reddish 
yellow  color.     This  reaction  is  characteristic  of  strychnia.     The  peroxide 


662  BRUCIA. 

of  manganese  in  small  quantity  is  preferable  for  this  experiment.  A  strong 
solution  of  strychnia  gives  crystalline  precipitates  with  sulphocyanide  and 
ferricyanide  of  potassium,  as  well  as  with  chromate  of  potash.  The  ferricy- 
anate  and  chromate  of  strychnia,  when  touched  with  sulphuric  acid,  acquire 
the  blue,  violet,  and  purple  colors  which  characterize  strychnia.  To  these 
may  be  added  the  sulpho-molybdic  acid  (see  Morphia),  which  produces  a 
peculiar  reaction  with  strychnia.  When  first  added  there  is  no  change  of 
color.  The  border  of  the  acid  liquid  soon  begins  to  show  a  fringe  of  a  pale 
blue  or  azure  color.  This  gradually  extends  by  exposure  to  the  whole  of 
the  liquid',  until  it  is  uniformly  of  a  light  azure  blue,  without  any  of  the  deep 
blue  tint  observed  in  morphia  and  other  alkaloids. 

This  alkaloid  perfectly  neutralizes  the  acids,  and  forms  soluble  and  very 
bitter  and  poisonous  salts :  they  are  mostly  crystal lizable.  The  caustic 
alkalies  throw  down  from  their  solutions  a  white  precipitate  of  strychnia, 
which  may  be  dissolved  and  removed  by  agitating  the  liquid  with  twice  its 
bulk  of  ether  or  chloroform.  This  is  the  process  usually  pursued  for  the 
extraction  of  strychnia  in  cases  of  poisoning.  The  liquid  is  acidulated, 
concentrated  in  a  w^ater-bath,  rendered  alkaline  by  potassa,  and  then  shaken 
with  two  volumes  of  ether.  The  ethereal  liquid  poured  off,  and  sponta- 
neously evaporated,  leaves  strychnia.  The  salts  of  strychnine  are  precipitated 
by  tincture  of  galls  (tannic  acid). 

Brucia  (C,,H,30,N,). 

This  alkaloid  is  most  abundantly  procured  from  the  bark  of  the  Strychnos 
nux-vomica,  common\y  C2i\\Q^  false  angustura.  This  bark  is  coarsely  pow- 
dered, and,  having  been  previously  digested  in  ether  to  free  it  from  fatty 
matter,  is  treated  with  alcohol,  the  alcoholic  solution  evaporated,  and  the 
residue  dissolved  in  water  saturated  with  oxalic  acid,  and  evaporated  to 
dryness.  Alcohol  digested  upon  this  residuum  dissolves  coloring  matter, 
and  leaves  pure  oxalate  of  brucia,  which  may  be  decomposed  by  lime,  and 
the  brucia  dissolved  out  by  boiling  alcohol,  from  which,  by  slow  evaporation, 
it  is  obtained  in  crystals. 

Brucia  forms  either  prismatic  or  foliated  crystals,  according  as  it  has  been 
slowly  or  rapidly  deposited  :  it  is  soluble  in  about  850  parts  of  cold,  and  in 
500  of  boiling  water.  Sometimes,  on  precipitating  a  salt  of  brucia  by 
ammonia,  the  alkaloid  separates  in  the  form  of  an  bi\,  which  after  a  time 
concretes,  if  left  in  contact  with  water.  The  taste  of  brucia  is  strongly  and 
permanently  bitter  :  its  poisonous  action  resembles  that  of  strychnia,  but  it 
has  only  one-sixth  of  the  strength.  It  is  very  soluble  in  alcohol,  but  insolu- 
ble in  ether,  and  in  the  fat  oils  :  it  is  sparingly  soluble  in  essential  oils.  It 
forms  soluble  salts  with  the  acids,  which  are  mostly  crystallizable ;  they  are 
bitter,  and  are  decomposed  not  only  by  the  alkalies,  but  by  morphia  and 
strychnia,  both  of  which  precipitate  the  brucia.  Brucia  is  strongly  reddened 
by  nitric  acid,  and  the  color  changes  to  violet  when  the  liquid  is  warmed 
and  protochloride  of  tin  is  added.  It  is  distinguished  from  strychnia  by  its 
not  producing  the  blue  and  purple  colors  when  mixed  with  sulphuric  acid 
and  peroxide  of  manganese.  It  is  also  known  from  this  alkaloid  by  the 
different  effect  produced  upon  it  when  it  is  touched  with  a  drop  of  sulpho- 
molybdic  acid.  A  flesh  or  pale  red  color  is  first  produced — the  spot  becom- 
ing of  a  dingy  olive-green  color  in  the  centre.  By  long  exposure  the  whole 
of  the  spot  acquires  a  deep  sapphire-blue  color. 

Strychnia  and  brucia,  as  they  exist  in  the  vegetable  structure,  are  com- 
bined with  a  peculiar  acid,  called  the  strychnic  or  igasuric. 


COLCHIOIA.      ATROPIA.  063 

YERATRTACCg^H^eOgN). 

This  alkaloid  is  contained  in  the  seeds  of  the  Veratrum  sahadilla,  and  in 
the  roots  of  the  Veratrum  album,  or  white  hellebore,  united  with  gallic  acid. 
Commercial  veratria  is  not  crystallizable  ;  it  has  a  pungeut  but  not  a  bitter 
taste,  and  powerfully  irritates  the  nostrils,  causing  the  most  violent  sneezing. 
A  small  dose  produces  nausea  and  vomiting.  It  is  a  poison.  It  fuses  at  a 
temperature  of  122°,  and  concretes,  on  cooling,  into  a  translucent  yellow 
mass.  Boiling  water  does  not  take  up  more  than  a  thousandth  part' of  its 
weight,  but  it  is  readily  soluble  in  alcohol,  and  somewhat  less  so  in  ether. 
Chloroform  dissolves  it  in  large  quantity.  Yeratria  is  characterized  by  its 
producing,  when  warmed  with  diluted  sulphuric  acid,  an  intense  crimson 
color.  If  strong  sulphuric  acid  is  used  a  greenish-yellow  color  is  first  pro- 
duced, which  becomes  slowly  dark  red  by  exposure,  but  rapidly  acquires  a 
most  intense  blood  red  color  when  heated.  As  sulphuric  acid  reddens  a 
great  variety  of  organic  substances,  e.  g.,  salicine,  cholesterine,  gallic  acid, 
etc.,  the  last  alone  is  not  sufficient.  Chloride  of  tin  evaporated  with  vera- 
tria leaves  a  reddish  colored-residue.  Nitric  and  hydrochloric  acids  produce 
in  it  a  characteristic  change.  The  sulpho-molybdic  acid  produces  with  it 
at  once  a  dingy  olive-green  color,  which  passes  after  a  time  to  a  rich  sapphire- 
blue. 

CoLCHiciA.     Colchidna. 

This  substance,  originally  confounded  with  veratria,  has  been  shown  by 
Geiger  and  Hesse  to  exist  in  the  Golchicum  autumnale,  as  a  distinct  alkaloid, 
but  it  has  not  been  analyzed,  nor  has  its  atomic  weight  been  determined.  It 
exists  in  the  bulb  and  flowers  gathered  in  July,  but  is  best  obtained  from  the 
pulverized  seed,  which  is  digested  in  alcohol  acidulated  by  sulphuric  acid ; 
lime  is  then  added  to  the  liquor,  which  is  filtered,  saturated  by  sulphuric 
acid,  and  the  alcohol  expelled  by  distillation.  The  remaining  concentrated 
aqueous  solution  having  been  decomposed  by  excess  of  carbonate  of  potassa, 
the  precipitate  is  dried  and  digested  in  absolute  alcohol.  The  alcoholic 
solution  of  the  alkaloid  is  then  decolorized  by  animal  charcoal,  filtered,  and 
gently  evaporated  :  the  product  is  afterwards  purified  by  repeated  crystalli- 
zations. 

Colchicia  is  a  powerful  poison.  It  crystallizes  in  colorless  needles,  which 
have  a  bitter  taste  and  are  very  poisonous ;  it  causes  purging  and  vomiting 
in  very  small  doses.  It  is  slightly  alkaline  and  easily  fusible.  It  is  rendered 
deep  violet  blue  by  concentrated  nitric  acid,  becoming  afterwards  olive-colored 
and  yellow ;  sulphuric  acid  renders  it  brown.  It  is  soluble  in  water,  alcohol, 
and  ether,  and  its  aqueous  solution  is  precipitated  by  tincture  of  iodine,  by 
solution  of  chloride  of  platinum,  and  by  infusion  of  galls.  It  neutralizes  the 
acids,  and  forms  salts  which  are  mostly  crystallizable,  permanent  in  the  air, 
and  very  bitter  and  acrid.  They  are  soluble  in  water  and  alcohol,  and  their 
aqueous  solutions  are  acted  upon  by  reagents  similarly  to  colchicia.  When 
not  too  dilute,  the  alkalies  precipitate  the  alkaloid. 

Atropia.  Hyoscyamia.  Daturia.  Piorotoxia. 
Atropia  is  the  poisonous  alkaloid  of  the  Atropa  Belladonna,  or  Deadly 
Nightshade;  Hyoscyamia,  of  the  Hyoscyamus  niger;  Daturia,  of  the  Datura^ 
Stramonium;  and  Picrotoxia,  of  Cocculus  Indicus.  Aconitina  and  Digitaline 
are  extracted  respectively  from  Aconitum  napellus  and  Digitalis  purpurea. 
These  are  all  active  poisons.  Their  composition  has  not  been  accurately 
determined.  There  are  other  alkaloids  of  less  interest,  which  require  no 
particular  notice  in  a  chemical  point  of  view. 


664  NICOTINA.      CONTA. 

The  bases  hitherto  considered  contain  oxygen.  There  are  two  volatile 
alkaloidal  bodies,  Nicotina  and  Conia,  which  contain  no  oxygen. 

NiCOTINA  (C^oH^N). 

Kicotina  is  obtained  by  boiling  dry  tobacco-leaves  in  water  acidufeted  by 
snlphuric  acid,  and  evaporating  the  decoction;  the  residue,  digested  in  alco- 
hol, yields  a  solution  of  sulphate  of  nicotina,  which,  when  concentrated  and 
distilled  with  quicklime,  furnishes  a  solution  of  ammonia  and  nicotina.  Ether 
abstracts  nicotina  from  this  solution,  and  when  a  sufficiently  concentrated 
ethereal  solution  has  been  thus  obtained,  it  must  be  deprived  of  water  by  agi- 
tation with  chloride  of  calcium,  decanted,  and  distilled;  the  nicotina  remains 
in  the  retort. 

Pure  nicotina  is  a  colorless,  limpid,  oleaginous  liquid,  having  a  slight  odor 
of  stale  tobacco ;  when  it  contains  ammonia,  this  odor  is  very  intense.  At  a 
temperature  below  475°  it  may  be  slowly  distilled,  but  at  that  temperature  it 
is  decomposed;  its  sp.  gr.  is  1-048.  It  is  powerfully  alkaline  to  test-papers; 
it  is  very  inflammable,  and  burns  with  a  smoky  flame.  When  dissolved  in 
water,  caustic  potassa  separates  it  in  the  form  of  oily  drops.  Ether  abstracts 
it  from  its  aqueous  solution.  It  dissolves  in  all  proportions  in  alcohol  and 
in  oils.  It  is  decomposed  when  heated  with  hydrate  of  potassa.  Exposed 
to  air,  it  becomes  brown  and  resinous:  it  is  decomposed  by  chlorine,  iodine, 
and  nitric  acid.  It  is  eminently  poisonous,  but  does  not  occasion  dilatation 
of  the  pupil :  half  a  drop  killed  a  rabbit ;  one  drop  was  fatal  to  a  dog ;  a 
tenth  of  a  grain  applied  to  the  eye  of  a  cat,  occasioned  violent  convulsions 
and  paralysis  of  the  hind-legs,  which  lasted  for  an  hour.  Nicotina  neutralizes 
the  acids  and  forms  salts  which  do  not  easily  crystallize,  but  are  very  soluble 
in  water  and  alcohol.  When  it  is  slightly  supersaturated  by  hydrochloric  acid, 
nicotina  gives  no  precipitate  with  bichloride  of  platinum,  but  the  mixture, 
after  some  hours,  deposits  acicular  crystals.  If  the  nicotina  contains  am- 
monia, it  occasions  an  immediate  precipitate.  The  solution  of  nicotina  pro- 
duces a  white  precipitate  with  corrosive  sublimate. 

Conia.    Conidna  (C,eH,6N). 

It  appears  from  the  experiments  which  have  been  made  upon  hemlock, 
that  its  active  principle  resides  in  a  volatile  and  uncrystallizable  alkaloid;  its 
properties  have  been  investigated  by  Geiger,  and  by  Dr.  Christison  {Edin. 
Phil.  Trans.,  1836,  p.  ^3).  When  the  seeds  or  leaves  of  hemlock  are  dis- 
tilled with  water,  the  fluid  which  passes  over  has  the  odor  of  the  plant,  but 
is  not  poisonous ;  but  when  caustic  lime  or  potassa  is  previously  added  to 
the  green  seeds  or  leaves,  and  these  are  distilled  with  water  at  as  low  a  tem- 
perature as  possible,  the  liquid  which  then  passes  over  is  both  alkaline  and 
poisonous.  When  10  or  12  pounds  of  the  seeds  are  worked  at  once,  an  oily 
matter  comes  over  at  first,  which  is  nearly  pure  conia,  but  the  greater  part 
of  the  alkaloid  is  dissolved  in  the  distilled  water ;  if  this  be  redistilled,  it 
loses  a  little  of  its  strength ;  but  if  previously  neutralized  by  an  acid,  such  as 
the  sulphuric,  the  poisonous  principle  becomes  fixed,  and  water  alone  distils 
over.  The  residue  consists  of  sulphate  of  conia,  sulphate  of  ammonia,  and 
resin,  the  latter  being  produced  by  the  decomposition  of  part  of  the  conia. 
To  obtain  the  conia,  the  above  residue  is  digested  in  a  mixture  of  2  parts  of 
•alcohol  and  1  of  ether,  which  leaves  the  sulphate  of  ammonia ;  and  then,  the 
alcohol  and  ether  being  carefully  distilled  off,  the  remaining  sulphate  of  conia 
is  heated  gently  with  a  little  water  and  caustic  potassa,  when  there  is  obtained 
in  the  receiver  a  watery  solution  of  conia  in  the  lower  part,  and  floating  on 
this  a  layer  of  nearly  pure  hydrate  of  conia,  containing  a  trace  of  ammonia; 


ANILINE.  CG5 

the  water  ^raay  be  abstracted  by  chloride  of  calcium,  and  the  ammonia  by 
exposure  i7i  vacuo. 

Conia  thus  obtained  has  the  appearance  of  a  colorless  volatile  oil,  lighter 
than  water,  of  a  powerful  diffusible  odor,  somewhat  like  that  of  hemlock,  and 
when  diluted  resembling  the  smell  of  mice :  it  is  intensely  acrid  to  the  taste. 
It  has  a  strong  alkaline  action  on  reddened  litmus  and  on  turmeric.  It  is 
readily  soluble  in  diluted  acids,  which  it  neutralizes,  but  its  salts  have  not 
been  crystallized.  It  is  sparingly  soluble  in  water,  ant  combines  with  about 
a  fourth  of  its  weight  of  water  to  form  a  hydrate. 

Conia  is  a  deadly  poison  to  all  animals :  it  first  paralyzes  the  voluntary 
muscles,  then  the  respiratory  muscles  and  the  diaphragm,  thus  producing 
death  by  asphyxia.  The  heart  continues  to  act  after  other  signs  of  life  are 
extinct.  Few  poisons  equal  it  in  subtlety  or  swiftness  ;  a  drop  put  into  the 
eye  of  a  rabbit  killed  it  in  nine  minutes  ;  three  drops,  in  the  same  way,  killed 
a  strong  cat  in  a  minute  and  a  half;  two  grains  of  conia,  neutralized  with 
hydrochloric  acid,  and  injected  into  the  femoral  vein  of  a  young  dog,  produced 
almost  instant  death  :  in  two  seconds,  or  three  at  farthest,  and  without  the 
slightest  warning  struggle,  respiration  had  ceased,  and  with  it  all  external 
signs  of  life.  If  conia  be  present  in  an  extract  or  other  preparation,  it  may 
be  detected  by  triturating  either  the  solid  or  liquid  with  a  solution  of  potassa, 
upon  which  the  odor  of  mice  will  be  strikingly  perceptible. 

Aniline.    Phenylia  (C^aHyN). 

This  is  an  artificial  base  which  contains  no  oxygen.  It  has  been  already 
referred  to  as  a  product  of  the  distillation  of  coal.  It  may  be  procured  by 
distilling  indigo  with  a  strong  solution  of  potassa.  It  is  now  obtained  in 
large  quantities,  for  dyeing  and  other  purposes,  by  distilling  nitrobenzole 
with  a  mixture  of  acetic  acid  and  zinc,  or  iron,  in  which  case  this  liqnid  is 
decomposed  by  nascent  hydrogen,  and  aniline  is  a  product.  The  proportions 
employed  are  10  parts  of  nitrobenzole,  6  parts  of  commercial  acetic  acid, 
and  15  parts  of  pounded  iron-turnings. 

Aneline  when  pure  is  a  colorless  or  oil-like  liquid,  possessing  a  very  high 
refractive  power  :  it  has  a  strong  disagreeable  odor,  and  a  hot  aromatic 
flavor.  It  boils,  according  to  Hofmann,  at  360°,  but  it  evaporates  rapidly 
at  common  temperatures,  and  the  greasy  spot  which  it  produces  on  paper 
quickly  disappears;  it  remains  perfectly  fluid  at  0°;  its  sp.  gr.  at  60-  is 
1020.  We  have  found  it  in  two  samples  to  be  1'023  and  1*024  respectively. 
It  is  soluble  to  a  slight  extent  in  cold  water,  the  greater  part  falling  in  oily 
globules :  the  solution  becomes  turbid  when  heated  ;  it  is  soluble  in  all  pro- 
portions, in  alcohol,  ether,  wood-spirit,  aldehyde,  acetone,  sulphide  of  carbon, 
and  in  fixed  and  volatile  oils.  It  has  no  alkaline  reaction  on  turmeric  or  on 
reddened  litmus.  When  a  glass  rod  dipped  in  hydrochloric  acid  is  held 
over  its  aqueous  solution,  white  fumes  are  produced,  resembling  those  formed 
by  ammonia.  Aniline  dissolves  sulphur  when  aided  by  heat,  and  on  cooling, 
deposits  it  in  prismatic  crystals  ;  it  also  dissolves  phosphorus,  camphor,  and 
colophony,  but  not  copal  or  caoutchouc  ;  like  creasote,  it  coagulates 
albumen. 

When  aniline  is  exposed  to  air,  it  absorbs  oxygen,  and  becomes  yellow, 
brown,  and  resinous.  A  few  drops  of  fuming  nitric  acid  added  to  anhydrous 
aniline  produces  a  fine  blue  color,  which  on  slightly  heating  the  mixture 
passes  into  yellow,  and  violent  action  ensues,  sometimes  followed  by  explosion  ; 
otherwise,  the  liquor  passes  through  various  hues,  and  crystals  of  picric  acid 
are  formed  in  it.  When  aniline  is  added  to  a  solution  of  permanganate  of 
potassa,  peroxide  of  manganese  is  thrown  down,  and  oxalic  acid  and  ammo- 
nia are  formed.     When  treated  with  a  solution  of  chloride  of  lime,  a  beauti- 


666  EMETINA    AND    OTHER    BASES 

ful  violet-color  is  produced,  which  is  reddened  by  the  addition  of  an  "acid; 
this  reaction  is  very  characteristic  of  aniline.  When  chlorine  is  passed  into 
aniline,  it  assumes  the  consistence  of  tar,  and  on  distilling  this  product,  a 
compound  passes  over,  composed  of  CiaHgNCl.  When  heated  with  corro- 
sive sublimate,  it  produces  a  splendid  red  dye.  It  is  now  largely  employed 
in  the  manufacture  of  the  coal-tar  colors. 

Aniline  forms  a  series  of  crystallizable  salts  with  different  acids. 

The  production  of^niline  from  nitrobenzole  furnishes  an  apt  illustration 
of  the  complexity  wTiich  it  is  proposed  to  introduce  into  chemical  formulae, 
in  place  of  the  simple  system  which  is  now  generally  employed.  When 
nitrobenzole  is  distilled  with  a  mixture  of  iron-filings  and  acetic  acid,  it  is 
converted  into  aniline,  as  a  result  of  the  evolution  of  nascent  hydrogen  ;  and 
the  simple  equation  which  represents  this  change  is  : — 

C,2H,(N0,) 


Nitrobenzole.  Hydrogen.  Aniline. 


The  following  represents  the  changes,  according  to  Dr.  Hofmann,  on  what 
is  called  the  unitary  system  : — 


(C6H5)NOO        +        HH  4-  HH  -f  HH 


(CeH,)) 


Nitrobenzole.  Hydrogen.  Water.  Aniline. 

Emetina,  Caffeine,  Theine,  and  other  Bases. 

Emetina  {C^'E.^^0^^. — This  term  is  applied  to  the  active  or  emetic  princi- 
ple of  Ipecacuanha.  It  is  a  white,  inodorous,  and  almost  insipid  powder, 
alkaline  to  test-paper,  and  sparingly  soluble  in  cold  water.  It  is  more  solu- 
ble in  alcohol ;  but  ether,  the  essential  oils,  and  the  caustic  alkalies,  scarcely 
act  upon  it ;  it  fuses  at  about  120^.  Concentrated  nitric  acid  converts  it  in 
the  first  instance  into  a  bitter  yellow  resinoid  substance,  and  ultimately  into 
oxalic  acid.  It  neutralizes  the  acids,  and  forms  salts  which  are  not  crystal- 
lizable except  with  excess  of  acid.  Emetina  has  a  powerful  emetic  action. 
In  a  dose  of  three  or  four  grains  it  acts  as  a  poison. 

Piperine  (Cj^H^gOgN). — This  substance  is  obtained  from  hlach  pepper.  It 
is  generally  a  pale  straw  color,  and  crystallizes  in  the  form  of  four-sided 
prisms,  insoluble  in  cold,  and  slightly  soluble  in  hot  water;  readily  soluble 
in  alcohol,  and  less  so  in  ether.  When  quite  pure,  it  is  inodorous  and  taste- 
less. It  fuses  at  a  little  above  212°,  and  is  not  volatile,  but  when  more 
highly  heated,  yields  ammoniacal  products.  It  is  regarded  as  a  feeble  alka- 
loid. 

Asparagine  {C^Jd^^-\-^^0). — This  principle  exists  in  asparagus.  It 
is  best  obtained  from  the  expressed  juice  of  asparagus,  evaporated  to  the 
consistency  of  syrup,  and  set  aside  ;  it  deposits  crystals,  which  are  purified 
by  solution  in  water  and  recrystallization.  Asparagine  forms  transparent 
prismatic  crystals,  which  are  hard,  brittle,  of  a  cooling  and  somewhat  nau- 
seous taste,  neither  alkaline  nor  acid  ;  soluble  in  58  parts  of  cold  water,  and 
more  soluble  in  hot ;  insoluble  in  anhydrous  alcohol,  and  in  ether.  When 
asparagine  is  long  boiled  with  hydrated  oxide  of  lead,  magnesia,  or  other 
bases,  it  is  resolved  into  ammonia  and  into  an  acid,  called  Aspartic  acid. 

Caffeine.  Theine.  (CgH.O^Ng).  Guaranine.  This  important  compound 
is  found  in  coffee  (the  seed  of  Goffea  Arahicd)  and  in  tea,  the  leaves  of  Thea 
Chinensis :  it  is  also  said  to  occur  in  the  leaves  of  Guarana  officinalis  or 
Paullinia  Sorbiiis,  and  in  Ilex  Paraguayensis  (^Paraguay  tea).     It  is  re- 


THEINE.      THEOBROMINE.      SALICINE.  GOT 

mark^le  that  one  and  the  same  principle,  and  that  belonging  to  the  class  of 
azotized  basic  bodies,  should  be  found  in  two  such  dissimilar  vegetables  as 
tea  and  coffee,  infusions  of  which  are  used  over  the  greater  part  of  the  known 
world. 

^  Caffeine  naay  be  procured  as  a  crystalline  sublimate  in  considerable  quan- 
tity in  the  roasting  of  large  quantities  of  coffee  ;  it  sublimes  in  an  impure 
form,  but  is  easily  deprived  of  its  adhering  impurities.  The  process  gene- 
rally recommended  for  its  preparation  is  that  of  Runge\  it  consists  in  making 
a  strong  aqueous  infusion  of  ground  raw  coffee,  adding  to  it  a  solution  of 
sugar  of  lead,  which  occasions  a  green  precipitate,  and  leaves  the  superna- 
tant liquid  colorless  :  the  excess  of  the  salt  of  lead  in  this  liquid  is  then  pre- 
cipitated by  sulphuretted  hydrogen,  it  is  filtered,  and  evaporated  ;  the  caf- 
feine remains,  and  must  be  treated  by  animal  charcoal  to  whiten  it,  and  re- 
crystallized.  Caffeine  (or  theine)  forms  white  silky  crystals,  soluble  in  boil- 
ing water  and  alcohol,  and  deposited  in  crystalline  filaments  as  these  solu- 
tions cool :  it  has  no  alkaline  reaction,  yet  it  appears  capable  of  combining 
definitely  with  some  of  the  acids,  especially  with  hydrochloric  acid. 

TJieine  is  thus  prepared :  a  decoction  of  tea  is  first  treated  with  a  slight 
excess  of  acetate  of  lead,  which  throws  down  the  tannic  acid  and  almost  all 
the  coloring  matter  it  contains  ;  it  is  then  filtered  whilst  hot,  and  the  clear 
liquid  is  evaporated  to  dryness.  It  forms  a  dark  yellowish  mass,  which  is 
to  be  intimately  mixed  with  a  quantity  of  sand,  and  introduced  into  Mohr's 
subliming  apparatus  aud  moderately  heated  for  10  or  12  hours.  The  theine 
sublimes  in  beautifully  white  anhydrous  crystals,  deposited  upon  the  paper 
diaphragm  which  runs  across  the  apparatus.  The  only  point  to  be  observed 
is  that  the  temperature  should  never  rise  too  high,  as  the  more  slowly  the 
operation  is  conducted,  the  finer  are  the  crystals  and  the  greater  their  quan- 
tity. From  a  pound  of  coffee,  Stenhouse  obtained  an  average  produce  of 
15  grains  of  theine,  sometimes  not  so  white  as  that  made  from  tea,  but  ren- 
dered so  by  a  second  sublimation.  From  hyson  tea  (green),  Stenhouse  ob- 
tained r05  per  cent,  of  theine;  from  Congou  (black)  1*02  per  cent.  ;  from 
Assam  (black)  r2t,  and  from  Tonkay  (green)  0-98.  But  Peligot,  guided 
by  the  large  proportion  of  nitrogen  evolved  in  the  ultimate  analysis  of  tea, 
was  led  to  suspect  a  larger  proportion  of  theine,  and  obtained  the  following 
quantities,  namely,  from  hyson,  2*56  to  3*40  per  cent,  and  from  gunpowder 
tea  2-20  to  4' 10  per  cent. 

Theohromine  (Cj^HgO^^J  is  a  base  which  is  contained  in  the  cacao-nut 
{Tlieohroma  cacao).  It  is  but  little  soluble  in  water,  alcohol,  and  ether.  It 
has  a  bitter  taste,  and  forms  crystallizable  salts  with  acids. 

Salicine  (CaBHjgO^). — This  is  a  crystalline  substance  which  is  extracted 
from  the  bark  of  the  willow.  It  is  soluble  in  water  and  alcohol :  its  solu- 
tions have  a  bitter  taste :  they  are  laevo-gyrate  with  regard  to  polarized 
light.  Salicine  is  characterized  by  the  deep  red  color  which  is  produced 
when  the  crystals  are  moistened  with  strong  sulphuric  acid.  When  salicine 
is  boiled  with  dilute  sulphuric  acid,  glucose  or  grape-sugar  is  a  product. 
Nitric  acid  converts  it  into  oxalic  and  carbazotic  acids.  When  distilled  with 
bichromate  of  potassa  and  dilute  sulphuric  acid,  salicylous  acid  or  hydride 
of  salicyl  {C^^Ufi^,W)  is  obtained  in  the  distillate.  This  is  identical  with 
the  essential  oil  of  Meadow-sweet  {Spirsea  uhnaris).  Salicine  yields  about 
one-fourth  of  its  weight  of  the  hydride.  When  fused  below  redness  with 
three  parts  of  hydrate  of  potassa,  a  salicylate  of  the  alkali  is  obtained,  from 
a  solution  of  which  salicylic  acid  is  precipitated  by  the  addition  of  hydro- 
chloric acid. 

A  solution  of  a  salicylate  is  characterized  by  its  striking  a  violet-hlMQ  color 
with  a  persalt  of  iron.    Certain  insects  which  feed  upon  willow  bark,  oxidize 


668  ORGANO-METALLTC    BASES. 

salicine  in  their  bodies.  If  placed  on  paper  impregnated  with  a  persalt  of 
iron,  and  they  are  irritated,  they  eject  a  liquid  which  produces  a  blue  or 
violet-colored  spot  on  the  paper. 

The  oil  or  essence  of  winter-green  (  Gaultheria  procumhens)  is  a  salicylate 
of  the  oxide  of  methyle  (CgllgO  +  C^HgOg).  It  has  a  strong  agreeable  odor, 
and  acquires  a  violet  color  on  the  addition  of  a  persalt  of  iron. 

Phloridzine  {G^^^O^,i^O)  is  a  crystallizable  principle  obtained  from 
the  bark  of  the  apple  and  pear  trees,  by  simply  boiling  the  decoction  in 
water,  and  allowing  the  liquid  to  cool.  When  boiled  with  diluted  acids, 
grape-sugar  is  one  of  the  products.  Salicine,  phloridzine,  and  some  other 
principles  of  a  similar  kind,  which  thus  yield  grape-sugar,  under  such  simple 
conditions,  have  received  the  name  of  Glucosides. 

Organo-metallic  Bases. 

We  have  elsewhere  referred  to  the  compounds  of  zinc  with  the  organic 
radicals  methyle  (p.  593),  amyle  (594),  and  ethyle  (600)  :  but  there  is  pro- 
bably no  compound  more  remarkable  for  its  constitution  and  range  of 
combination,  than  that  which  was  discovered  and  isolated  by  Bunsen  under 
the  name  of  Kakodyle. 

Kakodyle  (C4HgAs=Kd). — This  is  a  compound  of  metallic  arsenic  with 
carbon  and  hydrogen :  it  derives  its  name  from  its  highly  offensive  odor. 
Bunsen  procured  this  radical  by  decomposing  anhydrous  chloride  of  kakodyle 
with  pure  zinc,  and  distilling  the  product.  Owing  to  its  spontaneous  com- 
bustion in  air,  and  its  highly  poisonous  nature,  great  precautions  are  required 
in  its  preparation.  It  is  a  clear  colorless  liquid  (sp.  gr.  1'48);  the  density 
of  its  vapor  being  7  "2.  When  cooled  to  20°  it  crystallizes  in  square  prisms. 
When  exposed  to  air,  oxygen,  or  chlorine,  it  burns,  forming  with  oxygen, 
water,  carbonic  and  arsenious  acids.  It  is  resolved  at  a  red  heat  into  arsenic, 
light  carburetted  hydrogen,  and  olefiant  gas ;  and  by  these  results  its  exact 
constitution  has  been  determined  (C4HgAs=As-f-2CHa  +  C2H3). 

Kakodyle,  like  cyanogen,  combines  with  oxygen,  sulphur  and  chlorine. 
It  also  combines  with  cyanogen.  Oxide  of  kakodyle  (KdO)  is  known  under 
the  names  of  Alkarsine  and  CadeVs  fuming  liquor.  It  is  procured  by  distilling 
at  a  red  heat,  a  mixture  of  equal  weights  of  arsenious  acid  and  dry  acetate 
of  potassa.  The  vapor  has  an  offensive  odor  resembling  that  of  garlic,  and 
is  very  poisonous.  The  oxide  is  a  colorless  liquid  (sp.  gr.  1*64).  It  is 
insoluble  in  water,  but  dissolves  in  alcohol  and  ether.  Another  oxygen 
compound  (KdOgjHO)  is  known  under  the  name  of  Kakodylic  acid  or  Alkar- 
gen.  It  is  procured  by  mixing  red  oxide  of  mercury  with  oxide  of  kakodyle 
under  water.  TJhis  acid  may  be  obtained  crystallized  in  prisms.  Although 
it  contains  56  per  cent,  of  arsenic,  6  or  7  grains  of  it,  according  to  Bunsen, 
produced  no  ill  effect  on  a  rabbit.  The  chloride  is  procured  by  distilling 
the  oxide  with  corrosive  sublimate  and  hydrochloric  acid ;  and  the  cyanide 
by  distilling  the  oxide  with  concentrated  hydrocyanic  acid. 

The  preparation  of  any  of  these  compounds  is  attended  with  great  danger 
to  the  operator.  Bunsen  states,  that  in  distilling  the  oxide,  an  explosion  is 
very  likely  to  occur,  if  the  glass  bulb  above  the  level  of  the  liquid  becomes 
too  hot.  "  Should  a  drop  of  the  liquid,  during  ebullition,  fall  on  that  part, 
the  whole  of  the  apparatus  is  shattered  to  pieces,  and  an  arsenical  flame 
several  feet  high  rises  up,  covering  everything  near  it  with  a  black  offensive 
layer  of  arsenic."  Of  the  cyanide  of  kakodyle  he  says,  that  "the  vapor 
diffused  in  the  smallest  quantity  through  the  atmosphere,  produces  a  sudden 
cessation  of  muscular  power  in  the  hands  and  feet,  giddiness  and  insensibility, 
which  end  in  total  unconsciousness  !" 


ORGANIC    COLORING    MATTERS.  $$9 


CHAPTER    LIV. 

ORGANIC  COLORINa  MATTERS.  DYEING. 

Under  this  head  a  variety  of  substances  are  included,  of  very  different 
character  and  composition.  Many  of  them  are  important  in  the  arts  :  they 
are  used  as  pigments,  and  extensively  employed  by  dyers  and  calico-printers. 
Others  are  of  so  fugitive  a  nature  as  not  to  admit  of  this  application,  and  are 
chiefly  known  as  giving  variety  and  beauty  to  flowers,  or  as  communicating 
to  vegetables  in  general,  those  infinitely  varied  shades  of  color  which  charac- 
terize this  division  of  the  organic  creation.  By  far  the  greater  number  of 
these  substances  are  educts  of  vegetable  origin,  or  products  of  the  decom- 
position of  vegetable  substances.  The  coloring-matters  derived  from  animal 
substances  are  comparatively  few. 

A  colored  compound  is  a  frequent  product  of  chemical  changes  in  colorless 
organic  compounds.  When  gallic  acid  is  dissolved  by  heat  in  strong  sul- 
phuric acid,  a  rich  crimson-colored  liquid  is  produced.  On  dissolving  essen- 
tial oil  of  bitter  almonds  in  the  same  acid,  a  ruby-red  liquid  is  produced, 
which  becomes  yellow  on  exposure  to  air.  Pyroxanthine  gives  with  sulphuric 
acid  in  the  cold,  splendid  purple  and  crimson  compounds,  which  gradually 
darken  by  exposure.  When  crystallized  cane-sugar  in  powder  is  mixed  with 
arsenic  acid  and  water,  so  as  to  form  a  thick  paste,  the  mixture  slowly 
acquires,  by  exposure  to  air  at  a  temperature  of  about  Y0°,  a  splendid 
crimson  color,  which  gradually  darkens.  When  arsenious  acid  is  employed 
no  colored  compound  results.  The  substitution  of  aniline  for  sugar,  and  the 
application  of  heat  to  the  mixture  of  aniline  and  arsenic  acid,  has  been 
recently  made  the  subject  of  various  patents  for  the  production  of  permanent 
purple  dyes.  The  action  of  sulphuric  acid  and  bichromate  of  potassa  on 
strychnia  and  aniline,  in  producing  blue,  purple,  and  crimson-colored  com- 
pounds, furnishes  other  instances  of  the  production  of  splendid  colors  from 
colorless  organic  substances.  A  small  quantity  of  a  solution  of  gallic  acid 
added  to  lime-water  produces  a  white  precipitate,  which  speedily  becomes 
blue,  purple,  and  ultimately  olive-green.  Bile  produces  with  sulphuric  acid 
and  sugar,  aided  by  heat,  a  splendid  purple  color,  and  with  nitric  acid  a  rich 
green  color.  In  most  of  these  cases,  it  may  be  proved  that  color  is  produced 
as  a  result  of  the  oxidation  of  the  organic  substance ;  and  in  reference  to 
many  of  the  coloring  matters  described  in  this  chapter,  it  will  be  found  that 
they  do  not  exist  ready  formed  in  the  living  plant,  but  are  products  of  the 
oxidation  of  certain  principles  contained  in  the  sap  or  vegetable  fil3re. 
Chemical  compounds  which  impart  oxygen,  e.  g.,  chromic  acid,  the  peroxides 
of  manganese  and  lead,  and  arsenic  acid,  produce  color ;  while  those  which 
have  reducing  properties,  such  as  nascent  hydrogen,- sulphuretted  hydrogen, 
alkaline  sulphides,  and  the  protoxides  of  manganese  and  iron,  render  the 
colored  compounds  temporarily  colorless.  Organic  colors  are  easily  destroyed 
by  exposure  to  light.  This,  which  is  called  fading,  may  be  due  to  the  effect 
of  nascent  oxygen  or  ozone.  That  nascent  oxygen  has  a  powerfully  destruc- 
tive influence,  is  seen  in  the  action  of  ozone,  and  of  chlorine.  Humid  chlo- 
rine completely  destroys  all  organic  colors.  Sulphurous  acid  also  bleaches 
them  either  by  removing  oxygen,  or  by  forming  with  the  coloring  matter, 


670  PRODUCTION    OF    COLORS 

colorless  compounds,  which  are  soluble  in  water,  and  admit  of  removal  by- 
washing.  Acids  and  alkalies  sometimes  restore  the  color  when  sulphurous 
acid  has  been  used,  but  not  when  chlorine  has  been  employed. 

Some  coloring  principles,  although  neutral  in  reaction,  appear  to  act  like 
acids  in  combining  with  bases.  Thus  alumina  and  the  oxides  of  tin  and 
iron,  form  insoluble  compounds  with  organic  colors,  and  at  the  same  time 
modify  the  color.  Hydrate  of  alumina  precipitates  most  organic  colors 
which  are  soluble  in  water,  rendering  the  liquid  colorless.  Charcoal  in 
powder  has  a  similar  effect :  it  removes  the  color  without  altering  it.  Ani- 
mal and  vegetable  fibres  also  remove  and  fix  these  colors  by  a  powerful 
attraction,  and  they  are  sometimes  employed  for  the  purpose  of  separating 
the  coloring  principle  in  a  pure  state  (see  Carthameine).  As  a  general  rale, 
wool  appears  to  have  the  strongest  attraction  for  coloring  substances  ;  silk 
comes  next  to  it,  then  cotton,  and  lastly  hemp  and  flax. 

The  art  of  dyeing  and  calico-printing  consists  in  the  application  of  these 
organic  colors  to  animal  or  vegetable  fibre,  such  as  silk,  wool,  linen,  or  cotton. 
It  is  based  on  simple  chemical  principles.  In  the  first  place,  the  articles 
require  to  be  thoroughly  cleansed  from  all  foreign  matters  and  colors  :  this 
is  effected  by  washing  and  bleaching.  The  simple  operation  of  dyeing  is 
generally  performed  upon  animal  fibre,  such  as  wool  and  silk;  whilst  the  more 
refined  operation  of  printing  in  patterns  and  devices  of  various  colors  is 
chiefly,  though  by  no  means  exclusively,  conducted  upon  cotton,  or,  as  it  is 
usually  termed,  calico.  Some  colors  are  of  such  a  nature  as  to  combine  with 
the  fibre  without  any  medium;  and  when  this  is  the  case,  they  constitute 
what  have  been  termed  substantive  colors.  Other  colors  require  the  inter- 
vention of  a  base  or  mordant^  and  they  are  then  called  adjective  colors.  The 
mordants  which  are  most  frequently  resorted  to  are  the  salts  of  alumina, 
iron,  and  tin.  Albumen,  as  well  as  the  alkaline  phosphates  and  arsenates, 
are  also  employed  as  mordants  in  calico-printing.  The  substance  to  be  dyed, 
is  first  impregnated  with  the  mordant,  and  then  passed  through  a  solution 
of  the  coloring  matter,  which  is  thus  fixed  in  the  fibre,  and  its  tint  is  often 
modified  or  exalted  by  the  operation.  A  considerable  portion  of  the  mordant 
is  retained  in  the  fibre  of  the  calico  or  cloth  which  is  dyed.  Ure  found  that 
100  parts  of  the  ashes  of  Turkey-red  calico  (dyed  by  an  alum  mordant) 
afforded  between  16  and  H  parts  of  alumina,  whereas  the  ashes  of  white  and 
washed  calico  afforded  only  a  trace  of  that  earth. 

Calico-printing,  which  is  a  more  refined  and  difficult  branch  of  the  art,  is 
a  species  of  topical  dyeing.  In  this  process  adjective  colors  are  almost 
always  employed.  The  mordants,  the  principal  of  which  are  acetate  of 
alumina  and  acetate  of  iron,  and  albumen,  are  first  applied  to  the  calico  by 
means  of  wooden  blocks  or  copperplates,  or  cylinders,  upon  which  the  requi- 
site patterns  are  engraved.  When  albumen  is  used  as  a  mordant,  this  is 
fixed  by  exposure  to  a  steam-heat.  The  stuff  is  then  passed  through  the 
coloring  bath,  and  afterwards  exposed  on  the  bleaching-ground,  or  washed. 
The  color  flies  from  those  parts  which  have  not  received  the  mordant,  and  is 
permanently  retained  on  those  parts  to  which  the  mordant  has  been  applied. 
A  variety  of  colors  is  produced  by  employing  various  mordants,  and  different 
coloring  materials,  and  by  using  them  in  various  states  of  dilution  and  com- 
bination. Instead  of  first  applying  the  mordant,  and  afterwards  the  color- 
ing material,  they  are  occasionally  both  printed  together,  but  in  these  cases 
particular  management  is  requisite  in  the  selection  of  the  substances  em- 
ployed, and  in  the  mode  of  their  application  ;  when  this  method  is  resorted 
to,  the  color  is  ofi^w  fixed  by  the  application  of  steam.  Thus  in  the  employ- 
ment of  albumen,  either  of  Qg^  or  blood,  or  of  lactarine  (the  curd  of  cheese), 
the  coloring-matter  is  at  once  mixed  with  the  organic  principle,  and  the 


PRODUCTION    OP    INDIGO,  gYl 

colored  compound  is  printed  in  a  pattern  on  the  cloth.  When  the  cloth  has 
been  subjected  to  the  steaming  process,  the  color  and  the  albumen  mixed 
with  it  are  rendered  insoluble,  and  remain  fixed  on  the  fibres  of  the  stuff. 
Cottons,  which  receive  dyes  with  more  difficulty  than  silk  or  wool,  are  thus 
effectually  dyed.  By  the  aid  of  albumen  or  lactarine,  insoluble  mineral 
colors,  such  as  ultramarine,  or  Scheele's  green,  may  be  imprinted  on  the 
finest  fabrics. 

We  shall  here  consider  the  principal  coloring  matters  which  are  employed 
in  chemistry  and  the  arts. 

Indigo. — Indigo,  as  it  occurs  in  commerce,  is  usually  in  the  form  of  cubi- 
cal pieces,  or  cakes,  friable,  and  more  or  less  brittle,  and  of  various  shades 
of  a  peculiar  deep  blue.  When  rubbed  with  a  hard  body,  it  acquires,  like 
Prussian  blue,  a  coppery-red  color,  but  always  furnishes  a  deep-blue  powder ; 
it  is  tasteless,  nearly  inodorous,  and  almost  insoluble  in  water,  alcohol,  and 
ether.  The  masses  of  indigo  have  a  dull  conchoidal  fracture,  and  the  finest 
samples  are  those  which  are  lightest  and  most  copper-colored.  The  plants 
resorted  to  as  a  source  of  indigo,  are  different  species  o{  Indigofera ;  it  is 
also  obtained  from  other  genera,  as  Nerium,  Isatu,  Marsdenia,  Polygonum^ 
and  Asclepias.  Indigo  appears  to  exist  in  the  juices  of  these  plants,  in  the 
form  of  a  colorless  soluble  compound  ;  and  it  is  generally  obtained  by  fer- 
menting the  bruised  plant,  during  which  ammonia  is  evolved,  and  a  yellow 
liquid  obtained.  This  liquid,  on  the  addition  of  lime-water,  and  exposure  to 
air,  deposits  the  blue  indigo  in  the  form  of  a  flocculent  precipitate.  Its  chief 
sources  are  India  and  South  America. 

Indigo-hlue.  Indigoiine  (CigH-OgN). — It  is  this  coloring  matter  which 
gives  the  commercial  value  to  indigo,  of  which  it  forms  about  50  per  cent. 
In  order  to  obtain  the  pure  coloring  principle,  the  indigo  of  commerce  is 
successively  treated  with  hydrochloric  acid,  weak  solution  of  potassa,  and  hot 
alcohol,  to  remove  any  foreign  substances.  It  is  then  thoroughly  mixed  with 
twice  its  weight  of  freshly-slaked  lime,  and  the  mixture  put  into  a  bottle 
capable  of  holding  150  times  the  quantity  of  indigo  operated  on  ;  the  bottle 
is  then  filled  with  boiling-hot  water,  and  4  parts  of  crystallized  protosulphate 
of  iron  added  for  every  3  of  indigo;  it  is  then  securely  stopped  so  as  to  be 
air-tight,  and  having  been  well  shaken,  is  set  aside  for  several  hours.  In  this 
way  the  indigo-blue,  which  is  insoluble,  is  converted  into  indigo-white,  which 
is  soluble  in  the  solution  of  lime,  producing  a  yellow  liquid.  This  yellow 
liquor  is  then  poured  off,  mixed  with  dilute  hydrochloric  acid,  and  left  for  a 
long  time  exposed  to  air ;  the  acid  retains  the  lime  and  other  substances  in 
solution,  while  the  indigo-blue  is  deposited,  and  may  be  freed  from  hydro- 
chloric acid  and  chloride  of  calcium,  by  washing  with  water. 

Indigotine  is  volatile,  without  decomposition,  at  a  low  temperature.  If 
powdered  indigo  is  carefully  heated  in  a  tube  through  which  a  current  of 
hydrogen  is  passing,  the  indigotine  sublimes  in  a  violet-colored  vapor  resem-. 
bling  that  of  iodine,  and  is  deposited  in  purple  crystals  in  the  form  of  fine 
needles.  If  overheated,  or  heated  in  air,  it  is  decomposed.  The  sublima- 
tion takes  place  readily  at  about  550°  :  the  melting-point  of  this  substance, 
its  point  of  volatilization,  and  that  at  which  it  is  decomposed,  are  very  near 
to  each  other.  The  sp.  gr.  of  sublimed  indigo-blue  is  1*35.  When  the 
crystals  are  heated  in  an  open  vessel,  they  sublime  without  residue,  in  a 
reddish-violet  vapor ;  in  close  vessels,  as  the  heat  advances,  the  vapor 
acquires  a  scarlet  tinge,  and  then  becomes  orange-colored;  a  small  quantity 
of  aniline  is  formed,  and  charcoal  is  deposited. 

Heated  upon  platinum-foil, indigo-blue  gives  a  purple  smoke,  and  if  the 
heat  be  rapidly  augmented  it  fuses,  boils,  and  burns  with  a  bright  flame, 


6t2  CHEMICAL    PROPERTIES    OF    INDIGO. 

giving  off  much  smoke,  and  leaving  a  carbonaceous  residue,  which  may  be 
entirely  consumed.  Indigo-blue  is  insipid  and  inodorous,  and  neither  basic 
nor  acid.  It  is  insoluble  in  water,  alcohol,  ether,  and  the  oils.  Dilute  acids 
and  alkaline  solutions  have  no  action  upon  it. 

Indigo-white.  Indigogene  (CigHgOgN). — If  the  yellow  solution,  obtained 
by  the  action  of  lime  and  protosulphate  of  iron  upon  indigo  and  water,  is 
decomposed  by  an  acid  under  the  cautious  exclusion  of  oxygen,  a  white  pre- 
cipitate is  formed :  this  is  indigo-white.  It  may  be  obtained  by  siphoning 
the  yellow  liquor  into  a  stopper  bottle  previously  filled  with  hydrogen  or 
carbonic  acid  gas,  and  containing  some  acetic  or  dilute  hydrochloric  acid, 
the  siphon  itself  being  previously  filled  with  water  deprived  of  air.  Under 
these  circumstances  a  white,  flocculent,  and  often  somewhat  crystalline  pre- 
cipitate falls:  it  should  be  most  carefully  excluded  from  all  contact  with  air, 
and  allowed  to  subside ;  the  supernatant  liquor  must  then  be  decanted,  the 
precipitate  collected  upon  a  filter  in  an  atmosphere  of  hydrogen  or  of  carbonic 
acid,  washed  with  water  freed  from  air,  pressed  in  folds  of  bibulous  paper, 
and  dried  in  vacuo. 

Indigo-white,  when  dried,  has  always  a  greenish  or  bluish  tint,  though  it 
probably  would  be  perfectly  white,  if  quite  pure.  It  has  a  silky  fracture,  is 
destitute  of  taste  and  odor,  and  shows  no  acid  reaction.  It  is  not  volatile, 
and  when  heated  in  vacuo  it  gives  off  a  little  water,  while  indigo-blue  sub- 
limes, and  carbon  remains  :  no  permanent  gas  is  evolved.  It  is  insoluble  in 
pure  water,  and  in  dilute  acids.  It  forms  a  yellow  solution  in  alcohol  and 
in  ether,  and  these  solutions,  when  exposed  to  air,  gradually  deposit  indigo- 
blue.  When  moist,  it  speedily  passes  into  indigo-blue  under  the  influence 
of  air;  and  even  when  dry,  it  slowly  acquires  a  blue  color  :  this  change  goes 
on  even  in  vacuo,  in  consequence  probably  of  the  air  retained  in  the  pores 
of  the  substance  being  sufficient  to  communicate  to  it  a  blue  tinge.  When 
it  is  gradually  heated  in  air,  the  whole  mass  suddenly  acquires  a  dark-purple 
color,  being  converted  into  indigo-blue. 

Although  a  neutral  principle,  indigo-white  acts  in  the  manner  of  an  acid 
in  respect  to  bases.  It  forms  yellow  solutions  with  the  alkalies  and  alkaline 
earths,  which,  when  exposed  to  air,  become  immediately  covered  with  an 
iridescent  copper-colored  film  of  indigo-blue,  whilst  the  liquid  underneath 
acquires  at  first  a  peculiar  reddish-green  tint,  and  then  gradually  passes  into 
blue.  Hence  the  liquid  containing  it,  is  an  admirable  test  for  free  oxygen, 
either  as  a  gas,  or  as  it  is  contained  in  water. 

Indigo-white  was  originally  regarded  as  deoxidized  indigo,  or  as  a  lower 
oxide  of  the  base  of  indigo-blue;  the  processes,  therefore,  by  which  indigo- 
white  is  obtained,  were  considered  as  cases  of  deoxidation,  and  it  was  sup- 
posed that  simple  oxidation  was  the  cause  of  the  change  of  the  white  into 
the  blue  oxide.  But  Dumas  has  shown  that  in  passing  into  white  indigo, 
blue  indigo  acquires  an  additional  atom  of  hydrogen,  the  proportion  of 
oxygen  remaining  the  same  in  both. 

Sulphindigotic  Acid;  Sulphindylic  Acid  ([CigH^OgN-f  SgOJ  +  HO). — 
When  1  part  of  indigo-blue  is  digested  for  three  days  with  15  parts  of  oil 
of  vitriol,  in  a  stoppered  bottle,  at  a  temperature  between  120^  and  140°, 
a  deep  blue  solution  is  obtained,  without  any  evolution  of  sulphurous  acid. 
This  solution  mixes  perfectly  with  water,  and  if  the  preceding  proportions 
have  been  adhered  to,  there  is  no  sediment ;  it  is  a  solution  of  sulphindigotic 
acid.  The  Nordhausen  or  Saxon  sulphuric  acid  forms  a  better  solvent  than 
common  oil  of  vitriol.  When  evaporated  to  dryness,  the  acid  remains  in 
the  form  of  a  dark  blue  substance,  which  is  deliquescent,  and  has  a  peculiar 
odor;  it  forms  a  dark  blue  solution  with  water  and  alcohol,  of  a  sour  and 
somewhat  astringent  taste.     If  woollen  cloth  be  immersed  in  the  diluted 


SULPHOPURPURIC    ACID.      LICHEN-BLUES.  673 

blue  liquor,  it  becomes  effectually  dyed,  and  the  liquid  is  entirely  deprived 
of  color.  By  digesting  the  blue  wool  in  a  solution  of  carbonate  of  ammo- 
nia, a  solution  of  sulphindigotate  of  ammonia  is  obtained,  with  which  several 
other  salts  of  the  blue  acid  may  be  prepared. 

When  zinc  or  iron  is  put  into  the  aqueous  solution  of  this  acid,  it  loses 
its  color,  but  regains  it  by  long  exposure  to  air.  Sulphuretted  hydrogen 
does  not  affect  it  at  common  temperatures;  but  when  heated  to  120°,  sulphur 
is  thrown  down,  and  the  blue  color  disappears.  Protochloride  of  tin,  and 
all  those  substances  which  convert  indigo-blue  into  indigo-white,  act  simi- 
larly upon  this  acid.  When  protosulphate  of  iron  is  dissolved  in  a  solution 
of  a  neutral  sulphindigotate,  the  color  is  not  destroyed,  nor  is  it  affected 
when  part  of  the  oxide  of  iron  is  thrown  down  by  an  alkali,  but  the  moment 
that  the  whole  of  the  oxide  is  precipitated  and  an  excess  of  alkali  is  preserjt, 
decoloration  ensues ;  on  again  adding  an  excess  of  acid,  the  blue  color 
returns. 

Sulphopurpuric  Acid  ([Cg^H.oO^N.-f 2803]  + HO). —When  1  part  of 
indigo  is  triturated  with  7  or  8  parts  of  oil  of  vitriol  (or  better,  with  fuming 
sulphuric  acid),  the  mixture,  upon  the  addition  of  water,  deposits  sulpho- 
purpuric acid  in  the  form  of  a  purple  powder,  which  must  be  immediately 
washed  upon  a  strainer  with  water  acidulated  by  hydrochloric  acid,  until  all 
traces  of  free  sulphuric  acid  are  removed,  and  then  carefully  dried  in  vacuo. 
This  acid  is  soluble  in  pure  water  and  in  alcohol.  By  digestion  in  oil  of 
vitriol,  it  passes  into  the  sulphindigotic  acid.  It  saturates  only  1  atom  of 
base. 

Isatine  (CigHgO^N). — This  compound  is  the  result  of  the  oxidation  of 
indigo  by  chromic  or  nitric  acid.  A  diluted  aqueous  solution  of  chromic 
acid  is  gradually  added  to  pulverized  indigo ;  the  mixture  is  heated  nearly, 
but  not  quite,  to  its  boiling-point,  and  a  brown  solution  is  obtained.  The 
chromic  acid  should  only  be  of  such  strength  as  freely  to  dissolve  the  indigo  ; 
if  it  is  too  strong,  carbonic  acid  is  evolved,  oxide  of  chromium  is  precipi- 
tated, and  isatine  is  not  formed.  The  brown  solution  should  be  filtered 
whilst  hot,  and  the  isatine  crystallizes  as  the  liquor  cools. 

Isatine  forms  brilliant  reddish-brown  prismatic  crystals,  inodorous, 
sparingly  soluble  in  cold,  but  more  abundantly  in  hot  water,  and  readily 
soluble  in  alcohol,  but  less  so  in  ether.  The  alcoholic  solution  communicates 
a  peculiarly  unpleasant  and  permanent  odor  to  the  cuticle.  When  isatine 
is  heated  in  a  tube,  a  portion  of  it  sublimes,  but  the  greater  part  is  decom- 
posed, leaving  carbon,  which  is  with  difficulty  combustible.  Heated  in  air 
it  fuses,  exhales  a  suffocating  vapor,  burns  with  a  brilliant  flame,  and  leaves 
a  carbonaceous  residue.  By  the  action  of  chlorine  and  bromine,  it  forms 
chlorisatine,  hichlorisatine,  bromisatine,  and  hibromisatine.  It  dissolves  in 
solutions  of  ammonia,  potassa,  sulphuretted  hydrogen,  and  sulphide  of  amnao- 
nium,  producing  peculiar  compounds.  Isatine  may  be  regarded  as  indigo 
-f  2  atoms  of  oxygen  ;  or  CeH.OgN+Oa.  Isatinic  add  (CjeHeOgN-f-HO) 
is  procured  by  the  action  of  a  solution  of  potassa  upon  isatine. 

Isatyde  (CigHgO.N^  is  a  white  crystalline  compound  which  may  be  obtained 
by  adding  a  little  sulphide  of  ammonium  to  a  hot  alcoholic  solution  of  isatine 
*n  a  close  vessel.  *  •  j- 

Aniline  and  Picric  acid  are  also  products  of  the  decomposition  of  indig#- 
by  potassa  and  nitric  acid.     These  compounds  are  elsewhere  described. 

Lichen-blues.     Archil  ;  Litmus.— These  substances  are  prepared  from 

various  lichens,  amongst  which  Roccella  tinctoria  and  corallina,  Lecanora 

tartarea,  Variolaria  lactea,  and  dealbata  have  been  especially  resorted  to. 

The  lichens  are  principally  collected  from  rocks  adjoining  the  sea :  tney  grow 

43 


674  ORCINE    ANB    ITS    PROPERTIES. 

abundantly  on  the  Canary  and  Cape  Yerd  Islands ;  and  there  is  a  general 
similarity  in  the  mode  of  treatinpr  them  for  the  manufacture  of  the  above 
mentioned  colors.  They  are  cleaned,  and  ground  into  a  pulp  with  water; 
ammoniacal  liquids,  derived  chiefly  from  gas-works,  or  occasionally  from 
urine,  are  from  time  to  time  added,  and  the  mass  is  frequently  stirred  so  as 
to  expose  it  as  much  as  possible  to  the  action  of  air.  Peculiar  substances 
existing  in  the  lichens  are,  during  this  process,  oxidized  by  the  joint  action 
of  air  and  water,  in  the  presence  of  ammonia,  thereby  generating  the  coloring 
matter.  When  the  color  is  extracted,  the  mass  is  pressed,  and  chalk,  plaster 
of  Paris,  or  alumina,  is  added,  so  as  to  form  it  into  a  consistent  paste.  In 
this  state,  it  is  of  a  pnrple  or  violet-red  tint,  and  constitutes  the  archil  of 
commerce,  frequently  called  Cudbear  (from  Cuthbert,  one  of  the  manufac- 
turers of  the  article  at  Leith)  ;  it  is  the  orseille  and  persio  of  the  French 
and  Germans.  The  other  variety,  called  litmus,  or,  in  France  and  Germany, 
tournesol  and  lacmus,  is  generally  made  up  into  small  cubes,  and  has  a  fine 
violet  color.  The  lichens  which  are  proper  for  the  manufacture  of  these 
colors  may  be  recognized  by  moistening  them  with  a  little  solution  of 
ammonia,  and  setting  the  mass  aside  in  a  corked  vial  ;  if  of  the  proper 
kind,  the  lichen  and  the  liquid  will  acquire  a  purple  tint  in  the  course  of  a 
few  days. 

The  following  substances  have  been  discovered  in  these  coloring  princi- 
ples : — 

Lecanorine  ;  Lecanoric  or  OrselHnic  Acid  (CigHgO^-l-HO). — This  com- 
pound exists  in  different  species  of  lecanora.  It  is  obtained  by  exhausting 
the  lichen  with  ether,  which  is  then  distilled  oflf,  and  leaves  a  residue  contain- 
ing lecanoric  acid,  mixed  with  resinous  and  fatty  matter,  and  some  substances 
soluble  in  water.  Lecanoric  acid  forms  inodorous  and  tasteless  stellated 
groups  of  silky  acicular  crystals,  insoluble  in  water,  but  soluble  in  hot  alcohol 
and  ether.  Subjected  to  dry  distillation,  it  is  resolved  into  orcine  and  car- 
bonic acid  ;  and  it  undergoes  the  same  change  when  moistened  with  sulphuric 
acid  and  left  in  a  damp  place ;  or  when  boiled  in  a  solution  of  ammonia  or 
potassa. 

1  atom  of  Ipoanoric  acid   C    H  0     —     ^  ^  ^^^^  ^^  °^^^"^      *       *  ^'e^A 
1  atom  Of  lecanoric  acia,  I., gUgUg   —    ^^  u      carbonic  acid  Cg      O4 


Orcine  (C,eHgO^-|-HO). — This  substance  is  one  of  the  principal  sources 
of  the  coloring-matter  derived  from  lichens.  It  is  found  ready  formed  in 
Lichen  roccella,  parellus.  deustus,  tartarius,  dealbatus,  etc.,  and  is  produced 
by  various  processes  from  lecanorine.  It  is  obtained  by  exhausting  the 
dried  and  pulverized  lichen  in  boiling  alcohol,  and  filtering  while  hot.  The 
alcoholic  extract  dissolved  in  water,  deposits  long,  brown,  brittle  needles, 
which  may  be  redissolved  in  water,  treated  with  animal  charcoal,  filtered, 
and  again  crystallized.  Orcine  crystallizes  in  a  flat  four-sided  prism,  with 
dihedral  summits  ;  it  has  a  sweet  but  somewhat  repulsive  taste,  and  it  is 
perfectly  neutral.  When  dried  at  212°,  it  loses  a  portion  of  its  water  of 
crystallization;  at  about  550°,  it  rises  in  vapor,  may  be  distilled,  and  con-^ 
densed  in  crystals,  which  contain  1  atom  of  water.  It  is  soluble  in  watef 
find  in  alcohol. 

If  orcine  is  exposed  to  air,  it  gradually  reddens,  especially  when  the  sun 
occasionally  shines  upon  it.  W^hen  subjected  to  the  action  of  chlorine,  it 
heats,  fuses,  and  hydrochloric  acid  is  produced.  Nitric  acid  acts  upon  orcine 
with  the  evolution  of  nitrous  gas,  and  a  red  solution  is  formed,  which  deposits 
a  resin-like  substance.  The  fixed  alkalies  convert  it  into  a  brown  substance. 
Gaseous  ammonia  is  absorbed  by  orcine,  and  on  exposure  to  air  it  again 


LITMUS-PAPER.      MADDER.      GARANCINE.      ALIZARINE.  675 

escapes  ;  but  when  water  is  present,  the  oxygen  of  the  atmosphere  is 
absorbed,  and  a  colored  azotized  body  is  the  result,  to  which  the  name  of 
orceine  or  orceic  acid  has  been  pjiven. 

Orceine;  Orceic  Acid  (CmHj,0„N,  +  HO). — This  substance  may  be  ob- 
tained by  placing  pulverized  orcine  in  a  capsule,  together  with  a  saucer  of 
solution  of  ammonia,  under  a  bell-glass;  the  orcine  becomes  brown,  but  on 
exposure  to  air  the  excess  of  ammonia  escapes,  and  on  adding  a  little  water, 
and  a  few  drops  of  ammonia,  a  purple  liquid  is  obtained,  from  which  acetic 
acid  throws  down  orceine,  or,  as  Berzelius  terms  it,  orceic  acid.  Sul- 
phuretted hydrogen  decolors  the  purple  liquid,  not  by  deoxidation,  but  by 
entering  into  combination  with  orceic  acid,  for  the  color  reappears  on  expo- 
sure to  air,  on  saturating  the  sulphuretted  hydrogen  by  an  alkali.  A  solu- 
tion of  litmus,  when  kept  in  a  close-stopped  vessel  for  some  time,  acquires  a 
dirty-brown  color,  and  smells  offensively.  When  exposed  to  air,  it  rapidly 
assumes  a  purple  and  blue  color.  In  the  preparation  of  blues  from  lichens, 
orceic  acid  is  produced  under  the  influence  of  ammonia.  It  is  not  itself  a 
permanent  dye-stuff,  but  is  a  valuable  auxiliary  in  the  production  of  other 
blues  and  purples. 

Erythrine  ;  Erythryline  ;  Erythric  Acid{Q^^fi^^. — These  are  probably 
identical  with,  or,  at  all  events,  closely  related  to,  lecanorine. 

Litmus-paper. — The  lichen  blues  are  much  used  for  the  preparation  of 
litmus-paper.  In  order  to  prepare  this  paper  for  chemical  purposes,  an  ounce 
of  litmus,  finely  powdered,  should  be  infused  in  half  a  pint  of  boiling  water 
in  a  covered  vessel  for  an  hour.  The  clear  liquor  should  then  be  poured 
off,  and  fresh  quantities  of  hot  water  added  until  the  color  is  exhausted. 
White,  unsized  paper,  containing  but  little  mineral  matter,  cut  into  conve- 
nient lengths,  should  then  be  dipped  into  the  infusion  and  allowed  to  dry. 
It  should  have  a  full  blue  color.  Paper  thus  prepared,  if  not  tinted  of  too 
deep  a  color,  forms  the  best  tests  for  acids,  either  gaseous  or  liquid.  It  is 
sooner  or  later  reddened.  Red  litmus-paper  forms  a  very  delicate  test  for 
alkalies,  as  the  blue  color  is  restored  by  alkaline  liquids.  In  order  to  pre- 
pare it,  the  blue  litmus-paper  should  be  exposed  in  a  jar  to  the  diluted  vapor 
of  acetic  acid  or  to  a  damp  atmosphere.  In  order  to  act  with  delicacy  as  a 
test  for  an  alkali,  the  reddish  tint  thus  artificially  imparted  to  it,  should  be 
barely  perceptible.  These  test-papers  should  be  cut  in  strips  of  three  inches 
by  half  an  inch,  and  kept  in  well  stopped  bottles  in  a  dark  closet.  Light 
destroys  the  color,  and  exposure  to  air  reddens  the  paper  by  the  action  of 
carbonic  acid  and  other  acid  vapors  diffused  through  the  atmosphere.  A 
paper  prepared  from  an  infusion  of  the  best  cudbear,  without  the  addition 
of  either  alkali  or  acid,  has  a  purple  color,  and  is  affected  both  by  acids  and 
alkalies  ;  it  is  convenient  in  alkalimetry,  being  already  too  red  to  be  affected 
by  carbonic  acid,  while  it  is  distinctly  reddened  by  mineral  acids. 

Madder;  Garancine;  Alizarine;  Alizari.^The  plant  which  furnishes  this 
valuable  dye-stuff  {Eubia  tinctorum)  is  common  in  the  South  of  Europe  and 
in  many  parts  of  the  Levant,  where  it  is  known  under  the  name  of  alizan  : 
it  is  also  largely  cultivated  in  Holland.  It  has  a  long  spreading  fibrous  root, 
which  is  the  part  used  in  dyeing.  In  the  living  plant,  the  sap  is  yellowish 
colored :  and  contains  no  red  coloring  principle.  This  appears  to  be  de- 
yeloped  in  the  woody  fibre,  during  the  act  of  drying,  and  by  exposure  to  air. 
Madder-root  contains  three  coloring  principles,  named  respectively  xanthine, 
alizarine,  and  purpurine.  By  digesting  the  root  repeatedly  in  cold  water, 
the  xanthine,  or  madder-yellow,  is  removed,  as  this  principle  is  very  soluble 
in  water.  When  the  residue  is  treated  with  half  its  weight  of  sulphuric  acid 
at  21 2°,  the  woody  fibre  is  in  great  part  destroyed,  and  may  be  removed  by 


6Y6  CARTHAMINE. 

further  dij^estion  with  water.  A  brown  pulverulent  residue  is  left,  which  is 
known  under  the  name  of  garancine.  This  contains  a  red  coloring-matter, 
Alizarine  (CaoHgOg),  which  may  be  obtained  in  orange-colored  crystals  by 
digesting  the  garancine  in  boiling  alcohol,  or  by  subjecting  it  to  superheated 
steam.  It  is  scarcely  soluble  in  water,  hot  or  cold,  but  is  readily  dissolved 
by  alcohol  and  alkaline  solutions.  The  latter  change  the  red  to  a  violet 
color.  It  gives  a  bluish  precipitate  with  solutions  of  lime  and  baryta,  thus 
acting  like  a  weak  acid.  Sulphuric  acid  dissolves  it,  forming  a  brown  liquid, 
but  it  is  again  precipitated  unchanged  on  dilution  with  water. 

Purpurine  (CjgHgOe),  or  madder-purple,  is  a  red  coloring  principle,  which 
may  be  procured  by  digesting  the  washed  root  in  a  boiling  saturated  solution 
of  alum,  in  which  alizarine  is  insoluble.  On  adding  sulphuric  acid  to  the 
decoction,  the  purpurine  is  slowly  deposited.  It  may  be  obtained  as  a  deep 
red  powder,  by  repeated  digestion  in  alcohol  and  ether.  It  is  not  dissolved 
by  cold  water,  but  it  is  soluble  in  hot  water.  It  is  also  soluble  in  alcohol 
and  ether.  When  a  solution  of  carbonate  of  soda  is  added  to  a  decoction  of 
madder-root  in  alum,  there  is  an  abundant  precipitate  of  the  red  coloring 
matter  with  alumina,  constituting  what  is  called  madder-lake. 

Carthamine.  Carthameine. — This  is  the  coloring  principle  of  Safflower, 
the  petals  of  the  Carthamus  tinctorius,  or  Bastard  saffron.  It  is  cultivated 
in  Spain,  and  in  many  parts  of  the  Levant,  whence  it  is  chiefly  imported ; 
but  on  account  of  its  price  it  is  seldom  used,  except  to  give  the  finishing  hue 
to  some  silks,  and  in  the  preparation  of  the  article  called  rouge.  Safflower 
contains  a  red  coloring-matter  which  is  insoluble  in  water,  and  a  yellow 
soluble  substance.  The  former  has  been  distinguished  as  carthameine,  and 
appears  to  be  derived  from  the  oxidation  of  a  peculiar  principle  existing  in 
the  petals,  which  has  been  called  carthamine. 

Carthamine  (C26Hg05+2HO)  is  obtained  from  the  flowers,  after  all  soluble 
matters  have  been  extracted  by  water,  by  digesting  them  in  a  weak  solution 
of  carbonate  of  soda.  It  crystallizes  in  small  white  prismatic  needles  of  a 
bitterish  taste,  not  very  soluble  in  water,  but  more  soluble  in  alcohol ;  it  is 
not  volatile,  but  fuses  when  heated,  exhales  a  pungent  odor,  and  burns  away 
without  residue.  When  exposed  to  the  air,  it  gradually  acquires  a  yellow 
color.  When  an  alkaline  solution  of  carthamine  is  left  in  contact  with 
oxygen,  it  becomes  first  yellow,  and  then  red,  and  on  saturating  this  red 
liquor  with  citric  acid,  red  carthameine  is  thrown  down.  W^hen  air  is  ex- 
cluded, the  alkaline  solution  remains  colorless. 

Carthameine.  Carthamic  Acid  (CgeHgO^). — This  is  the  product  of  the 
oxidation  of  carthamine,  under  the  influence  of  alkaline  bases :  it  exists  in 
the  safflower,  from  which  it  may  be  extracted  by  digesting  it,  after  the  yellow 
matter  has  been  removed  by  water,  in  a  solution  of  carbonate  of  soda,  and 
then  precipitated  by  citric  acid.  It  forms  a  dark-red  powder,  insoluble  in 
water  and  in  acids,  and  sparingly  soluble  in  alcohol,  to  which  it  communi- 
cates a  fine  red  color ;  it  is  also  sparingly  soluble  in  ether.  It  is  not  volatile, 
but  is  decomposed  by  dry  distillation.  It  forms  salts  from  the  alkalies,  from 
which  it  is  thrown  down  by  organic  acids,  of  a  bright  rose-red  color. 

The  afl&nity  of  carthameine  for  cotton  and  silk  is  such,  that  when  it  is 
recently  precipitated,  these  substances  immediately  combine  with  it,  become 
at  first  rose-colored,  and  afterwards  of  a  fine  red,  so  that  they  may  be  thus 
dyed  without  the  intervention  of  a  mordant.  The  stuffs  so  dyed  are  rendered 
yellow  by  alkalies,  and  the  color  is,  to  a  certain  extent,  restored  by  acids. 
Carthameine  is  never  used  in  dyeing  wool.  When  it  is  precipitated  from 
concentrated  solutions,  it  furnishes  a  liquid  paint,  which,  evaporated  upon 
saucers,  leaves  a  residue  of  a  somewhat  greenish  metallic  lustre,  used  as  a 


BRAZILINE.      SANTALINE.      ANCHUSINE.  677 

pink  dye-stuff,  and  which,  mixed  with  finely-powdered  talc,  and  dried,  con- 
stitutes common  rouge. 

HiEMATOXYLiNE.  Hcemateine. — These  substances  are  extracted  from  log- 
wood, a  dye-stuff  of  considerable  importance :  it  is  the  heartwood  of  the 
Hcematoxylon  Campechianmn,  and  is  imported  from  Campeachy,  Honduras, 
and  Jamaica,  in  hard  and  dense  logs,  about  three  feet  long,  and  of  a  dark- 
red  or  purple  color.  In  the  dye-house  it  is  used  for  the  production  of  certain 
reds  and  blues,  but  its  chief  consumption  is  for  blacks,  which  are  obtained  of 
various  intensities,  by  means  of  iron  and  alum  bases. 

EcematoxyUne  (CigHyOg.HO),  which  has  also  been  called  hcematine,  is  pro- 
cured by  digesting  the  aqueous  extract  of  the  wood  in  alcohol.  The  alcoholic 
tincture,  when  submitted  to  spontaneous  evaporation,  deposits  crystals  of  this 
substance.  An  aqueous  solution  of  these  crystals  does  not  become  colored 
by  exposure  to  air,  but  the  addition  of  a  few  drops  of  ammonia  causes  the 
liquid  to  assume  an  intense-red  color.  By  this  reaction  the  hsematoxyline  is 
converted  into  hcemateine  (C^gHgOg),  which  may  be  procured  in  crystals  of  a 
purple-black  color  with  a  metallic  lustre.  The  crystals  dissolve  in  water, 
giving  to  the  liquid,  when  concentrated,  a  deep  purple  tint.  This  compound 
differs  from  ha^matoxyline  in  containing  one  atom  less  of  hydrogen. 

Braziline  (CggH^^Oj^)  is  the  red-coloring  principle  of  Brazil-wood.  It 
may  be  procured  in  small  prismatic  crystals,  which  are  soluble  in  water, 
alcohol,  and  ether.  A  decoction  of  the  wood  is  of  a  reddish-brown  color ; 
it  acquires  a  rich  purple  hue  by  the  addition  of  alkalies.  The  coloring  prin- 
ciple, Brazilme,  when  treated  with  ammonia  and  exposed  to  air,  is  converted 
into  a  new  compound,  brazileine,  which  is  of  a  deep  purple  color.  An 
alcoholic  solution  of  braziline  is  a  delicate  test  for  the  presence  of  alkalies ; 
and  paper  which  has  been  dipped  in  a  decoction  of  Brazil-wood  and  dried, 
is  sometimes  employed  for  this  purpose.  The  red  color  given  by  the  Brazil- 
wood is  very  fugitive. 

Brazil-wood  is  distinguished  from  logwood  by  its  paler  hue,  and  by  the 
precipitates  which  its  infusion  forms  with  acetate  of  lead,  protochloride  of 
tin,  and  lime-water :  these  are  crimson,  instead  of  being  violet-colored  as 
with  logwood.  The  infusions  of  both  woods  are  rendered  yellow  by  a  drop 
of  sulphuric  or  hydrochloric  acid.  Red  ink  is  usually  made  by  boiling  about 
two  ounces  of  Brazil-wood  in  a  pint  of  water  for  a  quarter  of  an  hour,  and 
adding  a  little  gum  and  alum. 

Santalinb.  ^awto/eme.— Red  Sanders  is  the  name  given  in  this  country 
to  the  wood  of  the  Pterocarpus  santalinus,  a  large  tree  which  grows  upon  the 
Coromandel  coast,  and  in  other  parts  of  India,  especially  Ceylon.  The 
coloring  principle  of  this  wood  is  Santaline,  a  white  crystalline  powder, 
which  speedily  reddens  on  exposure  to  air.  It  is  instantly  reddened  by 
alkalies,  and  furnishes  red  solutions  with  the  greater  number  of  the  dilute 
acids.  It  dissolves  in  water,  alcohol,  and  ether,  and  when  its  aqueous 
solution  is  long  boiled  under  exposure  to  air,  it  is  converted  into  santa^ne, 
which  is  a  dark  red  crystalline  substance.  Its  probable  formula  is  L.^hi^U^, 
but  the  composition  of  this  substance  and  of  santaline  has  not  been  accurately 
determined. 

ANCHUSINE.  Anchusic  Acid.— These  terras  have  been  applied  to  the 
coloring  matter  of  the  root  of  Alkanet  {Anchusa  tinctoria),  a  species  olbugtoss, 
which  is  a  native  of  the  warmer  parts  of  Europe,  and  is  cultivated  in  our 
gardens.     Large  quantities  are  raised  in  Germany  and  France.     Anchusme 


678  COCHINEAL.      GUANO-COLORS. 

(CjyHjoOJ  has  the  characters  of  a  resin  ;  it  is  of  a  dark  red  color  and  of  a 
resinous  fracture,  softened  by  heat,  insohible  in  water,  soluble  in  alcohol,  and 
very  soluble  in  ether  and  in  fat  and  volatile  oils,  to  all  which  it  communicates 
a  bright  red  color. 

Lac — This  is  a  resinoid  substance,  the  production  of  which  appears  to 
depend  upon  the  puncture  of  a  small  insect  (the  Coccus  ficus),  made  for  the 
purpose  of  depositing  its  ova,  upon  the  branches  of  several  plants,  especially 
the  Ficus  religiosa  and  Indica.  The  coloring  matter  of  lac  is  prepared  in 
India,  and  is  extensively  used  as  a  scarlet  dye-stuff,  for  the  production  of 
which  it  is  a  most  efficient  substitute  for  cochineal.  Two  forms  of  it  are  im- 
ported, called  lac-lake  and  lac-dye.  These  substances  contain  about  50  per 
cent,  of  the  red  coloring  matter,  mixed  with  more  or  less  of  the  resin,  and 
with  earthy  matters,  said  to  consist  chiefly  of  chalk,  gypsum,  and  sand. 

CocHiNEAL-RED.  Carmine. — The  substance  known  in  commerce  as  cochi- 
neal^ consists  of  the  dried  female  insects  of  a  species  of  coccus.  It  is  imported 
from  Mexico  and  other  countries.  The  insects,  when  powdered,  yield  a  deep 
reddish-black  substance,  which,  when  boiled  in  water,  forms  a  dark-red 
solution  that  speedily  undergoes  decomposition.  If  to  the  fresh-filtered 
liquid  a  solution  of  alum  or  acid  tartrate  of  potassa  is  added,  a  precipitate 
is  slowly  formed,  which  consists  of  the  coloring  principle  of  the  insect,  united 
to  some  animal  matter.  This  is  commercial  carmine.  In  general  the  pigment 
is  prepared  by  boiling  cochineal  in  a  weak  solution  of  carbonate  of  potassa 
or  soda,  and  adding  to  the  filtered  liquid,  a  solution  of  alum  and  cream  of 
tartar.  The  coloring  principle  is  then  slowly  precipitated  with  alumina, 
forming  carmine-lake.  The  precipitation  is  sometimes  accelerated  by  the 
use  of  gelatine  or  albumen.  The  purest  form  of  the  coloring  principle  is 
obtained  by  the  following  process  :  The  powdered  insects  are  boiled  in 
ether,  to  separate  fatty  matter.  They  are  then  boiled  in  alcohol,  until  this 
liquid  is  saturated  with  color,  and  from  the  alcoholic  decoction,  the  carmine 
is  deposited  on  cooling.  This  principle  is  soluble  in  water,  forming  a  rich 
red  solution,  which  is  heightened  by  acids,  and  changed  to  a  deep  red  crimson 
by  alkalies.  It  is  also  soluble  in  alcohol,  but  not  in  ether.  A  variety  of 
carmine  now  prepared  is  scarcely  dissolved  by  water ;  but  when  a  few  drops 
of  ammonia  are  added,  it  forms  a  splendid  red  solution  with  a  slight  crimson 
tint.  Its  composition  has  not  been  accurately  determined.  A  substance 
procured  from  cochineal  by  Pelletier,  by  a  process  similar  to  that  which  has 
been  above  described,  is  known  under  the  name  of  Carmeine  or  Cocdnelline, 
and  its  composition  is  represented  as  CgaHggOjjoN.  Carminic  acid,  which  is 
obtained  by  precipitating  an  aqueous  decoction  of  cochineal  by  acetate  of 
lead,  and  decomposing  the  washed  precipitate  by  sulphuretted  hydrogen,  has 
the  composition  of  CggHj^Oig. 

GuANO-coLORS.  Murexlde  (from  Murex,  a  shell-fish,  the  supposed  source 
of  Tyrian  purple.) — This  is  commonly  known  as  the  purpurate  of  ammonia 
of  Prout :  it  is  an  animal-red  of  a  rich  purple  shade.  It  is  procured  by  the 
reaction  of  nitric  acid  on  uric  acid,  and  has  been  lately  largely  manufactured 
from  guano  as  a  dye-pigment.  The  guano  is  first  digested  in  hydrochloric 
acid  to  remove  foreign  substances ;  the  residue,  consisting  of  acid  and  sand, 
is  treated  with  soda;  this  dissolves  out  the  uric  acid,  which  may  now  be 
readily  procured  by  neutralizing  the  liquids  with  hydrochloric  acid.  Nitric 
acid  converts  uric  acid,  in  the  cold,  into  alloxan  ;  and  dilute  nitric  acid 
heated,  converts  it  into  alloxantine.  When  uric  acid  is  dissolved  in  nitric 
acid  of  a  sp.  gr.  of  1-40,  and  the  solution  is  heated,  the  color  is  brought  out 


ANNOTTO.      QUERCITRINE.  6t9 

by  adding  to  the  acid  liquid  when  cold,  ammonia  or  its  carbonate,  until  a 
slight  aramoniacal  odor  is  imparted  to  it.  Dr.  Gregory  advises  that  seven 
parts  of  alloxan  and  4  parts  of  alloxantine  should  be  dissolved  in  240  parts 
of  boiling  water,  and  this  solution  added  while  hot  to  80  parts  of  a  cold 
saturated  solution  of  carbonate  of  ammonia.  The  liquid  becomes  opaque, 
owing  to  the  intense  purple  color  produced,  and  crystals  of  murexide  are 
deposited  on  cooling. 

The  crystals  are  square  prisms.  Like  rosaniline,  carthamine,  and  some 
other  reds,  they  have  a  rich  green  color  like  that  of  beetles'  wings  by  re- 
flected, but  are  purple-red  by  transmitted  light.  They  are  but  slightly  solu- 
ble in  cold  water,  which,  however,  acquires  a  strong  color ;  they  are  soluble 
in  boiling  water,  and  are  insoluble  in  alcohol  and  ether.  The  color  is  de- 
stroyed by  ammonia  and  sulphuretted  hydrogen.  Potassa  dissolves  murexide, 
forming  a  rich  purple  solution,  but  the  color  is  destroyed  on  boiling.  When 
to  this  colorless  solution,  an  excess  of  dilute  sulphuric  acid  is  added,  murexan 
is  precipitated.  This  is  considered  to  be  identical  with  uramile  and  the 
purpuric  acid  of  Dr.  Prout.  A  solution  of  murexide  is  precipitated  by  the 
solutions  of  various  metallic  salts.  In  dyeing  silk  with  murexide,  corrosive 
sublimate  is  used  as  a  mordant;  in  dyeing  cotton,  a  salt  of  lead,  and  in  dye- 
ing woollen,  a  double  chloride  of  tin  and  ammonium. 

There  is  no  agreement  among  chemists  respecting  the  formula  of  murexide ; 
and  the  discrepancies  which  exist  appear  to  be  at  present  utterly  irrecon- 
cilable. The  chemical  changes  which  take  place  in  its  production  cannot  be 
represented,  therefore,  by  any  correct  equation. 

The  vegetables  which  afford  the  different  shades  of  yellow  used  as  pig- 
ments, and  in  the  arts  of  dyeing  and  calico-printing,  are  very  numerous,  but 
definite  crystallizable  principles  have  been  only  in  a  few  instances  obtained 
from  them. 

Annotto. — This  substance  is  derived  from  the  pulp  of  the  seeds  of  the 
Bixa  Orellana,  a  shrub  which  is  native  in  South  America,  but  cultivated  in 
Guiana  and  St.  Domingo,  and  also  in  the  East  Indies.  It  is  usually  met 
with  in  a  pasty  form,  of  a  deep  orange-red  color,  nearly  tasteless,  and  of  a 
disagreeable  odor.  It  is  but  little  soluble  in  water,  but  alcohol  and  ether 
act  upon  it  more  readily,  forming  solutions,  which,  when  evaporated,  leave 
the  coloring-matter  in  the  state  of  powder.  It  is  soluble  in  the  alkalies  and 
their  carbonates,  forming  dark-red  liquids,  in  which  the  acids  occasion 
orange-red  precipitates.  Annotto  contains  a  yellow  and  a  red  coloring- 
matter;  the  former  soluble  in  water  and  in  alcohol,  and  slightly  soluble  in 
ether,  and  giving  a  yellow  dye  to  silk  and  wool  mordanted  with  alumina ; 
the  latter  little  soluble  in  water,  but  soluble  in  alcohol  and  ether,  as  well  as 
in  the  alkalies,  and  rendered  blue  by  sulphuric  acid.  Annotto  is  chiefly 
used  as  a  dye  for  silk,  giving  various  shades  of  orange.  The  color  which  it 
imparts  is  less  affected  by  soap,  acids,  and  chlorine,  than  most  other  similar 
dyeing  materials,  but  it  does  not  well  resist  the  joint  agency  of  light  and  air. 
In  Gloucestershire  and  Cheshire  it  is  used  to  color  cheese,  and  sometimes 
butter  and  milk.     It  is  employed  as  a  color  in  varnishes. 

QUERCITRINE. — This  is  the  coloring  principle  of  the  inner  bark  of  quercit- 
ron (Quercus  nigra  or  tinctoria).  It  may  be  obtained  from  the  aqueous  de- 
coction of  the  bark.  It  has  a  sweetish-bitter  taste,  and  is  soluble  in  water, 
alcohol,  and  ether.  On  exposing  its  aqueous  solution  to  air,  it  becomes 
deep  yellow  and  deposits  a  yellow  precipitate  :  if  this  solution  is  boiled  in  a 
shallow  basin,  it  becomes  turbid,  and  deposits  a  quantity  of  yellow  acicular 


680  PERSIAN    BERRIES.      EUXANTHINE. 

crystals  of  quercitreine.  Quercitrine  forms  yellow  solutions  with  the  dilate 
mineral  acids.  With  the  alkalies,  its  solution,  if  exposed  to  air,  is  dark 
brownish-yellow.  With  acetate  of  lead  the  precipitate  is  white,  and  may  be 
dried  without  change  of  color,  provided  air  is  excluded.  According  to 
Preisser,  the  formula  of  quercitrine  is  CggllijO^;  and  that  of  quercitreine, 
when  dried  at  212^,  Q^Jl^^O^^,  A  decoction  of  quercitron  bark  deprived  of 
its  tannic  acid,  by  a  little  gelatin,  produces  a  fine  yellow  upon  fabrics  mor- 
danted with  alumina,  and  various  shades  of  olive  with  iron  mordants.  It  is 
much  used  in  calico-printing. 

Fustic. — This  dye-stuflf  is  the  wood  of  the  Morus  tinctoria,  a  large  tree 
which  grows  in  Brazil,  Jamaica,  and  most  of  the  West  Indian  Islands. 
When  a  concentrated  decoction  of  fustic  cools,  it  deposits  a  yellow  crystal- 
line matter,  to  which  Chevreul  has  given  the  name  of  morine. 

Weld. — This,  which  is  the  gaude  or  vaude  of  the  French,  consists  of  the 
dried  leaves  and  stem  of  the  Reseda  luteola,  a  plant  indigenous  in  Britain 
and  other  parts  of  Europe.  The  whole  herb  is  gathered  when  in  seed,  at 
which  period  its  dyeing  power  is  greatest.  There  are  two  kinds  of  weld,  the 
cultivated  and  the  wild ;  the  former  is  richest  in  coloring  matter.  The 
decoction  of  this  plant  has  a  slightly  acid  reaction  and  a  greenish  yellow 
color,  which  is  deepened  by  alkalies,  and  rendered  paler  by  dilute  acids.  It 
contains  a  coloring  principle  called  luteoline. 

Persian  Berries. — Under  this  name,  the  berries  of  the  Rhamnus  tinctoria 
are  known  amongst  painters  and  calico-printers.  They  contain  a  coloring 
principle  called  rhamnine.  This  is  obtained  from  an  ethereal  tincture  of  the 
berries.  It  is  an  almost  colorless  crystalline  powder,  of  a  bitter  taste,  and 
soluble  in  water,  alcohol,  and  ether.  These  solutions  soon  acquire  a  yellow 
color  by  exposure  to  air,  the  rhamnine  passing  into  rhamnmie.  Nitric  and 
chromic  acids,  bichromate  of  potassa,  and  other  oxidizing  agents,  immedi- 
ately produce  the  same  change;  and  under  the  influence  of  alkalies,  the 
liquids  acquire,  on  exposure  to  air,  a  dark-brown  color. 

Cfhrysorhamnine,  or  Rhamneine,  and  Xaiithorhamnine,  are  yellow  coloring 
principles,  also  obtained  from  these  berries. 

Turmeric. — This  is  the  root  of  the  Curcuma  longa,  a  plant  which  is  a 
native  of  the  East  Indies,  and  much  cultivated  about  Calcutta,  and  in  all 
parts  of  Bengal ;  also  in  China  and  Cochin-China.  The  tubers  of  this  plant, 
commonly  called  turmeric,  contain  a  coloring  principle  called  curcumine. 
It  is  obtained  by  treating  the  watery  extract  of  turmeric  by  boiling  alcohol 
of  sp.  gr.  0'80,  and  evaporating  the  filtered  tincture.  The  residue  is  digested 
in  hot  ether :  this  dissolves  the  curcumine,  which  is  deposited,  on  the  evapo- 
ration of  the  ether,  in  the  form  of  an  inodorous,  transparent,  reddish  sub- 
stance, not  crystalline,  and  acquiring  a  fine  yellow  color  when  rubbed  to 
powder.  It  fuses  at  105^,  and  is  scarcely  soluble,  even  in  hot  water,  but 
readily  soluble  in  alcohol  and  ether,  and  in  fat  and  volatile  oils.  It  there- 
fore approaches  in  its  characters  to  the  resins. 

Turmeric  paper  for  chemical  use  is  best  prepared  with  a  strong  tincture  of 
turmeric  in  proof-spirit. 

EuxANTHiNE. — A  substancc  under  the  name  of  Purree,  or  Indian  yellow, 
is  imported  from  India  and  China;  its  origin  has  not  been  well  ascertained, 
but  it  is  supposed  by  Stenhouse  to  be  the  juice  of  some  unknown  plant, 
mixed  with  magnesia.     It  has  an  odor  somewhat  resembling  that  of  castor, 


COAL-TAR    COLORS.  681 

and  was  therefore  suspected  to  be  of  animal  origin,  derived  probably  from 
the  gall  of  the  elephant  or  camel.  The  crystallizable  principle  which  it 
contains,  and  which  may  be  conveniently  termed  euxanthine  (LowiG,  i.  888), 
may  be  separated  by  boiling  the  crude  purree  in  water,  and  treating  the 
residue,  which  is  of  a  fine  yellow  color  {euxanthate  of  magnesia),  with  hot 
dilute  hydrochloric  acid.  The  euxanthine  crystallizes  as  the  liquid  cools, 
and  may  be  purified  by  dissolving  the  washed  crystals  in  alcohol,  and  recrys- 
tallizing.  Euxanthine  is  readily  soluble  in  ammonia,  potassa,  and  soda, 
forming  yellow  solutions,  which  yield  crystalline  compounds,  soluble  in  water, 
but  insoluble  in  solutions  of  the  alkaline  carbonates.  When  euxanthine  is 
dissolved  in  a  hot  solution  of  carbonate  of  ammonia,  potassa,  or  soda,  car- 
bonic acid  escapes,  and  crystalline  euxanthates  are  formed.  These  salts  are 
soluble  in  alcohol.     Euxanthine  has  the  composition  of  04311^8033. 

Coal-tar  Colors. — The  use  of  many  of  the  coloring  matters  described  in 
the  preceding  pages,  has  been  in  a  great  measure  superseded  by  the  discovery 
of  various  simple  methods  of  producing  almost  every  variety  of  color,  in  its 
highest  perfection,  from  the  tarry  oils  obtained  in  the  distillation  of  coal. 
These  discoveries  are  among  the  most  remarkable  of  modern  chemistry.  We 
can  here  only  advert  to  them  in  general  terms.  The  gaseous  and  liquid 
products  of  the  destructive  distillation  of  coal  have  been  already  referred  to, 
(p.  271).  Although  coal  itself  is  simply  a  compound  of  five  elements,  C.H. 
O.N.S.,  yet,  according  to  the  mode  in  which  it  is  treated,  the  gaseous  and 
liquid  substances  obtained  from  it  amount  to  no  fewer  than  fifty-one,  some 
of  these  having  a  most  complex  composition.  Aniline  is  found  among  them, 
but  the  quantity  contained  in  coal-tar  oil  is  too  small  to  render  its  extrac- 
tion for  the  manufacture  of  colors  practically  available.  In  addition  to 
aniline,  the  tarry-oils  contain  benzole  (p.  610)  and  phenole,  or  carbolic  acid 
(p.  610),  which  are  the  principal  substances  employed  in  this  manufacture. 
They  may  be  separated  from  the  other  products  by  fractional  distillation,  and 
from  each  other  by  the  chemical  processes. 

Aniline-purple.  Mauveine  (CgyHjgNg). — Among  the  various  methods  of 
procuring  aniline-purple  may  be  mentioned  that  adopted  by  Messrs.  Dale,  of 
Manchester.  Their  process  is  based  upon  the  fact  that  salts  of  aniline,  when 
heated  with  a  solution  of  chloride  of  copper,  completely  reduce  it  to  the 
state  of  subchloride,  with  the  simultaneous  formation  of  a  black  precipitate, 
containing  aniline-purple.  One  equivalent  of  a  neutral  salt  of  aniline  ia 
dissolved  in  water,  and  boiled  for  several  hours  with  six  equivalents  of  chloride 
of  copper,  a  mixture  of  alkaline  chlorides  and  copper  salts  being  employed 
for  this  purpose.  When  the  reaction  is  completed,  the  mixture  is  filtered, 
the  black  precipitate  well  washed  and  dried,  and  afterwards  digested  repeat- 
edly in  dilute  alcohol,  in  order  to  dissolve  out  the  coloring-matter,  which  it 
contains  in  a  remarkably  pure  state.  By  heating  adhydrous  hydrochlorate 
of  aniline  with  nitrate  of  lead  to  360°,  a  bronze-like  brittle  mass  is  obtained, 
which  contains  aniline  red  mixed  with  aniline-purple.  The  red  may  be 
separated  from  the  purple  by  boiling  water ;  one  grain  of  it  will  strongly 
color  a  gallon  of  water.  These  coloring  matters  are  fixed  on  cotton  by  a 
new  mordant;  the  goods  are  prepared  with  a  solution  of  the  color  and 
tannic  acid,  and  are  then  passed  through  a  bath  containing  tartar  emetic. 
The  tannate  of  antimony  produced  serves  to  fix  the  dye. 

By  methods  already  described,  benzole  is  easily  converted  into  nitrobenzole, 
and  this  product  into  aniline  (p.  559).  When  bichromate  of  potassa  is  added  to 
a  mixture  of  aniline  and  sulphuric  acid  (sulphate  of  aniline),  a  splendid  purple 
dye  is  produced,  which  may  be  procured  as  a  dark-red  colored  solid.  When 
dissolved  in  water,  this  substance  forms  a  dye  of  a  rich  purple  color,  known 


682  PRODUCTION    OF    ANILINE-RED.      ROSANILINE. 

under  the  name  of  Mauve  or  aniline  purple.  This  important  discovery  was 
made  by  Mr.  Perkins.  Aniline  purple  is  not  very  soluble  in  cold  water,  but 
it  is  dissolved  more  readily  by  hot  water,  or  by  water  slig:htly  acidulated.  It 
is  thrown  down  from  its  solution  by  alkalies.  It  is  decomposed  and  de- 
stroyed by  strong  nitric  acid  and  chlorine.  Alcohol  dissolves  it,  and  its 
tinctorial  power  is  said  to  be  such,  that  one- tenth  of  a  grain  of  the  solid  dye 
will  form  a  rich  violet-colored  solution  with  a  gallon  of  alcohol  (Hofmann). 
The  exact  constitution  of  aniline-purple  is  not  known.  It  forms  insoluble 
blue  and  purple  precipitates  with  corrosive  sublimate  and  tannic  acid. 
Tannic  acid  is  used  as  a  mordant  for  fixing  the  dye  on  cotton,  the  aniline- 
purple  being  dissolved  in  acidulated  water.  In  calico-printing,  the  color  is 
mixed  with  gum  and  fixed  by  albumen,  according  to  the  method  already 
described  (p.  670).  Wool  and  silk  are  readily  dyed  by  an  aqueous  solution 
without  a  mordant,  at  a  temperature  of  about  120'^. 

Aniline-red.  Magenta. — Aniline  yields  red  colors  with  various  chemical 
reagents.  Thus,  when  mixed  with  sulphuric  acid  and  treated  with  peroxide 
of  lead,  it  yields  a  rose-colored  compound,  which  has  been  called  Roseine  ; 
and  when  heated  with  bichloride  of  tin,  corrosive  sublimate,  nitrate  of  mer- 
cury, arsenic  acid,  or  indigo,  it  produces  a  crimson  compound,  known  under 
the  name  of  Fuchsine.  The  production  of  color  from  a  colorless  organic 
compound,  is  remarkably  shown  in  the  reaction  of  corrosive  sublimate  on 
aniline.  The  white  mineral  solid  and  the  aniline  form  by  mixture  a  colorless 
paste  :  but  when  this  is  heated,  it  acquires  an  intense  crimson  color.  From 
this  colored  product,  which  appears  to  be  a  salt,  Mr.  Nicholson  succeeded  in 
procuring  a  colorless  crystalline  body,  Rosaniline  {G„^.^^^0),  which  acts 
the  part  of  a  base,  and  which,  on  entering  into  combination  with  acids  at  a 
moderate  heat,  produces  the  well-known  crimson  dye  {Magenta).  The  salts 
of  rosaniline  may  be  obtained  on  evaporation,  perfectly  crystalline.  The 
acetate  crystallizes  in  splendid  octahedral  crystals,  which  have  by  reflected 
light  the  metallic  greenish  color  of  beetles'  wings;  but  when  dissolved  in 
water,  they  form  a  solution  of  an  intense  crimson  color.  Silk  and  woollen 
readily  take  this  dye,  without  the  aid  of  a  mordant.  Cotton  and  linen 
require  to  be  mordanted  with  albumen.  When  aniline  is  heated  with  bichlo- 
ride of  tin  to  a  high  temperature  in  a  close  vessel,  a  rich  blue  dye  is  produced, 
which  is  known  under  the  name  of  Bleu  de  Paris. 

The  colors  which  are  obtained  by  these  processes,  depend  on  the  oxida- 
tion of  aniline,  and  they  vary  with  the  degree  of  oxidation.  Thus  the  same 
ingredients  yield  a  violet,  purple,  or  red  color,  according  to  the  proportions 
in  which  they  are  used.  Mr.  Price  found  that  aniline-red  (roseine)  was 
produced  by  boiling  together,  1  equivalent  of  aniline,  1  equivalent  of  sul- 
phuric acid,  and  2  equivalents  of  peroxide  of  lead;  and  aniline  purple  (pur- 
purine)  was  the  product,  when  2  equivalents  of  aniline,  2  equivalents  of 
sulphuric  acid,  and  1  equivalent  of  peroxide  of  lead  were  employed.  The 
redness  of  the  tint  appears  to  increase  with  the  degree  of  oxidation.  Girard 
discovered  that  10  parts  of  aniline,  added  to  a  mixture  of  12  parts  of  arsenic 
acid  in  12  parts  of  water,  gradually  heated  to  about  248°  and  not  above 
320°,  yielded  a  rich  aniline-red  with  a  slight  violet  tint.  When  the  same 
quantity  of  aniline  is  used  with  24  parts  of  arsenic  acid  in  24  parts  of  water, 
an  aniline  purple  or  violet  color  is  obtained.  Of  all  the  processes  yet  sug- 
gested, it  appears  that  there  is  none  which,  for  economy  and  perfection  of 
color,  surpasses  that  originally  devised  by  Mr.  Perkins.  In  this,  the  oxida- 
tion of  aniline  is  effected  by  bichromate  of  potassa.  The  selection  of  a 
proper  mordant  materially  affects  the  results.  Of  all  the  mordants  yet  pro- 
posed for  the  aniline  dyes,  the  stannate  of  soda  appears  to  be  the  most 
efficient. 


COLORING    MATTER    OF    FLOWERS.  683 

Aniline-yellow,  Chrysaniline  (C,oHj,N3)._-This  is  a  yellow  powder  ob- 
tamed  as  a  secondary  product  in  the  manufacture  of  aniline  red.  It  is  nearly 
insoluble  in  water,  but  is  soluble  in  alcohol.  It  combines  with  acids  like  a 
base,  forming  well-defined  salts.  These  are  for  the  most  part  soluble,  ex- 
cepting the  nitrate. 

A  yellow  dye  is  obtained  by  the  reaction  of  strong  nitric  acid  on  phenole 
or  carbolic  acid  {see  p.  610).  The  product  is  picric  or  carhazolic  acid,  the 
properties  of  which  have  already  been  described.  Silk  or  flannel,  when  im- 
pregnated with  alum,  acquires  a  rich  yellow  color  by  immersion  in  a  solu- 
tion of  this  acid.  Various  shades  of  green  may  be  obtained  by  the  admixture 
of  the  yellow  of  picric  acid,  with  indigo  and  other  blues. 

Aniline  blue. — When  the  acetate  or  hydrochlorate  of  rosaniline  is  boiled 
with  an  excess  of  aniline,  this  blue  compound  is  produced.  It  is  of  a 
brown  color,  not  soluble  in  water,  but  dissolved  by  alcohol,  forming  a  rich 
blue  solution.  M.  Clanel  renders  the  blue-dye  soluble  in  water  by  dissolving 
it  in  fuming  sulphuric  acid,  diluting  the  solution  considerably,  and  passing 
into  it  steam.  The  addition  of  common  salt  to  the  cooled  liquid  threw 
down  the  blue  pigment  in  flocculi  soluble  in  water  free  from  saline  matter. 
{Quart  Jour,  of  Science,  April,  1864,  322.) 

One  variety  of  coal-tar  blue,  called  azuline,  is  seen  in  bronze-colored  crys- 
tals, which  are  dissolved  by  water,  forming  an  intense  sapphire  blue  solu- 
tion, even  in  the  smallest  quantity.  A  small  quantity  of  ammonia  added  to 
the  solution  renders  it  colorless.  This  liquid  when  treated  with  a  strong 
solution  of  potash  or  soda  is  reddened ;  while  on  adding  an  acid,  hydrochloric 
or  sulphuric,  it  acquires  again  an  intense  blue  color.  The  color  can  be 
imparted  to  paper,  and  this  may  be  used  as  test-paper.  It  is  the  converse 
of  litmus;  it  is  reddened  by  a  fixed  alkali,  and  rendered  blue  by  an  acid; 
ammonia  iDleaches  it. 

A  green  dye  is  manufactured  by  acting  on  aniline  with  a  mixture  of  hydro- 
chloric acid  and  chlorate  of  potash,  or  on  magenta  with  aldehyde,  while  an 
aniline  black  has  been  obtained  by  the  use  of  similar  reagents. 

CoLORiNG-MATTER  OF  Flowers. — These  are  principally  blue,  {Antho- 
cya7iine)  ;  red,  {Anther ythrine) ;  and  yellow,  {Anthoxanthine) :  they  have  as 
yet  been  imperfectly  examined  ;  many  of  them  are  very  fugitive,  change  con- 
siderably in  tint,  and  are  often  altogether  destroyed,  on  drying;  others  are 
comparatively  permanent.  According  to  Thompson,  the  expressed  juice  of 
most  red  flowers  is  blue,  whence  he  infers  that  the  coloring-matter  in  the 
petals  is  reddened  by  carbonic  acid,  which  escapes  on  exposure.  The  violet 
is  colored  by  a  blue  matter  which  is  changed  to  red  by  acids,  and  first  to 
green  and  then  to  yellow  by  alkalies,  the  green  probably  resulting  from  the 
mixture  of  blue  and  yellow.  The  petals  of  the  red  rose,  when  triturated 
with  a  little  chalk  and  water,  yield  a  blue  liquid  which  is  rendered  green  by 
alkalies  and  their  carbonates,  and  restored  to  red  by  acids.  The  same  blue 
coloring-matter  as  that  of  the  violet,  exists  in  many  other  flowers,  and  seems 
also  to  form  the  most  usual  red  of  the  red  flowers,  in  which  it  is  apparently 
reddened  by  an  acid,  for  many  of  these  reds  become  blue  when  cautiously 
neutralized  by  an  alkali,  and  green  and  yellow  by  an  excess  of  alkali.  This 
is  also  the  case  with  the  red  of  the  red  cabbage  and  of  the  radish.  Some  of 
these  reds  become  blue  merely  on  being  bruised,  and  give  blue  infusions  with 
water.  The  color  of  yellow  flowers  is  generally  more  permanent  than  that 
of  the  blue  or  red ;  it  is  rendered  paler  by  acids,  and  deeper  by  alkalies. 
Most  of  the  coloring-matters  of  the  petals  of  flowers  are  extremely  suscep- 
tible of  the  bleaching  influence  of  sulphurous  acid  and  chlorine.  The  color- 
ing-matter of  yellow  flowers  is  partly  soluble  and  partly  iusoluble  in  water 


684  COLORING  MATTER  OF  LEAVES. 

and  spirit.  The  red  petals  of  Papaver  rhceas  yield  a  red  solution  with  lime- 
water  or  carbonate  of  soda  ;  potassa  renders  it  green,  and  hydrochloric  acid 
pale  red :  the  color  of  red  rose-leaves  is  brightened  by  acids,  and  rendered 
green  by  alkalies. 

A  strong  infusion  of  the  petals  of  the  French  rose  imparts  a  faint  reddish 
tint  to  bibulous  paper;  and  paper  thus  fully  impregnated  and  dried,  forms 
a  useful  test-paper.  It  indicates  alkalies  by  the  production  of  a  green  color  ; 
acids  by  a  deeper  red  tint ;  and  as  it  contains  tanno-gallic  acid  it  is  dark- 
ened by  the  persalts  of  iron. 

The  application  of  spectrum  analysis  to  the  red  coloring-matters  of 
flowers  and  prints  shows  that  they  bear  no  resemblance  to  the  red  coloring- 
matter  of  blood.  None  of  them  give  any  absorption  bands  in  the  green. 
Mr.  Sorley  states,  as  the  result  of  his  spectralytic  observations,  that  many 
flowers  contain  four  or  five  different-colored  substances. 

Coloring-matter  op  Leaves.  Cfhlorophylline.  Xanthophylline.  ErythrO' 
phylline. — Chlorophyll  or  Cltlorophylline  (CjgHjjOgN),  from  which  leaves  and 
herbage  derive  their  green  color,  may  be  procured  by  digesting  the  crushed 
leaves  in  renewed  portions  of  alcohol  or  ether;  this  tincture  is  then  evaporated 
on  a  water-bath,  and  the  deposit  which  is  formed  is  separated,  dried,  and 
digested  in  alcohol  so  long  as  any  green  soluble  matter  is  abstracted.  Chlo- 
rophylline  appears  as  a  dark-green  substance,  which  is  grass-green  when 
reduced  to  powder.  It  fuses  at  about  390°.  When  moist,  it  is  slightly 
soluble  in  alcohol,  with  a  grass-green  color;  when  dry,  it  is  less  soluble,  and 
the  color  of  the  solution  is  bluish-green.  It  is  similarly  soluble  in  ether, 
and  it  communicates  a  green  color  to  oil  of  turpentine  and  to  fat  oils.  It  is 
insoluble  in  water.  When  the  ethereal  solution  of  chlorophylline  is  long 
exposed  to  light,  it  acquires  a  yellow  color,  and,  on  evaporation,  leaves  a 
residue  having  all  the  characters  of  xanthophylline. 

Xanthophylline  is  a  term  applied  to  the  coloring-matter  extracted  from  the 
yellow  leaves  which  fall  in  autumn.  It  was  obtained  from  the  leaves  of  a 
pear-tree  by  Berzelius,  by  digesting  them  for  several  days  in  a  bottle  entirely 
filled  with  alcohol  of  sp.  gr.  0'833,  and  well  stopped,  so  as  to  exclude  air; 
for  when  it  is  in  contact  with  the  leaves  under  these  circumstances;  they 
change  from  yellow  to  brown.  On  distilling  off  the  alcohol  from  the  tincture 
thus  prepared,  and  allowing  the  residue  to  cool  slowly,  the  xanthophylline, 
together  with  a  little  resinous  and  fatty  matter,  was  deposited.  It  is  a  dark- 
yellow  substance,  fusible  at  about  110°,  and  becoming  transparent  on  cooling, 
it  is  insoluble  in  water,  sparingly  soluble  in  alcohol,  and  readily  soluble  in 
ether  or  benzole. 

Erythrophylline. — It  was  remarked  by  Berzelius  that  all  trees  and  shrubs, 
the  leaves  of  which  redden  in  autumn,  bear  red  fruit  or  berries.  (Sorbus 
aucuparia,  Prunus  cerasus,  Pibes  grossularia,  &c.)  He  obtained  this  red 
coloring-matter  from  cherry  and  red-currant  leaves,  by  digesting  them,  when 
in  a  proper  condition,  in  alcohol,  and  distilling  the  red  tincture.  The 
changes  of  color  which  the  leaves  of  many  forest-trees  undergo  in  autumn, 
passing  from  green  to  red,  and  from  red  to  yellow,  have  been  ascribed  by 
Macaire-Prinsep  to  the  action  of  certain  chemical  agents  upon  a  single 
coloring-matter.  {Ann.  Gh.  et  Ph.,  xxviii.  415.)  Spectral  analysis  has 
thrown  some  light  upon  these  changes  and  upon  the  coloring  principle  of 
leaves.  By  this  optical  method.  Prof.  Stokes  has  found  in  the  spectrum  of 
chlorophylline  of  land  plants  two  distinct  greens  and  two  yellows.  Accord- 
ing to  Mr.  Tichborne,  the  yellow,  brown,  and  red  coloring-matters  exist  in 
leaves  quite  independently  of  the  green  coloring  principle  {chlorophylline), 
which  in  the  presence  of  moisture  and  atmospheric  oxygen  is  very  sensitive 


NEUTRAL    NITROGENOUS    SUBSTANCES.  085 

to  light.  It  has  a  characteristic  spectrum  when  examined  in  an  alcoholic 
solution,  and  this  chlorophyll  spectrnra,  which  is  marked  by  a  broad  band  in 
the  red  rays,  is  always  present  in  leaves  when  in  an  active  state  of  vegetation, 
whatever  color  the  leaf  may  be,  and  however  it  may  be  modified  by  the 
presence  of  other  substances.  In  a  leaf  or  other  green  part  of  a  plant, 
chlorophyll  is  constantly  being  deposited,  and  as  fast  as  it  is  being  deposited 
it  is  being  converted  into  yellow,  brown,  or  reddish  products  of  decom- 
position— a  fact  demonstrated  by  spectral  observations ;  but  during  active 
growth  the  chlorophyll  is  being  deposited  much  more  rapidly  than  it  is  de- 
composed. Ordinary  leaves  fall  when  the  chlorophyll  is  no  longer  formed, 
their  existence  being  then  at  an  end.  The  autumnal  tints  of  leaves  may  be 
ascribed  to  the  slower  deposition  of  the  leaf-green.  In  dark-colored  leaves, 
although  the  natural  color  may  be  disguised  to  the  eye,  the  bands  charac- 
teristic of  chlorophyll  will  be  found  well  marked  in  the  spectra.  The  change 
in  the  leaves  of  the  Virginian  creeper,  observed  at  the  close  of  autumn,  shows 
that  they  have  a  power  of  vitality  for  some  time  after  the  deposition  of  chlo- 
rophyll has  ceased,  or  is  proceeding  very  slowly.  The  general  conclusion 
drawn  by  Mr.  Tichborne  from  his  observations  is  that  chlorophyll  is  directly 
concerned  in,  if  not  actually  the  medium  for  the  elaboration  of  the  crude 
pieces  of  the  plant,  and  that  it  is  intimately  connected  with  the  amylaceous 
series  of  vegetable  products.     {Laboratory,  June,  1867,  194.) 


CHAPTER  LV. 

NEUTRAL  NITROGENOUS  SUBSTANCES.  THE  SOLID  CON- 
STITUENTS OF  THE  ANIMAL  BODY;  AND  SUBSTANCES 
DERIVED   FROM  THEM. 

Neutral  nitrogenous  substances  are  found  in  the  vegetable  and  animal 
kingdoms  :  in  the  former  they  are  represented  by  gluten,  albumen,  casein,  or 
legumin:  and  in  the  latter  by  fibrin,  albumen,  casein,  and  gelatin.  In 
addition  to  carbon,  hydrogen,  and  oxygen,  they  all  contain  nitrogen,  and 
the  greater  number  contain  variable  quantities  of  sulphur  and  phosphorus : 
animal  gelatin  contains  neither  of  these  elements.  These  principles  are 
important  as  articles  of  food  to  animals,  and  they  are  frequently  described 
as  yesh^forming  substances,  in  order  to  distinguish  them  from  the  neutral 
compounds  of  the  three  elements  C.H.O.,  starch,  gum,  and  sugar,  which, 
according  to  modern  theory,  are  only  heat-producing.  Although  their 
elementary  composition  is  well  known,  yet,  as  they  form  no  definite  com- 
binations  with  other  bodies,  no  correct  rational  formulae  have  yet  been  con- 
structed to  represent  their  constitution.  There  is  no  material  diflference  in 
the  composition  of  these  substanqes,  whether  they  are  derived  from  the 
vegetable  or  the  animal.  It  has  been  suggested  that,  with  the  exception  ot 
gelatin,  they  are  derivatives  from  a  common  principle,  to  which  the  name  ot 
Iroteini^  given  (^pcotevo,  to  take  the  first  place)  ;  and  that  this  consists  of  a 
definite  number  of  atoms  of  carbon,  hydrogen,  oxygen,  and  nitrogen  :  hence 
they  are  sometimes  described  as  proteinaceous  substances.  Their  centesimal 
composition,  as  furnished  by  the  combustion-tube,  is  given  in  the  tollowing 
table.  From  this  it  will  be  perceived  that  the  differences  in  elementary 
constitution  are  slight,  and  that  differences  in  properties  are  probably  due 
to  molecular  arrangement. 


686 


NIT 

ROGENOUS    PRINCIPLES.      PUTREFACTION. 

Albumen. 

Emulsin. 

Casein. 

Legumin. 

Gluten. 

Fibrin. 

Protein. 

Carbon 

.     54-8 

50-9 

54-9 

50-7 

55-2 

54-6 

55-0 

Hydrogen 

.      7-1 

6-8 

7-1 

6-8 

7-5 

6-9 

6-9 

Oxygen     . 

.     21-2 

23-4 

22-2 

24-9 

21-4 

22-8 

22-0 

Nitrogen  . 

.     16-9 

18-9 

15-8 

17-6 

15-9 

15-7 

16-1 

In  the  above  analyses,  the  sulphur  and  phosphorus  are  included  in  the 
amount  of  oxygen.  The  proportion  of  sulphur  and  phosphorus,  according 
to  Mulder  and  Scherer,  is  on  an  average  about  1  per  cent.  :  in  seralbunien  it 
was  found  to  be  1*1 ;  in  ovalburaen,  0*82  ;  and  in  the  fibrin  of  ox-blood  it 
varied  from  1-31  to  1*59  per  cent.  In  casein  the  proportion  is  less  than  in 
albumen.  Owing  to  their  complex  constitution,  and  as  a  result  of  the  loose 
attraction  of  their  elements  out  of  the  living  body,  these  principles,  when 
exposed  in  a  moist  state  to  air  at  a  proper  temperature,  undergo  spontaneous 
changes,  and  are  ultimately  converted  into  water,  ammonia,  carbonic  acid, 
and  other  inorganic  compounds.  In  the  stage  of  transition,  noxious  and 
offensive  effluvia,  consisting  of  compounds  of  nitrogen,  sulphur,  and  phos- 
phorus, with  hydrogen,  are  evolved  ;  and  to  this  stage  the  term  putrefaction 
is  applied.     The  conditions  necessary  for  this  process  are  the  following  : — 

1.  Temperature. — Putrefaction  occurs  at  any  temperature  above  50°.  That 
which  is  most  favorable  varies  from  70°  to  100°.  It  most  probably  acts  by 
increasing  the  affinity  of  the  elements  for  each  other.  Too  high  a  tempera- 
ture coagulates  or  dries  the  substance,  and  thus  arrests  decomposition,  while 
too  low  a  temperature  also  prevents  it.  The  greater  number  of  animal 
substances  may  be  indefinitely  preserved  at  or  below  the  freezing  point,  and 
when  slowly  thawed,  they  generally  regain  their  original  characters  :  it  is  in 
this  way  that  supplies  of  animal  food  are  kept  in  a  fresh  state  in  many  parts 
of  the  north  of  Europe,  and  that  fish  is  preserved  for  the  London  market. 
A  remarkable  instance  of  the  preservative  power  of  cold  was  exhibited  in 
the  discovery  of  an  ancient  elephant,  in  a  mass  of  ice,  at  the  mouth  of  the 
river  Lena,  in  Siberia.  {Mem.  Imp.  Acad.  iSt.  Fetersb.,  and  Quart.  Journ. 
of  Science,  &c.,  viii.  95.)  The  Laplanders  preserve  reindeer's  milk  in  a 
frozen  state,  and  when  thawed,  after  the  lapse  of  several  months,  it  perfectly 
retains  its  original  characters. 

2.  Moisture  is  a  condition  essential  to  putrefaction.  When  flesh  is  care- 
fully and  thoroughly  dried,  either  by  a  current  of  warm  and  dry  air,  or  by 
other  methods  which  do  not  alter  its  composition,  it  resists  decay.  It  has 
thus  occasionally  happened  that  corpses  have  been  preserved  for  long  periods 
by  accidental  desiccation ;  and  animal  substances  which  are  either  naturally 
dry,  or  rendered  so  by  art,  retain  their  nutritive  powers,  and  resume  their 
former  appearance  when  cautiously  moistened.  The  various  forms  of  gelatin 
and  albumen,  when  desiccated,  are  imperishable;  whilst  in  aqueous  solution, 
or  in  their  original  humid  state,  they  are  the  most  perishable  of  all  animal 
proximate  principles. 

3.  Air,  or  at  least  oxygen,  if  not  absolutely  essential  to,  is  a  powerful 
promoter  of  putrefactive  changes,  and,  uifter  certain  circumstances,  its  ex- 
clusion indefinitely  retards  them.  Hence,  the  rapidity  of  putrefaction  in  pure 
oxygen  ;  and  its  retardation  in  gases,  which  either  do  not  contain  oxygen, 
or  in  which  it  is  held  by  superior  attractive  power.  Thus,  in  deutoxide  of 
nitrogen,  which  contains  more  than  half  its  weight  of  oxygen  in  an  intimately 
combined  state,  and  which  absorbs  all  free  oxygen  brought  in  contact  with 
it,  we  have  kept  pieces  of  beef  perfectly  fresh,  in  one  experiment  for  126, 
and  in  another  experiment  for  224  days.  Even  under  water,  when  oxygen  is 
strictly  excluded,  putrefaction  is  greatly  retarded,  and  modified  in  its  results. 
Meat  immersed  in  water  previously  boiled  to  expel  air,  and  then  covered  by 
a  layer  of  oil,  to  prevent  its  subsequent  absorption,  may  long  be  kept  fresh. 


CONDITIONS    FOR    AND    RESULTS    OF    PUTREFACTION.  687 

In  the  putrefaction  of  animal  matter,  if  there  is  not  a  suflBeient  supply  of 
air  to  oxidize  the  products,  ammonia  and  sulphuretted  hydrogen  abound. 
Thus,  in  bodies  buried  in  coffins,  we  have  found  these  products  even  after 
six  years'  interment.  If  water  has  had  access  to  the  body,  a  singular  change 
takes  place.  The  flesh  and  all  the  organs  become  sodden,  white,  and 
unctuous  to  the  touch,  and  the  soft  parts  are  so  coherent,  that  although  the 
animal  substance  is  preserved,  the  organs  can  no  longer  be  recognized.  On 
boiling  this  white  substance  in  water  a  large  quantity  of  oil  rises  to  the 
surface,  and  ammonia  escapes :  the  oily  matter  solidifies  on  cooling.  This 
substance  has  been  called  adipocere,  from  its  supposed  resemblance  to  a 
mixture  of  wax  and  fat ;  and  its  formation  has  been  ascribed  to  the  reaction 
of  ammonia,  evolved  during  putrefaction,  on  the  fatty  acids,  '^hereby  a  soap 
of  margarate,  stearate,  and  oleate  of  ammonia  is  produced.  We  have 
examined  a  body  thus  metamorphosed,  after  eight  years'  burial.  The  result 
was  that,  while  the  fatty  parts  of  the  body  had  undergone  this  change,  the 
muscular  tissue  still  preserved  a  fibrous  character.  It  was  simply  altered 
fibrin,  in  which  the  ordinary  course  of  decomposition  had  been  modified,  by 
constant  immersion  in  water  and  want  of  free  access  of  air. 

In  the  process  for  the  preservation  of  animal  and  vegetable  food,  the 
substances  are  heated  and  hermetically  sealed  in  tin  canisters,  the  included 
oxygen  is  converted  into  carbonic  acid,  or  enters  into  other  combinations. 
The  partially  boiled  or  roasted  meat  (free  from  any  tainted  portions),  with 
half-dressed  vegetables,  and  soup,  are  introduced  into  a  canister,  which  is 
then  soldered  up,  with  the  exception  of  a  small  hole  left  in  the  lid:  the 
canister  is  placed  in  a  salina  bath,  heated  to  a  few  degrees  above  the  boiling- 
point  of  water,  and  when  steam  is  copiously  issuing  from  the  aperture,  it  is 
dexterously  soldered  up,  so  that  the  canister  is  not  only  hermetically  sealed, 
but  a  vacuum  is  created  within  it:  it  should  be  strong  enough  to  resist 
atmospheric  pressure.  The  success  of  the  process  is  indicated  by  the  ends 
of  the  canister,  when  sealed,  being  concave  as  a  result  of  atmospheric  pres- 
sure. When  the  substances  have  undergone  putrefaction,  owing  to  the 
failure  of  the  process,  the  ends  of  the  canister  bulge  out,  if  the  gases  pro- 
duced cannot  escape.  In  1846  we  examined  one  of  the  canisters  that  had 
formed  part  of  the  stores  of  the  Blonde  frigate,  which  was  dispatched  to 
the  Sandwich  Islands  in  1826,  and  circumnavigated  the  globe.  Although 
twenty-years  had  elapsed,  the  contents  were  found  good  and  wholesome  : 
they  were  readily  consumed  by  persons  who  were  not  aware  of  the  long  time 
during  which  they  had  been  preserved.  In  April,  1867,  a  similar  canister 
having  been  part  of  the  stores  of  the  same  ship  was  opened  before  a  Com- 
mittee of  the  Society  of  Arts  and  the  contents  examined  chemically  and 
microscopically  (see  Journal  of  Society  of  Arts,  May  3,  1867,  p.  379). 
Although  forty^one  years  had  elapsed,  the  fibrous  character  of  the  meat 
(beef)  was  still  retained.  It  was  of  a  red  color,  but  became  brown  by  expo- 
sure to  air.  It  had  not  undergone  putrefaction,  but  was  soft  and  tasteless. 
The  coloring  matter  of  the  blood,  fibrin,  and  gelatin  were  detected  in  it. 
Even  the  striped  character  of  the  muscular  fibre  was  perceptible.  This  fact 
proves  for  what  a  long  period  animal  matter  partially  cooked  may  be  pre- 
served, provided  the  access  of  air  is  cut  off.  Oil,  butter,  suet,  and  such 
substances,  are  sometimes  effectual  as  preservatives  of  food;  and  potted 
meats,  when  covered  with  a  film  of  fatty  matter,  which  if  freed  from  mem- 
brane is  not  prone  to  change,  are  thus  preserved  from  the  contact  of  air. 
Paraffine  has  been  employed  by  Mr.  Redwood  on  the  same  principle,  the 
meat  being  thoroughly  impregnated  with  paraffine. 

For  the  preservation  of  animal  substances  for  scientific  purposes,  we  have 
found  the  following  solution,  recommended  by  Mr.  Goadby,  to  be  very  effi- 


638  ALBUMEN    AND    ITS    VARIETIES. 

cacious:  bay-salt,  4  ounces;  alum,  2  ounces;  corrosive  sublimate,  2  grains; 
water,  1  quart.  The  preparation  should  be  first  well  soaked  in  a  portion  of 
the  liquid,  and  then  transferred  to  a  vessel  containing  a  fresh  solution 
filtered.  We  have  preserved  in  this  liquid  for  upwards  of  sixteen  years,  the 
entire  body  of  a  bird,  as  well  as  hen's  eggs  deprived  of  their  shells  by  immer- 
sion in  dilute  acetic  acid. 

Various  chemical  liquids  have  been  recommended  as  antiseptics.  For  the 
purpose  of  embalming,  solutions  of  arsenic  and  chloride  of  zinc  have  been 
used.  Carbolic  acid  combined  with  an  alkali  has  been  found  to  possess 
strongly  preservative  properties ;  but  its  offensive  odor  is  adverse  to  its 
employment  for  anatomical  purposes. 

Albumen. 

This  terra  is  applied  to  an  organic  principle  which  is  soluble  in  cold  water, 
but  when  its  solution  is  heated  to  about  160^,  it  becomes  more  or  less 
opaque,  and  deposits  white  flakes,  or  if  concentrated,  forms  a  coagulum  ;  and 
when  thus  coagulated,  it  is  insoluble  in  water.  It  is  the  most  widely  diffused 
of  all  the  principles  in  the  animal  body.  It  exists  as  a  liquid  in  lymph,  chyle, 
milk,  and  in  the  blood,  of  which  it  forms  about  *l  per  cent.,  in  the  salivary 
and  pancreatic  fluids,  the  humors  of  the  eye  and  brain.  In  certain  forms  of 
disease  it  is  found  in  the  bile  and  urine.  As  a  solid  it  is  a  constituent  of 
skin,  of  the  brain,  nerves,  glands,  and  cellular  membrane,  and  it  is  the  chief 
component  of  horn,  hair,  nail,  feathers,  wool,  flannel,  and  silk.  Albumen  in 
a  s6luble  form  occurs  in  solution  in  the  sap  or  iuices  of  most  vegetables,  as 
of  the  potato,  carrot,  turnip,  cabbage,  asparagus,  &c.  :  it  is  a  constituent  of 
the  seeds  of  the  cereal  grasses,  and  of  almonds,  fiUoerts,  and  most  of  the  oily 
nuts ;  it  abounds  in  the  juice  of  the  common  houseleek,  and  in  the  shoots  of 
young  plants.  The  properties  of  albumen  are  best  studied  in  the  white  of 
Q^g  (ovalbnmen),  or  in  the  serum  of  the  blood  (seralbumen),  so  that  we  shall 
first  consider  its  characters  as  derived  from  these  sources,  and  afterwards 
advert  to  its  existence  in  other  animal  and  vegetable  products,  where  it  is 
found  both  in  the  liquid  and  solid  state. 

Ovalhumen. — The  albumen  of  the  white  of  ^^^  is  contained  in  a  delicate 
membranous  texture  {o'dnin),  from  which  it  may  be  separated  by  agitation  or 
trituration  with  three  or  four  parts  of  water,  when  the  cellular  membrane  is 
gradually  deposited,  and  the  albumen  remains  in  solution.  It  is  difficult  to 
obtain  it  in  a  clear  solution  unless  it  is  very  dilute,  in  which  case  it  passes 
the  filter :  a  drop  or  two  of  caustic  potassa  added  to  the  white  of  2g^ 
dissolves  the  membrane,  and  then  the  solution  may  be  more  easily  filtered. 
When  carefully  dried  by  a  gentle  heat,  or  by  evaporation  in  vacuo,  in  a 
vessel  containing  chloride  of  calcium,  ovalbnmen  is  obtained  in  the  form  of  a 
brittle  transparent  yellow  substance,  inodorous,  insipid,  and  when  triturated 
with  cold  water,  resuming  its  original  glairiness.  When  heated,  it  exhales 
the  nsual  products  of  azotized  organic  bodies,  and  a  residue  of  carbon 
remains,  which  is  very  difficult  of  incineration.  It  leaves  about  6  or  7  per 
cent,  of  saline  matter,  composed  of  carbonate,  phosphate,  and  sulphate  of 
soda,  phosphate  of  lime,  and  chloride  of  sodium,  with  traces  of  potassa  and 
magnesia.  100  parts  of  ovalbnmen,  when  evaporated  in  vacuo,  leave  a  resi- 
due of  from  10  to  15  parts  of  albumen  and  salts.  Direct  experiment  shows 
that  in  the  white  of  egg  (globidin),  the  solids  amount,  on  an  average,  to  12 
per  cent. ;  and  in  the  yelk  (vitellin)  to  37*1  per  cent.  In  the  latter  there  is 
a  large  quantity  of  yellow  oil  containing  phosphorus,  which  appears  to  give 
color  to  the  yelk.     This  oil  may  be  removed  by  alcohol  or  ether. 


PROPERTIES    OF    ALBUMEN.                 .  689 

The  following  Table,  based  on  direct  experiments,  shows  the  solid  contents 
of  the  principal  albuminous  liquids  in  100  parts: 

White  of  egg.         Yelk.        Serum  (blood).     Serum  (milk).  Serum  (Anasarca). 

Sp-gr 1-041                               1-030              1-027  1-009 

Dry  organic  matter  10-8            35-1                7*0                 4-5  1-1 

Ash 1-2              2-0                2-0                  1-1  0-6 

Water  ....      88-0            62-9              91-0                94-4  98-3 


White  of  egg      .... 

10  to  13 

Liquor  amnii  (4th  month) 

10-77 

(5th  month) 

7-07 

"            (6th  month) 

6-67 

"           (9th  month) 

0-82 

100-0  100-0  100-0  100-0  100-0 

The  average  proportions  of  albumen  per  cent,  in  various  animal  liquids 
are  given  below. 

c««„r«   fliuman     .     .     .  6-3  to  7 

S^^^^^i  animal     ...  6-7 

Chyle 3  to  6 

T„^„T,i  human    ...  0-43 

I^y^^P^t  horse       .     .     .  0-39 

Seralbume7i,. .»^The  albumen  of  the  serum  of  blood  resembles  that  of  white 
of  egg  ;  in  reference  to  chemical  properties,  they  may  be  considered  as  iden- 
tical. They  are  both  slightly  alkaline,  and  are  miscible  with  water  in  all 
proportions.  When  evaporated  to  dryness  at  a  low  temperature,  reduced 
to  powder,  and  digested  in  cold  water,  the  albumen  of  serum  is  difficult  of 
solution,  unless  a  small  quantity  of  potassa  or  soda  is  added. 

A  moderately  strong  aqueous  solution  of  albumen  (white  of  egg,  or  serum) 
is  without  taste  or  odor  :  it  is  adhesive,  and  when  dried  in  a  streak  on  paper, 
it  presents  a  varnished  surface.  Like  a  solution  of  gum  (arabine),  it  exerts 
a  left-handed  rotation  on  polarized  light.  It  is  insoluble  in  and  precipitated 
by  alcohol.  It  appears  to  be  converted  into  coagulated  or  solid  albumen 
by  this  reagent,  as  it  is  no  longer  soluble  in  water.  Heat. — When  the  solu- 
tion is  heated  to  about  150°  it  becomes  opalescent,  and  at  about  170°  it 
coagulates,  forming  a  white,  translucent,  and  somewhat  elastic  substance, 
with  which  we  are  familiar  in  the  white  parts  of  a  hard-boiled  egg  ;  and  when 
in  this  state,  it  is  cautiously  dried,  it  no  longer  remains  soluble  in  water,  but 
becomes  tough  and  horny ;  so  that  there  is  this,  a  characteristic  distinction 
between  albumen  which  has,  and  that  which  has  not  undergone  previous 
coagulation.  As  this  coagulation  ensues  in  close  as  well  as  in  open  vessels, 
it  may  be  concluded  that  the  proportion  of  water  in  the  recent  and  in  the 
concrete  albumen  is  the  same.  Two  parts  of  white  of  egg  and  one  of  water 
entirely  coagulate  or  set  into  a  solid  when  duly  heated,  but  equal  parts  remain, 
under  the  same  circumstances,  semifluid  ;  a  mixture  of  1  part  of  white  of  egg 
and  10  of  water  becomes  opaque,  but  is  not  coagulated ;  and  a  milkiness  is 
perceptible  when  the  white  of  egg  forms  only  a  thousandth  part  of  the  heated 
solution.  Hence,  heat  furnishes  the  best  test  for  the  detection  of  this  prin- 
ciple. Albumen  thus  coagulated  or  solidified  has  the  chemical  properties  of 
fibrin.  When  a  new-laid  egg  is  immersed  in  boiling  water,  the  white  does 
not  so  readily  coagulate  as  in  an  old  egg,  a  distinction,  perhaps  depending 
upon  the  egg  having,  in  the  latter  case,  lost  a  portion  of  water  by  evapora- 
tion through  the  shell,  and  being  therefore  in  a  somewhat  less  diluted  state 
than  in  the  fresh  egg.  When  diluted  albumen  is  boiled,  it  coagulates  and, 
though  heavier  than  water,  becomes  blended  with  air,  and  forms  a  scum, 
which  rises  to  the  surface,  and  is  effectively  used  in  the  clarification  of  certain 
liquids. 

The  cause  of  the  coagulation  of  albumen  by  heat  has  not  been  explained. 
44 


690  CHANGES    DURING    INCUBATION. 

**  It  is,"  says  Dnraas,  "  probably  a  simple  isomeric  modification  of  this  body, 
analogous  to  that  by  which  cyanic  acid  is  converted  into  cyanuric  acid  ;  so 
that  it  would  be  interesting  to  determine  whether  the  atomic  weight  of 
coagulated  albumen  is  not  double  or  triple  that  which  belongs  to  liquid 
albumen"  (p.  622).  When  coagulated  albumen  is  boiled  in  water  for  several 
hours,  it  becomes  horny,  communicating  to  the  water  traces  of  organic  and 
saline  matters. 

Acids. — A  clear  aqueous  solution  of  serum  or  of  white  of  egg  may  be 
neutralized  by  acetic  acid,  without  coagulation ;  hence  it  is  inferred  that  the 
solubility  of  albumen  does  not  depend  on  the  presence  of  free  alkali.  Among 
vegetable  acids  the  acetic,  tartaric,  oxalic,  and  gallic  acids  have  no  action 
upon  the  solution  ;  but  it  is  precipitated  in  an  insoluble  form  by  tannic  acid 
(tannate  of  albumen).  When  a  moderately  strong  solution  is  boiled  with 
acetic  acid,  it  is  not  coagulated;  but  a  gelatinous  compound  results,  which 
dissolves  in  an  excess  of  acetic  acid  and  water. 

An  acetic  solution  of  albumen  is  precipitated  by  sulphuric,  nitric,  and 
hydrochloric  acids,  as  well  as  by  a  solution  of  ferrocyanide  of  potassium.  It 
is  also  precipitated  slowly  in  the  cold,  but  rapidly,  when  warded,  by  solutions 
of  neutral  salts,  e.  g.,  chloride  of  sodium,  nitrate  of  potassa,  and  sulphate  of 
soda.  It  is  remarkable  that  the  solutions  of  these  salts  have  no  action  on 
a  solution  of  albumen,  and  do  not  prevent  its  coagulation  by  heat ;  but  when 
acetic  acid  is  present,  albumen  is  thrown  down,  at  even  a  low  temperature, 
in  an  insoluble  form. 

It  is  probable  that  by  some  chemical  change  analogous  to  this,  soluble  is 
converted  into  insoluble  albumen  in  the  living  body.  All  that  is  required  is 
the  presence  of  a  free  acid  (lactic,  acetic,  or  hydrochloric)  and  chloride  of 
sodium.  A  temperature  of  98°,  which  would  not  alone  suffice  for  the  trans- 
formation, would  in  the  presence  of  these  substances,  bring  about  the  con- 
version. 

It  is  less  easy  to  explain  the  metamorphoses  of  soluble  into  insoluble 
albumen,  during  the  process  of  incubation.  The  temperature  to  which  the 
egg  of  the  hen  is  submitted  at  intervals  for  a  period  of  three  weeks,  is  about 
104°.  Having  examined  a  freshly-laid  egg,  and  another  which  had  reached 
the  22d  day  of  incubation,  we  found  the  following  differences  :  in  the  recent 
egg  the  albumen  was  entirely  soluble  in  cold  water,  and  on  incineration,  iron 
and  phosphate  of  lime  were  found  both  in  the  albumen  of  the  white  and  the 
yelk.  In  the  incubated  egg,  there  was  a  perfectly  developed  chicken,  the 
albumen  of  the  yelk  being  contained  within  its  abdomen.  The  soluble 
albumen  of  the  white,  had  assumed  the  insoluble  condition,  and  existed  in 
the  form  of  feathers,  beak,  claws,  cellular  membrane,  and  of  the  soft  organs 
generally,  the  blood  retaining  a  portion  in  the  liquid  state.  There  was  no 
diflference  in  the  amount  of  iron  and  phosphate  of  lime.  The  shell  was 
thinner  and  more  brittle.  This  metamorphosis  cannot  be  explained  on 
purely  chemical  principles.  These  might  show  how  one  form  of  albumen 
passes  into  another ;  but  no  chemical  theory  can  account  for  the  conversion 
of  one  portion  of  insoluble  albumen  into  feathers,  and  another  portion  into 
cellular  membrane.  We  have  here  an  illustration  of  organization,  or  the 
arrangement  of  matter,  not  according  to  physical  and  chemical  laws,  but  by 
a  force  wholly  dififerent  from  them.  Boerhaave,  writing  in  1727,  says,  in 
reference  to  this  subject :  "All  the  parts  of  a  chick — as  the  blood,  flesh, 
bones,  etc. — are  formed  out  of  the  bare  white  of  egg ;  for  nothing  but  this 
is  consumed  during  the  time  of  incubation  of  the  hen,  the  yolk  all  the  while 
remaining  entire."  The  results  of  incubation  show  that  soluble  is  not  only 
converted  into  insoluble  albumen,  but  that  it  is  convertible  into  fibrin,  as 
muscular  fibre  is  formed,  and  into  gelatinous  tissues,  as  it  exists  in  the  bones 


ACTION    OF    ALKALIES    ON    ALBUMEN.  691 

of  the  chicken.  Farther,  althoufrh  the  soluble  albumen  is,  chemically  speak- 
ing, the  same  in  the  eggs  of  the  chicken  and  the  duck,  and  although  the 
physical  conditions  to  which  the  eggs  are  exposed  are  the  same,  it  is  invari- 
ably found  that  the  albumen  is  converted  into  beak,  claws,  feathers,  muscles, 
and  bones  of  a  bird  resembling  that  of  the  animal  which  produced  the  e»;g. 
The  chicken's  beak  and  feathers  are  not  produced  from  the  albumen  of  the 
duck's  egg,  or  vice  versa.  Those  chemists  who  look  upon  the  vital  force  in 
organic  bodies  as  a  myth,  have  failed  to  explain  these  facts  by  any  reasonable 
suggestion  based  on  the  laws  of  chemistry  or  physics. 

Concentrated  sulphuric  acid  precipitates  an  aqueous  solution  of  albumen 
immediately,  but  redissolves  the  precipitate.  Hydrochloric  acid  acts  in  a 
similar  manner;  when  these  acids  are  diluted,  no  immediate  precipitate 
ensues ;  but  after  some  hours  there  is  a  white  flocculent  deposit. 

Albumen,  even  in  the  coagulated  state,  like  other  protein-compounds, 
dissolves  slowly  in  concentrated  hydrochloric  acid,  at  a  boiling  temperature, 
forming  a  reddish  or  purple  liquid.  When  albumen  has  been  thrown  down 
by  hydrochloric  acid,  it  generally  becomes  reddish  after  washing  and  expo- 
sure to  the  air.  This  tint  is  somewhat  characteristic  of  the  varieties  of 
albumen ;  quill,  horn,  &c.,  exhibit  it  when  boiled  in  the  strong  acids;  almonds, 
cocoanut,  chestnuts,  and  other  substances  containing  vegetable  albumen, 
become  similarly  tinted. 

Nitric  acid  is  the  most  effectual  precipitant  of  albumen,  and  is  generally 
employed  as  a  test  for  its  presence.  Even  in  a  diluted  state,  it  throws  down 
a  white  precipitate  from  an  aqueous  solution  ;  but  this  precipitate  is  quite 
soluble  in  a  large  excess  of  water.  It  may  be,  however,  again  thrown  down, 
when  strong  nitric  acid  is  added  to  the  liquid.  Phosphoric  acid  produces 
different  effects  on  an  aqueous  solution  of  albumen,  according  to  its  state  of 
hydration.  The  monohydrated  acid  throws  it  down  in  white  flakes;  the 
terhydrated  acid,  not  only  does  not  precipitate  it,  but  redissolves  the  former 
precipitate  :  hence  albumen  serves  as  a  test  to  distinguish  these  acids. 

Alkalies. — Albumen  is  soluble  in  aqueous  ammonia,  potassa,  and  soda. 
Alcohol  added  to  the  cold  potassa  solution,  produces  no  precipitate  ;  and 
when  the  alkaline  solution  is  boiled,  the  liquid  becomes  yellow,  but  the 
albumen  is  not  coagulated.  This  alkali,  even  in  the  cold,  however,  alters 
the  chemical  characters  of  liquid  albumen.  Under  common  circumstances, 
acetic  acid  does  not  precipitate  aqueous  albumen  :  but  when  to  the  potassa- 
solution,  a  few  drops  of  acetic  acid  are  added,  a  dense  precipitate  is  imme- 
diately produced.  When  a  concentrated  aqueous  solution  of  albumen  is 
mixed  with  a  strong  solution  of  caustic  potassa  or  soda,  a  gelatinous  com-  ■ 
pound  is  the  result,  which  is  soluble  in  water ;  and  if  this  aqueous  solution 
is  evaporated  at  a  gentle  heat,  pellicles  like  those  which  form  on  boiled  milk, 
gradually  collect  upon  the  surface.  If  the  strong  alkaline  solution  is  boiled, 
ammonia  is  evolved,  and  an  alkaline  sulphide  is  produced  which  blackens  a 
salt  of  lead.  A  portion  of  coagulated  white  of  egg  boiled  with  a  diluted 
alkaline  solution  of  oxide  of  lead,  speedily  blackens  from  evolved  sulphur, 
and  in  this  way  sulphur  may  be  detected  in  quill,  wool,  hair,  in  the  almond, 
and  many  other  vegetable  substances.  Lime,  baryta,  and  strontia  form 
combinations  with  albumen,  which  harden  on  drying.  The  compound 
obtained  by  mixing  slaked  lime  with  white  of  egg,  is  used  as  a  lute ;  it 
resists  to  a  great  extent  the  action  of  acid  fumes. 

Serum  and  the  white  of  egg  are  coagulated  by  the  greater  number  of 
metallic  salts.  Those  of  iron,  copper,  lead,  mercury,  silver,  and  antimony 
yield  precipitates  which  are  compounds  of  albumen  and  the  metallic  oxides, 
hence  albumen  is  a  valuable  antidote  in  cases  of  poisoning  by  metallic  salts. 
The  precipitate  is  usually  soluble  in  an  excess  of  serum  or  white  of  egg,  and 


602  PROPERTIES    OF    COAGULATED    ALBUMEN. 

sometimes  in  the  salt  which  produces  it.  Thus  sulphate  of  copper  readily 
dissolves  the  precipitate,  which  it  first  produces  in  albumen.  When  excess 
of  potassa  is  added  to  a  mixture  of  albumen  and  hydrated  oxide  of  copper, 
a  transparent  solution  of  a  splendid  violet  color  is  obtained  ;  it  may  be 
produced  by  adding  the  alkaline  solution  (either  potassa  or  soda)  to  a  mix- 
ture of  serum  and  solution  of  sulphate  or  acetate  of  copper.  The  oxide  of 
copper  is  not  reduced  to  the  state  of  suboxide  on  boiling  this  liquid.  The 
subacetate  of  lead  is  a  perfect  precipitant  of  all  the  forms  of  albumen  :  one 
part  of  fresh  albumen  of  egg  in  2000  of  water,  is  rendered  turbid  by  this 
reagent.  Subnitrate  of  mercury  is  also  an  effectual  precipitant  of  this 
principle.  Corrosive  sublimate  is  a  delicate  test  of  the  presence  of  albumen ; 
a  liquid  containing  only  a  two-thousandth  part  of  solid  albumen  is  precipi- 
tated by  it.  The  white  precipitate  formed,  is  an  insoluble  compound  of  the 
salt  with  the  organic  substance.  Albumen,  it  is  well  known,  is  the  antidote 
which  is  employed  in  this  form  of  poisoning. 

Kreasote  and  carbolic  acid  cause  copious  precipitates  in  a  solution  of 
albumen.  It  is  not  affected  by  solutions  of  rennet,  which  copiously  coagu- 
late milk.  Ether  rather  gelatinizes  than  coagulates  the  white  of  egg,  when 
the  two  are  shaken  together ;  after  a  time,  a  yellow  liquid  separates,  which 
is  not  coagulated  by  heat,  and  a  spongy  albumen  remains.  When  serum  is 
similarly  treated,  no  such  precipitation  ensues ;  the  mixture  separates  into 
two  portions,  and  the  ether  which  floats  upon  the  surface,  holds  the  oil  of 
the  blood  in  solution. 

The  best  tests  for  liquid  or  soluble  albumen,  are  the  application  of  heat, 
the  action  of  nitric  acid,  and  the  nse  of  ferrocyanide  of  potassium  and  acetic 
acid. 

Coagulated  Albumen. — Albumen,  coagulated  by  heat,  presents  itself  as  a 
white  solid ;  it  dries,  by  exposure,  to  a  horny-looking  substance.  It  is  in 
this  state  identical  in  chemical  properties  with  horn,  hair,  nail,  quill,  wool, 
and  tortoiseshell.  It  is  quite  insoluble  in  water,  alcohol,  and  weak  acids:  it 
is  dissolved  by  strong  acids  and  concentrated  solutions  of  alkalies.  Acetic 
acid  added  to  the  alkaline  solution,  throws  down  the  substance  called  Protein. 
The  alkali  is  supposed  to  abstract  sulphur  and  phosphorus  ;  while  a  previous 
digestion  in  water,  alcohol,  ether,  and  diluted  hydrochloric  acid,  serves  to 
remove  all  soluble  matters  contained  in  the  albumen.  However  carefully 
prepared,  we  have  still  found  sulphur  in  the  precipitate ;  and  the  so-called 
protein,  appears  to  be  nothing  more  than  the  original  albuminous  principle 
somewhat  altered  in  its  properties,  by  the  variety  of  chemical  processes  to 
which  it  has  been  subjected. 

When  protein  or  its  compounds  are  boiled  in  a  moderately  strong  solution 
of  potassa,  until  ammonia  is  no  longer  disengaged,  and  the  liquid,  after  it 
has  cooled,  is  saturated  by  sulphuric  acid,  sulphate  of  potassa  is  formed, 
the  greater  part  of  which  may  be  separated  by  crystallization.  If  the  re- 
maining solution  is  poured  off  and  evaporated  to  dryness,  and  the  residue  is 
boiled  in  repeated  portions  of  alcohol,  this  dissolves  the  organic  products, 
and  leaves  sulphate  of  potassa :  as  the  alcoholic  solution  cools,  it  deposits  a 
brown  oleaginous  matter  {erythroprotide),  and  afterwards,  by  spontaneous 
evaporation,  it  deposits  leucine  (CiaH^aO^N),  and  retains  protide,  mixed 
with  formate  of  potassa  in  solution.  We  have  here  illustrated  the  produc- 
tion of  protein  and  its  derivatives,  by  the  conversion  of  albumen  ;  but  these 
compounds  may  be  equally  obtained  by  treating  in  a  similar  manner,  fibrin, 
casein,  or  horny  tissue. 

Albumen  presents  itself  in  a  variety  of  modifications  in  the  animal  body. 
Under  the  name  of  globulin,  it  partly  constitutes  the  transparent  humors  of 
the  eye,  including  the  crystalline  lens.     The  same  principle  associated  with 


PROPERTIES    or    CASEIN.  693 

coloring-matter,  or  hgematosine,  forms  the  mass  of  the  globules  of  the  blood. 
It  is  soluble  in  acetic  acid  and  alkalies ;  and  is  precipitated  when  either 
solution  is  brought  to  a  state  of  neutrality.  Ptyalin  is  a  modi6cation  of 
albumen  existing  in  saliva.  A  remarkable  property  which  characterizes  this 
principle,  is  its  power  of  rapidly  transforming  starch  and  dextrine  into 
glucose  or  grape-sugar.  If  starch  paste  is  heated  for  a  short  time  to  100° 
with  saliva,  it  is  converted  into  sugar.  Pyin  is  an  albuminous  principle 
found  in  pus ;  Mucin,  in  mucus ;  and  Echidnine,  in  the  viper-poison.  In 
general,  the  differences  are  slight,  but  in  pyin  and  echidnine  formidable 
poisons  are  produced. 

Oysters,  snails,  and  the  bodies  of  molluscous  animals  generally,  are  com- 
pounds of  modified  albumen  and  chondrin.  An  analysis  of  oysters  shows 
that  they  consist,  in  100  parts,  of  water,  80-11 ;  dry  organic  matter  (albumen 
and  chondrin),  18*69;  and  of  saline  matter,  1-2.  In  the  saline  residue, 
besides  chloride  of  sodium,  traces  of  the  iodide  of  sodium  were  found. 

Vegetable  Albumen.  Emulsin. — Albumen  in  the  vegetable  kingdom  is 
generally  associated  with  one  or  more  of  the  following  principles — gum, 
sugar,  starch,  or  oil.  It  may  be  procured  by  macerating  the  succulent  shoots 
of  young  plants  (turnips),  or  bruised  seeds,  like  those  of  the  almond,  in  cold 
water,  allowing  the  liquid  to  clear  itself  by  subsidence,  and  then  filtering  it. 
The  cake  of  the  almond,  after  the  oil  has  been  pressed  out  of  it,  yields  it 
abundantly.  The  liquid  coagulates  by  heat,  and  is  precipitated  by  nitric 
acid,  tannic  acid,  and  a  solution  of  corrosive  sublimate,  precisely  like  animal 
albumen.  It  has  all  the  properties  of  a  weak  solution  of  ovalbumen.  It 
contains  sulphur  and  nitrogen.  When  the  pulp  of  almond  is  boiled  with 
strong  hydrochloric  acid,  it  is  reddened  like  ordinary  albumen  :  when  boiled 
in  a  solution  of  potassa  holding  oxide  of  lead,  it  is  blackened,  thereby  show- 
ing the  presence  of  sulphur.  The  albumen  of  the  almond,  and  of  some  other 
seeds,  has  been  called,  Emulsin,  from  its  property  of  forming  a  white  or 
milky  emulsion  in  water  with  the  oil  of  the  seed.  Emulsin  is  stated  to  differ 
from  albumen  in  several  points.  Thus,  its  solution,  like  that  of  casein,  is 
precipitated  by  acetic  acid :  it  is  coagulated  by  rennet,  and  is  thrown  down 
by  the  terhydrate  of  phosphoric  acid,  which  has  no  action  on  albumen.  The 
term  Synaptase  has  been  applied  to  emulsin  by  Robiquet  (from  ovj/arttw, 
adsum)  in  consequence  of  its  necessary  presence  in  the  conversion  of  amyg- 
daline  into  hydrocyanic  acid  and  hydride  of  benzoyle. 

Casein.  Legumin. 
This  term  is  applied  to  the  coagulable  principle  of  milk,  as  it  is  this  which 
forms  cheese  {caseus).  A  similar  substance  is  occasionally  found  in  the 
blood,  and  in  the  pancreatic  liquids  of  the  ox  and  sheep :  it  occurs  also  m 
vegetables.  It  is  not  found  except  in  the  liquid  state,  and  according  to 
Robin  and  Yerdeil  the  only  liquid  in  which  its  presence  has  been  clearly 
demonstrated,  is  the  milk  of  the  human  being  and  of  animals  of  the  class 
mammalia.  It  is  therefore  a  principle  not  found  at  all  ages,  nor  in  the  male 
sex,  except  under  certain  abnormal  conditions.  100  parts  of  milk  contain 
the  following  proportions  of  casein  in  admixture  with  a  small  quantity  ot 
albumen : — 


Average  human 
"        inferior 
Colostrum 
Cows'  milk 
Dog 


.     3-5  Asses  .  .  .  1-9  to  2-3 

,     2-7  Mares  .  .  •  *          I 

.     4-0  G«'at  .  .  •  4-5  to  6-0 

3  to  7-0  Ewe  .  .  •  •     15-3 


11-3 


0)94  PROPERTIES    OF    CASEIN. 

The  proportion  is  subject  to  variation  according  to  food  and  other  circum- 
stances. Casein  is  in  a  state  of  solution  in  milk,  and  raay  be  procured  nearly 
])ure  by  coagulating  well-skiraraed  milk  heated  up  to  150°  or  160°,  by  a 
few  drops  of  acetic  acid.  The  curd  thus  obtained  is  thoroughly  washed, 
pressed,  and  digested  in  boiling  alcohol,  or  in  ether,  to  deprive  it  of  oil,  and 
then  carefully  dried.  As  it  is  thus  procured,  casein  presents  itself  in  white 
opaque  masses  (curds),  resembling  coagulated  albumen,  but  much  less  firm. 
It  is  without  odor  or  taste,  is  insoluble  in  water,  alcohol,  and  ether,  and 
when  dried  at  a  low  temperature,  presents  itself  in  yellow  horny-looking 
masses.  It  dissolves  in  weak  solutions  of  the  alkalies  and  their  carbonates, 
and  is  thrown  down  from  these  solutions  by  acids :  the  precipitate  is  a  com- 
pound of  the  acid  and  casein,  and  is  soluble  in  an  excess  of  the  acid.  Casein 
is  also  soluble  in  some  saline  solutions,  as  of  common  salt,  sal-ammoniac, 
and  nitre.  Its  compounds  with  the  earths  and  metallic  bases  are  insoluble 
in  water:  hence,  milk  may  be  beneficially  used  as  an  antidote  in  poisoning 
by  many  metallic  salts.  The  casein  of  milk  is  precipitated  by  sulphate  of 
copper.  The  caseate  of  oxide  of  copper  is  redissolved  by  potassa,  forming 
a  violet-blue  solution :  the  oxide  is  not  reduced  to  suboxide  on  boiling  the 
liquid,  unless  sugar  is  present. 

Casein,  or  a  principle  analogous  to  it  (legtimin),  is  contained  abundantly 
in  peas,  beans,  and  the  seeds  of  leguminous  plants ;  it  is  there  associated 
with  starch,  and  in  the  oily  seeds,  with  albumen  and  emulsin.  It  may  be 
obtained  by  digesting  coarsely-powdered  peas  in  cold  or  tepid  water  for  two 
hours,  allowing  the  starch  and  fibrous  matter  to  subside,  and  then  filtering 
the  liquid.  It  forms  a  clear  viscid  solution,  which  is  not  coagulated  by  heat, 
unless  albumen  is  also  present ;  but  like  emulsin,  and  unlike  albumen,  it  is 
precipitated  by  acetic  acid.  It  is  coagulated  by  lactic  acid,  also  by  alcohol ; 
in  the  latter  case  the  precipitate  is  redissolved  by  water.  Casein  is  distin- 
guished from  albumen  by  its  not  coagulating  when  heated  in  a  dilute  solu- 
tion, and  by  being  precipitated  from  its  solution  by  acetic  acid.  On  boiling 
milk  in  air  the  casein  appears  to  become  oxidized  and  rendered  insoluble, 
forming  a  kind  of  skin  on  the  surface  of  the  milk.  Like  albumen,  it  is  pre- 
cipitated by  tannic  acid.  The  fact  that  it  is  coagulated  by  rennet  (the  lining 
membrane  of  the  fourth  stomach  of  the  calf),  as  in  the  process  of  curd  and 
cheese-making,  is  also  one  of  its  distinctive  characteristics.  It  contains 
sulphur,  to  the  amount  of  0'36  per  cent.  (Mulder),  but  no  phosphorus — 
not  at  least  in  the  peculiar  state  of  combination  in  which  that  substance  is 
found  in  albumen  and  fibrin  ;  but  it  appears  to  be  intimately  combined  with  a 
certain  proportion  of  phosphate  of  lime.  The  sulphur  may  be  easily  detected 
in  it,  by  boiling  the  casein  in  a  solution  of  oxide  of  lead  in  potassa.  Like 
albumen  and  fibrin,  casein  is  dissolved  by  strong  hydrochloric  acid  at  a  boil- 
ing temperature,  forming  a  reddish-purple-colored  solution. 

Casein  is  stated  not  to  be  coagulable  by  heat :  but  it  is  found  in  practice, 
that  heat  greatly  facilitates  the  separation  of  the  curd  from  milk  when 
rennet  or  acids  are  employed.  (See  Milk,  p.  til.)  Thus,  in  procuring 
curd  by  rennet  for  the  manufacture  of  cheese,  the  milk  is  heated  to  a  tem- 
perature of  77°  to  86°,  and  at  the  same  time  agitated.  The  casein  separates 
in  a  mass,  with  more  or  less  oil,  according  to  the  richness  of  the  milk.  The 
curds  are  pressed  into  masses,  salted,  and  allowed  to  undergo  a  species  of 
fermentation,  by  which  peculiar  flavors  are  brought  out.  A  rich  cheese 
abounds  in  oil,  a  poor  cheese  in  casein.  The  casein  is  generally  colored  of 
a  pale-yellow  to  an  orange-red  color  by  annotto.  The  method  of  obtaining 
cream  in  Devonshire  and  Cornwall,  furnishes  another  proof  of  the  influence 
of  heat  in  aiding  the  separation  of  casein.  After  the  cream  has  risen  to  the 
surface,  in  a  pan  of  milk,  instead  of  removing  this  by  skimming  or  otherwise 


PROPERTIES    OF    LEGUMIN.      GLUTEN.  695 

disturbing  it,  the  pan  is  carefully  heated  over  a  charcoal  fire,  until  bubbles 
of  vapor  begin  to  appear  in  the  liquid,  below  the  surface.  A  serai-solid 
mass  is  thus  produced,  consisting  of  the  cream,  with  a  very  large  proportion 
of  casein.    The  milk  which  remains  is  of  course  proportionably  impoverished. 

Legumin  is  the  name  specially  applied  to  the  azotized  caseous  principle 
of  peas,  beans,  and  many  similar  seeds :  it  is  considered  to  be  identical  with 
casein  by  Liebig  and  Wohler  (Liebig,  Chim.  Organ.,  iii.  220),  and  with 
emulsin  by  Dumas  and  Cahours  {Ajin.  Ch.  et  Ph.,  1842).  A  solution  of  it 
may  be  obtained  from  ground  peas  by  the  process  above  described.  Acetic 
acid,  diluted  with  8  or  10  parts  of  water,  is  carefully  dropped  into  the  filtered 
solution  and  the  legumin  is  precipitated  :  an  excess  of  the  acid  should  be 
avoided,  as  this  would  dissolve  the  precipitate.  It  falls  in  the  form  of  white 
flakes,  and  after  having  been  washed  on  a  filter,  it  should  be  dried,  pul- 
verized, and  freed  from  adhering  fat,  by  digestion  in  ether.  Legumin  may 
be  obtained  from  lentils  with  the  same  facility  as  from  peas ;  but  it  is  less 
easily  procured  from  beans  (haricots),  in  consequence  of  their  containing  a 
gummy  matter,  which  interferes  with  its  precipitation,  and  with  the  filtra- 
tion of  the  liquids.  The  chemical  properties  of  legumin  are  identical  with 
those  of  casein. 

Liebig  supposes  that  grape-juice,  and  other  vegetable  juices  which  are 
deficient  in  albumen,  derive  their  fermentative  power  from  soluble  legumin. 
This  principle  is  soluble  in  tartaric  acid,  and  to  its  presence  he  ascribes  the 
tendency  of  sugar  to  form  alcohol  and  carbonic  acid,  instead  of  mucilage  and 
lactic  acid. 

Gluten. 

Vegetable  Fibrin. — The  term  gluten  is  applied  to  the  opaque,  white,  tena- 
cious, and  somewhat  elastic  substance  which  is  obtained  by  subjecting 
wheaten  flour  to  the  continuous  action  of  a  current  of  water.  The  best 
mode  of  proceeding  is  to  tie  up  the  flour  in  a  coarse  cloth,  and  knead  it 
under  a  stream  of  water  until  the  starch  and  soluble  matters  are  entirely 
washed  out,  and  the  water  runs  off  clear.  The  residuary  gluten  should  give 
no  blue  color  with  iodine  water.  According  to  some  chemists,  it  consists  of 
three  distinct  substances,  of  which  Vegetable  fibrin  forms  the  largest  pro- 
portion. Gluten,  as  it  is  thus  extracted,  is  a  white  tenacious  substance, 
capable  of  being  drawn  into  long  fibres.  When  dry,  it  becomes  hard,  horny 
and  brittle,  so  thaf  it  is  easily  pulverizable.  Macaroni  is  nearly  pure  gluten 
in  a  dry  state,  but  generally  associated  with  a  little  starch.  Gluten  when 
pure,  undergoes  no  change  of  color  on  the  addition  of  iodine.  It  is  quite 
insoluble  in  water,  but  is  dissolved  by  acetic  acid,  and  a  strong  solution  of 
potassa.  It  is  again  precipitated,  when  the  acid  and  alkaline  liquids  are 
exactly  neutralized.  It  contains  sulphur,  and  is  blackened  when  boiled  in 
a  potassa-solution  of  oxide  of  lead.  It  acquires  a  dark-red  color  when 
boiled  in  strong  hydrochloric  acid.  Bread  and  macaroni,  which  chiefly 
owe  their  nutritious  qualities  to  gluten,  undergo  similar  changes.  In  a 
partially  decomposed  state,  it  forms  yeast,  and  induces  alcoholic  fermentation 
in  saccharine  liquids.  It  also  separates  casein  in  milk  at  a  boiling  tempera- 
ture. In  most  of  the  chemical  characters  here  described  gluten  bears  a  close 
resemblance  to  fibrin. 

Gluten,  like  certain  ozonides,  has  the  remarkable  property  of  rapidly 
oxidizing  the  resin  of  guaiacum,  and  a  solution  of  this  resin  in  alcohol  may 
in  some  cases  be  employed  as  a  useful  test  of  the  presence  of  this  principle. 
If  a  solution  of  guaiacum  in  alcohol  (tincture  of  guaiacum)  is  poured  upon  a 
substance  containing  gluten,  such  as  wheat  flour,  a  beautiful  azure-blue  color 


696  PROPERTIES    OF    GLUTEN. 

is  speedily  brought  out,  even  when  the  flour  is  largely  mixed  with  other 
organic  or  mineral  substances.  It  produces  no  change  of  color  in  starch  if 
free  from  gluten,  in  gum,  or  sugar.  A  small  quantity  of  macaroni  in  powder, 
moistened  with  the  tincture  of  guaiacura,  rapidly  acquires  a  deep  indigo-blue 
color.  If  the  macaroni  is  previously  soaked  in  cold  water,  an  intense  blue 
color  is  produced  immediately  on  the  addition  of  the  tincture.  The  gluten 
appears  to  Jose  this  property  of  oxidizing  guaiacum  by  exposure  to  a  high 
temperature:  thus  tincture  of  guaiacum,  when  added  to  boiled  gluten  (boiled 
macaroni),  produced  no  change  of  color  either  by  itself  or  on  the  addition  of 
a  solution  of  peroxide  of  hydrogen.  When  the  tincture  was  applied  to  the 
crumb  of  aerated  bread,  it  produced  no  blue  color  until  after  the  addition  of 
a  small  quantity  of  peroxide  of  hydrogen. 

The  tenacious  properties  of  dough,  or  the  paste  of  flour,  are  mainly  owing 
to  gluten.  It  is  more  abundant  in  wheat  and  in  rye  than  in  other  cereals, 
and  in  these  grains  the  gluten  has  a  greater  tenacity  than  in  others :  hence, 
they  are  better  fitted  for  making  bread.  Calculated  in  the  dry  state,  gluten 
forms  from  T  to  14  per  cent,  of  wheat  flour,  that  of  Odessa  containing  the 
largest  proportion  (Duma's).  Wheat  grown  in  Algeria  and  other  hot  coun- 
tries contains  a  larger  proportion  of  gluten  than  wheat  grown  in  England  or 
countries  still  colder.  The  hard,  thin-skinned  wheat  contains  more  gluten 
than  the  softer  varieties.  The  proportions  of  gluten  in  100  parts  of  different 
seeds  are  as  follows : — 


Algerian  wheat . 

.     16 

Danzig  wheat 

.     9 

Odessa  wheat     . 

.     15 

Barley 

.     6 

South  Carolina  wheat 

.     14 

Oats    . 

.     6 

English  wheat    . 

.     10-7 

Rye     . 

.     5 

Canadian  wheat 

.      9-8 

Peas    . 

.     4 

The  nutritious  properties  of  the  grain  are  in  proportion  to  the  amount  of 
gluten. 

Gluten,  as  it  is  extracted  from  wheat  flonr,  does  not  appear  to  be  a  pure 
vegetable  principle.  It  contains  cellulose  and  fatty  matter ;  the  latter  may 
be  removed  from  it  by  boiling  alcohol  or  ether.  It  has  been  also  supposed 
to  contain  another  principle,  analogous  to  albumen,  called  Olutin :  but  all 
chemical  analogy  is  destroyed  in  the  process  by  which  it  is  extracted.  If 
gluten  is  digested  first  in  concentrated  and  afterwards  in  weak  alcohol,  in 
which  albumen  is  quite  insoluble,  a  yellow-colored  liquid  is  obtained,  which 
deposits  a  substance  said  to  resemble  casein,  called  vegetable  casein.  'When 
the  alcoholic  liquid  is  poured  off  and  evaporated,  a  yellowish  viscid  extract 
is  obtained,  to  which  the  name  of  gliiti7i  has  been  given.  It  may  be  precipi- 
tated as  a  white  substance  by  the  addition  of  water  to  the  alcoholic  liquid. 
It  still  contains  the  oily  matters  which  existed  in  the  original  gluten.  In 
this  process  the  greater  part  of  the  gluten  remains  unaffected  by  the  alcohol, 
and  this  insoluble  residue  is  called  Vegetable  Jibrm.  It  is  this  substance 
which  has  the  chemical  properties  of  animal  fibrin,  that  gives  to  the  dough 
or  paste  of  wheat  flour  the  peculiar  tenacity  which  allows  it  to  be  converted 
into  wholesome  bread.  This  tenacity  is  especially  observed  in  the  dough  or 
paste  made  from  wheat  and  rye  :  hence  these  grains  are  better  fitted  than 
other  cereals  for  the  making  of  bread.  Gluten  is  exclusively  a  vegetable 
product :  it  abounds  in  nitrogen,  and  thus  resembles  an  animal  principle. 
It  is  the  basis  of  flesh  in  herbivorous  feeders,  and  is  particularly  abundant  in 
hay.  There  is  reason  to  believe  that  it  is  a  complex  compound,  the  chemical 
characters  of  which  have  been  as  yet  but  imperfectly  ascertained.  Dumas 
and  Cahours  have  proved  by  their  analysis  that  the  undissolved  gluten  has 
the  same  chemical  composition  as  dissolved  glutin  ;  the  latter  is,  therefore, 
probably  only  a  small  portion  of  altered  gluten  removed  by  alcohol. 


properties  of  fibrin.  g9t 

Fibrin. 
Under  this  name  a  principle  has  been  described  common  to  animals  and 
Tegetables.     Animal  fibrin  is  obtained  by  agitating  blood,  as  it  flows  from 
the  vessels,  with  a  rod,  to  the  twigs  of  which  it  adheres  in  the  form  of  fibrous 
filaments,  which  may  be  cleansed  of  coloring  and  other  soluble  matters  by 
repeated  washings  in  fresh  portions  of  water.     The  essential  character  of 
this  principle,  as  it  is  contained  in  blood,  is  its  power  of  spontaneous  coagu- 
lation.    From  a  fluid  state  in  this  liquid,  when  removed  from  the  living 
vessels,  it  speedily  passes  into  a  solid  and  insoluble  condition,  assuming  a 
fibrous  or  reticulated  form.     It  undergoes  this  change  in  from  ten  to  twenty 
seconds  when  blood  comes  in  contact  with  threads  and  thin  rods,  or  with  a 
sponge  or  dust  which  can  absorb  water.     In  the  dead  body  it  takes  place 
slowly.    There  have  been  many  hypotheses  on  the  cause  of  this  solidification 
of  fibrin  or  coagulation  of  the  blood,  but  none  of  these  can  be  regarded  as 
furnishing  a  satisfactory  explanation  of  it.    It  has  been  supposed  that  the  loss 
of  a  small  quantity  of  ammonia  was  the  cause,  and  that  it  was  the  presence 
of  one  or  two  thousandths  of  ammonia  in  the  blood  of  the  living  body  which 
caused  it  to  retain  the  fluid  state.     It  has  been  shown,  however,  by  Dr. 
Davy  and  others,  that  healthy  blood  contains  no  appreciable  quantity  of 
ammonia,  and  that  ammonia  added  to  fresh  blood,  in  any  quantity,  did  not 
prevent  the.  fibrin  from  assuming  the  solid  state.    (See  Ed.  Monthly  Journal, 
1859,  vol.  xlv.  p.  537.)     When  ammonia  has  been  found  in  blood,  it  has 
been  probably  the  result  of  incipient  decomposition.     It  is  also  a  curious 
fact  that  ammonia  is  the  only  one  of  the  common  alkalies  which  has  no 
solvent  action   on   fibrin  when  it  has  once  solidified.     The  real  question 
appears  to  be,  not  what  causes  the  solidification  of  fibrin  out  of  the  living 
body,  but  what  causes  its  state  of  liquidity  in  the  body.    Whether  the  blood 
is  exposed  to  heat  or  cold,  whether  it  is  at  rest  or  in  motion,  whether 
exposed  to  air  or  not,  the  fibrin  will  solidify  and  the  blood  coagulate.     The 
only  conclusion  to  which  the  ascertained  facts  lead  is  this  :  In  order  that 
fibrin  should  retain  a  liquid  state,  it  must  be  kept  in  motion  in  a  living 
bloodvessel  at  or  about  a  temperature  of  98°.     If  the  motion  is  stopped  by 
two  ligatures  applied  to  a  vessel,  the  blood  will  coagulate  between  them  :  it 
coagulates  if  effused  into  the  living  textures,  although  it  does  not  escape 
from  the  body.     It  has  been  successfully  injected  by  transfusion  from  the 
vessels  of  one  living  body  into  those  of  another ;  but  if  injected  into  the 
vessels  of  a  dead  body  artificially  heated  to  98°,  it  would  still  coagulate. 
No  chemical  or  mechanical  forces  well  explain  this  phenomenon :  it  furnishes, 
like  the  reparative  power  which  manifests  itself  in  the  living  body  just  when 
it  is  required,  an  irrefragable  proof  of  the  presence  and  incessant  operation 
of  a  vital  force. 

Fibrin  is  found  in  two  other  fluids  of  the  body,  chyle  and  lymph,  and  from 
these  it  separates  as  a  solid  when  the  liquids  are  removed  and  exposed.  The 
proportion  of  fibrin  contained  in  healthy  venous  blood  has  been  variously 
stated  by  different  chemists.  The  average  is  about  2  parts  in  1000,  and  it 
seldom  exceeds  3  parts,  except  in  certain  diseases. 

Proportion  of  Jihrin  in  1000  parts 

Of  venous  blood  (Lehmann) 1-9    to  2-8 

«         «  «       (Scherer) 2-03  to  Z  b6 

"         "  "       (Denis) 2-20 

"       (Lecanu) ^f 

"         "  "       (Reguault) n  ^n  *     n  ro 

"    lymph  (humai)' o'-IS  ''  '*' 

"         "       (horse) l^fl 

chyle    (horse) 

"      (eow) \g 

♦*       (cat) -^  ^" 


(( 


698  PROPERTIES    OF    FIBRIN. 

Andral  and  Gavarret  found  that  the  proportion  of  fibrin  was  increased  in 
some  diseases  and  diminished  in  others.  Assuming  the  normal  average  in 
healthy  blood  at  3  parts  in  1000,  they  give  the  following  as  the  results  of 
their  observations : — 


Acute  rheumatism 

.     5  to  10 

Acute  diseases — 

Pneumouia 

. 

.     5  to  10 

Phlescmasiae 

5 

Bronchitis 

, 

.     6  to  9 

Phthisis  . 

.    4 

Pleuritis     . 

. 

.     5  to  6 

Advanced  phthisis    . 

.     5 

to  6 

Peritonitis 

, 

.     5  to  7 

Eruptive  fevers 

.     1 

to  4 

Typhoid  fever  . 

.     0-9 

to  1 

Properties. — Viewing  this  principle  in  its  chemical  relations,  it  may  be 
observed  that  in  a  humid  state  it  holds  about  75  per  cent,  of  water,  which 
may  be  removed  by  drying.  It  may  be  purified  by  digestion  in  ether,  by 
which  fatty  matter  is  removed,  and  when  dried,  at  240°  it  is  yellowish-gray, 
translucent,  and  horny.  It  is  insoluble  in  water,  but  when  long  boiled,  traces 
of  ammonia  are  evolved,  and  a  liquid  is  obtained  which,  when  evaporated, 
leaves  a  substance  having  the  smell  of  boiled  meat :  it  does  not  gelatinize, 
but  is  precipitated  by  infusion  of  galls.  The  insoluble  portion  resembles 
coagulated  albumen.  When  fresh  fibrin  is  covered  with  water,  it  becomes  in 
a  few  days  viscid,  and  acquires  the  odor  of  old  cheese :  it  produces  ammo- 
niacal  salts,  and  then  the  mixture  gradually  liquefies :  in  this  state  it  is 
coagulated  by  heat,  by  the  addition  of  alcohol,  or  of  solution  of  corrosive 
sublimate,  resembling,  in  these  respects,  serum.  Immersed  in  sulphuric  acid 
diluted  with  five  or  six  parts  of  water,  it  shrinks,  and  a  compound  of  the 
acid  with  fibrin  is  formed. 

When  fibrin  is  digested  in  nitric  acid,  nitrogen  is  evolved,  and  a  yellow 
substance  is  produced,  which  has  been  termed  Xanthoproteic  acid  (Mulder). 
Hydrochloric  acid  at  first  gelatinizes  fibrin,  and  afterwards  forms  with  it  a 
blue  or  purple  liquid,  which,  on  dilution  with  water,  lets  fall  a  white  hydro- 
chlorate  of  fibrin.  When  fibrin  is  immersed  for  about  12  hours  in  water 
slightly  acidulated  with  hydrochloric  acid,  it  becomes  gelatinous,  and  when 
this  jelly  is  triturated  with  water,  it  yields  a  solution  which  coagulates  by 
heat,  is  precipitated  by  ferrocyanide  of  potassium,  and  affords  a  precipitate 
on  the  addition  of  hydrochloric  acid,  not  soluble  except  in  an  excess  of  this 
acid.  These  facts  have  some  bearing  upon  the  theory  of  digestion.  Accord- 
ing to  Dumas  and  Cahours,  water  containing  a  millionth  part  of  hydrochloric 
or  hydrobromic  acid,  gelatinizes  fibrin,  and  if  a  few  drops  of  gastric  juice 
(pepsin)  be  then  added,  it  is  entirely  dissolved  in  a  couple  of  hours  at  a 
temperature  of  96°  to  100°.  Rennet  produced  the  same  effect.  Phosphoric 
acid  with  1  atom  of  water  acts  upon  fibrin  in  the  same  way  as  sulphuric  acid. 
The  acid  with  3  atoms  of  water  converts  fibrin  into  a  gelatinous  mass,  which 
is  soluble  in  water,  and  the  solution  is  not  affected  by  an  excess  of  the  acid. 
Fibrin  is  rapidly  penetrated  by  concentrated  acetic  acid,  and  converted  by 
it  into  a  thick  jelly  soluble  in  hot  water.  When  another  acid  (sulphuric)  is 
added  to  this  solution,  a  precipitate  is  formed,  composed  of  fibrin  and  the 
added  acid.  On  the  addition  of  an  alkali  (potassa),  the  fibrin  is  at  first 
precipitated,  but  it  is  redissolved  by  an  excess  of  the  alkali.  The  fibrin  of 
young  animals  is  more  easily  acted  on  by  acetic  acid  than  that  of  old  ones, 
BO  that  there  is  in  this  respect  a  material  difference  between  the  fibrin  of  veal 
and  of  beef.     (Dumas  ) 

Fibrin  is  soluble  in  weak  solutions  of  potassa  and  soda,  first  becoming 
gelatinous,  and  then  forming  a  yellowish  liquid  which  blackens  silver  and 
oxide  of  lead,  and  exhales  the  odor  of  sulphuretted  hydrogen  on  the  addition 
of  an  acid.  Caustic  ammonia  seems  to  act  upon  fibrin  in  the  same  way  as 
the  fixed  alkalies,  but  its  solvent  action  is  less  energetic.    The  fibriu  of  blood 


NUTRIENT    POWERS    OP    NITROGENOUS    PRINCIPLES.  699 

as  it  issues  from  the  living  body,  i.  e.,  before  it  has  coagulated,  is  soluble  in 
from  6  to  8  parts  of  fresh  serum,  and  also  in  a  saturated  solution  of  sulphate 
of  soda.  All  liquids  which  dissolve  this  principle  (solutions  of  potash,  soda, 
and  acetic  acid)  prevent  the  coagulation  of  the  blood. 

Ferrocyanic  and  ferricyanic  acids  combine  with  fibrin;  the  compounds  are 
obtained  in  the  form  of  white  and  yellow  precipitates,  by  adding  solutions 
of  ferrocyanide  and  ferricyanide  of  potassium  to  the  acetic  solution  of  fibrin. 
The  white  precipitate  is  insoluble  in  the  dilute  acids,  but  the  alkalies  decom- 
pose it,  and  forming  ferrocyanides,  separate  the  fibrin  in  a  gelatinous  form. 
The  yellow  precipitate  (obtained  by  the  ferricyanide)  is  more  soluble  than 
the  preceding. 

An  alkaline  solution  of  fibrin  yields  precipitates  with  several  of  the 
metallic  salts — e.  g.,  sulphates  of  iron  and  copper,  and  corrosive  sublimate. 
They  are  compounds  of  the  respective  oxides  with  the  organic  principle, 
which,  owing  to  this  combination,  loses  all  tendency  to  undergo  putrefac- 
tion. Tannic  acid  precipitates  fibrin  from  its  solutions,  and  the  compound 
(tannate  of  fibrin)  is  imputrescible. 

The  three  nitrogenous  principles,  alhmneii,  Jihrin,  and  casein,  are  the  con- 
stituents of  animal  food  ;  and  the  fact  that  principles  of  a  precisely  similar 
nature  are  found  in  the  vegetable  kingdom,  shows  that,  chemically  speaking, 
there  is  not  that  broad  distinction  between  animal  and  vegetable  food  which 
some  have  imagined.  The  constituents  of  flesh,  i.  e.,  fibrin  and  albumen, 
exist  in  vegetables,  and  from  these  vegetable  principles,  the  flesh  of  herbivora 
must  be  formed.  These  two  principles  find  their  way  directly  into  the  blood 
through  the  medium  of  the  chyle,  the  liquid  product  of  digested  food. 
Gelatin  is  not  found  in  the  blood,  but  it  is  no  doubt  formed  from  it  in  the 
living  body.  With  reference  to  the  human  body,  it  can  be  properly  nourished 
only  by  a  variety  of  food,  to  suit  the  variety  of  textures  of  which  it  is  con- 
stituted. A  theory  was  formerly  propounded  to  the  effect,  that  the  body 
could  be  supported  by  any  one  of  these  nitrogenous  principles,  excepting 
gelatin  ;  but  a  Commission  of  the  French  Academy  reported,  upon  due 
inquiry,  that  this  observation  was  equally  applicable  "to  albumen,  fibrin,  or 
casein,  if  employed  alone ;  and  that  neither  animals  nor  man  should  be  re- 
stricted to  any  course  of  diet  which  does  not  contain  all  the  proximate 
principles  of  the  frame."  (Todd  and  Bowman.)  These  four  principles, 
under  the  influence  of  life,  appear  to  be  convertible  into  each  other.  This 
is  proved  to  some  extent  by  the  process  of  incubation.  The  recently  laid 
Q^^  contains  only  soluble  albumen  and  oil.  When  incubation  is  complete, 
fibrin  and  gelatin  are  found  in  the  muscles  and  soft  parts  of  the  young  bird, 
and  a  large  proportion  of  the  soluble  albumen  has  passed  into  the  insoluble 
state.  Casein,'  as  it  is  contained  in  milk,  is  necessarily  converted  in  the 
living  body  into  the  other  principles. 

It  is  calculated  that  the  human  body  wastes  daily  about  one-twenty-fourth 
part  of  its  entire  weight,  and  another  physiologist  has  drawn  the  conclusion, 
that  the  body  will  lose  in  substance  unless  it  has  supplied  to  it  daily  one- 
twenty-third  part  of  its  weight.  These  averages  must  of  course  be  materially 
afi'ected  by  exercise,  temperature,  age,  and  state  of  health.  The  daily  waste 
compared  with  the  weight  of  the  body  appears  to  increase  in  all  animals  in 
an  inverse  ratio  to  the  size.  The  smaller  the  animal  the  greater  the  pro- 
portionate  waste. 

Gelatin. 

This  principle  is  abundantly  diffused  in  the  animal  kingdom.  It  derives 
its  name  from  the  fact  that  a  hot  solution  of  it,  on  cooling,  sets  into  a  jelly. 
A  principle  similar  to  it  in  gelatinizing  properties  is  found  among  vegeta- 


TOO  FISH    GELATIN.      ISINGLASS. 

bles,  especially  in  certain  kinds  of  algae  and  fuci.  Vegetable  gelatin  (gelose), 
which  has  already  been  described,  is,  however,  eminently  distinguished  from 
that  of  the  animal  kingdom,  by  the  absence  of  nitrogen,  and  by  a  difference 
in  its  chemical  properties.  Animal  gelatin  is  not  included  among  the  pro- 
teinaceous  principles.  When  dissolved  in  potassa,  no  protein-compound  is 
precipitated  from  the  solution,  on  the  addition  of  acetic  acid.  In  constitu- 
tion, also,  it  differs  from  the  other  principles  considered  in  this  chapter. 
When  freed  from  all  impurities,  it  contains  no  sulphur.  Owing  to  these 
marked  distinctions,  it  has  been  theoretically  supposed  to  be  deficient  in 
nutritive  power,  and  to  have  no  claim  to  be  regarded  as  a  flesh-forming  prin- 
ciple. There  are  no  facts,  however,  to  support  this  theory;  on  the  contrary, 
experience  shows  that  gelatin  may  be  a  source  of  nutriment  to  animals, 
although  in  a  less  degree  than  the  fibrin  and  albumen. 

Gelatin  is  characterized  by  its  insolubility  in  cold  and  solubility  in  hot 
water.  It  has  been  supposed  that  this  principle  had  no  independent  exist- 
ence in  the  animal  body ;  but  it  is  found  abundantly  in  all  young  animals, 
in  a  state  quite  distinct  from  albumen,  casein,  and  fibrin,  which  cannot  be 
converted  into  gelatin  by  boiling  water.  It  constitutes  exclusively  the  middle 
portion  of  the  air-bladder  of  the  sturgeon  and  other  fish,  requiring  only 
water  for  its  solution  ;  and  it  exists  ready  formed  in  skin,  in  a  condition  to 
produce  tanno-gelatin,  or  leather,  by  simple  immersion  in  a  solution  of  tannic 
acid.  Cold  acetic  acid  will  also  dissolve  gelatin  from  skin.  There  is,  there- 
fore, no  ground  for  the  statement  that  it  is  generated  by  the  action  of  boil- 
ing water  upon  the  membranous  tissues.  In  some  instances,  owing  proba- 
bly to  its  molecular  condition,  it  requires  a  long  application  of  heat  for  its 
perfect  extraction  by  water  ;  but  in  all  cases,  it  must  be  regarded  as  an 
educt  and  not  as  a  product.  The  term  gelatin  was  long  indiscriminately 
applied  to  all  the  gelatinous  substances,  obtained  by  the  action  of  boiling 
water  on  bone,  cartilage^  and  ligament,  until  Mtiller  pointed  out  the  pecu- 
liarities of  the  product  derived  from  cartilage,  and  appropriated  to  it  the 
name  of  Chondrin.     {Poggend.  Ann.,  xxxviii.  305.) 

To  obtain  common  gelatin,  the  substances  affording  it,  such  as  the  clip- 
pings of  hides,  hoofs,  horns,  calves'  feet,  cows'  heels,  sheep's  trotters,  are 
cleansed  in  cold  water,  and  then  subjected  to  the  action  of  boiling  water. 
The  solution  so  obtained  is  freed  from  fat,  and  from  any  deposit,  by  skim- 
ming and  straining,  and  allowed  to  gelatinize  on  cooling  :  the  jelly  so  formed 
is  more  or  less  colored  and  impure.     It  is  cut  into  slices  and  dried. 

Fish  Gelatin. — Isinglass  (probably  a  corruption  of  hasenhlase,  bladder  of 
the  sturgeon).  This  is  a  variety  of  commercial  gelatin  which  is  largely  con- 
sumed as  an  article  of  food,  and  is  chiefly  prepared  in  Russia,  from  the  air- 
bladders  and  sounds  of  certain  species  of  Acipenser,  or  sturgeon.  The  blad- 
ders are  cleansed,  dried,  and  scraped,  so  as  to  separate  from  them  the  exter- 
nal and  internal  membranes ;  and  without  further  preparation,  the  residue 
forms  leaf  isinglass.  Isinglass  was  formerly  picked  into  shreds,  but  is  now 
usually  cut  into  delicate  filaments  by  machinery.  It  should  be  colorless,  ino- 
dorous, and  tasteless  ;  soluble  in  hot  water  after  a  short  maceration  in  cold 
water  :  and  when  incinerated,  it  should  leave  only  traces  of  phosphate  of 
soda  and  of  lime.  There  are  many  varieties  of  isinglass.  The  Beluga  leaf, 
from  Astrachan,  is  the  best,  while  the  Brazilian  isinglass  is  of  the  worst 
quality.  All  kinds  of  commercial  isinglass  contain  a  certain  amount  of  in- 
soluble albuminoid  matter,  which  is  precipitated  on  cooling  the  hot  solution. 
We  have  found  this  to  amount  to  2  per  cent,  in  the  best  quality,  and  to  as 
much  as  20  per  cent,  in  the  worst.  When  any  of  the  varieties  of  isinglass 
are  refined,  they  yield  the  pure  principle  gelatin,  which  is  identical  with  that 


SKIN  GELATIN.   BONE  GELATIN.  TOl 

obtained  from  the  fresh  skins  of  calves  and  bullocks  by  the  process  mentioned 
below. 

Skill  Gelatin. — A  very  pure  form  of  gelatin  sold  under  the  name  of  Pateyit 
Refined  Isinglass  is  manufactured  from  glue-pieces,  or  the  cuttings  of  the 
skins  of  calves  and  bullocks.  These  are  cleansed  of  fat  and  dirt  by  washing 
in  lime-water  :  they  are  then  sliced  and  digested  in  water,  at  a  temperature 
of  about  200^.  The  gelatinous  liquid,  strained  through  flannel,  is  allowed 
to  cool  until  it  has  acquired  a  proper  consistency.  It  is  then  poured  on  a 
slab  of  wet  slate,  and  when  nearly  set,  the  sheet  of  gelatin  is  transferred  to 
an  open  network  for  the  purpose  of  drying.  It  is  subsequently  damped, 
rolled  into  thin  sheets,  and  cut  by  a  machine  into  fibres  of  various  degrees 
of  thickness.  This  process  applied  to  Brazilian  and  other  impure  kinds  of 
commercial  isinglass,  yields  equally  pure  gelatin.  A  cheaper  form  of  gelatin, 
but  improper  as  an  article  of  food,  has  been  manufactured,  under  a  patent, 
by  digesting  glue-pieces  in  an  alkaline  liquid,  and  afterwards  boiling  down 
the  whole  of  the  tissues. 

Bone  Gelatin. — This  is  obtained  by  heating  ground  or  rasped  bones  with 
water,  under  pressure,  to  a  temperature  of  250^  to  270°  ;  the  liquor  gelati- 
nizes on  cooling,  and  the  jelly  may  be  purified  as  in  the  previous  cases. 
But  the  gelatin  thas  procured  always  retains  an  offensive  odor  when  moist, 
and  a  disagreeable  flavor,  in  consequence  of  the  high  temperature  employed. 
Another  mode  of  obtaining  bone  jelly  consists  in  digesting  the  bones,  pre- 
viously boiled  in  water  to  remove  the  fat,  in  dilute  hydrochloric  acid,  so  as  to 
abstract  the  phosphate  of  lime.  The  animal  part  of  the  bone  is  thus  left, 
having  the  appearance  of  a  tough  flexible  cartilage :  this  is  thoroughly 
washed  in  water,  steeped  in  lime-water,  or  in  a  weak  solution  of  carbonate 
of  soda,  and  again  washed  and  dried.  The  dried  bone-gelatin  may  then  be 
made  into  glue  or  size  by  boiling,  gelatinizing,  and  drying,  as  with  the  other 
forms  of  gelatin.  It  has  been  sold  as  an  article  of  food  in  thin  sheets,  and 
sometimes  colored  to  conceal  its  impurity,  under  the  name  of  French  gelatin. 
It  is  a  variety  of  glue. 

From  whatever  source  obtained,  pure  gelatin  is  colorless,  transparent,  ino- 
dorous, and  insipid :  it  may  have  no  smell  in  the  dry  state,  and  therefore 
it  should  be  tested  by  immersing  a  small  quantity  in  boiling  water.  The 
agglutinated  mass,  if  a  bad  sample,  will  have  the  ofi'ensive  odor  of  glue. 
The  fibre  of  pure  gelatin  is  translucent,  and  when  wetted,  more  or  less 
elastic,  tough,  and  resisting.  It  at  the  same  time  nearly  retains  its  trans- 
parency. The  fibre  of  isinglass,  in  which  gelatin  is  always  associated  with 
albuminoid  matter,  becomes  quite  opaque  when  wetted,  is  inelastic,  and  with- 
out cohesion.  Gel.atin  is  heavier  than  water.  When  heated  it  softens,  then 
shrinks,  and  exhales  a  peculiar  odor,  burning  with  difficulty,  and  exhaling 
the  ammoniacal  odor  of  burned  horn  or  feathers.  Subjected  to  destructive 
distillation,  it  yields  an  abundance  of  carbonate  of  ammonia,  together  with 
the  other  products  of  azotized  organic  matters,  and  leaves  a  bulky  carbon 
difficult  of  incineration. 

In  cold  water,  gelatin  gradually  softens  and  swells,  but  scarcely  dissolves 
until  gently  heated,  and  on  again  cooling  the  solution,  it  forms  a  more  or  less 
firm  jelly.  By  its  solubility  in  hot  water  it  is  distinguished  and  separated 
from  fibrin  and  albitmen.  According  to  Bostock  I  part  of  isinglass  dissolved 
in  100  of  water,  gelatinizes  on  cooling;  but  in  150  of  water  it  remains 
liquid.  We  have  found  that  1  part  to  80  of  water,  was  required  to  produce 
a  moderately  firm  jelly.  This  eff'ect,  as  is  well  known,  varies  much  with  tem- 
perature, so  that  jellies  are  more  easily  prepared  in  winter  than  in  summer. 
The  stiffness  of  the  jelly  is  also  greatly  dependent  upon  the  source  whence 


T02  CHEMICAL    PROPERTIES    OF    GELATIN. 

the  gelatin  was  originally  obtained ;  the  skins  and  tissues  of  old  animals 
yielding  a  stronger  and  firmer  jelly  than  that  derived  from  young  animals. 
The  gelatinous  mass  cannot  be  regarded  as  a  definite  hydrate.  The  water 
slowly  evaporates  or  may  be  imbibed  by  porous  substances,  and  the  gelatin 
then  remains  in  a  dry  state  with  its  original  properties.  The  gelatinous  con- 
dition is  owing  to  physical  causes  and  is  common  to  organic  and  mineral 
matter.  Silica,  alumina,  and  starch,  as  well  as  the  coagulum  of  blood,  may 
be  obtained  in  a  gelatinous  state. 

When  a  solution  of  gelatin  is  repeatedly  warmed  and  cooled,  especially  if 
boiled,  it  gradually  loses  its  tendency  to  gelatinize,  and  it  becomes  more  and 
more  soluble  in  cold  water.  In  spite  of  this  well-known  fact,  some  have 
asserted  that  when  a  hot  decoction  is  made  of  any  animal  matter  and  it  does 
not  set  into  a  jelly  on  cooling,  no  gelatin  is  present.  But  the  proportion  of 
gelatin  may  be  too  small  for  this  purpose,  or  it  may  have  been  exposed  to 
heat  for  too  long  a  time — or  too  strongly  heated.  If  the  substance  is  dis- 
solved by  hot  water — if  the  solution  is  precipitated  by  tannic  acid,  corrosive 
sublimate,  chloride  of  platinum,  and  subnitrate  of  mercury,  these  facts  estab- 
lish that  the  animal  matter  so  dissolved  is  of  a  gelatinous  nature,  although 
when  cooled  it  may  have  a  thin  pasty  or  even  fluid  consistency.  The  so-called 
extract  of  meat  {extractum  carnis)  consists  chiefly  of  altered  gelatin  with 
kreatine,  osmazome,  and  other  soluble  principles  of  flesh.  It  is  obvious 
from  the  mode  of  preparation,  that  they  cannot  contain  either  fibrin  or 
albumen,  the  principal  nutritious  constituents  of  meat.  The  proportion  of 
nutritious  solids  thus  obtained  is  small  :  34  pounds  of  flesh,  containing  nearly 
24  pounds  of  water,  yield  only  1  pound  of  extract,  and  a  large  percentage 
of  this  is  water. 

In  close  vessels,  jelly  may  be  kept  in  cool  weather  for  some  days  without 
change ;  but  in  open  vessels,  it  soon  becomes  mouldy.  It  then  putrefies  and 
exhales  a  disagreeable  ammoniacal  odor.  A  little  acetic  acid  considerably 
retards  these  changes  without  materially  affecting  gelatinization.  The  fresh - 
made  aqueous  solution  is  neutral,  and  should  have  no  smell  or  taste.  A 
solution  of  isinglass  commonly  has  a  slight  fishy  odor  and  taste.  Gelatin  is  not 
soluble  in  absolute  alcohol ;  and  when  alcohol  is  added  to  a  warm  and  strong 
aqueous  solution,  the  gelatin  separates  in  the  form  of  a  white  viscid  substance. 
It  is  insoluble  in  ether,  and  in  fixed  and  volatile  oils.  It  is  dissolved  by 
acetic  acid. 

Gelatin  is  soluble  in  all  the  dilute  acids,  excepting  the  tannic,  diflfering 
essentially  in  this  respect  from  albumen  ;  of  these,  the  acetic  solution  only 
gelatinizes  on  evaporation.  Gallic  acid  gives  no  precipitate  with  it.  When 
the  dilute  nitric  solution  of  gelatin  is  evaporated,  nitrous  gas  is  evolved,  and 
the  residue  deflagrates  just  before  dryness ;  with  strong  nitric  acid,  oxalic 
acid  is  formed.  The  action  of  strong  sulphuric  acid  on  gelatin  is  attended 
by  the  formation  of  leucine,  and  of  a  peculiar  saccharine  product,  which  is 
known  under  the  names  of  glycocol  or  glycocine.     It  is  gelatin-sugar. 

The  dilute  caustic  alkalies,  and  ammonia,  do  not  prevent  the  gelatinization 
of  gelatin,  but  they  often  throw  down  a  portion  of  phosphate  of  lime.  When 
gelatin  is  dissolved  in  a  dilute  solution  of  caustic  potassa,  and  exactly  neu- 
tralized by  acetic  acid,  the  evaporated  liquid  does  not  gelatinize  on  cooling. 
When  boiled  with  caustic  potassa,  ammonia  is  evolved,  and  leucine  and 
gelatin-sugar  are  formed.  Gallic,  acetic,  and  nitric  acids  produce  no  pre- 
cipitate in  an  aqueous  solution  of  gelatin.  The  addition  of  common  salt  or 
other  neutral  salts,  or  of  ferrocyanide  of  potassium,  to  the  acetic  solution, 
does  not  cause  the  precipitation  of  gelatin.  When  gelatin  is  dissolved  in 
a  weak  solution  of  potassa,  acetic  acid  does  not  affect  the  liquid.     When  a 


TANNO-GELATIN.      LEATHER.      LEUCINE.  703 

solution  of  chloride  of  lime  is  added  to  gelatin  in  acetic  acid,  a  turbidness 
is  produced. 

A  solution  of  gelatin  is  not  precipitated  either  by  the  neutral  acetate,  or 
by  subacetate  of  lead.  With  protochloride  of  tin  it  gives  a  flocculent  pre- 
cipitate, but  none  with  the  perchloride.  With  sulphate  of  copper  there  is 
no  precipitate.  A  solution  of  gelatin  is  not  precipitated  by  a  solution  of 
corrosive  sublimate;  if  a  cloud  is  formed,  it  soon  disappears.  Gelatin 
is  not  precipitated  by  solution  of  silver  or  of  gold,  but  chloride  of  platinum 
precipitates  it  and  the  sulphate  of  platinum  throws  it  down  in  brown  viscid 
flakes,  which  blacken  and  become  brittle  when  dried  on  a  filter.  E.  Davy 
recommends  this  as  a  delicate  test  for  gelatin,  detecting  it  in  solutions  too 
weak  to  be  affected  by  tannic  acid,  and  not  liable  to  be  interfered  with  by 
the  presence  of  albumen.  {Phil.  Trans.,  1820,  p.  119.)  Subnitrate  of  mer- 
cury added  to  a  solution  of  gelatin  produces  a  dense  white  precipitate. 
Neither  sulphate  of  alumina  nor  alum  occasions  any  precipitate  in  a  solution 
of  gelatin ;  but  a  mixture  of  chloride  of  sodium  and  alum,  or  a  solution  of 
chloride  of  aluminum,  form  a  white  precipitate :  this  compound  exists  in 
taived  leather. 

Tannic  acid  or  cold  infusion  of  galls  is  a  most  delicate  test  of  the  presence 
of  gelatin ;  when  it  is  added  to  a  solution  of  1  part  of  gelatin  in  5000  of 
water  a  cloud  is  evident,  and  on  dropping  tincture  or  fresh  infusion  of  galls 
into  a  strong  solution  of  gelatin,  a  dense  white  curdy  precipitate  of  tanno- 
gelatin  falls,  which  becomes  gray  when  dried,  is  insoluble  in  water,  and  not 
putrescible.  Mulder  has  described  two  definite  combinations  of  tannic  acid 
with  gelatin:  1,  one  containing  1  atom  of  gelatin  and  1  of  tannic  acid, 
which  is  thrown  down  when  a  great  excess  of  the  latter  is  used ;  and  "2,  one 
containing  3  atoms  of  gelatin  and  2  of  tannic  acid,  formed  when  the  latter  is 
not  added  in  excess.  According  to  Davy,  when  gelatin  is  precipitated  by 
infusion  of  oak-bark,  100  parts  of  the  precipitate  contain  54  of  gelatin  and 
46  of  tannin.  Schiebel  found  that  when  a  solution  of  100  parts  of  gelatin  is 
precipitated  by  a  great  excess  of  an  infusion  of  1  part  of  oak-bark  in  9  of 
water,  it  combines  with  118  parts  of  tannin;  but  when  a  weak  solution  of 
extract  of  oak-bark  is  added  to  a  solution  of  gelatin,  so  as  not  to  precipitate 
the  whole  of  the  latter,  the  precipitate  which  slowly  falls  contains  100  of 
gelatin  and  60  of  tannin.  As  albumen  is  also  precipitated  by  tannic  acid, 
when  this  acid  is  used  as  a  test  for  gelatin,  the  absence  of  albumen  should  be 
previously  ascertained.  Tanno-gelatin  is  identical  with  leather.  In  the 
manufacture  of  leather,  the  precipitate  is  formed  in  the  skin  itself,  by 
immersing  it  first  in  a  weak  and  afterwards  in  a  strong  infusion  of  oak-bark. 
The  albumen  of  the  skin  is  also  at  the  same  time  converted  into  tannate  of 
albumen. 

A  solution  of  fish-gelatin  (isinglass)  has  the  same  properties  as  that  of 
skin-gelatin ;  the  latter  is  not  so  rapidly  dissolved  by  hot  water,  but  it 
dissolves  entirely,  leaving  no  sediment,  like  isinglass.  A  solution  of  bone- 
gelatin  differs  from  both  of  these  in  the  fact  that  as  phosphate  of  lime  is 
soluble  in  gelatin,  oxalate  of  ammonia  produces  a  turbidness  in  its  solution. 
As  isinglass  is  frequently  adulterated  with  bone-gelatin,  oxalate  of  ammonia 
occasionally  produces  a  turbidness  in  its  aqueous  solution.  Under  polarized 
light  a  filament  of  moistened  isinglass  when  examined  by  an  analyzer,  gives 
a  spleadid  display  of  iridescent  colors  owing  to  its  peculiar  organic  structure. 
A  filament  of  gelatin  similarly  treated  and  examined,  gives  a  uniform  band 
of  color  which  is  the  complementary  color  of  the  ground  on  which  it  is  placed. 
Leucine  {C.JI^fi,!^),  so  called  from  its  white  appearance.  This  com- 
pound,  which  bears  some  resemblance  to  cholesterine,  may  be  procured  by 
boiling  gelatin  in  sulphuric  acid,  diluted  with  4  parts  of  water.     It  is  also 


T04  GLYCOCINE        SIZE.       GLUE.       CHONDRIN. 

obtained  with  tyrosine,  when  dry  casein  is  fused  with  its  weight  of  hydrate 
of  potassa.  Tyrosine  (CigH^^OgN)  may  be  precipitated  from  the  lixivium 
by  the  addition  of  acetic  acid.  Leucine  melts  at  350°,  and  undergoes  de- 
composition. This  substance  is  also  known  under  the  names  of  Gaseous  oxide 
and  Aposepedine.  It  may  be  obtained  from  the  fibrin  of  muscle,  from  gluten, 
and  other  nitrogenous  principles. 

Glycocine  (C^HgO^N),  Glycocol.  Gelatin- sugar. — This  is  another  product 
of  the  reaction  of  dilute  sulphuric  acid  on  gelatin  at  a  boiling  temperature. 
It  is  also  procured  as  a  result  of  the  action  of  hydrochloric  acid,  at  a  boiling 
temperature,  on  one  of  the  organic  acids  of  bile,  or  on  hippuric  acid.  It 
assumes  a  crystalline  form,  is  not  very  soluble  in  water,  and  is  insoluble  in 
alcohol  and  ether.  It  has  a  sweet  taste,  but  differs  from  sugar  in  not  under- 
going vinous  fermentation.  When  treated  with  nitric  acid,  no  oxalic  acid  is 
formed  ;  but  a  new  acid,  called  the  Nitro-saccharic,  is  produced.  The  interest 
attached  to  this  product,  lies  in  the  variety  of  sources  from  which  it  may  be 
obtained,  and  in  the  numerous  compounds  which  are  derived  from  it. 

Various  formulae  have  been  assigned  to  gelatin.  That  which  is  now 
generally  admitted  represents  its  constitution  as  Ci3lIioO^N2.  It  contains 
a  large  proportion  of  nitrogen,  but  no  sulphur.  When  pure  gelatin  is  dis- 
solved by  boiling  it  in  a  solution  of  potassa,  containing  oxide  of  lead,  no 
discoloration  is  produced.  The  contrary  statement  appears  to  have  arisen 
from  the  application  of  this  test  to  commercial  isinglass,  which  always  con- 
tains a  certain  proportion  of  albuminoid  tissues.  When  these  have  been 
separated  by  refining  the  isinglass,  the  resulting  gelatin  produces  no  effect  in 
a  potassa-solution  of  oxide  of  lead. 

Sizt  is  usually  sold  in  the  form  of  a  stiff  tremulous  jelly :  it  is  obtained 
chiefly  from  the  waste  of  vellum,  parchment,  and  from  the  skins  of  horses, 
cats,  dogs,  and  rabbits,  and  sometimes  from  fish.  It  is  largely  employed  in 
the  manufacture  of  paper,  and  by  whitewashers,  painters  in  distemper,  paper-- 
stainers,  and  gilders.  Size  has  usually  a  putrid  odor  and  taste,  and  a  brown 
color. 

Glue  is  an  important  article  of  manufacture,  and  differs  in  price  and  quality 
according  to  its  source.  It  is  extracted  from  bones,  muscles,  tendons,  liga- 
ments, membranes,  and  skins,  the  latter  yielding  the  best  glue,  especially 
when  from  old  animals.  The  parings  of  hides  and  pelts  from  tanners  and 
furriers,  the  hoofs  and  ears  of  horses,  oxen,  calves,  sheep,  etc.,  are  employed 
in  the  manufacture  of  glue.  They  are  first  digested  in  lime-water,  washed, 
laid  in  a  heap  to  drain,  and  boiled  in  soft  water ;  the  impurities  are  carefully 
skimmed  off,  and  the  liquid  is  then  strained,  clarified  with  a  little  alum,  and 
allowed  to  settle.  The  solution  is  poured  off  from  the  sediment,  and  boiled 
down  to  a  proper  consistence,  so  as  to  concrete  on  cooling  :  the  glue  is  then 
cut  by  a  wire  into  slices,  which  are  dried  upon  netting.  Good  glue  is  hard, 
brittle,  of  a  uniform  brown  translucency,  and  when  immersed  for  some  time 
in  cold  water,  it  becomes  soft  and  gelatinous,  but  requires  to  be  heated,  in 
order  to  dissolve  and  fit  it  for  use.  It  should  be  heated  over  a  gentle  fire, 
or  in  a  water-bath,  and  it  may  then  be  applied  to  the  moistened  wood  by  a 
stiff  brush  :  it  will  not  harden  in  a  freezing  temperature  ;  the  adhesion  de- 
pends upon  the  absorption  and  evaporation  of  the  superfluous  water. 

Cfhondrin. — This  variety  of  the  gelatinous  principle  constitutes  cartilage, 
as  it  exists  in  the  windpipe,  nose,  and  ear,  as  well  as  in  the  cornea  of  the 
eye,  in  the  ribs,  and  at  the  ends  of  the  long  bones.  It  is  found  abundantly 
in  the  flesh  and  cartilaginous  skeletons  of  fish,  and  from  fish-bones  ;  it  may 
be  readily  extracted  by  boiling  water.  If  sufficiently  concentrated,  the  solu- 
tion sets  into  an  opaque  jelly  on  cooling.     It  is  not  so  soluble  in  hot  water 


COMPOSITION    OF    THE    SOFT    SOLIDS    AND    OP    BONES.  105 

as  gelatin.  An  aqneoiis  solution  of  chondrin  is  precipitated  by  acetic  acid, 
but  the  precipitate  is  dissolved  by  an  excess  of  the  acid.  It  is  precipitated 
by  nitric  and  tannic  acids,  as  well  as  by  sulphate  of  copper  and  acetate  of 
lead.     It  is  not  affected  by  caustic  alkalies.     Its  formula  is  Cg.^U.jgOi^N^. 

The  nitrogenous  principles  which  we  have  here  considered,  build  up  the 
animal  body.  The  soft  solids  of  animals  are  chiefly  formed  of  fibrin,  albu- 
men, and  gelatin. 

Fibrin  enters  largely  into  the  composition  of  muscle  or  flesh ;  thus, 
assuming  that  the  proportion  of  water  varies  from  71  to  74  per  cent.,  the 
fibrin  in  muscle,  averages  from  19  to  22  per  cent.,  and  the  gelatin  from  5  to 
7  per  cent.  In  addition  to  these  constituents,  muscle  consists  of  cellular 
tissue  (albumen),  nerves,  vessels,  and  fat.  Dry  muscle  yields,  by  ultimate 
analysis,  the  same  elements  as  blood.  In  the  juice  of  flesh,  which  is  always 
acid,  crystalline  nitrogenous  principles  exist,  which  may  be  separated  by 
complex  processes.  Among  these  may  be  enumerated  Kreatine  (CgH5,O^N3 
-I-2H0)  and  Kreatinine  (CgH^OaNg) :  this  is  also  a  product  of  the  decom- 
position of  kreatine.  Inosinic  or  Inosic  acid  {Q^^fi^^^^  +  llO)  and  Sar- 
cosine  (CgH^O^N)  are  other  principles,  the  former  being  an  educt  of  the 
juice  of  flesh,  and  the  latter  a  product  of  the  decomposition  of  kreatine. 
Inosin  {C^Jl^^fi^^-^^YiO),  a  variety  of  sugar,  has  been  found  in  the  juice  of 
the  involuntary  muscles.  Osmazome  (dafiij,  odor,  and  ^wjwos,  broth)  is  not  a 
definite  compound,  but  an  alcoholic  extract  of  the  residue  left  by  a  watery 
extract  of  flesh. 

Albumen  enters  into  the  composition  of  muscle,  of  the  brain,  spinal  cord, 
and  nerves.  It  is  1  constituent  of  cellular  tissue,  and  of  the  soft  organs,  such 
as  the  liver,  spleen,  lungs,  and  kidneys.  The  substance  of  the  brain  consists 
of  80  per  cent,  of  water,  with  7  per  cent  of  albumen  in  a  soluble  form.  It 
contains  two  acids,  a  solid  white  fatty  acid  (the  cerebric),  and  an  oily  liquid, 
the  oleophosphoric,  acid.  The  cerebric  acid  contains  phosphorus.  The  waxy 
secretion  of  the  ear  {Cerumen)  is  a  compound  of  albumen  with  an  oily  matter, 
and  a  yellow  bitter  extract,  which  is  soluble  in  alcohol. 

Gelatin  enters  into  the  composition  of  the  skin,  tendons,  ligaments,  and 
the  white  fibrous  tissue  generally,  as  well  as  of  bone,  cartilage,  ivory,  and 
the  teeth  of  animals.  100  parts  of  dry  human  bones  contain  about  33-3  of 
organic  matter  (gelatinous  tissues),  and  66  6  of  earthy  matter,  consisting 
chiefly  of  subphosphate  of  lime  with  carbonate  of  lime  and  phosphate  of 
magnesia.  Fluoride  of  calcium  is  found  only  in  fossil  bones.  The  propor- 
tions of  organic  and  inorganic  matter  vary  slightly  in  the  bones  of  different 
animals,  and  in  the  different  bones  of  the  same  animal.  ^  The  proportions  of 
mineral  and  organic  matter  also  vary  at  different  periods  of  life.  Thu*,. 
according  to  the  analysis  of  Schreger,  in  the  child,  the  earthy  matter  forms 
nearly  one-half  of  the  weight  of  the  bone  (48  48  per  cent.) :  in  the  adult 
three-fifths  (74-84  per  cent.),  and  in  old  age  seven-eighths  (84.10  per  cent.). 
The  bones,  at  this  period  of  life,  contain  much  oily  matter.  The  mode  in 
which  the  organic  and  inorganic  constituents  are  blended  in  the  skeleton,  is 
worthy  of  remark.  When  a  fresh  bone,  e.  g.,  the  scapula,  is  digested  in  dilute 
hydrochloric  acid,  all  the  mineral  matter  is  removed :  but  the  bone  perfectly 
retains  its  shape.  The  residue  consists  of  flexible  and  elastic  gelatinous 
tissue.  If  a  similar  bone  is  carefully  heated  to  a  high  temperature,  under  a 
free  access  of  air,  a  white  brittle  mineral  substance  is  obtained  which  retains 
the  perfect  shape  of  the  bone.  This  consists  of  phosphate  and  carbonate  ot 
lime.     These  results  show  that  every  atom  of  mineral  is-  associated  with  au 


45 


70fi      PROPORTION    OF    FLUIDS    AND    SOLIDS    IN    ANIMAL    BODIES. 

atom  of  organic  raatter.  Bones  contain,  not  merely  in  their  hollow  interior 
{cancelli),  but  in  their  substance,  a  large  quantity  of  oily  matter  which  is 
profitably  extracted  by  simply  boiling  crushed  bones  in  large  caldrons  of 
water.  It  rises  to  the  surface  like  an  oil,  and  is  removed  in  a  solid  cake 
when  the  liquid  has  cooled.  Bone  fat,  or  grease,  is  now  manufactured 
weekly  by  tons  in  this  metropolis.  Its  composition  does  not  differ  from  that 
of  other  animal  fats,  and  it  contains  the  same  principles,  but  rather  a  large 
proportion  of  oleine.  Bone  fat  is  soft,  inodorous,  and  easily  fusible.  It  is 
largely  used  in  the  manufacture  of  pomatum,  "bear's  grease,"  and  other 
cosmetics,  and  is  employed  for  some  of  the  finer  kinds  of  toilet  soaps,  in 
preference  to  other  animal  fats.  When  bones  are  heated  in  close  vessels, 
they  leave  a  porous  charcoal,  which  is  usefully  employed  in  chemistry  and 
the  arts,  under  the  name  of  animal  charcoal. 

Ivory  has  a  composition  similar  to  that  of  bone.  The  dentine  or  bony 
part  of  the  teeth,  contains  from  68  to  70  per  cent,  of  mineral  matter  ;  while 
the  enamel  contains  74  per  cent,  with  6  per  cent,  of  gelatin.  Pearls  and 
mother-of-pearl  contain  66  per  cent,  of  carbonate  of  lime  and  34  of  organic 
matter.  Shell,  coral,  and  madrepore  are  chiefly  composed  of  carbonate  of 
lime  cemented  with  animal  matter.  The  shell  of  the  egg  contains  98  per 
cent,  of  carbonate  of  lime,  and  2  per  cent,  of  organic  raatter.  The  effect  of 
incubation  is  to  render  it  thin  and  brittle. 

In  the  shell  of  the  lobster  and  crab,  the  mineral  matter  appears  to  be 
cemented  by  another  organic  principle,  Chitin  (C^^H^^Oj^N).  It  is  insoluble 
in  water,  but  soluble  in  strong  acids.  It  enters  into  the  composition  of  the 
elytra  of  certain  insects,  e.  g.,  the  cockchafer,  cockroach,  and  beetles. 


CHAPTER    LVI. 

THE   FLUID    CONSTITUENTS   OF    ANIMAL    BODIES,    AND    THE 
SUBSTANCES    DERIVED    FROM    THEM. 

Although  water  is  commonly  regarded  as  a  compound  belonging  to  the 
inorganic  kingdom,  it  is  a  most  abundant,  and  certainly  a  most  important, 
constituent  of  animal  bodies.  At  least  two-thirds  of  the  weight  of  the  human 
body  are  represented  by  water.  If  we  except  the  bones,  this  liquid  forms 
three-fifths  of  the  solid  organs  and  textures,  and  about  four-fifths  of  the  fluid 
■constituents.  The  flexibility,  softness,  elasticity,  and  tenacity  of  the  tissues 
are  due  to  the  presence  of  water.  Fibrin  and  albumen,  when  deprived  of  it, 
lose  their  most  important  physical  properties  as  parts  of  a  living  structure  ; 
and  it  is  a  matter  of  demonstration,  that  without  it,  vital  action  cannot  con- 
tinue. At  p.  544  we  have  given  the  results  of  recent  analyses,  whereby  it  is 
proved  that  some  vegetables  contain  96  per  cent,  of  this  liquid  ;  and  at  p. 
142  we  have  referred  to  the  constitution  of  the  AcalephcB,  animals  which  con- 
tain 99  per  cent.,  and  which  might  almost  be  described  as  living  water. 
From  calculations  based  upon  the  analysis  of  bone,  and  of  the  solid  and  fluid 
constituents  of  the  human  body,  we  find  that  the  body  of  a  male  adult,  weigh- 
ing 150  pounds,  consists  of  water  100  pounds  ;  dry  organic  solids  34  pounds; 
earthy  or  mineral  matter,  chiefly  the  phosphate  and  carbonate  of  lime  and 
chloride  of  sodium,  mixed  with  small  quantities  of  other  earthy  and  alkaline 
salts,  and  oxide  of  iron,  9  pounds  ;  and  of  oil,  or  fat,  7  pounds.     The  amount 


ANIMAL    LIQUIDS.       THE    BLOOD.  707 

of  mineral  mntter  Ims  been  deduced  from  the  actual  weighing  of  dry  adult 
skeletons;  and  the  fat  from  the  calculations  of  Burdach,  who  estimates  it  at 
about  5  per  cent,  of  the  weight  of  the  body.  The  ordinary  analyses  of  the 
solid  and  fluid  constituents,  furnish  the  remaining  elements  of  this  calcula- 
tion. It  is  pyobable  that  the  proportion  of  water  is  even  greater  than  that 
which  is  here  assigned  ;  as  it  is,  it  amounts  in  an  adult  to  100  pounds  or  ten 
gallons !  If  we  carry  this  inquiry  into  the  proportions  of  the  elements,  as 
they  are  known  to  constitute  the  dry  organic  solids  and  the  oil  or  fat,  we 
arrive  at  the  following  results  :  Of  the  41  pounds  of  the  dry  solids  and  of  oil 
or  fat,  carbon  forms  23  pounds ;  oxygen  8  pounds ;  nitrogen  6  pounds ;  hy- 
drogen Bj  pounds;  and  sulphur  and  phosphorus  together  (the  former  pre- 
ponderating), half  a  pound.  This  is  exclusive  of  the  oxygen,  hydrogen, 
carbon,  and  phosphorus,  which  exist  in  the  water  and  mineral  matter. 

The  fluids  of  the  animal  body  may  be  divided,  according  to  their  principal 
chemical  characters,  into,  1.  Those  which  are  at  the  same  time  fibrinous  and 
albuminous ;  2.  Those  which  are  albuminous ;  and  3.  Those  which  are  non- 
albuminous.  Gelatin  is  not  found  in  any  of  the  fluids  :  it  exists  in  the  body 
only  as  a  component  of  the  solid  tissues.  All  the  fluids  in  a  healthy  state 
contain  albumen,  excepting  the  bile  and  urine.  In  certain  diseased  states 
of  the  body,  albumen  is  found  in  the  last-mentioned  liquid.  Casein  exists 
chiefly  in  the  milk,  a  secretion  peculiar  to  the  class  mammalia.  Thejibrinous 
and  albuminous  liquids  are  the  blood,  chyle,  and  lymph. 

The  Blood. 

In  mammiferous  animals,  the  blood  is  of  a  red  color ;  florid  and  approach- 
ing to  scarlet  in  the  arteries,  and  of  a  deep  purple  in  the  veins.  Its  sp.  gr. 
varies  between  1*049  and  1  057,  and  its  temperature  in  the  healthy  human 
body  is  between  98°  and  100°.  It  has  an  unctuous  or  somewhat  soapy  feel, 
a  slightly  nauseous  odor  and  saline  taste,  and  an  alkaline  reaction.  It 
appears  homogeneous,  or  uniform,  whilst  circulating  in  its  vessels,  or  imme- 
diately upon  its  removal  from  them  ;  but  when  examined  by  a  microscope,  it 
is  seen  to  consist  of  numerous  red  particles  or  cells,  varying  from  one-three 
thousandth  to  oae-six  thousandth  of  an  inch  in  diameter,  floating  in  a  color- 
less transparent  fluid  ;  the  former  having  been  termed  the  red  corpuscles,  the 
latter  the  liquor  sanguinis. 

The  corpuscles  of  blood  are  mechanically  diffused  in  the  serum,  in  which 
the  fibrin  is  dissolved.  Under  ordinary  circumstances,  the  blood,  after  it 
has  been  drawn  from  its  vessels,  gelatinizes,  or  coagulates ;  and  the  jelly, 
or  coagulum,  gradually  separates  into  two  parts,  a  liquid  serum,  and  a  soft 
clot  or  crassamentum.  In  the  act  of  coagulation,  the  corpuscles  apparently 
coalesce  and  give  to  the  clot  a  uniformly  red  color.  This  arises  from  the 
tendency  of  fibrin,  when  removed  from  a  living  bloodvessel,  to  assume  the 
solid  and  insoluble  state.  The  particles  of  fibrin  cohere  in  a  sort  of  fibrous 
network,  retaining  the  red  corpuscles  in  the  interstices.  The  proportion 
which  the  clot  bears  to  the  serum  is  variable,  and  is  partly  dependent  upon 
the  shape  of  the  vessel  in  which  the  blood  is  contained.  According  to 
Lecanu,  in  1000  parts  of  healthy  blood,  there  are  869  parts  of  serum  and 
131  of  clot,  which  he  describes  under  the  general  name  of  "globules."  The 
mode  of  procuring  fibrin  and  its  chemical  properties  have  been  already 
described  (p.  698).  The  corpuscles  consist  of  an  envelope  or  membrane 
holding  a  liquid  of  an  albuminoid  nature  {globulin,  p.  692),  deeply  tinged  by 
a  very  small  proportion  of  an  organic  coloring-matter  (hamatosme,  C^jH.jg 
NgOfiFe).     The  proportion  of  fibrin  in  recent  healthy  blood  is  from  2  to  3 


T08        H^MATOSINE.       RED    CORPUSCLES.      COLORING- MATTER. 

parts  in  1000  by  weight,  and  the  proportion  of  coloring  principle  (Jisematosine) 
is  rather  less  than  this.  The  clot  (or  globules  of  Lecanu)  may  therefore  be 
considered  to  be  thus  constituted  in  1000  parts  of  blood  : — 

Fibrin 2-948 

Hsematosine  (coloring  matter)    ....         2-270 
Globulin  (albumen) 125-627 

130-845 

Arterial  blood  has  not  been  found  to  contain  more  fibrin  than  venous 
blood,  but  capillary  blood  contains  less  than  either.  With  the  exception  of 
color,  there  is  no  marked  physical  or  chemical  difference  between  arterial 
and  venous  blood.  If  blood  freshly  drawn  is  bottled  and  well  secured,  it 
may  be  kept  for  many  years  without  undergoing  any  material  change  in 
color.  It  loses  its  power  of  spontaneous  coagulation,  but  the  red  coloring 
matter  when  diluted  with  water  retains  its  bright  red  color,  and  its  usual 
chemical  properties.  No  corpuscles  could  be  seen  under  the  microscope. 
In  opening  a  bottle  after  keeping  it  for  some  years,  there  was  a  slight  smell 
of  sulphuretted  hydrogen. 

Hcematosine.  Coloring -matter. — This  consists  of  small  corpuscles,  blad- 
ders, or  flattened  cells,  containing  a  red  coloring  principle  combined  with 
globulin.  It  is  to  their  great  number  and  aggregation,  that  the  blood  owes 
its  red  color.  In  the  mammalia,  they  are  not  spherical,  hence  the  term 
globule  is  inappropriate.  They  are  disks  of  the  shape  of  a  circular  double 
concave  lens,  being  thicker  at  the  circumference  than  in  the  centre.  In  the 
Camel  tribe,  they  are  of  an  oval  form,  but,  in  these,  as  in  other  mammalia, 
there  is  no  nucleus.  In  birds,  reptiles,  and  fishes,  they  are  of  an  oval  shape, 
and  have  a  nucleus  in  the  centre.  Their  size  bears  no  proportion  to  the  size 
of  the  animal.  They  have  the  same  size  and  form  in  the  human  being  at  all 
stages  of  growth ;  but  the  average  size  varies  in  different  animals.  They 
are  larger  in  man  than  in  most  domestic  animals,  while  they  are  smaller  in 
the  sheep  and  goat  than  in  the  pig,  hare,  and  rabbit.  In  man,  they  have 
an  average  diameter  of  1-3500  of  an  inch  :  in  the  goat  of  l-6366th  of  an 
inch.  A  cubic  inch  of  blood  weighing  about  half  an  ounce,  contains  about 
sixty-four  thousand  millions  of  these  blood-cells  or  corpuscles. 

Miiller  found  that  these  corpuscles  were  so  large  in  the  blood  of  a  frog 
(1-27 45th  of  an  inch),  that  they  might  be  separated  by  filtration.  The 
liquor  sanguinis  passed  through  the  filter,  and  the  fibrin  separated  sponta- 
neously from  the  albumen,  in' a  colorless  state.  In  the  blood,  there  are  also 
colorless  nucleated  corpuscles  of  a  spherical  form  which  are  rather  larger  than 
the  red  corpuscles.  They  are  similar  to  the  nucleated  particles  found  in 
lymph  and  chyle. 

The  red  corpuscles  in  human  blood  have  a  sp.  gr.  of  10885,  and  as  the 
sp.  gr.  of  serum,  in  which  they  are  diffused,  is  1-030,  they  have  a  tendency 
to  sink  in  this  liquid.  The  corpuscles  may  thus  be  collected  and  examined 
in  serum,  which  does  not  dissolve  the  coloring-matter,  as  it  is  contained  in 
them.  The  coloring -matter  is  an  organic  principle  containing  nitrogen  and 
iron  in  some  unknown  state  of  combination.  It  has  an  intense  coloring 
power;  and  on  the  breaking  of  the  outer  membrane  of  the  corpuscles,  the 
red  color  is  diffused  and  communicated  to  water  or  other  liquids.  The  pro- 
portion of  iron  has  not  been  accurately  determined,  but  it  is  supposed  to 
form  from  0*43  to  05  per  cent,  of  the  dried  corpuscles,  or  6  per  cent,  of  the 
pure  coloring-matter.  The  albuminous  principle,  glolaulin,  is  dissolved  by 
water,  hence  an  aqueous  solution  of  the  coloring-matter  always  contains  a 
portion.     It  may  be  separated  by  a  mixture  of  alcohol  and  sulphuric  acid, 


ANALYSIS    OP    VENOUS    BLOOD.  709 

hy  which  globulin  is  coagulated,  while  the  coloring-matter,  as  it  is  supposed, 
is  unaffected. 

An  aqueous  solution  of  the  coloring-matter,  when  recent,  has  an  intensely 
red  color,  and  a  peculiar  odor :  it  is  quite  neutral.  When  the  solution  is 
heated  to  about  150°,  the  haematosine  is  coagulated  and  destroyed,  the 
liquid  assuming  a  muddy  brown  color.  It  is  now  rendered  quite  insoluble 
in  water.  Nitric  acid  and  chlorine  destroy  the  red  color,  turning  the  liquid 
brown  and  greenish  brown.  Weak  alkalies  (ammonia)  in  small  quantity, 
have  no  effect  upon  the  color.  In  excess  they  darken  it.  Neutral  salts  pro- 
duce no  change  in  it.  Alcohol  and  tannic  acid  render  the  solution  turbid,^ 
but  do  not  destroy  the  red  color. 

The  serum  of  blood  is  a  pale  straw-colored  albuminous  liquid,  of  a  slightly 
alkaline  reaction.  Its  sp.  gr.  is  1*030:  it  contains  about  90  per  cent,  of 
water.  It  sets  into  coagulura  when  heated  to  about  160°.  Its  properties 
have  been  already  described  under  the  head  of  seralbumen  (p.  689). 

The  blood  contains  fatty  and  saline  matters,  the  latter  consisting  chiefly 
of  alkaline  chlorides  and  phosphates.  Its  composition  concisely  stated 
would  therefore  stand  thus,  according  to  recent  analysis  (Regnault)  : — 

ANALYSIS  OF  VENOUS  BLOOD  IN  100  PARTS. 

Clot  or  crassamentum     ....       13-0 
Serum 87'0 

100-0 

(Fibrin 0-30 

Clot      -<  r^,  ,    ,       (  Hgeraatosine      ....       0*20 
I  Globules  lenobulin  ....     12-50 

13-00 

f  Water 79-00 

.    cj  !  Albumen 7-00 

Serum    \  ^^.^^  ^^  ^^^^^  matters  ....       0-06 

t^  Chloride  of  sodium  and  other  salts     .         .       0-94 

100-00 

The  use  of  the  blood  is  to  maintain,  by  its  incessant  distribution  to  all 
parts  of  the  body,  the  life  of  an  animal.  It  has  been  described  as  "liquid 
flesh"  (BoRDEu)  :  it  contains  the  animal  solids  in  a  state  of  solution ;  and 
analysis  shows  that  blood  and  flesh  yield  as  nearly  as  possible,  the  same 
elements  in  the  same  proportions.  The  daily  waste  of  the  blood  is  supplied 
by  the  chyle.  With  the  exception  of  chyle  and  lymph,  all  the  fluids  and 
solids  of  the  body  are  formed  by  the  blood,  and  at  the  expense  of  its  con- 
stituents. On  the  other  hand,  in  the  formation  of  the  body  of  the  young 
bird,  during  the  process  of  incubation,  blood,  with  its  usual  constituents, 
fibrin  and  hsematosiue,  is  actually  produced  from  soluble  albumen.  That 
such  widely  different  products  as  milk,  bile,  and  urine,  should  be  produced 
in  the  living  body  from  the  constituents  of  this  fluid,  with  such  remarkable 
uniformity  and  regularity,  is  one  of  those  marvels  of  vital  chemistry  which 
science  cannot  explain.  ,  .        .«   , 

Tests  for  5/oorf —Blood-stains  on  articles  of  clothing  may  be  identihed 
—1  By  their  peculiar  crimson-red  color.  2.  By  the  shining  and  raised 
surface  of  the  stain  or  spot  (dried  albumen  and  fibrin).  3.  By  their  ready 
solubility  in  water,  to  which  they  give  a  red  color.  The  water  under  these 
circumstances  contains  albumen,  as  well  as  haematosine.  ^^^f.'^/"'!"?!* 
does  not  change  the  red  color  to  a  blue,  green,  or  crimson  tint.  When 
boiled,  the  albumen  and  hsetnatosine  are  both  coagulated,  and  the  red  co  or 
is  entirely  destroyed  ;  a  muddy  brown  coagulum  subsides,  which  is  quite  m- 


TIO  ANALYSIS    OF    VENOUS    BLOOD. 

soluble  in  water  and  alcohol.  For  the  examination  of  small  stains  in  a  dry 
state,  an  inch  power  of  the  microscope  will  be  found  convenient. 

By  employing  a  small  quantity  of  water  on  a  glass  slide  in  order  to  dissolve 
the  stain,  the  clot  may  be  broken  up  and  the  red  corpuscles  separated.  These 
may  be  examined  by  a  qunrter-inch  power  under  the  microscope.  When 
detected,  the  evidence  of  the  presence  of  blood  is  placed  beyond  doubt. 
Xo  other  red  coloring-matter,  vegetable  or  animal,  owes  its  color  to  cor- 
puscles or  cells.  A  small  quantity  of  glycerine  added  to  the  water  which  is 
used  as  a  solvent,  prevents  it  from  drying  too  rapidly.  The  red  coloring- 
matter  of  the  blood  differs  from  all  other  red  coloring-matters,  animal  and 
vegetable.  It  is  very  soluble  in  water  as  it  issues  from  the  corpuscles,  and 
has  an  intense  tinctorial  power,  so  that  a  few  drops  of  blood  will  give  a  red 
tint  to  a  large  quantity  of  water.  When  exceedingly  diluted,  the  water  has 
a  very  pale  red  color.  Even  in  this  diluted  state  its  optical  and  chemical 
properties  are  highly  characteristic.  When  such  a  solution  is  examined  by 
a  spectroscopic  eye-piece  attached  to  the  microscope,  two  black  and  well- 
defined  absorption  bands  appear,  one  of  them  at  the  junction  of  the  yellow 
with  the  green,  and  the  other  traversing  the  green  ray  about  its  centre. 
By  acting  on  blood  with  sulphate  of  iron  and  other  chemicals,  other  bands 
characteristic  of  blood  may  be  made  to  appear.  No  other  red  coloring- 
matters  produce  spectra  with  bands  similar  in  number  or  position  to  those 
observed  in  the  blood.  Mr.  Sorley,  of  Sheffield,  has  brought  this  branch 
of  science  to  a  very  perfect  state,  and  has  been  able  to  prove,  by  a  series  of 
ingenious  experiments,  that  even  when  other  red  coloring-matters  are  mixed 
with  blood  so  as  to  conceal  the  blood-spectra,  these  may  be  again  brought 
out  by  the  use  of  an  alkaline  sulphite  which  destroys  the  foreign  coloring- 
matter  without  materially  affecting  the  optical  properties  of  blood. 

Another  remarkable  property  of  the  red  coloring-matter  of  blood  is  mani- 
fested in  its  action  on  the  precipitated  resin  of  gnaiacum.  A  small  quantity 
of  blood  added  to  the  precipitated  resin  of  gnaiacum,  produces  no  change 
of  color.  A  solution  of  peroxide  of  hydrogen  treated  with  the  red  coloring- 
matter  of  blood,  or  with  a  drop  of  the  tincture  of  gnaiacum  separately,  pro- 
duces no  other  effect  than  a  slight  reddish  tint  in  the  liquid  ;  but  if  to  a 
mixture  of  coloring-matter  of  blood  with  gnaiacum  resin  we  add  a  few  drops 
of  peroxide  of  hydrogen,  or  any  liquid  containing  it,  a  beautiful  blue  color 
is  brought  out  as  a  result  of  the  speedy  oxidation  of  the  resin.  For  the 
production  of  this  change  the  three  substances  must  be  together,  but  it 
matters  not  in  what  order  they  are  mixed.  So  delicate  is  this  test,  that  a 
quantity  of  blood  in  water,  not  suflBcient  to  give  a  red  stain  to  paper  or 
linen,  will  be  indicated  by  the  production  of  a  blue  color  under  these  cir- 
cumstances. Other  red  coloring-matters — e.  g.,  cochineal,  the  red  color  of 
rose-leaves,  red  wine.  Brazil-wood,  &c. — produce  no  such  effect  on  the  addi- 
tion of  peroxide  of  hydrogen.  The  persulphocyanide  of  iron  blues  the  resin, 
hut  this  is  owing  to  the  iron  salt,  and  the  bluing  takes  place  without  requiring 
the  addition  of  peroxide  of  hydrogen.  The  peculiarity  of  this  mode  of  test- 
ing depends  on  the  fact  that  neither  blood  nor  peroxide,  used  separately, 
has  any  effect  upon  the  resin  ;  but  when  used  together,  they  bine  it.  Other 
substances  turn  it  blue,  but  they  produce  this  change  of  color  at  once,  and 
without  the  addition  of  peroxide  of  hydrogen.  On  the  other  hand,  the  cochi- 
neal and  vegetable  red  coloring-matters,  so  far  as  they  have  been  examined, 
have  no  coloring  action  upon  the  resin,  even  when  peroxide  of  hydrogen  is 
added  to  the  mixture.  This  mode  of  testing  was  first  suggested  by  Van 
Pi'cu,  and  he  recommended  the  ozonized  oil  of  turpentine.  Dr.  Day,  of 
Geelong,  recommended  and  first  successfully  used  ozonized  ether,  and  proved 
that  this  really  contained  antozone;  but,  when  jt  can  be  procured,  a  solution 


COMPOSITION    OF    CHYLE    AND    LYMPH.  711 

of  pure  peroxide  of  hydrogen  will  be  found  a  better  liquid  for  employment. 
It  is  remarkable  that  when  the  colorino;.iuatter  has  undergone  the  action  of 
glacial  acetic  acid  and  chloride  of  sodium  to  produce  crystals,  it  still  ])os- 
sesses  the  power  of  bluing  a  mixture  of  resin  and  peroxide,  although  much 
more  slowly. 

It  would  carry  us  far  beyond  the  limits  of  this  work  if  we  entered  into 
more  minute  details  on  the  chemistry  of  the  blood.  No  treatise  on  the 
science  can  supply  the  special  information  now  required  by  students  of  medi- 
cine on  the  physiological  and  pathological  chemistry  of  this  important  fluid. 
We  therefore  advise  the  reader  who  desires  further  information  to  consult  one 
of  those  numerous  monographs  which  have  been  published  on  the  subject. 

Chyle. 

This  is  a  milky-looking  liquid  which  is  found  in  the  thoracic  duct.  It  has 
an  alkaline  reaction.  It  appears  to  consist  of  oily  matter  in  a  state  of  emul- 
sion, with  an  albuminous  liquid.  Under  the  microscope,  oil-globules  and 
colorless  nucleated  globules  (chyle-globules)  are  visible.  A  fibrinous  clot, 
which  amounts  to  from  1  to  6  per  cent,  of  the  liquid,  separates  by  sponta- 
neous coagulation,  as  in  the  blood,  and  no  doubt  owing  to  the  same  cause — 
^.  e.,  the  natural  tendency  of  this  principle,  when  not  in  free  motion  in  a 
living  vessel,  to  assume  a  solid  and  insoluble  state.  An  analysis  made  by 
Dr.  Rees  shows  that  100  parts  of  healthy  chyle  consist  of  7 '08  albumen, 
with  traces  of  fibrin,  extractive  matters  (undefined),  1'08;  fatty  matters, 
0-92;  chloride  of  sodium  and  other  salts,  0-44;  water,  90-48.  The  chyle 
conveys  the  elements  of  nutrition  immediately  into  the  blood  by  means  of 
the  thoracic  duct. 

Lymph. 

The  fibrin  and  albumen  in  this  liquid,  as  it  is  circulated  in  the  lymphatics, 
are  generally  stated  not  to  exceed  1  per  cent.  In  an  analysis  of  lymph  made 
some  years  since,  we  found  the  liquid,  which  was  feebly  alkaline,  to  consist 
of  albumen  and  fibrin,  2 ;  saline  matters,  2 ;  water,  96. 

The  albuminous  liquids  are  very  numerous,  and  comprehend  all  the  secre- 
tions of  the  body,  excepting  bile.  They  are  either  alkaline  or  neutral, 
generally  the  former,  and  their  principal  saline  ingredients  are  chloride  of 
sodium,  carbonate  of  soda,  and  the  phosphates  of  soda  and  lime.  The  most 
important  of  these  liquids  is  the  milk,  which  is  secreted  from  the  blood  by 
the  mammary  glands,  and  is  necessary  to  the  nourishment  of  the  young  of 
the  class  mammalia. 

Milk. 

This  is  an  opaque  white  liquid  consisting  of  water,  casein  with  some  albu- 
men, sugar  (lactine)  with  lactic  acid,  oil  (butter),  and  salts.  When  examined 
by  the  microscope,  it  is  found  to  contain  oil-globules  of  various  sizes,  floating 
in  a  clear  liquid  (serum  or  whey).  These  globules  are  remarkable  for  their 
perfect  sphericity  in  all  respects,  as  well  as  for  the  brightness  of  their  middle 
portions  in  contrast  with  the  dark  circumference,  an  optical  effect  depending 
probably  on  the  refractive  power  of  the  oil,  which  appears  to  be  containea 
within  a  transparent  membrane.  The  opacity  of  milk  is  owing  to  the  number 
and  diffusion  of  these  oil-globules,  which  vary  in  duameter  from  ^^u  l^  to 

^  th  of  an  inch  They  give  to  the  liquid  the  character  of  an  emuU  on, 
llirL  pi^dilced  when  tL'pulp  of  the  alJ^ond  is  mixed  with  wate.  When 
milk  is  allowed  to  stand,  it  separates  spontaneously  into  two  P«''tions.  1  he 
oil-globules,  by  reason  of  their  low  specific  gravity,  collect  upon  the  surface, 


712  ANALYSIS    OF    MILK.      ITS    COXSTITUENTS. 

forming  cream.  The  richness  of  milk  is  determined  by  the  relative  thickness 
of  this  stratum,  and  for  this  purpose  the  milk  is  placed  in  a  graduated  tube 
called  a  lactometer,  by  means  of  which  the  proportion  of  cream  may  be  at 
once  determined. 

The  oil-globules  are  not  dissolved  by  ether  on  simple  agitation  with  milk. 
If  a  little  acetic  acid  is  added,  and  the  liquid  boiled,  the  membrane  is  dis- 
solved by  the  acid,  and  the  oily  portion,  as  it  is  set  free,  is  dissolved  by  the 
ether.  Butter  is  the  result  of  the  aggregation  of  the  oil-globules.  The 
separation  of  the  oil  in  this  form  is  commonly  effected  by  the  process  of 
churning,  which  consists  in  the  mechanical  agitation  of  the  cream  at  a 
moderate  temperature.  The  milk  of  all  animals  is,  in  its  normal  state, 
neutral ;  although  it  very  soon  exhibits  acidity  when  exposed  to  air,  in  con- 
sequence of  the  formation  of  lactic  acid.  This,  after  a  time,  causes  the 
separation  of  casein  in  the  form  of  coagulura.  The  sp.  gr.  of  milk  varies ; 
that  of  the  cow  is  generally  about  1-030.  It  fluctuates  in  different  animals, 
according  to  Brisson,  from  1  0203  to  r0409;  but  as  it  is  affected  by  the 
presence  of  the  butter  on  the  one  hand,  which  diminishes,  and  by  the  casein 
and  salts  on  the  other,  which  increase  its  density,  it  is  difficult  to  estimate  a 
mean.  According  to  Berzelius,  the  sp.  gr.  of  skimmed  milk  is  1-033  ;  that 
of  cream,  1-024. 

Some  of  the  principal  properties  of  milk  are  due  to  the  presence  of  casein^ 
the  chemical  peculiarities  of  which  have  already  been  described  (p.  637). 
Fresh  milk  does  not  coagulate  when  boiled,  A  firm  and  coherent  pellicle 
forms  upon  the  surface  when  it  is  boiled  in  air,  as  the  result  of  the  oxidation 
of  a  part  of  the  casein;  and  on  the  removal  of  this,  a  fresh  pellicle  is 
formed  ;  but  there  is  no  coagulum.  In  this  form,  casein  is  insoluble  in  water. 
By  direct  analysis,  we  found  that  100  parts  of  good  cow's  milk  yielded  of 
water  86"4,  organic  matter  12-6,  and  saline  matters  1.  The  proportions  of 
oil,  casein,  and  sugar  are  subject  to  great  variation  in  different  animals,  as 
well  as  in  the  same  animal,  according  to  its  state  of  health  and  the  substances 
on  which  it  feeds.  The  milk  is  sometimes  a  source  of  elimination  of  noxious 
substances  which  may  have  been  taken  in  the  food.  According  to  Regnault, 
the  following  represents  the  constitution  of  100  parts  of  this  liquid  in  various 
animals : — 


Cow. 

Ass. 

Goat. 

Mare. 

Bitch. 

Human  Fern, 

Water 87-4 

90-5 

82-0 

89-6 

6(J-3 

88-6 

Oil  or  butter     .         .         .         .4-0 

1-4 

4-5 

traces. 

14-0 

2-6 

Lactine  and  soluble  salts           .     5-0 

6-4 

4-5 

8-7 

2-9 

4-9 

Casein,  albumeu, and  fixed  salts     3-6 

1-7 

9-0 

1-7 

16-8 

3-9 

100-0     100-0     100-0     100-0       100-0       100-0 

The  salts  of  the  milk  are  here  chiefly  included  in  the  weight  of  the  casein 
and  albumen.  They  amount  to  only  0  37  per  cent.,  of  which  018  are  phos- 
phate of  lime,  and  0  1 35  chloride  of  sodium.  The  phosphates  of  magnesia, 
soda,  and  iron  are  found  in  traces,  as  well  as  carbonate  of  soda.  It  is  stated 
by  some  authorities  that  casein  contains  no  phosphorus ;  but  it  is  certain 
that  phosphates  are  rather  abundantly  obtained  in  the  ash. 

The  colostrum,  or  milk  as  it  is  first  secreted,  is  thicker  than  milk,  and  of  a 
yellowish  color.  Under  the  microscope,  it  presents  oil-globules,  mucus,  and 
granules  of  an  irregular  shape.  It  contains  17  per  cent,  of  solid  matters, 
including  casein.  The  analysis  of  cream  shows  that  it  consists  of  about 
equal  parts  of  butter  and  casein,  with  a  variable  quantity  of  serum  or  whey. 
The  adulteration  of  milk  chiefly  consists  in  the  addition  of  water.  It  may 
be  discovered  by  the  lowering  of  the  specific  gravity,  and  by  the  deficiency 
of  oil-globules  under  the  microscope. 


MILK.      LACTINE.      LACTIC    ACID.  V13 

The  casein  of  milk  may  be  separated  by  warmiiif^  the  liquid  and  addin<r  a 
few  drops  of  acetic  or  any  other  acid  :  in  this  case  the  casein  combines  whh 
the  acid  (p.  693).  The  action  of  rennet  is  remarkable.  This  substance, 
which  consists  of  the  inner  membrane  of  the  fourth  or  dij^esting  stomach  of 
the  calf,  when  added  to  1800  parts  of  milk  heated  to  122°,  causes  a  perfect 
separation  of  the  whole  of  the  casein  in  flaky  masses,  a  pale  and  yellowish 
watery  liquid  remaining,  which  is  the  whey  or  serum,  sometimes  entirely 
deprived  of  the  casein.  This  is  probably  effected  by  the  action  of  the 
organic  principle,  pepsine. 

The  watery  portion,  or  whey,  i.  e.,  the  serum  of  milk,  is  neutral,  but  some- 
times acid.  It  is  rendered  opaline  by  heat,  owing  to  the  presence  of  albumen  ; 
also  by  acetic  acid,  if  any  casein  remains.  It  has  a  specific  gravity  of  1  02T, 
and  contains  94  4  per  cent,  of  water.  It  is  abundantly  precipitated  by 
tannic  acid  and  by  other  compounds  which  act  on  albumen.  Oxalate  of 
ammonia  generally  throws  down  a  precipitate  of  oxalate  of  lime,  owing  to 
the  presence  of  phosphate.  The  butter,  or  oil,  which  is  remarkable  for  its 
fusibility  at  a  low  temperature  (70°),  is  a  compound  of  various  fatty  princi- 
ples, which  have  been  already  described  (p  ()2T).  By  saponification,  these 
principles  form  fatty  acids,  including  butyric  acid. 

The  fact  that  milk  is  the  food  of  all  young  mammalia  in  the  first  stage  of 
life,  and  that  the  growth  of  the  body  depends  on  the  principles  contained  in 
this  liquid,  are  sufficient  proofs  that  casein,  in  the  living  body,  can  be  trans- 
formed into  fibrin  and  albumen  in  all  their  modifications;  the  phosphate  of 
lime  contained  in  milk,  being  appropriated  for  the  skeleton,  and  the  oil  of 
milk  for  the  production  of  fat. 

Lactine(CJI.,fi^„  or  G^Jl^fi.g-i-b'HO):  Sugar  of  Milh;  Lactose.— \t\% 
this  substance  which  gives  the  sweet  taste  to  fresh  milk.  It  is  procured  in 
large  crystalline  masses  by  the  evaporation  of  the  whey  of  fresh  milk,  after 
the  separation  of  the  casein  and  oil.  It  is  prepared  in  Switzerland  from 
whey,  in  the  manufacture  of  Gruyere  cheese.  It  is  white,  hard,  and  gritty, 
only  slightly  sweet  to  the  taste,  soluble  in  about  6  parts  of  cold  and  2  parts 
of  -boiling  water.  It  does  not  form  a  syrup.  It  is  insoluble  in  alcohol  and 
ether.  Its  aqueous  solution  turns  the  polarized  ray  to  the  right.  Dilute 
acids  convert  it  into  glucose.  Nitric  acid  produces  with  it  oxalic  as  well 
as  mucic  acid.  Lactine  differs  from  other  sugars,  and  resembles  gums,  in 
producing  the  last-mentioned  acid  with  nitric  acid.  It  does  not  reduce  an 
alkaline  solution  of  oxide  of  copper,  until,  by  the  agency  of  an  acid,  it  has 
been  converted  into  glucose.  Under  these  circumstances  it  darkens  when 
boiled  with  a  solution  of  potassa,  as  a  result  of  the  production  of  glncic 
acid.  It  readily  undergoes  fermentation,  the  casein  and  albumen  in  milk 
being  sufficient  ferments.  Thus  at  a  temperature  of  104°  the  lactine  of 
fresh  milk  is  converted  into  alcohol  and  carbonic  acid,  by  the  alcoholic  fer- 
mentation :  if  the  milk  has  been  exposed  to  air  for  some  time,  a  change  is 
induced  in  the  casein,  by  which  lactic  acid  is  produced,  as  a  result  of  the 
lactic  fermentation.  This  is  seen  in  the  spontaneous  souring  of  milk  when 
long  kept,  the  casein  being  separated  in  curds  by  the  lactic  acid,  either  im- 
mediately or  when  slightly  warmed.  Under  other  conditions  milk  passes 
through  the  butyric  fermentation,  and  butyric  acid  is  a  product.  Lactine  is 
represented  as  consisting  of  equal  equivalents  of  carbon,  hydrogen,  and 
oxygen ;  but  at  248°  it  loses  2  atoms  of  water,  and  at  302°  it  loses  3  atoms 
water.  According  to  Regnault,  in  combination  with  oxide  ofjead,  it  loses 
5  atoms  of  water :  hence  its  formula  in  the  anhydrous  state  is  C,,n,„0,g.  In 
the  hydrated  state  it  corresponds  to  2  of  fructose  or  uncrystalhzable  sugar, 
for  C,,H,,0,,  are  =2(C,,H,.Pj,).  .,,.,•  •  i 

Lactic  Acidic fi,0„  or  C«HA  +  HO).-This  acid,  which  gives  an  acid 


'714  LACTIC    ACID.       SALIVA.      PTYALIN. 

reaction  to  milk,  is  a  product  of  the  fermentation  of  lactine,  of  beet-root 
juice,  and  otiier  substances.  It  may  be  procured  from  the  whey  of  sour 
milii.  Sour  whey  is  evaporated  to  one-sixth  of  its  original  weight  and 
filtered  :  lime  is  added  to  the  filtrate,  to  precipitate  phosphoric  acid,  and  any 
excess  of  lime  is  removed  by  oxalic  acid  and  subsequent  filtration.  The 
liquid  is  concentrated,  and  the  lactic  acid  may  be  dissolved  out  by  alcohol, 
and  subsequently  purified.  It  is  a  colorless  liquid  of  the  consistency  of 
syrup,  miscible  in  all  proportions  with  water  and  alcohol.  It  dissolves 
phosphate  of  lime,  decomposes  the  acetates,  and  coagulates  albumen.  It 
produces  no  change  in  cold  fresh  milk,  but  the  presence  of  a  small  trace  of 
this  acid  in  boiling  milk  causes  coagulation.  It  is  supposed  to  be  present 
in  the  sweat  and  in  many  of  the  fluids  of  the  body.  Lactic  acid  is  simply  an 
isomeric  condition  of  lactine,  for  4.(CQRfi^.)  =  C.^^H^^0^^.  Lactic  acid  con- 
tains 1  atom  of  water,  hence  its  usual  formula  is  CeH^O^jHO. 

Saliva. 

This  is  a  transparent  viscid  liquid,  secreted  by  the  salivary  glands.  Its 
sp.  gr.  is  LOOS.  It  is  generally  mixed  with  the  mucous  secretions  of  the 
mouth  :  these  are  acid,  and  when  they  predominate,  give  an  acid  reaction  to 
the  saliva,  but  this  secretion,  in  a  pure  state,  is  always  alkaline  (Andral). 
The  alkalinity  probably  depends  upon  the  presence  of  phosphate  of  soda, 
which  with  chloride  of  sodium  and  phosphate  of  lime,  forms  the  bulk  of  the 
mineral  matter,  found  in  this  secretion.  Saliva  commonly  presents  itself  as 
a  ropy,  opaline  liquid,  depositing,  on  standing,  threads  or  flakes  of  opaque 
mucus.  Under  the  microscope  it  presents  mucous  globules  and  epithelial 
scales.  Alcohol  precipitates  from  the  clear  liquid  an  albuminoid  principle 
{ptyalin),  which  forms,  with  the  mucus,  from  1  to  2  per  cent,  of  saliva.  The 
mucus  which  gives  the  ropiness  to  saliva  may  be  separated  by  acetic  acid. 
The  ptyalin  precipitated  by  alcohol  is  redissolved  by  the  addition  of  water. 
The  liquid  is  rendered  more  opaline  on  boiling,  or  by  the  action  of  nitric 
acid.  Tannic  acid  and  subacetate  of  lead  also  throw  down  the  ptyalin.  The 
addition  of  a  drop  of  neutral  persulphate  of  iron  imparts  a  deep  red  color 
to  saliva,  which  disappears  on  the  addition  of  a  solution  of  corrosive  subli- 
mate. This  indicates  the  presence  of  a  trace  of  an  alkaline  sulphocyanide, 
which  is  found  in  all  healthy  saliva.  The  solid  contents  of  saliva  vary.  We 
have  found  by  experiment  that  the  solid  residue  does  not  exceed  2  per  cent. 
The  ptyalin  and  mucus,  according  to  Lehmann,  are  generally  below  1  per 
cent.  The  saliva  of  tobacco-smokers,  according  to  Gmelin,  contains  from 
1'14  to  1-19  percent,  of  solid  matter,  which  leaves,  when  burned,  0-25  of 
ash.  The  tartar  which  is  deposited  on  the  teeth,  and  salivary  calculi,  con- 
sists of  the  salts  of  the  saliva,  chiefly  phosphate  of  lime  cemented  with 
animal  matter. 

The  ptyalin  of  saliva  differs  from  albumen  in  its  power,  at  a  temperature 
of  100°,  of  rapidly  transforming  starch  and  dextrine  into  glucose.  The  use 
of  the  saliva  is  to  aid  in  the  reduction  of  the  food  to  a  perfectly  soft  state, 
so  that  it  may  not  only  be  more  easily  swallowed,  but  that  when  it -reaches 
the  stomach,  it  may  be  more  completely  penetrated  by  the  gastric  juice. 

Serpent-poison:  Echidnine  (from  ^x'-^voeihr^i,  viperous). — The  secretion 
from  the  poison-glands  of  the  viper  and  other  serpents,  is  a  clear  viscid  fluid, 
of  a  slightly  yellow  color,  and  neutral  in  its  reaction.  It  contains  albumen, 
mucus,  fatty  matter,  a  yellow  coloring  principle  ;  and  among  its  salts,  phos- 
phates and  chlorides.  There  is  associated  with  the  albumen,  a  peculiar 
nitrogenous  body  resembling  ptyalin  and  pepsine,  which  is  called  echidnine, 
and  which  appears  to  be  the  active  poisonous  principle  of  this  fluid.     It3 


GASTRIC    JUICE.      PEPSINE.       PANCREATIC    FLUID  115 

exact  constitution  is  unknown  (Bernard).  Echidnine  is  soluble  in  alcohol : 
and  may  be  separated  from  the  other  principles  by  the  employment  of  this 
liquid,  and  subsequently  evaporating  the  solution  in  vacuo.  The  fatty  matter 
may  be  removed  by  ether.  Echidnine  thus  obtained,  is  in  colorless  white 
uncrystalline  scales,  resembling;  tannic  acid.  It  is  neutral,  and  has  neither 
odor  nor  taste.  When  heated  with  potassa,  it  evolves  ammonia  :  it  is  solu- 
ble in  water,  hot  and  cold.  The  precipitate  which  is  first  produced  in  the 
aqueous  solution  by  alcohol,  is  redissolved  by  an  excess.  It  is  not  precipi- 
tated by  acetate  of  lead.  It  acts  upon  the  blood  of  animals  like  the  serpent 
poison.  De  Blainviile  considers  it  to  be  analogous  to  ptyalin,  and  that  the 
fluid  containing  it  is  a  peculiar  kind  of  saliva.  The  poison-bag  of  the  viper 
seldom  contains  more  than  one  grain  and  a  half  of  this  liquid :  l-250th  of  a 
grain  is  sufficient  to  kill  a  small  bird.  This  poison  produces  no  injurious 
effects  when  swallowed  (Dumeril). 

Salamandrine. — The  poison  of  the  salamander,  according  to  Zalesky,  is  a 
creamy  liquid  strongly  alkaline  and  possessing  a  bitter  taste.  It  contains 
an  active  principle  which  is  precipitated  by  phospho-molybdic  acid.  He  has 
given  to  this  principle  the  name  of  Salamandrine  and  assigns  to  it  the  follow- 
ing formula,  C^aHaoNgOio.  {Quarterly  Journal  of  Science,  Jan.  1867.) 

Gastric  Juice. 

This  is  a  secretion  from  the  mucous  membrane  of  the  stomach.  When 
separated  from  mucus  by  filtration,  it  presents  itself  as  a  colorless  limpid 
liquid,  of  an  acid  reaction,  from  the  presence  of  lactic  or  hydrochloric  acid, 
the  former  being  probably  derived  from  starch  or  sugar,  taken  as  food.  It 
contains  from  96  to  98  per  cent,  of  water,  the  residue  consisting  of  organic 
matter  and  salts,  of  which  chloride  of  sodium  and  alkaline  sulphates  are  the 
principal.  The  acid  mucus  of  the  stomach  is  associated  with  a  nitrogenous 
principle  {pepsine),  to  which  its  solvent  properties  are  due.  It  has  been 
precipitated  and  extracted  from  the  fluid  portion  by  alcohol  and  acetate  of 
lead,  but  probably  in  an  altered  condition.  Its  constituents  cannot,  there- 
fore, be  accurately  determined.  Fibrin  or  coagulated  albumen  plunged  into 
this  liquid,  at  the  temperature  of  the  body,  swells  up,  and  becomes  gradually 
disintegrated  and  dissolved.  This  property  of  dissolving  fibrin  and  analo- 
gous substances  has  been  verified  by  experiments  on  animals :  and  in  one 
remarkable  instance  in  a  human  being,  in  whose  stomach  there  was  a  fistulous 
opening.  Pepsine  loses  this  solvent  property  at  a  temperature  above  120°. 
From  the  researches  of  Dr.  Robiuson  on  the  human  foetus,  it  appears  that 
no  gastric  juice  is  secreted  in  the  stomach,  until  the  act  of  respiration  has 
been  performed.  He  found  that  the  contents  of  the  stomach  before  birth 
consisted  chiefly  of  the  liquor  amnii,  mixed  with  an  albuminous  matter  and 
saliva.     There  is  no  proper  digestion,  and  only  an   imperfect  process  of 

chymification.  ^u    •  *    •        c 

Medicinal  pepsine  consists  of  the  dried  mucus  escaped  from  the  interior  ot 
the  stomachs  of  animals  (the  sheep  and  the  pig).  It  is  sometimes  incorpo- 
rated  with  starch.  The  soluble  pepsine  consists  of  this  substai.ce  dissolveU 
in  a  solution  of  chloride  of  sodium.  It  is  supposed  to  supply  additional 
digestive  power  to  those  whose  stomachic  secretions  are  deficient  m  pepsine. 

Pancreatic  Fluid. 

This  is  a  colorless  viscid  liquid,  which  is  secreted  by  the  pancreas.     It  is 

always  alkaline,  and  is  rendered  frothy  by  agitation.     It  yields  from  8  to  9 

per  cent,  of  a  solid  residue,  of  an  albumiuoid  nature      When  heated   it  .ets 

into  a  solid  like  ovalbumen  :  but  xM.  Robin  found  that  if  sulphate  of  mag- 


716  MUCUS.      PUS.      SYNOVIA. 

nesia  was  first  added  to  the  liquid  it  gave  no  eoagulura  when  heated.  Sul- 
phate of  magnesia  added  to  a  solution  of  albumen  does  not  prevent  it  from 
coagulating  by  heat.  Like  albumen  it  is  precipitated  from  its  aqueous  solu- 
tion by  alcohol ;  but  an  excess  of  water  redissolves  the  precipitate,  even  after 
it  has  been  dried.  When  the  solid  residue  is  incinerated,  the  ash  yields 
chloride  of  sodium,  with  phosphate  and  carbonate  of  soda.  The  nature  of 
the  organic  principle  is  not  well  understood.  It  appears  to  resemble,  in 
some  respects,  ptyalin  (the  albumen  of  saliva)  and  casein,  but  its  character- 
istic property  is  to  assimilate  oily  matters.  It  forms  an  emulsion  with  all 
oils  and  fats,  when  mixed  with  these  substances,  and  the  mixture  is  heated 
to  about  100° — the  temperature  of  the  body.  Chemically  speaking,  this 
appears  to  be  a  process  of  saponification,  glycerine  is  produced,  and  the 
fatty  acids  are  set  free. 

Mucus. 

This  is  a  viscid  tenacious  liquid,  secreted  by  mucous  membranes  in  the 
healthy  state.  It  is  white,  yellow,  green,  and  sometimes  almost  black.  It 
is  thrown  out  from  the  membranes  of  the  nose,  mouth,  and  air-passages,  as 
well  as  from  the  whole  tract  of  the  alimentary  canal.  It  is  sometimes  opaque, 
at  others  transparent,  ropy,  or  gelatinous,  according  to  the  part  which 
secretes  it.  Mucus  generally  has  an  alkaline  reaction.  It  is  heavier  than 
water,  and  insoluble,  but  diffusible  in  tliis  liquid  :  it  is  not  coagulated  by 
heat.  It  is  precipitated  from  its  aqueous  mixture  by  acetic  acid  and  alcohol. 
It  appears  to  be  a  modified  state  of  albumen  {mucin).  Under  the  microscope, 
mucus  presents  nucleated  globules  and  epithelial  scales,  which  vary  in  shape 
with  the  situation  of  the  membrane  from  which  they  are  thrown  off. 

Pus. 

Pus  is  a  morbid  or  diseased  secretion  from  mucous  membranes,  ulcers,  or 
abscesses.  It  is  a  creamy-looking  liquid,  of  a  yellowish-white  color.  Its 
sp.  gr.  is  1'030.  When  in  a  normal  state  it  is  alkaline;  and,  according  to 
Andral,  it  is  never  acid  until  it  has  been  exposed  to  air.  It  contains  867 
water,  7 '4  albumen,  dissolved,  forming  a  serous  liquid,  and  5  9  of  fatty 
matter,  including  salts.  Examined  microscopically,  pus  presents  numerous 
white  nucleated  globules,  mixed  with  oil-globules,  floating  in  a  serous  liquid. 
When  diffused  in  water,  the  serum  dissolves,  and  the  wliite  mucous  globules 
subside.  The  aqueous  solution  is  coagulated  by  heat,  and  possesses  the 
other  properties  of  diluted  albumen.  By  this  character,  and  the  presence  of 
oil-globules,  pus  may  be  distinguished  from  mucus.  It  appears  to  be  serum 
in  which  colorless  globules  of  a  special  character  are  developed.  If  pus  is 
mixed  with  a  solution  of  potassa,  it  forms  a  jelly  resembling  bronchial  mucus. 
The  albuminous  principle  existing  in  pus  is  called  joym.  When  absorbed 
into  the  blood,  pus  appears  to  act  as  a  powerful  poison.  In  diseased  states 
of  the  body,  it  forms  a  vehicle  for  some  of  the  most  virulent  animal  poisons, 
such  as  that  of  glanders  and  smallpox. 

Synovia. 

Synovia  is  a  glairy  yellowish-white  fluid  :  it  derives  its  name  from  ovv,  cum, 
(Ibv,  ovum,  owing  to  its  resembling  the  white  of  an  egg  in  its  viscidity.  It  is 
secreted  by  the  lining  membranes  of  joints,  only  in  sufficient  quantity  to  keep 
the  surface  lubricated.  It  is  an  alkaline  fluid,  containing  albumen  and  salts, 
which  consist  chiefly  of  the  phosphates  of  lime  and  soda. 


LIQUOR    AMNII.      PULMONARY    EXHALATION.  tlT 

Liquor  Amnil 

The  organic  principle  in  this  liquid  is  albnmen,  associated  with  chloride 
of  sodiiira  and  phosphate  and  carbonate  of  lime.  It  is  remarkable  that  tlie 
proportion  of  albumen  varies  according  to  the  period  of  gestation.  At  the 
4th  month  in  the  human  female,  it  amounts  to  1077  per  cent.;  at  the  5th 
to  7-67  ;  at  the  6th  to  6  67  ;  and  at  the  9th  to  0-82.  In  the  latter  stage  of 
gestation,  it  contains  merely  traces  of  albumen  and  saline  matter. 

Cutaneous  Secretion. 

Pulmonary  Exhalation. — The  sudoriparous  glands  of  the  skin  secrete  a 
liquid  which  is  constantly  escaping  in  the  form  of  vapor,  and  is  speedily 
condensed  on  cold  surfaces.  Under  violent  exercise,  or  in  a  temperature  at 
or  above  100°,  it  is  deposited  on  the  skin  in  a  liquid  form  :  in  this  state  it 
has  an  acid  reaction.  It  is  said  to  contain  from  05  to  1-25  per  cent,  of  a 
solid  albuminous  substance,  including  saline  matter,  principally  consisting  of 
the  chlorides  of  sodium  and  ammonium,  with  alkaline  phosphates.  As  it  is 
secreted  from  the  axillae,  it  has  a  peculiar  odor.  It  produces  in  drying  a 
yellowish  stain  on  linen.  An  aqueous  solution  of  the  dried  excretion  is 
neutral :  like  albumen,  it  is  rendered  opaline  by  boiling,  and  is  coagulated  by 
nitric  acid.  A  large  quantity  of  chloride  of  sodium  is  continually  eliminated 
from  the  skin  by  this  excretion,  when  the  body  is  in  a  healthy  state.  If  the 
hands,  when  perfectly  clean,  are  dipped  for  a  short  time  in  distilled  water,  it 
will  be  found,  on  adding  a  solution  of  nitrate  of  silver  to  the  water,  that  it 
produces  a  whitish  precipitate,  indicative  of  the  presence  of  alkaline  chloride 
derived  from  the  skin.  This  excretion  is  sometimes  acid,  owing  to  the 
presence  of  lactic  and  acetic  acids  :  it  easily  undergoes  decomposition,  and 
sulphur  compounds  with  ammonia  and  other  offensive  effluvia  are  produced. 
In  these  chemical  changes  of  the  condensed  liquid,  we  have  probably  one  of 
the  sources  of  noxious  exhalations  in  closely  inhabited  dwellings. 

The  halitus^  or  aqueous  vapor  which  escapes  in  respiration,  also  contains 
nitrogenous  animal  matter,  which  is  liable  to  decomposition.  Ammonia  is 
said  to  be  thus  eliminated,  but  we  have  not  found  this  alkali  present  in 
expired  air  in  a  healthy  person.  When  extricated  from  the  lungs,  from  the 
blood,  or  from  the  skin,  it  is  probably  a  result  of  the  decomposition  of  nitro- 
genous matter.  This  exhalation  generally  contains  noxious  volatile  vapors, 
which  have  been  absorbed  into  the  blood.  Thus,  alcohol,  ether,  chloro- 
form, and  prussic  acid  have  been  recognized  by  their  odors,  in  the  vapor 
expired  by  persons  who  were  laboring  under  their  effects. 

Humors  of  the  Eye. — The  crystalline  lens,  of  which  the  refracting  index 
compared  with  that  of  water  is  1-339  to  1336,  contains  359  percent,  of 
the  albuminoid  principle  globulin.  The  vitreous  humor  consists  of  albumen 
0-18,  chloride  of  sodium  and  extractive  (?)  1'43,  water  98  40.  The  aqueous 
humor  is  water,  with  traces  of  animal  matter  and  common  salt. 

Tears. "flie  liquid  secreted  by  the  lachrymal  glands  and  poured  from  the 

eye  under  powerful  emotion,  is  chiefly  water,  with  a  trace  of  albumen  and 
chloride  of  sodium.  The  Liquor  Pericardii  and  Cerebrospinal  fluid  are 
also  of  an  albuminous  nature. 

The  two  principal  non-albuminous  fluids  produced  from  the  blood,  are  the 
Bile  and  Urine— WiQ  one  secreted  by  the  venous  blood  of  the  liver,  the  other 
by  the  arterial  blood  of  the  kidneys. 


18  BILE.       CHOLIC    ACID. 


Bile. 


This  is  a  ropy,  viscid,  and  saponaceous  liquid  of  a  greenish-yellow  color 
in  man,  greenish-brown  in  the  ox,  and  emerald  or  grass-green  in  birds,  rep- 
tiles, and  fish.  It  has  an  offensive  odor  and  a  bitter  taste.  Its  sp.  gr.  is 
1  024.  It  has  a  slightly  alkaline  reaction,  and  it  mixes  in  all  proportions 
with  water,  giving  a  yellow  color  to  this  liquid,  and  rendering  it  viscid  and 
frothy. 

The  bile  contaios  no  albumen  :  it  is  not  coagulated  by  heat.  Alcohol 
renders  it  turbid  by  precipitating  the  mucus.  Alkalies  readily  mix  with  it ; 
\Snt  acids,  including  the  acetic,  tlirovv  down  a  dense  precipitate,  consisting  of 
the  organic  acids  of  the  bile  with  mucus  and  coloring-matter.  100  parts  of 
oX'bile  evaporated  on  a  water-bath  left  a  residue  of  9  2  parts  solid  matters, 
and  this  residue,  when  incinerated,  yielded  a  strongly  alkaline  ash,  weighing 
1-2  grains.     It  contained  a  large  proportion  of  soda. 

The  bile  essentially  consists  of  the  salts  of  two  peculiar  organic  acids,  in 
which  soda  is  the  base,  namely,  the  chelate  and  chuleate  of  soda,  of  cholesterine, 
and  fat,  as  well  as  mucus  and  coloring-matter.  The  cholic  and  choleic  acids 
are  of  the  nature  of  the  resinous  and  fatty  acids  ;  hence  they  were  formerly 
included  under  one  substance,  which  was  called  biliary  matter,  or  resin  of 
the  bile.  They  give,  by  the  presence  of  their  salts,  a  saponaceous  character 
to  the  liquid  :  it  is  well  known  that  ox-gall  is  a  powerful  detergent,  and  is 
much  used  as  such,  in  the  arts  and  manufactures. 

By  digesting  the  dried  extract  of  bile  in  alcohol,  all  is  dissolved  excepting 
the  mucus,  the  cholate  and  choleate  of  soda  being  soluble  in  this  liquid. 
Cholic  acid  is  a  nitrogenous  acid,  while  choleic  acid  not  only  contains  nitro- 
gen, but  all  the  sulphur  which  is  found  in  the  bile.  The  cholic  acid  is  in 
much  larger  proportion  than  the  choleic. 

Cholic  Acid  {C^Jl^^O^^^).  Glycocholic,  Glycocholalic  Acid. — This  acid 
may  be  procured  by  mixing  the  filtered  solution  of  bile  in  absolute  alcohol, 
with  three  or  four  parts  of  ether.  This  causes  a  crystalline  deposit  of  cholate 
of  soda.  By  digesting  this  deposit  in  dilute  sulphuric  acid,  crystals  of  cholic 
acid  are  obtained.  They  are  very  soluble  in  alcohol,  but  are  not  readily  dis- 
solved by  water  or  ether.  If  the  coloring  matter  of  the  bile  has  been  pre- 
viously removed  by  animal  charcoal,  the  crystals  may  be  obtained  quite  white. 
Cholic  acid  is  what  has  been  termed  a  conjugated  compound  of  a  nitroge- 
nous substance,  Glycocine  or  gelatin  sugar  (p.  587),  and  a  non-nitrogenous 
acid  called  the  cholalic  When  cholic  acid  is  boiled  in  a  solution  of  potassa, 
these  compounds  result,  two  atoms  of  water  being  required  to  effect  the  de- 
composition : — 

^5,H,30,2N^      4-        2H0        =    ^C,gH,,0,^    -f       JC^H^N 

Cholic  acid.  Water.  Cholalic  acid.  Glycocine. 

When  cholic  acid  is  boiled  with  hydrochloric  or  other  acids,- glycocine  is 
set  free  ;  but  a  new  acid  appears,  namely,  the  choloidic  (C^gHggOg).  This  is 
an  isomeric  compound  of  the  anhydrous  cholalic  acid  ;  in  the  hydrated  state, 
the  latter  acid  contains  one  equivalent  of  water.  The  choloidic  acid  is  an 
uncrystalline  resinous-looking  substance,  insoluble  in  water  and  soluble  in 
alcohol,  like  a  resin.  This  was  no  doubt  the  resin  of  the  bile  as  described 
by  former  writers.  Cholalic  acid,  when  long  boiled  with  hydrochloric  acid, 
is  itself  decomposed  :  it  loses  three  equivalents  of  water,  becoming  Dyslysine 

Choleic  Acid  (CgyH^gOi^SyN).  Tauro-cholic.  Tauro-cholalic  Acid. — This 
acid  is  procured  from  the  choleate  of  soda,  by  adding  acetate  of  lead  to  a 


CHOLEIC    ACID.      CH0LE8TERINE.  719 

solution  of  bile  in  10  or  15  parts  of  water,  and  afterwards  a  little  ammonia. 
The  resulting  precipitate  is  gently  heated  ;  the  liquid  is  then  poured  from  it, 
and  it  is  triturated  and  washed  with  a  little  water,  and  afterwards  treated 
with  boiling  alcohol,  which  dissolves  an  acid  salt,  leaving  a  bnsic  salt,  and 
a  compound  of  coloring-matter  and  oxide  of  lead.  The  alcoholic  solution, 
decomposed  by  sulphuretted  hydrogen,  filtered,  and  evapornted  to  dryness, 
leaves  a  brown  resinous  magma,  from  which  fatty  matters  (margaric  acid  and 
cholesterine)  must  be  separated  by  ether :  it  is  then  redissolved  in  cold  weak 
alcohol,  filtered  and  evaporated  to  dryness  :  the  remaining  choleic  acid  is 
slightly  contaminated  by  soda,  sulphur,  and  margaric  acid.  (Demarcay.) 
It  has  not  yet  been  obtained  in  a  pure  state ;  but  its  constitution  may  be 
inferred  from  the  compounds  into  which  it  is  resolved,  when  boiled  with 
alkalies,  namely,  taurine  and  cholalic  acid.  Two  equivalents  of  water  are 
required  to  bring  about  this  change,  when  choleic  acid  is  boiled  iu  a  solution 
of  potassa  : — 

^52H,50,4S2N^     4-         2H0         =        C,8H,oO,o  ^  +         C^H.OeS.N 

Choleic  acid.  Water.  Cholalic  acid.  Taurine. 

It  is  remarkable  that  in  this  breaking-up  of  choleic  acid,  all  the  sulphur 
and  nitrogen  should  go  into  the  taurine.  Acids  produce  a  similar  change, 
but  they  convert  the  cholalic  into  choloidic  acid ;  and  this,  by  further  boil- 
ing, into  dyslysine.  It  appears  that  when  the  bile  is  spontaneously  changed 
by  putrefaction,  taurine  and  cholalic  acids  are  products  of  the  decomposi- 
tion of  the  cholic  and  choleic  acids.  The  impure  cholic  and  choleic  acids,  as 
they  are  obtained  in  combination  with  soda,  by  the  evaporation  of  bile,  form 
a  greenish-brown  resinous-looking  substance,  which  melts  like  a  resin,  burns 
with  a  smoky  flame,  and  leaves  a  carbonaceous  ash,  in  which  soda  may  be 
abundantly  detected.     It  was  formerly  called  Bilin. 

Taurine  (C^H-OnS^N)  —This  principle  is  obtained  directly  from  bile,  by 
boiling  it  with  hydrochloric  acid  until  the  liquor,  at  first  turbid,  becomes  clear: 
the  choloidic  acid  is  separated  by  decantation,  and  the  liquid  is  evaporated 
until  the  greater  part  of  the  chloride  of  sodium  has  been  deposited.  Five  or 
six  parts  of  alcohol  are  then  added  to  the  mother-liquor,  when  the  taurine 
gradually  falls  in  acicular  crystals,  which  may  be  purified  by  washing  with 
alcohol,  solution  in  boiling  water,  and  recrystallization.  Pure  taurine  forms 
colorless  four-sided  prisms,  which  are  inodorous  and  nearly  tasteless,  neutral, 
permanent  in  the  air,  soluble  in  water,  but  insoluble  in  absolute  alcohol. 
The  presence  of  a  large  amount  of  sulphur  in  taurine  (and  in  bile)  is  im- 
portant in  reference  to  chemical  physiology,  and  the  functions  of  the  liver. 
A  variety  of  other  products  have  been  described  as  derivatives  from  bile,  but 
they  have  not  been  adequately  defined  or  examined.  Some  of  them  appear 
to  be  the  preceding  substances  in  an  impure  state,  or  mixtures  of  them. 

Cholesterine  (C3,H,,0,  +  2HO).— This  is  a  solid  fatty  principle,  found  in 
traces  only  in  the  bile  :  according  to  Berzelius,  it  does  not  form  more  than 
one-10,000th  part  of  this  liquid.  It  cannot  be  readily  extracted  trom  bile, 
but  it  may  be  procured  from  gallstones.  These  consist  of  cholesterine 
ixo-Kn,  bile,  and  oteap,  fat),  or  inspissated  bile,  with  mucus  and  more  or  less 
coloring  matter.  These  stones  are  lighter  than  water,  of  various  colors, 
generally  brittle,  friable,  with  flat  surfaces  and  angles.  When  heated  they 
melt  and  burn.  To  obtain  cholesterine.  the  gall-stone  is  finely  powdered, 
and  the  powder  boiled  in  alcohol.  The  liquid  is  filtered  while  hot  and  on 
cooling,  the  cholesterine  is  deposited  in  pearly  scales.  Cholesterine  has  been 
found  in  the  brain,  in  yelk  of  egg,  and  in  some  morbid  secretions 

Pure  cholesterine  is  seen  in  colorless  scales,  which  are  lighter  than  water, 


'120  TESTS    FOR    BILE. 

and  fusible  at  293^  into  a  colorless  liquid,  which  does  not  concrete  until 
cooled  at  240°.  It  is  insoluble  in  water,  and  scarcely  soluble  in  cold  alco- 
hol;  it  dissolves  in  boilings  alcohol,  ether,  wood-spirit,  and  in  oils.  In  close 
vessels,  it  may  be  sublimed  unchanged.  It  is  not  acted  upon  by  the  alkalies 
even  when  long  boiled  in  their  solutions.  In  addition  to  the  cholesterine, 
there  is  a  peculiar  fatty  matter  in  bile  in  combination  with  soda.  It  exists 
as  margarate  and  oleate  of  soda. 

LithofelUc  Acid  (C^oHgjOy.HO). — This  compound  resembles  cholesterine 
in  its  properties.  It  is  found  in  the  form  of  brown  concretions  in  the  intes- 
tines of  certain  animals  in  eastern  countries.  Tht  concretions  are  known 
under  the  name  of  bezoars. 

Amhreine  {Q^^YL^^O). — This  is  obtained  from  ambergris,  which  is  a  diseased 
concretion  from  the  intestines  of  the  spermaceti  whale.  It  is  a  fat-like 
matter,  amounting,  in  some  specimens,  to  60  per  cent.,  and,  according  to 
Chevreul,  it  resembles  cholesterine.  Benzoic  acid  has  been  found  in  some 
specimens  of  ambergris  ;  in  others,  equally  genuine,  there  are  no  traces  of  it. 
Musk,  castor,  and  civet,  exclusive  of  their  peculiar  and  odorous  principles, 
contain  distinct  species  of  fat. 

Tests  for  Bile. — 1.  The  chelates  and  choleates  maybe  distinguished  by 
the  peculiar  action  of  sulphuric  acid  and  grape-sugar  upon  their  solutions, 
moderately  heated.  (Pettenkofer.)  If  to  half  an  ounce  of  diluted  bile  one 
drop  of  a  solution  of  sugar  is  added,  and  sulphuric  acid  is  gradually  dropped 
into  the  mixture,  a  brownish  precipitate  is  at  first  formed  ;  but  this  is  dis- 
solved on  the  addition  of  more  acid,  and  the  liquid  acquires  a  rich  red, 
gradually  passing  into  a  purple  color.  It  is  brought  out  by  warming  and 
agitating  the  mixture,  taking  care  that  the  temperature  does  not  exceed  120°. 
The  color  is  s'trikingly  shown  by  heating  the  mixture  in  a  white  plate. 

2.  The  coloring-matter  of  bile,  when  diluted  with  water,  appears  yellow  : 
it  imparts  a  yellow  stain  to  organic  substances.  Strong  nitric  acid  produces 
with  it  a  green  color,  passing  through  shades  of  blue,  violet,  and  red,  under 
exposure  to  air,  the  intensity  of  the  colors  depending  on  the  quantity  present. 
Nitric  acid  dropped  on  bile,  rendered  a  little  alkaline,  produces  a  red  and 
bluish,  followed  by  a  green  color.  One  mode  of  testing  for  diluted  bile  in 
liquids  is  dependent  on  this  reaction.  Add  a  small  quantity  of  nitric  acid 
to  the  liquid  and  allow  it  to  stand.  The  liquid  slowly  acquires  a  greenish 
color  if  the  coloring-matter  of  bile  is  present.  The  green  color  is  strikingly 
brought  out  by  adding  strong  hydrochloric  acid  to  the  colored  liquid,  and 
boiling  the  mixture  for  a  short  time.  The  production  of  a  green  color  by 
acids,  merely  indicates  the  presence  of  the  coloring-matter — not  of  the  bile 
itself.  The  only  true  test  for  bile  is  that  of  Pettenkofer  :  the  production  of 
a  red  color  by  the  action  of  sulphuric  acid  and  sugar,  indicates  the  presence 
of  cholic  and  choleic  acids.  It  has  been  noticed,  in  certain  cases,  that  the 
urine  contained  the  coloring-matter  only :  it  was  turned  green  by  nitric  acid, 
but  as  it  gave  no  results  with  the  sulphuric  acid  and  sugar  tests,  the  main 
constituents  of  the  bile  were  absent. 

We  subjoin,  in  a  concise  form,  an  analysis  of  100  parts  of  the  bile  of  the 
ox,  sp.  gr.  1024  : — 

Cholic  and  choleic  acids,  with  mucus  and  fat  .  .  8-0 
Mineral  matter  containing  much  soda  .  .  .  .  1-2 
Water 90-8 

100-0 

The  action  of  the  bile  in  chymification  in  the  living  body  does  not  admit 
of  ♦any  satisfactory  chemical  explanation.     It  assists  in  some  manner  to  con- 


ANALYSIS    OF    URINE.  721 

vert  the  chyme  (digested  food)  into  chylous  matter,  rendering  it  proper  for 
absorption  and  for  being  carried  into  the  blood. 

The  mecomum  which  collects  in  the  intestines  during  foetal  life  has  been 
found  to  consist  chiefly  of  excreted  bile  with  intestinal  mucus. 

Excrementitious  Matter. — This  has  been  supposed  to  consist,  in  great  part, 
of  biliary  matter ;  but  from  analyses  which  have  been  made,  it  appears  that, 
except  under  the  violent  action  of  purgative  medicines  or  in  disease,  the 
amount  of  bile  actually  discharged  is  very  small.  The  portion  which  is  ex- 
creted consists  chiefly  of  the  coloring  and  fatty  matters,  and  does  not  amount 
to  more  than  one-sixteenth  part  of  the  weight  of  the  secretion.  Hence  the 
organic  acids  of  the  bile  are  probably  reabsorbed  into  the  system  in  an 
altered  condition.  The  proportion  of  water  in  feculent  matter  is  about  70  to 
75  per  cent.,  and  the  residue  is  made  up  of  unassimilated  food,  woody  fibre, 
and  nitrogenous  matters.  Dr.  Marcet  has  extracted  from  faeces  a  crystalline 
principle  which  he  calls  Excretine. 

An  analysis  made  by  Berzelius  gives  the  following  results  :  Water,  73  3  ; 
soluble  organic  matters,  including  bile,  albumen,  and  salts,  5-7  ;  insoluble 
residue  of  food,  7*0;  insoluble  matters  from  the  intestines,  with  mucus,  14. 
The  salts  are  chiefly  phosphates  and  chlorides. 

The  Urine. 

In  animals  which  have  no  urinary  bladder,  and  in  which  the  ureters  open 
into  the  rectum,  the  urine  is  solid.  This  is  the  case  with  reptiles.  In  ani- 
mals provided  with  a  urinary  bladder,  it  is  liquid.  Liquid  urine  is  found 
throughout  the  whole  of  the  class  mammalia.  It  differs  a  little  in  the  car- 
nivorous, herbivorous,  and  omnivorous  varieties.  The  urine  of  the  carnivora 
is  a  clear,  transparent,  light-colored  liquid,  possessing  an  acid  reaction  and 
rarely  yielding  any  deposit  on  cooling.  The  urine  of  the  herbivora  is  a 
dark-colored  liquid,  with  a  strong  alkaline  reaction  and  depositing  a  copious 
sediment.  The  urine  of  the  omnivora  has  characters  between  the  two  ;  it  is 
clear,  slightly  acid,  and  only  occasionally  yields  a  deposit  on  cooling.  The 
urine  of  carnivora  contains  in  combination  uric  acid,  of  the  herbivora  hip- 
puric, and  in  omnivora  both  of  these  acids  are  found.  This  liquid,  as 
secreted  by  the  kidneys  in  the  human  body,  carries  off  several  substances 
from  the  blood,  which  may  be  termed  excrementitious,  and  which  would  be 
injurious  if  retained  :  these  substances,  for  the  most  part,  abound  in  nitrogen. 
According  to  Dr.  Thudichum,  the  average  quantity  of  urine  produced  in  a 
healthy  human  adult  in  24  hours  amounts  to  from  49  to  56  fluidounces,  at  a 
specific  gravity  of  1*020.  The  mean  amount  of  solids  excreted  is  from  850 
to  1020  grains,  and  the  water  varies  from  47  to  54  fluidounces.  The  solids 
are  thus  apportioned  by  weight  in  grains  : — 

Grains. 
.  154 
.  23. 
.  56. 
.  19 
.     IjO 

The  urine  when  first  voided  is  limpid,  and  of  various  tints  of  yellow, 
inclining  in  health  to  a  pale  straw-color.  Its  taste  is  saline  and  bitterish. 
Its  odor  is  peculiar,  urinous.  Its  sp.  gr.  ranges  from  1*015  to  1'030.  It  is 
usually  about  1*020;  but  in  some  forms  of  disease  it  is  found  to  be  much 
higher,  and  in  others,  mach  lower.  Its  solid  contents  may  in  general  be 
estimated  at  between  5  and  8  per  cent.  Recent  healthy  urine  almost  always 
has  more  or  less  of  an  acid  reaction.  According  to  Andral,  the  urine  is  acid 
46 


Grains. 

Urea 

Uric  acid  . 

Creatine     . 

Creatinine 

Hippuric  acid    . 

.  463  to  617 
7.5 
4-5 
7- 
7-5 

Chloride  of  sodium 
Sulphuric  acid 
Phosphoric  acid 
Earthy  phosphates 
Ammonia 

Y22  ANALYSIS    OP    URINE.      EXTRACTION    OP    UREA. 

in  health  and  disease ;  and  is  only  alkaline  when  the  mucous  membrane 
secretes  pus.  After  it  has  stood  in  an  open  vessel  for  a  few  hours,  the 
acidity  gradually  becomes  less  apparent,  and  it  generally  deposits  a  little 
mucus,  containing  traces  of  acid  urate  of  ammonia.  It  is  extremely  prone 
to  complicated  changes ;  and  in  warm  weather  it  begins  in  the  course  of  a 
few  hours  to  putrefy  and  to  acquire  new  properties.  It  becomes  alkaline, 
acquires  a  disagreeable  odor,  and  lets  fall  a  whitish  sediment,  consisting 
chiefly  of  ammonio-magnesian  phosphate,  and  phosphate  of  lime  ;  it  becomes 
afterwards  ammoniacal,  and  is  found  to  hold  carbonate  of  ammonia  in  solu- 
tion. Similar  changes  may  be  effected  by  continued  boiling  :  they  are  chiefly 
referable  to  the  decomposition  of  the  characteristic  ingredient  of  the  urine, 
namely,  urea,  a  substance  which  is  easily  resolved  during  putrefaction  into 
carbonate  of  ammonia. 

The  principal  constituents  of  healthy  urine  are  urea,  uric  add,  fixed  salts ^ 
coloring -matter,  organic  matters,  and  mucus.  As  the  urine  varies  in  sp.  gr., 
so  do  these  substances  vary  in  quantity  ;  and  in  the  same  individual,  at  dif- 
ferent hours  of  the  day,  the  urine  presents  very  different  proportions  of  solid 
contents.  The  late  Dr.  Bird  obtained  the  following  results,  in  examining 
1000  parts  of  the  urine  of  a  healthy  person  after  ten  hours'  fasting  {urina 
sanguinis),  and  the  urine  after  dinner  in  the  evening  {urina  cihi)  : — 

Analysis  of  urine.                             After  fasting.  After  eating. 

Specific  gravity 1-016  1-030 

Water 962-72  930-10 

Solids 37-43  69-90 

Urea 14-30  24-40 

Uric  acid 0-23  1-33 

Fixed   salts,  chiefly   chlorides,   sulphates,)  ^.-.q  q.qq 

and  phosphates  .         .         .         .       ) 

Organic  matter,  kreatine,  kreatinine,  color- 1  17. 80  34-27 

ing  matter,  and  volatile  salts      .         .       j 

The  acidity  of  fresh  healthy  urine  has  been  variously  ascribed  to  the  pre- 
sence of  uric  acid,  of  hippuric  acid,  of  lactic  acid,  and  superphosphates.  It 
is  most  probable  that  the  acid  reaction  is  due  to  the  presence  of  the  acid 
phosphates  of  soda  and  lime.  Robin  and  Yerdeil  have  found  both  the 
neutral  and  acid  phosphate  of  soda  in  urine.  It  is  well  known  that  the  urine 
of  herbivora  contains  the  carbonates  in  large,  and  the  phosphates  in  small 
proportion.  The  vegetable  salts  in  the  food  of  herbivora  have  chiefly  for 
their  acids,  the  tartaric,  malic,  and  oxalic,  and  these  are  easily  transformed 
into  carbonates  which  are  excreted  with  the  urine.  In  carnivora,  the  food 
is  rich  in  phosphates,  and  contains  but  a  small  proportion  of  salts  capable  of 
being  turned  into  carbonates  ;  hence  it  imparts  to  the  urine  more  phosphorus 
than  carbonates.  It  is  a  remarkable  fact,  that  while  the  acidity  of  the  urine 
chiefly  depends  on  acid  phosphates,  the  alkalinity  of  the  blood  depends  on 
the  presence  of  basic  phosphates,  or,  as  it  has  been  shown  by  Liebig,  these 
may  be  replaced  by  alkaline  carbonates. 

The  properties  and  composition  of  the  salts  found  in  the  urine,  have 
already  been  described  in  other  parts  of  the  work.  The  chemical  properties 
of  urea,  and  of  uric  acid,  bodies  which  peculiarly  characterize  urine,  remain 
to  be  noticed. 

Urea  {Q^fi^^. — This  is  the  principle  which  confers  upon  the  urine 
its  chief  peculiarities.  It  may  be  procured  by  the  following  processes  : 
(1.)  Evaporate  urine  by  the  gentle  heat  of  a  water-bath  (never  exceeding 
200^)  to  the  consistence  of  a  thin  syrup,  filter,  and  add  to  the  filtrate  an 


EXTRACTION    OF    UREA        PROPERTIES.  723 

equal  volume  of  colorless  nitric  acid  (sp.  gr.  1  35),  which  should  be  perfectly 
free  from  nitrous  acid.  A  brisk  effervescence  ensues,  and  there  is  at  the 
same  time  a  copious  deposition  of  crystallized  and  nearly  pure  nitrate  of 
urea,  this  compound  not  being  dissolved  by  an  excess  of  strong  nitric  acid. 
If  the  evaporated  urine  is  allowed  to  cool  before  the  acid  is  added,  the  crys- 
tals are  very  brown.  The  nitrate  of  urea  is  separated  from  the  acid  liquid, 
dissolved  in  a  small  quantity  of  water,  and  treated  with  carbonate  of  baryta 
or  of  potassa,  until  rendered  neutral :  on  evaporating  the  clear  solution, 
crystals  of  nitrate  of  baryta  (or  nitrate  of  potassa)  are  first  obtained,  and 
then  those  of  urea.  The  latter  are  purified  by  redissolving  them  in  alcohol, 
which  takes  up  the  urea,  and  yields  it  in  crystals,  when  evaporated.  If  the 
urea  is  colored,  a  little  permanganate  of  potassa  may  be  added  to  its  aqueous 
solution,  which  has  no  action  on  urea,  but  destroys  the  coloring  matter. 
Any  color  communicated  by  an  excess  of  permanganate,  is  instantly  de- 
stroyed by  a  few  drops  of  alcohol,  and  the  filtrate  then  yields  colorless  crys- 
tals of  urea.  (2.)  The  concentrated  urine  may  be  saturated  by  oxalic  acid, 
which  yields  crystals  of  oxalate  of  urea ;  these,  dissolved  in  water,  decolored 
by  animal  charcoal,  and  decomposed  by  digestion  with  carbonate  of  lime, 
yield  a  solution  from  which  colorless  crystals  of  urea  may  be  obtained.  (3.) 
From  cyanate  of  ammonia.  28  parts  of  dried  ferrocyanide  of  potassium, 
and  14  parts  of  binoxide  of  manganese,  are  mixed  in  powder,  and  calcined 
upon  an  iron  plate,  heated  to  dull  redness ;  the  mixture  takes  fire,  but  is 
gradually  extinguished,  and  must  be  stirred,  while  cooling,  to  prevent  agglu- 
tination. The  cold  mass  is  then  powdered  and  digested  in  cold  water,  which 
takes  up  the  cyanate  of  potassa;  this  solution  is  filtered  off  and  set  aside; 
the  remaining  powder  is  then  washed  with  a  second  portion  of  cold  water 
and  again  filtered,  and  in  this  filtrate,  205  parts  of  sulphate  of  ammonia  are 
dissolved,  and  the  solution. added  to  the  first  filtered  solution  of  the  cyanate. 
A  large  quantity  of  sulphate  of  potassa  is  deposited,  which  is  strained  off, 
and  the  filtered  liquor,  now  containing,  with  some  sulphate  of  potassa,  all 
the  cyanate  of  ammonia,  is  evaporated  to  dryness,  during  which  process  the 
cyanate  of  ammonia  is  transformed  into  urea  (p.  18).  The  dry  mass  is  di- 
gested in  alcohol,  which  dissolves  only  the  urea,  and  yields  it  pure,  on 
evaporation.  (Liebig,  Annalen  der  Pharm.,  xxxiii.  108.)  In  all  of  these 
processes  the  urine  is  first  concentrated  by  evaporation  at  a  comparatively 
high  temperature,  and  this  causes  an  unavoidable  loss  of  urea,  which  is  easily 
decomposed  by  heat.  In  order  to  prevent  this  loss,  and  to  procure  urea  in 
the  purest  possible  state,  Dr.  Thudichum  has  suggested  another  method 
which  he  has  found  to  yield  a  better  result.  It  is  as  follows  :  A  quantity 
of  urine  is  mixed  with  one-half  of  its  volume  of  a  solution  of  baryta  (consist- 
ing of  two  volumes  of  saturated  solution  of  baryta  or  baryta  water  and  one 
volume  of  a  saturated  solution  of  nitrate  of  baryta),  or  a  quantity  of  that 
solution  sufiBeieut  to  precipitate  the  sulphuric  and  phosphoric  acids.  The 
fluid  is  then  filtered  from  the  precipitate,  neutralized  with  nitric  acid,  and 
evaporated  to  dryness  in  a  water-bath.  The  residue  is  extracted  with  alco- 
hol. The  alcoholic  extract  is  again  evaporated  and  exhausted  a  second  time 
with  absolute  alcohol.  The  last  solution  contains  the  urea  very  pure,  so 
that  it  crystallizes  out  in  colorless  needles. 

Urea  crystallizes  in  flattened  four-sided  prisms ;  they  generally  resemble 
nitre  in  appearance,  and  have  a  similar  cooling  saline  taste:  they  are  ino- 
dorous. They  are  soluble  in  their  own  weight  of  cold  water,  and  in  every 
proportion  in  hot  water;  they  dissolve  in  45  of  cold,  and  in  2  parts  of 
boiling  alcohol ;  but  they  are  insoluble  in  ether,  and  in  an  excess  of  strong 
nitric  acid.  Their  solution  is  neither  acid  nor  alkaline;  but  urea  belongs 
to  the  class  of  neutral  organic  bases,  and  forms  crystallizable  compounds 


124  NITRATE    AND    OXALATE    OF    "UREA. 

with  several  of  the  acids.  Pure  urea  is  permanent  in  the  air ;  at  250°  it 
fuses  into  a  colorless  liquid  ;  at  a  higher  temperature  it  yields  ammonia, 
cj'anate  of  ammonia,  and  dry  solid  cyanuric  acid.  When  heated  in  her- 
metically sealed  vessels  to  between  428°  and  464°,  it  is  entirely  converted 
into  carbonate  of  ammonia.  Alkalies  do  not  evolve  ammonia  by  their  action 
upon  urea,  unless  aided  by  heat;  but  when  fused  with  them  it  is  resolved 
into  carbonic  acid  and  ammonia.  An  aqueous  solution  of  urea  remains  long 
without  change ;  but  the  addition  of  proteiniferous  substances  resolves  it 
more  rapidly  into  carbonate  of  ammonia.  In  this  case  1  atom  of  urea,  and 
2  atoms  of  water,  yield  2  atoms  of  carbonate  of  ammonia  :  C3H40|N2,  +  2HO, 
=2(NH3,C02).  Urea  produces  no  precipitate  in  a  solution  of  nitrate  of 
silver;  but  when  nitrate  of  silver  and  a  little  potassa  are  added  to  a  cold 
solution  of  urea,  a  compound  of  oxide  of  silver  with  urea,  is  thrown  down. 
If  the  mixed  solution  of  urea  and  silver  is  evaporated  at  about  120°, 
nitrate  of  ammonia  and  cyanate  of  silver  are  the  results ;  an  atom  of  urea 
containing  the  elements  of  an  atom  of  cyanic  acid,  an  atom  of  ammonia,  and 
an  atom  of  water  :  C3H,02N2=NC20,+NH3.  +  HO. 

Nitrate  of  Urea  (CaH^O^N^.NO^HO). — This  is  prepared  by  the  process 
above  described.  It  crystallizes  in  rhombic  plates.  The  crystals  are  soluble 
in  8  parts  of  cold  water.  Heated  above  212°,  nitrate  of  urea  is  decomposed, 
evolving  carbonic  acid  and  nitrogen.  At  284°  it  is  resolved,  according  to 
Pelouze,  into  carbonic  acid  and  nitrous  oxide,  in  the  proportion  of  2  volumes 
to  1,  and  the  residue  is  nitrate  of  ammonia;  at  a  higher  temperature,  water, 
nitrous  oxide,  carbonic  acid,  and  ammonia,  are  the  products.  Nitrous  acid 
immediately  decomposes  urea ;  equal  volumes  of  carbonic  acid  and  nitrogen 
are  evolved,  and  nitrate  of  ammonia  is  formed:  (C3H^02N3+2N04=2C03 
-f  2N  +  NH,0,N05).     (MiLLON,  Ann.  Ch.  et  Ph.,  Seme  ser.  viii.  233.) 

Oxalate  of  Urea  {Cfifi^l^^^-Cfi^-^YL0).—'Yh\^^2At  is  thrown  down  in 
short  flattened  prismatic  crystals,  on  mixing  strong  aqueous  solutions  of 
oxalic  acid  and  urea :  it  is  less  soluble  than  the  nitrate.  The  production  of 
the  nitrate  and  oxalate  can  be  well  observed  under  the  microscope  with  an 
inch  power,  on  adding  the  respective  acids  to  concentrated  urine.  Sal-am- 
moniac crystallizes  from  an  aqueous  solution  containing  a  little  urea,  in 
cubes  instead  of  octahedra  ;  while  common  salt,  under  the  same  circumstances, 
crystallizes  in  octahedra  instead  of  cubes  :  these  crystals  contain  only  a  trace 
of  urea. 

The  proportion  of  urea  contained  in  urine  is  subject  to  great  variation. 
Sometimes  it  can  scarcely  be  detected,  ovping  to  the  large  amount  of  other 
organic  matters  which  are  present  (diabetes).  It  is  deficient  in  hysteria. 
It  is  generally  in  larger  quantity  in  the  urine  of  males  than  in  that  of  females, 
and  is  more  abundant  in  youth  than  in  old  age.  It  is  the  great  medium  for 
the  elimination  of  nitrogen,  of  which  it  contains  28  per  cent.  It  is  found 
in  the  healthy  blood  in  small  quantity,  so  that  it  appears  to  be  simply  elimi- 
nated, and  not  secreted  by  the  kidneys.  When  these  organs  are  extensively 
diseased,  the  urea  accumulates  in  the  blood,  and  is  found  in  large  quantity 
in  this  and  other  fluids  of  the  body.  It  then  produces  a  form  of  narcotic 
poisoning,  known  under  the  name  of  urcemia. 

In  a  state  of  health,  human  urine  does  not  contain  sufficient  urea  to  be 
indicated  by  a  deposit  of  crystals,  on  the  addition  of  its  volume  of  nitric 
acid  ;  but  if  fresh  urine  is  gently  evaporated  in  a  watch-glass  to  about  one- 
third  of  its  bulk,  and  an  equal  volume  of  strong  colorless  nitric  acid  is  then 
added,  there  should  be,  after  a  time,  a  deposit  of  crystallized  nitrate  of  urea 
in  rhombic  plates. 

Uric  Acid  (C,oH,06N,=C,oH20,N,-f  2H0).  Lithic  Acid.  Urylic  Acid. 
— This  acid  forms  but  a  small  proportion  of  the  solid  contents  of  urine.     It 


URIC    ACID.  "[25 

is  not  in  a  free  state,  but  combined  with  soda  or  other  bases  forming  urates, 
hence  to  prove  its  presence,  it  is  necessary  to  add  to  a  large  quantity  of 
urine  (ten  or  twelve  ounces)  a  few  drops  of  hydrochloric  acid,  and  allow  the 
acid  liquid  to  stand.  In  about  24  hours  small  crystals  of  uric  acid,  generally 
colored  by  a  dark  red  coloring-matter,  will  be  found  deposited  and  adhering 
to  the  sides  of  the  glass  vessel.  The  quantity  of  this  acid  in  healthy  urine, 
in  the  combined  state,  is  too  small  to  allow  the  chemist  to  procure  the  acid 
readily  from  this  liquid.  Free  uric  acid  is  considered  to  be  only  an  acci- 
dental or  pathological  constituent  of  the  urine  of  man  and  of  that  of  the  car- 
nivora  and  omnivora.  It  has  been  found  in  the  urine  in  gout,  in  articular 
rheumatism,  and  in  some  inflammatory  diseases.  It  constitutes  the  most 
common  variety  of  urinary  calculus  (hence  it  is  called  lithic  acid),  and  it  is 
probably  slowly  separated  from  the  urates  in  this  case,  by  lactic  acid.  Uric 
gravel  is  another  morbid  state  in  which  the  acid  is  found  in  the  bladder.  It 
is  not  present  in  the  urine  of  herbivorous  animals:  but  it  exists  in  large 
quantity  in  a  solid  and  combined  state  in  the  urine  of  serpents,  of  birds  of 
prey,  and  of  those  which  feed  upon  fish  and  animal  matter.  The  substance 
called  Guano,  which  is  used  as  a  manure,  is  the  decomposed  excrement  of 
aquatic  birds  ;  it  contains  a  large  proportion  of  uric  acid.  The  excrement 
of  birds  generally  consists  of  a  white  chalky  mass  which  is  a  compound  of 
uric  acid  and  lime.  The  excrement  of  the  boa-constrictor  and  other  large 
snakes  is  chiefly  composed  of  urate  of  ammonia ;  it  is  voided  in  the  form  of 
a  gray  semi-fluid  mass,  which,  on  drying,  forms  a  whitish,  friable,  chalky- 
looking  substance. 

In  order  to  procure  pure  uric  acid,  the  dry-excrement  of  the  boa-constrictor 
should  be  reduced  to  powder  and  boiled,  first  in  alcohol,  and  then  in  water, 
to  remove  all  matters  soluble  in  these  liquids  ;  it  may  then  be  treated  with 
dilute  hydrochloric  acid  to  remove  phosphate  of  lime,  washed,  and  digested 
in  a  hot  solution  of  caustic  potassa.  The  liquid  is  then  poured  off  or  filtered, 
more  of  the  solution  of  potassa  is  added  to  it,  and  it  is  concentrated  by  evapo- 
ration, when  the  urate  of  potassa,  which  is  not  soluble  in  the  strong  alkaline 
liquid,  separates,  while  the  coloring  matters  are  retained.  On  cooling,  the 
whole  concretes  into  a  pasty  mass,  which  must  be  pressed  out  and  washed 
with  cold  water.  The  urate  of  potassa  which  remains,  is  then  dissolved  in 
boiling  water,  and  the  hot  solution  poured  into  hydrochloric  acid,  when  a 
white  gelatinous  precipitate  falls,  which  soon  assumes  a  crystalline  aspect, 
and  when  washed  and  dried,  is  pure  uric  acid.  Uric  acid  may  be  also  ob- 
tained by  boiling  the  excrement  of  the  snake  in  30  or  40  parts  of  a  weak 
solution  of  caustic  potassa,  until  the  odor  of  ammonia  is  no  longer  perceived  ; 
the  solution  is  then  filtered,  and  hydrochloric  acid  is  added. 

Uric  acid  is  a  soft  white  crystalline  powder ;  it  is  insipid  and  inodorous ; 
it  slightly  reddens  moistened  litmus-paper.  It  is  almost  insoluble  in  cold 
water,  requiring  10,000  parts  to  dissolve  it,  but  soluble  in  between  1800  to 
1900  parts  of  boiling  water  ;  it  is  insoluble  in  alcohol  and  in  ether.  Sul- 
phuric acid  dissolves  it,  but  it  is  again  precipitated  as  a  hydrate  on  adding, 
water.  It  is  dissolved  by  potassa  and  soda,  but  not  by  their  carbonates. 
When  dried  at  212°,  this  acid  retains  two  atoms  of  water,  being  bibasic  ; 
C  oH  0  N  -f  2H0.  When  heated  on  platinum  foil,  the  acid  is  decomposed, 
leaving^only  a  slight  residue  of  carbon.  If  heated  in  a  close  tube,  it  evolves, 
among  other  products,  ammonia. 

Owing  to  the  small  quantity  present  in  urine,  it  is  not  easily  detectea  m 
this  liquid.  It  may,  however,  be  discovered  by  the  use  of  the  microscope. 
As  it  exists  in  the  urine  in  a  combined  state,  an  acid  must  be  employed  for 
its  separation.  Two  or  three  ounces  of  urine  should  be  warmed  and  poured 
into  a  conical  test-glass ;  a  few  drops  of  hydrochloric  acid  are  added,  and 


T26  TESTS    FOR    THE    ACID. 

the  liquid  stirred.  After  some  hours,  either  a  dark-colored  pellicle  forms  on 
the  surface,  or  small  reddish-brown  crystals  are  deposited.  These,  when 
examined  microscopically,  have  a  rhombic  or  fascicular  form.  They  are  com- 
bined with  much  coloring  matter.  Uric  acid  has  been  found,  as  urate  of 
soda,  in  the  blood  of  gouty  persons.  It  is  observed  that  the  proportion  of 
uric  acid  is  diminished  in  the  urine,  immediately  before  a  paroxysm  of  gout. 
Tests  for  the  Acid — In  addition  to  the  chemical  characters  above  men- 
tioned, uric  acid  may  be  identified  by  the  peculiar  action  of  nitric  acid. 
The  powdered  acid  dissolves  with  effervescence  in  nitric  acid.  The  solution 
is  gently  evaporated  at  a  low  temperature,  and  when  the  excess  of  nitric 
acid  has  been  expelled,  and  the  yellowish-colored  residue  has  been  exposed 
to  the  vapor  of  ammonia,  the  rich  purple  color  of  purpurate  of  ammonia,  or 
murexide,  appears.     {See  p.  678.) 

Urates. — All  the  urates  are  sparingly  soluble  in  cold  water,  and  they  are 
mostly  white  insipid  powders.  By  dry  distillation  they  yield  carbonate  and 
hydrocyanate  of  ammonia,  cyanic  acid,  and  an  erapyreumatic  oil  ;  and  those 
with  alkaline  bases  leave  cyanides.  They  are  more  soluble  in  boiling 
water.  Acid  Urate  of  Ammonia  (NH^O.HO.CjoH^O^Nj. — When  uric 
acid  is  digested  in  a  solution  of  caustic  ammonia,  it  becomes  warm,  and  in- 
creases in  bulk,  forming,  when  dried,  a  white,  amorphous  salt,  scarcely  solu- 
ble in  cold  water.  It  may  be  obtained  in  minute  acicular  crystals,  by  adding 
excess  of  ammonia  to  a  boiling  mixture  of  uric  acid  and  water,  and  when 
dried  at  100*^,  has  the  above  composition.  It  requires  1608  parts  of  water 
at  60°  for  its  solution.  When  long  boiled  in  water,  it  is  decomposed,  ammo- 
nia is  evolved,  and  the  pure  acid  remains.  This  compound  forms  one  variety 
of  urinary  calculus  (stone),  and  is  frequently  deposited  from  urine  as  a  red- 
dish-brown sediment,  soluble  in  the  hot  liquid,  but  precipitated  on  cooling. 
Urate  of  Soda. — The  neutral  urate  of  soda  exists  in  the  urine  of  carnivora  ; 
it  exists  also  in  the  urine  of  herbivora,  when  they  are  deprived  of  food.  It 
has  been  found  in  blood  in  gout,  and  is  often  deposited  mixed  with  urates  of 
lime  and  ammonia,  in  persons  laboring  under  fever.  It  constitutes  what  are 
called  chalk-stones,  which  are  deposited  in  the  joints  of  the  fingers  in  gouty 
persons.  Its  alleged  production  from  neutral  nitrogeneous  matters  by  a 
species  of  combustion,  is  not  consistent  with  the  fact  that  it  is  not  usually 
found  in  the  urine  of  herbivora,  although  there  is  much  nitrogen  in  their 
vegetable  food. 

The  action  of  nitric  acid  upon  uric  acid  is  attended  with  the  production 
of  some  remarkable  compounds.  When  1  part  of  uric  acid  is  added  by 
small  portions  at  a  time  to  2  parts  of  nitric  acid  (sp.  gr.  1-41  to  1*45),  care 
being  taken  to  prevent  the  heating  of  the  mixture,  nitrogen  and  carbonic 
acid  (in  equal  volumes)  are  evolved,  and  the  mixture  becomes  a  crystalline 
magma,  from  the  formation  of  alloxan  (CgH^OioNg).  Nitrate  of  urea  is  pro- 
bably first  formed,  which  is  decomposed  by  the  evolved  hyponitrous  acid, 
and  nitrate  of  ammonia,  carbonic  acid,  and  nitrogen  are  produced.  If  the 
nitric  acid,  instead  of  being  concentrated,  is  very  dilute,  the  uric  acid  dis- 
solves with  effervescence,  and  alloxantiiie  (CgHgOjoNJ,  nitrate  of  ammonia, 
and  nitrate  of  urea,  are  found  in  solution.  If  uric  acid  is  dissolved  in 
moderately  strong  nitric  acid,  and  the  liquid  is  evaporated  until  gas  is  no 
longer  evolved,  the  alloxan  originally  produced  is  decomposed  ;  and  crystals 
of  par abanic  acid  (CfiHgOfiNa)  are  formed.  When  the  solution  of  parabanic 
acid  is  supersaturated  with  ammonia  and  evaporated,  it  combines  with  the 
elements  of  water  to  form  oxaluric  acid,  =CgH40gNg.  If  the  nitric  solution 
of  parabanic  acid,  instead  of  being  saturated  with  ammonia,  is  further  eva- 
porated, it  continues  to  evolve  carbonic  acid,  and  ultimately  yields  crystals 
of  nitrate  of  urea.     When  a  solution  of  uric  acid  in  very  dilute  nitric  acid, 


HIPPURIO   ACID.      COLORING-MATTER.  727 

is  evaporated  until  the  alloxantine  which  it  contains  crystallizes,  and  the 
residue  is' saturated  with  ammonia,  the  liquid  acquires  a  purple  color,  and 
deposits  murexide,  together  with  a  red  powder,  which  is  uramile  (C„H,0«NJ. 
(p.  678.)  V   8    5   6    a; 

Hippuric  Add.  Uro-benzoic  Acid  (C,^Y{fig'N).—The  properties  of  this 
acid  and  the  method  of  procuring  it  have  been  elsewhere  described  (p.  655). 
It  appears  to  have  been  for  a  long  time  mistaken  for  benzoic  acid  in  the 
urine  of  the  cow,  horse,  and  other  herbivora.  It  has  been  observed  that  in 
a  horse  at  rest  in  a  stable  hippuric  acid  is  produced,  but  in  a  horse  after 
violent  exercise  it  is  replaced  by  benzoic  acid.  It  will  be  only  necessary 
here  to  describe  the  method  of  detecting  the  acid  in  urine.  A  few  ounces 
should  be  evaporated  to  a  small  bulk  and  an  equal  bulk  of  hydrochloric  acid 
then  added.  A  mixture  of  hippuric  and  uric  acids  slowly  falls  mixed  with 
coloring-matter.  The  supernatant  liquid  being  decanted,  the  deposit  should 
be  boiled  in  alcohol,  in  which  hippuric  acid  alone  is  soluble.  As  it  is  ob- 
tained from  the  alcoholic  solution,  it  presents  itself  in  four-sided  prisms  with 
pointed  terminations. 

The  Coloring-matter  of  the  urine  has  not  been  separated  in  a  distinct 
form.  Heller  has  called  it  Uroxanthin.  The  late  Dr.  Bird  suggested  a  test 
for  this  principle.  A  small  quantity  of  urine  is  heated  in  a  tube  to  the 
boiling-point,  and  a  few  drops  of  hydrochloric  acid  are  added.  The  color 
produced  varies  from  a  pale  lilac  to  a  deep  crimson,  according  to  the  amount 
of  coloring-matter  present.  A  substance  analogous  to  indigo  has  been 
occasionally  found  in  this  liquid  :  we  have  in  one  instance  seen  the  urine  of 
a  deep  purple-black  color.  In  hysteria  the  coloring-matter  is  frequently  in 
very  small  proportion. 

Mucus. — This  presents  itself  in  healthy  urine  as  a  faint  cloud  subsiding 
after  some  hours  to  the  bottom  of  the  vessel.  It  may  be  separated  by 
filtration. 

Kreatine  and  Kreatinine. — Kreatine,  which  has  been  already  described 
with  fibrin  as  a  constituent  of  flesh,  is  found  in  urine  and  also  in  the  blood. 
It  appears  to  be  formed  in  the  muscles,  passes  into  the  blood,  and  is  thence 
thrown  out  through  the  kidneys.  Kreatinine  is  also  found  in  urine,  and  has 
been  detected  in  the  blood,  but  it  has  not  been  discovered  in  the  muscles. 
(Robin  and  Verdeil.)  For  the  detection  of  these  principles  in  the  urine  the 
following  process  may  be  adopted :  Evaporate  an  ounce  of  urine  and  allow 
it  to  cool.  Decant  the  fluid  extract  from  the  deposited  salts.  Dissolve  in 
the  extract,  a  portion  of  chloride  of  zinc  about  the  size  of  a  pea,  and  set  the 
whole  aside  for  twenty-four  hours.  When  the  residue  is  examined  by  the 
microscope,  radiating  crystals  like  minute  zeolites,  will  be  observed,  con- 
sisting of  a  triple  compound  of  zinc  and  chlorine  with  kreatine  and  kreati- 
nine. Their  crystalline  form  is  more  distinctly  seen,  by  dissolving  them  in  a 
drop  of  water  on  a  glass  slide  over  a  spirit-lamp,  and  allowing  the  solution 
to  evaporate  spontaneously. 

In  reference  to  the  fixed  salts,  it  may  be  observed  that  ammonia  or  lime- 
water  added  to  urine,  produces  a  white  precipitate,  by  neutralizing  the 
excess  of  acid  and  throwing  down  the  earthy  phosphates.  A  salt  ot  baryta 
(with  nitric  acid)  gives  a  dense  precipitate  indicative  of  the  presence  ot 
much  sulphuric  acid:  nitrate  of  silver  (with  nitric  acid)  throws  down  an 
abundance  of  chloride  (chlonne),  and  oxalate  of  ammonia  precipitates  Ume 


728       SALTS.      ABNORMAL    INGREDIENTS.      URINARY    CALCULI. 

from  the  lime-salts  dissolved  in  the  liquid.  Under  the  microscope,  this 
deposit,  if  slowly  formed,  appears  in  the  shape  of  octahedral  crystals  with  a 
square  base  {oxalate  of  lime).  The  ash  of  urine  indicates  by  the  usual  tests, 
the  presence  not  only  of  lime,  but  of  soda,  which  exists  chiefly  as  chloride  of 
sodium.  The  presence  of  magnesia  in  urine  is  indicated  by  the  stellated 
crystals  of  phosphate  of  ammonia  and  magnesia,  which  are  seen  under  the 
microscope,  on  adding  ammonia  to  a  few  drops  of  urine  on  a  microscopic 
slide.  By  evaporating  the  urine  (after  fasting)  chloride  of  sodium  may  be 
seen  in  the  form  of  crosses  and  daggers  mixed  with  plumose  crystals  of  phos- 
phate of  soda. 

The  abnormal  ingredients  in  the  urine  are  very  numerous.  Albumen  may 
be  detected  by  the  turbidness  or  coagulum  produced  on  heating  the  liquid, 
as  well  as  by  the  action  of  nitric  acid.  Albuminous  urine  is  frothy  and  of 
low  specific  gravity.  Sugar  may  be  detected  by  evaporating  the  urine  to  a 
syrup,  digesting  the  residue  in  boiling  alcohol,  and  testing  the  alcoholic 
extract  by  the  copper  test.  (See  p.  571.)  Pus  may  be  detected  in  the  sedi- 
ment, by  the  presence  of  oil-globules,  also  of  albumen  in  the  urine,  and  by 
the  production  of  a  jelly-like  mass,  on  adding  to  the  sediment  an  equal 
volume  of  solution  of  potassa.  Blood  may  be  distinguished  by  a  smoky 
color,  if  in  small  quantity,  or  by  a  reddish  color,  if  in  large  proportion.  The 
urine  also  contains  the  albumen  of  serum.  The  coloring  matter  of  blood 
may  be  readily  detected  in  urine,  either  by  the  guaiacum  test  or  by  spectral 
analysis.  When  tincture  of  guaiacum  is  added  to  urine  not  containing  blood, 
the  resin  is  simply  precipitated  of  a  dingy  white,  and  on  the  addition  of  per- 
oxide of  hydrogen  there  is  no  alteration  of  color.  If,  however,  blood  is 
present,  even  in  so  small  a  quantity  as  to  be  barely  perceptible  by  a  smoky  or 
pale  red  color,  the  addition  of  tincture  of  guaiacum  and  peroxide  of  hydrogen 
to  the  urine  produces  a  beautiful  blue  color.  When  a  portion  of  the  urine, 
containing  blood  in  small  quantity,  is  spectrally  examined  by  the  microscope, 
the  black  bands  in  the  yellow  and  green  rays  are  also  perceptible  up  to  an 
extreme  state  of  dilution.  They  are  more  faint  as  the  red  color  of  blood  is 
more  diluted  by  the  urine.  The  guaiacum  test,  however,  indicated  the  pre- 
sence of  the  red  coloring-matter  when  no  dark  bands  could  be  detected  by 
the  spectroscope. 

Urinary  Calculi. — These  usually  include — 1.  Uric  acid  ;  2.  Urate  of  am- 
monia ;  3.  Oxalate  of  lime ;  4.  Phosphate  of  lime,  and  5.  Phosphate  of 
ammonia  and  magnesia.  The  first  two  may  be  distinguished  by  the  action 
of  nitric  acid.  {See  p.  726.)  For  the  method  of  detecting  insoluble  phos- 
phates, see  p.  243  :  and  for  the  analysis  of  oxalate  of  lime,  p.  645. 


WEIGHTS    AND    MEASURES.  ^29 


APPENDIX 


WEIGHTS    AND    MEASURES. 

The  two  systems  of  weights  called  Troy  and  Avoirdupois  have  no  coramon 
integer  except  the  grain.  Although  the  names,  pound,  ounce,  and  drachm 
are  common  to  both  systems,  they  denote  different  quantities  in  each.  The 
English  Troy  pound  is  subdivided  into  twelve  ounces,  and  each  ounce  is 
equal  to  480  grains.  The  subdivisions  of  the  Troy  ounce,  called  Apothe- 
caries^ weight,  are  into  8  drachms,  each  drachm  into  3  scruples,  and  each 
scruple  into  20  grains.  The  Troy  ounce  is  also  divided  into  20  penny- 
weights, of  24  grains  each.  For  philosophical  purposes,  ambiguity  is  most 
easily  avoided  by  employing  the  grain  as  integer  :  and  the  Laboratory  should 
be  provided  with  good  sets  of  weights,  from  1000  grains  downwards ;  the 
grain  should  be  decimally  subdivided  into  tenths,  hundredths,  and  thou- 
sandths. 

apothecaries'  weight. 


Pound. 

Ounces. 

Drachms. 

Scruples. 

Grains. 

French  grammes. 

1 

=      12 

=      96 

=      288 

= 

5760 

=5 

372-96 

1 

=        8 

=        24 

= 

480 

= 

31-08 

1 

=          3 

— 

60 



3-885 

1 

= 

20 

1 

= 

1-295 
0-0647 

AVOIRDUPOIS  WEIGHT. 
Pound.  Ounces.  Drachms.  Grains.  French  grammes. 

1        =16        =256        =      7000  =      458-25 

1        =        16        =        437-5  =        28-328 

1        =  27-343  =  1-77 

The  avordupois  ounce  and  pound  being  the  weights  practically  used  in  the 
sale  of  medicines  and  generally  in  commercial  transactions,  were  substituted 
for  Apothecaries'  or  Troy  weight  in  the  British  Pharmacopoeia  of  1864,  and 
they  are  still  retained  in  the  edition  of  1867.  The  grain  is  a  convenient 
unit,  and  it  is  a  weight  which  is  well  understood  in  this  country  and  well 
adapted  for  estimating  the  weight  of  medicines.  There  is  no  weight  between 
the  grain  and  the  avoirdupois  ounce  of  437  5  grains,  which  it  will  be  per- 
ceived is  not  a  multiple  of  the  grain.  To  remedy  this  inconvenience  the 
scruple  and  the  drachm,  representing  respectively  twenty  and  sixty  grains, 
are  retained  for  the  purpose  of  prescribing.  In  the  measurement  of  liquids, 
the  Imperial  measure  is  used  for  the  higher  denominations,  and  the  fluidounce 
and  its  subdivisions  into  fluidrachms  and  minims  for  the  lower  denominations 
of  volume. 

Measures  of  Volume. — Weights  are  connected  with  measures  by  the  sub- 
divisions of  the  Imperial  gallon.  The  weight  of  an  Imperial  gallon  of 
absolutely  pure  water,  at  30  inches  pressure,  and  62°,  is  tea  Avoirdupois 


ISO  FRENCH    METRICAL    SYSTEM. 

pounds,  or  70,000  grains.  It  is  equal  to  277  2T4  cubic  inches.  It  is  one- 
fifth  more  than  the  old  Wine  gallon,  i.  e.,  30  Imperial  are  =  36  Wine  gallons. 
A  cubic  foot  of  water  represents  6*23  Imperial  gallons. 


IMPERIAL  MEASURE. 

Gallon. 

Pints. 

Fluidounces.            Fluidrachms. 

Minims. 

1          = 

8 

=          160             = 

1280 

=       76800 

1 

=           20           = 

160 

.=        9600 

1           = 

8 

1 

=          480 
=            60 

RKT.ATION  OF  MEASURES  TO  WEIGHTS. 

Weight  of  water  at  62°. 

Measure. 

Cubic  inches. 

Grains. 

1  Gallon 

=           277-274 

sss 

70,000 

1  Quart 

=              69-318 

= 

17,500 

1  Pint 

=              34-659 

^s 

8,750 

16  Fluidounces 

=             27-727 

z=s 

7,000 

1  Fluidounce 

=                1-732 

=: 

437-5 

1  Fluidrachm 

=                0-216 

= 

54-7 

1  Minim 

=                0*0336 

= 

0-91 

The  weight  of  owe  cubic  inch  of  distilled  water  at  62°  is  252*458  grains. 
The  Troy  ounce  of  distilled  water,  which  contains  480  grains,  is  equal  to 
1'8047  cubic  inches.  The  wine-pint  corresponds  to  28-875,  and  the  Imperial 
pint  to  84-65  cubic  inches  at  60°.  100  cubic  inches  are  equal  to  57  fluid- 
ounces. 

The  Metrical  System. — The  French  metre  is  equal  to  39-370788  English 
inches.  The  metre  is  in  France  the  integer  of  the  measure  of  length,  and 
from  it  all  measures  of  surface,  capacity,  and  weight,  are  derived.  The 
integer  of  the  measure  of  capacity  is  the  litre,  which  is  the  cubed  decimetre, 
and  is  equal  to  35'275  fluidounces,  or  1-763  Imperial  pints.  The  integer  of 
the  measure  of  weight,  is  the  gramme,  =  15  434  English  grains.  It  is 
exactly  equal  to  the  weight  of  a  cubic  centimetre  of  water  weighed  in  vacuo, 
at  its  maximum  density  (39°-38).  The  cubic  centimetre  is  employed  by 
French  chemists  in  all  measurements  of  gases  in  place  of  our  cubic  inch.  It 
is  equal  to  0*061  of  a  cubic  inch.  It  corresponds  to  about  17  minims,  and 
weighs  1  gramme  or  15  4  grains.  Two  fluidounces  by  measure  are  equal  to 
58  cubic  centimetres.  The  weight  of  the  cubic  centimetre  of  water  is  to 
the  cubic  inch  of  water  as  15  434  to  252*458  :  hence  there  are  16  34  cubic 
centimetres  to  an  English  cubic  inch. 

This  rule  is  sufficiently  correct  for  practical  purposes.  It  is  to  be  observed, 
however,  that  the  French  take  the  weight  of  the  cubic  centimetre  of  water  at 
39*38  in  vacuo:  the  English  take  the  weight  of  the  cubic  inch  (252-458 
grains)  at  62°  in  air.  Assuming  the  sp.  gr.  of  water  at  32°,  to  be  1  000000, 
the  sp.  gr.  at  39°*38  is  to  the  sp.  gr.  at  62°,  as  1-000099  to  0999000.  The 
French  measures  increase  and  decrease  in  decimal  proportions.  For  the 
increase,  a  prefix  is  used,  derived  from  the  Greek  deca,  hecto,  kilo,  and  myria; 
the  integer,  whether  metre,  litre,  or  gramme,  being  multiplied  by  10,  100, 
1000,  and  10,000  respectively.  To  indicate  the  decrease,  the  prefixes  deci, 
centi,  and  milii,  derived  from  the  Latin,  are  employed.  In  this  case  the 
integer  is  suppovsed  to  be  divided  by  10,  100,  or  1000. 

Various  plans  have  been  devised  for  converting  the  French  weights  and 
measures  into  their  English  equivalents.  The  following  Tables  will  be  found 
useful  for  this  purpose  : — 


METRICAL   EQUIVALENTS. 


731 


MEASURES  OF  LENGTH. 


MEA8DBE8  OF  VOLUME. 


English  inches. 

Cubic  Inches. 

Millimetre  .     .     =              '03937 

Millilitre     . 

=                 'OeiOS 

Centimetre       .     =               -39371 

Centilitre    . 

=                 -61028 

Decimetre  .     .     =            3-937(t8 

Decilitre      . 

=            6-1028 

MHre     .     .     .     =          39-37079 

Litre       .     .     . 

=           61-028 

Decamfetre  .     .     =         393-70788 

Decalitre     . 

.     =         610-28 

Hectometre      .     =       3937*0788 

Hectolitre   . 

=       6102-8 

Kilometre    .     .     =     39370-788 

Kilolitre 

=     61028- 

Mjriametre      .     =  393707-88 

Myrialitre  . 

=  610280- 

MEASURES  OP  WEIGHT. 

English  grains. 

Milligramme   . 

.      = 

•0154 

Centigramme  . 

.      = 

•1543 

Decigramme    . 

— 

1-5434 

Gramme 

.      = 

15-434 

•  Decagramme  . 

=s 

154-34 

Hectogramme 

.      = 

1543-4 

Kilogramme    ....,.     =     15434- 
Myriagramme =  154340- 

A  kilogramme  is  equal  to  22046  pounds  Avoirdupois,  and  1000  kilo- 
grammes are  equal  to  an  English  ton.  The  quintal,  or  50  kilogrammes,  is 
equal  to  an  English  cwt.  With  respect  to  the  equivalents  of  French  and 
English  weights  and  measures,  some  slight  differences  will  be  found  among 
English  writers.  These  arise  from  the  calculations  being  based  on  the  em- 
ployment of  a  larger  or  smaller  number  of  decimal  figures. 

The  gramme  is  the  French  unit  of  weight,  and  is  much  too  high  for  many 
purposes,  as  it  represents  15"43  grains  of  our  ordinary"  weight.  A  deci- 
gramme corresponds  to  about  one  grain  and  a  half  of  our  weight.  There  is 
no  weight  corresponding  to  our  well-known  and  highly  convenient  unit  of 
one  grain.  It  is  rather  less  than  seven  centigrammes,*  being  represented  by 
the  decimal  0-0648  grammes.  The  Troy  or  Apothecaries'  ounce  corresponds 
to  31  08  grammes,  while  the  Avoirdupois  ounce  is  represented  by  28  328 
grammes.  A  cubic  centimetre  is  the  unit  of  French  liquid  measure,  and, 
compared  with  our  cubic  inch,  is  as  much  too  small  as  the  gramme  is  too 
large  for  convenient  use.  It  corresponds  to  nearly  17  minims,  and  it  weighs 
one  gramme,  or  15" 4  grains.  In  reference  to  these  metrical  weights,  what- 
ever trouble  they  may  save  to  advanced  chemists  in  calculating  the  results 
of  their  analyses,  the  introduction  of  tliem  into  pharmacy  would  have  led  to 
serious  if  not  fatal  mistakes  in  the  preparation  and  dispensing  of  medicines. 
The  habits  of  a  profession  or  of  the  population  of  a  country  cannot  be  sud- 
denly changed  in  this  respect,  nor  can  such  a  change  as  the  metrical  system 
would  effect  be  only  partial.  It  must  include  weights,  measures,  depths, 
heights,  distances,  and  square  as  well  as  long  measure.  However  the  scien- 
tific physician  may  admire,  in  the  abstract,  the  rigorous  simplicity  of  the 
gramme,  the  metre,  and  the  litre,  he  would  not  venture  to  prescribe  medi- 
cines in  centigrammes  or  cubic  centimetres;  nor  would  a  scientific  chemist, 
wishing  to  make  his  processes  intelligible  in  the  arts  and  manufactures,  adopt 
the  metrical  system  of  weights  and  measures  without  giving  side  by  side  a 
translation  of  quantities  for  the  information  of  his  English  readers.  The 
constructors  of  the  British  pharmacopoeia  may  well  have  shrunk  from  the 
responsibility  of  imposing  on  the  profession  a  system  of  weights  and  measures 
which  not  one  dispenser  in  five  hundred  would  understand  or  know  hov7 
to  use. 

As,  however,  an  attempt  has  been  made  to  force  this  system  on  students 
of  chemistry  by  its  adoption  in  some  English  works  on  the  science,  it  will  be 
well  to  insert  here  the  tables  showing  the  relation  of  some  of  the  common 
weights  to  those  of  the  metrical  system. 


732 


BAROMETRICAL    EQUIVALENTS. 


RELATIONS  OF  THE  WEIGHTS  OF  THE  BRITISH  PHARMACOPCEIA  TO  THE  METRICAL  WEIGHTS. 


1  Pound 
1  Ounce 
1  Grain 


=     543*9525  grammes. 
=      28-3495         " 
=        0-0648         " 


1  Gallon    . 
1  Pint 

1  Fluidounce 
1  Fluidrachm 
1  Minim     . 


MEASURES  OP  CAPACITY. 

=  4-543487  litres.     . 

=  0-567936      "     or  567-936  cubic  centimetres. 

=  0-028396      "       "     28-396     "  " 

==  0-003549      "       "       3-549      "  " 

=  0-000059      "      "      0-059     "  " 


Surfaces  and  Capacities. — Surface  of  a  Sphere :  diameter  squared  x 
3"141593.  Capacity  of  a  Sphere:  diameter  cubed  X  0-5236.  Area  of  a 
Circle:  diameter  squared  x  0'785938.  Area  of  Rectangle,  Square,  Rhom- 
hus,  and  Rhomboid :  base  X  by  the  height.  Capacity  of  the  Prisfh  or  Cylin- 
der (rule  for  calculating  the  capacities  of  cylindrical  vessels  used  for  Gases)  : 
area  of  the  base  x  by  height. 

Barometric  Scale  in  Millimetres  and  Inches. 

In  foreign  scientific  works,  and  in  some  recent  English  works  on  chemistry, 
the  barometrical  pressure,  whether  for  meteorological  or  other  scientific  pur- 
poses, is  represented  in  millimetres.  The  subjoined  Table  gives  the  corre- 
sponding equivalents  in  English  inches :  the  pressure  to  which  gases  are 
submitted  may  be  thus  easily  ascertained  without  resorting  to  calculation  : 
762  mm  =  30  incljes  mean  pressure. 


Mm. 

In. 

Mm. 

In. 

Mm. 

In. 

700 

= 

27-560 

7.30 

= 

28-741 

760 

= 

29-922 

701 

r= 

27-599 

731 

^ 

28-780 

761 

= 

29-961 

702 

= 

27-638 

732 

= 

28-819 

*762 

= 

*30-000 

703 

=r 

27-678 

733 

= 

28-859 

763 

= 

30-040 

704 

= 

27-717 

734 

= 

28-898 

764 

=r 

30-079 

705 

= 

27-756 

735 

=3 

28-938 

765 

= 

30-119 

706 

= 

27-796 

736 

=s 

28-977 

766 

= 

30-158 

707 

= 

27-835 

737 

=: 

29-016 

767 

= 

30-197 

708 

= 

27-876 

738 

= 

29-056 

768 

= 

30-237 

709 

= 

27-914 

739 

= 

29-095 

769 

= 

30-276 

710 



27-953 

740 

_. 

29-134 

770 

^ 

30-315 

711 

= 

27-992 

741 

= 

29-174 

771 

= 

30-355 

712 

= 

28-032 

742 

= 

29-213 

772 

= 

30-384 

713 

= 

28-071 

743 

= 

29-252 

773 

= 

30-434 

714 

= 

28-111 

744 

= 

29-292 

774 

=: 

30-473 

715 

= 

28-150 

745 

= 

29-331 

775 

= 

30-512 

716 

= 

28-189 

746 

= 

29-371 

776 

= 

30-552 

717 

= 

28-229 

747 

= 

29-410 

777 

:^ 

30-591 

718 

s= 

28-268 

748 

= 

29-449 

778 

=: 

30-631 

719 

= 

28-308 

749 

= 

29-489 

779 

= 

30-670 

720 

_ 

28-347 

750 

__ 

29-528 

780 



30-709 

721 

= 

28-386 

751 

= 

29-567 

781 

= 

30-749 

722 

== 

28-426 

752 

= 

29-607 

782 

= 

30-788 

723 

r^ 

28-465 

753 

= 

29-646 

783 

= 

30-827 

724 

= 

28-504 

754 

s:= 

29-685 

784 

^=. 

30-867 

725 

= 

28-543 

755 

= 

29-725 

785 

=: 

30-906 

726 

= 

28-583 

756 

s=: 

29-764 

786 

= 

30-945 

727 

=s 

28-622 

757 

s= 

29-804 

787 

= 

30-985 

728 

=: 

28-661 

758 

= 

29-843 

788 

= 

31-024 

729 

= 

28-701 

759 

= 

29-882 

789 

= 

31-063 

THERMOMETRICAL    EQUIVALENTS, 


•733 


THERMOMETRICAL  EQUIVALENTS. 

Rules  for  converting  Degrees  of  Fahrenheit's,  Centigrade,   and  Reaumur's 
Thermometers  into  each  other. 

The  space  between  the  two  fixed  points  of  temperature— namely,  the 
freezing  and  boiling  of  water,  is  divided  by  Fahrenheit  into  180°,  by  Centi- 
grade into  100°,  and  by  Reaumur  into  80°: 

W  =  9.     »2"o°  =5.    |g  =  4     :    therefore  9  F.  represents  5  C.  and  4  R. 


5  X  1-8  =  9 

1-8: 


}  therefore   ^[i^'.^Z^'. 


The  zero  of  C.  and  of  R.  is  at  the  freezing  of  water:  the  zero  of  F.  is  32° 
F.  below  the  zero  of  C.  and  of  R. 

Therefore — L  For  temperatures  above  the  zero  of  C.  (32°  F.) 
Rule.  Examples. 

F.  — 32    -r-  1-8  =  C 40OF.  — 32(=8)-|-l-8=4o-44C. 

C.  X    1.8+32    =F 40-44C.  X  1-8  (=8)4- 32  =  400  F. 

2.  For  temperatures  helow  the  zero  of  C.  (32°),  but  not  below  the  zero  of 

F.  (— n°-t  C.) 

Rale.  Examples. 

F.  ~  32    -i-   1-8  =  C.     .     .     20OF. -32  (=12)-M-8  =  — 60-66C. 
~C.  X    1-8-32     =F.     .     .       60-66C.  Xl-8  (=12)~32  =  20OF. 

3.  For  temperatures  helow  the  zero  of  F.  ( — 17°'t  C.) 

Rule.  Examples,w 

— F.  +  32    -1.  1-8  =  — C.     .     .    20OF.  +  32  (=52) -r- 1-8  =  —280-8  C. 
— C.  X    1-8-32     =— F.     .     .     280.8C.  xl-8(=52)— 32  =  — 20OF. 

To  convert  Fahrenheit  and  Reaumur  into  each  other,  use  the  above  roles, 
only  substituting  for  C.  1-8,  R.  2-5  i//  =  2-5 

As  the  Centigrade  thermometer  is  employed  by  all  French  and  German 
writers  and  by  a  few  English  writers  on  Chemistry,  we  subjoin  for  convenient 
reference  a  Table  of  the  equivalent  degrees  of  Centigrade  and  Fahrenheit 
between  the  freezing  and  the  boiling  points  of  mercury. 


Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

—40° 

—40-0° 

—18° 

—  0-4° 

4°. 

.     39-2° 

26°.. 

.     78-8° 

48°.. 

.  118-4° 

—39 

—38-2 

—17 

4-  1-4 

5  .. 

.     41-0 

27  .. 

.     80-6 

49  .. 

120-2 

—38 

-36-4 

—16  . 

..       3-2 

6  . 

.     42-8 

28  .. 

.     82-4 

50  .. 

122-0 

—37 

—34-6 

—15  . 

..       5-0 

7  . 

.     44-6 

29  .. 

.     84-2 

51  .. 

123-8 

—36 

-32-8 

—14  . 

..       6-8 

8  . 

.     46-4 

30  . 

.     86-0 

52  .. 

125-6 

—35 

-30-0 

-13  . 

..       8-6 

9  . 

.     48-2 

31  .. 

.     87-8 

53  .. 

127-4 

—34 

—29-2 

—12  . 

..     10.4 

10  .. 

.     50-0 

32  .. 

.     89-6 

54  .. 

129-2 

—33 

—27-4 

—11  . 

..     12-2 

11  .. 

.     51-8 

33  .. 

.     91-4 

55  .. 

1310 

—32 

-25-6 

—10  . 

..     14-0 

12  .. 

.     53-6 

34  .. 

.     93-2 

56  .. 

132-8 

—31 

-23-8 

—  9  . 

..     15-8 

13  .. 

.     55-4 

35  .. 

.     95-0 

57  .. 

134-6 

—30 

-22-0 

—  8  . 

..     17-6 

14  .. 

.     57-2 

36  .. 

.     96-8 

58  .. 

136-4 

—29 

-20-2 

—  7  . 

..     19-4 

15  .. 

.     59-0 

37  .. 

.     98-6 

59  .. 

138-2 

—28 

-18-4 

—  6  . 

..     21-2 

16  .. 

.     60-8 

38  .. 

.  100-4 

60  .. 

140-0 

—27 

—16-6 

—  5   . 

..     23-0 

17  .. 

.     62-6 

39  .. 

.  102-2 

61   .. 

141-8 

—26 

-14-8 

—  4  . 

..     24-8 

18  .. 

.     64-4 

40  .. 

.  104-0 

62  .. 

143-6 

—25 

-13-0 

—  3  . 

..     26-6 

19  .. 

.     66-2 

41  .. 

.  105-8 

63  ... 

145-4 

—24 

-11-2 

—  2  . 

..     28-4 

20  .. 

.     68-0 

42  .. 

.  107-6 

64  ... 

147-2 

—23 

—  9-4 

—  1  . 

..     30-2 

21  .. 

.     69-8 

43  .. 

.  109-4 

65  ... 

149-0 

—22 

—  7-6 

0  . 

..     32-0 

22  .. 

.     71-6 

44  .. 

.  111-2 

66  ... 

150-8 

—21 

—  5-8 

+  1   • 

..     33-8 

23  .. 

.     73-4 

45  .. 

.  113-0 

67  ... 

152-6 

—20 

—  4-0 

2  . 

..     35-6 

24  .. 

.     75-2 

46  .. 

.  114-8 

68  ... 

154-4 

—19 

—  2-2 

3  . 

..     37-4 

25  .. 

.     77-0 

47  .. 

.  116-6 

69  ... 

156-2 

734 


THERMOMETRICAL    EQUIVALENTS. 


Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

70°.. 

158-0° 

129°... 

264-2° 

188°... 

370-4° 

247°.. 

476-6° 

306° 

..  582-8° 

71  .. 

159-8 

130  ... 

266-0 

189  .. 

372-2 

248  .. 

478-4 

307  . 

..  584-6 

72  .. 

161-6 

131  ... 

267-8 

190  .. 

3740 

249  .. 

480-2 

308  . 

..  586-4 

73  .. 

163-4 

132  ... 

269-6 

191  ... 

375-8 

250  .. 

482-0 

309  . 

..  588-2 

74  .. 

165-2 

133  ... 

271-4 

192  .. 

377-6 

251  .. 

483-8 

310  . 

..  590-0 

75  .. 

167-0 

134  ... 

273-2 

193  .. 

379-4 

252  .. 

485-6 

311  . 

..  591-8 

76  .. 

168-8 

135  ... 

275-0 

194  .. 

381-2 

253  .. 

487-4 

312 

..  593-6 

77  .. 

170-6 

136  ... 

276-8 

195  .. 

383-0 

254  .. 

489-2 

313 

..  595-4 

78  .. 

172-4 

137  ... 

278-6 

196  .. 

384-8 

255  .. 

491-0 

314 

..  597-2 

79  .. 

174-2 

138  ... 

280-4 

197  .. 

386-6 

256  .. 

492-8 

315 

..  599-0 

80  .. 

176-0 

139  ... 

282-2 

198  .. 

388-4 

257  .. 

494-6 

316 

..  600-8 

81  .. 

177-8 

140  ... 

284-0 

199  .. 

390-2 

258  .. 

496-4 

317 

..  6026 

82  .. 

179-6 

141  ... 

285-8 

200  .. 

392-0 

259  .. 

498-2 

318 

..  604-4 

83  .. 

181-4 

142  .. 

287-6 

201  .. 

393-8 

260  .. 

500-0 

319 

..  606-2 

84  .. 

183-2 

143  .. 

289-4  ' 

202  .. 

395-6 

261  .. 

501-8 

320 

..  608 -0 

85  .. 

185-0 

144  .. 

291-2 

203  .. 

397-4 

262  .. 

503-6 

321 

..  609-8 

86  .. 

186-8 

145  .. 

293-0 

204  .. 

399-2 

263  .. 

.  505-4 

322 

..  611-6 

87  .. 

188-6 

146  .. 

294-8 

205  .. 

401-0 

264  .. 

.  507-2 

323 

..  613-4 

88  .. 

190-4 

147  .. 

296-6 

206  .. 

402-8 

265  .. 

.  509-0 

324 

..  615-2 

89  .. 

192-2 

148  .. 

298-4 

207  .. 

404-6 

266  .. 

.  510-8 

325 

..  617-0 

90  .. 

194-0 

149  .. 

300-2 

208  .. 

406-4 

267  .. 

.  512-6 

326 

...  618-8 

91  .. 

195-8 

150  .. 

302-0 

209  .. 

.  408.2 

268  .. 

.  514-4 

327 

...  620-6 

92  .. 

197-6 

151  .. 

303-8 

210  .. 

.  410-0 

269  .. 

.  516-2 

328 

...  622-4 

93  .. 

.  199-4 

152  .. 

305-6 

211  .. 

.  411-8 

270  .. 

.  518-0 

329 

...  624-2 

94  .. 

.  201-2 

153  .. 

307-4 

212  .. 

.  413-6 

271  .. 

.  519-8 

330 

...  626-0 

95  .. 

.  203-0 

154  .. 

309.2 

213  .. 

.  415-4 

272  .. 

.  521-6 

331 

...  627-8 

96  .. 

.  204-8 

155  .. 

.  311.0 

214  .. 

.  417-2 

273  .. 

.  523-4 

332 

...  629-6 

97  .. 

.  206-6 

156  .. 

312.8 

215  .. 

.  419-0 

274  .. 

.  525-2 

333 

...  631-4 

98  .. 

.  208-4 

^57  .. 

%58  .. 

314.6 

216  .. 

.  420-8 

275  .. 

.  527-0 

334 

...  633-2 

99  .. 

.  210-2 

.  316.4 

217  .. 

.  422-6 

276  .. 

.  528-8 

335 

...  635-0 

100  .. 

.  212-0 

159  .. 

.  318.2 

218  .. 

.  424-4 

277  .. 

.  530-6 

336 

...  636-8 

101  .. 

.  213-8 

160  .. 

.  320-0 

219  .. 

.  426-2 

278  .. 

.  532-4 

337 

...  638-6 

102  .. 

.  215-6 

161  .. 

.  321-8 

220  .. 

.  428-0 

279  .. 

.  534-2 

338 

...  640-4 

103  .. 

.  217-4 

162  .. 

.  323-6 

221  .. 

.  429-8 

280  .. 

.  536-0 

339 

...  642-2 

104  .. 

.  219-2 

163  .. 

.  325-4 

222  .. 

.  431-6 

281  .. 

.  537-8 

340 

...  644-0 

105  .. 

.  221-0 

164  .. 

.  327-2 

223  .. 

.  433-4 

282  .. 

.  539-6 

341 

...  645-8 

106  .. 

.  222-8 

165  ,. 

.  329-0 

224  .. 

.  435-2 

283  .. 

.  541-4 

342 

...  647-6 

107  .. 

.  224-6 

166  .. 

.  330-8 

225  .. 

.  437-0 

284  .. 

.  543-2 

343 

...  649-4 

108  .. 

.  226-4 

187  .. 

.  332-6 

226  .. 

.  438-8 

285  .. 

.  545-0 

344 

...  651-2 

109  .. 

.  228-2 

168  .. 

.  334-4 

227  .. 

.  440-6 

286  .. 

.  546-8 

345 

...  653-0 

110  .. 

.  230-0 

169  .. 

.  336-2 

228  .. 

.  442-4 

287  .. 

.  548-6 

346 

...  654-8 

Ill  .. 

.  231-8 

170  .. 

.  338.0 

229  .. 

.  444-2 

288  .. 

.  550-4 

347 

...  656-6 

112  .. 

.  233-6 

171  .. 

.  339-8 

230  .. 

.  446-0 

289  .. 

.  552-2 

348 

...  658-4 

113  .. 

.  235-4 

172  .. 

.  341-6 

231  .. 

.  447-8 

290  .. 

.  554-0 

349 

...  660-2 

114  .. 

.  237-2 

173  .. 

.  343-4 

232  .. 

.  449-6 

291  .. 

.  555-8 

350 

...  662-0 

115  .. 

.  239-0 

174  .. 

.  345-2 

233  .. 

.  451-4 

292  .. 

.  557-6 

351 

...  663-8 

116  .. 

.  240-8 

175  .. 

.  347-0 

234  .. 

.  453-2 

293  .. 

.  559-4 

352 

...  665-6 

117  .. 

.  242-6 

176  .. 

.  348-8 

235  .. 

.  455-0 

294  .. 

.  561-2 

353 

...  667-4 

118  .. 

.  244-4 

177  .. 

.  350-6 

236  .. 

.  456-8 

295  .. 

.  5630 

354 

...  669-2 

119  .. 

.  246-2 

178  .. 

.  352-4 

237  .. 

.  458-6 

296  .. 

.  564-8 

355 

...  671-0 

120  .. 

.  248-0 

179  .. 

.  354-2 

238  .. 

.  460-4 

297  .. 

.  566-6 

356 

...  672-8 

121  .. 

.  249-8 

180  .. 

.  356-0 

239  .. 

.  462-2 

298  .. 

.  568-4 

357 

...  674-6 

122  .. 

.  251-6 

181  .. 

.  357-8 

240  .. 

.  464-0 

299  .. 

.  570-2 

358 

...  676-4 

123  .. 

.  253-4 

182  .. 

.  359-6 

241  .. 

.  465-8 

300  .. 

.  572-0 

359 

...  678-2 

124  .. 

.  255-2 

183  .. 

.  361-4 

242  .. 

.  4«7-6 

301  .. 

.  573-8 

360 

...  680-0 

125  .. 

.  257-0 

184  .. 

.  363-2 

243  .. 

.  469-4 

302  .. 

.  575-8 

126  .. 

.  258-8 

185  .. 

.  365-0 

244  . 

.  471-2 

303  .. 

.  577-4 

127  .. 

.  260-6 

186  .. 

.  366-8 

245  .. 

.  473-0 

304  .. 

.  579-2 

128  .. 

.  262-4 

187  .. 

.  368-6 

246  .. 

.  474-8 

305  . 

.  581-0 

RULE   FOR   CALCULATING   CHANGES   OF   VOLUME   IN   GASES   BY   PRESSURE. 

The  mean  height  of  the  barometer  is  to  the  observed  height  as  the  ob- 
served volume  to  the  volume  required,  or  the  mean  pressure  (30  inches)  is  to 


CHANGES  OF  VOLUME  IN  GASES  BY  TEMPERATURE.     735 

the  observed  pressure.     Hence,  assuming  100  cubic  inches  of  gas  to  be  at  28 
inches  pressure :  required  the  volume  at  30  inches  pressure. 

Mean  pr.  Obs.  pr.  Observed  volume.        Required  volume. 

30  :  28  ::  100  :  93-33 

Thus  100  cubic  inches  are  condensed  to  9333  cubic  inches  by  the  baro- 
meter rising  two  inches,  from  28  to  30.  The  increase  of  pressure  is  l-15th. 
and  the  diminution  of  volume  is  in  the  same  proportion. 

The  increase  in  the  weight  of  100  cubic  inches  of  gas  at  different  pressures, 
may  be  determined  by  the  following  rule:  if  100  cubic  inches  of  gas  weigh 
30  grains,  when  the  barometer  is  at  29  inches — required  the  weight  at  30 
inches. 

Obs.  pr.  Mean  pr.  Observed  weight.         Required  weight. 

29  :  30  :  :  30  :  31-03 

The  pressure  to  which  a  gas,  standing  over  mercury,  is  submitted,  is  indi- 
cated by  the  height  of  the  barometer,  when  the  mercury  on  the  inside  and 
outside  of  the  vessel  has  the  same  level  :  but  if  the  mercury  on  the  inside  be 
higher  than  on  the  outside,  the  difference,  in  inches  must  be  deducted  from 
the  height  of  the  barometer,  in  order  to  obtain  the  exact  pressure  to  which 
the  gas  is  subjected. 

RULE   FOR  CALCULATING   CHANGES   OF   VOLUME  IN  GASES  BY  TEMPERATURE. 

According  to  the  researches  of  Gay-Lussac,  1000  volumes  of  air  at  32° 
are  increased  to  1375  volumes  at  212°.  Hence  the  increase  is  f||,  or  2*08. 
for  each  degree  between  32°  and  212°:  and  1000H-2-08=480.  Hence  the 
increase  for  each  degree,  is  equal  to  l-480th  part  of  the  volume  at  32°  ;  or, 
assuming  that  the  volume  of  gas  at  this  temperature  is  480  cubic  inches, 
there  will  be  an  addition  of  one  cubic  inch  for  every  degree  of  increase  in 
temperature  up  to  212°.  By  taking  this  as  the  proportionate  increase  at 
any  two  temperatures,  it  will  be  easy  to  calculate  the  change  of  volume  for 
any  other  temperature.  The  mean  temperature  is  taken  at  60°,  and  480 
cubic  inches  at  this  temperature  would  become  (60 — 32  +  480)  508  cubic 
inches.  If  the  observed  temperature  be  70°,  then  480  cubic  inches  at  this 
temperature  would  be  (70—32  +  480)  518  cubic  inches.  The  number  32  is 
deducted  from  the  temperatures  because  it  is  from  this  degree  (32°)  that  the 
rate  of  expansion,  on  which  the  calculation  is  based,  commences.  It  is 
obvious  that  it  matters  not  whether  the  number  32  is  deducted  from  the  two 
temperatures,  or  from  the  number  480,  as  the  sura  will  be  the  same  in  the 
two  cases  ;  but  it  makes  this  important  difference  in  the  calculation,  that 
480—32=448  furnishes  a  constant,  which  needs  only  to  be  added  to  each 
temperature,  in  order  to  produce  the  proportionate  numbers.  This  constant 
is  easily  remembered,  by  the  fact  that  the  last  figure  of  the  three  is  produced 
by  the  addition  of  the  two  figures  that  precede  it,  each  being  equal  to  one- 
half  of  the  sum. 

The  rule  for  correction  is,  therefore,  as  follows:  The  increase  at  the 
T)bserved  temperature  (70°)  is  to  the  increase  at  the  mean  temperature  (60°) 
as  the  observed  volume  of  gas  (100  cubic  inches)  to  the  volume  required,  or 

Obs.  temp.  Mean  temp.  Obs.  vol.  Required  vol. 

448  +  70°        :         448  +  GO*'         : :         100        :        98-069 

Thus  100  cubic  inches  of  gas  at  70°  are  reduced  in  volume  to  98-069 
cubic  inches  by  cooling  10°,  i.  e.,  from  70°  to  60°.  The  rule  may  be  repre- 
sented under  the  following  simple  equation  : — 


136 


SPECIFIC    GRAVITY    OP    LIQUIDS. 


448  +  t'  X  V 
448  +  t 


t'  Mean  temperature, 
t  Observed  temperature. 
V  Observed  volume. 


100  cubic  inches  at  40°.  Required  the  volume  at  60°.  Answer  :  448  + 
60x100-^448  +  40  =  1041. 

With  an  alteration  in  volume  there  is  an  alteration  in  weight,  and  thus  the 
difference  at  any  two  temperatures  may  be  found  by  the  following  rule,  in 
which  observed  weight  is  substituted  for  observed  volume:  Thus  100  cubic 
inches  of  air  weigh  31  grains  at  60°.     Required  the  weight  at  212°. 


Obs.  temp. 
448  +  212= 


Mean  temp. 
448  +  60 


Grs.  obs.  weight. 
::         31 


Required  weight. 
23-86 


AQUEOUS   VAPOR  IN   GASES. 


The  subjoined  Table  represents  the  proportion  hy  volume  of  aqueous  vapor 
which  exists  in  any  gas,  standing  in  contact  with  water  at  the  corresponding 
temperatures  and  a  mean  barometric  pressure.  This  must  be  deducted  from 
the  measured  volume  in  order  to  determine  the  actual  volume  of  any  gas. 
(Faraday.) 


Temp. 

A.  V.  by  vol. 

Temp. 

A.  V.  by  vol. 

Temp. 

A.  V.  by  vol 

40°   . 

•00933 

54° 

•01533 

68°   . 

•02406 

41 

•00973 

55 

•01585 

69 

•02483 

42 

•01013 

56 

•01640 

70 

•02566 

43 

•01053 

57 

•01693 

71 

•02653 

44 

•01093 

58 

•01753 

72 

•02740 

45 

•01133 

59 

•01810 

73 

•02830 

46 

•01173 

60 

•01866 

74 

•02923 

47 

•01213 

61 

•01923 

75 

•03020 

48 

•01253 

62 

•01980 

76 

•03120 

49 

•01293 

63 

•02050 

77 

•03220 

50 

•01333 

64 

•02120 

78 

•03323 

51 

•01380^ 

65 

•02190 

79    . 

•03423 

52 

•01426 

QQ 

•02260 

80 

•03533 

53 

•01480 

67 

•02330 

SPECIFIC   GRAVITIES. 

All  bodies  on  the  surface  of  the  earth  are  attracted  towards  its  centre  by 
gravitation.  The  comparative  force  with  which  gravitation  acts  on  different 
bodies,  is  called  their  relative  weight.  Equal  masses  of  the  same  substance 
gravitate  equally  ;  that  is,  have  equal  weights  :  but  equal  masses  of  different 
substances  gravitate  unequally  ;  or,  in  other  words,  each  species  of  substance 
has  its  own  peculiar  force  of  gravitation.  Specific  gravity,  therefore,  is  the 
relative  gravitating  power  (or  weight)  of  equal  volumes  of  different  sub- 
stances. 

In  determining  specific  gravities,  two  processes  are  necessary  :  first,  that 
the  substances  compared  should  be  reduced  to  equal  volumes ;  secondly, 
that  the  comparative  weight  of  these  equal  volumes  should  be  found. 

Specific  Gravity  op  Liquids. — All  liquids  are  easily  reduced  to  equal 
volumes  by  filling  the  same  bottle  at  the  same  temperature  successively  with 
each  of  them,  and  weighing  it  when  so  filled.  These  different  weights, 
minus  that  of  the  bottle,  are  the  comparative  specific  gravities  of  the  liquids 
experimented  on.  The  specific  gravity  of  water,  is  the  unit  to  which  that  of 
all  liquids  and  solids  is  adjusted.  The  volume  of  liquids  varies  with  their 
temperature,  and  that  of  62°  F.  is  generally  adopted  in  this  country  as  the 
standard. 


BAUME'S    HYDROMETERS. 


737 


Light  glass  bottles  with  perforated  stoppers  are  sold,  with  a  counterpoise, 
for  the  purpose  of  taking  the  specific  gravities  of  liquids  and  small  solids. 
They  are  so  made  that  when  counterpoised  at  62°,  they  are  calculated  to  hold 
from  100  to  1000  grains  of  pure  (distilled)  water.  The  specific  gravity  of  a 
liquid  is  then  at  once  determined  by  its  weight.  Thus  the  1000-graiu  bottle 
would  hold  796  grains  of  absolute  alcohol  (0*796),  and  1846  grains  of  concen- 
trated sulphuric  acid  (1-846).  In  delicate  experiments  it  is  always  advisable 
to  take  the  exact  weight  of  water  which  the  counterpoised  bottle  will  hold ; 
as  slight  differences  in  the  volume,  and  therefore  in  the  weight  of  water, 
arise  in  fluctuations  in  temperature.  Thus,  according  to  the  temperature, 
the  bottle  will  sometimes  hold  more  and  sometimes  less  than  1000  grains. 

In  pathological  researches,  it  is  occasionally  required  to  take  the  sp.  gr. 
of  a  very  small  quantity  of  liquid.  A  light  glass  tube  about  three  inches 
long,  and  about  three-eighths  of  an  inch  in  diameter,  may  be  employed  for 
this  purpose.  It  may  be  fixed  in  a  hole  in  a  cork,  and  accurately  balanced. 
It  should  be  marked  in  horizontal  lines,  at  different  levels,  by  a  diamond ; 
and  the  weight  of  distilled  water  at  any  one  of  these  levels  being  ascertained, 
the  weight  of  the  liquid  at  the  same  level  may  be  afterwards  determined. 
The  two  weights  will,  by  the  rule  of  proportion,  give  the  specific  gravity. 

Baume's  hydrometer  is  much  used  on  the  Continent.  We  subjoin  a  Table, 
in  which  the  degrees  of  this  hydrometer  are  compared  with  the  ordinary 
range  of  the  specific  gravities  of  liquids. 

FOR  LIQUIDS  HEAVIER  THAN  WATER. 


jgrees. 

Sp.  gravity. 

Degrees. 

-Sp.  gravity. 

Degrees. 

Sp.  gravity. 

Degrees. 

Sp.  gravity 

0     . 

.      1-000 

20     .. 

.     1-152 

40      . 

.     1-357 

60     . 

.     1-652 

1     . 

.     1-007 

21     .. 

.     1-160 

41     . 

.     l-3b'9 

61     . 

.     1-670 

2     . 

.     1-013 

22     .. 

.     1-169 

42     . 

.     1-381 

62     . 

.     1-689 

3     . 

.     1-020 

23     .. 

.     1-178 

43     . 

.     1-395 

63     . 

.     1-708 

4     . 

.     1-027 

24     .. 

.     1-188 

44     . 

.     1-407 

64     . 

.     1-727 

5     . 

.     1-034 

25     .. 

.     1-197 

45     . 

.     1-420 

65     . 

.     1-747 

6     . 

.     1-041 

26     .. 

.     1-206 

46     . 

.     1-434 

66     . 

.     1-767 

7     . 

.     1-048 

27     .. 

.     1-216 

47     .. 

.     1-448 

•   67     . 

.     1-788 

8     . 

.     1-056 

28     .. 

.     1-225 

48     . 

.     1-462 

68     . 

.     1-809 

9     . 

.     1-063 

29     .. 

.     1-235 

49     . 

.     1-476 

69     . 

.     1-831 

10     . 

.     1-070 

30     .. 

.     1-245 

50     . 

.     1-490 

70     . 

.     1-854 

11     . 

.     1-078 

31     .. 

.     1-256 

51     .. 

.     1-505 

71     . 

.     1-877 

12     . 

.     1-085 

32     .. 

.     1-267 

52     . 

.     1-520 

72     . 

.     1-900 

13     . 

.     1-094 

33     .. 

.     1-277 

53     . 

.     1-535 

73     . 

.     1-924 

14     . 

.     1-101 

34     . 

.     1-288 

54     . 

.     1-551 

74     . 

.     1-949 

15     . 

.     1-109 

35     .. 

.     1-299 

55     . 

.     1-567 

75     . 

.     1-974 

16     . 

.     1-118 

36     . 

.     1-310 

56     . 

.     1-583 

76     . 

.     2-000 

17     . 

.     1-126 

37     . 

.     1-321 

57     . 

.     1-600 

18     . 

.     1-134 

38     . 

.     1-333 

58     . 

.     1-617 

19     . 

.     1-143 

39     . 

.     1-345 

59     . 

.     1-634 

FOR  LIQUIDS  LIGHl 

'ER  THAN  WATER. 

agrees. 
10     . 

Sp.  gravity. 
..     1-000 

Degrees. 
23     . 

Sp.  gravity. 
.      0-918 

Degrees, 
36     . 

Sp.  gravity. 
.      0-849 

Degrees. 
49     . 

Sp.  gravity; 
.     0-789 

11    . 

..     0-993 

24     . 

.     0-913 

37     . 

.     0-844 

•     50     . 

.     0-785 

12     . 

..     0-986 

25     . 

.     0-907 

38     . 

.     0-839 

51     . 

.     0-781 

13     . 

..     0-980 

26     . 

.     0-901 

39     . 

.     0-834 

52     . 

.     0-777 

14     . 

..     0-973 

27     . 

.     0-896 

40     . 

.     0-830 

53     . 

.     0-773 

15     . 

..     0-967 

28     . 

.     0-890 

41     . 

.     0-825 

54     . 

.     0-768 

16     . 

..     0-960 

29     . 

.     0-885 

42     . 

.     0-820 

55     . 

.     0-764 
.     0-760 

17     . 

..     0-954 

30     . 

.     0-880 

43     . 

.     0-816 

56     . 

18     . 

..     0-948 

31     . 

..     0-874 

44     . 

.     0-811 

57     . 

.     0-757 
.     0-753 

19     . 

..     0-942 

32     . 

.     0-8(59 

45     . 

.     0-807 

58     . 

20     . 

..     0-936 

33     . 

..     0-864 

46     . 

..     0-802 

59     . 

.     0-749 

21     . 

..     0-930 

34     . 

..     0-859 

47     . 

..     0-798 

60     . 

.     0  745 
.     0-741 

22     . 

..     0-924 

35     . 

..     0-854 

48     . 

..     0-794 

61     . 

47 


738 


SPECIFIC    GRAVITY    OF    SOLIDS. 


Twaddell's  hydrometer  is  employed  by  English  Chemical  manufacturers. 
The  degrees  on  Tvvaddell  are  readily  converted  into  equivalent  specific 
gravities,  by  multiplying  them  by  5°,  and  adding  1000.  Thus  8°  Twaddell, 
8x5  =  40  +  1000  =  1040.     We  subjoin  a  Table  of  their  equivalents. 


rees 

Sp.  gravity. 

Degrees. 

Sp.  gravity. 

Degrees. 

Sp.  gravity. 

Degrees. 

Sp.  gravity 

1 

...      1-005 

8 

..      1-040 

15      . 

..     1-075 

22      . 

.     1-110 

2 

...      1-010 

9 

..     1-045 

16      . 

..     1-080 

23     . 

.     1-115 

3 

...     1-015 

10 

..     1-050 

17     . 

..     1-085 

24     . 

.     1-120 

4 

...     1-020 

11 

..     1-055 

18     . 

..     1-090 

25     . 

.     1-125 

5 

...     1-025 

12 

...     1-060 

19     . 

..     1-095 

26     . 

.     1-130 

6 

...     1-030 

13 

...     1-065 

20     . 

..     1-100 

27     . 

.     1-135 

7 

...     1-035 

14 

..     1-070 

21     . 

..     1-105 

28     . 

.     1-140 

Specific  Gravity  of  Powders  or  Small  Solids. — The  sp.  gr.  of  solids 
in  powder  or  in  small  pieces  may  also  be  conveniently  determined  by  a  bottle. 
Thus  :  weigh  the  powder,  pour  it  into  the  bottle,  and  fill  it  with  water  at 
62°  F.,  taking  care  to  dislodge  all  adhering  bubbles  of  air.  Then  weigh  it 
and  deduct  the  known  weight  of  the  bottle  :  the  remainder  is  the  conjoint 
weight  of  the  powder  and  water.  Deduct  from  this  last  sum  the  found 
weight  of  the  powder,  and  the  difference  is  the  weight  of  the  water ;  deduct 
this  difference  from  the  known  weight  of  water,  required  to  fill  the  bottle, 
and  the  remainder  is  the  weight  of  a  volume  of  water,  equal  to  the  volume 
of  the  solid  in  powder;  then,  as  this  is  to  the  known  weight  of  water,  required 
to  fill  the  bottle  :  :  sp.  gr.  water  :  sp.  gr.  powder. 

We  subjoin  an  example  in  reference  to  native  platinum  in  grains  : — 


Weight  of  water  in  the  bottle 

Weight  of  native  platinum  grains  (in  air)    . 

Weight  of  water  and  platinum  in  bottle 


Grains. 
1000 
40 

1040 
1037-5 


Difference  =:  vol.  of  water  displaced     ...  2-5 

40     -r-     2-5     =:     1 6  sp.  gr.  of  native  platinum. 

The  sp.  gr.  of  mercury,  or  any  liquid  or  solid,  not  dissolved  by  water,  may 
be  obtained  by  the  same  rule.  When  the  substance  is  soluble  in  water, 
another  liquid  of  known  sp.  gr.,  which  does  not  act  upon  the  solid,  must  be 
employed.  Alcohol,  oil  of  turpentine,  or  olive  oil,  may  be  used,  or,  in  some 
cases,  the  substance  may  be  coated  with  varnish.  ^  ssuming  that  the  sp.  gr.  of 
sugar  is  required,  and  the  liquid  selected  is  oil  of  turpentine,  sp.  gr.  0-870  ; 
the  sugar  is  first  weighed  in  air,  and  then  in  the  oil ;  the  difference  gives  the 
weight  of  an  equal  bulk  of  the  oil  ;  then,  if  the  weight  of  the  sngar  in  air 
be  400  grains,  and  its  weight  in  oil  of  turpentine  182 '5,  the  weight  of  an 
equal  bulk  of  the  oil  will  be'400— 182-5=217 '5.  Then  0*870  :  1000  :  :  217-5 
:  250,  and  400-7-250=1-6,  which  is  the  sp.  gr.  of  the  sugar. 

Specific  Gravity  of  Solids  Heavier  than  Water. — Weigh  the  solid 
in  air,  then  suspend  it  by  a  fine  thread  to  one  arm  of  a  balance;  exactly 
counterpoise  it,  and  immerse  the  solid  so  counterpoised  in  distilled  water  at 
62*^  F. ,  and  note  how  much  less  it  weighs  now  than  when  weighed  in  air. 
The  difference  between  the  two  is  the  weight  of  a  volume  of  water  exactly 
equal  to  that  of  the  immersed  solid.  Divide  the  weight  of  the  solid  in  air 
by  this  difference,  and  the  result  is  the  sp.  gr.  of  the  solid.  Thus,  in  re- 
ference to  a  small  bar  of  aluminum : — 


SPECIFIC    GRAVITY    OF    GASES.  739 

Grains. 

Weight  of  aluminum  in  air 46 "3 

Weight  of  aluminum  in  water         .         .         .         .29-0 

Difference  =  volume  of  water      ....     17*3 
46-3  -f-  17*3  =  2-6  sp.  gr.  of  aluminum. 

A  portion  of  bone  in  air  weighed  90*6  grains:  in  water  45'6.  Differ- 
ence =  45  grains  ;  and  90-6-^45=2'01  sp.  gr.  of  hone.  A  portion  of  muscle 
weighed  in  air  91-2  grains  :  in  water  7*2  grains.  Difference  =  84  grains  ; 
and  91'2-^84  =  1'085  sp.  gr.  of  muscle., 

A  knowledge  of  the  specific  gravity  of  solids  enables  a  chemist  to  deter- 
mine the  weight  of  bodies  from  their  volume.  A  cubic  foot  of  water  con- 
tains 1728  cubic  inches,  and  weighs  1000  ounces  (strictly,  997*145  ounces 
or  62'4  pounds  Av.)  ;  hence  a  cubic  foot  of  sulphur  (sp.  gr.  1-957)  would 
weigh  1957  ounces,  and  a  cubic  foot  of  marble  (sp.  gr.  2-5)  would  weigh 
2500  ounces.  A  cubic  foot  of  ice  weighs  937 '6  ounces,  or  58'6  pounds  Av. ; 
a  cubic  foot  of  air  weighs  535*161  grains. 

Specific  Gravity  of  Solids  Lighter  than  Water. — 1.  Find  the  weight 
of  the  solid  {a)  in  air.  2.  Take  a  piece  of  metal  heavy  enough  to  make  a 
sink  in  water,  and  find  its  weight  in  air  and  in  water.  8.  Tie  together  a  and 
the  metal,  and  find  the  weight  of  the  compound  mass  in  water.  The  differ- 
ence between  the  weight  of  the  metal  in  air  and  in  water  is  the  weight  of  a 
volume  of  water,  equal  to  that  of  the  metal ;  deduct  this  from  the  difference 
between  the  weights  in  air  and  in  water  of  the  compound  mass,  and  the 
remainder  is  the  weight  of  a  volume  of  water  equal  to  a.  We  divide  the 
weight  of  a  by  the  remainder,  and  obtain  the  sp.  gr.  Thus  with  reference 
to  beef-fat : — 

Grains. 

Weight  of  the  fat  in  air 117-3 

Add  brass  weight  to  sink  it 1000-0 

Weight  of  compound  mass  in  air  .         .         .         .     1117-3 

Grains. 

Loss  of  weight  by  the  compound  mass  in  water     .       245-5 

"  brass  weight  (1000)      "  .       119-4 

Weight  of  the  water  displaced  by  the  fat      .        .       126-1 
Hence  117-3  -f-  126-1  =  0-930  sp.  gr.  of  beef-fat. 

Specific  Gravity  of  Gases. — The  principles  are  the  same  as  those  above 
described  for  determining  the  specific  gravity  of  solids  and  liquids.  The 
weighing  of  the  air  and  gas  should  take  place  at  the  same  temperature  and 
pressure,  or  a  calculation  should  be  made  according  to  the  rules  already 
given  (p.  735).  In  reference  to  Gases  and  Vapors,  air  is  taken  as  the 
standard  of  unity  (pp.  84  and  743). 

Gases.— A  light  glass  flask,  of  about  40  or  50  c.  i.  capacity,  is  employed. 
This  is  capable  of  being  screwed  to  the  air-pump  plate,  and  of  being  sus- 
pended to  a  scale-beam  and  accurately  balanced.  The  flask  is  exhausted, 
balanced,  filled  with  dry  air,  and  again  balanced.  The  increase  in  weight 
represents  the  weight  of  the  volume  of  dry  air  in  the  flask,  at  the  pressure 
and  temperature  at  which  it  was  filled.  The  experiment  is  repeated  with 
the  dry  gas,  the  sp.  gr.  of  which  is  proposed  to  determine.  The  following 
is  an  example  of  the  sp.  gr.  of  Carbonic  acid  : — 


•740  SPECIFIC    GRAVITY    OF    VAPORS. 

Grains. 
Weight  of  the  flask  with  drj  air  .  .  .  .  2033-8 
Weight  of  the  flask  exhausted       ....     2021-4 


Weight  of  dry  air  in  the  flask       ....        12*4 

Grains. 
Weight  of  the  flask  with  dry  carbonic  acid  .  .  2040-24 
Weight  of  flask  exhausted  .         •        .         .  2021-40 


Weight  of  dry  carbonic  acid  in  flask     .         .         .       18-84 
Hence  18-84  -J-  12-4  =  1-520  sp.  gr.  of  carbonic  acid. 

When  the  sp.  gr.  of  a  gas  has  been  ascertained,  the  weight  of  100  cubic 
inches  is  determined  by  multiplying  the  sp.  gr.  of  the  gas  by  the  weight  of 
100  cubic  inches  of  air  =  31  grains  (pp.  158  and  143).  Thus,  100  cubic 
inches  of  dry  carbonic  acid  are  found  by  experiment  to  weigh  41 '08  grains, 
and  its  sp.  gr.  (r520x31=4t'l)  gives  471  grains  for  the  weight  of  100 
cubic  inches,  calculated  by  this  rule.  Conversely,  when  we  have  ascertained 
the  weight  of  100  cubic  inches  of  a  gas,  we  can  determine  its  sp.  gr.  by 
dividing  this  weight  by  31.  Thus  4t"l-i- 31  =  1-520.  The  sp.  gr.  of  a  gas, 
of  which  the  atomic  weight  is  known,  may  also  be  determined,  by  multiplying 
the  atomic  weight  by  the  sp.  gr.  of  hydrogen.  Thus  the  atomic  weight  of 
carbonic  acid  is  22,  and  22  x  "0691  =  1*5202,  the  sp.  gr.  of  carbonic  acid. 
On  the  other  hand,  if  the  sp.  gr.  is  known,  the  atomic  weight  may  be  de- 
termined by  dividing  the  sp.  gr.  of  the  gas,  by  the  sp.  gr.  of  hydrogen,  thus 
1-502 "7- -0691=22,  the  atomic  weight  of  carbonic  acid.  When  however  the 
atomic  weight  of  a  gas  corresponds  to  2  volumes  then  the  quotient  must  be 
divided  by  2,  to  obtain  the  real  sp.  gr.  Thus  in  reference  to  ammonia,  the 
atomic  weight  is  lY,  and  17x-0691  =  l*1747.  As  the  atom  of  ammonia 
corresponds  to  2  volumes,  then  l'1747-^2='5873,  sp.  gr.  of  ammonia. 

A  knowledge  of  the  sp.  gr.  of  gases,  enables  a  chemist  to  control  the 
results  of  an  analysis  of  a  compound  gas.  Thus  if  2  volumes  of  ammonia 
consist  of  1  volume  of  nitrogen  and  3  volumes  of  hydrogen,  it  follows  that 
the  sum  of  the  specific  gravities  of  its  constituents,  divided  by  8,  should 
exactly  represent  the  sp.  gr.  of  the  gas.     {See  p.  158,  also  p.  743.) 

Specific  Gravity  of  Yapors. — The  determination  of  the  sp.  gr.  of 
vapors  is  attended  with  greater  practical  difficulties,  but  the  principle  of  the 
operation  is  the  same.  We  compare  the  weights  of  equal  volumes  of  the 
vapor  and  air  under  the  same  temperature  and  pressure.  A  thin  glass  globe 
of  about  three  inches  diameter  is  drawn  out  at  its  neck  to  a  narrow  tube,  six 
or  seven  inches  long,  the  point  of  the  tube  being  cut  across  with  a  file,  but 
not  sealed.  The  globe  is  then  weighed,  and  the  temperature  and  pressure 
at  the  time  are  observed.  In  order  to  introduce  the  volatile  liquid,  the  globe 
is  warmed  so  as  to  expel  a  portion  of  its  air,  and  the  end  of  the  tube  is  then 
dipped  into  the  liquid.  As  the  globe  cools,  the  air  within  contracts,  and 
the  liquid  is  forced  into  it  by  atmospheric  pressure.  When  a  suflScient  quan- 
tity (from  100  to  150  grains)  of  liquid  has  entered,  the  globe  is  firmly 
inclosed  in  a  wire  holder,  and  immersed  in  a  bath  of  water,  oil,  or  other 
'medium,  heated  to  50°  or  60°  above  the  boiling-point  of  the  liquid  in  the 
globe.  Under  these  circumstances,  a  stream  of  vapor  rushes  rapidly  through 
the  orifice,  carrying  with  it  the  air  of  the  globe.  When  this  ceases,  the 
point  of  the  tube  is  sealed  by  a  blowpipe  flame,  the  temperature  of  the  bath 
being  observed  at  the  same  moment.  The  globe  is  removed  from  the  bath, 
and  when  cool  is  cleaned  and  weighed. 

The  next  point  to  be  determined  is  the  capacity  of  the  globe.     For  this 


SPECIFIC    GRAVITY    OP    VAPORS.  Y41 

purpose  the  neck  is  broken  under  the  surface  of  water  or  mercury,  when  the 
cold  fluid  enters  the  globe  and  fills  it  completely,  if  the  operation  has  been 
properly  conducted,  and  all  the  air  has  been  expelled  by  the  vapor.  By 
pouring  out  the  water  or  mercury  into  a  graduated  vessel,  the  capacity  of 
the  globe  is  accurately  ascertained.  We  thus  obtain  the  data  necessary  for 
the  calculation. 

1.  The  weight  of  the  globe  full  of  air  at  the  common  temperature  and 
pressure. 

2.  The  weight  of  the  globe,  and  of  the  vapor  filling  it  at  the  temperature 
of  the  bath,  and  under  the  same  pressure. 

3.  The  capacity  of  the  globe.  Having  these  results,  we  obtain  by  calcu- 
lation— 

4.  The  weight  of  the  empty  globe. 

5.  The  weight  of  the  vapor  filling  the  globe  at  the  temperature  of  the 
bath,  as  well  as  its  volume  at  this  or  any  other  temperature  that  may  be 
required. 

Let  it  be  assumed  that  the  object  is  to  determine  the  specific  gravity  of 
the  vapor  of  Chloroform.  1.  The  weight  of  the  globe  full  of  air  at  60° 
and  bar.  30,  is  found  to  be  2012-4  grains.  2.  The  liquid  chloroform  having 
been  introduced  into  the  globe,  in  the  manner  described,  the  globe  is  main- 
tained at  a  temperature  of  200°  in  the  bath,  until  nothing  but  vapor  remains 
in  the  interior.  The  aperture  of  the  small  tube  is  then  sealed.  The  globe, 
when  dry,  and  cooled  at  600,  is  found  to  weigh  2040  grains.  This  gives 
the  weight  of  the  globe  and  vapor  together.  3.  The  capacity  of  the  globe 
is  determined  by  breaking  the  point  of  the  tube  under  water.  The  liquid 
rushes  in  and  entirely  fills  the  vessel.  When  this  liquid  is  poured  into  a 
graduated  glass,  it  is  found  that  at  60°  there  are  40  cubic  inches  ;  hence,  40 
cubic  inches  of  air  were  contained  in  the  globe  at  common  temperature  and 
pressure.  4.  The  weight  of  this  air  would  be  12-4  grains  (100  c.  i.  :  31 
grs.  :  :  40  c.  i.  :  12-4  grs.)  :  and  as  the  globe  and  air  weighed  together  20124 
grains,  then  2012'4 — 12*4=2000  grains,  the  weight  of  the  empty  globe. 
5.  The  weight  of  the  vapor  filling  the  globe  may  now  be  determined.  The 
globe  was  found  to  weigh,  on  cooling,  2040  grains,  hence,  2040 — 2000=40 
grains,  the  weight  of  the  vapor.  It  is  now  necessary  to  determine  either 
the  weight  of  air  which  would  fill  the  globe  at  the  temperature  of  the  bath, 
or  the  volume  of  vapor  which  by  calculation  would  be  contained  in  the  globe 
when  cooled  at  60°.  The  reduction  of  the  volume  by  cooling  from  200°  to 
60°  is  the  more  simple  process.  Thus,  40  cubic  inches  of  vapor  at  200° 
would  be  reduced  to  30-78  cubic  inches  at  60°  (648  :  508  :  :  40  :  30-^8)  (p. 
136).  Hence,  assuming  that  chloroform  vapor  was  cooled  to  60°,  and 
could  still  exist  as  a  vapor  at  that  temperature,  it  is  obvious  that  its  specific 
gravity  would  be  determined  by  ascertaining  the  weight  of  30*78  cubic  inches 
of  air  at  the  same  temperature  and  pressure.  100  cubic  inches  of  air  weigh 
31  grains,  hence  100  :  31  :  :  30*78  :  9*54.  Hence,  at  the  same  temperature, 
60°,  30-78  cubic  inches  of  chloroform  vapor  would  weigh  40  grains,  while  an 
equal  volume  of  air  would  weigh  only  9-54  grains;  and  40-^9-54=4*19, 
which  is  nearly  the  specific  gravity  of  the  vapor  of  chloroform,  as  determined 
by  calculation  from  its  elementary  composition.  We  subjoin  a  summary  of 
these  results ; — 

Capacity  of  the  globe  at  60O  =  40  cubic  inches. 
Weight  of  the  globe  with  dry  air  =  2012*4  grains. 
Weight  of  the  air  by  calculation  =  12*4  grains. 
Weight  of  the  globe  without  air  =  2000  grains. 
Weight  of  the  globe  with  chloroform  vapor  =2040  grains. 
Weight  of  the  chloroform  in  vapor  =  40  grains. 


•742  SPECIFIC    GRAVITY    OF    VAPORS. 

40  c.  i.  of  air  or  vapor  at  200O,  reduced  to  30-78  c.  i.  at  60O. 

Weight  of  30-78  c.  i.  of  air  at  60O  =:  9-54  grains. 

Weight  of  30-78  c.  i.  of  chloroform  vapor  at  60O  =40  grains. 

Hence — 


Wt.  of  air. 

Wt.  of  chlor,  V. 

Sp.  gr.  air. 

Sp.  gr.  chlor. 

9-54 

:            40            :: 

1-000 

4-192 

It  may  be  observed  that  the  ascertained  sp.  gr.  of  chloroform -vapor  is 
4*20,  and  the  sp.  gr.  of  the  vapor  calculated  from  its  elementary  composition 
is  4"1805,  differences  which^re  comparatively  unimportant  (p.  755). 

The  relations  of  sp.  gr.  to  weight  and  volume  are  the  same  with  vapors 
as  with  gases.  In  fact,  all  the  conditions  which  affect  gases  equally  affect 
vapors,  so  long  as  these  bodies  have  a  temperature  above  the  boiling  points 
of  the  liquids  which  produce  them. 

The  weight  of  100  cubic  inches  of  the  vapor  of  water  may  be  determined 
from  its  sp.  gr.  by  the  rule  already  given  (p.  739).  Thus  0.6129  x  31  =  19-27 
grains.  The  sp.  gr.  of  the  vapor  of  arsenic  being  10-39,  100  cubic  inches 
of  this  vapor  would  weigh  32209  grains  (1039x31). 

A  determination  of  the  specific  gravity  of  vapors  or  of  vapor-density  is  of 
considerable  importance  in  the  analysis  of  volatile  organic  liquids.  There 
are  many  liquid  hydrocarbons  which,  so  far  as  centesimal  composition  is 
concerned,  yield  precisely  similar  weights  of  hydrogen  and  carbon,  by  the 
combustion-tube.  The  specific  gravity  of  their  vapors,  however,  differs ; 
and  this  difference  often  enables  a  chemist  to  apportion  with  great  accuracy 
^their  atomic  constitution.  The  specific  gravity  of  a  compound  vapor  must 
always  be  the  sum  of  the  specific  gravity  of  its  constituent  elements,  or  a 
multiple  of  them.  We  need  not  go  further  into  this  subject,  as  the  reader 
will  find  several  examples  given  at  page  556. 


TABLE  OF  GASES  AND  VAPORS. 


743 


TABLE  OF  SIMPLE  AND  COMPOUND  GASES  AND  VAPOBS. 


Gases  and  vapors. 

Symbols. 

Atom, 
vol. 

Atomic 
weight. 

Sp.  gr.  of 
airl. 

Sp.  gr.  of 
hydrogen' 

Weight  of 

100  c.  i.  iu 

grains. 

Air 

1-000 

14-48 

31-00 

Hydrogen 

H 

*i* 

"i 

0-0691 

1- 

2-14 

Oxygen 

0 

h 

8 

1-1057 

16- 

34-24 

Nitrogen 

N 

1 

14 

0-9674 

14- 

29-96 

Chlorine 

CI 

1 

36 

2-4876 

36- 

77-04 

Bromine 

Br 

1 

78 

5-3898 

78- 

166-92 

Fluorine 

F 

1? 

19 

19- 

Iodine  . 

I 

1 

126 

8-7066 

126- 

269-64 

Sulphur 

S 

^ 

16 

6-6336 

96- 

205-44 

Selenium 

Se 

i. 

40 

16-6390? 

240- 

515-80 

Phosphorus  . 

P 

^ 

32 

4-3555 

64- 

136-96 

Carbon 

C 

1? 

6 

0-4146 

6- 

12-84? 

Tellurium     . 

Te 

k 

64 

4-4190 

38-4 

136-98 

Arsenic 

As 

^ 

75 

10-3900 

150- 

322-09 

Aqueous  vapor 

HO 

1 

9 

0-6219 

9- 

19-26 

Protox.  of  nitrogen 

NO 

1 

22 

1-5202 

22- 

47-08 

Deutox.  of  nitrogen 

NO, 

2 

30 

1-0365 

15- 

32-10 

Nitrous  acid 

NO, 

1 

46 

1-5890 

1. 

49-15 

Ammonia 

NH3 

2 

17 

0-5873 

18-19 

Hypochlorous  acid 

CIO 

1 

44 

3-0404 

44. 

94-16 

Peroxide  of  chlorine 

CIO. 

2 

68 

2-3494 

34- 

72-76 

Hydrochloric  acid 

HCI 

2 

37 

1-2783 

18-5 

39-59 

Hydrobromic  acid 

HBr 

2 

79 

2-7294 

39-5 

84.53 

Hydriodic  acid 

HI 

2 

127 

4-3878 

63-5 

135-89 

Hydrofluoric  acid 

HF 

2? 

20 

10- 



Sulphurous  acid    . 

SO, 

1 

32 

2-ini 

32- 

68-48 

Hydrosulphuric  acid 

HS 

1 

17 

1-1747 

17- 

36-38 

Hydroselenic  acid 

HSe 

1 

41 

2-7950 

41- 

86-64 

Phosph.  hydrogen 

PH3 

2 

35 

1-1925 

17-5 

36-96 

Terchlor.  of  phosph. 

PCI3 

2 

140 

4-7420 

70- 

147-00 

Pentachl.  of  phosph. 

PCI5 

4 

212 

3-6600 

53- 

113-46 

Carbonic  oxide 

CO 

1 

14 

0-9674 

14- 

29-96 

Carbonic  acid 

CO2 

1 

22 

1-5202 

22- 

47-08 

Light  carb.  of  hydroger 

CH2 

1 

8 

0-5528 

8- 

17-12 

defiant  gas  . 

CoHo 

1 

14 

0-9674 

14- 

29-96 

Cyanogen      . 

NC/ 

1 

26 

1-7966 

26- 

55-64 

Hydrocyanic  acid 

HCy 

2 

27 

0-9328 

13-5 

28-89 

Tellur.  hydrogen  . 

TeHj 

1 

65 

4-4881 

65- 

139-11 

Arsen.  hydrogen  . 

AsHg 

2 

78 

2-7010 

39- 

83.73 

Alcohol 

C4  HgOj 

2 

46 

1-6100 

23- 

49-91 

Ether    . 

C   H^O' 

1 

37 

2-5567 

37- 

80-25 

Chloroform    . 

C2  HCI3 

2 

121 

4-1805 

60-5 

129-59 

Oil  of  turpentine  . 

^^20^  16 

2 

136 

4-6980 

68- 

145-63 

[The  reader  is  referred  to  page  67  for  a  table  of  the  symbols  and  equivalent  weights 
of  the  Elements.  Tables  showing  the  proportion  per  cent,  of  dry  acids  and  alkalies, 
as  well  as  of  alcohol  with  water,  will  be  found  in  their  proper  places  in  the  body  of 
the  work.] 

OLD  AND   NEW   NOTATIONS. 

In  Chapter  lY.  a  table  of  the  elements  has  been  given,  representing  their 
symbols  and  the  equivalent  weights  in  which  they  combine  with  each  other. 
By  many  chemists  of  repute  they  have  been  and  are  still  regarded  as  syno- 
nymous with  atomic  weights.  An  atom,  however,  in  the  opinion  of  many 
eminent  chemists,  is  the  smallest  quantity  of  an  element,  indivisible  by 
chemical  means,  which  can  exist  in  a  compound  body ;  and  a  molecule  is  a 


744  OLD    AND    NEW    NOTATIONS. 

group  of  atoms,  either  of  simple  or  compound  bodies,  forming  the  smallest 
quantity  which  can  exist  in  a  free  state,  or  can  take  part  in  a  chemical 
reaction.  The  words  "smallest  quantity"  are  left  undefined.  On  the  old 
notation  the  smallest  quantity  of  oxygen  which  enters  into  combination  with 
one  part  of  hydrogen  to  form  water  is  8,  and  this  is  taken  to  represent  the 
equivalent  or  combining  weight  or  atom  of  oxygen.  On  the  new  systems, 
which,  however,  are  based  on  the  old  system  of  Berzelius,  the  smallest  quan- 
tity of  oxygen  which  can  go  to  constitute  water  is  16.  The  atom  of  oxygen 
is  thus  made  to  represent  two  equivalents,  but  this  requires  the  admission  of 
the  assumption  that  one  atom  of  hydrogen  cannot  possibly  form  water,  that 
a  molecule  or  double  atom  is  required  for  this  purpose  (H^),  and  that  hydro- 
gen cannot  combine  with  oxygen  until  after  it  has  combined  with  itself  to 
form  a  hydride  of  hydrogen. 

In  1848  Gerhardt  introduced  a  system  of  notation  on  which  the  equiva- 
lents of  a  certain  number  of  elements  were  doubled.  Various  modifications 
have  been  introduced  since  his  time,  which  have  completely  changed  the 
aspect  of  chemistry  as  represented  by  its  symbolic  language.  Great  differ- 
ences of  opinion  and  many  conflicting  theories  have  been  introduced  by  these 
frequent  changes.  I  agree  with  Mr.  Bloxam  in  thinking  that  the  advantages 
in  adopting,  the  new  notation  is  chiefly  seen  in  speculative  chemistry,  and 
that  the  new  formulae  are  likely  to  be  of  less  service  in  practice  than  those 
based  on  the  doctrine  of  equivalent  or  combining  weights.  {Bloxam's  Che- 
mistry, 1867.)  Dr.  Apjohn,  after  showing  that  the  exceptions  to  the  propo- 
sitions on  which  the  new  system  is  founded  are  such  as  to  render  them 
inadmissible  in  a  purely  experimental  science,  asserts  that  the  existing 
method  (the  ordinary  notation)  is  entitled  to  preference,  from  its  compara- 
tive simplicity,  and  from  its  resting  exclusively  on  experimental  evidence. 
(On  the  Metalloids,  1864.) 

Sir  Benjamin  Brodie,  who  at  one  time  adopted  Gerhardt's  notation,  has 
remarked  recently,  in  introducing  his  own  views  to  chemists  under  the  name 
of  "  Ideal  Chemistry,"  that  "  system  has  followed  system  and  doctrine  has 
followed  doctrine,  but  these  systems  and  doctrines  have  one  after  another 
fallen  to  the  ground."  {Chemical Neivs,  June  14,  1867.)  This  gentleman, 
considering  that  the  present  systems  of  notation,  whether  old  or  new,  are 
utterly  inadequate  to  deal  with  the  complicated  chemical  facts  brought  to 
light  by  modern  discoveries,  proposes  to  abolish  the  whole  of  those  now  in 
use,  and  to  substitute  for  them  an  entirely  new  symbolic  language  in  which 
Greek  letters  are  employed  to  indicate  elements  and  compounds  based  upon 
a  certain  definite  quantity  assumed  as  unity.  According  to  this,  the  newest 
view,  a  unit  of  ponderable  matter  is  that  portion  of  ponderable  matter  which 
in  the  condition  of  a  perfect  gas  at  the  temperature  of  0°  C,  and  under  the 
pressure  of  760  millimetres,  occupies  the  space  of  1000  cubic  centimetres. 
The  unit  of  space  is  1000  cubic  centimetres  of  space,  divested  of  all  matter 
whatever,  represented  by  the  symbol  1  ;  hence  1=0.  Translated  into  Eng- 
lish, this  implies  a  volume  of  matter  occupying  at  a  temperature  of  32°  and 
under  a  pressure  of  30  inches,  612  cubic  inches.  One  of  the  difficulties 
which  must  attend  all  calculations  based  on  volume,  or  in  reasoning  from 
volume  to  weight,  is  that  the  volume  of  a  large  number  of  substances  must 
be  purely  speculative.  Carbon,  silicon,  and  boron,  and  most  of  the  metals, 
are  not  convertible  into  perfect  gas  or  vapor,  so  as  to  be  made  the  subject 
of  measurement.  We  may  conceive  a  unit  of  space  represented  by  61*2 
cubic  inches,  but  there  is  no  method  of  determining  by  experiment  the  por- 
tion of  ponderable  matter,  in  the  shape  of  gaseous  carbon  or  diamond,  which 
would  till  that  space  at  32°  under  a  pressure  of  30  inches.  These  views, 
however,  have  not  at  present  been  fully  brought  before  the  public. 


OLD    AND    NEW    NOTATIONS. 


T45 


TABLE  OF  SYMBOLS  AND  EQUIVALENT  AND  ATOMIC  WEIGHTS  ACCORDING  TO  VARIOUS 

SYSTEMS  OP  NOTATION. 

Equivalent  Gerhard t's 

Atomic 

Equivalent 

Gerhardt's 

Atomic 

Symbols. 

weights, 

new  nota- 

weights, 

Symbols. 

weights, 

new  nota- 

weights, 

old  nota- 

tion. 

new  nota- 

old nota- 

tion. 

new  nota- 

tioa. 

tion. 

tion. 

tion. 

H      .     .     . 

1 

1 

1 

Mu  .     .     . 

27-5 

27-5 

55 

0 

8 

16 

16 

Cr    . 

26-7 

26-25 

53-5 

N 

14 

14 

14 

U     . 

60 

60 

120 

Ce 

35-5 

35-5 

35-5 

Fe   . 

28 

28 

56 

Br 

80 

80 

80 

Co   . 

29-5 

29-5 

59 

I        , 

127 

127 

127 

Ni    . 

29-5 

29-5 

59 

F 

19 

19 

19 

Zn   . 

32-6 

32-6 

65-2 

S 

16 

32 

32 

Cd  . 

56 

56 

112 

Se 

39-7 

79-5 

79-5 

Cu  . 

3] -7 

31-75 

63-5 

Te 

64 

129 

129 

Pb  . 

103-5 

103-5 

207 

P 

31 

31 

31 

Bi    . 

210 

210 

210 

As 

75 

75 

75 

Sn   . 

59 

56 

118 

C 

6 

12 

12 

Ti    . 

• 

25 

137-32 

50 

B 

10-9 

11 

11 

Wo. 

92 

92 

184 

Si 

14 

... 

28 

Mo  . 

48 

48 

96 

Zr 

44-8 

... 

89-6 

Va  . 

68-5 

48 

137-2 

K 

39 

39 

39-1 

Sb    . 

122 

122 

122 

Na 

23 

23 

23 

Hg  . 

100 

100 

200 

Li 

7 

7 

7 

Ro   . 

52 

... 

104-4 

Ag 

108 

108 

108 

Pd  . 

53-3 

... 

106-6 

Ba 

68-3 

68-5 

137 

Pt    . 

98-7 

98-5 

197 

Sr 

43-8 

43-75 

87-5 

Ir    . 

99 

98-5 

198 

Ca 

20 

20 

40 

Ru  . 

52-2 

... 

104-4 

Mg 

12 

12 

24 

Os    . 

99-5 

199-2 

Al     . 

13-7 

13-75 

27 

Au  . 

197 

... 

196-98 

This  table  has  been  compiled  from  the  tables  published  by  Wurtz  {Intro- 
duction to  Chemical  Philosophy,  translated  by  Crookes,  1867).  In  this  small 
volume  the  reader  will  find  a  good  exposition  of  the  various  systems  of  nota- 
tion now  in  use.  For  an  account  of  Sir  B.  Brodie's  new  views  on  "  Ideal 
Chemistry,"  I  would  refer  the  reader  to  his  published  lecture  in  the  Labora- 
tory, No.  11,  June  15,  1867,  or  Chemical  News,  June  14,  1867. 


746 


OLD    AND    NEW    NOTATIONS. 


TABLE  OF  THE  ORDINARY  AND  UNITARY  FORMULA  OF  SOME  OF  THE  MORE  IMPORTANT 
CHEMICAL  COMPOUNDS. 


Names  of  the  compounds. 

Ordinary  or  dualistic 
formula. 

Unitary  formulae. 

Water 

HO 

H2O 

Potash 

.     KO 

K2O 

Hydrate  of  Potash 

KO,HO 

HKO 

Oxide  of  Silver 

AgO 

Ag^O 

Hydrochloric  Acid  . 

HCl 

HCl 

Chloride  of  Potassium    . 

KCl 

KCI 

Ammonia 

NH„ 

NH3 

Nitrous  Oxide 

NO 

N2O 

Nitric  Oxide  .... 

NO, 

NO 

Hyponitrous  Acid  . 

N03^ 

NA 

Hyponitric  Acid 

NO, 

NO. 

Anhydrous  Nitric  Acid    . 

NO. 

N2O, 

Hydrated  Nitric  Acid 

HO,NO. 

NO3H 

Nitrate  of  Potash   . 

KO.NO, 

NO3K 

Carbonic  Acid 

* 

CO, 

CO, 

Carbonate  of  Potash 

K0,C02 

K2C03 

Bicarbonate  of  Potash    . 

HO,KO,2C02 

HKC03 

Anhydrous  Sulphuric  Acid 

SO3 

S03 

Hydrated  Sulphuric  Acid 

H0,S03 

S0,H2 

Sulphate  of  Potash 

K0,S03 

S0,K2 

Bisulphate  of  Potash      . 

KO,HO,2S03 

SO.KH 

Sesquioxide  of  Iron 

FeA 

Fe,03 

Chromic  Acid 

0 

Cr03 

Cr203 

Chromate  of  Potash 

K0,Cr03 

K2Cr04 

Bichromate  of  Potash^    . 

KO,2CrO, 

K2Cr04,Cr203 

Phosphoric  Acid  (anhydrous) 

PO, 

P2O5 

Terhydrate 

3H0,P0, 

H3PO4 

Tribasic  Phosphate  of  Soda 

HO,2NaO,P05 

HNagPO^ 

Pyrophosphate  of  Soda  . 

2NaO,P05 

Na.P^O, 

Metaphosphate  of  Soda  . 

NaO,P05 

NaP03 

Cyanogen 

C^NCCy) 

CN(Cy) 

Cyanide  of  Potassium     . 

KC2N 

KCN 

Ferrocyanide  of  Potassium 

K,FeCy3 

K.FeCye 

Ferricyanide  of  Potassium 

KgFe.Cye 

KsFeCy^ 

Sulphocyanide  of  Potassium 

KCyS, 

KCyS 

Hydrated  Acetic  Acid     . 

HO,C,H303 

C2HA 

Alcohol  .... 

C^HeO^ 

C2HgO 

Ether      .... 

cI<o' 

C4H.0O 

In  making  his  election  between  these  two  systems,  the  student  of  chemistry 
will  do  well  to  bear  in  mind  the  following  judicious  remarks  by  Dr.  Miller, 
in  the  second  edition  of  his  Elements  of  Chemistry,  Part  2,  p.  861.  After 
observing  that  the  notation  in  common  use  has  many  advantages  over  that 
proposed  by  Gerhardt,  he  says : — 

•  "  1.  The  ordinary  system  is  known  to  every  one  who  has  made  the  science 
of  chemistry  his  study.  2.  All  the  memoirs,  with  the  exception  of  a  few  in 
later  years,  are  written  in  accordance  with  this  system,  and  a  change  of  nota- 
tion would  at  once  render  these  memoirs  less  easily  accessible  and  intelligible. 
3.  The  new  notation  is  not  in  harmony  with  the  language  of  chemistry. 

'  It  is  difficult  to  give  any  consistent  unitary  formulas  to  the  chromates.  Those  chemists 
who  adopt  the  new  notation  do  not  agree  either  in  the  arrangement  of  the  atoms  or  molecules, 
or  in  the  nomenclature.  Thus,  while  the  composition  of  this  salt  is  plainly  indicated  in  the 
ordinary  system  as  Bichromate  of  Potash,  KO,2Cr03,  it  is  described  by  Dr.  Koscoe  as  Potas- 
sium  Anhydro-chromate,  with  the  formula  KaCrOi.CrOa,  and  by  Dr.  Williamson  as  Potassic 
dichromate,  with  the  formula  CraOiKa ;  while  according  to  Gerhardt  the  same  salt  has  the 
formula  K2Cr204,Cr203.  Another  recent  chemical  writer,  Dr.  S.  Macadam,  adopts  Williamson's 
formula,  but  places  the  symbols  in  an  inverted  order,  KaCraO,. 


OLD    AND    NEW    NOTATIONS.  Y4t 

NO,  for  example,  would  (or  ought  to)  be  called  binoxide  of  nitrogen,  but 
written  as  a  protoxide.*  4.  The  present  system  of  notation  is  capable  of 
expressing  all  the  later  theories  with  perfect  precision,  while  it  is  applicable 
to  the  older  views ;  but  the  new  notation  is  not  applicable  to  many  of  the 
older  views.  By  the  ordinary  notation,  nitrate  of  potash,  for  instance,  may 
be  represented  either  as  a  compound  of  potash  and  nitric  acid  (KO.NO^),  or 
as  a  combination  of  potassium  with  nitrion  (K,NOfl),  or  as  an  aggregation 
of  particles  without  indicating  any  specific  mode  of  combination  (KNOg) ; 
whereas  in  the  new  notation,  unless  its  principle  is  abandoned  by  doubling 
the  formulae,  it  is  impossible  that  KNO3  should  be  represented  as  formed  of 
potash  and  nitric  acid.  It  would,  therefore,  be  a  retrograde  step  thus  to 
exclude  from  our  notation  the  power  of  indicating  the  constitution  of  a  large 
class  of  compounds  upon  a  view  which  has  long  been  more  or  less  prevalent. 
5.  Any  extensive  change  of  nomenclature  or  of  notation,  while  the  truth  of 
the  theory  upon  which  it  rests  is  still  under  discussion,  cannot  but  lead  to 
serious  inconvenience.  If  such  a  practice  were  admitted,  every  new  theory 
would  be  privileged  to  introduce  a  new  language,  which,  in  a  continually 
progressive  science  like  chemistry,  would  soon  give  way  to  an  equally  transi- 
tory successor.  Chemistry,  it  must  be  remembered,  is  not  merely  a  science : 
it  is  also  an  art  which  has  introduced  its  nomenclature  and  its  notation  into 
our  manufactories,  and,  in  some  measure,  even  into  daily  life  :  it  is  therefore 
specially  necessary  to  beware  of  needless  innovation  in  its  terms  and  symbols.' 
Any  system  of  notation,  it  must  also  be  borne  in  mind,  is  a  mere  artificial 
contrivance  to  represent  to  the  mind  certain  changes  or  certain  hypotheses ; 
and  to  argue  for  a  system  of  notation  as  though  it  were  anything  more,  as 
has  sometimes  been  done,  shows  a  want  of  true  appreciation  of  its  meaning. 

"The  question  to  be  considered  is  not  simply — What  is,  in  the  abstract, 
the  best  mode  of  notation  ?  but  What,  considering  all  the  circumstances  of 
the  science,  possesses  the  greatest  advantage  ?  That  system  of  notation 
which  is  consistent  with  itself,  and  which  lends  itself  most  completely  to  the 
various  theories  and  aspects  of  the  science  which  have  been  maintained  or 
may  be  maintained,  is  therefore,  philosophically  speaking,  the  best.^  And 
such  grounds,  it  appears  to  me,  exist  for  continuing  to  use  the  system  hitherto 
generally  adopted.  This  question  of  notation,  it  must  be  observed,  is  entirely 
independent  of  Gerhardt's  theory  of  the  atomic  constitution  of  the  elements 
to  which  he  proposes  to  apply  it.  Even  those  who  admit  the  truth  of  his 
hypothesis  may  still  express  the  molecular  constitution  of  compounds,  as  he 
did  himself  in  his  Traite,  by  the  ordinary  mode  of  notation." 

It  is  impossible  to  advance  stronger  or  better  reasons  against  these  new 
systems  of  notation  than  those  here  given  in  detail  by  Dr.  Miller.  Although 
published  in  1860,  his  objections  to  the  proposed  change  are  as  valid  now  as 
they  were  then.  The  objection  under  5  is  indeed  unanswerable.  If  a  sweep- 
ing change  is  to  be  made,  it  must  not  be  to  a  system  which  is  still  upon  its 
trial,  but  to  one  which  is  really  based  on  experiment,  and  which  will,  above 
all,  command  the  assent  of  all  inquirers  after  truth.  A.  S.  T. 

"■  This  difficulty  has  been  evaded  by  going  back  to  the  old  name  which  the  compound  bore 
half  a  century  ago— nitric  oxide ;  but,  in  adopting  this  course,  there  is  no  longer  any  relation 
between  the  name  and  composition  of  the  gas.  ^         j  xv  * 

^  This  remark  equally  applies  to  weights  and  measures,  and  the  barometer  and  thermometer. 
Unless  we  succeed  in  deanglicizing  the  nation,  it  is  vain  to  expect  that  articles  will  be  sold  by- 
kilogrammes,  medicines  prepared  by  centigrammes  or  cubic  centimetres,  or  that  the  rise  and 
fall  of  the  barometer  and  thermometer  will  be  indicated  by  mUlimetres  and  centigrade  degrees. 

A.  b.  1. 


INDEX. 


A. 

A.ciT>—cont. 

PAGE 

kcir)—cont. 

PAOB 

PAGE 

chlorocarbonic 

263 

hydronitroprussio 

396 

ACALEPH^ 

142,  706 

chlorochromic 

447 

hydrosulphocyanic 

289 

Acetates 

649 

chloromolybdic 

453 

hydrosulphuric 

226 

Acetic  acid 

646 

chlorous 

193 

hypoazotic 

172 

anhydrous 

648 

chlorovalerisic 

628 

hypochlorous 

192 

glacial 

649 

chlorovalerosic 

628 

hyponitric 

172 

monohydrated 

649 

cholalic 

718 

hyponitrous 

171 

Acetification 

646 

cholic 

718 

hypophosphorotis 

239 

Acetometer 

648 

choleic 

718 

hyposulphuric 

225 

Acetone 

651 

choloidic 

719 

hyposulphurous 

224 

Acetyle 

648 

chromic 

445 

inosinic 

705 

Acetylene 

269,  271 

cinchonic 

661 

iodic 

207 

Acid,  acetic 

646 

cinnamic 

653 

isatinic 

673 

aconitic 

639 

citraconic 

639 

isethionic 

600 

acrylic 

633 

citric 

638 

isotartaric 

637 

adipic 

627 

citricic 

639 

itaconic 

639 

aerial 

263 

citridic 

639 

kakodylio 

668 

aldehydic 

689 

cobaltocyanio 

441 

kinic 

661 

althionic 

600 

colopholic 

618 

lactic 

713 

amidobenzoic 

654 

columbic 

450 

lauric 

631 

amygdalic 

655 

comenic 

656 

lecanoric 

674 

anchusic 

677 

crenic 

607 

lithic  (uric) 

724 

antimonic 

460 

croconic 

261 

lithofellio 

720 

antimonious 

460 

cyarihydric 

282 

maleic 

640 

apocrenic 

607 

cyanic 

280 

malic 

640 

apoglucic 

571 

cyanuric 

282 

manganic 

401 

arsenic 

470 

dithionic 

225 

margaric 

624 

arsenious 

467 

dithionous 

224 

meconic 

656 

aspartic 

666 

ellagic 

642 

melassinic 

668 

auric 

617 

equisetic 

639 

mellitic 

261 

azotic 

174 

ethalic 

631 

mesoxalic 

260 

azotous 

171 

ferric 

385 

metameconic 

656 

benzaraic 

654 

fluoboric 

296 

metagallio 

641 

benzoic 

653 

fluoric 

210 

metapectic 

667 

bismuthic 

437 

fluosilicio 

305 

metaphosphoric 

241 

boracic 

294 

formic 

662 

metastannic 

412 

borohydrofluoric 

298 

fulminic 

281 

metatartaric 

637 

bromic 

203 

fumaric 

640 

molybdic 

452 

butyric 

627 

gallic 

641 

molybdous 

462 

camphoric 

616 

gallotannic 

640 

mucic 

666 

capric 

628 

geic 

607 

muriatic 

196 

caproie 

628 

glucic 

571 

myristio 

631 

caprylic 

628 

glycocholalio 

718 

myronic 

616 

carbanilic 

654 

glycocholic 

718 

naphthalic 

610 

carbazotic 

613 

hippuric 

656,  727 

nitric 

174 

carbolic 

610 

humic 

607 

nitrobenzoio 

654 

carbonic 

263 

hydriodic 

208 

nitrohydrochloric 

199 

carminic 

678 

hydrobromic 

203 

nitromuriatic 

199 

carthamie 

676 

hydrochloric 

196 

nitroso-nitrio 

176 

cerebric 

705 

hydrocyanic 

282 

nitrous 

171 

ehloracetic 

649 

hydroferricyanic 

395 

cenanthic 

679 

chlorbydric 

196 

hydroferrocyanic 

394 

oleic 

624 

chloric 

194 

hydrofluoric 

210 

oleophosphoric 

705  , 

chlorobenzoic 

654 

hydrofluosilicic 

306 

orceic 

675 

750 

INDEX. 

Acid — co7it. 

PAGE 

Acid — cont. 

PAGE 

Alcohol— cojj^               page 

orsellinic 

674 

sulphomolybdic 

659,  662 

ethylic 

583 

osmic 

529 

sulphonaphthalic 

609 

latent  heat  of  vapor  of 

141 

oxalic 

643 

sulphopurpuric 

673 

methylic 

692 

oxamic 

645 

sulphosaccharic 

570 

properties  of 

684 

oxaluric 

726 

sulphostearic 

627 

propylic 

688 

palmic 

630 

sulphovinic 

696 

solvent  powers  of 

586 

palmitic 

631 

sulphuric 

219 

sp.  gr.  of,  table  of 

■  586 

parabanic 

726 

sulphurous 

216 

tests  for 

588 

paramaleic 

640 

sulphydric 

226 

uses  of 

588 

parapectic 

667 

tannic 

640 

Alcoholic  fermentation 

673 

paratartaric 

638 

tantalic 

450 

liquors,  strength  of 

683 

pectic 

567 

tantalous 

450 

Aldehyde 

689 

pectosic 

567 

tartaric 

634 

Ale 

579 

pelargonic 

627 

tartralic 

637 

Alembroth,  salt  of 

483 

pentathionio 

226 

tartrelic 

637 

Algaroth,  powder  of 

461 

perchloric 

195 

taurocholalic 

71-S 

Alizarine 

674 

perehromic 

445 

taurocholic 

718 

Alkalies  defined 

73 

periodic 

207 

telluric 

456 

Alkaline     reaction,    influ- 

permanganic 

402 

tellurous 

456 

ence  of  water  on 

43 

phenic,  or  phenylic 

610 

tetrathionic 

226 

Alkaloids,  organic 

657 

phocenic 

631 

titanic 

458 

formulae  of 

554 

phosphatic 

240 

trichloracetic 

649 

solubility  of,  in  chloro- 

phosphoglyceric 

626 

trithionic 

226 

form 

49 

phosphoric 

240 

tungstic 

450 

tests  for                     484 

,  657 

phosphorous 

239 

ulmic 

607 

Alkalimetry 

315 

picric 

613 

uric 

724 

Alkanet 

677 

pimaric 

618 

uro-benzoic 

727 

Alkargen 

668 

pimelic 

627 

valerianic 

628 

Alkarsin 

668 

pinic 

618 

vanadic 

448 

Allotropic  carbon 

248 

propionic 

625 

xanthoproteic 

698 

hydrogen 

126 

plumbic 

430 

Acid  reaction,  influence  of 

oxygen 

110 

prussic 

282 

water  on 

43 

phosphorus 

237 

pthalic 

610 

Acids,  constitution  of          93 

sulphur 

214 

purpuric 

679 

defined 

73 

Allotropy 

18 

pyrocitric 

639 

dibasic 

241 

Alloxan 

726 

pyrogallic 

509,  641 

monobasic 

241 

Alloxantin 

726 

pyroligneous 

648 

nomenclature  of 

74 

Alloys  of  steel 

392 

pyromellitic 

261 

organic 

554 

Allyl 

017 

pyrophosphorio 

241 

vegetable 

634 

Alum 

369 

pyrotartaric 

638 

Aconitina 

663 

chrome 

447 

pyruvic 

638 

Acrolein 

625,  633 

varieties  of 

270 

quercitannic 

640 

Actinism 

505 

Alumina 

367 

racemic 

638 

Adamantine  spar 

368 

acetates  of 

650 

rhodizonic 

260 

Adhesion 

23 

hydrates  of 

368 

ricinelaidio 

630 

of  air 

157 

oxalates  of 

645 

rutic 

628 

Adipocire 

687 

phosphates  of 

371 

salycilic 

667 

Aeration  of  water 

141 

silicates  of 

371 

eebacic 

627 

Aerolites 

444 

sulphates  of 

369 

selenic 

231 

Affinity 

62 

tests  for 

372 

selenious 

231 

single 

52 

Aluminates 

368 

silicic 

299 

double 

55 

Aluminite 

369 

silicofluoric 

306 

predisposing 

55 

Aluminum 

367 

silvic 

618 

Agate 

300 

chloride  of 

369 

sorbic 

640 

Air,  atmospheric 

156 

fluoride  of 

367 

stannic 

412 

fixed 

263 

Amalgam                         51 

488 

stearic 

623 

thermometer 

82 

for  electrical  machines 

489 

suberic 

627 

weight  of 

158 

of  ammonium            43 

,  183 

succinic 

620 

Alabaster 

356 

Amalgamation  of  silver 

492 

sulphacetic 

649 

Albumen 

688 

Amarin 

655 

sulphantimonic 

461 

vegetable 

693 

Amber 

620 

sulpharsenic 

475 

use  of  iij  dyeing 

670 

Ambergris 

720 

sulpharsenious 

475 

Albuminates 

691 

Ambligonite 

371 

sulphindigotic 

672 

Alcohates 

586 

Ambreine 

720 

sulphindylic 

672 

Alcohol 

583 

Amethyst 

300 

sulphobenzoic 

654 

absolute 

584 

Amides 

182 

sulphobenzolic 

610 

butylio 

588 

Amidogen 

182 

sulphocyanic 

488 

caproic 

588 

Ammelid 

289 

sulphoglyceric 

627 

caprylic 

588 

Ammeline 

289 

sulpholeic 

627 

composition  of 

588 

Ammonia 

178 

sulphomannitic 

573 

equivalent      of. 

deter- 

acetate  of 

650 

sulphomargaric 

627 

mined 

556 

alum 

370 

INDEX. 


751 


Ammonia — cont.  page 

analysis  of  181 

aqueous  179 

carbonates  of  186 

decomposition  of  181 

formate  of  652 

hydrochlorate  of  186 

hydrosulphate  of  187 

metallization  of  183 

muriate  of  186 

nitrate  of  186 

oxalates  of  644 

proportion  in  air  163 
in  water         130 

salts  of  186 

tests  for  180 

sp.  gr.  of  solution  180 
Ammonias,  hypothetical    659 

Ammonium  183 
amalgam  of               43,  183 

chloride  of  186 

sulphides  of  187 

Amorphous  bodies  25 

phosphorus  237 

Amygdaline  654 

Amyle  694 

oxide  of  594 

hydrated  693 

Amylene  594 

Amylic  alcohol  593 

Amylum  561 

Analysis  62 
prismatic,  or  spectrum      61 

proximate  organic  641 
qualitative,    of   metal- 
lic compounds      376,  531 

ultimate  organic  545 
of  organic  compounds      550 

Anatase  457 

Anchusine  677 

Anhydrates  143 

Anhydrides  143 

Anhydrite  357 
Anhydrous  compounds       143 

salts  32 

Aniline  665 

colors  from  681 

Animal  fluids  706 

Anions  and  cations  60 

Annotto  679 

Anode  59 

Antherythrine  683 

Anthocyanine  683 

Anthoxanthine  683 

Anthracene  610 

Anthracite  607 

Antimonial  poisoning  464 

Antimoniates  460 

Antimony  459 

acids  of  460 

alloys  of  462 

butter  of  461 

chlorides  of  461 

golden  sulphur  of  462 

oxides  of  459 

sulphides  of  461 

tests  for  463 

Antiseptic  liquids  688 

Antozone  116 

Apatite  357 

Apophyllite  358 

Aposepedine  (leucine)  704 


1 

PAGE 

Attraction— coM^ 

PAGE 

Apple  oil 

603 

electrical 

19 

Aqua  chlorinata 

190 

gravitative 

19 

Aqua  fortis 

174 

magnetic 

19 

regia 

199 

varieties  of 

22 

Aqueous  vapor 

138 

Atropia 

663 

in  air 

163 

Aurates 

517 

in  gases 

735 

Aurochlorides 

617 

Arabinates 

666 

Auripigmentum 

475 

Arabine 

665. 

Aurum  musivum 

414 

Arbor  Diange 

496 

Aventurine 

300 

Archil 

673 

Axes  of  crystals 

36 

Argento-cyanides 

498 

Azobenzole 

610 

Argol                            679 

,  636 

Azote 

153 

Arrack 

583 

Arragonite 

358 

Arrowroot 

663 

B. 

Arsenamine 

660 

Arsenates 

471 

Balduin's  phosphorus 

354 

Arsenic 

465 

Ball  soda 

335 

acid 

470 

Balsam  of  Peru 

653 

alloys  of 

475 

tolu 

653 

butter  of 

474 

Balsams 

617 

chlorides  of             473 

,474 

Barilla 

334 

extraction  of 

466 

Barium 

346 

in  coal 

466 

chloride  of 

347 

in  copper 

418 

nitroprusside  of 

396 

in  mineral  waters 

150 

oxides  of 

346 

in  vegetables 

543 

sulphide  of 

348 

Marsh's  test  for 

477 

Barley  sugar 

568 

native 

466 

Barometer,con8truction  of  158 

oxides  of 

467 

uses  of 

159 

properties  of 

465 

(water) 

159 

Eeinsch's  test  for 

477 

French  scale  of 

732 

sulphides  of 

474 

Baryta 

346 

tests  for 

476 

acetate  of 

650 

white 

467 

carbonate  of 

348 

Arsenical  pyrites 

466 

nitrate  of 

347 

Arsenides 

475 

oxalate  of 

645 

Arsenious  acid 

467 

plumbate  of 

431 

Arsenites 

469 

sulphate  of 

348 

Arsenuretted  hydrogen 

472 

sulphonaphthalate  of 

609 

Artesian  well  water 

133 

tartrate  of 

635 

Artificial  camphor 

615 

tests  for 

348 

Ashes  of  vegetables 

641 

Bases,   alkaline   and 

estimation  of 

643 

earthy,  tests  for 

378 

Asparagin 

666 

defined 

73 

Asphalt                         608 

619 

organic 

657 

Asphaltene 

608 

Basic  water 

144 

Assay  of  gold 

629 

Bassorine 

566 

of  silver 

601 

Beans 

694 

Atacamite 

422 

Bear's  grease 

706 

Atmosphere 

156 

Beeswax 

631 

ammonia  in 

163 

Beer 

578 

analysis  of        _       160 

165 

Bell -metal 

425 

aqueous  vapor  in 

163 

Benzine 

610 

composition  of 

164 

Benzoic  acid  (anhydrous) 

663 

density  of 

158 

Benzole 

610 

height  of 

158 

Benzyle 

653 

magnetism  of 

92 

Benzoates 

553 

organic  matter  in 

163 

Benzoin 

653 

physical  properties  of 

156 

Benzoine 

655 

pressure  of 

158 

Benzoline 

655 

uniform  constitution  of  165  | 

Benzoyle 

653 

Atomic  theory 

65 

hydride  of 

654 

volumes 

68 

Bergmehl 

399 

weights 

67 

Beryl 

374 

Atoms,  size  and  weight  of 

22 

Bessemer  process 

382 

Attraction,  adhesive 

23 

Bezoars                          643 

720 

capillary 

24 

Bibroraisatine 

673 

chemical 

20 

Bicarbnretted  hydrogen 

276 

cohesive 

23 

Bichlorisatine 

673 

152 


PAGE 

Bile 

718 

tests  for 

720 

Biliary  calculi 

719 

Bilin 

719 

Binary  compounds 

74 

Binitrobenzole 

610 

Bismuth 

437 

alloys 

439 

arsenic  in 

438 

butter  of 

438 

chloride  of 

438 

nitrates  of 

438 

oxides 

437 

sulphate  of 

438 

tests  for 

439 

Bisulphide  of  carbon  ' 

289 

Bitter-almond  oil 

654 

spar 

305 

Bittern 

363 

Bitumen 

608 

Bituminous  coal 

607 

schist 

608 

Black  ash 

334 

flux 

324 

Jack 

408 

lead 

251 

Blanc  d'Espagne 

438 

INDEX. 

PAGE 

Bristol  diamonds 

300 

Britannia  metal 

463 

Bromal 

600 

Bromates 

203 

Bromides 

204 

Bromine 

201 

chloride  of 

204 

in  organic  bodies 

550 

Bromisatine 

673 

Bromobenzole 

610 

Bronze 

425 

castings 

425 

coinage 

426 

Bronzing  medals 

419 

tin 

415 

Brucia 

662 

Brunswick  green 

422 

Bude  light 

106 

Butter 

712 

of  antimony 

461 

of  bismuth 

438 

of  tin 

413 

Butyrates 

628 

Butyric  fermentation 

628 

Bleaching  189,  217,  332 

Bleaching-powder  352 

Blende  408 

Bleu  de  Paris  682 

Blood  707 

coloring-matter  of  708 

corpuscles  707 

tests  for  709 

Bloodstone  300 

Blowers  in  coal  mines  270  j 

Blowpipe,  oxhydrogen  124  | 

Blue  dyes  671  | 

John  354 i 

Prussian  394  : 

Thenard's  441 

vitriol  423 

Boghead  coal  611 

Bog  iron  ore  386 

Boiling-points  138 

Bone  705 

weight  of  in  adult  707 

gelatine       "  701 

Bone  earth  356 

Bone  grease  632,  706 

Boracite  365 

Borates  295 

Borax  336 

Borneen  618 

Borneo  camphor  618 

Boron  292 

chloride  of  295 

fluoride  of  296 

nitrate  of  295 

Botryolite  358 

Boules  de  Nancy  637 

Bouquet  of  wines  578 

Boyle's  fuming-liquor  187 

Brain  705 

Brandy  582 

Brass  425 

analysis  of  426 

Brazilwood  677 

Braziline  and  Brazileine    677 

Bread  696 


Cadet's  fuming-liquor      668 

Cajsium  343 

Cadmium  415 

chloride  of  416 

oxide  of  416 

salts  of  416 

tests  for  417 

Caffeine  666 

Cairngorm  stones  300 

Calamine  408 

Calcareous  spar  357 

Calcedony  301 

Calcium  350 

chloride  of  352 

fluoride  of  353 

oxide  of  351 

phosphide  of  351 

sulphide  of  ,  354 

Calculi,  biliary  719 

salivary  714 

urinary  728 

Calico-printing  670 

Calomel  481 

Calotype  612 

Camphine  615 

Camphor  616 

artificial  615 

Borneo  616 

Camphyle  615 

Cane-sugar  668 

Cane-coal  607 

Canton's  phosphorus  354 

Caoutchine  620 

Caoutchouc  620 

vulcanized  59,  621 

Capillarity  24 

Capillary  tubes  24 

Caput  mortuum  389 

Carrageenin  667 

Caramel  670 

Carbazotates  613 

Carbides  258 


PAGE 

Carbolic  acid  610 

Carbon  248 
antiseptic  powers  of        257 

amount  of,  expired  267 

bisulphide  of  289 

estimation  of  546 

gaseous  oxide  of  261 

of  coal  252 
.  source  of,  in  organic 

bodies  645 

Carbonated  waters  149 

Carbonates  269 

Carbonic  acid  263 

quantity  expired  267 

decomposed  by 

plants                    266,  645 
decomposition  of  266 
liquefaction  of  268 
present  in  air  161 
properties  of  264 
solidification  of  268 
sources  of  264 
tests  for  267 
Carbonic  anhydride  266 
Carbonic  oxide  261 
Carburet  hydrogen  275 
(light)  270 
Carmeine  624 
Carmine  623 
Carnelian  300 
Carre's  freezing  apparatus,  79 
Carthamic  acid  676 
Carthamein  676 
Carthamine  676 
Cartilage  700 
Casehardening  391 
Casein  637 
Cassel  yellow  432 
Cassius,  purple  of  518 
Cast  iron  381 
Castor  720 
Castor  oil  ^0 
Catalysis  68 
Cathode  69 
Cations  60 
Cedriret  612 
Cellulose  603 
Cementation  391 
Cements  359 
Cerasin  666 
Cerebro-spinal  fluid  717 
Cerin  631 
Cerolein  631 
Cerium  376 
Cerumen  705 
Cetene  631 
Cetine  631 
Chalcolite  454 
Chalk  358 
Chalk-stones  726 
Chalybeate  waters  149 
Charcoal  253 
absorption  of  gases  by    256 
animal  259 
ashes  of  255 
antiseptic  powers  of  257 
catalytic  power  of  257 
combustion  of  in  oxy- 
gen 92 
decoloring  power  of  258 
filters  258 


INDEX, 


753 


ChAECOAL — C07lt.  PAGE 

preparation  of  253 

properties  of  255 

quantity  from  various 

woods  255 

Cheese  638 

Chemical  analysis  52 

change,  proof  of  51 

compounds  defined  46 

equivalents  64 

force  20,  40 

nomenclature  73 

notation  69 

and  physical  properties     20 

Chemistry  defined  17 

China  374 

Chitin  706 

Chloracetates  649 

Chloral  589 

Chloric  ether  275,  590 

Chlorides  191 

Chlorimetry  353 

Chlorine  188 

aqueous  190 

combustion  in  190 

in  organic  bodies  550 

oxides  of  192 

properties  of  188 

tests  for  191 

Chlorisatine  673 

Chlorites  192 

Chlorobenzole  610 

Chloroform  590 

formula  of  determined    557 

Chlorophyllin  684 

Chlorophane  354 

Chocolate  630 

Choke-damp  264 

Cholesterine  719 

Chondrin  704 

Chromates  445 

Chrome-alum  447 

yellow  446 

Chromic  acid  445 

Chromium  444 

chlorides  of  447 

fluoride  of  447 

oxides  of  444,  445 

sulphates  of  447 

tests  for  448 

Chromomolybdic  acid        453 

Chrysene  610 

Chrysoberyl  374 

Chrysocolla  424 

Chrysolite  366 

Chrysoprase  300 

Chrysorhamnine  680 

Chyle  711 

Chinchonia  660 

Cinnabar  486 

Cinnamyle  616 

Citric  acid,  characters  of  638 

Citrates  539 

Civet  720 

Clay  371 

Clay — iron-stone  380 

Cleavage  of  crystals  27 

Clot  of  blood  707 

Coal  607 

analysis  of  607 

bituminous  607 

b  oghead  cannel  611 

48 


Coal — cont.  page 
cannel  607 
carbon  of  252 
gas  271 
composition  of  271 
measures  607 
mines,  fire-damp  of         273 
naphtha  609 
oil  609 
origin  of  607 
parrot  607 
products  of  its  distilla- 
tion 271 
steam  607 
tar  609 
colors  from  631 
Welsh  607 
Cobalt  439 
ammonia  compounds  of  441 
arsenate  of  439 
arsenide  of  439 
borate  of  441 
carbonate  of  441 
chloride  of  440 
cyanides  of  441 
glance  439 
nitrate  of  440 
oxides  of  439,  440 
sulphate  of  440 
sulphides  of  440 
tests  for  441 
uses  of  441 
Cobaltocyanides  441 
Coccinelline  678 
Cochineal  678 
Cocoa  630 
Cocoa-nut  oil  630 
Codeia  659 
Coffee  666 
Cohesion  23 
influence  of,  on  chemi- 
cal force  41 
Coke  252 
Colchicia  663 
Colcothar  389 
Cold,  production  of  33 
Collodion  507 
process  in  photography  607 
Colophene  618 
Colophony  618 
Color  of  the  blood  707 
of  flowers  and  leaves 
of  light  107 
of  gases  102 
of  incandescent  gases        84 
solids  105 
of  salts  influenced  by 
water  144 
Coloring  matters  669 
of  blood  708 
influence  of  water  on        42 
Colors,  production  669 
substantive  and  adjec- 
tive 670 
Colostrum  712 
Columbium  450 
Combination,  laws  of  65 
Combustibles  defined  103 
Combustion  defined  103 
in  air  153 
in  oxygen  92,  100 
in  rarefied  air  158 


Combustion— ro??f.  page 
heat  and  light  evolved 

in  103 

products  of  108 

without  oxygen  101 

Combustion-tube  550 
Compound  radicals       74,  558 

Compounds,  binary  74 
Compressibility  of  liquids  136 

Concrete  359 
Concussion,  influence  of 

on  crystallization  34 
Conduction,  electric,  by 

metals  311 
by  water  135 
of  heat,  by  metals  310 
by  water  135 
Condy's  disinfectant  402 
Confectionery,  poisonous    470 
Congelation,  line  of  per- 
petual 158 
Conia  664 
Constitution  of  salts  73 
Conversion  of  heat  135 
Copal  619 
Copper  417 
alloys  of  424 
acetates  of  650 
azure  424 
ammonio-sulphate  423 
bronzing  of  419 
carbonates  of  424 
chlorides  421 
cyanides  424 
emerald  424 
formate  of  652 
iodide  of  422 
manufacture  of  417 
nitrate  of  421 
ores  of                      419,  423 
oxides  of  419 
use  in  organic  analysis    546 
poisoning  by  427 
pyrites  423 
silicate  of  424 
sulphate  of  423 
sulphides  of  422 
smelting  of  417 
tartrates  of  637 
tests  for  426 
tinned  426 
Copperas  389 
Coral  706 
Cornish  clay  371 
diamonds  299 
Corpuscles  of  the  blood      708 
Corrosive  sublimate  482 
tests  for  490 
Corundum  368 
Crassamentum  707 
Cracklings  631 
Cream  702 
of  tartar  636 
Creasote  (see  Kreasote)      612 
Crocus  of  antimony  462 
Crucibles                 '  373 
Cryolite  367 
Cryophorus  141 
Crystalline  solids  28 
structure  26 
Crystallization  26 
by  fusion  26- 


Y54 


INDEX. 


PAGE 

Crystallization — cont. 

by  sublimation  28 

salts  separated  by  30 

by  solution  29 

systems  of  35 

theory  of  35 

Crystals,  axes  of  36 

artificial  mineral  28 

biaxial  36 

cleavage  of  27 

deposition  of  30 

double  refracting  36 

forms  of  25 

microscopic  37  , 

production  of  28  i 

structure  of  26 

unequal  expansion  of        28 

uniaxial  36  ' 

Weis's  system  of  35 

Cudbear  674 

Camole  609 

Cupellation  427,  502 

Curagoa  582 

Curcumine  680 

Curd  694 

Cyamelide  281 

Cyanates  281 

Cyanides  287 

tests  for  287 

Cyanogen  278 

bromide  of  288 

chlorides  287,  288 

iodide  of  288 

sulphide  of  288 

tests  for  278 

Cyanurates  282 

Cymol  609 


Daguerreotype 

Datolite 
Daturia 
Decay 
of  wood 


506 
358 
663 
98 
606 


Decomposition,  electric         59 

of  salts  59 

Decrepitation  32 

Definite  proportions  40 

Deflagration  108 

Deliquescence  32 

Dentine  706 

Deoxidation  97 

Derbyshire  spar  354 

Dextrine  664 

Diabetic  sugar  572 

Diachylon  632 

Dialysis  50,  146 

Diamagnetic  bodies  312 

Diamond  249 

cleavage  of  27 

combustion  of  249 

valuation  of  251 

Diaspora  •  369 

Diastase  564 

Diatomacse  299 

Didymium  376 

Diffusion  of  gases  85 

law  of  87 

of  metallic  vapors  86 


Diffusion — cont.  page 

of  liquids  50 

of  vapors  86 

volume  87 

Digestion  715 

Digitalia  663 

Dimorphism  37 

Dipples  oil  (acroleine)         632 

Disacryle  633 

Distillation — fractional      644 

Distilled  vinegar  648 

water  134 

Divisibility  of  matter  21 

Dolomite  365 

Double  affinity  55 

Dough  696 

Dry  rot  606 

Drummond's  light  124 

Ductility  308 

Dutch  gold  425 

liquid  277 

white  435 

Dyeing  670 

Dyslysine  718,  719 


E. 


372 
621 
714 
537 


688 


Earthenware 
Ebonite 
Echidnine 
Educts,  organic 
Efflorescence 
Eggs,  white  of 

yelk  of  ess 

Elaine  623 

Elaioptene  614 

Elayle  275 

Electric  flame,  heat  of  108 

Electrodes  69 

Electrolysis  59 

Electro-negative  bodies  60 

Electro-plating  501 

Electro-positive  bodies  60 

Elements  17 

arrangements  of  78 

relative  proportions  of 

in  animals  706 

table  of  68 

Elementary  analysis  545 

Emerald  374 

Emerald-green  469 

Emery  368 

Emetic  tartar  637 

Emetina  666 

Emulsin  654 

Enamel  339 

of  teeth  704 
Endosmose  and   exos- 

mose  50,  87,  146 

Epsom  salt  363 

Equivalent  weights  64 

volumes  68 

Equivalents  chemical  65 

tablfe  of  67 

of  organic  bodies  554 

barometrical  732 

thermometrical  733 

Erbium  376 

Eremacausis  98 

Erythrine  675 


PAGE 

675 
684 
692 
613 
614 
631 
595 
602 
698 
602 
602 
603 
602 
279 
602 
602 
595 
602 
602 
602 
602 
602 
602 
601 
latent  heat  of  its  vapor  141 
muriatic  602 

nitric  601 

nitrous  601 

cenanthio  579,  603 

ozonized  698 

pelargonic  603 

perchloric  602 

phosphoric  597 

production  of  595 

products  of  its  combus- 

598 


Erythrylene 
Erythrophylin 
Erythroprotide 
Essential  oils 

adulteration  of 
Ethal 
Ether 

acetic 

antozonized 

benzoic 

boracic 

butyric 

carbonic 

chloric 

citric 

cyanic 

formation  of 

formic 

hydriodic 

hydrobromic 

hydrochloric 

hydrocyanic 

hydrosulphuric 

hyponitrous 


tion 
silicic 
succinic 
sulphatic 
sulphuric 
tests  for 


602 
602 
601 
595 
600 

theory  of  its  formation     596 

washed  696 

Etherification,  theory  of    596 

Etherole  601 

Ethers,  compound  603 

double  603 

Ethiops  mineral  486 

Ethogen  295 

Ethylamine  560 

Ethyle  601 

bromide  of  602 

chloride  of  602 

cyanide  of  602 

iodide  of  602 

Ethyle,  sulphide  602 

Ethylic  alcohol  (Alcohol)  683 

Ethylene  275 

Eucalyn  673 

Euchlorine  195 

Euclase  374 

Eudiometry  160 

Eupion  612 

Euxanthates  681 

Euxanthin  681 

Expansion  of  gases  82 

liquids  136 

metals  310 

solids  310 

Excrement  721 

Excretine  721 


INDEX, 


T55 


PAGE 

Explosions  in  coal  mines    274 
Eye,  liquids  of  the  717 


F. 


Fats,  general  properties 

of  622 
Fatty  acids  623 
Fecula  560 
Felspar  299 
Fergusonite  450 
Fermentation  573 
acetic  646 
alcoholic  573 
butyric                      628,  713 
lactic                        628,  713 
panary  573 
pectic  567 
viscous  579 
Fermented  liquids  578 
Ferments  573 
Ferrates           .  385 
Ferric  acid  385 
Ferricyanogen  289 
Ferricyanides  289 
Ferrocyanogen  289 
Ferrocyanides  289 
Ferrum  redatum  383 
Fibrin                          697,  705 
tests  for  699 
vegetable  695 
Fire-clay  372 
Fire-damp                    270,  274 
indicator  275 
Fixed  air  263 
oils  622 
stars,  light  of  108 
Flame,  nature  of  107 
temperature  of  107 
Flesh, juice  of  705 
Flint  300 
Flowers,  colors  of  681 
scents  of  613 
Fluoborio  acid  296 
Fluorides  212 
Fluorine  210 
Fluor-spar  353 
Food  of  animals  539 
preservation  of  687 
Force,  chemical  20 
physical  19 
Formates  652 
Formulae,  chemical  67 
from  vapor  densities       656 
empirical  558 
in  organic  analysis,         654 
rational  558 
Formyle  652 
Fowler's  mineral  solu- 
tion 469 
Fractional  distillation        544 
Freezing  mixtures  33 
by  evaporation  79 
French  chalk  366 
polish  619 
Fructose                        569, 672 
Fruits,  sugar  of  669 
Fuchsine  682 
Fuller's  earth  371 
Fulminating  mercury         488 
powder  320 


PAGE 

Fulminating  silver  499 

Fulminic  acid  281 

Fuming  liquor  of  Boyle  187 

of  Cadet  668 

of  Libavius  413 
Functions  of  vegetables 

and  animals  266 

Fusel  oil  593 

Fusibility  of  metals  310 

Fusible  metal  439 

Fustic  680 

G. 

Gadolinitb  376 

Galena  433 

Gallates  642 

Gall-nuts  641 

Gall-stones  719 

Gallic  acid  641 

Galvanized  iron  409 

Garancin  675 

Garlic,  oil  of  617 

Gas  explosions  274 

in  mines  273 

Gaseous  diffusion  85 

Gases  78 

and  vapors  defined  78 
bulk  of,  at  different 

temperatures  83 

desiccation  of  146 

diamagnetism  of  85 

diffusion  of  86 

expansion  of,  by  heat  83 

incandescence  of  83 

liquefaction  of  79 

magnetism  of  85 
measurement  of  82,  734 
passage  of,  through 

diaphragms  87 

physical  properties  of  81 

refractive  powers  of  85 
specific  gravities  of   84,  677 

specific  heat  of  84 

solidification  of  80 

solubility  of,  in  water  141 
effect  of  pressure  and 

temperature  on    734,  735 

aqueous  vapor  in  736 

Gastric  juice  715 

Geine  607 

Geodes  26 

Gelatin  699 

offish  700 

of  skin  701 

of  bone  701 

sugar  704 

tests  for  703 

Gelose            _  667 

Gems,  artificial  28 

imitations  of  338 

Gerhardt's  notation  69 

German  silver  444 

Geyser  water  303 

Gibbsite  369 

Gilding  by  amalgam  619 

Gin  682 

Glass,  analysis  of  338 

aventurin  339 

Bohemian  650 

bottle  338 


Glass,  colored 
crown 
devitrified 
expansion  of 
flint 


PAOB 

339 
338 
338 
310 
338 


Glass,  manufacture  of       337 

optical  338 

plate  338 

soliible  304 

Glauberite  356 

Glauber's  salt  332 

Glaze  for  iron  pots      339,  373 

for  earthenware  373 

Globulin  692, 717 

Glonoine  626 

Glucina,  salts  of  374 

Glucinum  374 

Glucose  660 

Glucosides  668 

Glue  704 

Gluten  696 

Glutin  695 

Glycerine  625 

Glycocine  704 

GlydocoU  704 

Glvcyrrhizine  673 

Gold  515 

alloys  of  51» 

amalgam  of  519 

assay  of  519 

bromide  of  618 

chlorides  of  517 

coin  619 

cyanide  of  518 

iodides  518 

oxides  of  517 

pure  516 

quality  of,  ascertained    619 

separation  of,  from 

silver  620 
standard  519 
sulphides  of  518 
tests  for  620 
trinkets  519 
use  of,  in  photography     512 
Goniometers  40 
Goulard's  extract  of  lead  651 
Granite  299 
Grape-sugar  669 
Graphite  251 
Gravity  influences  solu- 
tion 48 
specific  736 
Greaves  631 
Green  paper-hangings        469 
Scheele's  469 
vitriol  389 
Guaiacum  618 
Guano  725 
colors  from  678 
Gum  665 
elastic  620 
resins  617 
Gun-cotton  604 
photographic  605 
Gunpowder  320 
for  needle-gun  109 
unexplosive  321 
Gutta-percha  622 
Gypsum  365 


756 

INDEX. 

H. 

Hydrogen — cont.            page 

Iron — co7it. 

page 

pIge 

light  carburetted 

270 

bog,  ore  of 

386 

H^MATEINE 

677 

nascent 

125 

bromides  of 

387 

Hsematosine 

708 

penetrating  power  of 

121 

carbonates  of 

392 

Haematite 

386 

peroxide  of 

151 

carbides  of 

390 

Haematoxylin 

677 

persulphide  of 

187 

cast 

381 

Hair 

688 

preparation  of 

118 

change  of  structure 

Halogens 

188 

properties  of 

120 

of 

34,  382 

Haloid  salts 

75 

sulphuretted 

226 

chlorides  of 

386 

Hamburgh-white 

435 

telluretted 

457 

cold  short 

382 

Hardening  of  steel 

392 

Hydrophane 

300 

combustion  of,  in 

3xy- 

Hardness  of  minerals 

301 

Hydrosulphuric  acid 

226 

gen 

95 

of  metals 

309 

Hyoscyamia 

663 

cyanides  of 

393 

Harmonicon  chemical 

123 

Hydrometers 

585 

ferricyanide  of 

395 

Hartshorn,  salt  of 

187 

Baume's 

737 

ferrocyanide  of 

393 

Hatchetine 

611 

Twaddell's 

738 

galvanized 

409 

Hausmannite 

401 

Hygrometric  water 

147 

gray  cast 

381 

Heat,  conduction  of   135 

310 

Hyponitrites 

172 

hot-short 

382 

convection  of 

135 

Hypophosphites 

239 

hyposulphite 

389 

influence  of  on  chemi- 

Hyposulphates 

225 

iodide  of 

387 

cal  force 

44 

Hyposulphites 

224 

magnetic  oxide  of 

385 

expansion  by            136 

310 

Hyposulphuric  acid 

224 

magnetism  of 

383 

latent 

140 

Hyposulphurous  acid 

224 

malleable 

381 

specific 

139 

manufacture  of 

380 

Heating  powers  of  differ- 

I. 

meteoric 

444 

ent  combustibles 

103 

mottled 

381 

Heavy  spar 

248 

Ice 

136 

native 

444 

Heliotrope 

300 

crystalline  texture  of 

137 

nitrates  of 

387 

Hellebore 

663 

expansion  of 

137 

ores  of 

385,  393 

Hippuric  acid 

656 

specific  gravity  of 

132 

oxides  of 

383 

Hippurates 

656 

Ice  water 

137 

passive  state  of 

388 

Hoffmann's  anodyne 

599 

Iceland  spar 

357 

persalts  of 

397 

Homberg's  pyrophorus 

370 

Igasuric  acid 

662 

phosphates  of 

390 

Honey 

572 

Ignition 

101 

phosphide  of 

390 

Hops,  use  of,  in  beer 

578 

temperature  of 

105 

protoxide  of 

383 

Horn 

688 

in  vacuo 

102 

pure 

382 

Horn-lead 

431 

voltaic 

102 

pyrites 

388 

silver 

494 

Ilmenium 

451 

reduced 

383 

Hot  blast 

104 

Incandescence               33 

,  101 

refining  of 

381 

Humboldtite 

643 

Incubation,  changes   of 

separation  of  the  oxides  397 

Humic  acid 

607 

the  egg  in 

690 

smelting  of 

380 

Humors  of  the  eye 

717 

Indian  fire 

474 

specular  ore  of 

386 

Humus 

603 

rubber 

620 

succinate  of 

620 

Hyacinth 

375 

yellow 

680 

sulphates  of 

389 

Hydracids 

43 

Indigo 

671 

sulphides  of 

388 

Hy  drargochl  orides 

485 

Indigogene 

672 

tartrates  of 

637 

Hydrargyroiodides,  test 

Indigotine 

671 

tests  for 

396 

for  alkaloids 

484 

Indium 

410 

welding  of 

382 

Hydrate  of  soda  from  salt  330 

Ink,  marking 

496 

wrought 

381 

Hydrated  salts 

32 

printing 

629 

zinced 

409 

Hydrates 

143 

sympathetic 

440 

Isatide 

673 

Hydraulic  lime 

359 

writing 

641 

Isatine 

673 

Hydrie  nitrate 

174 

Inuline 

665 

Isinglass 

700 

Hydrides 

124 

lodates 

207 

Japan 

567 

Hydrobenzamide 

655 

Iodides 

209 

.     patent 

701 

Hydrocarbons 

269 

Iodine 

205 

Isomerism 

18,  536 

analysis  of 

653 

chloride  of 

209 

Isomorphism 

38 

oily 

615 

in  organic  bodies 

550 

Isomorphous  bodies 

38,39 

Hydrochloric  acid 

196 

tests  for 

206 

Ivory 

706 

Hydrocyanic  acid 

281 

Ions 

60 

tests  for, 

286 

Ipecacuanha 

666 

Hydrogen 

118 

Iridium 

629 

J. 

allotropic 

125 

salts  of 

630 

Jade 

386 

a  metallic  vapor 

126 

Iron 

380 

Japan  isinglass 

567 

antimonuretted 

461 

acetates  of 

650 

varnish 

619 

arsenic  in 

119 

alloys  of 

396 

Jargon 

375 

arsenuretted 

472 

alum 

390 

Jasper 

300 

compounds  of 

124 

ammonio-chloride  of 

387 

estimation   of,  in   or- 

arsenates of 

472 

K. 

ganic  analysis 

546 

bar 

382 

high  temperature  of  its 

benzoate  of 

654 

Kakodylb 

668 

flame 

123 

black  oxide  of         383 

385 

Kaolin 

371 

INDEX. 


157 


PAGE 

Kapnomor 

612 

Kelp 

324 

Kermes-mineral 

462 

Kerosine 

609 

King's  yellow 

475 

Kinic  acid 

661 

Kirschwasser 

582 

Kreasote 

612 

Kreatine 

705,  727 

Kreatinine 

705,  727 

Krems  white 

435 

Kupfernickel 

442,  476 

Kyanol  (aniline) 

665 

L. 

Labarraque's   disin- 
fectant 331,  335 

Lac  619 

dye  678 

lake  678 

sulphuris  214 

Lacmus  673 

Lacquer  619 

Lactarine  670 

Lactic  fermentation  628 

Lactine  713 

Lactose,  op  lactine  713 

Lakes  368 

Lake  water  130 

Lampblack  260 

Lanthanum  376 

Laquers  619 

Lard  623 

Latent  heat  140 

of  steam  140 

of  vapors  141 

Laughing  gas  167 

Laws  of  combination  65 

Lazulite  371 

Lead  427 

acetates  of  650 
action  of  air  and  water 

on  428 

alloys  of  436 

amylate  of  562 
borate  of                      .      436 

bromide  of  432 

black  251 

carbonate  of  433 

chloride  of  431 

chromates  of  446 

cupellation  of  428 

cyanide  of  436 

desilvering  of  427 
extraction    of,    from 

ores  427 

fluoride  of  432 

formate  of  652 

hyponitrite  of  431 

iodine  of  432 

in  vegetables  542 

nitrates  of  431 

oxichloride  of  432 

oxides  of  429 

phosphates  of  433 

pyrophoric  41 

saccharide  of  570 

sugar  of  651 

sulphate  of  433 


Lead — cont.  page 

sulphide  of  432 

sulphite  of  433 

tartrate  of  637 

tests  for  430 

white  433 

Leather  703 

Leaves,  colors  of  628 

Lecanorine  674 

Legumin  695 

Lepidolite  341 

Leucine  703 

Levulose  5 1 2 

Lichenine  565 

Lichens  567 

colors  from  673 

Light,  chemical  action  of 

446,  455,  503 
and  heat  of  combustion  103 
chemistry  of  503 
color  of,  in  gases  102 
emitted  in  crystalliza- 
tion 467 
evolved  in  combustion  105 
influence   of,    on  com- 
bination 85 
influence  of,  on  chemi- 
cal force  44 
polarized  570 
refraction  of,  by  gases  85 
carburetted  hydrogen  270 
Lightning,  color  of  102 
Lignine  606 
Lignite  607 
Lime  351 
acetate  of  650 
benzoate  of  ■  653 
carbonate  o  357 
chloride  oi  362 
citrate  of  639 
hypochlorite  of  352 
hypophosphite  of  356 
hyposulphite  of  355 
meconate  of  656 
muriate  of  352 
nitrate  of  354 
oxalate  of  645 
phosphates  of  356 
plumbate  of  431 
silicates  of  358 
sulphate  of  355 
sulphite  of  355 
tartrate  of  637 
tests  for  359 
water  352 
Lime-kiln  351 
Lime-light  124 
Limestones  358 
Liquation  492 
Liquefaction,  cooling  by  33 
of  gases  79 
Liquors  582 
Liquids,  compressibility  of  136 
conduction  of  heat  by  135 
convection  of  heat  by  135 
expansion  of  136 
spirituous  682 
Liquor  amnii 

pericardii 
Liquorice  sugar 
Litharge 
Lithia 

48* 


PAGB 

Lithia,  oxalate  of 

645 

salts  of 

341 

tests  for 

342 

Lithium 

341 

in  organic  bodies 

642 

Litmus 

673 

paper 

674 

Liver  of  antimony 

462 

of  sulphur 

322 

Loam 

374 

Logwood 

677 

Lozenges 

563 

Luna  cornea 

494 

Lunar  caustic 

495 

Luteolin 

680 

Lutes 

374 

Lymph 

711 

717 
717 
573 
429 
341 


Macaroni  695 
Macquer's  arsenical  salt     471 
Madder  675 
Madrepore  706 
Magenta  dye  682 
Magistery  of  bismuth         438 
Magnesia  361 
ammonia-phosphate  of    364 
borate  of  365 
carbonates  of  364 
chloride  of  362 
euxanthate  of  681 
hydrate  of  361 
hypochlorite  of  362 
nitrate  of  362 
phosphates  of  364 
silicates  of  365 
sulphate  of  363 
tests  for  366 
Magnesian  limestone  365 
Magnesium  360 
bromide  of  362 
chloride  of  362 
combustion  in  oxygen       95 
in  chlorine  101 
oxides  of  361 
platino-cyanide  of,    33,  524 
Magnetic  iron  ore  385 
Magnetism  of  the  atmo- 
sphere 92 
of  metals  312 
of  gases  85 
Malachite  424 
Malates  640 
MalleabUity  308 
Malt  678 
Malt-spirit  678 
Manganates  401 
Manganese  398 
carbide  of  405 
carbonate  of  406 
chlorides  of  403 
nitrates  of  404 
oxides  of  399 
sulphate  of  404 
sulphide  of  404 
tests  for  405 
,  Manganic  acid  401 
I      oxide  399 
I  Manganite  400 


758 


INDEX. 


PAGE 

Manganous  oxide  399 

Manheim  gold  425 

Manna  572 

Mannite  572 
formula  of,  calculated     556 
Manure                          357,  725 

Maraschino  682 

Marble  358 

Marcasite  437 

Margarine  624 

Marking-ink  496 

Marl  358 

Marsh  gas  270 

Marsh's  arsenic  test  477 

Martial  Ethiops  385 
Mass,  influence  of,  on 

aflBnity  54 

Massicot  429 

Matter,  properties  of  17 

divisibility  of  21 

Mauve  dye  681 

Meadowsweet,  oil  of  667 

Measures  and  weights  729 

Meconine  659 

Meconium  721 
Medals,  bronzing  of   415,  419 

Meerschaum  365 

Viennese  365 

Melam  289 

Melamine  289 

Melitose  573 

Melinite  261 

Mellone  280 

Melon,  essence  of  603 
Membranes  traversed  by 

gases  and  vapors  87 

Mercaptan  602 

Mercurius  vitas  461 

Mercury  479 

acetate  of  651 

amalgams  of  488 

amidochloride  of  483 

amidonitrate  of  486 

bromides  of  484 

carbonates  of  487 

chlorides  of  481 

chlorosulphide  of  487 

cyanide  of  487 

detection  of,  in  cases  of 

poisoning  490 

freezing  of  480 

fulminating  488 

iodides  of  484 

nitrates  of  485 

nitride  of  485 

ores  of  479 

oxides  of  480 

phosphates  of  487 

purification  of  480 

sulphates  of  487 

sulphides  of  486 

sulphocyanide  of  288 

tests  for  489 

Metalochromes  431 

Metalloids  78 
Metallic  compounds,  quali- 
tative analysis  of  376,  531 

Metals  307 

diamagnetism  of  312 

ductility  of  308 
electro-coflduction  by     312 


Metals—  cont.  page 

expansion  of  310 

fusibility  of,  310 

general  properties  of       308 

hardness  of  308 

lustre  of  308 

magnetic  312 

magnetism  of  312 

malleability  of  308 

penetration  of,  by  gases    89 

specific  gravity  of  309 

specific  heat  of  311 

table  of  307 

tenacity  of  308 

Metameric  compounds  19 

Metantimoniates  460 

Metaphosphates  244 

Metastannates  412 

Meteoric  stones  444 

Methylamine  560 

Methylated  spirit  693 

Methyle  593 

salicylate  of  603 

Methylic  alcohol  692 

ether  693 

Metre  730 

Metrical  system  730 

equivalents  731 

Mica  (talc)  365 

Microcosmic  salt  333 

Milk  693,  711 

Mindererus's  spirit  650 

Mineral  cameleon  401 

green  424 

oil  608 

pitch  608 

tar  608 

waters  148 

Minium  430 

Mirbane,  essence  of  610 

Mirrors,  silvering  of,  489 

by  silver  496 

Mispickel  475 

Mocha-stone  300 

Moire  metallique  414 

Molybdates  452 

Molluscous  animals  693 

Molybdenum  451 

chlorides  of  452 

oxides  of  451 

sulphide  of  453 

tests  for  453 

Mordants  67 

Morine  680 

Morphia  658 

formula  of,  determined  454 

tests  for  452,  659 

Mortars  and  cements  358 

Mosaic  gold  414 

Moss-agate  300 

Mother-liquors  29 

Mountain  blue  424 

green  424 

meal  299 

Mucilage  •  566 

adhesive  566 

Mucin  693 

Mucus  716 

Multiple  proportions  96 

Muntz's  metal  424 

Murexan  679 

Murexide  678 


Muriacite 

Muscle 

Musk 

Mustard,  oil  of 

Myricin 

Myrosin 


N. 


PAGE 

356 
705 
720 
616 
631 
616 


Naphtha,  coal 

609 

native 

608 

wood 

592 

Naphthalin 

609 

Narceia 

659 

Narcotina 

660 

Nascent  state 

45,  125 

Natrium 

328 

Needle-gun  powder  109 
Negative  photographs         607 
Neutralization  77 
Neutral  nitrogenous  prin- 
ciples 685 
Nickel  442 
alloys  of  444 
carbonate  of  443 
carbide  of  443 
chloride  of  443 
cyanide  of  444 
nitrate'  of  443 
oxides  of  442 
phosphate  of  443 
potassio-cyanide  of  444 
pyrites  442 
sulphate  of  443 
sulphide  of  443 
tests  for  444 
Nicotina  664 
Nihil  album  407 
Niobium  451 
Nitrates  177 
Nitre  319 
Nitric  acid,  tests  for  177 
oxide  168 
pentoxide  174 
tetroxide  172 
tritoxide  171 
Nitrides  155 
Nitro-benzole  610 
Nitrogen  153 
bicarbide  of  278 
binoxide  of  168 
chloride  of  200 
deutoxide  of  16.8 
estimation  of,  in  organic 

analysis  552 

iodide  of  209 

in  the  atmosphere  156 

oxides  of  166 

peroxide  of  172 

phosphide  of  246 

preparation  of  153 

properties  of  154 

protoxide  of  168 

tests  for        •  155 

Nitro-glycerine  626 

Nitro-muriatic  acid  199 

Nitro-prussides  289 

Nitrous  gas  168 

oxide  166 

Nitrum  flammans  186 


INDEX. 


"[59 


PAGE 

Nomenclature,  chemical  73 

of  organic  compounds  569 

Non-metallic  bodies  78 

Nordhausen  sulphuric  acid  222 

Norium  451 

Normal  salts  77 

Notation,  chemical  64 

Gerhardt-s  69 

old  and  new  745 

unitary  69 

Notations  compared  70 

Noyau  582 

Nutmeg  butter  631 

Nutrition  of  animals  685,  699 

plants  539 

Nux  vomica  661 


Obsidian  301 

Ochre  372 

(Enanthic  ether  679 

(Enanthin  579 

Oil-gas  277 

Oil  of  almonds  630 

ben  630 

bitter  almonds  654 

castor  630 

chocolate-nut  630 

cocoa-nut  630 

coal -tar  609 

cod-liver  630 

colza  670 

Dippel's  (acrolein)  632 

hemp  630 

laurel  671 

linseed  629 

meadow-sweet  667 

nutmeg  671 

olive  670 

palm  630 

poppy-seed  630 

rock  608 

sperm  630 

turpentine  615 

walnut  630 

whale  630 

of  vitriol  219 

of  wine  601 

Oils,  drying  629 

essential  613 

fixed  629 

specific  gravity  of  630 

volatile                   .  618 

Oil-bath  629 

Oleates  624 

Olefiant  gas  275 

chloride  of  277 

Oleine  624 

Oleum  sethereum  601 

Olivine  366 

Onyx  300 

Oolite  358 

Oonin  688 

Opacity  of  metals  308 

Opal  300 

Opium  668 

Orceine  675 

Orcine  674 

Organic  chemistry  535 


Organic  analysis 
bodies,  test  for 
coloring  matters 
elements 
equivalents 
metamorphoses 
principles 
radicals 


PAGE 

541 
645 
669 
356 
554 
640 
356 
658 

substances,  tests  for  645 
Organoleptic  properties  20 
Organo-metallic  bases  668 
Orpiment  475 

Orseille  674 

Osmazome  705 

Osmium  528 

compounds  of  529 

Osmosis  50,  87,  146 

Ovalbumen  688 

Oxacids,  constitution  of        93 
Oxalates  644 

Oxalic-acid,  manufacture 
of  643 

properties  of  643 

tests  for  646 

ultimate  analysis  of  545 
Oxamic  acid  645 

Oxamide  644 

Ox-gall  718 

Oxidation  95 

Oxides  defined  96 

nomenclature  of  96 

reduction  of  97 

Oxychlorates  195 

Oxygen  90 

allotropic  110 

deodorizing  power  of        99 
in  the  atmosphere  160 

equivalent  of  99 

magnetism  of  92 

preparation  of  90 

properties  of  92 

determination  of  in  or- 
ganic analysis  547 
refractive  power  of  92 
specific  heat  of  92 
tests  for                               99 
Oxygennesis                           91 
Oxyhydrogen  blowpipe      124 
Oxymuriatic  acid                 188 
Oxy  water                              151 
Oysanite                                457 
Oysters                        '          693 
Ozokerite                              611 
Ozone                                    110 
bleaching  power  of          112 
constitution  of                 116 
in  the  atmosphere            115 
from  ether                         111 
in  oil  of  turpentine          113 
in  permanganates            113 
reconverted  into  oxygen  114 
tests  for                             114 
Ozonides                                113 
Ozonized  water                     403 
Ozonometry                         115 


Pakfovg 
Palladium 


444 
526 


PAGE 

Palladium,  carbide  of 

527 

oxides  of 

626 

■  salts  of 

526 

tests  for 

527 

Pancreatic  fluid 

715 

Papaverine 

669 

Papier  Moure 

472 

Paracyanogen 

278 

Paraffine 

611 

oils 

611 

Paranaphthaline 

610 

Parchment,  vegetable         603 

Patent  yellow  432 

Pear-oil  603 

Pearl-ash  323 

Pearl-white  439 

Peas  695 

Pea-stone  358 

Pectase  667 

Pectic  acid  667 

fermentation  667 

Pectine  566 

Pectose  566 

Pelargonic  ether  603 

Pelopium  451 

Pepper  666 

Pepsine  716 

Perchlorates  195 

Perchromic  acid  445 

Percussion  caps  488 

Periodates  208 

Permanganates  402 

Peroxide  of  hydrogen  151 

Persian  berries  680 
Persistent  soap-bubbles 

625,  633 

Persulphide  of  hydrogen    187 

Peru  balsam  653 

Petalite  341 

Petrolene  608 

Petroleum  608 

Pettenkofer's  test  for  bile  720 

Pewter  436,  463 

Pharaoh's  serpents  289 

Phene  (benzole)  610 

Phenakite  374 

Phenol  610 

Phenylia  (aniline)  665 

Phenalamine  (aniline)  560 

Philosopher's  lamp  125 

wool  407 

Phloridzine  668 

Phosgene  gas  263 

Phosphamide  246 

Phosphates  243 

tests  for  243 

Phosphides  of  hydrogen     244 

Phosphites  240 

Phospbori  solar  354 

Phosphorus  233 

acids  of  239 

allotropic  237 

amorphous  237 

Balduin's  350 

bromides  of  247 

Canton's  354 

chlorides  of  246 

deoxidation  by  236 

in  organic  bodies  550 

iodides  of  247 

nitride  of  246 


t60 


INDEX. 


Phosphorus — cont.         page 

oxide  of  238 

sulphide  of  247 

tests  for  237 

Phosphorized  alcohol  234,  587 

ether  254,  597 

oils  234 

Phosphuretted  hydrogen    244 

Photographic  pyroxyline   605 

Photography  603 

collodion  process  in        507 

on  glass  507 

on  paper  512 

Photometry  196 

Physical  forces  19 

Picamar  612 

Picric  acid  613 

tinctorial  properties  of  6 1 3 

Picrotoxia  663 

Pine-apple  oil  603 

Pinchbeck  425 

Pink  saucers  676 

Pins,  tinning  of  415 

Piperine  666 

Pisolite  858 

Pitch  608 

Pitch-blende  453 

mineral  608 

Pittacal  612 

Plants,  functions  of  547 

nutrition  of  539 

Plaster  of  Paris  355 

lead  633 

Plaster-stone  355 

Plating  .     498 

Platino-chlorides  623 

Platinocyanides  624 

Platinum  620 

alloys  of  625 

ammonio-chloride  of       623 

black  621 

bromides  of  524 

catalytic  58,  522 

chlorides  of  523 

condensation   of  gases 

by                          128,  522 
cyanide  of  624 
fulminating  523 
iodides  of  624 
malleable,   manufac- 
ture of  620 
ore  of  620 
oxides  of  522 
potassio-chloride  of         524 
sulphate  of  524 
a  test  for  gelatin  703 
sulphide  of  524 
tests  for  525 
Plumbago  251 
Plumbates  431 
Poling  of  copper  417 
Polymeric  compounds  19 
Porcelain  374 
Reaumur's  338 
Porter  678 
Portland  arrowroot  563 
cement  359 
stone  358 
Pot-ash  323 
Potassa          •  313 
acetate  of  650 
alum  369 


Potassa — cont.               page 
antimonio -tartrate  of      637 
bicarbonate  of  325 
bisulphate  of  323 
bitartrate  of  636 
carbonates  of  323 
chlorate  of  317 
chlorinated  316 
chromates  of  445 
cyanate  of  325 
hydrates  of  314 
hypochlorite  of  316 
hyponitrate  of  320 
in  organic  bodies  641 
iodate  of  319 
nitrate  of  319 
nitrite  ;i21 
oxalates  of  645 
oxychlorate  of  318 
perch  1  orate  of  318 
plumbate  of  431 
silicates  of  327 
sodio-tartrate  of  636 
solutions,  sp.  gr.  of         315 
Stan  n  ate  of  412 
sulphates  of  323 
tartrates  of  636 
tests  for  327 
Potassiamide  321 
Potassio-tartrate  of  anti- 
mony 637 
of  iron  637 
of  soda  636 
Potassium  312 
bromide  of  319 
chloride  of  316 
cobalto-cyanide  of  441 
cyanide  of  325 
ferricyanide  of  327 
ferrocyanide  of  326 
iodide  of  318 
iodohydrargyrate  of        657 
nitride  321 
oxides  of                   313,  314 
sulphides  of  322 
sulphocyanide  of  326 
Potato-spirit  693 
Pottery  374 
Prase  300 
Precipitate,  signification  of  53 
per  se  481 
white  483 
Precipitation                  '        53 
Predisposing  affinity  66 
Preservation   of   animal 

substances  687 
Prince  Rupert's  metal        425 
Printer's  ink  629 
Prismatic  analysis  61 
Products,  organic  637 
of  combustion  108 
Proof-spirit  685 
Proofs  of  chemical  change    51 
Propylene  617 
iodized  617 
Proteic  compounds  686 
Protein  685 
Protide  692 
Proximate  organic  ana- 
lysis 641 
principles  560 
Prussian  blue  394 


Prussian  blue — cont.    page 

soluble  395 

TurnbuU's  396 

Prussic  acid  282 

tests  for  286 

Ptyalin  693,  714 

Puddling  of  iron  381 

Pulmonary  exhalation        717 

Pumice  301 

Purple  of  Cassius  517 

Purpurutes  679 

Purpuric  acid  679 

Purpurine  676 

Purree  681 

Pus  716 

Putrefaction  98 

animal  686 

Puzzuolana  359 

Pyin  693,  716 

Pyrene  610 

Pyrites,  arsenical  475 

copper  423 

iron  388 

Pyrogallic  acid  642 

use  of,  in  eudiometry      160 

in  photography  508 

Pyroligneous  acid  648 

Pyrolusite  400 

Pyrophori  41 

Pyropborus,  Homberg's      370 

of  lead  637 

Pyrophosphates  243 

Pyroxanthine  693 

Pyroxylic  spirit  692 

Pyroxyline  604 

photographic  606 


Q. 

Quartz  299 

Quercite  573 

Quercitron  bark  679 

Quercitrine   and  quer- 

cifcreine  679 

Quicklime  351 

Quinces,  essence  of  603 

Quinia  660 

sulphate  of  660 

Quinidine  661 

Quinoidine  661 


R. 


638 


Racemates 

Racemic  acid  638 

Rack  682 

Radicals,  hypothetical  74 

organic  658 

simple  and  compound  74 

Range  of  oxidation  96 

Raphides  641 

Ratafia  582 

Rays,  actinic  505 

chemical  505 

Realgar  474 

Reaumur's  porcelain  338 

Rectified  spirit  of  wine  583 

Red  dyes  676 

glass  339 

ink  677 

lead  430 


INDEX 


701 


Red — co7it.  PAGE 

ore  of  antimony  462 

ore  of  silver  497 

Sfinders  wood  677 

Reduction  of  oxides  97 

of  iron  383 

Regains  of  a  metal  97 

Reinsch's  arsenic  test        468 

Rennet  694,  713 

Resins  617 

Respiration  97 

of  animals  267 

of  plants  539 

Rhamnine  and  rhamneine  680 

Rhodium  527 

oxides  of  527 

salts  of  528 

sulphides  of  528 

Rhubarb,  acid  of  643 

River  water  130 

Rochelle  salts  636 

Rock-crystal  299 

Rock-oil  608 

Rock-salt  330 

Roestone  358 

Roman  cement  359 

Rosaniline  (Roseine)  682 

Rosin  615 

Rouge  677 

Rubidum  343 

in  vegetables  542 

Ruby  368 

silver  ore  497 

Rue,  oil  of  628 

Rutic  acid  628 

Rupert's  drops  338 

metal  425 

Ruthenium  628 

Rutilite  457 


S. 


Sacchulmine 

568 

Safety  lamp 

273 

Safflower 

676 

Sago 

563 

Sal  alembroth 

483 

ammoniac 

186 

de  duobus 

323 

enixum 

323 

gummosum 

636 

mirable  (Glauber's) 

332 

prunella 

320 

Salicine 

667 

Salicyle 

667 

Salicylic  acid 

667 

Saline  waters 

149 

Saliva 

714 

its  action  on  starch 

562 

Salivary  calculi 

714 

Saltpetre 

319 

Salt  of  sorrel 

645 

Salt  of  tartar 

323 

Salt,  spirit  of 

196 

Salts,  acid 

74 

anhydrous 

32 

basic 

74 

binary 

74 

constitution  of 

73 

decrepitation  of 

32 

defined 

73 

Salts — cont.  page 

deliquescent  32 

eiflorescent  32 

electric  decomposition  of  76 

haloid  75 

hydrated  32 

nature  of  73 

neutral  77 

nomenclature  of  74 

normal  77 

Sandstone  299 

Santaline  and  santaleine    677 

Saponification  631 

Sapphire,  oriental  368 

Sarcosine  705 

Sardonyx  3^0 

Satin  spar  368 

Saturation  defined  50,  77 

Saturn  427 

Sawdust,  oxalic  acid  from  643 

Saxon  sulphuric  acid  222 

Scheele's  green  469 

Schists,  bituminous  608 

Schweinfiirth  green  469 

Scotch  topaz  300 

Sealing-wax  619 

Sea-salt  330 

Sea-water  147 

sp.  gr.  of  148 

saline  contents  of  148 

Sea-weed  567 

Sedative  salt  294 

Seignette's  salt  636 

Seleniates  232 

Selenite  366 

Selenium  230 

Seleniuretted  hydrogen      232 

Seralbumen  689 

Serpentine  366 

Serpent-poison  714 

Serum  of  blood  689 

Sheathing  of  metal  424 

Shell- lac  619 

Shells  706 

bherry,  analysis  of  680 

Shot  476 

Silica  299 

in  plants  299 

Silicates  304 

Silicic  acid  299 

Silicon  297 

bromide  of  306 

chloride  of  306 

fluoride  of  306 

nitride  of  306 

sulphide  of  306 

Silk  613 

Silver  492 

acetate  of  650 

alloys  of  500 

amalgam  of  600 

ammonio-nitrate  of         497 

arsenate  of  500 

arsenio-nitrate  600 

arsenite  of  499 

assay  of  601 

bromide  of  495 

carbonate  of  498 

chloracetate  of  649 

chloride  of  494 

chromates  of  500 

coin  600 


Silver — cont. 
cupellation  of 
cyan  ate  of 
cyanide  of 
cyanurate  of 
electro-plating  of 
extraction  of 
frosted 
fulminate  of 
fulminating 
German 

hyposulphite  of 
iodide  of 
in  lead 
nitrate  of 
ores  of 

reduction  of 
oxides  of 
phosphates  of 


PAGE 

602 
499 
498 
499 
499 
492 
600 
499 
499 
444 
497 
495 
428 
495 
492 
492 
493 
498 


salts  of,  their  characters  602 

effects  of  light  on  503 

use  of, in  photography  603 

standard  600 

steel  600 

sulphate  of  498 

sulphide  of  497 

tests  of  502 

Silver-white  435 

Silvio  acid  618 

Silvius,  febrifuge  salt  of  650 

Similor  425 

Sinapine  617 

Single  affinity  52 

Size  704 

Slags,  iron  380 

Smalt  441 

Smelting  of  copper  417 

iron  380 

lead  427 

silver  492 

Snow  138 

Soap        ^  ^  631 

composition  of  631 

Soap-bubbles,    persistent 

625,  633 

Soap-stone  366 

Soap-test  for  water  132 

Soda  329 

acetate  of  650 

alum  371 

ash,  manufacture  of  334 

bicarbonate  of  336 

bisulphate  of  332 

borate  of  336 

carbonate  of  334 

chloride  of  331 

chlorinated,  carbonate 

of  335 

chromate  of  446 

hydrates  of  329 

hypochlorite  331 

hyposulphite  of  332 
use  of  in  photography  506 

metantimoniate  of  461 

muriate  of  330 

nitrate  of         ^  331 

in  organic  bodies  641 

phosphates  of  333 

plumbate  of  431 

silicates  of  337 

solutions,  sp.  gr.  of  329 

spectrum  of  340 


762 


INDEX. 


Soda — cont.  page 

stanuate  of  412 

sulphates  of  332 

sulphites  of  332 

tartrates  of  636 

tests  for  340 

Soda-alum  371 

Soda-lime  552 

Sodium  328 

bromide  331 

chloride  of  330 

in  the  photosphere  of 

the  sun  108 

iodide  of  331 

nitroprusside  of  396 

oxides  of  329 

sulphides  of  332 

Solder  436 

Solidification  of  gases  80 

Solubility    of    gases    in 

water  142 

of  salts  48 

specific  48 

Soluble  tartar  636 

Solution  defined  47 

Sorbine  573 

Sound  in  hydrogen  gas       123 

Spathose  iron  ore  393 

Specific  gravity  736 

of  gases  84,  739 

liquids  736 

metals  309,  738 

solids  738 

vapors  84,  740 

Specific  heat  139 

of  liquids  140 

metals  311 

gases  84 

solids  140 

Spectrum-analysis  61 

solar  505 

actinic  rays  of  505 

chemical  actions  of         505 

in  manufacture  of  steel     63 

photographic  influence 

of  505 

Specular  iron  ore  386 

Speculum  metal  425 

Speiss  442 

Spermaceti  631 

oil  631 

Spheroidal  state  of  liquids  138 

Spirit,  methylated  593 

Mindererus's  650 

of  salt  197. 

of  turpentine  616 

of  wine  683 

of  wood  692 

pyroxylic  592 

Spirituous  liquids  582 

Spongy  platinum  522 

action  of  129 

Spring-water  133 

StaflFordshire  ware  272 

Stalactite  358 

Stalagmite  358 

Standard  gold  519 

silver  500 

Standards  of  weight  and 

measure  729 

Stan  nates  412 

Stannic  acid  412 


PAGE 

Starch  561 

analysis  of  551 

granules  of  561 

in  animals  560 

metamorphoses  562 

potato  563 
proportions  of  in  seeds 

and  roots  561 

rice  663 


sugar 

tests  of 

uses  of 

varieties  of 

wheat 
Steam 

latent  heat  of 

sp.  gr.  of 

superheated 
Stearates 
Stearine 
Stearopten 
Steatite 
Steel 

alloys 

blistered 

cast 

natural 

shear 

tempering  of 

tilted 
Stibamine 
Stibium 
Stick-lac 
Stilbyl 
Stinkstone 
Stone-blue 
Stoneware 
Storm-glass 
Stream  tin 
Strontia 

oxalate  of 

salts  of 

tests  for 
Strontium 

chloride  of 

oxides  of 


569 
562 
563 
562 
562 
138 
140 
127 
138 
624 
623 
614 
366 
391 
392 
391 
391 
391 
391 

391,  392 
391 
560 
459 
619 
655 
358 
566 
372 
31 
410 
349 
645 

349,  350 
350 
369 
350 
349 


Structure  of  minerals  34 

Strychnia  661 

salts  of  662 

poisoning  by  661 

tests  for                   327,  661 

Suberates  627 

Sublimate,  corrosive,  tests 

for  490 

Sublimation  29 

Substitutions,  chemical  558 

Succinates  620 

Sucrose  568 

Suet  622 

Sugar  668 
action  of,  on  polarized 

light  570 

beet-root  568 

composition  of  668 

cane  668 

diabetic  572 

fermentation  of  573 

formula  of  555 

fruit  569 

grape  669 

of  lead  661 


Sugar— cow*. 

PAGE 

manufacture  of 

568 

maple 

568 

milk 

713 

refining  of 

568 

starch 

669 

of  gelatin 

704 

tests  for 

671 

varieties  of 

572 

Sulphantimoniates 

462 

Sulpharsenates 

476 

Sulpharsenites 

476 

Sulphates 

224 

Sulphatic  ether 

601 

Sulphides 

229 

Sulphites 

218 

Sulphobenzide 

610 

Sulphobenzolic  acid 

610 

Sulphocarbonates 

291 

Sulphocyanides 

288 

sulphocyanogen 

288 

Sulphoglyceric  acid 

627 

Sulphonaphthalates 

609 

Sulphosjnapsine 

618 

Sulphovinic  acid 

646 

Sulphur 

212 

allotropism  of 

214 

bromides  of 

230 

chlorides  of 

229 

compounds  of,  with  oxy- 
gen 215 
density  of  vapor  215 
estimation  of,  in  organ- 
ic bodies  653 
flowers  of  213 
iodide  of  230 
liver  of  322 
modifications  of  213 
nitride  of  230 
precipitated  214 
tests  for  215 
Sulphuretted  hydrogen  226 
Sulphureous  waters  149 
Sulphurets  229 
Sulphuric  acid  219 
anhydrous  222 
densities  of  221 
its  action  on    organic 

bodies  545 

manufacture  of  219 

Nordhausen  222 

tests  for  222 

Sulphurous  acid  216 

Sun,  light  of  108 

Supporters  of  combustion  102 

Sweat  717 

Sweet-wort  663 

Swinestone  358 

Symbols,  chemical  66 

old  and  new  compared  745 

Synaptase                     654,  693 

Synovia  716 

Synthesis  52 

Systems  of  crystallization  36 


Table  of  absorption  of 
gases  by  charcoal        256 

of  aqueous  vapor  in 
gases  736 

of  crystalline  forms  36 


INDEX. 

7G3 

Table — coyit.                   page  | 

PAGE 

PAGE 

of  affinities                    53 

,  54 

Talbotype 

512 

Tombac 

425 

albuminous  liquids 

639 

Talc 

365 

Toning  photographs 

612 

of  anions  and  cations 

69 

Tallow 

631 

Topaz,  Oriental 

368 

of  atomic  weights 

67 

fossil 

611 

Scotch 

300 

of     atmospheric    pres- 

Tannin 

640 

Tortoise-shell 

693 

sures 

158 

a  test  for  gelatin 

703 

Touchstone 

300 

of  composition  of  air 

165 

Tanning,  process  of 

703 

Tous  les  mois 

563 

of  coal 

607 

Tantalite 

450 

Tragacan  thine 

666 

of  glass 

338 

Tantalum 

450 

Triacetyline 

610 

of  proof  spirit 

585 

Tapioca 

563 

Triphane 

341 

of  cyanogen  compounds 

280 

Tar,  Coal 

609 

Tripoli 

301 

of  elementary  substances  67 

mineral 

608 

Trommer's  sugar-test 

421 

of  difiFusion  volume 

87 

wood 

643 

Trona 

336 

of  equivalents 

67 

shale 

608 

Tungstates 

480 

of    heating    powers   of 

Tartar 

634,  636 

Tungsten 

449 

combustibles 

103 

cream  of 

636 

chlorides  of 

450 

of  hydrates  of  phospho- 

soluble 

636 

oxides  of 

449 

ric  acid 

243 

emetic 

637 

sulphides  of 

450 

of  isomorphous  bodies 

39 

soluble 

636 

tests  for 

450 

of  liquefaction  of  gases 

80 

of  the  teeth 

714 

Turmeric 

680 

of  magnetics  and  dia- 

Tartaric  acid 

634 

paper 

680 

magnetics 

312 

Tartrates 

635 

Turner's  yellow 

432 

of  magnetism  of  gases 

85 

Tartralates 

637 

Turpentine 

615 

of  metals 

307 

Tartrelates 

638 

oil  of 

615 

their  expansion 

310 

Taurine 

719 

its  formula  deter 

. 

of  fusibility  of  metals 

311 

Tawed  leather 

703 

mined 

557 

specific  gravity 

309 

Tea 

666 

latent  heat  of  its 

va- 

specific  heat  of  metals 

311 

Tears 

657 

por 

141 

tenacity  of  metals 

308 

Teeth 

646 

Turpeth  mineral 

487 

of    non-metallic     ele- 

Telluretted hydrogen         457 

Turquois 

371 

ments 

78 

Tellurium 

456 

Turps 

615 

of  simple  and  compound 

tests  for 

457 

Tutenag 

425 

gases  and  vapors 

743 

Tempering  of  steel 

392 

Type-metal 

463 

of  produce  of  charcoal 

Tenacity 

308 

Tyrosin 

694 

from  different  woods 

259 

Terbium 

376 

of  proportions   of    oil 

Terebene 

618 

U. 

from  seeds 

622 

Terra  foliata  tartari 

650 

of  protein  compounds 

686 

Test-papers 

675,  680 

Ulmine 

607 

of  refractive  powers  of 

Thallium 

344 

Ultimate  analysis 

645 

gases 

85 

oxides  of 

345 

Unitary  notation 

69 

of  solubility  of  gases  in 

salts  of 

345 

Uramile 

679 

water 

142 

tests  for 

345 

Uranite 

453 

of  salts  in  water      48,49 

Thebaia 

659 

Uranium 

463 

of  alkaloids  in  chlo- 

Thein 

666 

acetate  of 

651 

roform 

49 

Thenard's  blue 

441 

oxides  of 

454 

of   specific  gravity  of 

Theobromine 

667 

salts  of 

454 

fixed  oils 

630 

Thermometers 

733 

tests  for 

465 

of  gases  and  vapors 

743 

equivalents  of 

733 

Urates 

726 

of  metals 

309 

Thorina 

375 

Urea 

722 

of  spirituous  liquors 

586 

Thorinum 

375 

artificial 

281,  723 

of  alcoholic  mixtures  586 

Thorite 

375 

compounds  of 

722,  724 

of  solutions  of  ammo- 

Tin 

410 

tests  for 

724 

nia 

179 

alloys  of 

414 

Uric  acid 

724 

of  hydrochloric  acid 

198 

amalgam  of 

489 

tests  for 

726 

of  nitric  acid 

176 

butter  of 

413 

Urinary  calculi 

728 

of  potassa  solutions 

315 

chlorides  of 

413 

deposits 

726 

of  soda  solutions 

329 

foil 

411 

Urine 

721 

of  sulphuric  acid 

221 

ores  of 

410 

of  animals 

721,  727 

of  wines 

581 

oxides  of 

411 

albuminous 

728 

of  specific  heats 

140 

stream 

410 

saccharine 

728 

of  gases 

84 

sulphides 

413 

Usquebaugh 

582 

of  liquids 

140 

tests  for 

414 

of  metals              311 

531 

Tin-plate 

414 

V. 

of  solids 

140 

Tinned  copper 

426 

of  symbols 

67 

Tinning  of  pins 

415 

Vacuum-light 

102 

of  starch  in  seed  anc 

Titannic  acid 

458 

Valerianates 

628 

roots 

561 

Titanite 

457 

Valerianic  acid 

594,  628 

of     temperatures     of 

Titanium 

457 

Valeric  acid 

594 

flames 

108 

Tobacco 

664 

Vanadates 

649 

tests  for  metals 

378 

Tolu  balsam 

663 

Vanadium 

448 

weights  and  measures 

730 

Toluole 

609 

chloride  of 

449 

7G4 

INDEX. 

Vanadium — cont. 
oxides  of 
sulphides  of 

Vapor,  aqueous 
densities 

PAGE 

448 
449 
138 
656 

"Water— co7^i. 
density  of 
distilled 
estimation  of 
electrolysis  of 

page 
186 
134 
146 
130 

Vapors  and  gases  defined     78 

diffusion  of  85 

physical  properties  of       85 

table  of  743 

specific  gravity  739,  740 

Varnishes  619 

Varvicite  401 

Vegetable  albumen  693 

alkaloids  657 

parchment  603 

Vegetables,  functions  of     547 

Venice-white  435 

Veratria  663 

Verd  antique  358 

Verdigris  650 

Verd  iter  424 

Vermilion  486 

Vinegar  646 

adulterations  of  647 

distilled  648 

manufacture  of  646 

strength  of  647 

of  wood  648 

Vinous  fermentation  573 

Viper-poison  693, 714 

Viscous  fermentation  679 

Vitellin  688 

Vitriol,  blue  423 

green  389 

oil  of  219 

white  408 

Voltaic  light  102 

current  69 

Volumes,  atomic  68,  743 

equivalent  68 

Vulcanized  caoutchouc       621 


W. 


Wad 

401 

Wash 

583 

Water 

127 

analysis  of 

130 

anomalous  expansion  of  136 

barometer  159 

basic  143 

boiling  of  138 

capacity  of,  for  heat  139 

color  of  136 

combined  31 

composition  of  127 

compressibility  of  136 
conduction  of  electri- 

•  city  by  135 

of  heat  by  135 

convection  of  heat  by  13» 

decomposition  of  130 


explosive  ebullition  of  138 
freezing  of  136 
hard  and  soft  132 
hygrometrio  146 
influence  of,  on  chemi- 
cal force  42,  142 
influence  of,  on  color  42 
on  reaction  43 
in  crystals  144 
in  organic  substances  142 
interstitial  31 
maximum  density  of  136 
of  crystallization  32 
of  lakes  130 
of  rivers  130 
of  springs  133 
organic  matter  in  164 
physical  properties  of  135 
proportion  of,  in  ani- 
mals 706 
sea  147 
synthesis  of  128 
soap  test  for  132 
solid  contents  in  the 

gallon  of  132 

specific  gravity  of  136 

specific  heat  of  139 

spheroidal  state  of  138 

tests  of  its  presence  146 

tests  of  its  purity  132 

varieties  of  130 

weight  of  136 

Waters,  aerated  266 

arsenicated  150 

carbonated  149 

chalybeate  150 

mineral  147 

sulphurous  149 

silicated  303 

Wavelite  371 

Wax  631 

fossil  611 

vegetable  631 

weights,  atomic  67 

Weights  and  measures  729 

Weld  680 

Welding  382 

Whey  712 

Whisky  582 

White  arsenic  467 

White  copper  444 

White  fire  474 

White  flux                    320,  324 

White  lead  433 

White  precipitate  483 

White  vitriol  408 

Wine  678 

acid  in  578 


WixE — cont.                       PAGE 
anal^^sis  of  581 
composition  of  680 
perfume  of  678 
solia  contents»of  680 
strength  of  581 
varieties  of  578 
Winter  green,  oil  of   603,  606 
Witherite  348 
Wolfram  449 
Wood  606 
decay  of  606 
preservation  of  606 
products  of  its  distil- 
lation 612 
Wood-ash  323 
Woody  fibre  603 
Wood-opal  300 
Wood-spirit  692 
Wood-tar  612 
Wood-vinegar  612 
Wort                              574,  583 
Wothly-type  454 
Writing  ink  641 


Xanthine  675 

Xanthorhamnine  680 

Xanthophylline  684 

Xyloidine  605 

Y. 

Yeast,  artificial  575 
change  of,  in  fermen- 
tation 575 
composition  of  575 
German  575 
growth  of  574 
Yellow  dyes                  679,  681 
Yttria  376 
Yttrotantalite  450 
Yttrium  376 


Z. 


Zapfre 

441 

Zinc 

406 

amalgam  of 

489 

carbonate  of 

408 

chloride  of 

408 

combustion  of,  in  oxy- 
gen 95 
flowers  of  407 
oxide  of  407 
nitrate  of  407 
sulphate  of  408 
sulphide  of  408 
tests  for  409 
white  407 
Zircon  375 
Zirconia  375 
Zirconium  374 


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America  and  Europe. 

To  old  subscribers,  many  of  whom  have  been  on  the  list  foT  twenty  or  thirty  years, 
the  publisher  feels  that  no  promises  for  the  future  are  necessary;  but  gentlemen  who 
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pied as  a  national  exponent  of  scientific  medicine,  and  as  a  medium  of  intercommu- 
nication between  the  profession  of  Europe  and  America — to  render  it,  in  fact,  neces- 
sary to  every  practitioner  who  desires  to  keep  on  a  level  with  the  progress  of  his 
science. 

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vance, for  which  sum  the  subscriber  receives  in  addition  the  "Medical  News  and 
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II. 

THE  MEDICAL  NEWS  AND  LIBRARY 

is  a  monthly  periodical  of  Thirty-two  large  octavo  pages,  making  384  pages  per 
annum.  Its  "News  Department"  presents  the  current  information  of  the  day.  with 
Clinical  Lectures  and  Hospital  Gleanings;  while  the  "  Library  Department"  is  de- 
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*  Commuaications  are  invited  from  gentlemen  in  all  parts  of  the  country  AIT  elaborate  articles  inserted 
by  the  Editor  are  paid  for  by  the  Publisher. 


Henry  C.  Lea's  Publications — (Am,  Journ.  Med.  Sciences).        3 

separately,  so  that  they  can  be  removed  and  bound  on  completion.  In  this  manner 
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&c.  &c.  The  work  i^w  appearing  in  its  pages  is  Dr.  Hudson's  valuable  "  Lectures 
ON  THE  Study  of  Fever,"  which  was  commenced  in  the  number  for  July,  1867.  Gen- 
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Ill- 

RANKIKG'S  ABSTRACT  OF  THE  MEDICAL  SCIENCES 

is  issued  in  half-yearly  volumes,  which  will  be  delivered  to  subscribers  about  the  first 
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ports to  be  "^  Digest  of  British  and  Continental  Medicine,  and  of  the  progress  of 
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of  1867,  for  instance,  thus  contained 

FIFTY-FIVE  articles  ON  GENERAL  QUESTIONS  IN  MEDICINE. 

NINETY-SEVEN  ARTICLES  ON  SPECIAL  QUESTIONS  IN  MEDICINE. 

FIVE  ARTICLES  ON  FORENSIC  MEDICINE 

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ONE  HUNDRED  AND  SEVEN  ARTICLES  ON  SPECIAL  QUESTIONS  IN  SURGERY. 

SEVENTY-TWO  ARTICLES  ON  MIDWIFERY  AND  DISEASES  OF  WOMEN  AND  CHILDREN. 

FORTY-EIGHT  ARTICLES  ON  MATERIA  MEDICA  AND  THERAPEUTICS. 

SIXTY-THREE  REVIEWS  AND  BIBLIOGRAPHICAL  NOTICES. 

THREE  ARTICLES  IN  APPENDIX. 

Making  in  all  four  hundred  and  eighty-two  articles  in  a  single  year.  Each  volume, 
moreover,  is  systematically  arranged,  with  an  elaborate  Table  of  Contents  and  a  very 
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world. 

In  this  effort  to  bring  so  large  an  amount  of  practical  information  within  the  reach 
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the  attention  of  their  acquaintances  to  the  advantages  thus  offered,  and  that  he  will 
be  sustained  in  the  endeavor  to  permanently  establish  medical  periodical  literature  on 
a  footing  of  cheapness  never  heretofore  attempted. 

%*  Gentlemen  desiring  to  avail  themselves  of  the  advantages  thus  offered  will  do 
well  to  forward  their  subscriptions  at  an  early  day,  in  order  to  insure  the  receipt  of 
complete  sets  for  the  year  1868. 

1^  The  safest  mode  of  remittance  is  by  postal  money  order,  drawn  to  the  order  of 
the  undersigned.  Where  money  order  post-offices  are  not  accessible,  remittances  for 
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letters.     Address, 

HENRY  C.  LEA, 

Nos.  706  and  708  Sansom  St.-,  Philadelphia,  Pa. 


Henry  C.  Lea's  Publications — {Dictionaries). 


'QUNGLISON  {ROBLEF),  M.D., 

Professor  of  Institutes  of  Medicine  in  Jefferson  Medical  College,  Philadelphia. 

MEDICAL   LEXICON;   A  Dictionary   of  Medical  Science:   Con- 
taining a  concise  explanation  of  the  various  Subjects  and  Terms  o^  Anatomy,  Physiology, 
Pathology,  Hygiene,  Therapeutics,  Pharmacology,  Pharmacy,  Surgery,  Obstetrics,  Medical 
Jurisprudence,  and  Dentistry.     Notices  of  Climate  and  of  Mineral  Waters;   Formulae  for 
OfiRcinal,  Empirical,  and  Dietetic  Preparations ;  with  the  Accentuation  and  Etymology  of 
the  Terms,  and  the  French  and  other  Synonj-mes;  so  as  to  constitute  a  French  as  well  as 
English  Medical  Lexicon.    Thoroughly  Revised,  and  very  greatly  Modified  and  Augmented 
In  one  very  large  and  handsome  royal  octavo  volume  of  1048  double-columned  pages,  in 
small  type;  strongly  done  up  in  extra  cloth,  $6  00;  leather,  raised  bands,  $6  75. 
The  object  of  the  author  from  the  outset  has  not  been  to  make  the  work  a  mere  lexicon  or 
dictionary  of  terms,  but  to  afford,  under  each,  a  condensed  view  cf  its  various  medical  relations, 
and  thus  to  render  the  work  an  epitome  of  the  existing  condition  of  medical  science.     Starting 
with  this  view,  the  immense  demand  which  has  existed  for  the  work  has  enabled  him,  in  repeated 
revisions,  to  augment  its  completeness  and  usefulness,  until  at  length  it  has  attained  the  position 
of  a  recognized  and  standard  authority  wherever  the  language  is  spoken.     The  mechanical  exe- 
cution of  this  edition  will  be  found  greatly  superior  to  that  of  previous  impressions.    By  enlarging 
the  size  of  the  volume  to  a  royal  octavo,  and  by  the  employment  of  a  small  but  clear  type,  on 
extra  fine  paper,  the  additions  have  been  incorporated  without  materially  increasing  the  bulk  of 
the  volume,  and  the  matter  of  two  or  three  ordinary  octavos  has  been  compressed  into  the  space 
of  one  not  unhandy  for  consultation  and  reference. 
It  would  be  a  work  of  supererogation  to  bestow  a      .  It  is  undonbtedly  the  most  complete  and  useful 


word  of  praise  upon  this  Lexicon.  We  can  only 
wonder  at  the  labor  expended,  for  whenever  we  refer 
to  its  pages  for  information  we  are  seldom  disap- 
pointed in  finding  all  we  desire,  whether  it  be  in  ac- 
centuation, etymology,  or  definition  of  terms. — New 
York  MediealJournal,  November,  1S65. 

It  would  be  mere  waste  of  words  in  us  to  express 
our  admiration  of  a  worli  which  is  so  universally 
and  deservedly  appreciated.  The  most  admirable 
work  of  its  kind  in  the  English  language.  As  a  book 
of  reference  it  is  invaluable  to  the  medical  practi- 
tioner, and  in  every  instance  that  we  have  turned 
over  its  pages  for  information  we  liave  been  charmed 
by  the  clearness  of  language  and  the  accuracy  of 
detail  with  which  each  abounds.  We  can  most  cor- 
dially and  confidently  commend  it  to  our  readers. — 
Glasgoio  Medical  Journal,  January,  1866. 

A  work  to  which  there  is  no  equal  in  the  English 
language. — Edinburgh  Medical  Journal. 

It  is  something  more  than  a  dictionary,  and  some- 
thing less  than  an  encyclopaedia.  This  edition  of  the 
well-known  work  is  a  great  improvement  on  its  pre- 
decessors. The  book  is  one  of  the  very  few  of  which 
it  may  be  said  with  truth  that  every  medical  man 
should  possess  it. — London  Medical  Times,  Aug.  26, 
1S6.5. 

Few  works  of  the  class  exhibit  a  grander  monument 
of  patient  research  and  of  scientific  lore.  The  extent 
of  the  sale  of  this  lexicon  is  sutticient  to  testify  to  its 
u-efulness,  and  to  the  great  service  conferred  by  Dr. 
Robley  Dunglison  on  the  profession,  and  indeed  on 
others,  by  its  issue. — London  Lancet,  May  13,  1865. 

The  old  edition,  which  is  now  super.seded  by  the 
new,  has  been  universally  looked  upon  by  the  medi- 
cal profession  as  a  work  of  immense  research  and 
great  value.  The  new  has  increased  usefulness  ;  for 
medicine,  in  all  its  brancl^es,  has  been  making  such 


medical  dictionary  hitherto  published  in  this  country. 
— Chicago  Med.  Examiner,  February,  1S65. 

What  we  take  to  be  decidedly  the  best  medical  dic- 
tionary in  the  Euglish  language.  The  present  edition 
is  brought  fully  up  to  the  advanced  state  of  science. 
For  many  a  long  year  "Dunglison"  has  been  at  our 
elbow,  a  constant  companion  and  friend,  and  we 
greet  him  in  his  replenished  and  improved  form  with 
especial  satisfaction.— Paei/ic  Med.  and  Surg.  JouT' 
nal,  June  27,  1865. 

This  is,  perhaps,  the  book  of  all  others  which  the 
physician  or  surgeon  should  have  on  his  shelves.  It 
is  more  needed  at  the  present  day  than  a  few  years 
back. — Canada  Med.  Journal,  July,  1865. 

It  deservedly  stands  at  the  head,  and  cannot  be 
surpassed  in  excellence.— .Bw/ato  Med.  and  Surg. 
Journal,  April,  186.5. 

We  can  sincerely  commend  Dr.  Dunglison's  work 
as  most  thorough,  scientific,  and  accurate.  We  have 
tested  it  by  searching  itit  pages  for  new  terms,  which 
have  abounded  so  much  of  late  in  medical  nomen- 
clature, and  our  search  has  been  successful  in  every 
instance.  We  have  been  particularly  struck  with  the 
fulness  of  the  synonymy  and  the  accuracy  of  the  de- 
rivation of  words.  It  Is  as  necessary  a  work  to  every 
enlightened  physician  as  Worcester's  Euglish  Dic- 
tionary is  to  every  one  who  would  keep  up  his  know- 
ledge of  the  English  tongue  to  the  standard  of  the 
present  day.  It  is,  to  our  mind,  the  most  complete 
work  of  the  kind  with  which  we  are  acquainted. — 
Boston  Med.  and  Surg.  Journal,  June  22,  1865. 

We  are  free  to  confess  that  we  know  of  no  medical 
dictionary  more  complete;  no  one  better,  if  so  well 
adapted  for  the  use  of  the  student ;  no  one  that  may 
be  consulted  with  more  satisfaction  by  the  medical 
practitioner. — Am.  Jour.  Med.  Sciences,  April,  1S65. 

The  value  of  the  present  edition  has  been  greatly 
enhanced  by  the  introduction  of  new  subjects  and 


progress  that  many  new  terms  and  subjects  have  re 

cently  been  introduced :  all  of  which  may  be  found 

fully  defined  in  the  present  edition.     We  know  of  no 

other  dictionary  in  the  English  language  that  can  ,       a  a     ■     u] 

bear  a  comparison  with  it  in  point  of  completeness  of    ^"^„^^f^"'^^^® 

subjects  and  accuracy  of  statement. — N.   Y.  Drug' 

gists'  Circular,  1S65. 

For  many  years  Dunglison's  Dictionary  has  been 
the  standard  book  of  reference  with  most  practition- 
ers in  this  country,  and  we  can  certainly  commend 

this  work  to  the  renewed  confidence  and  regard  of  I  in  the  English  language  for  accuracy  and  extent 
our  readers. — Cincinnati  Lancet,  April,  1865.  I  references. — London  Medical  Gazette, 


terms,  and  a  more  complete  etymology  and  accentua- 

o'therircti7nk"rrrQ''the"  EnTlishTanguagTthat'c^^  !  tion,  which  renders  the  work  not  only  satisfactory 

•'  -.-•■'.-  o     »  -  -  I  and  desirable,  but  indispensable  to  the  physician.— 

Chicago  Med.  Journal,  April,  1865. 

No  intelligent  member  of  the  profession  can  or  will 
be  without  it. — St.  Louis  Med.  and  Surg  Journal, 
April,  1865. 
It  has  the  rare  merit  that  it  certainly  has  no  rival 


prOBLYN  {^RICHARD  D.),  M.D. 

A  DICTIONARY  OF  THE  TERMS  USED  IN  MEDICINE  AND 

THE  COLLATERAL  SCIENCES.  A  new  American  edition,  revised,  with  numerous 
additions,  by  Isaac  Hay.s,  M.D.,  Editor  of  the  "American  Journal  of  the  Medical 
Sciences."  In  one  large  royal  12mo.  volume  of  over  500  double-columned  pages;  extra 
cloth,  $1  50 ;  leather,  $2  00. 
It  is  the  best  book  of  definitions  we  have,  and  ought  always  to  be  upon  the  student's  tdiblQ. —Southern 
Med.  and  Surg.  Journal. 


Henry  C.  Lea's  Publications — (Manuals). 


^EILL  {JOHN),  M.D.,    and    ^MITH  [FRANCIS  G.),  M.D., 

Prof,  of  the  Institutes  of  Medicine  in  the  Univ.  of  Penna. 

AN    ANALYTICAL    COMPENDIUM   OF   THE   VARIOUS 

BRANCHES  OF  MEDICAL  SCIENCE  ;  for  the  Use  and  Examination  of  Students.  A 
new  edition,  revised  and  improved.  In  one  very  large  and  handsomely  printed  royal  12mo. 
volume,  of  about  one  thousand  pages,  with  374  wood  cuts,  extra  cloth,  $4 ;  strongly  bound 
in  leather,  with  raised  bands,  $4  75. 


The  Compend  of  Drs.  Neilland  Smith  is  incompara- 
bly the  most  valuable  work  of  its  class  ever  published 
ia  this  country.  Attempts  have  been  made  in  various 
quarters  to  squeeze  Anatomy,  Physiology,  Surgery, 
the  Practice  of  Medicine,  Obstetrics,  Materia  Medica, 
and  Chemistry  into  a  single  manual;  but  the  opera- 
tion has  signally  failed  in  the  hands  of  all  up  to  the 
advent  of"  Neill  and  Smith's"  volume,  which  is  quite 
a  miracle  of  success.  The  outlines  of  the  whole  are 
admirably  drawn  and  illustrated,  and  the  authoi-s 
are  eminently  entitled  to  the  grateful  consideration 
of  the  student  of  every  class. — N.  0.  Med.  and  Surg. 
Journal. 

This  popular  favorite  with  the  student  is  so  well 
known  that  it  requires  no  more  at  the  hands  of  a 
medical  editor  than  the  annunciation  of  a  new  and 
improved  edition.  There  is  no  sort  of  comparison 
between  this  work  and  any  other  on  a  similar  plan, 
and  for  a  similar  object. — Nash.  Journ.  of  Medicine. 

There  are  but  few  students  or  practitioners  of  me- 
dicine unacquainted  with  the  former  editions  of  this 
unassuming  though  highly  instructive  work.  The 
whole  science  of  medicine  appears  to  have  been  sifted, 
as  the  gold-bearing  sands  of  El  Dorado,  and  the  pre- 
cious facts  treasured  up  in  this  little  volume.  A  com- 
plete portable  library  so  condensed  that  the  student 
may  make  it  his  constant  pocket  companion. — West- 
ern Lancet. 

To  compress  the  whole  science  of  medicine  in  less 
than  1,000  pages  is  an  impossibility,  but  we  think  that 
the  book  before  us  approaches  as  near  to  it  as  is  pos- 
sible. Altogether,  it  is  the  best  of  its  class,  and  has 
met  with  a  deserved  success.  As  an  elementary  text- 
book for  students,  it  has  been  useful,  and  will  con- 
tinue to  be  employed  in  the  examination  of  private 
classes,  whilst  it  will  often  be  referred  to  by  the 
country  practitioner. —  Va.  Med.  Journal. 


I  As  a  handbook  for  students  it  is  invaluable,  con- 
taining in  the  most  condensed  form  the  established 
facts  and  principles  of  medicine  and  its  collateral 
sciences. — N.  H.  Journal  of  Medicine. 

In  the  rapid  course  of  lectures,  where  work  for  the 
students  is  heavy,  and  review  necessary  for  an  exa- 
mination, a  compend  is  not  only  valuable,  but  it  is 
almost  a  sine  qua  non.    The  one  before  us  is,  in  most 
of  the  divisions,  the  most  unexceptionable  of  all  books 
of  the  kind  that  we  know  of.    The  newest  and  sound- 
est doctrines  and  the  latest  improvements  and  dis- 
coveries are  explicitly,  though  concisely,  laid  before 
the  student.     Of  course  it  is  xiseless  for  us  to  recom- 
mend it  to  all  last  course  students,  but  there  is  a  class 
j  to  whom  we  very  sincerely  commend  this  cheap  book 
I  as  worth  its  weight  in  silver — that  class  is  the  gradu- 
I  ates  in  medicine  of  more  than  ten  years'  standing, 
I  who  have  not  studied   medicine  since.      They  will 
perhaps  find  out  from  it  that  the  science  is  not  ex- 
!  actly  now  what  it  was  when  they  left  it  off. — The 
I  Stethoscope. 

I      Having  made  free  use  of  this  volume  in  our  exami- 

!  nations  of  pupils,  we  can  speak  from  experience  ia 

I  recommending  it  as  an  admirable  compend  for  stu- 

j  dents,  and  especially  useful  to  preceptors  who  exam- 

j  ine  their  pupils.     It  will  save  the  teacher  much  labor 

by  enabling  him  readily  to  recall  all  of  the  points 

upon  which  his  pupils  should  be  examined.     A  work 

of  this  sort  should  be  in  the  hands  of  every  one  who 

takes  pupils  into  his  office  with  a  view  of  examining 

them ;  and  this  is  unquestionably  the  best  of  its  class. 

Let  every  practitioner  who  has  pupils  provide  himself 

with  it,  and  he  will  find  the  labor  of  refreshing  his 

knowledge  so  much  facilitated  that  he  will  be  able  to 

do  justice  to  his  pupils  at  very  little  cost  of  time  or 

trouble  to  \i\ms.eM.— Transylvania  Med.  Journal. 


J^VDLOW  {J.L.),  M.D„ 

A   MANUAL    OF   EXAMINATIONS    upon   Anatomy,   Physiology, 

Surgery,  Practice  of  Medicine,  Obstetrics,  Materia  Medica,  Chemistry,  Pharmacy,  and 
Therapeutics.  To  which  is  added  a  Medical  Formulary.  Third  edition,  thoroughly  revised 
and  greatly  extended  and  enlarged.  With  370  illustrations.  In  one  handsome  royal 
12mo.  volume  of  816  large  pages,  extra  cloth,  $3  25;  leather,  $3  75. 

The  arrangement  of  this  volume  in  the  form  of  question  and  answer  renders  it  especially  suit- 
able for  the  office  examination  of  students,  and  for  those  preparing  for  graduation. 


We  know  of  no  better  companion  for  the  student 
during  the  hours  spent  in  the  lecture-room,  or  to  re- 
fresh, at  a  glance,  his  memory  of  the  various  topics 
crnrnmed  into  his  head  by  the  various  professors  to 
whom  he  is  compelled  to  listen. — Western  Lancet. 

As  it  embraces  the  whole  range  of  medical  studies 
it  is  ueceasarily  voluminous,  containing  816  large 
duodecimo  pages.  After  a  somewhat  careful  exami- 
nation of  its  contents,  we  have  formed  a  much  more 
favorable  opinion  of  it  than  we  are  wont  to  regard 
such  works.  Although  well  adapted  to  meet  the  wants 


of  the  student  in  preparing  for  his  final  examination, 
it  might  be  profitably  consulted  by  the  practitioner 
also,  who  is  most  apt  to  become  rusty  in  the  very  kind 
of  details  here  given,  and  who,  amid  the  hurry  of  his 
daily  routine,  is  but  too  prone  to  neglect  the  study  of 
more  elaborate  works.  The  possession  of  a  volume 
of  this  kind  might  serve  as  an  inducement  for  him  to 
seize  the  moment  of  excited  curiosity  to  inform  him- 
self on  any  subject,  and  which  is  otherwise  too  often 
allowed  to  pass  unimproved. — St.  Louis  Med,  and 
Surg.  Journal. 


JiANNER  ( THOMAS  HA  WKES),  M  />., 

A  MANUAL  OF  CLINICAL  MEDICINE  AND  PHYSICAL  DIAG- 

NOSIS.  Third  American,  from  the  second  enlarged  and  revised  English  edition.  To 
which  is  added  The  Code  of  Ethics  of  the  American  Medical  Association.  In  one  band- 
some  volume  12mo.     (^Preparing  for  early  publication.) 

This  work,  after  undergoing  a  very  thorough  revision  at  the  hands  of  the  author,  may  now  be 
expected  to  appear  shortly.  The  title  scarcely  affords  a  proper  idea  of  the  range  of  subjects  em- 
braced in  the  volume,  as  it  contains  not  only  very  full  details  of  diagnostic  symptoms  propeply 
classified,  but  also  a  large  amount  of  information  on  matters  of  every  day  practical  importance, 
not  usually  touched  upon  in  the  systematic  works,  or  scattered  through  many  different  volumes. 

J 


Henry  C.  Lea's  Publications — {Anatomy). 


QRAY  {HENRY),  F.B.S., 

Lecturer  on  Anatomy  at  St.  George! 8  Hospital,  London. 

ANATOMY,    DESCRIPTIVE    AND    SURGICAL.      The  Drawinirs  by 

H.  V.  Carter,  M.  D.,  late  Demonstrator  on  Anatomy  at  St.  George's  Hospital ;  the  Dissec- 
tions joii^tly  by  the  Author  and  Dr.  Carter.     Second  American,  from  the  second  revised 
and  improved  London  edition.     In  one  magnificent  imperial  octavo  volume,  of  over  800 
pages,   with  .388  large  and  elaborate  engravings  on  wood.     Price  in  extra  cloth,   $6  00 ; 
leather,  raised  bands,  $7  00. 
The  author  has  endeavored  in  this  work  to  cover  a  more  extended  range  of  subjects  than  is  cus- 
tomary in  the  ordinary  text-books,  by  giving  not  only  the  details  necessary  for  the  student,  but 
also  the  application  of  those  details  in  the  practice  of  medicine  and  surgery,  thus  rendering  it  both 
a  guide  for  the  learner,  and  an  admirable  work  of  reference  for  the  active  practitioner.     The  en- 
gravings form  a  special  feature  in  the  work,  many  of  them  being  the  size  of  nature,  nearly  all 
original,  and  having  the  names  of  the  various  parts  printed  on  the  body  of  the  cut,  in  place  of 
figures  of  reference,  with  descriptions  at  the  foot.    They  thus  form  a  complete  and  splendid  series, 
which  will  greatly  assist  the  student  in  obtaining  a  clear  idea  of  Anatomy,  and  will  also  serve  to 
refresh  the  memory  of  those  who  may  find  in  the  exigencies  of  practice  the  necessity  of  recalling 
the  details  of  the  dissecting  room;  while  combining,  as  it  does,  a  complete  Atlas  of  Anatomy,  with 
a  thorough  treatise  on  systematic,  descriptive,  and  applied  Anatomy,  the  work  will  be  found  of 
essential  use  to  all  physicians  who  receive  students  in  their  offices,  relieving  both  preceptor  and 
pupil  of  much  labor  in  laying  the  groundwork  of  a  thorough  medical  education. 

Notwithstanding  its  exceedingly  low  price,  the  work  will  be  found,  in  every  detail  of  mechanical 
execution,  one  of  the  handsomest  that  has  yet  been  offered  to  the  American  profession  ;  while  the 
careful  scrutiny  of  a  competent  anatomist  has  relieved  it  of  whatever  typographical  errors  existed 
in  the  English  edition. 

Thus  it  is  that  book  after  book  makes  the  labor  of  I  and  with  scarce  a  reference  to  the  printed  text.  The 
the  student  easier  than  before,  and  since  we  have  surgical  application  of  the  various  regions  is  also  pre- 
seeu  Blanchard  &  Lea's  new  edition  of  Gray's  Ana-  sented  with  force  and  clearness,  impressing  upon  the 
tomy,  certainly  the  finest  work  of  the  kind  now  ex-  stndent  at  each  step  of  his  research  all  thelmportant 
tant,  we  would  fain  hope  that  the  bugbear  of  medical  j  relations  of  the  structure  demonstrated. — Cincinnati 
students  will  lose  half  its  horrors,  and  this  necessary  '  Lancet. 

foundation  of  physiological  science  will  be  much  fa-  j      This  is.  we  believe,  the  handsomest  book  on  Ana- 
cilitated  and  advanced. — N.  0.  Med.  News.  tomy  as  yet  published  in  our  language,  and  bids  fair 

I  to  become  in  a  short  time  the  standard  text-book  of 
The  various  points  illustrated  are  marked  directly  1  our  colleges  and  studies.  Studeuts  and  practitioners 
on  the  structure;  that  is,  whether  it  be  muscle,  pro  j  will  alike  appreciate  this  book.  We  predict  for  it  a 
cess,  artery,  nerve,  valve,  etc.  etc. — we  say  pach  point  bright  career,  aud  are  fully  prepared  to  endorse  the 
is  distinctly  marked  by  lettered  engravings,  so  that  statement  of  the  London  Lancet,  that  "We  are  not 
the  student  perceives  at  once  each  point  described  as  !  acquainted  with  any  work  in  any  language  -which 
readily  as  if  pointed  out  on  the  subject  by  the  de- 1  can  take  equal  rank  with  the  one  before  us."  Paper, 
monstrator.  Most  of  the  illustrations  are  thus  ren- '  priuting,  binding,  all  are  excellent,  aud  we  feel  that 
dered  exceedingly  satisfactory,  and  to  the  physician  a  grateful  profession  will  not  allow  the  publishers  to 
they  serve  to  refresh  the  memory  with  great  readiness  [  go  unrewarded. — Aashville  Med.  and  Surg.  Journal. 


^MITH  [HENRY B.),  M.D.,         and    TJORNER  (  WILLIAM  E.),  M.D., 

Prof,  of  Surgery  in  the  Univ.  of  Penna.,  &c.  Late  Prof,  of  Anatomy  in  the  Univ.  of  Penna.,  Ac- 

AN    ANATOMICAL    ATLAS,  illustrative   of  the   Structure  of  the 

Human  Body.     In  one  volume,  large  imperial  octavo,  extra  cloth,  with  about  six  hundred 

and  fifty  beautiful  figures.     $4  60. 
The  plan  of  this  Atlas,  which  renders  it  so  pecu- 1  the  kind  that  has  yet  appeared;  and  we  must  add, 
liarly  convenient  for  the  student,  and  its  superb  ar-  |  the  very  beautiful  manner  in  which  it  is  "got  up" 
tistical  execution,  have  been  already  pointed  out.  We    is  so  creditable  to  the  country  as  to  be  flattering  to 
must  congratulate  the  student  upon  the  completion    our  national  pride.— .American  MedicalJournal. 
of  this  Atlas,  as  it  is  the  most  convenient  work  of  I 


ff" 


RNER  [WILLIAM  E.),  M.D., 
SPECIAL  ANATOMY  AND  HISTOLOGY.    Eighth  edition,  exten- 

sively  revised  and  modified.     In  two  large  octavo  volumes  of  over  1000  pages,  with  more 
than  300  wood-cuts ;  extra  cloth,  $6  00. 


OHARPEY  ( WILLIAM),  M.D.,     and       Q  VAIN  [JONES  Sr  RICHARD). 
HUMAN  ANATOMY.  Revised,  with  Notes  and  Additions,  by  Joseph 

Leidv,  M.D.,  Professor  of  Anatomy  in  the  University  of  Pennsylvania.     Complete  in  two 
large  octavo  volumes,  of  about  1300  pages,  with  511  illustrations;  extra  cloth,  $6  00. 
The  very  low  price  of  this  standard  work,  and  its  completeness  in  all  departments  of  the  subject, 
should  command  for  it  a  place  in  the  library  of  all  anatomical  students. 


A 


LLEN  [J.M.),  M.D. 

THE  PRACTICAL  ANATOMIST;  or.  The  Student's  Guide  in  the 

Dissecting  Room.     "With  266  illustrations.     In  one  very  handsome  royal  12mo.  volume, 
of  over  600  pages;  extra  cloth,  $2  00. 
One  of  the  most  useful  works  upon  the  subject  ever  written. — Medical  Examiner. 


Henry  C.  Lea's  Publications — (Anatomy). 


JYILSON  {ERASMUS),  F.R.S. 


A  SYSTEM  OF  HUMAN  ANATOMY,  General  and  Special.     A  new 

and  revised  American,  from  the  last  and  enlarged  English  edition.     Edited  by  W.  H.  Go- 
BRECHT,  M.D.,  Professor  of  General  and  Surgical  Anatomy  in  the  Medical  College  of  Ohio. 
Illustrated  with  three  hundred  and  ninety-seven  engravings  on  wood.     In  one  large  and 
handsome  octavo  volume,  of  over  600  large  pages;  extra  cloth,  $4  00;  leather,  $5  00. 
The  publisher  trusts  that  the  well-earned  reputation  of  this  long-established  favorite  will  be 
more  than  maintained  by  the  present  edition.     Besides  a  very  thorough  revision  by  the  author,  it 
has  been  most  carefully  examined  by  the  editor,  and  the  efforts  of  both  have  been  directed  to  in- 
troducing everything  which  increased  experience  in  its  use  has  suggested  as  desirable  to  render  it 
a  complete  text-book  for  those  seeking  to  obtain  or  to  renew  an  acquaintance  with  Human  Ana- 
tomy.    The  amount  of  additions  which  it  has  thus  received  may  be  estimated  from  the  fact  that 
the  present  edition  contains  over  one-fourth  more  matter  than  the  last,  rendering  a  smaller  type 
and  an  enlarged  page  requisite  to  keep  the  volume  within  a  convenient  size.     The  author  has  not 
only  thus  added  largely  to  the  work,  but  he  has  also  made  alterations  throughout,  wherever  there 
appeared  the  opportunity  of  improving  the  arrangement  or  style,  so  as  to  present  every  fact  in  its 
most  appropriate  manner,  and  to  render  the  whole  as  clear  and  intelligible  as  possible.    The  editor 
has  exercised  the  utmost  caution  to  obtain  entire  accuracy  in  the  text,  and  has  largely  increased 
the  number  of  illustrations,  of  which  there  are  about  one  hundred  and  fifty  more  in  this  edition 
than  in  the  last,  thus  bringing  distinctly  before  the  eye  of  the  student  everything  of  interest  or 
importance. 

J^Y  THE  SAME  AUTHOR.  ^ 

THE  DISSECTOR'S   MANUAL;   or,  Practical  and  Surgical  Ana- 

,  TO  MY.  Third  American,  froxn  the  last  revised  and  enlarged  English  edition.  Modified  and 
rearranged  by  William  Hunt,  M.  D.,  late  Demonstrator  of  Anatomy  in  the  University  of 
Pennsylvania.  In  one  large  and  handsome  royal  12mo.  volume,  of  582  pages,  with  154 
illustrations;  extra  cloth,     $2  00. 


TTODGES,  {RICHARD  M.),  M.D., 

J-L  Late  Demonstrator  of  Anatomy  in  the  Medical  Department  of  Harvard  University. 

PRACTICAL   DISSP:CTI0NS.     Second  Edition,  thoroughly  revised.     In 

one  neat  royal  12mo.  volume,  half-bound,  $2  00.  {Just  Issued.) 
The  object  of  this  work  is  to  present  to  the  anatomical  student  a  clear  and  concise  description 
of  that  which  he  is  expected  to  observe  in  an  ordinary  course  of  disseefcions.  The  author  has 
endeavored  to  omit  unnecessary  details,  and  to  present  the  subject  in  the  form  which  many  years' 
experience  has  shown  him  to  be  the  most  convenient  and  intelligible  to  the  student.  In  the 
revision  of  the  present  edition,  he  has  sedulously  labored  to  render  the  volume  more  worthy  of 
the  favor  with  which  it  has  heretofore  been  received. 


31 


ACLISE  {JOSEPH). 

SURGICAL   ANATOMY.      By  Joseph   Maclise,  Surgeon.     In  one 

^  volume,  very  large  imperial  quarto;  with  68  large  and  splendid  plates,  drawn  in  the  best 

style  and  beautifully  colored,  containing  190  figures,  many  of  them  the  size  of  life;  together 
with  copious  explanatory  letter-press.      Strongly  and  handsomely  bound  in  extra  cloth. 
Price  $14  00. 
As  no  complete  work  of  the  kind  has  heretofore  been  published  in  the  English  language,  the 
present  volume  will  supply  a  want  long  felt  in  this  country  of  an  accurate  and  comprehensive 
Atlas  of  Surgical  Anatomy,  to  which  the  student  and  practitioner  can  at  all  times  refer  to  ascer- 
tain the  exact  relative  positions  of  the  various  portions  of  the  human  frame  towards  each  other 
and  to  the  surface,  as  well  as  their  abnormal  deviations.     The  importance  of  such  a  work  to  the 
student,  in  the  absence  of  anatomical  material,  and  to  practitioners,  either  for  consultation  in 
emergencies  or  to  refresh  their  recollections  of  the  dissecting  room,  is  evident.     Notwithstanding 
the  large  size,  beauty  and  finish  of  the  very  numerous  illustrations,  it  will  be  observed  that  the 
price  is  so  low  as  to  place  it  within  the  reach  of  all  members  of  the  profession. 


We  know  of  no  work  on  surgical  anatomy  which 
can  compete  with  it. — Lancet. 

Tlie  work  of  Maclise  on  surgical  anatomy  is  of  the 
highest  value.  In  some  respects  it  is  the  best  publi- 
cation  of  its  kind  we  have  seen,  and  is  worthy  of  a 
place  in  the  libiary  of  any  medical  man,  while  the 
student  could  scarcely  make  a  bptter  investment  than 
this. — The  Western  Journal  of  Medicine  and  Surgery. 

No  such  lithographic  illnstrations  of  surgical  re- 
gions have  hitherto,  we  think,  been  given.  While 
the  operator  is  shown  every  vessel  and  nerve  where 
an  operation  is  contemplated,  the  exact  anatomist  is 


refreshed  by  those  clear  and  distinct  dissections, 
which  every  one  must  appreciate  who  has  a  particle 
of  enthusiasm.  The  English  medical  press  has  quite 
exhausted  the  words  of  praise,  in  recommending  this 
admirable  treatise.  Those  who  have  any  curiosity 
to  gratify,  in  reference  to  the  perfectibility  of  the 
lithographic  art  in  delineating  the  complex  mechan- 
ism of  the  human  body,  are  invited  to  examine  our 
specimen  copy.  If  anything  will  induce  surgeons 
and  students  to  patronize  a  book  of  such  rare  vulne 
and  everyday  importance  to  them,  it  will  be  a  survey 
of  the  artistical  skill  exhibited  in  these  fac-similes  of 
nature. — Boston  Mtd.  and  Surg.  Journal. 


PEASLEE  {E.  R.),  M.D., 
Professor  of  Anatomy  and  Physiology  in  Dartmotith  Med.  College,  N.  H. 

HUMAN  HISTOLOGY,  in  its  relations  to  Anatomy,  Physiology,  and 

Pathology;  for  the  use  of  medical  students.     With  four  hundred  and  thirty-four  iII«Btra- 
tions.     In  one  handsome  octavo  volume  of  over  600  pages,  extra  cloth.     $3  75. 


Henry  C.  Lea's  Publications — {Physiology). 


rjARPENTER  [WILLIAM  B.),  M.D.,  F.R.S., 

Examiner  in  Physiology  and  Comparative  Anatomy  in  the  University  of  London. 

PRINCIPLES  OF  HUMAN  PHYSIOLOGY;  with  their  chief  appli- 

cations  to  Psychology,  Pathology,  Therapeutics,  Hygiene  and  Forensic  Medicine.  A  new 
American  from  the  last  and  revised  London  edition.  With  nearly  three  hundred  illustrations. 
Edited,  with  additions,  by  Francis  Guhney  Smith,  M.  •.,  Professor  of  the  Institutes  of 
Medicine  in  the  University  of  Pennsylvania,  &c.  In  one  very  large  and  beautiful  octavo 
volume,  of  about  900  large  pages,  handsomely  printed;  extra  cloth,  $5  50  ;  leather,  raised 
bands,  $6  50. 


The  highest  coinpliment  that  can  he  extended  to 
this  great  work  of  Dr.  Carpenter  is  to  call  attention 
to  this,  another  new  edition,  which  the  favorahle 
regard  of  the  profession  has  called  for.  Carpenter  is 
the  standard  authoiity  on  physiology,  and  no  physi- 
cian  or  medical  student  will  regard  his  library  as 
complete  without  a  copy  of  \i.— Cincinnati  Med.  Ob- 
server. 

With  Dr.  Smith,  we  confidently  believe  "that  the 
present  will  more  than  sustain  the  enviable  reputa- 
tion already  attained  by  former  editions,  of  being 
one  of  the  fullest  and  most  complete  treatises  on  the 
subject  in  the  English  language."  We  know  of  none 
from  the  pages  of  which  a  satisfactory  knowledge  of 
the  physiology  of  the  human  organiKm  can  be  as  well 
obtained,  none  better  adapted  for  the  use  of  such  as 
take  up  the  study  of  physiology  in  its  reference  to 
the  institutes  and  practice  of  medicine. — Am.  Jour. 
Med.  Sciences. 

A  complete  cyclop ajdia  of  this  branch  of  science.— 
N.  Y.  Med.  Times. 


We  doubt  not  it  is  destined  to  retain  a  strong  hold 
on  public  favor,  and  remain  the  favorite  text-book  iu 
our  colleges. — Virginia  Medical  Journal. 

We  have  so  often  spoken  in  terms  of  high  com- 
mendation of  Dr.  Carpenter's  elaborate  work  on  hu- 
man physiology  that,  in  announcing  a  new  edition, 
it  is  unnecessary  to  add  anything  to  what  has  hereto- 
fore been  said,  and  especially  is  this  the  case  since 
every  intelligent  phy.siciau  is  as  well  aware  of  the 
chai-acter  and  merits  of  the  work  as  we  ourselves  are. 
— St.  Louis  Med.  and  Surg.  Journal. 

The  above  is  the  title  of  what  is  emphatically  the 
great  work  on  physiology ;  and  we  are  conscious'that 
it  would  be  a  u.seless  elfort  to  attempt  to  add  any- 
thing to  the  reputation  of  this  invaluable  work,  and 
can  only  say  to  all  with  whom  our  opinion  has  any 
influence,  that  it  is  our  authority. — Atlanta  Med. 
Journal. 

The  greatest,  the  most  reliable,  and  the  best  book 
on  the  subject  which  we  know  of  in  the  English  lab- 
guage.  —Stethoscope. 


JDT  THE  SAME  AUTHOR.  

PRINCIPLES  OF  COMPARATIVE  PHYSIOLOGY.    New  Ameri- 

can,  from  the  Fourth  and  Revised  London  Edition.     In  one  large  and  hjindsome  octavo 
volume,  with  over  three  hundred  beautiful  illustrations     Pp.  752.    Extra  cloth,  $5  00. 
As  a  complete  and  condensed  treatise  on  its  extended  and  important  subject,  this  work  becomes 

a  necessity  to  students  of  natural  science,  while  the  very  low  price  at  which  it  is  offered  places  it 

within  the  reach  of  all. 


B 


Y  THE  SAME  A  UTHOR. 

THE  MICROSCOPE  AND  ITS  REVELATIONS.    With  an  Appen- 

dix  containing  the  Applications  of  the  Microscope  to  Clinical  Medicine,  &c.  By  F.  G. 
Smith  M.  D.  Illustrated  by  four  hundred  and  thirty-four  beautiful  engravings  on  wood. 
In  one  large  and  very  handsome  octavo  volume,  of  724  pages,  extra  cloth,  $5  25. 


rpODD  [ROBERT  B.),  M.D.  F.R.S.,  and  JDOWMAN  [W.),  F.R.S. 
THE    PHYSIOLOGICAL   ANATOMY   AND   PHYSIOLOGY   OF 

MAN.     With  about  three  hundred  large  and  beautiful  illustrations  on  wood.     Complete  in 
one  large  octavo  volume  of  950  pages,  extra  cloth.     Price  $4  75. 

practitioner  can  consult  relating  to  physiology. — N. 
Y.  Journal  of  Medicine. 


The  names  of  Todd  and  Bowman  have  long  been 
familiar  to  the  student  of  pl)ysiology.  In  this  work 
we  have  the  ripe  experience  of  these  laborious  physi- 
ologists on  every  branch  of  this  science.  They  gave 
each  subject  the  most  thorough  and  critical  examina- 
tion before  making  it  a  matter  of  record.  Thus,  while 
they  advanced  tardily,  apparently,  in  their  publica- 
tion, the  work  thus  issued  was  a  complete  exponent 
of  the  science  of  physiology  at  the  time  of  its  final 
appearance.  We  can,  therefore,  recommend  this 
work  as  one  of  the  most  reliable  which  the  student  or 


To  it  the  rising  generation  of  medical  men  will 
owe,  in  great  measure,  a  familiar  acquaintance  with 
all  the  chief  truths  respecting  the  healthy  structure 
and  working  of  the  frames  which  are  to  form  the 
subject  of  their  care.  The  possession  of  such  know- 
ledge will  do  more  to  make  sound  and  able  practi- 
tioners than  auything  else. — British  and  Foreign 
Medico- Chirurgical  Review. 


K 


IRKES  [WILLIAM  SENHOUSE),  M.D., 


A  MANUAL  OF  PHYSIOLOGY.    A  new  American  from  the  third 

and  improved  London  edition.     With  two  hundred  illustrations.     In  one  large  and  hand- 
some royal  12mo.  volume.     Pp.  586.     Extra  cloth,  $2  25  ;  leather,  $2  75. 
By  the  use  of  a  fine  and  clear  type,  a  very  large  amount  of  matter  has  been  condensed  into  a 
comparatively  small  volume,   and  at  its  exceedingly  low  price  it  will  be  found  a  most  desirable 
manual  for  students  or  for  gentlemen  desirous  to  refresh  their  knowledge  of  modern  physiology. 

It  is  at  once  convenient  in  size,  comprehensive  in  lent  guide  in  the  study  of  physiology  in  its  most  ad- 
design,  and  concise  in  statement,  and  altogether  well  vauced  and  perfect  form.  The  author  has  shown 
adapted  for  the  purpose  designed. — St.  Louis  Med.  himself  capable  of  giving  details  sufilciently  ample 
and  Surg.  Journal.  in  a  condensed  and  concentrated  shape,  on  a  science 

in  which  it  is  necessary  at  once  to  be  correct  and  not 
The  physiological  reader  will  find  it  a  most  excel-     Lengthened.— JSdm&itry/t  Med.  and  Surg.  Journal. 


Henry  C.  Lea's  Publications — (PKysiology). 


9 


T)ALTON  [J.  a),  M.D., 

-^-^  Professor  of  Physiology  in  the  College  of  Physicians  and  Surgeons,  New  York,  See. 

A  TREATISE  ON  HUMAN  PHYSIOLOGY,  Designed  for  the  use 

of  Students  and  Practitioners  of  Medicine.  Fourth  edition,  revised,  with  nearly  three  hun- 
dred illustrations  on  wood.  In  one  very  beautiful  octavo  volume,  of  about  700  pages,  extra 
cloth,  $5  25  ;  leather,  $6  25.     {Now  Ready.) 

From  the  Preface  to  the  New  Edition. 
**  The  progress  made  by  Physiology  and  the  kindred  Sciences  during  the  last  few  years  has  re- 
quired, for  the  present  edition  of  this  work,  a  thorough  and  extensive  revision.  This  progress 
has  not  consisted  in  any  very  striking  single  discoveries,  nor  in  a  decided  revolution  in  any  of 
the  departments  of  Physiology;  but  it  has  been  marked  by  great  activity  of  investigation  in  a 
multitude  of  different  directions,  the  combined  results  of  which  have  not  failed  to  impress  a  new 
character  on  many  of  the  features  of  physiological  knowledge.  ...  In  the  revision  and 
correction  of  the  present  edition,  the  author  has  endeavored  to  incorporate  all  such  improve- 
ments in  physiological  knowledge  with  the  mass  of  the  text  in  such  a  manner  as  not  essentially 
to  alter  the  structure  and  plan  of  the  work,  so  far  as  they  have  been  found  adapted  to  the  wants 
and  convenience  of  the  reader.  .  .  .  Several  new  illustrations  are  introduced,  some  of  them 
as  additions,  others  as  improvements  or  corrections  of  the  old.  Although  all  parts  of  the  book 
have  received  more  or  less  complete  revision,  the  greatest  number  of  additions  and  changes  were 
required  in  the  Second  Section,  on  the  Physiology  of  the  Nervous  System." 

The  reputation  which  this  work  has  acquired,  as  a  compact  and  convenient  summary  of  the 
most  advanced  condition  of  human  physiology,  renders  it  only  necessary  to  state  that  the  author 
has  assiduously  labored  to  render  the  present  edition  worthy  a  continuance  of  the  marked  favor 
accorded  to  previous  impressions,  and  that  every  care  has  been  bestowed  upon  the  typographical 
execution  to  make  it,  as  heretofore,  one  of  the  handsomest  productions  of  the  American  press. 

The  advent  of  the  first  edition  of  Prof.  Dalton's 
Physiology,  about  eight  years  ago,  marked  a  new  era 
in  the  study  of  physiology  to  the  American  student. 
Under  Dalton's  skilful  management,  physiological 
science  threw  off  the  long,  loose,  ungainly  garments 
of  probability  and  surmise,  in  which  it  had  been  ar- 
rayed by  most  artists,  and  came  among  us  smiling 
and  attractive,  in»the  beautifully  tinted  and  closely 
fitting  dress  of  a  demonstrated  science.  It  was  a 
stroke  of  genius,  as  well  as  a  result  of  erudition  and 
talent,  that  led  Prof.  Dalton  to  present  to  the  world 
a  work  on  physiology  at  once  brief,  pointed,  and  com- 
prehensive, and  which  exhibited  plainly  in  letter  and 
drawings  the  basis  upon  which  the  conclusions  ar- 
rived at  rested.  It  is  no  disparagement  of  the  many 
excellent  works  on  physiology,  published  prior  to 
that  of  Dalton,  to  say  that  none  of  them,  either  in 
plan  of  arrangement  or  clearness  of  execution,  could 
be  compared  with  his  for  the  use  of  students  or  gene- 
ral practitioners  of  medicine.  For  this  purpose  his 
book  has  no  equal  in  the  English  language. —  Western 
Journal  of  Medicine,  Nov.  1S67. 

A  capital  text-book  in  every  way.  We  are,  there- 
fore, glad  to  see  it  in  its  fourth  edition.  It  has  already 
been  examined  at  full  length  in  these  columns,  so  that 
we  need  not  now  further  advert  to  it  beyond  remark- 
ing that  both  revision  and  enlargement  have  been 
most  judicious.— 2/owd6»»  Med.  Times  and  Gazette, 
Oct.  19,  1867. 

No  better  proof  of  the  value  of  this  admirable 
work  could  be  produced  than  the  fact  that  it  has  al- 
ready reached  a  fourth  edition  in  the  short  space  of 
eight  years.    Possessing  in  an  eminent  degree  the 


merits  of  clearness  and  condensation,  and  being  fully 
brought  up  to  the  present  level  of  Physiology,  it  is 
undoubtedly  one  of  the  most  reliable  text-books 
upon  this  science  that  could  be  placed  in  the  hands 
of  the  medical  student. — Am.  Journal  Med.  Sciences, 
Oct.  1867. 

Prof.  Dalton's  work  has  such  a  well-established 
reputation  that  it  does  not  stand  in  need  of  any  re- 
commendation. Ever  since  its  first  appearance  it  has 
become  the  highest  authority  in  the  English  language ; 
and  that  it  is  able  to  maintain  the  enviable  position 
which  it  has  taken,  the  rapid  exhaustion  of  the  dif- 
ferent successive  editions  is  sufficient  evidence.  The 
present  edition,  which  is  the  fourth,  has  been  tho- 
roughly revised,  and  enlarged  by  the  incoi'poratioa 
of  all  the  many  important  advances  which  have 
lately  been  made  in  this  rapidly  progressing  science. 
—N.  Y.  Med.  Record,  Oct.  15,  1867. 

As  it  stands,  we  esteem  it  the  very  best  of  the  phy- 
siological text-books  for  the  student,  and  the  most 
concise  reference  and  guide-book  for  the  practitioner. 
—N.  Y.  Med.  Journal,  Oct.  1867. 

The  present  edition  of  this  now  standard  work  fully 
sustains  the  high  reputation  of  its  accomplished  au- 
thor. It  is  not  merely  a  reprint,  but  has  been  faith- 
fully revised,  and  enriched  by  such  additions  as  the 
progress  of  physiology  has  rendered  desirable.  Taken 
as  a  whole,  it  is  unquestionably  the  most  reliable  and 
useful  treatise  on  the  subject  that  has  been  issued 
from  the  American  press.— CViica^ro  Med.  Journal, 
Sept.  1867. 


-nUNGLISON  [ROBLEY],  M.D., 

J-^  Professor  of  Institvies  of  Medicine  in  Jefferson  Medical  College,  Philadelphia. 

HUMAN  PHYSIOLOGY.     Eighth  edition.     Thoroughly  revised  and 

extensively  modified  and  enlarged,  with  five  hundred  and  thirty-two  illustrations.     In  two 
large  and  handsomely  printed  octavo  volumes  of  about  1500  pages,  extra  cloth.     $7  00. 


TEHMANN  {G.  G.) 

PHYSIOLOGICAL  CHEMISTRY.  Translated  from  the  second  edi- 
tion by  George  E.  Day,  M.  D.,  P.  R.  S.,  Ac,  edited  by  R.  E.  Rogers,  M.  D.,  Professor  of 
Chemistry  in  the  Medical  Department  of  the  University  of  Pennsylvania,  with  illustrations 
selected  from  Funke's  Atlas  of  Physiological  Chemistry,  and  an  Appendix  of  plates.  Com- 
plete in  two  large  and  handsome  octavo  volumes,  containing  1200  pages,  with  nearly  two 
hundred  illustrations,  extra  cloth.     $6  00. 


'  THE  SAME  AUTHOR. 

MANUAL  OF  CHEMICAL  PHYSIOLOGY.     Translated  from  the 

German,  with  Notes  and  Additions,  by  J.  Chbston  Morris,  M.  D.,  with  an  Introductory 
Essay  on  Vital  Force,  by  Professor  Samuel  Jackson,  M.  D.,  of  the  University  of  Pennsyl- 
vania. With  illustrations  on  wood.  In  one  very  handsome  octavo  volume  of  336  pages 
extra  cloth.     $2  25. 


10 


Henry  C.  Lea's  Publications — {Chemistry). 


DRANDE  (  WM.  T.),  D.  C.L,,  and   J^AYLOR  [ALFRED  S.),  M.D.,  F.R.S. 
CHEMISTKY.     Second  American  edition,  thorongbly  revised  l\y  Dr. 

Taylok.     In  one  handsome  8vo.  volume  of  764  pages,  extra  cloth,  $5  00  ;  leather,  $6  00. 
{Now  Ready.) 

From  Dr.  Taylor's  Preface. 

"The  revision  of  the  second  edition,  in  consequence  of  the  death  of  ray  lamented  colleague, 
has  devolved  entirely  upon  myself.  Every  chapter,  and  indeed  every  page,  has  been  revised, 
and  numereus  additions  made  in  all  parts  of  the  volume.  These  additions  have  been  restricted 
chiefly  to  subjects  having  some  practical  interest,  and  they  have  been  made  as  concise  as  possible, 
in  order  to  keep  the  book  within  those  limits  which  may  retain  for  it  the  character  of  a  Student's 
Manual  " — London,  June  29,  1867. 


A  book  that  has  already  so  established  a  reputa- 
tion, as  has  Brande  and  Taylor's  Chemistry,  can 
hardly  need  a  notice,  save  to  raentiou  the  additions 
and  improvements  of  the  edition.  Doubtless  the 
work  will  long  remain  a  favorite  text-book  iai  the 
school.-',  as  well  as  a  convenient  book  of  reference  for 
all.— iV.  r.  Medical  Gazette,  Oct.  12,  1S67. 

For  this  reason  we  hail  with  delight  the  republica- 
tion, in  a  form  which  will  meet  with  general  approval 
and  command  public  attention,  of  this  really  valua- 
ble standard  work  on  chemistry — more  particularly 
as  it  has  been  adapted  with  such  care  to  the  wants  of 
the  general  puhlic.  The  %vell  known  scholarship  of 
its  authors,  and  their  extensive  researches  for  many 
years  in  experimental  chemistry,  have  been  long  ap- 
preciated in  the  scientific  world,  but  in  this  work  they 
have  been  careful  to  give  the  largest  possible  amount 
of  information  with  the  most  sparing  use  of  technical 
terms  and  phraseology,  so  as  to  furnish  the  reader, 
"whether  a  student  of  medicine,  or  a  man  of  the 
world,  with  a  plain  introduction  to  the  science  and 
practice  of  chemistry." — Journal  of  Applied  Chem- 
istry, Oct.  1867. 


I      This  second  American  edition  of  an  excellent  trea- 
tise on  chemical  science  is  not  a  mere  republication 
from  the  English    press,  hut  is   a  revision  and   en- 
I  largement  of  the  original,  under  the  supervision  of 
'  the   surviving   author.   Dr.   Taylor.      The   favorahle 
opinion  expressed  on  the  puhlication  of  the  former 
\  edition  of  this  work  is  fully  sustained  by  the  present 
:  revision,  in  which  Dr.  T.  has  increased  the  size  of 
the  volume,  by  an  addition  of  sixty -eight  pages. — Am. 
JOurn.  Ated.  Sciences,  Oct.  IStJT. 

'  The  H.tNUBOOK  in  Chemistry  of  the  Student. — 
For  clearness  of  language,  accuracy  of  description, 
extent  of  information,  and  freedom  from  pedantry 
and  mysticism,  no  other  text-book  comes  into  com- 
petition with  it. — Tlie  Lancet. 
I  The  authors  set  out  with  the  definite  purpose  of 
'  writing  a  book  which  shall  be  intelligible  to  any 
educated  man  Thus  conceived,  and  worked  out  in 
the  most  sturdy,  common-sense  method,  this  book 
gives  in  the  clearest  and  most  summary  method 
possible  all  the  facts  and  doctrines  of  chemistry. — 
Medical  Times. 


nOWMAN  [JOHN  E.),M.  D. 


PRACTICAL  HANDBOOK  OF  MEDICAL  CHEMISTRY.     Edited 

by  C.  L.  Bloxam,  Professor  of  Practical  Chemistry  in  King's  College.  London.  Fourth 
American,  from  the  fourth  and  revised  English  Edition.  In  one  neat  volume,  royal  12mo., 
pp.  351,  with  numerous  illustrations,  extra  cloth.     $2  25. 


The  fourth  edition  of  this  invaluable  text-book  of 
Medical  Chemistry  was  published  in  England  in  Ocio- 
ber  of  the  last  year.  The  Editor  has  brought  down 
the  Handbook  to  that  date,  introducing,  as  far  as  was 
compatible  with  the  necessary  coDcisene.ss  of  such  a 
work,  all  the  valuable  discoveries  in   the   science 


which  have  come  to  light  since  the  previous  edition 
was  printed.  The  work  is  indispensable  to  every 
student  of  medicine  or  enlightened  practitioner.  It 
is  printed  in  clear  type,  and  the  illustrations  are 
numerous  and  intelligible. — Bo-iton  Med.  and  Surg. 
Journal. 


DY  THE  SAME  A  UTHOR.  

INTRODUCTION   TO   PRACTICAL  CHEMISTRY,  INCLUDING 

ANALYSIS.     Fourth  American,  from  the  fifth  and  revised  London  edition.     With  numer- 
ous illustrations.     In  one  neat  vol.,  royal  12mo.,  extra  cloth.     $2  25.     {Just  Issued.) 


One  of  the  most  complete  manuals  that  has  for  a 
long  time  been  given  to  the  medical  student. — 
Atlienceurn. 

We  regard  it  as  realizing  almost  everything  to  be 
desired  in  an  introduction  to  Practical  Chemistry. 


It  is  by  far  the  best  adapted  for  the  Chemical  student 
of  any  that  has  yet  fallen  in  our  way. — British  and 
Foreign  Medico-Ghirurgical  Review. 

The  best  introductory  work  on  the  subject  with 
which  we  are  acquainted. — Edinburgh  Monthly  Jour. 


QRAEAM  [THOMAS],  F.R.S. 


THE   ELEMENTS   OF   INORGANIC   CHEMISTRY,  including  the 

Applications  of  the  Science  in  the  Arts.  New  and  much  enlarged  edition,  by  Henry 
Watts  and  Robert  Bridges,  M.  D.  Complete  in  one  large  and  handsome  octavo  volume, 
of  over  800  very  large  pages,  with  two  hundred  and  thirty-two  wood-cuts,  extra  cloth. 

$5  60. 

Part  II.,  completing  the  work  from  p.  431  to  end,  with  Index,  Title  Matter,  &c.,  may  be  had 
separate,  cloth  backs  and  paper  sides.     Price  $3  00. 


From  Prof.  E.  N.  Horsford,  Harvard  College. 

It  has,  in  its  earlier  and  less  perfect  editions,  been 
familiar  to  me,  and  the  excellence  of  its  plan  and 
the  clearness  and  completeness  of  its  discussions. 
have  long  been  my  admiration. 

No  reader  of  English  works  on  this  science  can 


afford  to  be  without  this  edition  of  Prof.  Graham's 
Elements. — Silliman^s  Journal,  March,  185S. 

From.  Prof.  Wolcott  Gibbs,  N.  Y.  Free  Academy. 

The  work  is  an  admirable  one  in  all  respects,  ana 
its  republication  here  cannot  fail  to  exert  a  positive 
influence  upon  the  progress  of  science  in  this  country. 


Henry  C.  Lea's  Publications — (ChemiHfn/^  Pharmacy^ &c.).       11 


rpOWNES  {GEORGE),  Ph.  D. 
A  MANUAL  OF  ELEMENTARY  CHEMISTRY;   Theoretical  and 

Practical.    With  one  hundred  and  ninety-seven  illuptrations.    Edited  by  Robert  Bridges, 
M.  D.     In  one  large  royal  12mo.  volume,  of  600  pages,  extra  cloth,  $2  00;  leather,  $=2  60. 


We  know  of  no  treatise  in  the  language  so  well 
calculated  to  aid  the  student  in  becoming  familiar 
with  the  numerous  facts  in  the  intrinsic  science  on 
which  it  treats,  or  one  better  calculated  as  a  text- 
book for  those  attending  Chemical  lectures.  *  *  *  * 
The  best  text-book  on  Chemistry  (hat  has  issued  from 
our  press. — American  Medical  Journal. 

We  again  most  cheerfully  recommend  it  as  the 
best  text-book  for  students  in  attendance  upon  Chem- 
ical lectures  that  we  have  yet  examined. — III.  and 
Ind.  Med.  and  Surg.  Journal. 

A  fii"st-rate  work  upon  a  first-rate  subject. — St. 
Louis  Med.  and  Surg.  Journal. 

No  manual  of  Chemistry  which  we  have  met 
comes  so  near  meeting  the  wants  of  the  beginner. — 
Western  Journal  of  Medicine  and  Surgery. 


We  know  of  none  within  the  same  limits  which 
has  higher  claims  to  our  confidence  as  a  college  class- 
book,  both  for  accuracy  of  detail  and  scientific  ar- 
rangement.— Augusta  Medical  Journal. 

We  know  of  no  text-book  on  chemistry  that  we 
would  sooner  recommend  to  the  student  than  this 
edition  of  Prof.  Fownea'  work. — Montreal  Medical 
Chronicle. 

A  new  and  revised  edition  of  one  of  the  best  elemen- 
tary works  on  chemistry  accessible  to  the  Araericaa 
and  English  student. — N.  Y.  Journal  of  Medical  and 
Collateral  Science. 

We  unhesitatingly  recommend  it  to  medical  stu- 
dents.— N.  W.  Med.  and  Surg.  Journal. 

This  is  a  most  excellent  text-book  for  class  instruc- 
tion in  chemistry,  whether  for  schools  or  colleges. — 
Silliman's  Journal. 


ABEL  AND  BLOXAM'S  HANDBOOK  OF  CHEMIS- 
TRY, Theoretical,  Practical,  and  Technical.  In  one 
vol.  Sro.  of  662  pages,  extra  cloth,  $1  50. 

GARDNER^S  MEDICAL  CHEMISTRY.  1  vol.  12mo., 
with  wood-cuts  ;  pp.  396,  extra  cloth,    $1  00. 


KNAPP'S  TECHNOLOGY  ;  or  Chemistry  Applied  to 
the  Arts,  and  to  Manufactures.  With  American 
additions,  by  Prof.  Walter  R.  Johnson.  In  two 
very  handsome  octavo  volumes,  with  500  wood 
engravings,  extra  cloth,  $6  00. 


JpARRISH  [ED  WARD\ 

Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Pharmacy. 

A  TREATISE  ON  PHARMACY.     Designed  as  a  Text-Book  for  the 

Student,  and  as  a  Guide  for  the  Physician  and  Pharmaceutist.     With  many  Formulae  and 
Prescriptions.     Third  Edition,  greatly  improved.     In  one  handsome  octavo  volume,  of  850 
pages,  with  several  hundred  illustrations,  extra  cloth.     $5  00. 
The  immense  amount  of  practical  information  condensed  in  this  volume  may  be  estimated  from 
the  fact  that  the  Index  contains  about  4700  items.      Under  the  head  of  Acids  there  are  312  refer- 
ences ;  under  Emplastrum,  36 ;  Extracts,  169 ;  Lozenges,  25  j  Mixtures,  55  ;  Pills,  56 ;  Syrups, 
131 J  Tinctures,  138 ;  Unguentum,  57,  &c. 


We  have  examined  this  large  volume  with  a  good 
deal  of  care,  and  find  that  the  author  has  completely 
exhausted  the  subject  upon  which  he  treats  ;  a  more 
complete  work,  we  think,  it  would  be  impo.ssible  to 
find.  To  the  student  of  pharmacy  the  work  is  indis- 
pensable ;  indeed,  so  far  as  we  know,  it  is  the  only  one 
of  its  kind  in  existence,  and  even  to  the  physician  or 
medical  student  who  can  spare  five  dollars  to  pur- 
chase it,  we  feel  sure  the  practical  information  he 
will  obtain  will  more  than  compensate  him  for  the 
outlay. — Canada  Med.  Journal,  Nov.  1864. 

The  medical  student  and  the  practising  physician 
will  find  the  volume  of  inestimable  worth  for  study 
and  reference. — San  Francisco  Med.  Press,  July, 
1864. 

When  we  say  that  this  book  is  in  some  respects 
the  best  which  has  been  published  on  the  subject  in 
the  English  language  for  a  great  many  years,  we  do 
not  wish  it  to  be  understood  as  very  extravagant 
praise.  In  truth,  it  is  not  so  much  the  best  as  the 
only  book. — The  London  Chemical  News. 

An  attempt  to  furnish  anything  like  an  analysis  of 
Parrish's  very  valuable  and  elaborate  Treatise  on 
Practical  Pharmacy  would  require  more  space  than 
we  have  at  our  disposal.  Thi.s,  however,  is  not  so 
much  a  matter  of  regret,  inasmuch  as  it  would  be 
ditflcult  to  think  of  any  point,  however  minute  and 
apparently  trivial,  connected  with  the  manipulation 
of  pharmaceutic  substances  or  appliances  which  has 


not  been  clearly  and  carefully  discussed  in  this  vol- 
ume. Want  of  space  prevents  our  enlarging  further 
on  this  valuable  work,  and  we  must  conclude  by  a 
simple  expression  of  our  hearty  appreciation  of  its 
merits. — Dvhliri,  Quarterly  Jour,  of  Medical  Science, 
August,  1864. 

We  have  in  this  able  and  elaborate  work  a  fair  ex- 
position of  pharmaceutical  science  as  it  exists  in  the 
United  States  ;  and  it  shows  that  our  transatlantus 
friends  have  given  the  subject  most  elaborate  con- 
sideration, and  have  brought  their  art  to  a  degree  of 
perfection  which,  we  believe,  is  scarcely  to  be  sur- 
passed anywhere.  The  book  is,  of  course,  of  more 
direct  value  to  the  medicine  maker  than  to  the  physi- 
cian ;  yet  Mr.  Parrtsh  has  not  failed  to  introduce 
matter  in  which  the  prescriber  is  quite  as  much 
interested  as  the  compounder  of  remedies.  In  con- 
clusion, we  can  onlyexpress  our  high  opinion  of  the 
value  of  this  work  as  a  guide  to  the  pharmaceutist, 
and  in  many  respects  to  the  phy.sician,  not  only  in 
America,  but  in  other  parts  of  the  world. — British 
Med.  Journal,  Nov.  12th,  1864. 

The  former  editions  have  been  sufllciently  long 
before  the  medical  public  to  render  the  merits  of  the 
work  well  known.  It  is  certainly  one  of  the  most 
complete  and  valuable  works  on  practical  pharmacy 
to  which  the  student,  the  practitioner,  or  the  apothe- 
cary can  have  diCCQ^s.— Chicago  Medical  Examiner, 
March,  1864.  y 


J^VNGLISON  {ROBLEY),  M.D., 

Professor  of  Institide^  of  Medicine  in  Jefferson  Medical  College,  Philadelphia. 

GENERAL  THERAPEUTICS  AND  MATERIA  MEDICA;  adapted 

for  a  Medical  Text-Book.     With  Indexes  of  Remedies  and  of  Diseases  and  their  Remedies. 
Sixth  edition,  revised  and  improved.    With  one  hundred  and  ninety-three  illustrations.    In 
two  large  and  handsomely  printed  octavo  vols,  of  about  1100  pages,  extra  cloth.     $6  50. 
■DY  THE  SAME  AUTHOR.  

NEW  REMEDIES,  WITH  FORMULAE  FOR  THEIR  PREPARA- 
TION AND  ADMINISTRATION.  Seventh  edition,  with  extensive  additions.  In  one 
very  large  octavo  volume  of  770  pages,  extra  cloth.     $4  00. 


12       Henry  C.  Lea's  Publications — {Mat.  Med.  and  Therapeutics). 


O 


RIFFITH  [ROBERT  E.),  M.D. 

A  UNIVERSAL  FORMULARY,   Containing  the  Methods  of  Pre- 

paring  and  Administering  Officinal  and  other  Medicines.  The  whole  adapted  to  Physicians 
and  Pharmaceutists.  Second  edition,  thoroughly  revised,  with  numerous  additions,  by 
Robert  P.  Thomas,  M.D.,  Professor  of  Materia  Medica  in  the  Philadelphia  College  of 
Pharmacy.  In  one  large  and  handsome  octavo  volume  of  650  pages,  double-columns. 
Extra  cloth,  $4  00 ;  leather,  $5  00. 

In  this  volume,  the  Formulary  proper  occupies  over  400  double-column  pages,  and  contains 
about  5000  formulas,  among  which,  besides  those  strictly  medical,  will  be  found  numerous  valuable 
receipts  for  the  preparation  of  essences,  perfumes,  inks,  soaps,  varnishes,  <fec.  &c.  In  addition  to 
this,  the  work  contains  a  vast  amount  of  information  indispensable  for  daily  reference  by  the  prac- 
tising physician  and  apothecary,  embracing  Tables  of  Weights  and  Measures,  Specific  Gi'avity, 
Temperature  for  Pharmaceutical  Operations,  Hydrometrical  Equivalents,  Specific  Gravities  of  some 
of  the  Preparations  of  the  Pharmacopoeias,  Relation  between  different  Thermometrical  Scales, 
Explanation  of  Abbreviations  used  in  Formula3,  Vocabulary  of  Words  used  in  Prescriptions,  Ob- 
servations on  the  Management  of  the  Sick  Room,  Doses  of  Medicines,  Rules  for  the  Administration 
of  Medicines,  Management  of  Convalescence  and  Relapses,  Dietetic  Preparations  not  included  in 
the  Formulary,  List  of  Incompatibles,  Posological  Table,  Table  of  Pharmaceutical  Names  which 
diflFer  in  the  Pharmacopoeias,  Officinal  Preparations  and  Directions,  and  Poisons. 

Three  complete  and  extended  Indexes  render  the  work  especially  adapted  for  immediate  consul- 
tation. One,  of  Diseases  and  their  Remedies,  presents  under  the  head  of  each  disease  the 
remedial  agents  which  have  been  usefully  exhibited  in  it,  with  reference  to  the  formulae  containing 
them — while  another  of  Pharmaceutical  and  Botanical  Names,  and  a  very  thorough  General 
Index  aflFord  the  means  of  obtaining  at  once  any  information  desired.  The  Formulary  itself  is 
arranged  alphabetically,  under  the  heads  of  the  leading  constituents  of  the  prescriptions. 


This  is  one  of  the  most  useful  books  for  the  prac- 
tising physician  which  has  been  issued  from  the  press 
of  late  yeai's,  containing  a  vast  variety  of  formulas 
for  the  safe  and  convenient  administration  of  medi- 
cines, all  arranged  upon  scientific  and  rational  prin- 
ciples, with  the  quantities  stated  in  full,  without 
signs  or  abbreviations. — Memphis  Med.  Recorder. 


We  know  of  none  in  our  language,  or  any  other,  so 
comprehensive  in  its  details. — London  Lancet. 

One  of  the  most  complete  works  of  the  kind  in  any 
language. — Edinburgh  Med.  Journal. 

We  are  not  cognizant  of  the  existence  of  a  parallel 
work. — London  Med.  Gazette. 


OTILLE  (ALFRED),  31.  D., 

A^  Professor  of  Theory  and  Practice  of  Medicine  in  the  University  of  Penna. 

THERAPEUTICS  AND  MATERIA  MEDICA;  a  Systematic  Treatise 

on  the  Action  and  Uses  of  Medicinal  Agents,  including  their  Description  and  History. 

Third  edition,  revised  and  enlarged.   In  two  large  and  handsome  octavo  volumes.     {Nearly 

Ready.) 
Owing  to  the  author's  engagements,  this  work  has  been  for  some  time  out  of  print.  It  is  now, 
however,  passing  rapidly  through  the  press,  and  its  publication  may  be  expected  at  an  early 
moment.  That  two  large  editions  of  a  work  of  such  magnitude  should  be  exhausted  in  a  few 
years,  is  sufficient  evidence  that  it  has  supplied  a  want  generally  felt  by  the  profession,  and  the 
unanimous  commendation  bestowed  upon  it  by  the  medical  press,  abroad  as  well  as  at  home, 
shows  that  the  author  has  successfully  accomplished  his  object  in  presenting  to  the  profession  a 
systematic  treatise  suited  to  the  wants  of  the  practising  physician,  and  unincumbered  with  de- 
tails interesting  only  to  the  naturalist  or  the  dealer. 

We  have  placed  first  on  the  list  Dr.  Stille's  great  j  than  formerly.  Wecancordiallyrecommendtotho.se 
work  on  Therapeutics.  When  the  first  edition  of  this  i  of  our  readers  who  are  interested  in  Therapeutics  a 
woi-k  made  its  appearance  nearly  five  years  ago,  we  |  careful  perusal  of  Dr.  Still6'swork. — Edinburgh  Med. 
expressed  our  high  sense  of  its  value  as  containing  a  I  Journal,  1865. 

full  and  philosophical  account  of  the  existing  state  [  An  admirable  digest  of  our  present  knowledge  of 
of  Therapeutics.  From  the  opinion  expressed  at  that  ,  Materia  Medica  and  Therapeutics. — Am.  Journ.  Med. 
time  we  have  nothing  to  retract;  we  have,  on  the    Sciences.  July,  1860. 

contrary,  to  state  that  the  introduction  of  numerous  I  Dr.  Stillfe's  splendid  work  on  therapeutics  and  ma- 
additions  has  rendered  the  work  even  more  complete  I  teria  medica. — London  Med.  ^imes,  April  8,  1865. 


J^LLIS  [BENJAMIN),  M.D. 

THE  MEDICAL  FORMULARY:  being  a  Collection  of  Prescriptions 

derived  from  the  writings  and  practice  of  many  of  the  most  eminent  physicians  of  America 
and  Europe.  Together  with  the  usual  Dietetic  Preparations  and  Antidotes  for  Poisons.  To 
which  is  added  an  Appendix,  on  the  Endermic  use  of  Medicines,  and  on  the  use  of  Ether 
and  Chloroform.  The  whole  accompanied  with  a  few  brief  Pharmaceutic  and  Medical  Ob- 
servations. Eleventh  edition,  carefully  revised  and  much  extended  by  Robert  P.  Thomas, 
M.  D.,  Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Pharmacy.  In  one 
volume  8vo.,  of  about  350  pages.     $3  00. 

frequently  noticed  in  this  Journal  as  the  successive 
editions  appeared,  that  it  is  sufficient,  on  the  present 
occasion,  to  state  that  the  editor  has  introduced  into 
the  eleventh  edition  a  large  amount  of  new  matter, 
derived  from  the  current  medical  and  pharmaceutical 
works,  as  well  as  a  number  of  valuable  prescriptions 
furnished  from  private  sources.  A  very  comprehen- 
sive and  extremely  useful  index  has  also  been  sup- 
plied, which  facilitates  reference  to  the  particular 
arti^e  the  prescriber  may  wish  to  administer;  and 
the  language  of  the  Formulary  has  been  made  to  cor- 
respond with  the  nomenclature  of  the  new  national 
Pharmacopoeia. — Am.  Jour.  Med.  Sciences,  Jan.  186-L 


We  endorse  the  favorable  opinion  which  the  book 
has  so  long  established  for  itself,  and  take  this  occa- 
sion to  commend  it  to  our  readers  as  one  of  the  con- 
venient handbooks  of  the  oflBce  and  library. — Cin- 
cinnati Lancet,  Feb.  1864. 

The  work  has  long  been  before  the  profession,  and 
its  merits  are  well  known.  The  present  edition  con- 
tains many  valuable  additions,  and  will  be  found  to 
be  an  exceedingly  convenient  and  useful  volume  for 
reference  by  the  medical  practitioner.  —  Chicago 
Medical  Examiner,  March,  1864. 

The  work  is  now  so  well  known,  and  has  been  so 


Henry  C.  Lea's  Publications — (3Iat.  3Ied.  and  Therajwutics),      13 


pEREIRA  [JONATHAN),  M.D.,  F.R.S.  and  L.S. 

MATERIA   MEDICA   AND  THERAPEUTICS;   being  an  Abridg- 

ment  of  the  late  Dr.  Pereira's  Elements  of  Materia  Medica,  arranged  in  conformity  with 
the  British  Pharmacopoeia,  and  adapted  to  the  use  of  Medical  Practitioners,  Chemists  and 
Druggists,  Medical  and  Pharmaceutical  Students,  &c.  By  F.  J.  Faure,  M.D.,  Senior 
Physician  to  St.  Bartholomew's  Hospital,  and  London  Editor  of  the  British  Pharmacopoeia; 
assisted  by  Robert  Bentlev,  M.R.C.S.,  Professor  of  Materia  Medica  and  Botany  to  the 
Pharmaceutical  Society  of  Great  Britain;  and  by  Robert  Warington,  F.R.S.,  Chemical 
Operator  to  the  Society  of  Apothecaries.  With  numerous  additions  and  references  to  the 
United  States  Pharmacopoeia,  by  Horatio  C.  Wood,  M.D.,  Professor  of  Botany  in  the 
University  of  Pennsylvania.  In  one  large  and  handsome  octavo  volume  of  1040  closely 
printed  pages,  with  236  illustrations,  extra  cloth,  $7  00;  leather,  raised  bands,  $8  00. 
\Ji(st  Issued.) 

pceia,  none  will  be  more  acceptable  to  the  student 
and  practitioner  than  the  present.  Pereira's  Materia 
Medica  had  long  ago  asserted  for  itself  the  position  of 
being  the  most  complete  worlc  on  the  subject  in  the 
English  language.  But  its  very  completeness  stood 
in  the  way  of  its  success.  Except  in  the  way  of  refer- 
ence, or  to  those  who  made  a  special  study  of  Materia 
Medica,  Dr.  Pereira's  worli  was  too  full,  and  its  pe- 
rusal required  an  amount  of  time  which  few  had  at 


The  task  of  the  American  editor  has  evidently  been 
no  sinecure,  for  not  only  has  he  given  to  us  all  that 
is  contained  in  the  abridgment  useful  for  our  pur- 
poses, but  by  a  careful  and  judicious  embodiment  of 
over  a  hundred  new  remedies  has  increased  the  size 
of  the  former  work  fully  one-third,  besides  adding 
many  new  illustrations,  some  of  which  are  original. 
We  unhesitatingly  say  that  by  so  doing  he  has  pro- 
portionately increased  the  value,  not  only  of  the  con- 
densed edition,  but  has  extended  the  applicability  of  I  their  disposal.  Dr.  Farre  has  very  judiciously  availed 


the  great  original,  and  has  placed  his  medical  coun- 
trymen under  lasting  obligations  to  him.  The  Ame- 
rican physician  now  has  all  that  is  needed  in  the 
shape  of  a  complete  treatise  on  materia  medica,  and 
the  medical  student  has  a  text-book  which,  for  prac- 
tical utility  and  intrinsic  worth,  stands  unparalleled. 
Although  of  considerable  size,  it  is  none  too  large  for 
the  purposes  for  which  it  has  been  intended,  and  every 
medical  man  should,  in  justice  to  himself,  spare  a 
place  for  it  upon  his  book-shelf,  resting  assured  that 
the  more  he  consults  it  the  better  he  will  be  satisfied 
of  its  excellence.— iV.  Y.  Med.  Record,  Nov.  15,  1866. 

It  will  fill  a  place  which  no  other  work  can  occupy 
in  the  library  of  the  physician,  student,  and  apothe- 
cary.— Boston  Med.  and  Surg.  Journal,  Nov.  8,  1866. 

We  have  here  presented,  in  a  volume  of  a  thousand 
pages,  that  which  we  sincerely  believe  the  best  work 
on  materia  medica  in  the  English  language.  No  phy- 
sician, no  medical  student,  can  purchase  this  book, 
and  make  anything  like  a  proper  use  of  it,  without 
being  amply  rewarded  for  his  outlay. — The  Cincin- 
nati Journal  of  Medicine,  November,  1866. 

The  American  editor  can  very  justly  say,  then,  that 
•'his  ofiice  has  been  no  sinecure."  The  result,  how- 
ever, of  the  labors  of  the  different  gentlemen  engaged 
on  the  work  has  been  to  give  us  a  compendium  that 


himself  of  the  opportunity  of  the  publication  of  the 
new  Pharmacopoeia,  by  bringing  out  an  abridged  edi- 
tion of  the  great  work.  This  edition  of  Pereira  is  by 
no  means  a  mere  abridged  re-issue,  but  contains  ma- 
ny improvements,  both  in  the  descriptive  and  thera- 
peutical departments.  We  can  recommend  it  as  a 
very  excellent  and  reliable  text-book. — Edinburgh 
Med  Journal,  February,  1866. 

The  reader  cannot  fail  to  be  impressed,  at  a  glance, 
with  the  exceeding  value  of  this  work  as  a  compend 
of  nearly  all  useful  knowledge  on  the  materia  medica. 
We  are  greatly  indebted  to  Professor  Wood  for  his 
adaptation  of  it  to  our  meridian.  Without  his  emen- 
dations and  additions  it  would  lose  much  of  its  value 
to  the  American  student.  With  them  it  is  an  Ameri- 
can \)no^.  — Pacific  Medical  and  Surgical  Journal, 
December,  1866. 

Altogether,  the  work  is  a  most  valuable  addition  to 
the  literature  of  this  subject,  and  will  be  of  great  use 
to  the  practitioner  of  medicine  and  medical  student. 
The  work,  as  issued  by  the  American  publisher,  is  a 
handsome  volume  of  10.30  pages,  most  amply  illus- 
trated, the  wood-cuts  being  of  superior  finish,  and 
clearly  impressed. — Ca,nada.  Med.  Journal,  Nov.  1866. 

Only  .592  pages,  while  Pereira's  original  volumes 
included  2000,  and  yet  the  results  of  many  years'  ad- 


is  admirably  adapted  for  the  wants  and  nece-ssities-of  ,  ditional  research  in  pharmacology  and  therapeutics 
the  student.     We  willingly  concede  to  the  American  |  ^re  embodied  in  the  new  edition.     Unquestionably 


editor  that  we  have  rarely  examined  a  work  that, 
the  whole,  is  more  carefully  and  laboriously  edited 
than  this ;  or,  we  may  add,  that  is  more  improved  in 
the  process  of  editing. — New  York  Medical  Journal, 
December,  1866. 

Of  the  many  works  on  Materia  Medica  which  have 
appeared  since  the  issuing  of  the  British  Pharmaco- 


Dr.  Farre  has  conferred  a  great  benefit  upon  medical 
students  and  practitioners.  And  in  both  respects  we 
think  he  has  acted  very  judiciously.  And  the  work 
is  now  condensed — brought  fully  into  accordance  with 
the  pharmacological  opinions  in  vogue,  and  can  be 
used  with  great  advantage  as  a  handbook  for  exami- 
nations.— The  Lancet,  December,  1865. 


fl ARSON  [JOSEPH],  M.D., 

vy  Professor  of  Materia  Medica  and  Pharmacy  in  the  University  of  Pennsylvania,  &c. 

SYNOPSIS  OF  THE   COURSE   OF   LECTURES   ON  MATERIA 

MEDICA  AND  PHARMACY,  delivered  in  the  University  of  Pennsylvania.  With  three 
Lectures  on  the  Modus  Operandi  of  Medicines.  Fourth  and  revised  edition,  extra  cloth, 
$3  00.     {Now  Ready.) 


ROYLE'S  MATERIA  MEDICA  AND  THERAPEU- 
TICS; including  the  Preparations  of  the  Pharma- 
copoeias of  London,  Edinburgh,  Dublin,  and  of  the 
United  States.  With  many  new  medicines.  Edited 
by  Joseph  Carson,  M.D.  With  ninety-eight  illus- 
trations. In  one  large  octavo  volume  of  about  700 
pages,  extra  cloth.     $3  00. 

CHRISTISON'S  DISPENSATORY;  or.  Commentary 
on  the  Pharmacopoeias  of  Great  Britain  and  the 
United  States;  comprising  the  Natural  History, 
Description,  Chemistry,  Pharmacy,  Actions,  Uses, 
and  Do.ses  of  the  Articles  of  the  Materia  Medica. 
Second  edition,  revised  and  improved,  with  a  Sup- 
plement containing  the  most  important  New  Reme- 
dies. With  copious  additions,  and  two  hundred 
and  thirteen  large  wood-engravings.  By  R.  Eoles- 
FELD  Grfffitit,  M.  1).  In  one  very  handsome  octavo 
▼olume  of  over  1000  pages,  extra  cloth,    i^i  00. 


CARPENTER'S  PRIZE  ESSAY  ON  THE  USE  OF 
Alcoholic  Liquors  in  Health  and  Disease.  New 
edition,  with  a  Preface  by  D.  F.  Condie,  M.D.,  and 
explanations  of  scientific  words.  In  one  neat  12mo. 
volume,  pp.  178,  extra  cloth.    60  cents. 

De  JONGH  ON  THE  THREE  KINDS  OF  COD-LIVER 
Oil,  with  their  Chemical  and  Therapeutic  Pro- 
perties.    1  vol.  12mo.,  cloth.    75  cents. 


MAYNE'S  DISPENSATORY  AND  THERAPEUTICAL 
Remkmbraxcer.  With  every  Practical  Formula 
contained  in  the  three  British  Pharmacopoeias. 
Edited,  with  the  addition  of  the  Formulae  of  the 
U.  S.  Pharmacopoeia,  by  R.  E.  Griffith,  M.  D.  la 
one  12mo.  volume,  300  pp.,  extra  cloth.    75  cents. 


14 


Henry  C.  Lea's  Publications — {Pathology). 


QROSS  [SAMUEL  D.),  M.  D., 

Professor  of  Stirgery  in  the.  Jefferson  Medical  College  of  Philadelphia. 

ELEMENTS    OF    PATHOLOGICAL   ANATOMY.     Third    edition, 

thoroughly  revised  and  greatly  improved.     In  one  large  and  very  handsome  octavo  volume 
of  nearly  800  pages,  with  about  three  hundred  and  fifty  beautiful  illustrations,  of  which  a 
large  number  are  from  original  drawings  ;   extra  cloth.     $4  00. 
The  very  beautiful  execution  of  this  valuable  work,  and  the  exceedingly  low  price  at  which  it 
is  offered,  should  command  for  it  a  place  in  the  library  of  every  practitioner. 

Charles- 


To  the  student  of  medicine  we  would  say  that  we 
know  of  no  work  which  we  can  more  heartily  com- 
mend than  Gross's  Pathological  Anatomy. — Southern 
Med.  and  Surg.  Journal. 

The  volume  commends  itself  to  the  medical  student ; 
it  will  repay  a  careful  perusal,  and  should  be  upon 


the  book-shelf  of  every  American  physician. 
ton  Med.  Journal. 

It  contains  much  new  matter,  and  brings  down  our 
knowledge  of  pathology  to  the  latest  period. — London 
Lancet. 


J 


ONES  [C.  HANDFIELD),  F.R.S.,  and  SIEVEKING  [ED,  H.),  M.D., 

Assistant  Physicians  and  Lecturers  in  St.  Mary's  Hospital. 

A  MANUAL  OF   PATHOLOGICAL  ANATOMY.     First  American 

edition,  revised.     With  three  hundred  and  ninety-seven  handsome  wood  engravings.     In 
one  large  and  beautifully  printed  octavo  volume  of  nearly  750  pages,  extra  cloth,  $3  50. 


Our  limited  space  alone  restrains  us  from  noticing 
more  at  length  the  various  subjects  treated  of  in 
this  interesting  work;  presenting,  as  it  does,  an  excel- 
lent summary  of  the  existing  state  of  knowledge  in 
relation  to  pathological  anatomy,  we  cannot  too 
strongly  urge  upon  the  student  the  necessity  of  a  tho- 
rough acquaintance  with  its  contents. — Medical  Ex- 
aminer. 

We  have  long  had  need  of  a  hand-book  oT  patholo- 
gical anatomy  which  should  thoroughly  reflect  the 
present  state  of  that  science.  In  the  troritise  before 
us  this  desideratum  is  supplied.  Within  the  limits  of 
a  moderate  octavo,  we  have  the  outlines  of  this  great 
department  of  medical  science  accurately  defined. 


and  the  most  recent  investigations  presented  in  suffi- 
cient detail  for  the  student  of  pathology.  "We  cannot 
at  this  time  undertake  a  formal  analysis  of  this  trea- 
tise, as  it  would  involve  a  separate  and  lengthy 
consideration  of  nearly  every  subject  discussed  ;  nor 
would  such  analysis  be  advantageous  to  the  medical 
reader.  The  work  is  of  such  a  character  that  every 
physician  ought  to  obtain  it,  both  for  reference  and 
study. — N.  Y.  Journal  of  Medicine. 

Its  importance  to  the  physician  cannot  be  too  highly 
estimated,  and  we  would  recommend  our  readers  to 
add  it  to  their  library  as  soon  as  they  conveniently 
can. — Montreal  Med.  Chronicle. 


T>OKITANSKY  [CARL),  M.D., 

Curator  of  the  Imperial  Pathological  Museum,  and  Professor  at  the  University  of  Vienna. 

A   MANUAL    OF   PATHOLOGICAL   ANATOMY.      Translated  by 


W.  E.  SwAiNE,  Edward  Sieyeking,  C.  H.  Moore,  and  G.  E.  Day. 
bound  in  two,  of  about  1200  pages,  extra  cloth.     $7  50. 


Four  volumes  octavo, 


GLUGE'S  ATLAS  OF  PATHOLOGICAL  HISTOLOGY. 
Translated,  with  Notes  and  Additions,  by  Joseph 
Leidy,  M.  D.  In  one  volume,  very  large  imperial 
quarto,  with  320  copper-plate  figures,  plain  and 
colored,  extra  cloth.    $i  00. 


SIMON'S  GENERAL  PATHOLOGY,  as  conducive  to 
the  E^'tablishnient  of  Rational  Principles  for  the 
Prevention  and  Cure  of  Disease.  In  one  octavo 
volume  of  212  pages,  extra  cloth.     $1  2.3. 


y^lLLIAMS  [CHARLES  J.  B.),  M.D., 

Professor  of  Clinical  Medicine  in  University  College,  London. 

PRINCIPLES  OF  MEDICINE.     An  Elementary  View  of  the  Causes, 

Nature,  Treatment,  Diagnosis,  and  Prognosis  of  Disease ;  with  brief  remarks  on  Hygienics, 
or  the  preservation  of  health.  A  new  American,  from  the  third  and  revised  London  edition. 
In  one  octavo  volume  of  about  500  pages,  extra  cloth.     $3  50. 


The  unequivocal  favor  with  which  this  work  has 
been  received  by  the  profession,  both  in  Europe  and 
America,  is  one  among  the  many  gratifying  evidences 
which  might  be  adduced  as  going  to  show  that  there 
is  a  steady  progress  taking  place  in  the  science  as  well 
as  in  the  art  of  medicine.— /S<.  Louts  Med.  and  Surg. 
Journal. 

No  work  has  ever  achieved  or  maintained  a  more 
deserved  reputation. —  Virginia  Med.  and  Surg. 
Journal. 

One  of  the  best  works  on  the  subject  of  which  it 
treats  in  our  language. 

It  has  already  commended  itself  to  the  high  regard 
of  the  profession  ;  and  we  may  well  say  that  we 
know  of  no  single  volume  that  will  afford  the  source 
of  so  thorough  a  drilling  in  the  principles  of  practice 
as  this.  Students  and  practitioners  should  make 
themselves  intimately  familiar  with  its  teachings — 
they  will  find  their  labor  and  study  most  amply 
repaid. — Cincinnati  Med.  Observer. 

There  is  no  work  in  medical  literature  which  can 
fill  the  place  of  this  one.  It  is  the  Primer  of  the 
young  practitioner,  the  Koran  of  the  scientific  one. — 
Stethoscope. 


A  text-book  to  which  no  other  in  our  language  is 
comparable. — Charleston  Med.  Journal. 

The  lengthened  analysis  we  have  given  of  Dr.  Wil- 
liams's Principles  of  Medicine  will,  we  trust,  clearly 
prove  to  our  readers  his  perfect  competency  for  the 
task  he  has  undertaken — that  of  imparting  to  the 
student,  as  well  as  to  the  more  experienced  practi- 
tioner, a  knowledge  of  those  general  principles  of 
pathology  on  which  alone  a  correct  practice  can  be 
founded.  The  absolute  necessity  of  such  a  work 
must  be  evident  to  all  who  pretend  to  more  than 
mere  empiricism.  We  must  conclude  by  again  ex- 
pressing our  high  sense  of  the  immense  benefit  which 
Dr.  Williams  has  conferred  on  medicine  by  the  pub- 
lication of  this  work.  We  are  certain  that  in  the 
present  state  of  our  knowledge  his  Principles  of  Medi- 
cine could  not  pos.sibly  be  surpassed.  While  wo 
regret  the  loss  which  many  of  the  rising  generation 
of  practitioners  have  sustained  by  his  resignation  o 
the  Chair  at  University  College,  it  is  comforting  to 
feel  that  his  writings  must  long  continue  to  exert  a 
powerful  influence  on  the  practice  of  that  profession 
for  the  improvement  of  which  he  has  so  assiduously 
and  successfully  labored,  and  in  which  he  holds  so 
distinguished  a  ^os.iiioD..— London  Jour,  of  Medicine 


Henry  C.  Lea's  Publications — {Practice  of  Medicine). 


15 


TILINT  [AUSTIN],  M.D., 

J~  Professor  of  the  Principles  and  Practice  of  Medicine  in  Bellevue  Med.  College,  N.  T. 

A   TREATISE    ON    THE    PRINCIPLES    AND    PRACTICE    OF 

MEDICINE  ;  designed  for  the  use  of  Students  and  Practitioners  of  Medicine.  Second 
edition,  revised  and  enlarged.  In  one  large  and  closely  printed  octavo  volume  of  nearly 
]000  pages;  handsome  extra  cloth,  $6  50;  or  strongly  bound  in  leather,  with  raised  bands, 
$7  60.    {J?ist  Issued.) 

From  the  Preface  to  the  Second  Edition. 
Four  months  after  the  publication  of  this  treatise,  the  author  was  notified  that  a  second  edition 
was  called  for.  The  speedy  exhaustion  of  the  first  edition,  unexpected  in  view  of  its  large  size, 
naturally  intensified  the  desire  to  make  the  work  still  more  acceptable  to  practitioners  and 
students  of  Medicine;  and,  notwithstanding  the  brief  period  allowed  for  a  revision,  additions 
have  been  made  which,  it  is  believed,  will  enhance  the  practical  utility  of  the  volume. 


We  are  happy  in  being  able  once  more  to  commend 
this  work  to  the  students  and  practitioners  of  medicine 
who  seek  for  accurate  information  conveyed  in  lan- 
guage at  once  clear,  precise,  and  expressive. — Amer. 
Journ.  Med.  Sciences,  April,  1867. 

Dr.  Flint,  who  has  been  known  in  this  country  for 
many  years,  both  as  an  author  and  teacher,  wlio  has 
discovered  truth,  and  pointed  it  out  clearly  and  dis- 
tinctly to  others,  investigated  the  symptoms  and  na- 
tural history  of  disease  and  recorded  its  language  and 
facts,  and  devoted  a  life  of  incessant  study  and 
thought  to  the  doubtful  or  obscure  in  his  profession, 
has  at  length,  in  his  ripe  scholarship,  given  this  work 
to  the  profession  as  a  crowning  gift.  If  we  have  spoken 
highly  of  its  value  to  the  profession  and  world  ;  if  we 
have  said,  all  considered,  it  is  the  very  best  work 
upon  medical  practice  in  any  language;  if  we  have 
spoken  of  its  excellences  in  detail,  and  given  points 
of  special  value,  we  have  yet  failed  to  express  in  any 
degree  our  present  estimate  of  its  value  as  a  guide  in 
the  practice  of  medicine.  It  does  notcontain  too  much 
or  too  little  ;  it  is  not  positive  where  doubt  should  be 
expressed,  or  hesitate  where  truth  is  known.  It  is 
philosophical  and  speculative  where  philosophy  and 
speculation  are  all  that  can  at  present  be  obtained, 
but  nothing  is  admitted  to  the  elevation  of  established 
truth,  wiiliout  the  most  thorough  investigation.  It 
is  truly  remarkable  with  what  even  hand  this  work 
has  been  written,  and  how  it  all  shows  the  most  care- 
ful thought  and  untiring  study.  "We  conclude  that, 
though  it  may  yet  be  susceptible  of  improvement,  it 
still  constitutes  the  very  best  which  human  knowledge 
can  at  present  produce.  "When  knowledge  is  in- 
creased," the  work  will  doubtless  be  again  revised; 
meanwhile  we  shall  accept  it  as  the  rule  of  practice. 
— Buffalo  Med.  and  Surg.  Journal,  Feb.  1867. 

He  may  justly  feel  proud  of  the  high  honor  con- 
ferred on  him  by  the  demand  for  a  second  edition  of 
his  work  in  four  months  after  the  issue  of  the  first. 
No  American  practitioner  can  afford  to  do  without 
Flint's  Practice. — Pacific  Med.  and  Surg.  Journal, 
Feb.  1867. 

Dr.  Flint's  book  is  the  only  one  on  the  practice  of 
medicine  that  can  benefit  the  young  practitioner. — 
Nashville  Med.  Journal,  Aug.  1866. 

We  consider  the  book,  in  all  its  essentials,  as  the 
best  adapted  to  the  student  of  any  of  our  numerous 
text-books  on  this  subject. — AM'  3ied.  Journ..  Jan.'Gl . 

Its  terse  conciseness  fully  redeems  it  from  being 


ranked  among  heavy  and  common-place  works,  while 
the  unmistakable  way  in  which  Dr.  Flint  gives  his 
own  views  is  quite  refreshing,  and  far  from  common. 
It  is  a  book  of  enormous  research  ;  the  writer  is  evi- 
dently a  man  of  observation  and  large  experience ; 
his  views  are  practically  sound  and  theoretically 
moderate,  and  we  have  no  hesitation  in  commending 
his  magnum  opus  to  our  readers  — Dublin  Medical. 
Press  and  Circtdar,  May  16,  1866. 

In  the  plan  of  the  work  and  the  treatment  of  indi- 
vidual subjects  there  is  a  freshness  and  an  originality 
which  make  it  worthy  of  the  study  of  practitioners 
as  well  as  students  It  is,  indeed,  an  admirable  book, 
and  highly  cre4itable  to  American  medicine.  For 
clearness  and  conciseness  in  style,  for  careful  reason- 
ing upon  what  is  known,  for  lucid  distinction  betweeu 
what  we  know  and  what  we  do  not  know,  between 
what  nature  does  in  disease  and  what  the  physician 
can  do  and  should,  for  richness  in  good  clinical  ob- 
servation, for  independence  of  statement  and  opinion 
on  great  points  of  practice,  and  for  general  sagacity 
and  good  judgment,  the  work  is  most  meritorious. 
It  is  singularly  rich  in  good  qualities,  and  free  from 
faults. — London  Lancet,  June  23,  1866. 

In  following  out  such  a  plan  Dr.  Flint  has  suc- 
ceeded most  admirably,  and  gives  to  his  readers  a 
work  that  is  not  only  very  readable,  interesting, 
and  concise,  but  in  every  respect  calculated  to  meet 
the  requirements  of  professional  men  of  every  class. 
The  student  has  presented  to  him,  in  the  plainest 
possible  manner,  the  symptoms  of  disease,  the  prin- 
ciples which  should  guide  him  in  its  treatment,  and 
the  difficulties  which  have  to  be  surmounted  in  order 
to  arrive  at  a  correct  diagnosis.  The  practitioner, 
besides  having  such  aids,  has  offered  to  him  the  con- 
clusion which  the  experience  of  the  professor  has 
enabled  him  to  arrive  at  in  reference  to  the  relative 
merits  of  different  therapeutical  agents,  and  different 
methods  of  treatment.  This  new  work  will  add  not 
a  little  to  the  well-earned  reputation  of  Prof.  Flint  as 
a  medical  teacher.— A^.  ¥.  Med.  Record,  April  2,  1866. 

We  take  pleasure  in  recommending  to  the  profession 
this  valuable  and  practical  Avork  on  the  practice  of 
medicine,  more  particularly  as  we  have  had  oppor- 
tunities of  appreciating  from  personal  observation 
the  author's  preeminent  merit  as  a  clinical  observer. 
This  work  is  undoubtedly  one  of  great  merit,  and  we 
feel  confident  that  it  will  have  an  extensive  circula- 
tion.— The  N.  0.  Med.  and  Surg.  Journal,  Sept.  1866. 


jnUNGLISON,  FORBES,  TWEEDIE,  AND  CONOLLY. 

THE  CYCLOPEDIA  OF   PRACTICAL  MEDICINE:    comprising 

Treatises  on  the  Nature  and  Treatment  of  Diseases,  Materia  Medica  and  Therapeutics, 
Disea.ses  of  Women  and  Children,  Medical  Jurisprudence,  &e.  <fec.  In  four  large  super-royal 
octavo  volumes,  o  13254  double-columned  pages,  strongly  and  handsomely  bound  in  leather, 
$15;  extra  cloth,  $11, 
*^*  This  work  contains  no  less  than  four  hundred  and  eighteen  distinct  treatises,  contributed 
by  sixty-eight  distinguished  physicians. 


The  most  complete  work  on  practical  medicine 
extant,  or  at  least  in  our  language, — Buffalo  Medical 
and  Surgical  Journal. 

For  reference,  it  is  above  all  price  to  every  practi- 
tioner.—  Western  Lancet. 

One  of  the  most  valuable  medical  publications  of 


the  day.     As  a  work  of  reference  it  is  invaluable. — 
Western  Journal  of  Medicine  and  Surgery. 

It  has  been  to  us,  both  as  learner  and  teacher,  a 
work  for  ready  and  frequent  reference,  one  in  which 
modern  English  medicine  is  exhibited  in  the  most  ad- 
vantageous light. — Medical  Examiner. 


BARLOW'S  MANUAL  OF  THE  PRACTICE  OF 
MEDICINE.  With  Additions  by  D.  F.  Condie, 
M.  D.     1  vol.  Svo.,  pp.  600,  cloth.     $2  50. 


HOLLAND'S  MEDICAL  NOTES  AND  REFLEC- 
TIONS. From  the  third  and  enlarged  English  edi- 
tion. In  one  handsome  octavo  volume  of  about 
500  pages,  extra  cloth.    $3  50. 


16 


Henry  C.  Lea's  Publications — {Practice  of  Medicine). 


TTARTSHORNE  [HENRY],  M.D., 

•^^  Profesfsor  of  Hygiene  in  the  University  of  Pennsylvania. 

ESSENTIALS  OP  THE  PRINCIPLES  AND  PRACTICE  OF  MEDI- 
CINE.    A  handy-book  for  Students  and  Practitioners.     In  one  handsome  royal  ]2mo. 
volume  of  about  350  pages,  clearly  printed  on  small  type,  cloth,  $2  38  j  half  bound,  $2  63. 
{Jtist  Issued.) 
The  very  cordial  reception  with  which  this  work  has  met  shows  that  the  author  has  fully  suc- 
ceeded in  his  attempt  to  condense  within  a  convenient  compass  the  essential  points  of  scientific 
and  practical  medicine,  so  as  to  meet  the  wants  not  only  of  the  student,  but  also  of  the  practi- 
tioner who  desires  to  acquaint  himself  with  the  results  of  recent  advances  in  medical  science. 

nearly  than  any  similar  manual  lately  before  us  the 
standard  at  which  all  such  books  should  aim  —  of 
teaching  much,  and  suggesting  more.    To  the  student 


As  a  strikingly  terse,  fiiU,  and  comprehensive  em- 
bodiment in  a  condensed  form  of  the  essentials  in 
medical  science  and  art,  we  hazard  nothing  in  saying 
that  it  is  incomparably  in  advance  of  any  work  of  the 
kind  of  the  past,  and  will  stand  long  in  the  future 
without  a  rival.  A  mere  glance  will,  we  think,  im- 
press others  with  the  correctness  of  our  estimate.  Nor 
do  we  believe  there  will  be  found  many  who,  after 
the  most  cursory  examination,  will  fail  to  possess  it. 
How  one  could  be  able  to  crowd  so  much  that  is  valu- 
able, especially  to  tbe  student  and  young  practitioner, 
within  the  limits  of  so  small  a  book,  and  yet  embrace 
aad  present  all  that  is  important  in  a  Avell-arrauged, 
clear  form,  convenient,  satisfactory  for  reference,  with 
so  full  a  table  of  contents,  and  extended  general  index, 
with  nearly  three  hundred  formulas  and  recipes,  is  a 
marvel. —  Western  Journal  of  Medicine,  Aug.  1867. 

The  little  book  before  us  has  this  quality,  and  we 
can  therefore  say  that  all  students  will  find  it  an  in- 
valuable guide  in  their  pursuit  of  clinical  medicine. 
Dr.  Hartshorne  speaksofitas  "an  unambitious  eflbrt 
to  make  useful  the  experience  of  twenty  years  of  pri- 
vate and  hospital  medical  practice,  with  its  attendant 
study  and  reflection."  That  the  effort  will  prove  suc- 
cessful we  have  no  doubt,  and  in  his  study,  and  at 
the  bedside,  the  student  will  find  Dr.  Hartshorne  a 
safe  and  accomplished  companion.  We  speak  thus 
highly  of  the  volume,  because  it  approaches  more 


can  heartily  recommend  the  work  of  our  transat- 
lantic colleague,  and  the  busy  practitioner,  we  are 
sure,  will  find  in  it  the  means  of  solving  many  a 
doubt,  and  will  rise  from  the  perusal  of  its  pages, 
having  gained  clearer  views  to  guide  him  in  his  daily 
struggle  with  disease.— i>w6.  Med.  Press,  Oct.  2,  1S67. 

Pocket  handbooks  of  medicine  are  not  desirable, 
even  when  they  are  as  carefully  and  elaborately  com- 
piled as  this,  the  latest,  most  complete,  and  most  ac- 
curate which  we  have  seen. — British  Med.  Journal, 
Sept.  21,  1S67. 

This  work  of  Dr.  Hartshorne  must  not  be  confound- 
ed with  the  medical  manuals  so  generally  to  be  found 
in  the  hands  of  students,  serving  them  at  best  but  as 
blind  guides,  better  adapted  to  lead  them  astray  than 
to  any  useful  and  reliable  knowledge.  The  work  be- 
fore us  presents  a  careful  synopsis  of  the  essential 
elements  of  the  theory  of  diseased  action,  its  causes, 
phenomenal  and  results,  and  of  the  art  of  healing,  as 
recognized  by  the  most  authoritative  of  our  profes- 
sional writers  and  teachers.  A  very  careful  and  can- 
did examination  of  the  volume  has  convinced  us  that 
it  will  be  generally  recognized  as  one  of  the  best  man- 
uals for  the  use  of  the  student  that  has  yet  appeared. 
— American  Journal  Med.  Sciences,  Oct.  1S67. 


Tm  TSON  ( THOMAS),  M.  D.,  ^c. 

LECTURES     ON    THE     PRINCIPLES    AND    PRACTICE    OF 

PHYSIC.     Delivered  at  King's  College,  London.     A  new  American,  from  the  last  revised 
and  enlarged  English  edition,  with  Additions,  by  D.  Francis  Condie,  M.  D.,  author  of 
•'  A  Practical  Treatise  on  the  Diseases  of  Children,"  &c.     With  one  hundred  and  eighty- 
five  illustrations  on  wood.     In  one  very  large  and  handsome  volume,  imperial  octavo,  of 
over   1200  closely  printed  pages  in  small  type;    extra  cloth,  $6  60;  strongly  bound  in 
leather,  with  raised  bands,  $7  50. 
Believing  this  to  be  a  work  which  should  He  on  the  table  of  every  physician,  and  be  in  the  hands 
of  every  student,  every  effort  has  been  made  to  condense  the  vast  amount  of  matter  which  it  con- 
tains within  a  convenient  compass,  and  at  a  very  reasonable  price,  to  place  it  within  reach  of  all. 
In   its  present  enlarged  form,  the  work  contains  the  matter  of  at  least  three  ordinary  octavos, 
rendering  it  one  of  the  cheapest  works  now  offered  to  the  American  profession,  while  its  mechani- 
cal eixecution  makes  it  an  exceedingly  attractive  volume. 


DICKSON'S  ELEMENTS  OF  MEDICINE  ;  a  Compen- 
dious View  of  Pathology  and  Therapeutics,  or  the 
History  and  Treatment  of  Diseases.  Second  edi- 
tion, revised.  1  vol.  Svo.  of  750  pages,  extra  cloth. 
$1  00. 

.WHAT  TO  OBSERVE  AT  THE  BEDSIDE  AND  AFTER 
Death  in  Medical  Cases.  Published  under  the 
authority  of  the  London  Society  for  Medical  Obser- 


vation. From  the  .second  London  edition.  1  vol. 
royal  12rao.,  extra  cloth.  $1  00. 
LAYCOCK'S  LECTURES  ON  THE  PRINCIPLES 
AND  Methods  of  Medical  Observation  and  Re- 
search. For  the  use  of  advanced  students  and 
juQior  practitioners.  In  one  very  neat  royal  12mo. 
volume,  extra  cloth.    $1  00. 


-nARCLAT  {A.  W.),  M.  D. 
^A  MANUAL  OF  MEDICAL  DIAGNOSIS;  being  an  Analysis  of  the 

Signs  and  Symptoms  of  Disease.     Third  American  from  the  second  and  revised  London 
edition.     In  one  neat  octavo  volume  of  451  pages,  extra  cloth.     I|i3  50. 
A  work  of  immense   practical    utility. — London  \      The  book  should  be  in  the  hands  of  every  practice 
Med.  Times  and  Gazette.  ,  man. — Dublin  Med.  Press. 


JPULLER  [HENRY  WILLIAM),  M.  D., 

-*•  Physician  to  St.  George^ s  Hospital,  London. 

ON  DISEASES  OF  THE   LUNGS   AND   AIR-PASSAGES.     Their 

Pathology,  Physical  Diagnosis,  Symptoms,  ard  Treatment.  From  the  second  and  revised 
English  edition.  In  one  handsome  octavo  volume  of  about  500  pages,  extra  cloth,  $3  50. 
{Now  Ready.) 

Dr.  Fuller's  work  on  diseases  of  the  chest  was  so  ;  accordingly  we  have  what  might  be  with  perfect  ju.s- 
favorably  received,  that  to  many  who  did  not  know  j  tice  styled  an  entirely  new  work  from  his  pen,  the 
the  extent  of  his  engagements,  it  was  a  matter  of  won-  !  portion  of  the  work  treating  of  the  heart  and  great 
der  that  it  should  be  allowed  to  remain  three  years  j  vessels  being  excluded.  Nevertheless,  this  volume  is 
out  of  print.  Determined,  however,  to  improve  it,  of  almost  equal  size  with  the  first. — London  Medical 
Dr.  Fuller  would  not  consent  to  a  mere  reprint,  and  I  Times  and  Gazette,  July  20,  1867. 


Henry  C.  Lea's  Publications — {Practice  of  Medicine). 


IT 


J^LINT  {A  USTIN),  M.  D., 

-*■  Professor  of  the  Principles  and  Practice  of  Medicine  in  Bellevue  Hospital  Med.  College,  N.  Y. 

A   PRACTICAL   TREATISE    ON   THE    PHYSICAL   EXPLORA- 
TION OF  THE  CHEST  AND  THE  DIAGNOSIS  OF  DISEASES  AFFECTING  THE 
RESPIRATORY  ORGANS.    Second  and  revised  edition.    In  one  handsome  octavo  volume 
of  595  pages,  extra  cloth,  $4  60.     {^Just  Issued.) 
Premising  this  observation  of  the  necessity  of  each 
student  and  practitioner  making  himself  acquainted 


with  auscultation  and  percussion,  we  may  state  our 
honest  opinion  that  Dr.  Flint's  treatise  is  one  of  the 
most  trustworthy  guides  which  he  can  consult.  The 
style  is  clear  and  distinct,  and  is  also  concise,  being 
free  from  that  tendency  to  over-refinement  and  unne- 
cessHry  minuteness  which  characterizes  many  works 
on  the  same  subject. — Dublin  Medical  Press,  Feb.  6, 
1S67. 

In  the  invaluable  work  before  us,  we  have  a  book 
o^  facts  of  nearly  600  pages,  admirably  arranged, 
clear,  thorough,  and  lucid  on  all  points,  without  pro- 
lixity; exhausting  every  point  and  topic  touched;  a 
monument  of  patient  and  loug-coutinued  observation, 
which  does  credit  to  its  author,  and  reflects  honor  on 


American  medicine. — Atlanta  Med,  and  Surg.  Jour- 
nal, Feb.  1867. 

The  chapter  on  Phthisis  is  replete  with  interest; 
and  his  remarks  on  the  diagnosis,  especially  in  the 
early  stages,  are  remarkable  for  their  acumen  and 
great  practical  value.  Dr.  Flint's  style  is  clear  and 
elegant,  and  the  tone  of  freshness  and  originality 
which  pervades  his  whole  work  lend  an  additional 
force  to  its  thoroughly  practical  character,  which 
cannot  fail  to  obtain  for  it  a  place  as  a  standard  work 
on  diseases  of  the  respiratory  system,  —  London 
Lancet,  Jan.  19,  1867. 

This  is  an  admirable  book.  Excellent  in  detail  and 
execution,  nothing  better  could  be  desired  by  the 
practitioner.  Dr.  Flint  enriches  his  subject  with 
much  solid  and  not  a  little  original  observation. — 
Banking's  Abstract,  Jan.  1867. 


B 


Y  THE  SAME  A  UTHOR. 


A  PRACTICAL  TREATISE  ON  THE  DIAGNOSIS,  PATHOLOGY, 

AND  TREATMENT  OF  DISEASES  OF  THE  HEART.     In  one  neat  octavo  volume  of 
nearly  500  pages,  with  a  plate  ;  extra  cloth,  $3  50. 


We  question  the  fact  of  any  recent  American  author 
in  our  profession  being  more  extensively  known,  or 
more  deservedly  esteemed  in  this  country  than  Dr. 
Flint.  We  willingly  acknowledge  his  success,  more 
particularly  in  the  volume  on  diseases  of  the  heai't,  in 


makingan  extended  personal  clinical  study  available 
for  purposes  of  illustration,  in  connection  with  cases 
which  have  been  reported  by  other  trustworthy  ob- 
servers.— Brit,  and  For.  Med.-Chir.  Review. 


ffff AMBERS  [T.  K.),  M.  D., 

^  Consulting  Physician  to  St.  Mary's  Hospital,  London,  &c. 

THE  INDIGESTIONS ;  or,  Diseases  of  the  Digestive  Organs  Functionally 

Treated.     Second  Edition,  revised.     In  one  handsome  octavo  volume  of  over  300  pages, 

extra  cloth,  $3  00.     {Now  Ready.) 

and  practical  skill — that  his  success  as  a  teacher  or 
literary  expositor  of  the  medical  art  consists;  and  the 
volume  before  us  is  a  better  illustration  than  its  au- 


He  is  perhaps  the  most  vivid  and  brilliant  of  living 
medical  writers ;  and  here  he  supplies,  in  a  graphic 
series  of  illustrations,  bright  sketches  from  his  well- 
stored  portfolio.  His  is  an  admirable  clinical  book, 
like  all  that  he  publishes,  original,  brilliant,  and  in- 
teresting. Everywhere  he  is  graphic,  and  his  work 
supplies  numerous  practical  hints  of  much  value. — 
Edinburgh  Med.  and  Surg.  Journal,  Nov.  1867. 

Associate  with  this  the  rare  faculty  which  Dr. 
Chambers  has  of  infusing  an  enthusiasm  in  his  sub- 
ject, and  we  have  in  this  little  work  all  the  elements 
which  make  it  a  model  of  its  sort.  We  have  perused 
it  carefully;  have  studied  every  page;  our  interest 
in  the  subject  has  been  intensified  as  we  proceeded, 
and  we  are  enabled  to  lay  it  down  with  unqualified 
praise.— A^.  Y.  Med.  Record,  April  la,  1867. 

It  is  in  the  combination  of  these  qualities — clear  and 
vivid  expression,  with  thorough  scientific  knowledge 


thor  has  yet  produced  of  the  rare  degree  in  which 
those  combined  qualities  are  at  his  command.  Next 
to  the  diseases  of  children,  there  is  no  subject  on 
which  the  young  practitioner  is  oftener  consulted,  or 
on  which  the  public  are  more  apt  to  form  their 
opinions  of  his  professional  skill,  than  the  various 
phenomena  of  indigestion.  Dr.  Chambers  comes  most 
opportunely  and  effectively  to  his  assistance.  In  fact, 
there  are  few  situations  in  which  the  commencing 
practitioner  can  place  himself  in  which  Dr.  Cham^ 
bers'  conclusions  on  digestion  will  not  be  of  service. 
— London  Lancet,  February  23,  1867. 

This  is  one  of  the  most  valuable  works  which  it 
has  ever  been  our  good  fortune  to  receive. — London 
Med.  Mirror,  Feb.  1867. 


B 


RINTON  [WILLIAM),  M.D.,  F.R.S. 

LECTURES  ON  THE  DISEASES  OF  THE   STOMACH;   with  an 

Introduction  on  its  Anatomy  and  Physiology.     From  the  second  and  enlarged  London  edi- 
tion.    With  illustrations  on  wood.      In  one  handsome  octavo  volume  of  about  300  pages, 
$3  25.     {Just  isstied.) 

The  most  complete  work  in  our  langiiage  upon  the 
diagnosis  and  treatment  of  these  puzzling  and  impor- 
tant diseases.— £o6-<o?i  Med.  and  Surg.  Journal,  Nov. 
1865. 


extra  cloth. 


Nowhere  can  be  found  a  more  full,  accurate,  plain, 
and  instructive  history  of  these  diseases,  or  more  ra- 
tional views  respecting  their  pathology  and  therapeu- 
tics.—^m.  Joum.  of  the  Med.  Sciences,  April,  1865. 


H 


H 


ABERSHON  [S.  0.),  M.D. 

PATHOLOGICAL  AND  PRACTICAL  OBSERVATIONS  ON  DIS- 
EASES OF  THE  ALIMENTARY  CANAL,  (ESOPHAGUS,  STOMACH,  C^CUM,  AND 
INTESTINES.  With  illustrations  on  wood.  In  one  handsome  octavo  volume  of  312 
pages,  extra  cloth.     $2  60. 

UDSON  (A.),  M.D.,  M.  R.LA., 

Phy,9ieian  to  the  Meath  Hospital. 

LECTURES  ON  THE  STUDY  OF  FEYER.     In  one  vol.  8vo. 

lishing  in  the  "Medical  News  and  Library"  for  1867  and  1868.) 


(Pub- 


18 


Henry  C.  Lea's  Publication& — {Practice  of  Medicine). 


'DUMSTEAD  [FREEMAN  J.),  M.D., 

•J-^        Lecturer  on  Materia  3fedica  and  Venereal  Diseases  at  the  Col.  of  Phys.  and  Surg.,  New  Yorlt,  &c. 

THE  PATHOLOGY  AXD  TREATMENT  OF  YENEREAL  DIS- 

EASES.     Including  the  results  of  recent  investigations  upon  the  subject.     A  new  and  re- 
vised edition,  with  illustrations.     In  one  large  and  handsome  octavo  volume  of  640  pages, 
extra  cloth,  $5  00.     {Lately  Issued.) 
During  the  short  time  which  has  elapsed  since  the  appearance  of  this  work,  it  has  assumed  the 
position  of  a  recognized  authority  on  the  subject  wherever  the  language  is  spoken,  and  its  transla- 
tion into  Italian  shows  that  its  reputation  is  not  confined  to  our  own  tongue.     The  singular  clear- 
ness with  which  the  modern  doctrines  of  venereal  diseases  are  set  forth  renders  it  admirably 
adapted  to  the  student,  while  the  fulness  of  its  practical  details  and  directions  as  to  treatment 
makes  it  of  great  value  to  the  practitioner.     The  few  notices  subjoined  will  show  the  very  high 
position  universally  accorded  to  it  by  the  medical  press  of  both  hemispheres. 

Well  known  as  one  of  the  best  authorities  of  the  i  which  has  long  been  felt  in  English  medicalliterature. 


present  day  on  the  subject. — British  and  For.  Med.- 
Ghirurg.  Review,  April,  1866. 

A  regular  store-house  of  special  information. — 
London  Lancet,  Feb.  24,  1866. 

A  remarkably  clear  and  full  systematic  treatise  on 
the  whole  subject. — Lond.  Med.  Times  and  Gazette. 

The  best,  completest,  fullest  monograph  on  this 
subject  in  our  language. — British  American  Journal. 

Indispensable  in  a  medical  library. — Pacific  Med. 
and  Surg.  Journal. 

We  have  no  doubt  that  it  will  supersede  in  America 
every  other  treatise  on  Venereal. — San  Francisco 
Med.  Press,  Oct.  1864. 

A  perfect  compilation  of  all  that  is  worth  knowing 
on  venereal  diseases  in  general.     It  fills  up  a  gap 


— Brit,  and  Foreign  Med.-Chirurg.  Review,  Jan.,  '6.5. 

We  have  not  met  with  any  which  so  highly  merits 
our  approval  and  praise  as  the  second  edition  of  Dr. 
Burastead'swork. — Glasgow  Med.  Journal,  Oct.  1S61. 

We  know  of  no  treatise  in  any  language  which  la 
its  equal  in  point  of  completeness  and  practical  sim- 
plicity.—  Boston  Medical  and  Surgical  Journal, 
Jan.  .30,  1S64. 

The  book  is  one  which  every  practitioner  should 
have  in  his  possession,  and,  we  may  further  say,  the 
only  book  upon  the  subject  which  he  should  acknow- 
ledge as  competent  authority. — Buffalo  Medical  and 
Surgical  Journal,  July,  1864. 

The  best  work  with  which  we  are  acquainted,  and 
the  most  convenient  hand-book  for  the  busy  practi- 
tioner — Cincinnati  Lancet,  July,  1864. 


(lULLERIER  [A.),  and 

^  Surgeon  to  the  Udpital  du  Midi. 


"DUMSTEAD  [FREEMAN  J.), 

J~^       Professor  of  Venereal  Diseases  in  the  College  of 

Physicians  and  Surgeons,  N.  Y. 

AN     ATLAS    OF    VENEREAL    DISEASES.       Translated    and    Edited    by 

Freeman  J.  Bumstead.     To  be  issued  in  five  parts,  at  Three  Dollars  each,  making  a  large 
imperial  4to.  volume,  with  26  plates,  containing  about  150  figures,  beautifully  colored,  many 
of  them  the  size  of  life.     (Parts  I.  and  II.  noiv  ready.) 
In  charge  of  the  celebrated  Ilopital  du  Midi,  where  M.  Eicord  gained  his  immense  experience, 
M.  Cullerier  is  known  as  one  of  the  most  profound  syphilographers  of  the  present  day.     This 
work  presents  the  results  of  his  observations  and  reflections  on  the  whole  round  of  venereal  acci- 
dents and  afiFections,  and  is  illustrated  with  a  complete  series  of  colored  plates,  more  minute  and 
extensive  than  anything  of  the  kind  that  has  yet  been  laid  before  the  profession.     The  translator 
and  editor.  Dr.  Bumstead,  is  so  well  known  in  this  country  as  an  authority  on  the  subject,  and 
as  a  clear  and  elegant  writer,  that  his  connection  with  the  work  is  suflBcient  guarantee  that  its 
value  will  be  increased  in  passing  through  his  hands. 

*^*  A  specimen  of  the  plates  and  text  sent  free  by  mail,  on  receipt  of  25  cents. 


BUCKLER  ON  FIBRO-BRONCHITIS  AND  RHEU- 
MATIC PNEUMONIA.  In  one  octavo  vol.,  extra 
cloth,  pp.  1.50.     *1   2.5. 

FISKE  FUND  PRIZE  ESSAYS.— LEE  ON  THE  EF- 
FECTS OF  CLIMATE  ON  TUBERCULOUS  DIS- 
EASE. AND  WARREN  ON  THE  INFLUENCE  OF 
PREGNANCY  ON  THE  DEVELOPMENT  OF  TU- 
BERCLES. Together  in  one  neat  octavo  volume, 
extra  cloth,     $1  00. 


HUGHES'  CLINICAL  INTRODUCTION  TO  AUS- 
CULTATION AND  OTHER  MODES  OF  PHYSICAL 
DIAGNOSIS.  Second  edition.  One  volume  royal 
12mo.,  extra  cloth,  pp.  304.     $1  2.5. 

WALSHE'S  PRACTICAL  TREATISE  ON  THE  DIS- 
EASES OF  THE  HEART  AND  GREAT  VESSELS. 
Third  American,  from  the  third  revised  and  much 
enlarged  London  edition.  In  one  handsome  octavo 
volume  of  420  pages,  extra  cloth.    $3  00. 


J^A  ROCHE  [R.),  31.  D. 


YELLOW  FEYER,  considered  in  its  Historical,  Pathological,  Etio- 
logical, and  Therapeutic.nl  Relations.  Including  a  Sketch  of  the  Disease  as  it  has  occurred 
in  Philadelphia  from  1699  to  1854,  with  an  examination  of  the  connections  between  it  and 
the  fevers  known  under  the  same  name  in  other  parts  of  temperate  as  well  as  in  tropical 
regions.  In  two  large  and  handsome  octavo  volumes,  of  nearly  1500  pages,  extra  cloth,  $7  00. 
jyT  THE  SAME  AUTHOR.  

PNEUMONIA ;  its  Supposed  Connection,  Pathological,  and  Etiological, 

with  Autumnal  Fevers,  including  an  Inquiry  into  the  Existence  and  Morbid  Agency  of 
Malaria.     In  one  handsome  octavo  volume,  extra  cloth,  of  500  pages.     $3  00. 


J^YONS  [ROBERT  D.),  K.  C.  C. 

A  TREATISE  ON  FEYER;  or.  Selections  from  a  Course  of  Lectures 

on  Fever.    Being  part  of  a  Course  of  Theory  and  Practice  of  Medicine.   In  one  neat  octavo 
volume,  of  362  pages,  extra  cloth.     $2  25. 


CLYMER  ON  FEVERS;  THEIR  DIAGNOSIS,  PA- 
THOLOOY  AND  TREATMENT.  In  OQe  octavo  volume 
of  600  pages,  leather.    $1  75. 


TODD'S  CLINICAL  LECTURES  ON  CERTAIN  ACUTE 
DisEA!!ES.  In  one  neat  octavo  volume,  of  320  pages 
extra  cloth.    $2  50. 


Henry  C.  Lea's  Publications — {Practice  of  Medicine). 


19 


IJOBERTS  (  WILLIAM),  M.  D., 

-*•  ^  Lecturer  on  Medicine  in  the  Manchester  School  of  Medicine,  &c. 

A  rilACTICAL  TREATISE   ON  URINARY  AND   RENAL   DIS- 

EASES,  including  Urinary  Deposits.     Illustrated  by  numerous  cases  and  engravings.     In 
one  very  handsome  octavo  volume  of  516  pp.,  extra  cloth.     $4  50.      {^Just  Issued.) 


In  carrying  out  this  design,  he  has  not  only  made 
good  use  of  his  own  practical  knowledge,  but  has 
brought  together  from  various  sources  a  vast  amount 
of  information,  some  of  which  is  not  generally  pos- 
sessed by  the  profession  in  this  country.  We  must 
now  bring  our  notice  of  this  book  to  a  close,  re- 
gretting only  that  we  are  obliged  to  resist  the  temp- 
tation of  giving  further  extracts  from  it.  Dr.  Roberts 
has  already  on  several  occasions  placed  before  the 
profession  the  results  of  researches  made  by  him  on 
various  points  connected  with  the  urine,  and  had  thus 
led  us  to  expect  from  him  something  good — in  which 


sive  work  on  urinary  and  renal  diseases,  considered 
in  their  strictly  practical  aspect,  that  we  possess  in 
the  English  language. — British  Medical  Journal^ 
Dec.  9,  lS6r>. 

We  have  read  this  book  with  much  satisfaction. 
It  will  take  its  place  beside  the  best  treatises  in  our 
language  upon  urinary  pathology  and  therapeutics. 
Not  the  least  of  its  merits  is  that  the  author,  unlike 
some  other  book-makers,  is  contented  to  withhold 
much  that  he  is  well  qualified  to  discuss  in  order  to 
impart  to  his  volume  such  a  strictly  practical  charac- 
ter as  cannot  fail  to  render  it  popular  among  British 
readers. — London  Med.  Times  and  Gazette,  March 
17,  1SH6. 


expectation  we  have  been  by  no  means  disappointed 
The  book  is,  beyond  question,  the  most  comprehen 

J^^,  "  Bird  on  Urinary  Deposits,"  being  for  the  present  out  of  print,  gentlemen  will  find  in  the 
above  work  a  trustworthy  substitute. 


MORLAND  ON  RETENTION  IN  THE  BLOOD  OF 
THE  ELEMENTS  OF  THE  URINARY  SECRE- 
TION.    1  vol.  8vo.,  extra  cloth.    75  cents. 

BLOOD  AND   URINE  (MANUALS  ON).     By   J.  W. 


Griffth,  G.  0.  Reese,  and   A.  Markwick.     1  vol, 
12mo.,  extra  cloth,  with  plates,     pp.  460.    $1  25. 
BUDD  ON  DISEASES  OF  THE  LIVER.  Tliird  edition. 
1  vol.  8vo.,  extra  cloth,  with  four  beautifully  colored 
plates,  and  numerous  wood-cuts.     pp.  500.    $4  00. 


jyUGKNILL  [J.  a),M.D.,         and 

-*-''  Med.  Superintendent  of  the  Devon  Lunatic  Asylum. 


T^ANIEL  H.  TDKE,M.D., 

-^-^  Visiting  Medical  Officer  to  the  York  Retreat. 


A  MANUAL  OF    PSYCHOLOGICAL    MEDICINE;  containing  the 

History,  Nosology,  Description,  Statistics,  Diagnosis,  Pathology,  and  Treatment  of  In- 
sanity.   With  a  Plate.    In  one  handsome  octavo  volume,  of  536  pages,  extra  cloth.    $4  25. 


TONES  [G.  HANDFIELD),  M.  D., 

^  Physician  to  St.  Mary's  Hospital,  &c. 

CLINICAL    OBSERVATIONS    ON    FUNCTIONAL   NERVOUS 

DISORDERS.       In   one  handsome    octavo   volume   of    348   pages,    extra  cloth,    $3  25. 

{Just  Issiced.) 

Taken  as  a  whole,  the  work  before  us  furnishes  a  1      We  must  cordially  recommend  it  to  the  profession 

short  but  reliable  account  of  the  pathology  and  treat-  '  of  this  country  as  supplying,  in  a  great  measure,  a 

ment  of  a  class  of  very  common  but  certainly  highly  j  deficiency  which  exists  in  the  medical  literature  of 

obscure  disorders.    The  advanced  student  will  find  it  !  the  English  language. — New  York  Med.  Journ.,  April, 


a  rich  mine  of  valuable  facts,  while  the  medical  prac- 
titioner will  derive  from  it  many  a  suggestive  hint  to 
aid  him  in  the  diagnosis  of  "nervous  cases,"  and  in 
determining  the  true  indications  for  their  ameliora- 
tion or  cure. — Amer.  Journ.  Med.  Sci.,  Jan.  1S67. 


1867. 

The  volume  is  a  most  admirable  one— full  of  hints 
and  practical  suggestions.  —  Canada  Med.  Journal, 
April,  1867. 


HARRISON'S  ESSAY  TOWARDS  A  CORRECT 
THEORY  OF  THE  NERVOUS  SYSTEM,  In  one 
octavo  volume  of  292  pp.     $1  50. 

SOLLY   ON  THE  HUMAN   BRAIN:    its  Structure, 


Physiology,  and  Diseases.  From  the  Second  and 
much  enlarged  London  edition.  In  one  octavo 
volume  of  500  pages,  with  120  wood-cuts;  extra 
cloth.     *2  50. 


OMITH  {EDWARD),  M.D. 
CONSUJMPTION;  ITS  EARLY  AND  REMEDIABLE  STAGES. 

one  neat  octavo  volume  of  254  pages,  extra  cloth.     $2  25. 

gALTER  {H.  H.),  M.D. 

ASTHMA ;  its  Pathology,  Causes,  Consequences,  and  Treatment. 

one  volume;  octavo,  extra  cloth.     $2  50. 
gLADE  [D.  D.), 


In 


In 


M.D. 


DIPHTHERIA;  its  Nature  and  Treatment,  with  an  account  of  the  His- 
tory of  its  Prevalence  in  various  Countries.  Second  and  revised  edition.  In  one  neat 
royal  12mo,  volume,  extra  cloth.     $1  25.     {Just  issued.) 


ALLEMAND  AND   WILSON. 

A   PRACTICAL  TREATISE    ON    THE    CAUSES,    SYMPTOMS, 

AND   TREATMENT   OF   SPERMATORRHCEA.     By  M.  Lallemand.     Tran.«lated  and 

edited  by  Henry  J.  McDougall.     Fifth  American  edition.     To  which  is  added ON 

DISEASES  OF  THE  VESICUL^  SEMINALES,  and  their  associatrd  organs.  With 
special  reference  to  the  Morbid  Secretions  of  the  Prostatic  and  Urethral  Mucous  Membrane. 
By  Mauris  Wilson,  M.D.   In  one  neat  octavo  volume,  of  about  400  pp.,  extra  cloth,  $2  76. 


20 


Henry  C.  Lea's  Publications — (Diseases  of  the  Skin). 


T^ILSON  {ERASMUS),  F.R.S., 

ON  DISEASES  OF  THE  SKIN.     The  sixth  American,  from  the  fifth 

and  enlarged  English  edition.     In  one  large  octavo  volume  of  nearly  700  pages,  extra 
cloth.     $4  60.     Also— 

A  SERIES   OF   PLATES   ILLUSTRATING  "WILSON   ON  DIS- 
EASES OF  THE  SKIN;"  consisting  of  twenty  beautifully  executed  plates,  of  which  thir- 
teen are  exquisitely  colored,  presenting  the  Normal  Anatomy  and  Pathology  of  the  Skin, 
and  embracing  accurate  representations  of  about  one  hundred  varieties  of  disease,  most  of 
them  the  size  of  nature.     Price,  in  extra  cloth,  $5  50. 
Also,  the  Text  and  Plates,  bound  in  one  handsome  volume,  extra  cloth.     Price  $9  50. 
This  classical  work  has  for  twenty  years  occupied  the  position  of  the  leading  authority  on  cuta- 
neous diseases  in  the  English  language,  and  the  industry  of  the  author  keeps  it  on  a  level  with  the 
advance  of  science,  in  the  frequent  revisions  which  it  receives  at  his  hands.     The  large  size  of  the 
volume  enables  him  to  enter  thoroughly  into  detail  on  all  the  subjects  embraced  in  it,  while  its 
very  moderate  price  places  it  within  the  reach  of  every  one  interested  in  this  department  of  practice. 


Such  a  work  as  the  one  before  us  is  a  most  capital 
and  acceptable  help.  Mr.  Wilson  has  long  been  held 
as  high  authority  in  this  department  of  medicine,  and 
his  book  on  diseases  of  the  skin  has  long  been  re- 
garded as  one  of  the  best  text-books  extant  on  the 
subject.  The  present  edition  is  carefully  prepared, 
and  brought  up  in  its  revision  to  the  present  time  In 
this  edition  we  have  also  included  the  beautiful  series 
of  plates  illustrative  of  the  text,  and  in  the  last  edi- 
tion published  separately.  There  are  twenty  of  these 
plates,  nearly  all  of  them  colored  to  nature,  and  ex- 
hibiting with  great  fidelity  the  various  groups  of 
diseases  treated  of  in  the  body  of  the  work. — Cin- 
cinnati Lancet,  June,  1863. 

No  one  treating  skin  diseases  should  be  without 
a  copy  of  this  standard  work.  —  Canada  Lancet. 
August,  1863. 


We  can  safely  recommend  it  to  the  pi-ofession  as 
the  best  work  on  the  subject  now  in  existence  in 
the  English  language. — Medical  Times  and  Gazette. 

Mr.  Wilson's  volume  is  an  excellent  digest  of  the 
actual  amount  of  knowledge  of  cutaneous  diseases; 
it  includes  almost  every  fact  or  opinion  of  importance 
connected  with  the  anatomy  and  pathology  of  the 
skin. — British  and  Foreign  Medical  Review. 

These  plates  are  very  accurate,  and  are  executed 
with  an  elegance  and  taste  which  are  highly  creditable 
totheartisticskillofthe  American  artist  who  executed 
them. — St.  Louis  Med.  Journal. 

The  drawings  are  very  pei'fect,  and  the  finish  and 
coloring  artistic  and  correct ;  the  volume  is  an  indis- 
pensable companion  to  the  book  it  illustrates  and 
completes. — Charleston  Medical  Journal. 


JDY  THE  SA3IE  AUTHOR.  

THE  STUDENT'S  BOOK  OF  CUTANEOUS  MEDICINE  and  Dis- 

EASES  OP  THE  SKIN.     In  One  very  handsome  royal  12mo.  volume.    $.3  50.     {Now  Ready.) 
This  new  class-book  will  be  admirably  adapted  to  I     Thoroughly  practical  in  the  best  sense. — Brit.  Med. 
the  necessities  of  students. — Lancet.                              \  Journal. 
DF  THE  SAME  AUTHOR.  

HEALTHY  SKIN;   a  Popular  Treatise  on  the  Skin  and  Hair,  their 

Preservation  and  Management.     One  vol.  12mo.,  pp.  291,  with  illustrations,  cloth.     $1  00 


ISJELIGAN  [J.  MOORE),  M.D.,  M.R.I.A., 

A    PRACTICAL    TREATISE    ON    DISEASES    OF    THE    SKIN. 

Fifth  American,  from  the  second  and  enlarged  Dublin  edition  by  T.  W.  Belcher,  M.  D. 

In  one  neat  royal  12mo.  volume  of  462  pages,  extra  cloth.  $2  25.  {Just  Issued.) 
Of  the  remainder  of  the  work  we  have  nothing  be-  !  This  instructive  little  volume  appears  once  more, 
yond  unqualified  commendation  to  offer.  It  is  so  far  Since  the  death  of  its  distinguished  author,  the  study 
the  most  complete  one  of  its  size  that  has  appeared,  :  of  skin  diseases  has  been  considerably  advanced,  and 
and  for  the  student  there  can  be  none  which  can  com-  [  the  results  of  these  investigations  have  been  added 
pare  with  it  in  practical  value.  All  the  late  disco-  by  the  present  editor  to  the  original  work  of  Dr.  Neli- 
veries  in  Dermatology  have  been  duly  noticed,  and  !gan.  This,  however,  has  not  so  far  increased  its  bulk 
their  value  justly  estimated;  in  a  word,  the  work  is  as  to  destroy  its  reputation  as  the  most  convenient 
fully  up  to  the  time.*,  a,nd  is  thproughly  stocked  with  manual  of  diseases  of  the  .skin  that  can  be  procured 
most  valuable  information. — Mw  York  Med.  Record,  by  the  student. — Chicago  Med.  Journal,  Dec.  1866. 
Jan.  15,  1867.  |  »  « 

j^F  THE  SAME  AUTHOR.  

ATLAS   OF   CUTANEOUS   DISEASES.     In   one  beautiful  quarto 

volume,  with  exquisitely  colored  plates,  Ac,  presenting  about  one  hundred  varieties  of 
disease.     Extra  cloth,  $5  50. 


The  diagnosis  of  eruptive  disea.se,  however,  under 
all  circumstances,  is  very  difficult.  Nevertheless, 
Dr.  Neligan  has  certainly,  "as  far  as  possible,"  given 
a  faithful  and  accurate  representation  of  this  class  of 
diseases,  and  there  can  be  no  doubt  that  these  plates 
will  be  of  great  use  to  the  student  and  practitioner  in 
drawing  a  diagnosis  as  to  the  class,  order,  and  species 
to  which  the  particular  case  may  belong.  While 
looking  over  the  "Atlas"  we  have  been  induced  to 
examine  also  the  "Practical  Treatise,"  and  we  are 
Inclined  to  consider  it  a  very  superior  work,  com- 
bining accurate  verbal  description  with  sound  views 


of  the  pathology  and  treatment  of  eruptive  diseases. 
It  possesses  the  merit  of  giving  short  and  condensed 
descriptions,  avoiding  the  tedious  minuteness  of 
many  writers,  while  at  the  same  time  the  work,  as 
its  title  implies,  is  strictly  practical. — Glasgow  Med. 
Journal. 

A  compend  which  will  very  much  aid  the  practi- 
tioner in  this  diflicult  branch  of  diagno.sis.  Taken 
with  the  beautiful  plates  of  the  Atlas,  which  are  re- 
markable for  their  accuracy  and  beauty  of  coloring, 
it  constitutes  a  very  valuable  addition  to  the  library 
of  a  practical  m^n.— Buffalo  Mid.  Journal. 


TJILLIER  [THOMAS),  M.D., 

-^-^  Physician  to  the  Skin  Department  of  University  College  Hospital,  &e. 

HAND-BOOK  OF  SKIN  DISEASES,  for  Students  and  Practitioners, 

In  one  neat  royal  12mo.  volume  of  about  300  pages,  with  two  plates;  extra  cloth,  $2  25. 
{Just  Issued.) 


Henry  C.  Lea's  Publications — (Diseases  of  Children). 


21 


ftONDIE  [D,  FRANCIS),  M.  D. 


A  PRACTICAL  TREATISE  ON  THE  DISEASES  OF  CHILDREN. 

Sixth  edition,  revised  and  augmented.     In  one  large  octavo  volume  of  nearly  800  closely, 
printed  pages,  extra  cloth,  $5  25  ;  leather,  $6  25.       {Now  Beady.) 

it  are  based,  as  all  practice  should  be,  upon  a  familiar 
knowledge  of  disease.  Tlie  opportunities  of  Dr.  Con- 
die  for  the  practical  study  of  the  diseases  of  children 
have  been  ji;reat,  and  his  worlc  is  a  proof  that  they  have 
not  been  thrown  away.  He  has  read  much,  but  ob- 
served more  ;  and  we  think  that  we  may  safely  say 
that  the  American  student  cannot  find,  in  his  owa 
language,  a  better  book  upon  the  subject  of  which  it 
treats. — Am.  Journal  Medical  Sciences. 


Dr.  Condie's  scholarship,  acumen,  industry,  and 
I»Tactical  sense  are  manifested  in  this,  as  in  all  his 
numerous  contributions  to  science. — Dr.  Holmes's 
Report  to  the  American  Medical  Association. 

Taken  as  a  whole,  in  our  judgment.  Dr.  Condie's 
treatise  is  the  one  from  the  perusal  of  which  the 
practitioner  in  this  country  will  rise  with  the  great- 
est satisfaction. —  Western  Journal  of  Medicine  and 
Surgery. 

In  the  department  of  infantile  therapeutics,  the  work 
of  Dr.  Condie  is  considered  one  of  the  best  in  the  Eng- 
lish language. — The  Stethoscope. 

As  we  said  before,  we  do  not  know  of  a  better  book 
on  Diseases  of  Children,  and  to  a  large  part  of  its  re- 
commendations we  yield  an  unhesitating  concurrence. 
— Buffalo  Medical  Journal. 

The  work  of  Dr.  Condie  is  unquestionably  a  very 
able  one.  It  is  practical  in  its  character,  as  its  title 
ln^)ort8 ;  but  the  practical  precepts  recommended  in 


We  pronounced  the  first  edition  to  be  the  best  work 
on  the  diseases  of  children  in  the  English  language, 
and,  notwithstanding  all  that  has  been  published,  we 
still  regard  it  in  that  light. — Medical  Examiner. 

The  value  of  works  by  native  authors  on  the  dis- 
eases which  the  physician  is  called  upon  to  combat 
will  be  appreciated  by  all,  and  the  work  of  Dr.  Con- 
die has  gained  for  itself  the  character  of  a  safe  guide 
for  students,  and  a  useful  work  for  consultation  by 
those  eng^ed  in  practice. — N.  Y.  Med.  Times. 


'^/'EST  [CHARLES),  M.D., 

Physician  to  the  Hospital  for  Sick  CJiildren,  &c. 

LECTURES  ON   THE   DISEASES   OF   INFANCY  AND  CHILD- 

HOOD.  Fourth  American  from  the  fifth  revi.'sed  and  enlarged  English  edition.  In  one 
large  and  handsome  octavo  volume  of  656  closely-printed  pages.  Extra  cloth,  $4  50 ; 
leather,  $5  50.     {Just  issued.) 

This  work  may  now  fairly  claim  the  position  of  a  standard  authority  and  medical  classic.  Five 
editions  in  England,  four  in  America,  four  in  Germany,  and  translations  in  French,  Danish, 
Dutch,  and  Russian,  show  how  fully  it  has  met  the  wants  of  the  profession  by  the  soundness  of  its 
views  and  the  clearness  with  which  they  are  presented.  Few  practitioners,  indeed,  have  had  the 
opportunities  of  observation  and  experience  enjoyed  by  the  Author.  In  his  Preface  he  remarks, 
"The  present  edition  embodies  the  results  of  1200  recorded  cases  and  of  nearly  400  post-mortem 
examinations,  collected  from  between  30,000  and  40,000  children,  who,  during  the  past  twenty- 
six  years,  have  come  under  my  care,  either  in  public  or  in  private  practice."  The  universal  favor 
with  which  the  work  has  been  received  shows  that  the  author  has  made  good  use  of  these  unusual 
advantages. 


Of  all  the  English  writers  on  the  diseases  of  chil- 
dren, there  is  no  one  so  entirely  satisfactory  to  us  as 
Dr.  West.  For  years  we  have  held  his  opinion  as 
judicial,  and  have  regarded  him  as  one  of  the  highest 
living  authorities  in  the  difficult  department  of  medi- 
cal science  in  which  he  is  most  widely  known.  His 
writings  are  characterized  by  a  sound,  practical  com- 
mon sense,  at  the  same  time  that  they  bear  the  marks 
of  the  most  laborious  study  and  investigation.  We 
commend  it  to  all  as  a  most  reliable  adviser  on  many 
occasions  when  many  treatises  on  the  same  subjects 
will  utterly  fail  to  help  us.  It  is  supplied  with  a  very 
copious  general  index,  and  a  special  index  to  the  for- 
mulae scattered  throughout  the  work. — Boston  Med. 
and  Surg.  Journal,  April  26,  1866. 

Dr.  West's  volume  is,  in  our  opinion.  Incomparably 
the  best  authority  upon  the  maladies  of  children 
tliat  the  practitioner  can  consult.  Withal,  too — a 
miaor  matter,  truly,  but  still  not  one  that  should  be 
neglected — Dr.  West's  composition  possesses  a  pecu- 
liar charm,  beauty  and  clearness  of  expression,  thus 
affording  the  reader  much  pleasure,  even  independent 
of  that  Avhich  arises  from  the  acquisition  of  valuable 
truths. — Cincinnati  Jour,  of  Medicine,  March,  1866. 

We  have  long  regarded  it  as  the  most  scientific  and 
practical  book  on  diseases  of  children  which  has  yet 
appeared  in  this  country. — Buffalo  Medical  Journal. 

Dr.  West's  book  is  the  best  that  has  ever  been 
written  in  the  English  language  on  the  diseases  of 


infancy  and  ♦hildhood. — Columhus  Review  of  Med. 
and  Surgery. 

To  occupy  in  medical  literature,  in  regard  to  dis- 
eases of  children  the  enviable  po.sition  which  Dr. 
Watson's  treatise  does  on  the  diseases  of  adults  is 
now  very  generally  assigned  to  our  author,  and  his 
book  is  in  the  hands  of  the  profession  everywhere  as 
an  original  work  of  great  value. — Md.  and'  Va,  Med. 
and  Surg.  Journal. 

Dr.  West's  works  need  no  recommendation  at  this 
date  from  any  hands.  The  volume  before  u.s,  espe- 
cially, has  won  for  itself  a  large  and  well-deserved 
popularity  among  the  profession,  wherever  the  Eng- 
lish tongue  is  spoken.  Many  years  will  elapse  before 
it  will  be  replaced  in  public  estimation  by  any  similar 
treatise,  and  seldom  again  will  the  same  subject  be 
discussed  in  a  clearer,  more  vigorous,  or  pleasing 
style,  with  equal  simplicity  and  power. — Charleston 
Med.  Jour,  and  Review. 

There  is  no  part  of  the  volume,  no  subject  on  which 
it  treats  which  does  not  exhibit  the  keen  perception, 
the  clear  judgment,  and  the  sound  reasoning  of  the 
author.  It  will  be  found  a  most  useful  guide  to  the 
young  practitioner,  directing  him  in  his  management 
of  children's  diseases  in  the  clearest  pos.sible  manner, 
and  enlightening  him  on  many  a  dubious  pathological 
point,  while  the  older  one  will  find  in  it  many  a  sug- 
gestion and  practical  hint  of  great  value.— i?ri/.  Am, 
Med.  Journal. 


r)EWEES  [WILLIAM  P.),  M.D., 

-*-^  Late  Professor  of  Midwifery,  &c.,  in  the  University  of  Pennsylvania,  &c. 

A  TREATISE  ON  THE  PHYSICAL  AND  MEDICAL  TREAT- 
MENT OF  CHILDREN.  Eleventh  edition,  with  the  author's  last  improvements  and  cor- 
rections.     In  one  octavo  volume  of  548  pages.     $2  80. 


22 


Henry  C.  Lea's  Publications — (Diseases  of  Women). 


rPHOMAS  [T.  GAILLARD),  M.  D., 

-*-  Professor  of  Obstetrics,  d-c  in  the  College  of  Physicians  and  Surgeons,  N.  Y.,  d^c. 

A  COMPLETE   PRACTICAL   TREATISE  ON  THE   DISEASES  OF 

FEMALES.  In  one  large  and  handsome  octavo  volume  of  over  600  pages,  with  219  illus- 
trations, extra  cloth,  $5;  leather,  $6.  {Now  Ready.) 
In  this  work  Professor  Thomas  has  endeavored  to  supply  the  want  of  a  complete  treatise  on 
Gynaecology,  embracing  both  the  medical  and  surgical  treatment  requisite  to  the  diseases  and 
accidents  peculiar  to  women.  The  investigations  and  improvements  of  the  last  few  years  have 
worked  so  great  a  change  in  this  important  department  of  practical  medicine  that  a  work  like  the 
present,  thoroughly  on  a  level  with  the  most  advanced  condition  of  the  subject,  can  hardly  fail 
to  possess  claims  on  the  attention  of  every  practitioner. 

To  show  the  scope  of  the  work,  a  very  condensed  summary  of  the  contents  is  subjoined. 

Chapter  I.  History  of  Uterine  Pathology. — II.  Etiology  of  Uterine  Diseases  in  America. — III.  Diagnosis 
of  Diseases  of  Female  Genital  Organs. — IV.  Diseases  of  the  Vulva. — V.  Diseases  of  the  Vulva  (conAinued). 
VI.  Vaginismus. — VII.  Vaginitis. — VIII.  Atresia  Vaginse. — IX.  Prolapsus  Vaginae.  —  X.  Fistulae  of  the 
Female  Genital  Organs. — XI.  Fecal  and  Simple  Vaginal  Fistulse. — XII.  General  Remarks  on  Inflammatiou 
of  the  Uterus. — XIII.  Acute  Endo-Metritis  and  AcuTe  Metritis. — XIV.  Cervical  Endo-Meti'itis. — XV.  Chronic 
Cervical  Metritis. — XVI.  Chronic  Corporeal  Endo-Metritis  and  Metritis. — XVII.  Ulceration  of  the  Os  and 
Cervix  Uteri. — XVIII.  General  Considerations  on  Displacements  of  the  Uterus. — XIX.  Ascent  and  Descent 
of  the  Uterus. — XX.  Versions  of  the  Uterus. — XXI.  Flexions  of  the  Uterus — XXII.  Inversion  of  the  Ute- 
rus.—XXIII.  Peri-Uterine  Cellulitis.  — XXIV.  Pelvic  Peritonitis.— XXV.  Pelvic  Absces.s.— XXVI.  Pelvic 
Hseraatocele.  — XXVII.  Fibrous  Tumors  of  the  Uterus. —  XXVIII.  Uterine  Polypi.  —  XXIX.  Cancer  of  the 
Uterus.— XXX.  Cancroid  Tumors  of  the  Uterus  —XXXI.  Epithelial  Cancer  of  the  Uterus. —  XXXII.  Dis- 
eases resulting  from  Pregnancy.  —  XXXIII.  Dysmenorrhcea.  —  XXXIV.  Menorrhagia  and  Metrorrhagia. — 
XXXV.  Amenorrhoea.  — XXXVI.  Leucorrhoea.— XXXVII.  Sterility.  — XXXVIII.  Amputation  of  the  Cer- 
vix Uteri.— XXXIX.  Diseases  of  the  Ovaries  —XL.  Ovarian  Tumors. — XLI.  Ovariotomy. — XLII.  Ovarian 
Tumors  (continued). — XLIII.  Diseases  of  the  Fallopian  Tubes. 


Jj^EIGS  {CHARLES  D.),  M.  D., 

Late  Professor  of  Obstetrics,  dec.  in  Jefferson  Medical  College,  Philadelphia. 

WOMAN:    HER  DISEASES  AND  THEIR  REMEDIES.    A  Series 

of  Lectures  to  his  Class.     Fourth  and  Improved  edition.     In  one  large  and  beautifully 
printed  octavo  volume  of  over  700  pages,  extra  cloth,  $5  00  ;  leather,  $6  00. 

Every  topic  discussed  by  the  author  is  rendered  80 
plain  as  to  be  readily  understood  by  every  student : 
and,  for  our  own  part,  we  consider  it  not  only  one  of 
the  most  readable  of  books,  but  one  of  priceless  value 
to  the  practitioner  engaged  in  the  practice  of  those 
diseases  peculiar  to  females. — N.Am,.  Med.-Chir.  Re- 


That  this  work  has  been  thoroughJy  appreciated 
by  the  profession  of  this  country  as  well  as  of  Europe, 
is  fully  attested  by  the  fact  of  its  having  reached  its 
fourth  edition  in  a  period  of  less  than  twelve  years. 
Its  value  has  been  much  enhanced  by  many  impor- 
tant additions,  and  it  contains  a  fund  of  useful  in- 
formation, conveyed  in  an  easy  and  delightful  style. 


J^Y  THE  SAME  AUTHOR.  

ON  THE  NATURE,  SIGNS,  AND  TREATMENT  OF  CHILDBED 

FEVER.     In  a  Series  of  Letters  addressed  to  the  Students  of  his  Class.     In  one  handsome 
octavo  volume  of  365  pages,  extra  cloth.     $2  00. 


QHURGHILL  [FLEETWOOD),  M.  D.,  M.  R.  L  A. 

ON  THE  DISEASES   OF  WOMEN;   including  those  of  Pregnancy 

and  Childbed.  A  new  American  edition,  revised  by  the  Author.  With  Notes  and  Additions, 
by  D.  Francis  Condie,  M.  D.,  author  of  '*  A  Practical  Treatise  on  the  Diseases  of  Chil- 
dren." With  numerous  illustrations.  In  one  large  and  handsome  octavo  volume  of  768 
pages,  extra  cloth,  $4  00;  leather,  $5  00. 
As  an  epitome  of  all  that  is  known  in  this  depart-  I  fullest  and  most  valuable  in  the  English  language, 
ment  of  medicine,  the  book  before  us  is  perhaps  the  |  — Dublin  Medical  Pre^ss. 

J^Y  THE  SAME  AUTHOR.  

ESSAYS  ON  THE  PUERPERAL  FEVER,  AND  OTHER  DIS- 
EASES PECULIAR  TO  WOMEN.  Selected  from  the  writings  of  British  Authors  previ- 
ous  to  the  close  of  the  Eighteenth  Century.  In  one  neat  octavo  volume  of  about  460 
pages,  extra  cloth.     $2  50. 

'^RO  WN  (ISAAC  BAKER),  M.  D. 

ON  SOME  DISEASES  OF  WOMEN  ADMITTING  OF  SURGICAL 

TREATMENT.     With  handsome  illustrations.      One  volume  8vo.,  extra  cloth,  pp.   276. 
$]  60. 


ASHWELL'S  PRACTICAL  TRE.\.TISE  ON  THE  DIS- 
EASES PECULIAR  TO  WOMEN.  Illustrated  by 
Cases  derived  from  Hospital  and  Private  Practice. 
Third  American,  from  the  Third  and  revised  Lon- 
don edition.  In  one  octavo  volume,  extra  cloth, 
of  r>2S  pages.     $3  uO. 

EIOBY  ON  THE  CONSTITUTIONAL  TREATMENT 
OF  FEMALE  DISEASES.  In  one  neat  royal  12mo. 
volume,  extra  cloth,  of  about  250  pages.    $1  00. 


DEWEES'S  TREATISE  ON  THE  DISEASES  OF  FE- 
MALES. With  illustrations.  Eleventh  Edition, 
with  the  Author's  last  improvements  and  correc- 
tions. In  one  octavo  volume  of  536  pages,  with 
plates,  extra  cloth,  $3  00. 

COLOMBAT  DE  L'ISERE  ON  THE  DISEASES  OP 
FEMALES.  Translated  by  C.  D.  Mfeios,  M.  D.  Se- 
cond edition.  In  one  vol.  8vo,  extra  cloth,  with 
numerous  wood-cuts.    pp.  720.    $3  75. 


Henry  C.  Lea's  Publications — (Diseases  of  Women). 


23 


JJODGE  {HUGH  L.),  M.D. 


OX  DISEASES  PECULIAR  TO  WOMEN;,  including  Displacements 

of  the  Uterus.     With  original  illustrations.     Second  edition,  revised.     In  one  beautifully 

printed  octavo  volume  of  about  500  pages.     {Preparing.) 

Indeed,  although  no  part  of  the  volume  is  not  emi-    the  day — one  which  every  accoucheur  and  pliysiciHn 

nently  deserving  of  perusal  and  study,  we  think  that  j  should   most  can^fully  read:    for  we  are  persuaded 

the  nine  chapters  devoted  to  this  subject  are  espe-     that  he  will^rise  from  its  perusal  with  new  ideas, 

ill      


cially  so,  and  we  know  of  no  more  valuable  mono- 
graph upon  the  symptoms,  prognosis,  and  manage- 
ment of  these  annoying  maladies  than  is  constituted 
by  this  part  of  the  work.  We  cannot  but  regard  it  as 
one  of  the  most  original  and  most  practical  works  of 


which  will  iWlnct  him  into  a  more  rational  practice 
in  regard  to  many  a  suffering  female  who  may  have 
placed  her  health  in  his  hands.— .Br#i*ft  American 
Journal,  Feb.  ISGl. 


l^EST  {CHARLES),  M.D. 


LECTURES  ON  THE  DISEASES  OF  WOMEN.    Third  American, 

from  the  Third  London  edition.     In  one  neat  octavo  volume  of  about  550  pages,  extra 
cloth.     $3  75;  leather,  $4  75.     {Now  Ready.) 
The  reputation  which  this  volume  has  acquired  as  a  standard  book  of  reference  in  its  depart- 
ment, renders  it  only  necessary  to  say  that  the  present  edition  has  received  a  careful  revision  at 
the  hands  of  the  author,  resulting  in  a  considerable  increase  of  size.     A  few  notices  of  previous 
editions  are  subjoined. 


The  manner  of  the  author  is  excellent,  his  descrip- 
tions graphic  and  perspicuous,  and  his  treatment  up 
to  the  level  of  the  time— clear,  precise,  definite,  and 
marked  by  strong  common  sense.  —  Chicago  Med. 
Journal,  Dec.  1861. 

We  cannot  too  highly  recommend  this,  the  second 
edition  of  Dr.  West  s  excellent  lectures  on  the  dis- 
eases uf  females.  We  know  of  no  other  book  on  this 
subject  from  which  we  have  derived  as  much  pleasure 
and  instruction.  Every  page  gives  evidence  of  tlie 
honest,  earnest,  and  diligent  searcher  after  truth.  He 
is  not  the  m«re  compiler  of  other  men's  ideas,  but  his 
lectures  are  the  result  often  years'  patient  investiga- 
tion in  one  of  the  widest  fields  for  women's  diseases — 
St.  Bartholomew's  Hospital.  As  a  teacher.  Dr.  West 
is  simple  and  earnest  in  his  language,  clear  and  com- 
prehensive in  hi^  perceptions,  and  logical  in  his  de- 
ductions.— Cinc^nati  Lancet,  Jan.  1862. 

We  have  thus  embodied,  in  this  series  of  lectures, 
one  of  the  most  valuable  treatises  on  the  diseases  of 
the  female  sexual  system  unconnected  with  gestation, 
in  our  language,aHd  one  which  cannot  fail,  from  the 
lucid  manner  in  which  the  various  subjects  have 
been  treated,  and  the  careful  discrimination  used  in 
dealing  only  with  facts,  to  recommend  the  volume  to 
the  careful  study  of  every  practitioner,  as  affording 
his  safest  guides  to  practice  within  our  knowledge. 
We  have  seldom  perused  a  work  of  a  more  thoroughly 
practical  character  than  the  one  before  us.  Every 
page  teems  with  the  most  truthful  and  accurate  infor- 
mation, and  we  certainly  do  not  know  of  any  other 
work  from  which  the  physician,  in  active  practice, 
can  more  readily  obtain  advice  of  the  soundest  cha- 
racter upon  the  peculiar  diseases  which  have  been 
made  the  subject  of  elucidation. — British  Am.  Med. 
Journal. 

T>T  THE  SAME  AUTHOR.  — 


We  return  the  author  our  grateful  thanks  fdr  the 
vast  amount  of  instruction  he  has  afforded  us.  His 
valuable  treatise  needs  no  eulogy  on  our  part.  His 
graphic  diction  and  truthful  pictures  of  disease  all 
speak  for  themselves. — Medico-Chirurg .  Review. 

Most  justly  esteemed  a  standard  work It 

bears  evidence  of  having  been  carefully  revised,  and 
is  well  worthy  of  the  fame  it  has  already  obtained, 
— Duh.  Med.  Quar.  Jour. 

As  a  writer.  Dr.  West  stands,  in  our  opinion,  se- 
cond only  to  Watson,  the  "Macaulay  of  Medicine;" 
he  possesses  that  happy  faculty  of  clothing  instruc- 
tion in  easy  garments;  combining  pleasure  with 
profit,  he  leads  his  pupils,  in  spite  of  the  ancient  pro- 
verb, along  a  royal  road  to  learning.  His  work  is  one 
which  will  not  satisfy  the  extreme  on  either  side,  but 
it  is  one  that  will  please  the  great  majority  who  are 
seeking  truth,  and  one  that  will  convince  the  student 
that  he  has  committed  himself  to  a  candid,  safe,  and 
valuable  guide. — N.  A.  Med. -Chii-urg  Review. 

We  must  now  conclude  this  hastily  written  sketch, 
with  the  confident  assurance  to  our  readers  that  the 
work  will  well  repay  perusal.  The  conscientious, 
painstaking,  practical  physician  is  apparent  on  every 
page. — .A^.  Y.  Journal  of  Medicine. 

We  have  to  say  of  it,  briefiy  and  decidedly,  that  it 
is  the  best  work  on  the  subject  in  any  language,  and 
that  it  stamps  Dr.  West  as  the  facile  princeps  of 
British  obstetric  authors. — Edinburgh  Med.  Journal. 

We  gladly  recommend  his  lectures  as  in  the  highest 
degree  instructive  to  all  who  are  interested  in  ob- 
stetric practice. — London.  Lancet. 

We  know  of  no  treatise  of  the  kind  so  complete, 
and  yet  so  compact. — Chicago  Med.  Journal. 


AN  ENQUIRY  INTO  THE  PATHOLOGICAL  IMPORTANCE!  OF 

ULCERATION  OF  THE  OS  UTERI.     In  one  neat  octavo  volume,  extra  cloth.     $1  25. 


s 


IMPSON  {SIR  JAMES  F.),  M.D. 

CLINICAL  LECTURES  ON  THE  DISEASES  OF  WOMEN.    With 

numerous  illustrations.  In  one  octavo  volume  of  over  500  pages.    Second  edition,  preparing. 
'DENNET  {HENRY),  M.D. 

A   PRACTICAL    TREATISE    ON    INFLAMMATION    OF    THE 

UTERUS,  ITS  CERVIX  AND  APPENDAGES,  and  on  its  connection  with  Uterine  Dis- 
ease.  Sixth  American,  from  the  fourth  and  revised  English  edition.    In  one  octavo  volume 
of  about  500  pages,  extra  cloth.     $3  75.     {Recently  Issued.) 
From  the  Author'' s  Preface. 
During  the  past  t'wo  years,  this  revision  of  former  labors  has  been  my  principal  occupation,  and 
in  its  present  state  the  work  may  be  con.sidered  to  embody  the  matured  experience  of  the  many 
years  I  have  devoted  to  the  study  of  uterine  disease. 

Indeed,  the  entire  volume  is  so  replete  with  infor- 
mation, to  all  appearance  so  perfect  in  its  details,  that 
we  could  scarcely  have  thought  another  page  or  para- 
graph was  required  for  the  full  description  of  all  that 
is  now  known  with  regard  to  the  diseases  under  con- 
sideration if  we  had  not  been  so  informed  by  the  au- 


thor. To  speak  of  it  except  in  terms  of  the  highe.st 
approval  would  be  impossible,  and  we  .gladly  avail 
ourselves  of  the  present  opportunity  to  recommend 
it  in  the  most  un<i'ialiQed  manner  to  the  profession. 
—Dublin  Med.  Press. 


24 


Henry  C.  Lea's  Publications — {Midwifery). 


JJODGE  {HUGH  L.),  31.  D., 

Late  Professor  of  Midwifery,  &c. 


the  University  of  Pennsylvania,  &c. 


THE  PRINCIPLES  AND  PRACTICE  OF  OBSTETRICS.  Illus- 
trated with  large  lithographic  plates  containing  one  hundred  and  fifty-nine  figures  from 
original  photographs,  and  with  numerous  wood-cuts.  In  one  large  and  beautifully  printed 
quarto  volume  of  550  double-columned  pages,  strongly  bound  in  extra  cloth,  $14.  {Lately 
published. )  ^ 


The  work  of  Dr.  Hodge  is  something  more  than  a 
simple  presentation  of  his  particular  views  in  tlie  de- 
partment of  Obstetrics;  it  is  something  more  than  an 
ordinary  treatise  on  midwifery  ;  it  is,  in  fact,  a  cyclo- 
pjedia  of  midwifery.  He  has  aimed  to  embody  in  a 
single  volume  the  whole  science  and  art  of  Obstetrics. 
An  elaborate  text  is  combined  with  accurate  and  va- 
ried pictorial  illustrations,  so  that  no  fact  or  principle 
is  left  unstated  or  unexplained. — Am.  Med.  Tirn.es, 
Sept.  3,  1S64. 

We  should  like  to  analyze  the  remainder  of  this 
excellent  work,  but  already  has  thi.s  review  extended 
beyond  our  limited  space.  We  cannot  conclude  this 
notice  without  referring  to  the  excellent  finish  of  the 
work.  In  typography  it  is  not  to  be  excelled ;  the 
paper  is  superior  to  what  is  usually  afi'orded  by  our 
American  cousins,  quite  equal  to  the  best  of  English 
books.  The  engravings  and  lithographs  are  most 
beautifully  executed.  The  work  recommends  itself 
for  its  originality,  and  is  in  every  way  a  most  valu- 
able addition  to  those  on  the  subject  of  obstetrics. — 
Canada  Med.  Journal,  Oct.  1864. 

It  is  very  large,  profusely  and  elegantly  illustrated, 
and  is  fitted  to  take  its  place  near  the  works  of  great 
obstetricians.  Of  the  American  works  on  the  subject 
it  is  decidedly  the  best. — Edinb.  Med.  Jour.,  Dec.  *64. 

***  Specimens  of  the  plates  and  letter-press  will  be  forwarded  to  any  address,  free  by  mail, 
on  receipt  of  six  cents  in  postage  stamps. 


We  have  examined  Professor  Hodge's  work  with 
great  satisfaction ;  every  topic  is  elaborated  most 
fully.  The  views  of  the  author  are  comprehensive, 
and  concisely  stated.  The  rules  of  practice  are  judi- 
cious, and  will  enable  the  practitioner  to  meet  every 
emergency  of  obstetric  complication  with  confidence. 
— Chicago  Med.  Journal,  Aug.  186-4. 

More  time  than  we  have  had  at  our  disposal  8hic« 
we  received  the  great  work  of  Dr.  Hodge  is  necessary 
to  do  it  justice.  It  is  undoubtedly  by  far  the  most 
original,  complete,  and  carefully  composed  treatise 
on  the  principles  and  pi*actice  of  Obstetrics  which  has 
ever  been  issued  from  the  American  press. — Pacific 
Med.  and  Surg.  Journal,  July,  1S64. 

We  have  read  Dr.  Hodge's  book  with  great  ple^ 
sure,  and  have  much  satisfaction  in  expressing  our 
commendation  of  it  as  a  whole.  It  is  certainly  highly 
instructive,  and  in  the  main,  we  believe,  correct.  The 
great  attention  which  the  author  has  devoted  to  tha 
mechanism  of  parturition,  taken  along  with  the  con- 
clusions at  which  he  has  arrived,  point,  we  think, 
conclusively  to  the  fact  that,  in  Britain  at  least,  the 
doctrines  of  Naegele  have  been  too  blindly  received. 
— Glasgow  Med.  Journal,  Oct.  1864. 


JfANNER  [THOMAS  H),  M.  D., 


ON  THE  SIGNS  AND  DISEASES  OF  PREGNANCY.     Vmt  American 

from  the  Second  and'Enlarged  English  Edition.     With  four  colored  plates  and  illustrations 
on  wood.     In  one  handsome  octavo  volume  of  about  600  pages,  extra  cloth,  $4  25.      {Now 
Heady.) 
The  reputation  of  Dr.  Tanner  as  a  correct  observer  and  skilful  teacher  is  so  widely  known  that 
anything  from  his  pen  necessarily  commands  the  attention  of  the  profession.     The  present  work 
is  one  to  which  he  has  devoted  especial  attention  in  the  hope  of  rendering  it  a  useful  guide  to 
practitioners  in  the  important  subjects  of  which  it  treats.     In  the  systematic  treatises  on  obstet- 
rics and  the  diseases  of  females  so  little  space  is  usually  accorded  to  the  disorders  and  aflfections  of 
the  gravid  state  that  a  treatise  devoted  to  them  exclusively  would  seem  to  be  a  necessary  addition 
to  the  library  of  every  working  practitioner.     The  scope  of  the  work  may  be  judged  from  the 
subjoined  condensed 

SUMMARY  OF  CONTENTS. 
Chapter  I.  General  Observations  on  the  State  of  Pregnancy.— II.  The  Signs  and  Symptoms  of  Pregnancy. 
— III.  The  Diseases  which  Simulate  Pregnancy. — IV.  The  Duration  of  Pregnancy. — V.  The  Premature  Ex- 
pulsion of  the  Foetus. —  VI.  The  Examination  of  Substances  Expelled  from  the  Uterus,  &c.  — VII.  Extra- 
Uterine  Gestation — VIII.  Superfoitation— Missed  Labor.  —  IX.  The  Diseases  which  may  coexist  with  Preg- 
nancy and  their  Reciprocal  Influence. — X.  The  Sympathetic  Disorders  of  Pregnancy.  —  XI.  The  Diseases  of 
the  Urinary  and  Generative  Organs. — XII.  The  Displacements  of  the  Gravid  Uterus. 


lj^0NTG03IERY  [W.  F.),  M.  D., 

Professor  of  Midwifery  in  the  King's  and  Queen's  College  of  Physicians  in  Ireland. 

AN  EXPOSITION  OF  THE  SIGNS  AND  SYMPTOMS  OF  PREG- 

NANCY.  With  some  other  Papers  on  Subjects  connected  with  Midwifery.  From  the  second 
and  enlarged  English  edition.  With  two  exquisite  colored  plates,  and  numerous  wood-cuta. 
In  one  very  handsome  octavo  volume  of  nearly  600  pages,  extra  cloth.     $3  75. 


M 


ILLER  [HENRY),  M.D., 

Professor  of  Obstetrics  and  Diseases  of  Women  and  Children  in  the  University  of  Louisville. 

PRINCIPLES  AND  PRACTICE  OF  OBSTETRICS,  &c.;  incliidmg 

the  Treatment  of  Chronic  Inflammation  of  the  Cervix  and  Body  of  the  Uterus  considered 
as  a  frequent  cause  of  Abortion.  With  about  one  hundred  illustrations  on  wood.  In  ond 
very  handsome  octavo  volume  of  over  600  pages,  extra  cloth.     $3  75. 


EIGBT'S  SYSTEM  OP  MIDWIFERY.  With  Notes 
and  Additional  Illustrations.  Second  American 
editioa.  One  volume  octavo,  extra  cloth,  422  pages. 
$2  50. 


DEWEES'S  COMPREHENSIVE  SYSTEM  OF  MIIV 
WIFERY.  Twelfth  edition,  with  the  author's  last 
improvements  and  corrections.  In  one  octavo  vol- 
ume, extra  cloth,  of  600  pages.    $3  50. 


Henry  C.  Lea's  Publications — {Midwifery). 


25 


lifEIGS  {CHARLES  D.),  M.D., 

-*^"  Lately  Professor  of  Obstetrics,  &c  ,  in  the  Jefferson  Medical  College,  Philadelphia. 

OBSTETRICS:   THE   SCIENCE   AND   THE   ART.     Fifth  edition, 

revised.     With  one  hundred  and  thirty  illustrations.     In  one  beautifully  printed  octavo 
volume  of  760  large  pages.     Extra  cloth,  $5  50;  leather,  $6  50.      {Now  ready.) 
The  original  edition  is  already  so  extensively  and 
favorably  known  to  the  profession  that  no   recom- 
mendation is  necessary;  it  is  sufficient  to  say,  the 


present  edition  is  very  much  extended,  improved, 
and  perfected.  Whilst  the  great  practical  talents  and 
unlimited  experience  of  the  author  render  it  a  most 
valuable  acquisition  to  the  practitioner,  it  is  so  con- 
densed as  to  constitute  a  most  eligible  and  excellent 
text-book  for  the  student.— /Sow</ier?i  Med.  and  Surg. 
Journal,  July,  1S67. 

It  is  to  the  student  that  our  author  has  more  par- 
ticularly addressed  himself;  but  to  the  practitioner 
we  believe  it  would  be  equally  serviceable  as  a  book 
of  reference.  No  work  that  we  have  met  with  so 
thoroughly  details  everything  that  falls  to  the  lot  of 
tlie  accoucheur  to  perform.  Every  detail,  no  matter 
how  minute  or  how  trivial,  has  found  a  place, — 
Canada  Medical  Journal,  July,  1867. 

This  very  excellent  work  on  the  science  and  art  of 
obstetrics  should  be  in  the  hands  of  every  student  and 


practitioner.  The  rapidity  with  which  the  very  large 
editions  have  been  exhausted  is  the  best  test  of  its 
true  merit  Besides,  it  is  the  production  of  an  Ame- 
rican who  has  probably  had  more  experience  in  this 
branch  than  any  other  living  practitioner  of  the  coun- 
try.— St.  Louis  Med.  and  Surg.  Journal,  Sept.  1867. 

He  has  also  carefully  endeavored  to  be  minute  and 
clear  in  his  details,  with  as  little  reiteration  as  possi- 
ble, and  beautifully  combines  the  relations  of  science 
to  art,  as  far  as  the  different  classifications  will  admit. 
— Detroit  Review  of  Med  and  Pharm.,  Aug.  1867. 

We  now  take  leave  of  Dr.  Meigs.  There  are  many 
other  and  interesting  points  in  his  book  on  which  we 
would  fain  dwell,  but  are  constrained  to  bring  our  ob- 
servations to  a  close.  We  again  heartily  express  our 
approbation  of  the  labors  of  Dr.  Meigs,  extending  over 
many  years,  and  culminating  in  the  work  before  us, 
full  of  practical  hints  for  the  inexperienced,  and  even 
for  those  whose  experience  has  been  considerable. — 
Glasgow  Medical  Journal,  Sept.  1867. 


J^AMSBOTHAM  {FRANCIS  ff.),  M.D. 


THE    PRINCIPLES   AND    PRACTICE    OF    OBSTETRIC    MEDI- 

CINE  AND  SURGERY,  in  reference  to  the  Process  of  Parturition.  A  new  and  enlarged 
edition,  thoroughly  revised  by  the  author.  With  additions  by  W.  V.  Keating,  M.  D., 
Professor  of  Obstetrics,  Ac,  in  the  Jeiferson  Medical  College,  Philadelphia.  In  one  large 
and  handsome  imperial  octavo  volume  of  650  pages,  strongly  bound  in  leather,  with  raised 
bands ;  with  sixty-four  beautiful  plates,  and  numerous  wood-cuts  in  the  text,  containing  in 
all  nearly  200  large  and  beautiful  figures.     $7  00. 

To  the  physician's  library  it  is  indispensable,  while 
to  the  student,  as  a  text-book,  from  which  to  extract 
the  material  for  laying  the  foundation  of  an  education 
on  obstetrical  science,  it  has  no  superior. — Ohio  Med. 
a.nd  Surg.  Journal. 

When  we  call  to  mind  the  toil  we  underwent  in 
acquiring  a  knowledge  of  this  subject,  we  cannot  but 
envy  the  student  of  the  present  day  the  aid  which 
this  work  will  afford  him. — Am.  Jour,  of  the  Med. 
Sciences. 


We  will  only  add  that  the  student  will  learn  from 
it  all  he  need  to  know,  and  the  practitioner  will  find 
It,  as  a  book  of  reference,  surpassed  by  none  other. — 
Stethoscope. 

The  character  and  merits  of  Dr.  Ramsbotham's 
work  are  so  well  known  and  thoroughly  established, 
that  comment  is  unnecessary  and  praise  superfluous. 
The  illustrations,  which  are  numerous  and  accurate, 
are  executed  in  the  highest  style  of  art.  We  cannot 
too  highly  recommend  the  work  to  our  readers. — St. 
Louis  Med.  and  Surg.  Journal. 


QHURCfflLL  {FLEETWOOD),  M. D.,  M.  R. L  A. 
ON  THE  THEORY  AND  PRACTICE  OF  MIDWIFERY.     A  new 

American  from  the  fourth  revised  and  enlarged  London  edition.     With  notes  and  additions 
by  D.  Francis  Condie,  M.  D.,  author  of  a  "Practical  Treatise  on  the  Diseases  of  Chil- 
dren,'' &c.     With  one  hundred  and  ninety- four  illustrations.     In  one  very  handsome  octavo 
volume  of  nearly  700  large  pages.     Extra  cloth,  $4  00;  leather,  $5  00, 
In  adapting  this  standard  favorite  to  the  wants  of  the  profession  in  the  United  States,  the  editor 
has  endeavored  to  insert  everything  that  his  experience  has  shown  him  would  be  desirable  for  the 
American  student,  including  a  large  number  of  illustrations.     With  the  sanction  of  the  author, 
he  has  added,  in  the  form  of  an  appendix,  some  chapters  from  a  little  "Manual  for  Midwives  and 
Nurses,"  recently  issued  by  Dr.  Churchill,  believing  that  the  details  there  presented  can  hardly 
fail  to  prove  of  advantage  to  the  junior  practitioner.     The  result  of  all  these  additions  is  that  the 
work  now  contains  fully  one-half  more  matter  than  the  last  American  edition,  with  nearly  one- 
half  more  illustrations ;  so  that,  notwithstanding  the  use  of  a  smaller  type,  the  volume  contains 
almost  two  hundred  pages  more  than  before. 


These  additions  render  the  work  still  more  com- 
plete and  acceptable  than  ever;  and  with  the  excel- 
lent style  in  wliich  the  publishers  have  presented 
this  edition  of  Churchill,  we  can  commend  it  to  the 
profession  with  great  cordiality  and  pleasure.— Cm- 
cinnati  Lancet. 

Few  works  on  this  branch  of  medical  science  are 
equal  to  it,  certainly  none  excel  it,  whether  in  regard 
to  theory  or  practice,  and  in  one  respect  it  is  superior 
to  all  others,  viz.,  in  its  statistical  information,  and 
therefore,  on  these  grounds  a  most  valuable  work  for 
the  physician,  student,  or  lecturer,  all  of  whom  will 
find  in  it  the  information  which  they  are  seeking. — 
Ba'it.  Am.  Journal. 

The  present  treatise  is  very  much  enlarged  and 
amplified  beyond  the  previous  editions  but  nothing 


has  been  added  which  conld  be  well  dispensed  with. 
An  examination  of  the  table  of  contents  shows  how 
thoroughly  the  author  has  gone  over  the  ground,  and 
the  care  he  has  taken  in  the  text  to  present  the  sub- 
jects in  all  their  bearings,  will  render  this  new  edition 
even  more  necessary  to  the  obstetric  student  than 
were  either  of  the  former  editions  at  the  date  of  their 
appearance.  No  treatise  on  obstetrics  with  which  we 
are  acquainted  can  compare  favorably  with  this,  in 
respect  to  the  amount  of  material  which  has  been 
gathered  from  every  source. — Boston  Mtd.  and  Surg. 
Journal. 

There  is  no  better  text-book  for  students,  or  work 
of  reference  and  study  for  the  practising  physician 
than  this.  It  should  adorn  and  enrich  every  medical 
library. — Chicago  Med.  Journal. 


26 


Henry  C.  Lea's  Publiications — {Surgery). 


QROSS  {SAMUEL  D.),  31. D., 

Professor  of  Surgery  in  the  Jefferson  Medical  College  of  Philadelphia. 

A  SYSTEM  OF  SURGERY:    Pathologiccal,  Diagnostic,  Therapeutic, 

and  Operative.    Illustrated  by  upwards  of  Thirteen  Hundred  Engravings.    Fourth  edition, 
carefully  revised,  and  improved.    In  two  large  and  beautifully  printed  royal  octavo  volumes 
of  2200  pages,  strongly  bound  in  leather,  with  raised  bands.     $15  00. 
The  continued  favor,  shown  by  the  exhaustion  of  successive  large  editions  of  this  great  work, 
proves  that  it  has  successfully  supplied  a  want  felt  by  American  practitioners  and  students.    Though 
but  little  over  six  years  have  elapsed  since  its  first  publication,  it  has  already  reached  its  fourth 
edition,  while  the  care  of  the  author  in  its  revision  and  correction  has  kept  it  in  a  constantly  im- 
proved shape.     By  the  use  of  a  close,  though  very  legible  type,   an  unusually  large  amount  of 
matter  is  condensed  in  its  pages,  the  two  volumes  containing  as  much  as  four  or  five  ordinary 
octavos.     This,  combined  with  the  most  careful  mechanical  execution,  and  its  very  durable  binding, 
renders  it  one  of  the  cheapest  works  accessible  to  the  profession.     Every  subject  properly  belonging 
to  the  domain  of  surgery  is  treated  in  detail,  so  that  the  student  who  possesses  this  work  may  be 
said  to  have  in  it  a  surgical  library. 


It  must  long  remain  the  most  comprehensive  work 
on  this  important  part  of  medicine. — Boston  Medical 
and  Surgical  Journal,  March  23,  1S65. 

We  have  compared  it  with  most  of  our  standard 
■works,  such  as  those  of  Erichsen,  Miller,  Fergusson, 
Syme,  and  others,  and  we  must,  in  justice  to  our 
aiithor,  award  it  the  pre-eminence.  As  a  work,  com- 
plete in  almost  every  detail,  no  matter  how  minute 
or  trifling,  and  embracing  every  subject  known  in 
the  principles  and  practice  of  surgery,  we  believe  it 
stands  without  a  rival.  Dr.  Gross,  in  his  preface,  re- 
marks "ray  aim  has  been  to  embrace  the  whole  do- 
main of  surgery,  and  to  allot  to  every  subject  its 
legitimate  claim  to  notice ;"  and,  we  assure  our 
readers,  he  has  kept  his  word.  It  is  a  work  which 
we  can  most  confidently  recommend  to  our  brethren, 
for  its  utility  is  becoming  the  more  evident  the  longer 
it  is  upon  the  shelves  of  our  library. — Canada  Med. 
Journal,  September,  lS6o. 

The  first  t^o  editions  of  Professor  Gross'  System  of 
Surgery  are  so  well  known  to  the  profession,  and  so 
highly  prized,  that  it  would  be  idle  for  us  to  speak  in 
praise  of  this  work. —  Chicago  Medical  Journal, 
September,  1S65. 

We  gladly  indorse  the  favorable  recommendation 
of  the  work,  both  as  regards  matter  and  style,  which 
we  made  when  noticing  its  first  appearance. — British 


tioner  shall  not  seek  in  vain  for  what  they  desiue.— 
San  Francisco  Med.  Press,  Jan.  1S6.5. 

Open  it  where  we  may,  we  find  sound  practical  in- 
formation conveyed  in  plain  language.  This  book  is 
no  mere  provincial  or  even  national  system  of  sur- 
gery, but  a  work  which,  while  very  largely  indebted 
to  the  past,  has  a  strong  claim  on  the  graiiiude  of  the 
future  of  surgical  science.— Edinburgh  Med.  Journal, 
Jan.  1S65. 

A  glance  at  the  work  is  sufficient  to  show  that  the 
author  and  publisher  have  spared  no  labor  in  making 
it  the  most  complete  "System  of  Surgery"  ever  pub- 
lished in  any  country— 5^  Louis  Med.  and  Surg. 
Journal,  April,  186.5. 

The  third  opportunity  is  now  ofiered  during  our 
editorial  life  to  review,  or  rather  to  indorse  and  re- 
commend this  great  American  work  on  Surgery. 
Upon  this  last  edition  a  great  amount  of  labor  has 
been  expended,  though  to  all  others  except  the  author 
the  work  was  regarded  in  its  previous  editions  as  so 
full  and  complete  as  to  be  hardly  capable  of  improve- 
ment. Every  chapter  has  been  revised  ;  the  text  aug- 
mented by  nearly  two  hundred  pages,  and  a  con 
siderable  number  of  wood-cuts  have  been  introduced. 
Many  portions  have  been  entirely  re-written,  and  the 
additions  made  to  the  text  are  principally  of  a  prac 
tical  character.      This  comprehensive  treatise  upon 


and  Foreign  Medico-Chirurgical  Review,  Oct.  1865.     |  surgery  has  undergone  revisions  and  enlargements. 


The  most  complete  work  that  has  yet  issued  from 
the  press  on  the  science  and  practice  of  surgery. — 
London  Lancet. 

This  system  of  surgery  Is,  we  predict,  destined  to 
take  a  commanding  position  in  our  surgical  litera- 
ture, and  be  the  crowning  glory  of  the  author's  well 
earned  fame.  As  an  authority  on  general  surgical 
subjects,  this  work  is  long  to  occupy  a  pre-eminent 
place,  not  only  at  home,  but  abroad.  We  have  no 
hesitation  in  pronouncing  it  without  a  rival  in  our 
language,  a«d  ♦qual  to  the  best  systems  of  surgery  in 
any  language. — N.  Y.  Med.  Journal. 

Not  only  by  far  the  best  text-book  on  the  subject, 
as  a  whole,  within  the  reach  of  American  students, 
hut  one  which  will  be  much  more  than  ever  likely 
to  be  resorted  to  and  regarded  as  a  high  authority 
abroad. — Am.  Journal  Med.  Sciences,  Jan.  186.). 

The  work  contains  everything,  minor  and  major, 
operative  and  diagnostic,  inclndiag  mensuration  and 
examination,  venereal  diseases,  and  uterine  manipu- 
lations and  operations.  It  is  a  complete  Thesaurus 
of  modern  surgery,  where  the  student  and  piacti- 


keeping  pace  with  the  progress  of  the  art  and  science 
of  surgery,  so  that  whoever  is  in  possession  of  this 
work  may  consult  its  pages  upon  any  topic  embraced 
within  the  scope  of  its  department,  and  rest  satisfied 
that  its  teaching  is  fully  up  to  the  present  standard 
of  surgical  knowledge.  It  is  also  so  comprehensive 
that  it  may  truthfully  be  said  to  embrace  all  that  is 
actually  known,  that  is  really  of  any  value  in  the 
diagnosis  and  treatment  of  surgical  diseases  and  acci- 
dents. Wherever  illustration  will  add  clearness  to  the 
subject,  or  make  better  or  more  lasting  impression,  it 
is  not  wanting;  in  this  respect  the  work  is  eminently 
superior. — Buffalo  Med.  Journal,  Dec.  1864. 

A  system  of  surgery  which  we  think  unrivalled  in 
our  language,  and  which  will  indelibly  associate  his 
name  with  surgical  science.  And  what,  in  our  opin- 
ion, enhances  the  value  of  the  work  is  that,  while  the 
practising  surgeon  will  find  all  that  he  requires  in  it, 
it  is  at  the  same  time  one  of  the  most  valuable  trea- 
tises which  can  be  put  into  the  hands  of  the  studeut 
seeking  to  know  the  principles  and  practice  of  this 
branch  of-  the  profession  which  he  designs  subse- 
quently to  follow.— T/ie  Brit.  Am.  Journ.,  Montreal. 


jyT  THE  SAME  AUTHOR.  

A   PRACTICAL    TREATISE    OX   THE    DISEASES,   INJURIES, 

AND  MALFORMATIONS  OF  THE  URINARY  BLADDER,  THE  PROSTATE  GLAND, 
AND  THE  URETHRA.     Second  edition,  revised  and  much  enlarged,  with  one  hundred 
and  eighty-four  illustrations.    In  one  large  and  very  handsome  octavo  volume,  of  over  nine 
hundred  pages,  extra  cloth.     $4  00. 
Whoever  will  peruse  the  vast  amount  of  valuable  I  guage  which  can  make  any  just  pretensions  to  he  it« 

practical  information  it  contains  will,  we  think,  agree    equal. — N.  Y.  Journal  of  Medicine. 

with  us,  that  there  is  no  work  in  the  English  Ian-  | 

DY  THE  SAME  AUTHOR.  

A   PRACTICAL    TREATISE    ON    FOREIGN    BODIES   IN   THE 

AIR-PASSAGES.       In   one  handsome  octavo  volume,   extra  cloth,   with  illustrations, 
pp.  468.     $2  75. 


Henry  C.  Lea's  Publications — (Surgery), 


21 


PRICHSEN  {JOHN), 

J-^  Professor  of  Surgery  in  University  College,  London. 

THE  SCIENCE  AXD  ART  OF  SURGERY;  being  a  Treatise  on  Sur- 

gical  Injuries,  Diseases,  and  Operations.  New  and  improved  American,  from  the  Second 
enlarged  and  carefully  revised  London  edition.  Illustrated  with  over  four  hundred  wood 
engravings.  In  one  large  and  handsome  octavo  volume  of  1000  closely  printed  pages;  extra 
cloth,  $6;  leather,  raised  bands,  $7. 

We  are  bound  to  state,  and  we  do  so  without  wish-  as  one  of  the  very  best,  if  not  the  best  text-book  of 
ing  to  draw  invidious  comparisons,  that  the  work  of  surgery  with  which  we  were  acquainted,  permits  us 
Mr.  Erichsen,  in  most  respects,  surpasses  any  that  to  give  it  but  a  passing  notice  totally  unworthy  of  its 
has  preceded  it.  Mr.  Erichsen's  is  a  practical  work,  merits.  It  may  be  confidently  asserted,  that  no  work 
combining  a  due  proportion  of  the  "Science  and  Art  on  the  science  and  art  of  surgery  has  ever  received 
of  Surgery."  Having  derived  no  little  instruction  more  universal  commendation  or  occupied  a  higher 
from  it,  in  many  important  branches  of  surgery,  we  position  as  a  general  text-book  on  surgery,  than  this 
can  have  no  hesitation  in  recommending  it  as  a  valu-  treati!=e  of  Professor  Erichsen. — Savannah  Journal  of 
able  book  alike  to  the  practitioner  and  the  student.  Medicine. 
-^Dublin  Quarterly.  j      Jq  fulness  of  practical  detail  and  perspicuity  of 

Gives  a  very  admirable  practical  view  of  the  sci-  style,  convenience  of  arrangement  and  soundness  of 
ence  and  art  of  surgery. — Edinburgh  Med.  and  Surg,  discrimination,  as  well  as  fairness  and  completeness 
Jcnirnal.  i  of  discussion,  it  is  better  suited  fo  the  wants  of  both 

We  recommend  it  as  the  best  compendium  of  sur-  !  student  and  practitioner  than  any  of  its  predecessors, 
gery  in  our  language. -ion^o«  Lancet.  -^"^-  'Journal  of  Med.  Sciences. 

It  is,  we  think,  the  most  valuable  practical  work  I  ^fter  careful  and  frequent  perusals  of  Erichsen's 
on  surgery  in  existence,  both  for  young  and  old  prac-  ^^}'^Sevy,we^^e  at  a  loss  tul  y  to  express  our  admira- 
titioners.-iVa.57m«e  Med.  and  Surg.  Journal.  t^«^  «f  '^-    Jhe  author's  style  is  enainently  didactic, 

"  and  characterized  by  a  most  admirable  directness, 


The  limited  time  we  have  to  review  this  improved    clearness,  and  compactness. — Ohio  Med.  and  Surg. 
edition  of  a  work,  the  first  issue  of  which  we  prized    Journal. 


jyY  THE  SAME  AUTHOR.     (Ready  in  June.) 

ON    RAILWAY,    AND    OTHER    INJURIES   OF    THE    NERA^OUS 

SYSTEM.     In  small  octavo  volume.     Extra  cloth,  $1  00. 


We  welcome  this  as  perhaps  the  most  practically 
useful  treatise  written  for  many  a  day. — Sledical 
Times. 

It  will  serve  as  a  most  useful  and  trustworthy  guide 


to  the  profession  in  general,  many  of  whom  may  be 
consulted  in  snch  cases;  and  it  will,  no  doubt,  take 
its  place  as  a  text-book  on  the  subject  of  which  it 
treats. — Medical  Press. 


JlflLLER  {JA3IES), 

-^Kl.  Late  Professor  of  Surgery  in  the  University  of  Edinburgh,  &c. 

PRINCIPLES  OF  SURGERY.     Fourth  American,  from  the  third  and 

revised  Edinburgh  edition.     In  one  large  and  very  beautiful  volume  of  700  pages,  with 
two  hundred  and  forty  illustrations  on  wood,  extra  cloth.     $3  75. 


B 


T  THE  SAME  AUTHOR.  

THE   PRACTICE   OF   SURGERY.    Fourth  American,  from  the  last 

Edinburgh  edition.     Revised  by  the  American  editor.     Illustrated  by  three  hundred  and 

sixty-four  engravings  on  wood.     In  one  large  octavo  volume  of  nearly  700  pages,  extra 

cloth.     $3  75. 

It  is  seldom  that  two  volumes  have  ever  made  so  I  acquired.    The  author  is  an  eminently  sensible,  prac- 

profound  an  impression   in  so   short  a  time   as  the  |  tical,  and  well-informed  man,  who   knows  exactly 

"Principles"  and  the  "Practice"  of  Surgery  by  Mr.     what  he  is  talking  about  and  exactly  how  to  talk  it. — 

Miller,  or  so  richly  merited  the  reputation  they  have  |  Kentuclcy  Medical  Recorder. 


piRRTE  ( WILLIAM),  F.  R.  S.  E., 

-*-  Professor  of  Surgery  in  the  University  of  Aberdeen. 

THE  PRINCIPLES  AND  PRACTICE  OF  SURGERY.     Edited  by 

John  Neill,  M.  D.,  Professor  of  Surgery  in  the  Penna.  Medical  College,  Surgeon  to  the 
Pennsylvania  Hospital,  <fec.  In  one  very  handsome  octavo  volume  of  780  pages,  with  316 
illustrations,  extra  cloth.     $3  75. 


^ARGENT  [F.  W.),  M.D. 


ON  BANDAGING  AND  OTHER  OPERATIONS  OF  MINOR  SUR- 

GERY.    New  edition,  with  an  additional  chapter  on  Military  Surgery.    One  handsome  royal 
12mo.  volume,  of  nearly  400  pages,  with  184  wood-cuts      Extra  cloth,  $1  76. 

We  cordially  commend  this  volume  as  one  which 
the  medical  student  should  most  closely  study ;  and 
to  the  surgeon  in  practice  it  must  prove  itself  instruct- 
ive on  many  points  which  he  may  have  forgotten. — 
Brit.  Am.  Journal,  May.  1862. 


Exceedingly  convenient  and  valuable  to  all  mem- 
bers of  the  prot'essiou.— Chicago  Medical  Examiner, 
May,  1862. 

The  very  best  manual  of  Minor  Surgery  we  have 
Been. — Buffalo  Medical  Journal. 


MALGAIGNE'S  OPERATIVE  SURGERY.  With  nu- 
merous illustrations  on  wood.  In  one  handsome 
octavo  volume,  extra  cloth,  of  nearly  600  pp.    $2  50. 


SKEY'S  OPERATIVE  SURGERY.  In  one  very  hand- 
some octavo  volume,  extra  cloth,  of  over  650  pagee, 
with  about  100  wood-cats.    $3  25. 


28 


•  Henry  C.  Lea's  Publications — {Surgery). 


JJRUITT  {ROBERT),  M.R.  C.S.,  Sfc 


THE  PRINCIPLES  AND   PRACTICE  OF  MODERN  SURGERY. 

A  new  and  revised  American,  from  the  eighth  enlarged  and  improved  London  edition.  Illus- 
trated with  four  hundred  and  thirty -two  wood-engravings.  In  one  very  handsome  octavo 
volume,  of  nearly  700  large  and  closely  printed  pages.    Extra  cloth,  $4  00  ;  leather,  $5  00. 

Besides  the  careful  revision  of  the  author,  this  work  has  had  the  advantage  of  very  thorough 
editing  on  the  part  of  a  competent  surgeon  to  adapt  it  more  completely  to  the  wants  of  the  Ameri- 
can student  and  practitioner.  Many  illustrations  have  been  introduced,  and  every  care  has  been 
taken  to  render  the  mechanical  execution  unexceptionable.  At  the  very  low  price  affixed,  it  will 
therefore  be  found  one  of  the  most  attractive  and  useful  volumes  accessible  to  the  American 
practitioner. 

All  that  the  surgical  student  or  practitioner  could 
desire. — Dublin  Quarterly  Journal. 

It  is  a  most  admirable  book.  We  do  not  know 
when  we  have  examined  one  with  more  pleasure. — 
Boston  Med.  and  Surg.  Journal. 

In  Mr.  Druitt's  book,  though  containing  only  some 
seven  hundred  pages,  both  the  principles  and  the 
practice  of  surgery  are  treated,  and  so  clearly  and 
perspicuously,  as  to  elucidate  every  important  topic. 
The  fact  that  twelve  editions  have  already  been  called 


theoretical  surgical  opinions,  no  work  that  we  are  at 
present  acquainted  with  can  at  all  compare  with  it. 
It  is  a  compendium  of  sargical  theory  (if  we  may  use 
the  word)  and  practice  in  itself,  and  well  deserves 
the  estimate  placed  upon  it. — Brit.  Am.  Journal. 

Thus  enlarged  and  improved,  it  will  continue  to 
rank  among  our  best  text-books  on  elementary  sur- 
gery.— Coltimbun  Rev.  of  Med.  and  Surg. 

We  must  close  this  brief  notice  of  an  admirable 
work  by  recommending  it  to  the  earnest  attention  of 

for,  in  these  days  of  active  competition,  would  of    every  medical  student. — Charleston  Medical  Journal 

itself  show  it  to  possess  marked  superiority.    We    and  Review. 

have  examined  the  book  most  thoroughly,  and  can  ' 

say  that  this  success  is  well   merited.     His  book, 


moreover,  possesses  the  inestimable  advantages  of 
having  the  subjects  perfectly  well  arranged  and  clas- 
sified, and  of  being  written  in  a  style  at  once  clear 
and  succinct. — Am.  Journal  of  Med.  Sciences. 

Whether  we  view  Druitt's  Surgery  as  a  guide  to 
operative  procedures,  or  as  representing  the  latest 


A  text-book  which  the  general  voice  of  the  profes- 
sion in  both  England  and  America  has  commended  as 
one  of  the  most  admirable  "manuals,"  or,  "vade 
mecum"  as  its  English  title  runs,  which  can  be 
placed  in  the  hands  of  the  student.  The  merits  of 
Druitt's  Surgery  are  too  well  known  to  every  one  to 
need  any  further  eulogium  from  us. — Nashville  Med. 
Journal. 


TJAMILTON  [FRANK  n.l  M.D., 

Professor  of  Fractures  and  Dislocations,  &c.  in  BeJZevue  Hosp.  Med.  College,  New  York. 

A  PRACTICAL  TREATISE   ON   FRACTURES  AND   DISLOCA- 

TIONS.  Third  edition,  thoroughly  revised.  In  one  large  and  handsome  octavo  volume 
of  777  pages,  with  294  illustrations,  extra  cloth,  $5  75.  {Jttst  Issued.) 
The  demand  which  has  so  speedily  exhausted  two  large  editions  of  this  work  shows  that  the 
author  has  succeeded  in  supplying  a  want,  felt  by  the  profession  at  large,  of  an  exhaustive  treatise 
on  a  frequent  and  troublesome  class  of  accidents.  The  unanimous  voice  of  the  profession,  abroad 
as  well  as  at  home,  has  pronounced  it  the  most  complete  work  to  which  the  surgeon  can  refer  for 
information  respecting  all  details  of  the  subject.  In  the  preparation  of  this  new  edition,  the 
author  has  sedulously  endeavored  to  render  it  worthy  a  continuance  of  the  favor  which  has  been 
accorded  to  it,  and  the  experience  of  the  recent  war  has  aflforded  a  large  amount  of  material  which 
he  has  sought  to  turn  to  the  best  practical  account. 

In  fulness  of  detail,  simplicity  of  arrangement,  and    American  professor  of  surgery;  and  his  book  adds 


accuracy  of  description,  this  work  stands  unrivalled. 
So  far  as  we  know,  no  other  work  on  the  subject  in 
the  English  language  can  be  compared  with  it.  While 
congratulating  our  trans-Atlantic  brethren  on  the 
European  reputation  which  Dr.  Hamilton,  along  with 
many  other  American  surgeons,  ha.«  attained,  we  also 
may  be  proud  that,  in  the  mother  tongue,  a  cla8s^ical 
work  has  been  produced  which  need  not  fear  compa- 
rison with  the  standard  treatises  of  any  other  nation. 
— Edinburgh  Med.  Journal,  Dec.  IStitj. 

The  credit  of  giving  to  the  profession  the  only  com 
plete  practical  treatise  on  fractures  and  dislocations 
in  our  language  during  the  present  century,  belougs 


one  more  to  the  list  of  excellent  practical  works  which 
have  emanated  from  his  country,  notices  of  which 
have  appeared  from  time  to  time  in  our  columns  du- 
ring the  last  few  montiis.— London  Lancet,  Dec.  15, 
1S66. 

These  additions  make  the  work  much  more  valua- 
ble, and  it  must  be  accepted  as  the  most  complete 
monograph  on  the  subject,  certainly  in  our  own,  if 
not  even  in  any  other  language.— .dTnertcan  Journal 
Med.  Sciences,  Jan.  1867. 

This  is  the  most  complete  treatise  on  the  subject  in 
the  'E,nf(i\sh.\-An.s,\x?ige.—  Ranking' s  Abstract,  Jan.lS67. 

A  mirror  of  all  that  is  valuable  in  modern  surgery. 


to  the  author  of  the  work  before  us,  a  distinguished   Richmond  Med.  Journal,  Nov.  1S66, 


'DARWELL  [RICHARD),  F.R.C.S., 

"^  Assistant  Surgeon  Charing  Cross  Hospital,  &c. 

A  TREATISE  ON  DISEASES  OF  THE  JOINTS.    Illustrated  with 

engravings  on  wood.    In  one  very  handsome  octavo  volume  of  about  500  pages ;  extra  cloth, 
$3. 


BRODIE'S  CLINICAL  LECTURES  ON  SURGERY. 
1  vol.  8vo.,  350  pp.;  cloth,  $1  25. 

COORER  ON  THE  STRUCTURE  AND  DISEASES  OF 
THE  Testis,  aito  on  the  Thymus  Gland.  One  vol. 
imperial  8vo.,  extra  cloth,  with  177  figures  on  29 
plates.    $2  50. 


COOPER'S  LECTURES  ON  THE  PRINCIPLES  AND 
Practice  of  Surgery.  In  one  very  large  octav-o 
volume,  extra  cloth,  of  750  pages.     $2  00. 

GIBSON'S   INSTITUTES  AND  PRACTICE  OF  SUR- 

OERY.  Eighth  edition,  improved  and  altered.  With 
thirty-four  plates.  In  two  handsome  octavo  vol- 
umes, about  1000  pages,  leather,  raised  bands.  $6  50. 


29 


Henry  C.  Lea's  Publications — (Surgery). 
rpOYNBEE  {JOSEPH),  F.R.S., 

-*-  Aural  Surgeon  to  and  Lecturer  on  Surgery  at  St.  Mary^s  Hospital. 

THE  DISEASES  OF  THE  EAR:  their  Nature,  Diagnosis,  and  Treat- 

ment.     With  one  hundred  engravings  on  wood.     Second  American  edition.     In  one  very 
handsomely  printed  octavo  volume  of  440  pages ;  extra  cloth,  $4. 


The  appearance  of  a  volume  of  Mr.  Toynbee's,  there- 
fore, in  which  the  subject  of  aural  disease  is  treated 
in  the  most  scientific  manner,  and  our  knowledge  in 
respect  to  it  placed  fully  on  a  par  with  that  which 
we  possess  respecting  most  other  organs  of  the  body, 
is  a  matter  for  sincere  congratulation.  We  may  rea- 
sonably hope  that  henceforth  the  subject  of  this  trea- 
tise will  cease  to  be  among  the  opprobriu  of  medical 
science. — London  Medical  Review. 


The  work,  as  was  stated  at  the  outset  of  our  notice, 
is  a  model  of  its  kind,  and  every  page  and  paragraph 
of  it  are  worthy  of  the  most  thorough  study.  Con- 
sidered all  in  all — as  an  original  work,  well  written, 
philosophically  elaborated,  and  happily  illustrated 
with  cases  and  drawings— it  is  by  far  the  ablest  mo- 
nograph that  has  ever  appeared  on  the  anatomy  and 
diseases  of  the  ear,  and  one  of  the  most  valuable  con- 
tributions to  the  art  and  science  of  surgery  in  the 
nineteenth  century. — N.  Am.  Med.-Chirurg.  Semew. 


TA  URENCE  [JOHN Z.),  F.  R.  G. S.,    and      llfOON  [ROBERT  C.\ 

■^  Editor  of  the  Ophthalmic  Review,  &c.  ^^      -£f'^«*«  Surgeon  to  theSoidhwark  Oph- 

thalmic Hospital,  &c. 

A  HANDY-BOOK  OF   OPHTHALMIC   SURGERY,  for  the  use  of 

Practitioners.     With  numerous  illustrations.     In  one  very  handsome  octavo  volume,  extra 
cloth.     $2  50.     {Jttst  Isstted.) 


No  book  on  ophthalmic  surgery  was  more  needed. 
Designed,  as  it  is,  for  the  wants  of  the  busy  practi- 
tioner, it  is  the  neplus  ultra,  of  perfection.  It  epito- 
mizes all  the  diseases  incidental  to  the  eye  in  a  clear 
and  masterly  manner,  not  only  enabling  the  practi-  vember,  1S66 
tioner  readily  to  diagnose  each  variety  of  disease,  but 
affording  him  the  more  important  assistance  of  proper 
treatment.  Altogether  this  is  a  work  which  ought 
certainly  to  be  in  the  hands  of  every  general  practi- 
tioner.— Dublin  Med.  Press  and  Circular,  Sept.  12,  '66. 

We  cordially  recommend  this  book  to  the  notice  of 
our  readers,  as  containing  an  excellent  outline  of 
modern  ophthalmic  surgery. — British  Med.  Journal, 
October  13,  1S66. 


Not  only,  as  its  modest  title  suggests,  a  "Handy- 
Book"  of  Ophthalmic  Surgery,  but  an  excellent  and 
well-digested  risumi  of  all  that  is  of  practical  value 
in  the  specialty.— iVezo  York  Medical  Journal,  No- 


This  object  the  authors  have  accomplished  in  a 
highly  satisfactory  manner,  and  we  know  no  work 
we  can  more  highly  recommend  to  the  "busy  practi- 
tioner" who  wishes  to  make  himself  acquainted  with 
the  recent  improvements  in  ophthalmic  science.  Such 
a  work  as  this  was  much  wanted  at  this  time,  and 
this  want  Messrs.  Laurence  and  Moon  have  now  well 
supplied. — Am,.  Journal  Med.  Sciences,  Jan.  1867. 


TAWSON  [GEORGE),  F.  R.  C.  S.,  Engl 

-*^  Assistant  Surgeon  to  the  Royal  London  Ophthalmic  Hospital,  Moorfields,  &c. 

INJURIES  OF  THE  EYE,  ORBIT,  AND  EYELIDS:  their  Imme- 

diate  and  Remote  Effects.  With  about  one  hundred  illustrations.  In  one  very  hand- 
some octavo  volume,  extra  cloth,  $3  50.  {Now  Ready.) 
This  work  will  be  found  eminently  fitted  for  the  general  practitioner.  In  cases  of  functional 
or  structural  diseases  of  the  eye,  the  physician  who  has  not  made  ophthalmic  surgery  a  special 
study  can,  in  most  instances,  refer  a  patient  to  some  competent  practitioner.  Cases  of  injury, 
however,  supervene  suddenly  and  usually  require  prompt  assistance,  and  a  work  devoted  espe- 
cially to  them  cannot  but  prove  essentially  useful  to  those  who  may  at  any  moment  be  called  upon 
to  treat  such  accidents.  The  present  volume,  as  the  work  of  a  gentleman  of  large  experience, 
may  be  considered  as  eminently  worthy  of  confidence  for  reference  in  all  such  emergencies. 
It  is  an  admirable  practical  book  in  the  highest  and    fulness  of  practical  knowledge.     We  predict  for  Mr 


best  sense  of  the  phrase.  Copiously  illustrated  by 
excellent  woodcuts,  and  with  well-selected,  well- 
described  cases,  it  is  written  in  plain,  simple  lan- 
guage, and  in  a  style  the  transparent  clearness  and 
frankness,  so  to  speak,  of  which,  add  greatly  to  its 
value  and  usefulness.  Only  a  master  of  his  subject 
could  so  write  ;  every  topic  is  handled  with  an  ease, 
decision,  and  straightforwardness,  that  show  the 
skilful  and  highly  educated  surgeon  writing  from 


Lawson's  work  a  great  and  well-merited  success. 
We  are  confident  that  the  profession,  and  especially, 
as  we  have  said,  our  country  brethren,  will  feel 
grateful  to  him  for  having  given  them  in  it  a  guide 
and  counsellor  fully  up  to  the  most  advanced  state  of 
Ophthalmic  Surgery,  and  of  whom  they  can  make  a 
trusty  and  familiar  friend.— London  Medical  Times 
and  Gazette,  May  18,  1867. 


J 


ONES  [T.  WHARTON),  F.R.S., 

Professor  of  OpMhalmic  Med.  and  Surg,  in  University  College,  London. 

THE  PRINCIPLES  AND  PRACTICE  OF  OPHTHALMIC  MEDI- 
CINE AND  SURGERY.  With  one  hundred  and  seventeen  illustrations.  Third  and  re- 
vised American,  with  Additions  from  the  second  London  edition.  In  one  handsome  octavo 
volume  of  455  pages,  extra  cloth.     $3  25. 


llfA CKENZIE  [W.),  M. D., 

jLfJ-  Surgeon  Ocxdist  in  Scotland  in  ordinary  to  her  Majesty,  &c, 

A  PRACTICAL  TREATISE  ON  DISEASES  AND  INJURIES  OF 

THE  EYE.  To  which  is  prefixed  an  Anatomical  Introduction  explanatory  of  a  Horizontal 
Section  of  the  Human  Eyeball,  by  Thomas  Wharton  Jones,  F.  R.  S.  From  the  fourth 
revised  and  enlarged  London  edition.  With  Notes  and  Additions  by  Addinell  Hewson, 
M.  D.,  Surgeon  to  Wills  Hospital,  «tc.  Ac.  In  one  very  large  and  handsome  octavo  volume 
of  1027  pages,  extra  cloth,  with  plates  and  numerous  wood-cuts.     $6  50. 


30  Henry  C.  Lea's  Publications — (Surgery). 


jyA^^^  {PHILIP  S,),  M.  D.,  Surgeon  U.  S 


iV. 


MECHANICAL  THERAPEUTICS:  a  Practical  Treatise  on  Surgical 

Apparatus,  Appliances,  and  Elementary  Operations  :    embracing  Minor  Surgery,   Band- 
aging, Orthopraxy,  and  the  Treatment  of  Fractures  and  Dislocations.     With  six  hundred 
and  forty-two  illustrations  on  wood.     In  one  large  and  handsome  octavo  volume  of  about 
700  pages:  extra  cloth,  $5  75;  leather,  $6  75.      {Now  Ready.) 
The  author  has  attempted  in  this  volume  to  supply  a  want  which  has  been  generally  felt  by 
Btudents  and  practitioners  of  a  work  which  should  present,  minutely,  but  concisely,  the  various 
details  in  surgical  operations,  which  are  apt  to  be  passed  over  in  systematic  treatises.     It  falls 
to  the  lot  of  comparatively  few  surgeons  to  perform  the  major  operations,  but  every  physician, 
especially  in  the  country,  is  liable  at  any  moment  to  be  called  upon  to  remedy  some  accident  or 
to  prevent  some  deformity,  and  the  aim  of  the  present  treatise  is  to  present  that  kind  of  informa- 
tion with  such  detail  that  it  may  be  regarded  as  an  unfailing  book  of  reference.     The  very  com- 
plete series  of  illustrations  renders  the  whole  easy  of  comprehension  by  the  student,  while  the 
author's  practical  experience  in  the  naval  service,  and  the  care  with  which  he  has  collected  the 
results  of  the  latest  authorities,  at  home  and  abroad,  give  assurance  of  the  value  of  his  teachings. 
A  very  condensed  summary  is  subjoined  of  the 

COnSTTEISTTS. 

PART  I.    Op  the  Apparatus?  op  Dressing. 

Chap.  I.  Of  the  Instruments  of  Dressing. — II.  Of  the  First  Pieces  of  Dressing. — III.  On  the 
Use  of  some  Topical  Remedies. — IV.  On  the  Use  of  Water  in  Surgical  Dressings  and  Inju- 
ries.— V.  Injections. — VI.  On  the  Use  of  Gases  and  Vapors. — VII.  Bandages. — VIII. 
Special  or  Regional  Bandaging. 
PART  II.    Mechanical  Bandages  and  Apparatus. 

Chap.  I.  Apparatus  for  Remedying  Loss  of  Parts. — II.  Apparatus  for  Remedying  Loss  of 
Function. — III.  Apparatus  for  Remedying  Loss  of  Symmetry. 
PART  III.    Fractures;  their  Reduction,  Dressing,  and  Apparatus. 

Chap.  I.  General  Consideration  of  Fractures. — II.  Fractures  of  Particular  Bones. 
PART  IV.  Dislocations;  their  Reduction,  Dressing,  and  Apparatus. 

Chap.  I.  Sprains  or  Strains. — II.  Dislocations  in  General. — III.  Particular  Dislocations. 
PART.  V.    The  Minor  Operations  op  Surgery. 

Chap.  I.  Rubefaction. — II.  Vesication. — III.  Cauterization. — IV.  Moxa. — V.  Issues. — VI. 
Setons. — VII.  Acupuncture  and  Electropuncture. — VIII.  Puncturing. — IX.  Vaccination. 
— X.  Incisions. — XI.  Bloodletting.  —  XII.  Extraction  of  Teeth.  —  XIII.  Catheterism  — 
XT;V.  Removal  of  Foreign  Bodies. — XV.  On  the  Modes  of  Arresting  Hemorrhage. — XVI. 
On  the  Dressings  of  Wounds. — XVII.  Anaesthesia. 

The  adoption  of  this  work  for  use  in  both  the  Army  and  Navy  of  the  United  States  is  a  guffi- 
cient  guarantee  of  its  usefulness  to  the  practitioner. 


A 


SHTON  {T.  J.) 
ON  THE   DISEASES,  INJURIES,  AND  MALFORMATIONS   OF 

THE  RECTUM  AND  ANUS;  with  remarks  on  Habitual  Constipation.  Second  American, 
from  the  fourth  and  enlarged  London  edition.  With  handsome  illustrations.  In  one  very 
beautifully  printed  octavo  volume  of  about  300  pages.     $3  25.      {Jnst  Issued.) 

The  short  period  which  has  elapsed  since  the  ap- 
pearance of  the  former  American  reprint,  and  the 
numerous  editions  published  in  England,  are  the  best 
arguments  we  can  oflfer  of  the  merits,  and  of  the  u.-^e- 
lessne.ss  of  any  commendation  on  our  part  of  a  book 
already  so  favorably  known  to  our  readers. — Boston 
Med.  and  Surg.  Journal,  Jan.  25,  1866. 


We  can  recommend  this  volume  of  Mr  Ashton's  in 
the  strongest  terms,  as  containing  all  the  latest  details 
of  the  pathology  and  treatment  of  diseases  connected 
with  the  rectum. — Canada  Med,.  Jnurn.,  March,  1S66. 

One  of  the  most  valuable  special  treatise**  that  the 
physician  and  surgeon  can  have  in  his  library. — 
Chicago  Medical  Examiner,  Jan.  1S66. 


JirORLAND  [W.  W.),  31. D. 


DISEASES  OF  THE  URINARY  ORGANS;  a  Compendmm  of  their 

Diagnosis,  Pathology,  and  Treatment.     With  illustrations.     In  one  large  and  handsome 
octavo  volume  of  about  600  pages,  extra  cloth.     $3  50. 
Taken  as  a  whole,  we  can  recommend  Dr  Morland's  I  of  every  medical  or  surgical  practitioner. — Brit,  and 
compendium  as  a  very  desirable  addition  to  the  library  |  For.  Med.-Chir.  Review,  April,  18.59. 


rtURLING  [T.B.),  F.R.S., 

Surgeon  to  the  London  Hospital,  President  of  the  Hunterinn  Society,  &c. 

A  PRACTICAL   TREATISE   ON   DISEASES   OF   THE   TESTIS, 

SPERMATIC  CORD,  AND  SCROTUM.  Second  American,  from  the  second  and  enlarged 
English  edition.  In  one  handsome  octavo  volume,  extra  cloth,  with  numerous  illustxa- 
tions.     pp.  420.     $2  00. 


Henry  C.  Lea's  Publications — {Medical  Jurisprudence^  &c.).     31 


rPAYLOR  [ALFRED  S.),  M.D., 

•*-  Lecturer  on  Med.  Jurisp.  and  Chemistry  in  Guy's  Hospital. 

MEDICAL   JURISPRUDENCE.     Sixth   American,  from   the   eighth 

and  revised  London  edition.     With  Notes  and  References  to  American  Decisions,  by  Cle- 
ment B.  Penrose,  of  the  Phihidelphia  Bar.     In  one  large  octavo  volume  of  776  pages, 
extra  cloth,  $4  50  ;  leather,  $5  60.      {Now  Ready.) 
Considerable  additions  have  been  made  by  the  editor  to  this  edition,  comprising  some  important 
Bections  from  the  author's  larger  work,  "  The  Principles  and  Practice  of  Medical  Jurisprudence," 
as  well  as  references  to  American  law  and  practice.     The  notes  of  the  former  editor,  Dr.  Harts- 
horne,  have  likewise  been  retained,  and  the  whole  is  presented  as  fully  worthy  to  maintain  the 
distinguished  position  which  the  work  has  acquired  as  a  leading  text-book  and  authority  on  the 
subject 


A  new  edition  of  a  work  acknowledged  as  a  stand- 
ard authority  everywhere  within  the  range  of  the 
English  langurtge.  Considering  the  new  matter  intro- 
duced, on  trichiniasis  and  other  subjects,  and  the 
plates  representing  the  crystals  of  poisons,  etc. ,  it  may 
fairly  be  regarded  as  the  most  compact,  comprehen- 
sive, and  practical  work  on  medical  jurisprudence 
which  has  issued  from  the  press,  and  the  one  best 
fitted  for  students. — Pacific  Med.  and  Surg.  Journal, 
Feb.  1857. 

The  sixth  edition  of  this  popular  work  comes  to  us 
in  charge  of  a  new  editor,  Mr.  Penrose,  of  the  Phila- 
delphia bar,  who  has  done  much  to  render  it  useful, 
not  only  to  the  medical  practitioners  of  this  country, 
but  to  those  of  his  own  profession.  Wisely  retaining 
the  references  of  the  former  American  editor.  Dr. 
Hiirtshorne,  he  has  added  many  valuable  notes  of  his 
own.  The  reputation  of  Dr.  Tnylor's  work  is  so  well 
e^stablished,  that  it  needs  no  recommendation.  He  is 
now  the  highest  living  authority  on  all  matter.s  con- 
nected with  forensic  medicine,  and  every  successive 
edition  of  his  valuable  work  gives  fresh  assurance  to 
his  many  admirers  that  he  will  continue  to  maintain 
his  well-earned  position.  No  one  should,  in  fact,  be 
without  a  text-book  on  the  subject,  as  he  does  not 
know  bat  that  his  next  case  may  create  fur  him  an 


elaborate  treatises. — New  York  Medical  Record,  Feb. 
LO,  1867. 

The  present  edition  of  this  valuable  manual  is  a 
great  improvement  on  those  which  have  preceded  it. 
Some  admirable  instruction  on  the  subject  of  evidence 
and  the  duties  and  re.>sponsibilities  of  medical  wit- 
nesses has  been  added  by  the  distinguished  author, 
and  some  fifty  cuts,  illustrating  chiefly  the  crystalline 
forms  and  microscopic  structure  of  «ubstaaces  used 
as  poisons,  inserted.  The  American  editor  has  also 
introduced  several  chapters  from  Dr  Taylor's  larger 
work,  "The  Principles  and  Practice  of  Medical  Juris- 
prudence," relating  to  trichiniasis,  sexual  malforma- 
tion, insanity  as  affecting  civil  responsibility,  suicidal 
mania,  and  life  insurance,  &c.,  which  add  cou.siderably 
to  its  value.  Besides  this,  he  has  introduced  nume- 
rous references  to  cases  which  have  occurred  in  this 
country.  It  makes  thus  by  far  the  be.-^t  guide-book 
in  this  department  of  medicine  for  students  and  the 
general  practitioner  in  our  language. — Boston  Med. 
and  Surg.  Journal,  Dec.  27,  1866. 

Taylor's  Medical  Jurisprudence  has  been  the  text- 
book in  our  colleges  for  years,  and  the  present  edi- 
tion, with  the  valuable  additions  made  by  the  Ameri- 
can editor,  render  it  the  most  standard  work  of  the 
day,  on  the  peculiar  province  of  medicine  on  which 


emergency  for  its  use.  To  those  who  are  not  the  for-  '  it  treats.  The  American  editor.  Dr.  Hartshorne,  has 
tuuate  possessors  of  a  reliable,  readable,  interesting,  t  done  his  duty  to  the  text,  and,  upon  the  whole,  we 
and  thoroughly  practical  work  upon  the  subject,  we  !  cannot  but  consider  this  volume  the  best  and  richest 
would  earnestly  recommend  this,  as  forming  the  best  ^  treatise  on  medical  jurisprudence  in  our  language. — 
groundwork  for  all  their  future  studies  of  the  more  i  Brit.  Am.  Med.  Journal.  ^ 

TYIiVSLOW  [FORBES),  Mly~D.C.L.,  fcT 

ON  OBSCURE  DISEASES  OF  THE  BRAIN  AND  DISORDERS 

OF  THE  MIND;  their  incipient  Symptoms,   Pathology,  Diagnosis,  Treatment,  and  Pro- 
phylaxis.   Secpnd  American,  from  the  third  and  revised  English  edition.    In  one  handsome 
octavo  volume  of  nearly  600  pages,  extra  cloth.     $4  25.      {Jiist  Isstied.) 
Of  the  merits  of  Dr.  Winslow's  treatise  the  profes-  1  our  conviction  that  it  is  long  since  so  important  and 
Biou  has  sufftciently  judged.    It  has  taken  its  place  in  {  beautifully  written  a  volume  has  issued  from  the 
the  front  rank  of  the  works  upon  the  special  depart-    British  medical  press.     The  details  of  the  manage- 
ment of  confirmed  cases  of  insanity  more  nearly  in- 
terest tho.se  who  have  made  mental  disea-ses  their 
special  study;  but  Dr.  Winslow's  masterly  exposi- 
tion of  the  early  symptoms,  and  his  graphic  descrip 
tions  of  the  insidious  advances  of  incipient  insanity, 
together  with  his  judicious  observations  on  the  treat- 
ment of  disorders  of  the  mind,  should,  we  repeat,  be 
carefully  studied  by  all  who  have  undertaken  the 
responsibilities  of  medical  practice. — Dublin  Medical 
Press. 

It  is  the  most  interesting  as  well  as  valuable  book 
that  we  have  seen  for  a  long  time.  It  is  truly  fasci- 
nating.— Arn.  Jour.  Med.  Sciences. 

Dr.  Winslow's  work  will  undoubtedly  occupy  an 
unique  position  in  the  medico-psycli^ilogical  litera- 


ment  of  practical  medicine  to  which  it  pertains. — 
Cincinnati  Journal  of  Medicine,  March,  1866. 

It  is  an  interesting  volume  that  will  amply  repay 
for  a  careful  perusal  by  all  intelligent  readers  — 
Chicago  Med.  Examiner  Feb.  1866. 

A  work  which,  like  the  present,  will  largely  aid 
the  practitioner  in  recognizing  and  arresting  the  first  ' 
insidious  advances  of  cerebral  and  mental  disease,  is  j 
one  of  immense  practical  value,  and  demands  earnest 
attention  and  diligent  study  on  the  part  of  all  who  i 
have  embraced  the  medical  profession,  and  have  | 
thereby  undertaken  responsibilities  in  which  the  j 
welfare  and  happiness  of  individuals  and  families  j 
are  largely  involved.  We  shall  therefore  close  this  \ 
lirief  and   necessarily  very  imperfect   notice  of  Dr 


Winslow's  great  and  classical  work  by  expressing  j  ture'of  this  country. — London  Med.  Review. 


EA  [HENRY  C.) 

'  SUf'ERSTITlON    AND    FORCE:    ESSAYS    OX    TRE   WAGER   OF 

LAW,  THE  WAGER  OF  BATTLE,  THE  ORDEAL,  AND  TORTURE.     In  one  hand- 
some volume  royal  12mo.,  of  406  pages;  extra  cloth,  $2  50. 

a  humor  so  fine  and  good,  that  he  makes  us  regret  it 
was  not  within  his  intent,  as  it  was  certainly  within 
his  power,  to  render  the  whole  of  his  thorough  work 
more  popular  in  manner.— At/antic  Monthly,  Feb.  '«7. 
This  is  a  book  of  extraordinary  research.  Mr.  Lea 
has  entered  into  his  subject  con  am  ore ;  and  a  more 
striking  record  of  the  cruel  superstitions  of  our  un- 
happy Middle  Ages  could  not  possibly  have  been  com- 
piled. ...  As  a  work  of  curious  in«5|Uiry  on  certain 
outlying  points  of  obsolete  law,  "Superstition  and 
Force"  is  one  of  the  most  remarkable  books  we  have 
me;  yv'xih..— London  At/ienceum,  Nov.  3,  1866. 


The  copious  collection  of  facts  by  which  Mr.  Lea  has 
illustrated  his  subject  shows  in  the  fullest  manner  the 
constant  conflict  and  varying  success,  the  advances 
*id  defeats,  by  which  the  progress  of  humane  legisla- 
tion has  been  and  is  still  marked.  This  work  fills  up 
with  the  fullest  exemplification  and  detail  the  wise 
remarks  which  we  have  quoted  above.  As  a  book  of 
ready  reference  on  the  subject  it  is  of  the  highest 
value. — Westminster  Review,  Oct.  1867. 

When — half  in  spite  of  himself,  as  it  appears — he 
sketches  a  scene  or  character  in  the  history  of  legalized 
©iTor  and  cruelty,  he  betrays  so  artistic  a  feeling,  and 


32 


Hexry  C.  Lea's  Publications. 


INDEX    TO    CATALOGUE, 


Abel  and  Bloxam's  Handbook  of  Chemistry 
Allen's  Dissector  and  Practical  Anatomist 
American  Journal  of  the  Medical  Sciences 
Abstract,  Half-Yearly,  of  the  Med,  Sciences 
Anatomical  Atlas,  by  Smith  and  Horner 
Ashton  on  the  Kectum  and  Anus  . 
Ashwell  on  Diseases  of  Females  . 
Brinton  on  the  Stomach 
Barclay's  Medical  Diagnosis  . 
Barlow's  Practice  of  Medicine 
Barwell  on  the  Joints     .... 
Bennet  (Henry)  on  Diseases  of  the  Uterus 
Bowman's  (John  E.)  Practical  Chemistry 
Bowman's  (John  E.)  Medical  Chemistry 
Brande  &  Taylor's  Chemistry 
Brodie's  Clinical  Lectures  on  Surgery  . 
Brown  on  the  Surgical  Diseases  of  Women 
Buckler  on  Bronchitis     .... 
Bucknill  and  Tuke  on  Insanity 
Budd  on  Diseases  of  the  Liver 
Bumstead  on  Venereal    .... 
Bumstead  and  Cullerier's  Atlas  of  "Venereal 
Carpenter's  Human  Physiology    . 
Carpenter's  Comparative  Physiology  . 
Carpenter  on  the  Microscope 
Carpenter  on  the  Use  and  Abuse  of  Alcohol 
Carson's  Synopsis  of  Materia  Medica    . 
Chambers  on  the  Indigestions 
Christison  and  Griffith's  Dispensatory 
Churchill's  System  of  Midwifery  . 
Churchill  on  Diseases  of  Females 
Churchill  on  Puerperal  Fever 

Clyraer  on  Fevers 

Colombat  de  I'lsere  on  Females,  by  Meigs 
Condie  on  Diseases  of  Children     . 
Cooper's  (B.  B.)  Lectures  on  Surgery    . 
Cooper  (Sir  A.  P.)  on  the  Testis,  &c'     . 
Cullerier's  Atlas  of  Venereal  Diseases 
Curling  on  Diseases  of  the  Testis  . 
Cyclopedia  of  Practical  Medicine  . 
Daltou's  Human  Physiology  . 
De  Jongh  on  Cod-Liver  Oil     . 
Dewees's  System  of  Midwifery 
Dewees  on  Diseases  of  Females     . 
Dewees  on  Diseases  of  Children    . 
Dickson's  Practice  of  Medicine 
Druitt's  Modern  Surgery 
Dunglison's  Medical  Dictionary    . 
Dunglison's  Human  Physiology    . 
Duuglison  on  New  Remedies 
Dunglison's  Therapeutics  and  Materia  Medica 
Ellis's  Medical  Formulary,  by  Thomas 
Erichsen's  System  of  Surgery 
Erichsen  on  Nervous  Injuries 
Flint  on  Respiratory  Organs  . 

Flint  on  the  Heart 

Flint's  Practice  of  Medicine   . 
Fownes's  Elementary  Chemistry  . 
Fuller  on   the  Lungs,  &c. 
Garduer's  Medical  Chemistry 

Gibson's  Surgery 

Gluge's  Pathological  Histology,  by  Leidy 
Graham's  Elements  of  Chemistry  . 

Gray's  Auatomy 

Griffith's  (R.  E.)  Universal  Formulary  . 
Griffith's  (J.  W.)  Manual  on  the  Blood,  &c. 
Gross  on  Urinary  Organs 
Gross  on  Foreign  Bodies  in  Air-Passages 
Gross's  Principles  and  Practice  of  Surgery 
Gross's  Pathological  Anatomy 
Hartshorne's  Essentials  of  Medicine    . 
Habershon  on  Alimentary  Canal  . 
Hamilton  oq  Dislocations  and  fractures 
Harrison  on  the  Nervous  Systei..  . 
Hoblyn's  Medical  Dictionary 

Hodge  on  "Women 

Hodge's  Obstetrics 

Hodge's  Practical  Dissections 
Holland's  Medical  Notes  and  Reflections 
Horner's  Anatomy  and  Histology 
Hudson  on  Fevers,  .... 

Hughes  on  Auscultation  and  Percussion 
Hillier's  Handbook  of  Skin  Diseases 


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6 

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22 

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16 

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18 
30 
15 

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13 
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21 
16 
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9 
11 
11 
12 
27 
27 
17 
17 
15 
11 
16 
11 
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10 

6 
12 
19 
26 
26 
26 
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16 
17 
28 
19 

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24 

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15 

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17 
18 
20  i 


Jones's  (T.  "W.)  Ophthalmic  Medicine  and  Surg. 

Jones  and  Sieveking's  Pathological  Anatomy 

Jones  (C.  Handfield)  on  Nervous  Disorders 

Kirkes'  Physiology  .... 

Knapp's  Chemical  Technology 

Lea's  Superstition  and  Force 

Lallemand  and  "Wilson  on  Spermatorrhoea 

La  Roche  on  Yellow  Fever     . 

La  Roche  on  Pneumonia,  &c. 

Laurence  and  Moon's  Ophthalmic  Surgery 

Lawson  on  the  Eye  .... 

Laycock  on  Medical  Observation  . 

Lehmann's  Physiological  Chemistry,  2  voli 

Lehmann's  Chemical  Physiology  . 

Ludlow's  Manual  of  Examinations 

Lyons  on  Fever 

Maclise's  Surgical  Anatomy  . 

Malgaigne's  Operative  Surgery,  by  Brittan 

Markwick's  Examination  of  Urine 

Mayne's  Dispensatory  and  Formulary 

Mackenzie  on  Diseases  of  the  Eye 

Medical  News  and  Library     . 

Meigs's  Obstetrics,  the  Science  and  the  Art 

Meigs's  Letters  on  Diseases  of  Women 

Meigs  on  Puerperal  Fever 

Miller's  System  of  Obstetrics 

Miller's  Practice  of  Surgery  .        » 

Miller's  Principles  of  Surgery 

Montgomery  on  Pregnancy    . 

Morlaud  on  Urinary  Organs   . 

Morland  on  Uraemia         .... 

Neill  and  Smith's  Compendium  of  Med.  Science 

Neligan's  Atlas  of  Diseases  of  the  Skin 

Neligan  on  Diseases  of  the  Skin    . 

Prize  Essays  on  Consumption 

Parrish's  Practical  Pharmacy 

Peaslee's  Human  Histology   . 

Pirrie's  System  of  Surgery     . 

Pereira's  Mat.  Medica  and  Therapeutics,  abridged 

Quain  and  Sharpey's  Anatomy,  by  Leidy 

Ranking's  Abstract  .... 

Roberts  on  Urinary  Diseases  . 

Ramsbothara  on  Parturition  . 

Reese  on  Blood  and  Urine 

Rigby  on  Female  Diseases 

Rigby's  Midwifery 

Rokitansky's  Pathological  Anatomy    . 

Royle's  Materia  Medica  and  Therapeutics 

Sargent's  Minor  Surgery 

Sharpey  and  Quain's  Anatomy,  by  Leidy 

Simon's  General  Pathology    . 

Simpson  on  Females        .... 

Skey's  Operative  Surgery 

Slade  on  Diphtheria        .... 

Smith  (H.  H.)  and  Horner's  Anatomical  Atlas 

Smith  (Edward)  on  Consumption  . 

Solly  on  Anatomy  and  Diseases  of  the  Brai 

Still6's  Therapeutics        .... 

Salter  on  Asthma 

Tanner's  Manual  of  Clinical  Medicine  . 
Tanner  on  Pregnancy     .... 
Taylor's  Medical  Jurisprudence     . 
Thomas  on  Diseases  of  Females    . 
Todd  and  Bowman's  Physiological  Anatomy 
Todd  on  Acute  Diseases  .... 
Toynbee  on  the  Ear         .... 
Wales  on  Surgical  Operations 
Walshe  on  the  Heart      .... 
Watson's  Practice  of  Physic  . 
West  on  Di8ea.«es  of  Females 
West  on  Diseases  of  Children 
West  on  Ulceration  of  Os  Uteri      . 
What  to  Observe  in  Medical  Cases 
Williams's  Principles  of  Medicine 
Wilson's  Human  Anatomy    .        .        .        , 

Wilson's  Dissector 

Wilson  on  Diseases  of  the  Skin     . 
Wilson's  Plates  on  Diseases  of  the  Skin 
Wilson's  Handbook  of  Cutaneous  Medicine 
Wilson  on  Healthy  Skin 
Wilson  on  Spermatorrhoea     . 
Winslow  on  Brain  and  Mind 


I 


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